Application of optoelectronics to communication has come to a transition from point-to-point transmission to photonic backbone networks. This paper reviews recent progress of photonic device research with emphasis on the key technologies concerning this transitions. Among them are multi-channel WDM and photonic switching. Photonic integration is becoming a reality on monolithic as well as hybrid scheme.

Thermally induced strain caused by device packaging is studied in high-power semiconductor laser arrays by a novel non-invasive technique. Measurements with intentionally strained laser array devices for 808 nm emission reveal spectral shifts of quantum-confined optical transitions in the optical active region. These shifts by up to 10 meV serve as a measure for strain and are compared with model calculations. We demonstrate that different packaging techniques cause different packaging-induced strains. We also show that the packaging-induced strain portion, which gets transmitted through the solder material, differs for different packaging technologies. An intentionally strain- reduced packaging technique is shown to transmit about one quarter of the potential packaging-induced strain towards the optical active layer, whereas another packaging technique, which provides highly reliable 'single-chip' devices is found to transmit about half of the potential amount. Spatially resolved measurements demonstrate strain gradients within the devices. Also temporal strain evolution is monitored. We show that 'the burn-in' is accompanied by strain accumulation whereas for long-term operation strain relaxation occurs.

High power diode lasers can be used for a lot of applications such as pumping of solid state lasers, direct material processing and printing. The successful use of high power diode lasers depends on their high efficiency and reliability in combination with a long lifetime. For a further increase in the quality of high power diode lasers the properties of semiconductor laser bars have to be improved as well as the mounting techniques for these bars onto specially designed heat sinks. For most applications the electro-optical properties of the high power diode lasers have to be known exactly. Detailed information on the propagation characteristics and the transverse mode distribution of diode laser beams is necessary for the optimization of the overall performance. In addition the electro-optical characterization is a first test for the quality of high power diode lasers. An automated test set-up developed at the Fraunhofer-Institut für Lasertechnik will be presented. The electro-optical data such as threshold current, slope efficiency, center wavelength, spectral width, total conversion efficiency and cw-output power can be measured as a function of driving current as well as the beam divergence angles in fast and slow direction of the high power diode lasers. Different methods to determine the exact divergence angles will be discussed.

Stimulated Emission and Pump-Probe studies were performed in GaN, InGaN, and AlGaN epilayers as well as GaN/AlGaN separate confinement heterostructures. We show that in GaN epilayers the near-threshold gain mechanism is inelastic exciton-exciton scattering for temperatures below approximately 150 K, whereas at elevated temperatures electron-hole plasma is the dominant gain mechanism. An analysis of the relative shift between the spontaneous emission and lasing peaks in SCH samples, combined with the temperature dependence of the lasing threshold, reveals that exciton-exciton scattering is the dominant gain mechanisms leading to low-threshold UV lasing in the GaN/AlGaN SCH over the entire temperature range studied. We further performed optical pumping of AlGaN epilayers at different temperatures. Stimulated emission has been observed in Al_xGa_1-xN thin films for Al concentrations as high as x = 0.26, with a resultant stimulated emission wavelength as low as 328 nm at room temperature. This result indicated that AlGaN-based structures are suitable not only for use in deep-UV detectors, but also as a potential source of deep-UV laser radiation. The interband optical transitions in GaN and InGaN have also been studied at 10 K and room temperature using nondegenerate nanosecond optical pump-probe techniques. At low temperatures, strong, well- resolved features were seen in the absorption and reflection spectra corresponding to the 1s A and B exciton transitions. Broadening and decrease in intensity of these features were studied as the function of excitation pump density. We found that values of induced transparency and induced absorption are extremely large in GaN epilayers. The pump-probe results in GaN epilayers were directly compared to ones obtained from InGaN films. Significant differences in near-bandedge absorption changes were clearly observed between the two materials.

Experimental data on photoluminescence of various bulk and quantum-well epitaxial InGaN/GaN structures grown by MOCVD are interpreted in terms of a band-tail model of inhomogeneously broadened radiative recombination. The anomalous temperature-induced blue spectral is shown to result from band-tail recombination under non-degenerate conditions. Significant differences are observed between epilayers grown on sapphire substrates and on GaN substrates prepared by the sublimination method, with no apparent evidence of band tails in homoepitaxial structures, indicating their higher crystalline quality.

Static, field-mounted and time-resolved spectroscopic measurements were carried out to compare the electronic structures between AlGaN/GaN binary and GaN/InGaN ternary single quantum wells (SQWs). The internal field exits across the quantum well (QW) naturally induces quantum-confined Stark effects, namely the redshift of the QW resonance energy and separation of electron-hole wavefunction overlap. Thus AlGaN/GaN SQWs exhibited a weak luminescence peak due to the presence of nonradiative channels. However, optical absorption and degenerate pump-probe measurements revealed that excitonic character still remains for the thin QWs having the well width nearly the same as the bulk free exciton Bohr radius even under high electric field as high as 0.73 MV/cm. A slightly In-alloyed InGaN SQW exhibited bright luminescence peak in spite of the pronounced effective bandgap inhomogeneity in the QW, which was confirmed by the point excitation and monochromatic cathodoluminescence mapping methods to have the lateral potential interval smaller than 40 nm. Therefore the light emitting area of the potential minima has the size defined as 'quantum-disk'. Carriers generated in the InGaN QWEs are effectively localized in these regions to form localized QW excitons exhibiting highly efficient spontaneous emissions.

ZnCdSe ternary alloys form an important class of semiconducting system, which has a wide range of applications in opto-electronic devices in the entire visible spectrum. They are used in the fabrication of blue light emitting diodes, blue lasers, solar cells, thin film transistors and photoelectrochemical solar cells, etc. Synthesis of such an important material using low cost technique is necessary for the effective application of this valuable system. Electrodeposition is a cost effective, versatile and viable technique for the synthesis of thin film materials. In this study, synthesis of thin films of (ZnCd)Se system from aqueous acidic mixture using potentiostatic electrodeposition is discussed. The physical properties of these films deposited onto transparent conducting tin oxide coated glasses are estimated. The optimized deposition conditions are determined and the films were used as photoelectrodes in poly sulphide electrolytes. The films are found to exhibit reproducible good photoelectrochemical behavior. The result of these studied are reported.

Oxide-confined vertical-cavity surface-emitting laser diodes (VCSELs) are optimized for multi-Gbit/s data rate optical transmission systems. Noise characteristics and small-signal modulation response of high-performance transverse single- and multi-mode devices under different operation conditions are investigated. We demonstrate for the first time 12.5 Gbit/s data rate fiber transmission with a bit-error rate of better than 10^-11 for pseudo-random bit sequence signals over 100m multimode fiber and 1 km single-mode fiber. Maximum electrical and optical bandwidths obtained at 3 mA driving current are 12 GHz and 13 GHz, respectively. For pumping levels above 2.8 times threshold current, the relative intensity noise is below -150 dB/Hz up to 5 GHz for output powers of about 1mW. In detail, we investigate the low frequency intensity noise of high efficiency small area selectively oxidized VCSELs emitting in the fundamental transverse mode up to 7 times threshold current at room temperature and in multiple transverse modes up to 20 times threshold current. For low temperature operation quantum efficiency of the VCSEL is increased leading to photon- number fluctuations 1.4 dB below the shot noise limit. This is to our best knowledge the largest amount of squeezing ever reported for VCSELs.

The evolution of dense wavelength division multiplexing (DWDM) has allowed service provides a convenient and cost effective method to dramatically increase transmission capacity over existing and new fiber network systems. As the demand for bandwidth continues to increase, systems designers are responding by increasing both the number of channels and the data rates. This trend has placed considerable pressure on many of the underlying system components. One component that has been particularly challenged by this trend is the manufacture of semiconductor lasers. This paper reviews the technical and logistical challenges faced in the high volume manufacture of lasers to support DWDM systems. As the product portfolio continues to expand, precise execution and team work among multiple organizations is required to assure reliable shipping performance. Production scheduling and manufacturing operations must work closely to continuously re-prioritize the work in process in response to constantly changing channel demand and yield fluctuations. Wavelength prediction models must be developed that correlate in-process parameters to final device wavelength. These models are then applied to both in-process specification targeting and inventory management. Once the in-process specifications are properly targeted, the challenge moves to the fabrication processes, where processes are pushed to the limits of their control. Underpinning the entire effort must be an information management system in which parametric data is collected, wavelength prediction models are executed, and work in process inventory is controlled with respect to the final output volume and wavelength distribution.

An integrated thermal-electrical-optical solver of vertical- cavity surface-emitting lasers has been developed on the basis of the effective frequency method combined with the rate equations for photon and carrier densities. The integrated solver is applied to analyze the performance characteristics of GaAs-based proton-implanted top-surface- emitting lasers, oxide-confined surface-emitting lasers and intracavity-contacted oxide-confined surface-emitting lasers. Numerical results confirm the experimentally observed significant advantage of oxide-confirmed structures over proton-implanted devices, and identify the intracavity- contacted design as the most advantageous for oxide-confined structures.

