For next generation fiber to the home (FTTH) system, we are asked to use inexpensive optical devices. For that the use of soft-lithography instead of standard photolithography and dry etching technologies is attractive because cost saving optical device can be realized. Polymerization using multi-photon absorption of materials is also a good method for optical waveguide fabrication. Using these processes, we can fabricate the waveguide and connect it with optical fibers at the same time. In this presentation, several simple fabrication methods will be discussed. Optical characteristics evaluation method for polymer optical waveguides to accelerate the development of optical circuits will also be presented.

I review recent progress on optical fiber amplifiers and their applications in fiber-optic communication systems. This study focuses on rare-earth doped fiber amplifiers (RDFAs) and fiber Raman amplifiers (FRAs). There are three types of RDFA, namely erbium, thulium, and praseodymium doped fiber amplifiers (EDFAs, TDFAs, and PDFAs, respectively) and EDFAs have been widely deployed in trunk networks for about a decade. EDFAs have wideband, low noise, and high pumping efficiency characteristics, and are key components of high-capacity and cost-effective wavelength-division-multiplexing (WDM) transmission systems in the low loss 1.5 μm band. In contrast, distributed Raman amplification (DRA) has been recognized as a powerful and practical technology in long-haul trunk networks in recent years. DRA/EDFA or DRA/lumped FRA hybrid-amplification systems yield significantly higher signal-to-noise ratios than lumped optical amplification systems that use EDFAs or FRAs. The latter are hybrid systems called all-Raman systems. As regards the bandwidth enhancement of optical fiber amplifiers, which is indispensable for cost-effectively realizing a rapid increase in communication traffic, silica Raman amplifiers have seamless single band bandwidths (Δλ) up to ~100 nm wider than those of RDFAs (~30 to ~80 nm). Further bandwidth enhancement can be achieved by using tellurite-based Raman amplifiers with Δλ up to ~160 nm or multi-band amplifiers. Each multi-band amplifier uses plural single-band RDFAs and/or FRAs in the parallel configuration in the low loss wavelength region (1.3-1.6 μm band) of silica transmission fibers.

Bismuth (Bi) -doped silicate glass for future photonics applications was proposed by Y. Fujimoto et al. in 2001 [1]. And its broadband fluorescence characteristic at 1.3um band was demonstrated for the first time. From this report, several studies such as clarifying the fluorescence mechanism, surveying the optical properties of Bi-doped glass with various host glass materials and so on have been done. However, there was no report on fabricating Bi-doped silicate glass fiber (BiDF) for the demonstration of optical amplification and laser oscillation. In 2005, Haruna et al. succeeded in fabricating the BiDF by Modified Chemical Vapor Deposition (MCVD) method for the first time, and evaluated its absorption and fluorescent characteristics [2]. In this report, the absorption bands around 0.5 um, 0.7 um, 0.8 um and 1.0um were shown, and the very wide fluorescence band with a FWHM of 192 nm centered at 1.06um was also indicated. The background loss of the fiber was as low as <0.05 dB/m at 1.55 um because of the MCVD method that is well-established method for the conventional optical fibers. Furthermore, the 1.3 um band amplification using the BiDF prepared by the similar MCVD method was reported by V. V. Dvoyrin et al. in 2005 [3], and the laser oscillation by this fiber was also demonstrated in 2006 [4]. In this paper, a current research progress on the Bi-doped glasses and fibers is reviewed. By looking at the optical properties such as fluorescence characteristics, future possible applications are explained and its fluorescence mechanism is also discussed.

We present a monolithic integrated Raman silicon laser and amplifier based on silicon-on-insulator rib waveguide race-track ring resonator with an integrated p-i-n diode structure. Under reverse biasing, we efficiently reduced the nonlinear loss due to two-photon absorption induced free carrier absorption and achieved continuous-wave net gain and stable, single-mode lasing with output power exceeding 30mW and 10% slope efficiency. The laser emission has high spectral purity with a side mode suppression exceeding 70dB and a laser linewidth of <100 kHz. This ring resonator architecture allows for on-chip integration with other silicon photonics components to provide a highly integrated and scaleable monolithic device. Using the ring resonator architecture, we can build a compact, chip scale Raman amplifier that takes advantage of the resonance effect to increase the effective pump power and reduce the device size. Our simulations suggest that a 3dB net gain can be achieved with 4dB less pump power in a 3cm ring compared to a straight waveguide of the same length.

Starting with a waveguide amplifier as a crucial building block among many others, we demonstrate a library of optical elements that can be seamlessly integrated on a single silica-on-silicon chip and produce complex integrated optical circuits. This new level of planar waveguide integration is made possible by recent advances in our waveguide manufacturing technology capable of combining up to three different core materials on the same wafer. We discuss in details the performance and applications of these elements as well as new circuits, such as an amplified reconfigurable add-drop module.