Calculations are done and compared for two AlGaInP single- quantum-well (SQW) LED structures: step separate- confinement-heterostructure (SCH) SQW structure and graded- index (GRIN) SCH-SQW structure. It is found that the latter has better performance in terms of spontaneous lifetime and injection efficiency. This is attributed to greater barrier height to electron leakage and substantial overlap between wavefunctions of different quantum numbers in the GRIN-SCH- SQW structure. Results also show that the GRIN layer thickness has no influence on the QW energy levels. spontaneous lifetime and injection efficiency in a GRIN-SCH- SQW.

Integration of a laser and modulator is shown to be possible in the InGaAs/AlGaAs material system by growing on a B GaAs substrate and utilizing the piezoelectric effect. The absorption characteristics of the modulator section are initially red shifted due to the built-in piezoelectric field and can be easily blue shifted with applied reverse bias. Since even under lasing conditions there is found to be a significant residual piezoelectric field in the quantum well, the modulator can be biased to a shorter wavelength than the lasing emission. Utilizing these effects a simple two-section laser-modulator device in which the absorber section lies within the laser cavity has been fabricated. The result show that the threshold current of the laser- modulator structure is controlled by the reverse bias voltage and hence absorption in the modulator section.

The Diffused Quantum Well (DFQW) structures created by both impurity induced and impurity free or vacancy promoted processes have recently been advanced to a higher level. The interdiffusion mechanisms is no longer confined to two consistent atoms, but consists of two or multiple phase interdiffusion as well as multiple species, such as three cations interdiffusion and two pairs of cation-anion interdiffusion. Results show that the outcome of these interdiffusions is quite different. For instance, both compressive or tensile strain materials and both blue or red shifts in the bandgap can be achieved dependent on the type of interdiffusion. The advantage of being able to tune the material properties allows the realizations of higher performance lasers and modulators. Two lasing wavelengths are produced at λ ≈ 1.55 μm, on the same substrate, with threshold currents of 290mA, and an extremely large relative reflectance change is predicted with power consumption reduced by 67%. A six fold enhancement of the third order susceptibility over that of the bulk materials can be achieved by using the inter- subband transitions in the DFQW at λ ≈ 10 μm. Broadband detectors have also been realized due to the wide DFQW spectral bandwidth. Several state-of-the-art results of the DFQW will be summarized with an emphasis on the future developments and directions of the DFQW.

We report the development of a new quantum well intermixing technique in GaAs/AlGaAs laser structure. This technique uses a grown-in AlAs sacrificing layer as intermixing source and with the same layer, but oxidized using a one-step rapid thermal process (RTP), as the intermixing mask. Selective intermixing can therefore be achieved across the wafer using a one-step RTP cycle. Differential bandgap shift of as large as 47 meV has been observed from the masked and oxidized regions.

Using impurity free vacancy enhanced disordering (IFVD), the shift in the band gap of Al_0.3Ga_0.7As/GaAs QW structures can be precisely controlled by an Al layer buried between a spin-on silica film and wet-oxidized GaAs surface. The blue shift in wavelength of Al_0.3Ga_0.7As/GaAs QW photoluminescence (PL) depends linearly on the thickness of the buried Al layer. By changing the Al layer thickness, the PL peak wavelength can be tuned from 7870 angstrom for the as-grown sample to 7300 angstrom and 7050 angstrom after 20s and 45s rapid thermal annealing at 850°C respectively. Applying this technology, three wavelength lasers were successfully fabricated in a single chip. The laser is a GaAs/Al_0.3Ga_0.7As three quantum well GRIN-SCH structure. Al layers with different thickness, i.e., no Al, 200 angstrom and 300 angstrom thick respectively, were buried between the oxidized GaAs surface and the silica film by two step photo-lithography and lift- off in three adjacent regions with 200 μm spacing. After one step rapid thermal annealing, the wafer was processed into 6 μm oxide-strip lasers. At room temperature the intermixed lasers covered with different thickness of Al layer show different lasing wavelengths. All the lasers have similar threshold current and slope efficiency.

We report the development and characterizations of GaAs via hole processes using BCl₃/Ar and Cl₂/Ar plasmas generated by an electron cyclotron resonance (ECR) system. The effect of the in- and out-diffuse of the reactive species and etch by-products, of the BCl₃/Ar plasma, on the etch rate of the GaAs vias has been studied. The average GaAs etch rate was found to increase with increasing of both BCl₃ and Cl₂ flow rates. Under similar conditions, namely 800W microwave power, 150W RF power, 10sccm Ar flow rate, same flow rate, the etch rates of Cl₂/Ar plasma were found to be 7-16 times higher than those of BCl₃/Ar plasma. As the microwave power increased from 0 to 1500W, the etch rate increased by a factor of as large as 124 for the Cl₂/Ar process. Etch rate as high as 6.7micrometers /min was observed from sample etched in Cl₂/Ar plasma using a microwave power, RF power and process pressure of 800W, 150W and 50mTorr, respectively. Compared to the BCl₃/Ar plasma, Cl₂/Ar plasma is a better candidate, as this process gives higher etch rate and smoother etched surface.

InGaAs/InGaAsP quantum well structures have wide applications, such as the integration of optoelectronic devices and low threshold current density laser, as well as low loss waveguides and optical switching elements. In many case, high temperature operations are necessary during the course of processing a wafer. Here, we report the influence of low and high etch pit densities (EPD) InP substrates on the thermal stability of InGaAs/InGaAsP quantum well laser structure. Both the n-type of S-doped (EPD<500 cm^-2)and Sn-doped (EPD≈5x10⁴cm^-2) InP substrates were grown under the same run with half wafer each. To assess the thermal stability, the samples were annealed, using a rapid thermal processor, between 650 °C and 750 °C, for 60 seconds. 77 K photoluminescence measurements were performed on the samples after annealing to study the degree of bandgap shift. It was found that S-doped InP substrate with low EPD, i.e. low point defect density, is thermally stable up to an annealing temperature of 625 °C for 60 seconds. Compared to the S-doped materials, laser structure grown on the Sn-doped InP substrate was found to exhibit larger degree of bandgap shift resulted from defects induced quantum well intermixing.

We proposed highly scattering optical transmission (HSOT) polymers and applied it to a light pipe of a backlighting system for liquid crystal displays (LCDs). The HSOT polymer backlighting system having not only approximately twice the brightness but also twice the efficiency of the conventional one was realized based on analysis of multiple scattering in the HSOT polymers. The problem of color dispersion which had been believed to be the nature of scattering phenomenon was solved by optimizing the heterogeneous structures in the HSOT polymers. As a result, the HSOT polymer backlighting system with sufficient color uniformity was achieved. In addition, the HSOT polymer backlighting system was composed of fewer parts than those of the conventional transparent one. The HSOT polymer backlighting system is suitable for recent thin LCDs because of these advantages.

Most of the work in organic electroluminescent polymers has been focused on organic conjugated polymers. However, polymers attached with transition metal complex have received relatively less attention. We have synthesized and studied the light emitting properties of some metal containing polymers based on the polypyridine complexes of rhenium and ruthenium. These complexes exhibit long-lived excited states caused by the metal to ligand charge transfer transitions. By varying the structure of the ligand and/or the transition metal, we are able to fine-tune the electronic properties of the resulting metal complexes. We have synthesized a series of poly(phenylenevinylene) (PPV) derivatives which are functionalized with ruthenium polypyridine complexes at the polymer mainchain or side chain. These complexes are able to act as photosensitizers which enhance the photoconductivity of these polymers at longer wavelength. Both the conjugated backbone and the metal complex can emit light upon excitation. As a result, it is possible to tune the color by loading different amount of ruthenium complex to the polymer. Luminescence studies showed that the ruthenium complex could quench the emission of the conjugated backbone in some polymers, which suggests an energy transfer process between the backbone and the metal complexes. It was also found that the presence of metal complexes could enhance the charge carrier mobilities of the polymers, as the metal and/or ligands can act as extra charge carriers in the charge transport process.

Conjugated polymers are a novel class of semiconductors that combine the optical and electronic properties of semiconductors with the processing advantages and mechanical properties of polymers. Since the first discovery of electroluminescence from conjugated polymer, PPV has been reported by JH Burroughs, et al, in 1990, the research on polymer light emitting diodes (PLEDs) has progressed rapidly. However, the number of soluble conjugated polymers with relatively high luminescence efficiency is still limited. In this paper, a recently synthesized soluble PPV derivative MBPPV is adopted to fabricate PLEDs. We studied the photoluminescence and electroluminescence properties of MBPPV and its polyblend with PVK. The energy transfer between MBPPV and PVK matrix in different blending concentration is also investigated. The emission peak and efficiency of the device ITO/MBPPV: PVK/Alq₃/Al are 570nm and 1.35% respectively.

Third-order optically nonlinear polymeric material built of rigid-rod molecules are often insoluble and transmit visible light poorly. We report on optical and waveguiding properties of a new soluble derivative of PPV: a π- conjugated polymer DFP-PDPV. We found that solvents used for processing of the DFP-PDPV polymer may influence the film optical properties. Changes in absorption spectra, birefringence, optical attenuation and the nonlinear refractive index were observed in the films made by spin coating and solution cast using different solvents. The films are birefringent and dispersive. Refractive indices vary from 1.76 to 1.63 for the TE polarisation of the incident light and from 1.70 to 1.60 for the TM polarisation for wavelengths from 476.5 nm to 1.55μ, respectively. The birefringence is an order ofmagnitude lower than that in films ofunsubstituted PPV. DFP-PDPV is suitable for fabrication of optical waveguides. Low loss waveguiding layers could be prepared. Propagation losses were measured at 632.8nm, 8lOnm and 1064nm. The losses decrease at longer wavelengths reaching the level of 1 dB/cm at 1.06μ. The waveguiding properties of DFP-PDPV films depend on the solvents used in processing of the polymer. We investigated thin films of DFP-PDPV for their potential for nonlinear waveguide applications. The modulus of nonlinear refractive index |n₂| in the range (0.9-1.5) x10^-14 cm²/W was measured in DFP-PDPV films at 8OOnm using a femtosecond degenerate four wave mixing (DFWM) technique. These studies supplement the results of nonlinear optical studies of this polymer in solution using the Z-scan technique described in Proceedings of SPIE 3473, 79-90 (1998).

Recent status of the polymer optical fiber (POF) for high speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time at Keio University, and several methodologies to fabricate GI POF have been currently proposed. In this paper, we clarify the great advantage of perfluorinated (PF) polymer as the polymer matrix of low-loss and high bandwidth graded-index (GI) POF. It is generally known that the PF polymer can decrease the intrinsic absorption loss compared with poly methyl methacrylate (PMMA), which is the conventional material of POF. Furthermore, it was found that low material dispersion of the PF polymer is another advantage to obtained the high bandwidth GI POF. It was clarified for the first time that the power distribution of modes formed by the mode dependent attenuation was the dominant factors of the higher bandwidth of the GI POF than theoretically predicted bandwidth, while the effect of the mode coupling was small.

Optoelectronic integrated devices can be found in an increasing number of applications in optical system and are expected to play a major role in future optical system. They offer the potential of compact, lightweight optics that can be mass-produced in polymeric materials by low-cost replication techniques. The fabrication technology that can achieve such micro-optical elements has been well developed. The direct He-Cd laser writing system is adopted to fabricate micro-optical elements in this work. Continuous- relief microlens elements and microlens arrays fabrication process, which can be used in applications requiring integration of optoelectronic devices, are described. The continuous-relief microlens elements and microlens arrays are fabricated at different conditions and the optimum conditions have been determined. The intensity of the laser beam, the moving speed of the movable stages, the distance between the top surface of the photoresist coated on the substrate to the UV objective lens, and the overlap of the adjacent patterns are the key parameters that significantly influence the surface roughness, profile and surface-relief height of the drawn continuous-relief microlens elements.

Vertical-cavity surface-emitting lasers (VCSELs) with emission wavelengths in the range from 850 nm to 950 nm are highly attractive light sources for low-cost, high-speed data transmission over several hundred meters of perfluorinated graded-index plastic-optical fibers (GI- POFs). Multi-Gigabit/s data transmission over common PMA- based step-index POFs is generally limited to several meters predominantly due to dispersion. Here, we demonstrate 3 Gbit/s and 7 Gbit/s pseudo-random-bit-sequence non-return- to-zero data transmission over 80 m perfluorinated GI-POF made of CYTOP using a single mode butt-coupled selectively oxidized InGaAs VCSEL source emitting at 935 nm emission wavelength. For 3 Gbit/s data rather the received optical power for a bit error rate (BER) of 10^-11 is -22.5 dBm for back-to-back (BTB). A power penalty of 1 dB is found for transmission over 100 m graded-index multimode glass fiber and 2 dB for 80 m GI-POF for 80 m GI- POF transmission. Reduced power penalty observed at 7 Gbit/s is attributed to the restricted modulation bandwidth of the VCSEL used in the experiment.

To solve the 'lower frequency gain' that limits the sped of conventional CMOS detectors, we spatially modulate CMOS photo diode junctions. This gives a differential photodiode with a flat responsivity curve up to a -3db bit rate of more than 500 Mbit/s. Detector and circuitry can now be combined on a single low cost CMOS chip for datacom applications. Here we report on the first integration of a receiver with a 300 μm diameter detector intended for use in plastic optical fiber (POF) links. The diameter of the detector allows to choose for large multimode POF cores (e.g. 250 μm) and low precision mechanical connectors. The receiver circuit is fully differential from the detector onwards, for improved power supply rejection. A differential feedback mechanism filters out the DC-level. A final symmetric OTA converts the differential signal to a single ended digital output. The total chip area including bonding pads is 440 μm x 600 μm. The received optical power to obtain a BER of 10^-9 (635 nm wavelength with PRBS 2¹⁵-1)is -17.6 dBm (17.2 μW) at a bit rate of 155 Mbit/s and -12.2 dBm (60 μW) at 250 Mbit/s bit rate. The chip dissipates only 25.3 mW at a 3.3V power supply. The bit rate is receiver limited. A design in a smaller feature size CMOS technology will show even better bit-rate and/or sensitivity performance. In conclusion, it is now possible to make detector/receivers combinations in standard CMOS lowering the overall cost of a POF data link system.

Fiber Bragg Gratings (FBGs) are high-performance versatile devices that have had a major impact on different ares of optical fiber technology. Their unique filtering and dispersion properties allow them to be used in DFB and DBR fiber laser, wavelength-stabilized semiconductor lasers, gain-flattened EDFAs, Raman amplifiers and lasers, dispersion-compensators and add/drop multiplexers. We report some of the latest advances in the area of grating fabrication, fiber grating dispersion-compensators and all- fiber DFB lasers and address how our improved dispersion- compensating gratings have a performance close to that theoretically predicted.

A novel mode-locked erbium-ytterbium fiber laser operating at 1550 nm using multiple quantum well (MQW) saturable absorbers was developed. The laser was constructed in a Fabry-Perot configuration using a fiber Bragg grating as a front reflector and a fiber Bragg grating output as a back reflector of the laser cavity. The passive mode-locking element placed inside the laser cavity is a 75 period InGaAs/InAlAs MQW saturable absorber grown lattice matched on an InP substrate. The output of the laser was taken through the other available port of a wavelength-division demultiplexer. The laser produced mode-locked output pulse trains at 16.67-MHz repetition rate and 10 mW of average output power.

Tellurite glasses doped with Er³⁺, Tm³⁺ and Nd³⁺ are investigated for broadband amplifiers in the third telecommunications window. Fluorescence spectra and lifetimes of Er³⁺, Tm³⁺ and Nd³⁺ in tellurite glass were measured. Stimulated emission cross- sections were calculated using the McCumber method for Er³⁺ and the Judd-Ofelt analysis for Tm³⁺ and Nd³⁺. The obtained emission parameters are compared with those in other glass hosts. The potential advantages of tellurite glass as amplifier host are discussed.

This paper discusses measurement technology, standards, and traceability for the optoelectronics industry. Examples include the development of artifact standards, known as standard reference materials, for the calibration of instrumentation, and the calibration of laser and optical fiber power meters and detectors.

Imaging the local evanescent intensity gradients by using a tapping-mode near-field scanning optical microscope is developed. Two different optical structures, one a well- characterized BK-7 glass prism in the total internal reflection configuration, and the other a side-polished optical fiber waveguide with a step index of refraction, were studied. Results show distinct imaging contrast of the intensity gradients, the reveal the variations of the local index of refraction of waveguide. This is a novel near-field optical method, and can be used in the imaging of local index of refraction of a variety of optical waveguide structures.

A method of index measurement, the so-called rn-line technique has been applied to measure the refractive index of planar waveguides fabricated by ion exchange method in BK7 substrate. By placing a prism coupler on the surface of the planar waveguide, the coupling angle of modes guided in the waveguide was measured. The prism has apex angle of 44.9° and is made of ZnSe with refractive index 2.59073 . The values of the coupling angles were then processed mathematically to obtain the effective indices of the guided modes. The number of modes guided in the waveguide depends on the duration of ion exchange process, and the effective refractive indices have been determined for the respective modes. The result for zero order mode, ranging from 1.5183 to 1.6887 for TM modes and from 1.5182 to 1.6891 for TE modes. On the other hand,for the duration of ion exchange process of 48 hours, five modes were guided in the waveguide and the effective refractive indices were 1.6887; 1.6167; 1.5818; 1.5649 and 1.5465 for zeroth, the first, the second, the third and the fourth modes, respectively. The use of the rn-line technique has been proved to be simple and effective with high accuracy in the characterization purpose of waveguides.

The measurement and evaluation of power spectrum of a semiconductor laser by delayed self-heterodyne interferometer is demonstrated with the use of a short delay fiber. The measured spectrum is analyzed numerically including the effect of a delay time much less than the laser coherence time. The theoretical formulation developed here is found to be found to be accurate since it exhibits a peak with finite width at the center frequency of the measured lineshape. The white and 1/f components of the laser FM noise are then separated successfully by fitting numerical analysis to the experimental results.

A characterization method of planar waveguides, namely m- line measurement has been utilized to reconstruct refractive index profile in planar waveguide. This method gives some values of incident angle that can be coupled in to waveguide, which after some mathematical calculations can provide its mode indices. To reconstruct the refractive index profile from mode indices as a function of normalized film thickness we use Inverse Wentzel-Kramers-Brillouin method. Furthermore, we select the value of n₀ that give the smoothest refractive index profile by finding the minimum sum of the squares of second differences of the profile. For this purpose, we implement reiterative, trial and error method on some values above the measured fundamental effective index value as a guess of the surface index. The result has been smoothed using curve fitting algorithm to exponential and Gaussian profile. The result confirm that index profile of planar waveguide can be reconstructed mathematically and the profile can be obtained more accurate by the proposed curve fitting technique than the basic IWKB method.

We propose a novel 6-port planar waveguide coupler device for adding and/or dropping tow different wavelengths from a WDM channel using a single grating. By writing a blazed Bragg grating into a few-moded core at a slight angle to the waveguide propagation direction, power can be coupled from the fundamental mode into higher-order, backward-propagating modes and vice-versa. Each such mode is channelled into a particular output port using an adiabatic splitter. Modeling results indicate that more than 99.99 percent of the power in the fundamental mode can be coupled into the higher-order modes at their respective Bragg wavelengths.

In this work planar and rib (beta) -SiC-on-insulator waveguides were investigated. The waveguides were fabricated by two different methods. In the first a technological process similar to that of SIMOX was used, a buried SiO₂ layer was formed by a two-step high-energy ion implantation of oxygen in SiC/Si wafers. For the second type of waveguides we used heteroepitaxy of SiC on SOI. The losses have been measured at 1.3 and 1.55micrometers . Rib waveguides were fabricated using dry-etching. These types of waveguides have great potential for high-speed silicon-based photonic devices compatible with silicon technology.

Grating couplers can be more efficient than end-fire coupling, in coupling light into a thin film waveguide. The aim of this work is to fabricate a low cost, highly efficient silicon waveguide grating coupler which is to be use data the telecommunication wavelength of 1.3 micrometers . Silicon-on-insulator (SOI) is chosen for fabricating the gratings as it is low cost using the exiting silicon technology. Unibond wafers were used because they offer flexibility in the choice of the thickness' of both the silicon film and the buried oxide layer, and they have low optical waveguide loss. The wafers used in this work have a Si film thickness of 1.14 μm and a SiO₂ buried layer thickness of 0.67 μm. Gratings that have asymmetrical profiles, such as blazed gratings are known to have higher directionality than the symmetrical rectangular gratings, and hence a higher output efficiency. Using perturbation theory, Si blazed gratings with an optimum grating height were predicted to have a maximum output efficiency of the order of 90% towards the substrate. The design and fabrication of the blazed gratings will be discussed in this paper.

In this paper, we apply the recently proposed effective- index method with built-in perturbation correction to the study of direcitonal coupler that consists of two parallel rectangular-core waveguides. We show with numerical examples that the splitting ratio of the directional coupler can be made insensitive to the polarization state of the input light by using proper waveguide parameters.

We present a fiber Bragg gratings for amplifier gain flattening which combine both an extremely high performance gain flattening response with a high-rejection ASE filter. The maximum shape error on the filter is <+/- 10% with an insertion loss of < 0.15 dB and group delay variation of <+/- 0.6 psec.

A systematic study has been carried out to understand how avalanche multiplication is modified by heterojunction band- edge discontinuities in Al_xGa_1-xAs/GaAs PIN diodes. A series of Al_xGa_1-xAs/GaAs structures have been investigated with well and barrier thicknesses fixed at 500 angstrom while the periods range from one up to twenty-five. Whereas the band-edge discontinuity of these structures has previously been suggested as responsible for producing large ratios of electron to hole ionization coefficients, this investigation shows that a significant ratio is only present in the thinnest 0.1 μm single period devices and that this is due to 'dead-space' effects rather than that of the heterojunction. In fact the multiplication characteristics of all structures are shown to approach those of the average alloy of the device as the number of periods increase, which also strongly suggests that the role of the heterojunction is insignificant. Varying the Al composition had little or no effect on the ionization coefficient ratio. The measured multiplication behavior is interpreted using a simple Monte-Carlo model which shows that the effect of the band-edge discontinuity is negligible because it is offset by different rates of energy relaxation in GaAs and Al_xGa_1-xAs.

Feasibility of a new integrated waveguide amplitude modulator/switch with more than 100GHz bandwidth in the visible and IR spectrum, based on the absorption of light due to linear interaction of the incident laser and a 2D plasma layer has recently been demonstrated. Plasma layers were generated via Muller's effect at the waveguide's interfaces. In this article, properties of the charge layers are investigated using quantum mechanics. First, the density of states and unperturbed energy eigenvalues are calculated. Then electron wave functions are obtained using the solution of Shrodinger's equation in the presence of an external applied electrostatic field in the structure. In the next step, energy eigenvalues are estimated by means of a perturbation technique. The electron density in the interfaces and the effective thickness of the charge layers are obtained using the calculated wave functions. The reflection problem is treated classically by direct solution of Maxwell's equations.

Acousto-optic tunable filter (AOTF), acousto-optic switch (AOS) and acousto-optic equalizer with high acousto-optic interaction efficiency are important in WDM networks. The technologies of unidirectional and focused transducer were adopted for the design of integrated acousto-optic device. Extensive usage for the acousto-optic device such as optical switches, gain equalizer and optical add-drop multiplexer have been studied. The concept that changing the radius of focus transducer can adjust the switching speed and FWHM of the filter was proposed for the first time.

Ion exchange, plasma deposition and flame hydrolysis are typically employed techniques for fabricating glass waveguides and gratings. These techniques have several drawbacks such as involvement of expensive instruments, multi-step procedure and high temperature treatment. These drawbacks make it difficult for their adoption mass production. The sol-gel process is a simple and inexpensive way for making glass, and embossing into sol-gel films provides a simple alternative for fabricating surface profile gratings and other integrated optical devices. In this paper, we report the usage of the embossing technique to fabricate gratings and diffractive optical elements (DOEs) in the sol-gel cladding layer of a waveguide. The designed DOEs manipulate out-coupled light from a slab waveguide and form 3 lines of equal intensity at a stipulated distance. The DOEs were designed as two-level optics by the direct binary search method based on the scalar diffractive theory, and the master molders used in the embossing were fabricated by UV laser writing on photoresist combined with reactive ion etching. We chose organic modified silane in the sol-gel process and no baking was needed, greatly minimizing possible shrinkage of the thin film.

In this paper, we present the fabrication of sol-gel derived silica based films on InP using both inorganic and composite material precursors. Thin silica films with thicknesses less than 0.5 μm, are achieved using an inorganic precursor by means of multiple spin coatings and rapid thermal processing at an annealing temperature of 450°C. The cracking pattern of the inorganic silica film on InP is analyzed. Thick films are derived from composite materials by multiple spin coatings with only furnace baking at 150°C. In addition, the different properties of each type of films and their potential applications in terms of monolithic integration are discussed.

Potassium lithium niobate (KLN) films have been prepared by sol-gel method using metal ethoxides as starting materials. The films were deposited by spin coating and were annealed in air in a conventional oven as well as in a rapid thermal processor (RTP). X-ray diffraction and Raman scattering measurements have shown that polycrystalline KLN films with tetragonal tungsten-bronze-type structure could be obtained on both SiO₂ buffered Si and fused quartz substrates. Surface morphology studies indicated that RTP annealing could avoid film cracking and enable nanostructured low- surface roughness KLN films to be formed. Optical waveguiding experiments showed that the films have refractive indices close to those of their single crystal and could support several modes. The films deposited on fused quartz were highly transparent in the visible-near IR spectral range and the absorption edges of the films, as determined from the absorption data, were found to shift towards the violet spectral side.

For rare earth doped silica-based glasses derived by sol-gel process, Al was used as a modifier in order to improve the dispersion of the rare earth ion in silica lattices, and thus, make the higher rare earth doped silica glasses without clustering possible. In this research, the influence of the ratio of Al to Nd on the fluorescence intensity and lifetime was studied in details to get the material which has a strong fluorescence intensity as well as the long fluorescence lifetime enough for integrated amplifier and laser use. Ten samples in the from of powder with different Al/Nd and different Nd concentration were prepared by sol- gel process. These powders were gotten by heating the dried gels in a surface in air environment. The result of the fluorescence intensity and lifetime show that the Al/Nd equals 10 with 1 mole Nd, that is the recipe 100SiO₂:10AlO_1.5:1 NdO_1.5 has the strongest fluorescence intensity in the ten samples. But its τ_1/e is only 110 μs. For 100SiO₂:20ALO_1.5:0.25 NdO_1.5, the obtained τ_1/e is 216 μs without special OH movement treatment. The research results show that we need to balance the fluorescence intensity and the lifetime to choose the suitable recipe for practice use.

SiO₂ films prepared using sol-gel technique have found enormous potential applications in photonics, electronics and sensor devices. However, the feasibility of the devices utilizing sol-gel technology lies on the ease of the fabrication processes such as patterns transfer using wet or dry etchings. Dry etching is preferred over wet etching as it is able to produce finer features with high anisotropic etch profile. In this paper, we report the development of a dry reactive ion etching process for sol-gel SiO₂ using a mixture of CF₄ and O₂ plasma. Parameters such as RF power, chamber pressure, CF₄ and O₂ flow rate, were optimized using a statistical method called Taguchi Technique. Etch rate of as high as 50nm/min, with high anisotropy etched profile, has been obtained.

We report the preparation of sol-gel derived planar waveguides from high titanium content hybrid materials. By incorporating organic molecules into the inorganic TiO₂- SiO₂ sol-gel glass matrix, porous-free waveguide films are obtained with low temperature heat treatment. The single spin-on thickness is measured to be more than 1.7 micrometers , enough to support light guiding and the refractive index of the film is found to depend on the heat treatment temperature. We also studied the microstructural and optical properties of the waveguide films using atomic force microscopy, ellipsometry, thermal gravimetric analysis, and UV-visible spectroscopy. Based on these experimental results, we found that heat-treatment at a temperature about 100 degrees C is sufficient to produce a relatively dense film with high transmission in the visible and near IR range. We believe that this process is very useful for the fabrication of passive photonic circuits on temperature sensitive substrates such as III-V compound semiconductors. Meanwhile, it has also been noted that a purely inorganic and crack-free silica-titan films could be obtained after baking the hybrid material film at 500 degrees C or higher.

In this research, silica based planar waveguide and powdered glasses doped with Er₂O₃, Yb₂O₃, TiO₂ and Al₂O₃ have been fabricated by sol-gel process. The photoluminescence enhancement has been demonstrated to be seven and four times that without Yb co-doping when pumped by a 980 nm laser diode and a 488 nm Ar⁺ laser respectively. The strongest fluorescence is observed form the 93 SiO₂: 7 TiO₂: 10 AlO_1.5: 1 YbO_1.5 glass. Dependence of the photoluminescence intensity and lifetime on Er³⁺ as well as Yb³⁺ concentration has been experimentally studied.

Temperature-dependent luminescence spectra, lifetimes and energy transfer in Eu³⁺ and other rare earths co- doped sol-gel SiO₂ glasses, were investigated in the temperature range from 10K to 300K. Due to the addition of the other rare earths as co-dopants, luminescence spectra of Eu³⁺ have shown significant changes not only in spectral intensities but also in emission peak features. Evaluation of the temperature-dependent energy transfer rates and lifetimes and the computation of critical energy transfer distances by employing two different energy transfer model schemes, have provided evidence for such luminescence behavior in the nanometer-size confined glass matrices.

BaTiO₃ thin films are prepared on ITO-coated Corning 1737 glass. The solution is prepared from a double metal ethoxide and the films are deposited by spin coating and annealing at 700°C for 2 hours in an O₂ atmosphere. The films are characterized using x-ray diffraction, atomic force microscopy, micro-raman, UV-VIS spectroscopy, and Sawyer-Tower Bridge. The pure perovskite phase of BaTiO₃ is identified by x-ray diffraction. The tetragonality is revealed from Raman study by identifying the symmetrical dependent Raman shift at about 306 cm^-1. The ferroelectricity of the film is confirmed by the P-E hysteresis loop. The films are highly transparent, with an absorption edge at 3.73eV. These desirable features indicate that the films have potential in electronic display and electro-optical applications.

Tin Sulphide (SnS), a layered semiconducting material which finds wide applications in optoelectronic devices and window material for heterojunction solar cell. This paper reports on the material properties of thin films of SnS prepared by electrodeposition and brush plating. Brush plating is an electroplating process usually adopted to coat large area thin metal or alloy film. The films of 0.6-1.0 μm and 1.0-2.5 μm thickness were prepared by electrodeposition and brush plating respectively. X-ray diffraction studies showed that the as prepared films of both techniques revealed polycrystalline nature of the films and the lattice parameter values are: a=0.403 nm; b=1.145 nm; and c=0.399 nm. The surfaces were analyzed by electron spectroscopy for chemical analysis and SEM for surface morphology. The band gap, refractive index and extinction coefficient values were estimated from the optical studied in the wavelength region of 400-1500 nm. The adhesion of the films prepared by brush plating was found to be excellent. Photoelectrochemical solar cells were fabricated using SnS photoelectrodes. Capacitance-voltage studies revealed the p- type nature of all the films. The flat band potentials were 0.52 V and 0.47 V respectively. The quality of the films prepared by electrodeposition and brush plating are compared.

Two-layer light emitting devices were fabricated using electrochemical deposited polybithiophene (PBTh) as the hole-transport layer and spin coated blend of polyoctylthiophene and a butadiene derivative as the emitting layer. It was found that the current density used for depositing polybithiophene greatly affects the effectiveness of the PBTh films as the hole-transport layers in enhancing the electroluminescent (EL) intensity and efficiency. Through analyzing the oxidation-reduction properties and conductivity of the PBTh films and the EL efficiency of the device, it can be concluded that there is an optimal current density for depositing the PBTh hole transport layer for the El devices.

Comparing with EDFA, one prominent disadvantage of semiconductor optical amplifier (SOA) is that its gain is sensitive to the state of polarization of incident light. Reducing the polarization sensitivity of SOA is one of the important aims that man goes in for in the research of SOA. In this paper, we analyze the polarization performance of SOA, and also successfully develop a mixed-strain quantum well, polarization insensitive SOA. Ultra low residual reflectivity film is coated on the cleaved ends of active- layer to eliminate the resonant effect of the cavity and suppress self-simulated emission, thus the incident optical signals could obtain single path gain while traveling through the active-layer, which forms the traveling-wave amplification.

The solidus-liquidus phase diagram of oriented In_xGa_1-xAs_ySb_1-y quaternary alloy, which is latticed-matched to the GaSb substrate, has been calculated. We used the Levenberg-Marquardt method to deal with the nonlinear equations and find the phase curves at different temperatures. We obtained a series of phase diagrams from 500°C to 730°C. The phase plots of the indium content in the GaSb-lattice matched In_xGa_1-xAs_ySb_1-y quaternary as a function of the antimony content of the metal at different temperatures bear three kinds of shapes. The plots below 532.7°C are similar, displaying a hyperbola with two branches, and the lower the temperature, the larger is the gap between the branches. The phase plot changes to two intersected lines at 532.7°C. At temperatures higher than 532.7°C, the phase diagram includes a nearly symmetrical curve and a segment. The higher is the temperature, the shorter is the segment. A new growth region have been discovered, where GaSb-lattice matched In_xGa_1-xAs_ySb_1-y with high indium content can be grown.

We describe our research on the fabrication of GaInAsP/InP Light Emitting Diodes (LEDs)/Laser Diodes (LDs) at wavelength of 1.5 micrometers using wafer grown by Liquid Phase Epitaxy (LPE) system. The source materials are baked at temperature of 610 degrees C at the horizontal LPE system. The epitaxially layers are formed on InP substrate in the graphite boat with the cooling rate of 0.7 degrees C/min. The wafers are characterized using Scanning Electron Microscope (SEM), Photoluminescence (PL) and x-ray Diffraction (XRD) techniques. It is formed into LED chips by cleaving method after metalization, annealing and lapping processes. About 20-30 LED chips can be obtained from a wafer. Characterization has been conducted to examine the LED basics characteristics which showing the diode characteristics of the chips at its voltage-current curve. Furthermore, electroluminescence process is conducted by giving an instantaneous current pulse on the chip and detecting the output light using Ge detector; resulting a voltage-time curve displayed at a digital storage oscilloscope. The spectrum of the LED chip was observed by using an optical spectrum analyzer, giving peak wavelength at (lambda) approximately 1.5 micrometers with spectral width between 90-105 nm. Future works in fabrication of GaInAsP/InP LD at this wavelength is still underway starting with preliminary experiment of photolithography and etching techniques of LPE grown wafers is conducted.

Fabrication of periodic grating is very important for photonic devices such as Distributed Feedback (DFB) lasers, optical fiber Bragg grating based devices and optical couplers. Here, we report the development of holographic grating techniques utilizing a rotary mirror holder for grating period from 10 μm to 0.5 μm and Fresnel bimirrors for period greater than 1 μm. These holographic technique offers a wide range of tunability, good resolution, relatively simple apparatus, high uniformity and large-coverage of pattern area. A single line HeCd laser was used in these set ups. The grating patterns have been successfully transferred onto GaAs substrate after dry etching with photoresist as mask. In addition, with the insertion of orthogonal Fresnel bimirror in the systems, square grating patterns have been successfully obtained with grating period of 2 μm x 2 μm.

The preparation of polycrystalline GaAs films by using electrodeposition technology is described. Influences of electrodeposition parameters on the quality of films were discussed, such as the current density, the relative concentration of ions, the value of pH of the electrolyte. On the basis of observing the micrographs, we have measured the chemical composition, microstructure and parameters of the energy band of the films. The result show that the composition of the films deposited is Ga_0.9946 As_1.0054, and the direct gap nature of the deposited material, its band gap is 1.40eV.

In order to study the Mn macrosegregation in accelerated crucible rotation Bridgman (ACRT-B) growth of Hg_1-xMn_xTe crystal, a mathematics model was established for the evaluation of the solute (Mn) distribution in the growth direction based on quantitative analyses and several assumptions. The results reveal that in Hg_1-xMn_xTe crystal grown by ACRT-B method, Mn content is much higher than the average value in the initial region and reduces gradually to a lower value in the final region because of solute redistribution. Only a section of the crystal fit the required composition with the acceptable error. The crystal section with acceptable composition can be also obtained in Hg_1-xMn_xTe ingot grown from the melt with no stoichiometric compositions. The length of the section increases with decreasing in x₀ value. Meanwhile, it moves toward the initial region. To grow Hg_1-xMn_xTe crystal with a certain composition, such as x=0.11 ,it is preferable to use the melt with a lower average Mn content, so that the crystal with the acceptable composition will be longer and located in the early region where the crystalline quality is better. A 5mm-diameter Hg_0.89Mn_.011Te ingot was grown by ACRT-B method for the comparison. A single crystal is obtained in the early part of the ingot after the competitive growth of several grains in the initial region. However, the single crystal is blocked by several new grains, which were nucleated on the ampoule wall after about 1 cm. The composition distribution along the growth direction was analyzed by electron microprobe. The experimental data are essentially coincident with the calculation result in the main part of the ingot, but lower than it in the initial region and higher in the final region. These errors may tem from the approximation of homogeneous mixture in the liquid in the mathematical model, which is not true in the initial and final regions because the convection there is limited.

Kinetics of AlAs steam oxidation process is investigated theoretically in cylindrically symmetric mesa structures. Under the assumption of a steady-state process, compact analytical formulae are obtained for time evolution of the oxidation front and for the oxidation rate. Values of main oxidation process parameters are extracted from existing experimental data for T = 350 °C and the layer thickness d = 250 nm. The oxidation rate is found to first decrease from its initial value of B/A and remain almost constant for a large range of intermediate sizes of unoxidized region. When the unoxidized region becomes very small, a rapid increase in this rate up to the value of B/[A(1-β)] is predicted. This renders the process control of fabricating miniature oxide apertures with diameters < 2 μm extremely difficult. Comparison with 1D model of oxidation process in cartesian geometry reveals significant differences in time evolution of the oxidation front. Understanding these differences is important for achieving a good control of the oxidation process in cylindrical structures.

Quantum well IR photodetector (QWIP) which exhibits the dual wavelength response in region of 3-5 and 8-12 μm was demonstrated in one stack of double barrier quantum well (DBQW) structures. These dual-band photoresponse originate from intersubband absorption between bound-to-quasi-bound and bound-to-continuum states, respectively. The symmetric DBQW consists of two subsequence barriers on both sides of the well i.e. inner thin high barrier and outer thick low barrier. The inner barrier was designed to be thin enough to allow photocarriers in quasi-bound-state tunnel through and also to make the continuum-state occurs at the top of the outer barrier. Due to photoresponse from the transitions between bound-to-quasi-bound and bound-to-continuous states, the desired wavelength regions were tailored by the barrier height of both inner and outer carriers while the sensitivities of each band were designed by thickness of the inner barrier. The optimum structure was proposed by 14-band Hamiltonian including six p-like conduction band states. The absorption in TE and TM mode were separately derived and illustrated in each response wavelength for the optimum structure.

A novel method to suppress noise in a high harmonically mode-locked erbium fiber laser with external optical modulator using DFB-laser diodes is presented. The DFB-diode laser played both roles as external-cavity modulator and as stabilizer. The driving frequency is of 2.5 GHz and the wavelength difference between DFB-diode laser emission and fiber laser dominant was adjusted in range of +/- 2 nm. The fiber laser modulation frequencies can be tunable at 2.5; 5 and 10 GHz by the adjusting an external laser diode modulation rounding 2.5 GHz +/- 66 KHz. A fiber laser so stabilized has enabled at 2.5 or 5 GHz remaining error free for more 4 hours with nearly transform-limited pulse width of 25-35 ps.

We propose and use for the first time tunable long-period fiber gratings to facilitate the gain equalization of an erbium-doped fiber amplifier (EDFA). The ASE peak of an EDFA around the wavelength 1534 nm was equalized by 7.5 dB and the gain peak by 3 dB.

A white light-emitting organic/polymeric electroluminescent (EL) device with multilayer thin-film structure is demonstrated. The device structure of glass substrate/indium-tin oxide/poly(N- vinylcarbazole)/phenylpyridine beryllium(BePP₂)/8- (quinolinolate)-aluminum (Alq) doped with 5,6,11,12- petraphenylnaphthacene/Alq/LiF/Al was employed. The turn-on voltage is as low as 2.9 V. Blue fluorescent BePP₂ yellow fluorescent rubrene, and green fluorescent Alq are used as three primary colors. The Commission Internationale de l'Eclariage coordinates of the emitted light are at 10V, which is located in the white-light region. Bright white light, over 6800cd/m², was successfully obtained at about 17V, and the maximum efficiency reaches to 1.38m/W at 8.5V.

Refractive index profile of surface channel waveguides can be determined by analyzing the near-field intensity pattern. A mathematical model, the inverse Helmholtz equation, is derived in order to use these data to reconstruct the refractive index profile under consideration. In this work, the measured near-field intensities are preprocessed by means of gamma correction, background noise subtraction, Fast Fourier Transform, and low pass finite impulse response (FIR) digital filter. Several types of FIR windows are chosen. The results are used to reconstruct the refractive index profile of the waveguide. The results show that the application of low pass FIR digital filter by using Hamming window reduces noises better than other windows. The application of this method in determination of refractive index profile of annealed proton exchange LiNbO₃ channel waveguides is demonstrated.

The extended coupled mode equation incorporating the intensity dependent refractive index nonlinear optical effect of the medium was applied to a basic study of beam propagation in a symmetrically configured five-layer planar structure composed of two optically coupled waveguides with identical optically nonlinear guiding media. The three cladding layers are constituted of linear optical materials of the same refractive index. The result of this study and the result of simulation employing an extended Finite- Difference Beam Propagation Method explicitly demonstrate the feasibility of developing an optical device serving both as an all optical directional coupler and optical switch using the basic multilayer planar structure considered in this study. Restricting ourselves to the lowest TE waveguide modes, the power transfer efficiency and coupling length L_c were determined and described as functions of the input light intensity and the waveguide parameters such as the waveguide separation and the refractive indices.

Bloch modes can be excited in planar array due to its periodic lateral refractive index. The power coupled into each eigenmode of the array waveguides is calculated through the overlap integrals of the input field with the eigenmode fields of the coupled infinite array waveguides projected onto the x-axis. Low losses can be obtained if the transition from the array to the free propagation region is adiabatic. Due to the finite resolution of lithographic process the gap between the waveguides will stop abruptly, however, when the waveguides come into too close together. Calculation results show that losses will occur at this discontinuity, which are dependent on the ratio of the gap between the waveguides and grating pitch and on the confinement of field in the array waveguides. Tapered waveguides and low index contrast between the core and cladding layers can lower the transmitted losses.

In this article the relation between the directions of eigen-polarizations of light waves with the stored electrical energy in an anisotropic medium is discussed, and it is shown that each of two eigen-polarizations correspond to an extremum in the stored electrical energy. So for a given direction of a wave vector and a given magnitude of displacement electric field vector, there exist two extrema that result in the eigen-polarizations. It is shown that this conclusion also holds for plane waves in materials with anisotropic permeability tensor. An interesting effect is found that normal to the crystal axes, the distribution of energy in different directions is uniform. THerefore, for uniaxial crystals, only one of such plane directions could exist while for biaxial crystals, two such planes could be found, corresponding to the two optical axes.

Doping ZnO and Ga₂O₃ in LiNbO₃ crystal, the Zn:Ga:LiNbO₃ was grown by Czochralski method. The IR transmission spectra and the photon damage resistance ability of the LiNbO₃ and Zn:Ga:LiNbO₃ crystal were measured. The proton exchange technology was used to make the LiNbO₃ and Zn:Ga:LiNbO₃ crystal waveguide substrates. The m-line method was taken to study the photo damage of waveguide substrate. We observed that the threshold of Zn:Ga:LiNbO₃ is above two magnitude higher than that of Mg:LiNbO₃. Zn:Ga:LiNbO₃ crystal is better performance than LiNbO₃ crystal.

This paper presents a new cost-effective fiber-to-waveguide coupling method for self-aligning optical fibers on silicon platforms, and for achieving optical quality end-polished silicon-on-insulator (SOI) single-mode rib waveguide devices using wet chemical micromachining techniques. Through accurate alignment to the <011> plane(s) of the (100) device layer of a SOI wafer, rib waveguide devices with self-alignment features are fabricated with the ends of each waveguide wet etched and concurrently polished providing an optical quality facet or fiber-to waveguide interface. Eliminating the need to saw cut and then mechanically polish the waveguide device ends, the overall fabrication process is simplified and provides a fiber alignment capability at the ends of the waveguide devices with an alignment accuracy limited by fiber size tolerance. Experimental measurements were carried out to verify the optical quality of the waveguide facets formed using this new technique, which proved excess facet losses of practically unmeasurable quantities. Both simulation and experimental results were obtained to verify the single-mode nature of the rib waveguides.

A 16 X 16 Crossover photonic switching network with hybrid integrated CMOS/SEED smart pixel device and 2D optical fiber bundle array I/O access device is reported in this paper. SEEd array devices ar used as light receivers and transmitters, while CMOS devices make efficient logical processing. 4 X 40 2D multilayer optical fiber bundle arrays are fabricated and are used as I/O access devices in the crossover photonic switching network. The center to center spacing between adjacent optical fibers in the same layer of the fiber array is 125micrometers , and the spacing between adjacent layers is 250micrometers . Displacing tolerance of the fiber bundle arrays is less than 4 micrometers and the angular tilt error is less than 0.03 degree. It has the feature of high density, high precision, array permutation and easy to couple with 2D CMOS/SEED smart pixel device.

Radiative transitions in porous silicon (PS) have been studied using a new variant of the time-resolved photoluminescence (TRPL) spectroscopic measurement, in which beside the pulsed light source the sample was irradiated additionally by a continuous light source. With this modification a certain photoluminescence (PL) region in the TRPL spectrum of PS may be quelched, the position and width of which depends strictly on the wavelength range and intensity and the continuous light source. Using different continuous light sources, the quenching of different PL regions has been observed experimentally. The results obtained are discussed with the model of recombination in the core and on the surface of nanocrystallites. It seems that the selective quenching of PL in the TRPL spectrum is helpful to reveal the origin of the light emission for PS.

A new highly sensitive photoreceptor in visible-spectrum region with high contrast voltage ratio has been developed for an electrophotographic device. The multilayered amorphous silicon photoreceptor has been prepared with PE- LPCVD and sputtering system. The structure of the photoreceptor consists of four part: (a) Al substrate, (b) a-WO₃ blocking layer, (c) a-Si:H(i) photogeneration and transport layer, (d) a-C:H surface protecting layer. In this study, the photoreceptor is exposed with different wavelength and illumination. Keithley 236 Semiconductor Parameter Analyzer is used to measure the current-voltage curves of photoreceptor. In addition, Electrostatic Parameter Analyzer is used to measure the photo-induced discharge curves, which is used to simulate the processes of copying machines. According to the I-V curves and PID curves, we can investigate the transport of photocarrier in photoreceptor and the optoelectronic parameters.

This paper embodies the first report on the pulse reversal deposition of CdSe thin films. The as-deposited and heat treated films were characterized by XRD, optical absorption spectroscopy and electrical properties. The polycrystalline deposits of CdSe obtained indicated a hexagonal structure after heat treatment at 550°C. From the otpical absorption studies the bandgap was found to be 1.70 eV and absorption co-efficient of 10⁴ cm^-1 were obtained. At an illumination of 80 mWcm^-2 conversion efficiencies of 5.56% and 6.74% were obtained for the photoelectrodes without and with pulse reversal.

We report the optical characterization of Sm³⁺:SiO₂ + Al₂O₃ + Li₂O + Na₂O + MgO glass from the measurements of optical absorption spectra, total luminescence spectra and fluorescence lifetimes of the prominent emission transitions of the Sm³⁺ ions. Besides the analysis of spectral properties, physical and nonlinearity characterizing property parameters have also been computed to understand the optical dispersive power of this glass. By the application of Judd-Ofelt parameters (Ω_λ) of the measured absorption spectrum, the radiative transition probability factors (A) and stimulated emission cross-section (σ^E_P) of the observed fluorescent levels have been analyzed. Both emission intensity and measured lifetimes of the prominent luminescent transition (⁴G_5/2 → ⁶H_7/2) concerning Sm³⁺-glass are showing a descending trend with a rise in temperature having a N₂-laser (337.1 nm)as the excitation source.

Here, we bring out an IR transmitting new optical glass based on TeO₂ added with AlF₃ and LiF, containing dual rare earth ions as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu³⁺ (⁵D₀ → ⁷F₂ at 615 nm) as a function of temperature both in the presence and absence of Nd³⁺ ions. The energy transfer rates (W_tr) critical distances (R₀)and transfer efficiencies (η_tr) have been evaluated based on the measured lifetime data of this glass.

This short paper reports both the photoluminescence and the lifetime measurements of a prominent emission transmission (⁵D₀ → ⁷F₂) of Eu³⁺ both in the presence and absence of the codopant rare earth ion (Dy₃₊)in an optical glass of the composition (79-x)TeO₂ + 6AlF₃ + 15LiF + xLn₂O₃ as a function of temperature down to 10K.

Using the sol-gel process, we prepared three groups of Er-doped glasses, namely, Er-doped Si0₂-A10_1.5 (SAB) glass, Er-doped Si0₂-Ti0₂-A10_1.5 (STAE) glass, and Er-doped Si0₂-Ge0₂-Al0_1.5 (SGAE) glass. Various erbium concentration and different host composition under the same processing condition have been studied in order to optimize the material composition to get the strongest fluorescence emission for each material system. It has been found that for SAE glass, the strongest fluorescence emission is obtained when the mole ratio of the three constituent oxides is lOOSiO₂ : 20A10_1.5 2ErO_1.5. For the STAE material system, the best composition ratio for the strongest fluorescence emission is 93 Si0₂ : 7TiO₂: 20A10_1.5 : lErO_1.5, whereas the value for SGAE glass is 9OSiO₂:lOGeO₂ : 2OAlO_1.5: 1ErO_1.5. But the relative lifetimes were obtained with the recipe lOOSiO₂:10A10_1.5:1ErO_1.5 for SAE series, 90 Si0₂:lOGeO₂:1OAlO_1.5: 1ErO_1.5 for STAE group and 93 Si0₂:7Ti0₂:20A10_1.5:1ErO_1.5 for STAE group. Using these recipes, three 20-layer (up to 2.5 μm) crack-free films have been deposited on silica-on-silicon (SOS) substrates with multiple spin-coating and rapid thermal annealing (RTA). Only the STAE film and the SGAE film are found to guide light. The experimental results show that STAB glasses have higher hydrophilicity than SGAE glasses and SGAE glasses has lower crystallization temperature than STAE glasses. The fact that these waveguiding films emit relatively strong fluorescence around the wavelength of 1.55 μm implies that such planar waveguides are potential candidates from which integrated optical waveguide amplifiers and lasers operating at the third optical fiber communication window can be fabricated.

Silica/Titania optical waveguides have been prepared by the sol-gel technique using Glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as the starting materials. Scanning electron microscopy, atomic force microscopy, thermal gravimetric analysis, differential thermal analysis, and UV- visible spectroscopy have been used to characterize the morphology, the optical and structural properties of the waveguide films. The waveguides are also characterized by measuring their refractive index, thickness, and propagation loss as a function of titanium content and thermal treatment. The obtained results show that after an annealing at 500°C or above, an inorganic silica/titania crack-free film could be obtained. The single layer spin- coated film has high transparency in the visible range and is more than 0.5 micron thick. The propagation loss of the waveguide films was also estimated by using the scattered- light measurement method and was found to be around 1.0 dB/cm at the wavelength of 632.8 nm.

The cracking of sol-gel derived films on Si(100), Si(111), and glass substrates has been studied experimentally using optical microscopy, scanning electron microscopy and optical scattering method, as well as theoretically using the static method and the dynamic method. The experimental observations show that the primary cracking directions of the sol-gel derived film depend strongly on the symmetry of the substrate. As all the studied substrates have a uniform biaxial elastic modulus, the static method cannot explain such cracking behavior. However, the most probably directions of the primary cracks can be determined by considering the anisotropy of the longitudinal and the transversal elastic waves, and these directions are in good agreement with the experimental observations.

Polycrystalline thin films of Ca-modified lead titanate (PCT) were deposited on Pt/SiO₂/Si substrates using a diol-based sol-gel process. Calcium acetylacetonate hydrate was adopted as a starting material instead of calcium acetate or calcium nitrate tetra-hydrate used in general. By changing the Ca content and heating temperature, the influences of various processing parameters on the characteristics of thin films are studied. With the increase of Ca content, the relative dielectric constant of PCT thin film increases from 43 up to 70 at the heating temperature of 700°C. It was found that the coercive field and the remanent polarization decreased, but the pyroelectric coefficient increased with an increase of Ca content. The results show that PCT thin film exhibits the largest figures of merit for the voltage responsivity and the specific detectivity at heating temperature of 700°C and Ca content of 25 mol%.

Thin films of poly(N-vinylcarbazole) (PVK) were prepared by spincoating upon fused silica substrates. PVK was dissolved in dimethyl formamide (DMF) and processed at elevated temperatures. Thin films with the required thickness and low surface roughness were obtained by careful optimization of the preparation parameters, such as concentration, spinning speed and temperature of these spincoating process. The dispersion of refractive indices of PVk films was measured by reflectometry and by prism coupling at 633 nm and 1064 nm. The attenuation loss of slab waveguides was measured by monitoring the stray light of the guided mode with a diode array. The loss depends significantly on the relative ratio of surface roughness to thickness. As this ratio depends on preparation conditions, we succeeded in fabricating planar waveguides of PVK that had an attenuation loss of only 1 dB/cm at 633 nm.

Electro-optical properties of an epoxy-based polymer dispersed liquid crystal (PDLC) have been investigated. A morphological analysis has been performed by optical microscopy in order to estimate initially the average diameter of the liquid crystal microdroplets dispersed in the polymeric matrix. We present the observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a PDLC. Optical responses of the composite film under the conditions of an externally applied ac electric field and a film thickness of 50μm, were determined using an Argon laser. The experimental result showed promising switching times with a rise time of 200 μsec and a decay time of 2.2 msec and an exceptionally high contrast ratio up to 410. These result demonstrate the validity of employing this new PDLC in electro-optical devices.

A nearly perfect single crystal DAST thin film has been grown in this study. The polarized optic microscopy photograph demonstrated an ordered morphology for the surface of this thin film. The FTIR spectrum shoed that the intensities of the characteristic absorption bands for the single crystal thin film were different from that for the crystalline thin film. With 3D luminance image analysis, it was found that the intensity of a guided laser light passing through the single crystal thin film along its a-axis is a little bit stronger than that guided along a standard 8.5/125 μm silica optic fiber. The diameter of the guided light and the space between the two guided lights estimated were about 25 μm and 65 μm, respectively. This study indicates that only the single crystal thin film can be used as a waveguide without further process and is a promising candidate for electro-optic modulators and other active optical devices.

The direction of this paper is to describe the various analytical tools and measurement techniques used at SilkRoad to evalute the transmission-laser cavity control and optical beam train going into the electro optical modulator and subsequently into the otpical transmission fiber. The measurement values for the line width and the coherent length of the laser beam,and the subsequent Laguerre orders that are generated in the electro-optical modulator, are critical to the operation of the SilkRoad Optical Refractive Synchronization transmission technique. We begin the paper with the various analytical techniques that are used to calculate the line width and the coherency length. Following the analytical model, we describe the various measurement techniques and the subsequent data that results from our experiments.

The Stark effect modulations with Doppler broadening have been analyzed by semiclassical theory. The absorption coefficient and modulating depth of Stark effect system have been derived by density matrix method. Modulation characteristics between line of the isotropic ¹³CO₂ laser at 10.784 micrometers and as Q transition of NH₃ molecular have been researched. When modulating frequency is 1MHz, modulating frequency is 1MHz, modulating depth reaches 33 percent. An isotopic ¹³CO₂ laser, which outputs 4W and has 25 lines of spectrum, was fabricated. Instability of laser intensity is less than 1 percent.

0.78% tensile strained InGaAs/InAlGaAs and InGaAs/InGaAsP QW lasers emitting at 1.55 micrometers are studied theoretically. Independent of material system, large band discontinuity results in a large number of subbands and high density of states, which gives rise to lower optical gain and T₀. Besides, the 3 dB bandwidth is increased and is more resilient to high temperature. InGaAs/InAlGaAs QW lasers can achieve threshold of 572 Acm^-2, T₀ of 45K and 3 dB bandwidth of 38 GHz at gain of 100 cm^-1. InGaAs/InGaAsP QW lasers can only achieve 22 GHz. This suggests that the low conduction band offset ratio limits the bandwidth of InGaAs/InGaAsP QW lasers. InGaAs/InAlGaAs laser, on the other hand, could be designed to give low threshold, large bandwidth and high T₀.

A newly developed inverted tapping-mode tuning-fork near- field scanning optical microscope is used to study the local near-field radiation properties of a strained AlGaInP/Ga_0.4In_0.6P low power visible multiquantum-well laser diode. With this novel technique, we can easily image the local near-field optical intensity gradients. In the intensity ratio image there are remarkable contrasts among the various regions on the laser diode facet. The anomalous phenomenon manifests the different origins of the near-field optical waves from various regions on the laser diode facet. We believe that this method should be very important for further understanding the optical radiation properties in the near-field region.

The 'optoelectronics industry' is a collection of six or more distinct industries that all depend on OE technology. The major markets are in communication, imaging, storage and displays. This paper gives a brief overview of the anticipated paradigm shifts, the potential markets and the promising new technologies in various OE markets.

The development of vertical-cavity surface-emitting lasers (VCSELs) has led to new types of low power, high efficiency light sources for data communication. The small size, low power, and surface-normal emission of VCSELs has enabled relatively dense 2D arrays for highly parallel data communication and optical signal processing. In this paper we examine the issues of device scaling on VCSEL performance. We look specifically at what benefits may be derived from continued scaling of the active volume down to minimum sized dimensions, and what device schemes may be required to obtain the scaling. Laser rate equations are used to show that when the VCSEL mode volume is reduced to wavelength cubed dimensions, a significant improvement in modulation speed is predicted based on the radiative lifetime change due to the Purcell effect. However, several parasitic effects must be controlled in order to realize these benefits. Most important are control of the optical loss due to diffraction or scattering, and control of the electronic losses due to carrier diffusions and surface effects. Novel optical confinement schemes based on oxide- apertures, photonic bandgaps, and/or closely coupled 2D arrays may be useful for controlling optical loss, while self-assembled quantum dots are attractive for controlling electronic diffusion to dimensions within the minimum optical mode volume.

A microscopic many-body theory for the nonlinear optical response of semiconductors is reviewed. The importance of Coulomb interaction induced carrier correlations is demonstrated in excitonic pump-probe spectra. The influence of excitonic and biexcitonic contributions to coherent pump- induced absorption changes at the exciton frequency are discussed. Absorption changes induced by incoherent exciton and unbound electron-hole populations are studied.

This paper discusses the role and impact of advancements in Photonics Technology on the performance enhancement of guided missile weapon systems with specific reference to the development of Indian guided missiles program. India is emerging as a technologically strong nation with core competence in Space, Missile and Nuclear technologies, advanced computing including supercomputers and software. Based on the realization of the fact that high technology areas that help in attaining the global competitiveness. Photonics is identified as one of the important areas in this direction and hence high priority has been accorded for R and D in Photonics. This paper reviews the current trends and developments in missile technology and highlights some of the important developments in Photonics that have a force multiplying effect on the performance enhancement of guided missile systems.