We systematically doped WO₃ (up to 10 mol%) and P₂O₅ (up to 16 mol%) in TeO₂-BaO-SrO-Nb₂O₅ (TBSN) glass system and studied thermal and optical properties of the doped glasses. The dependence of the dopant concentration on glass transition (Tg) and crystallization (Tx) temperatures are presented. The TBSN glass doped with greater-than or equal to 4 mol% WO₃ and P₂O₅ showed high stability against crystallization. The dependence of optical band gap energy due to WO3 and P2O5 doping, studied using UV-Vis-NIR absorption spectrometry, is presented. The WO₃ doping shifted the optical band gap to longer wavelength side, whereas P₂O₅ doping shifted that to shorter wavelength side. Structural details of the doped glasses are studied using Raman spectrometry. New Raman bands due to WO₄ and PO₄ tetrahedra are observed in the Raman spectrum of the doped glasses that broadened the Raman spectrum. The Raman gain coefficient and bandwidth of tellurite glasses has been tailored by systematically adding WO₃ and P₂O₅ in a TeO₂-BaO-SrO-Nb₂O₅ glass system. The Raman gain coefficients of the resultant glasses were obtained from spontaneous Raman scattering experiments using a 633 nm laser. The glasses here developed showed the widest gain bandwidth so far achieved in tellurite glasses while maintaining higher gain coefficients. The gain bandwidths of these glasses are more than twice that of a conventional tellurite-based glass and 70% larger than that of the silica glass. Present glasses developed are promising candidates for fiber amplifiers in photonic systems.

As demands for bandwidth continue to increase, telecommunication networks would greatly benefit from the development of broader-band amplifiers. The currently erbium doped fiber amplifiers are limited to amplification of approximately 100 nm bandwidth window. One method to increase the bandwidth of the fiber amplifier would be to incorporate multiple rare earths (REs) into a single fiber which exhibit emissions from ~1000-1800 nm. Unfortunately, energy transfer between rare earth ions typically results in quenching all but selected emissions negating this approach to potential ultra-broadband amplification. It would be ideal if one could take the individual spectra of an ion and place that ion into a host with no regard to other lanthanides that also are present in the host. This problem can be solved by using a composite material that utilizes nanoparticles to constrain different REs to individual particles thereby controlling or preventing energy transfer. In order to control energy transfer, RE doped LaF₃ nanocrystals were grown in an aqueous solution using a core/shell technique to constrain different rare earth into separate particles or shells within a single particle. Using these techniques, we show that energy transfer can be controlled.

Fiber lasers and amplifiers offer unique characteristics that are derived from the use of a waveguide and the properties of rare-earth doped silica glass. Their capability for high output power, with high efficiency, has been demonstrated both in CW and pulsed regimes. Cladding-pumped Yb-doped fiber lasers have now reached beyond kW levels with good beam quality. Advances in both fiber technology and high-power multimode diode pump sources, and the inherent power scalability of cladding-pumped fibers, lie behind this power surge. However, there are still many challenges to overcome in the high-power fiber laser area. These include, for example, single-mode output at higher powers and power scaling of a three-level laser. This paper reviews novel W-type fiber and depressed clad hollow optical fiber waveguide structures designed with distributed wavelength filter characteristics to achieve an efficient and high power cladding-pumped three-level lasers such as Nd-doped fiber laser operating at 930 nm and Yb-doped fiber laser at 980 nm. Moreover, such fiber geometries enable to scale up the output power in a small and single-mode core for generating a single-mode output beam in a robust and reliable manner.

Plastic optical fibers (POFs) are beginning to replace electrical wiring in many automotive and home applications. In view of this, we have reported the inexpensive wavelength-division-multiplexing (WDM) device for POF system using the LISW waveguide. The LISW waveguides are an attractive and a low-cost process for realizing self alignment between a POF and a waveguide. In this study, we have investigated about the method for precisely aligned LISW polymeric optical waveguides by using an "optical solder" effect. The "optical solder" effect makes it possible to realize a waveguide connection between two faced optical fibers by radiating from both sides even if a significant gap and a small degree of misalignment exist. When we utilize POFs with core diameters of 700μm, waveguides are combinable on the condition that an offset is 700μm or less and a gap is from 6mm to 13mm. By applying this effect, we fabricated precisely positioned LISW waveguides for optical devices. The fiber ends were set at certain mounting positions with respect to the LEDs and PDs. And we evaluated the positioning accuracy. The resulting positional accuracy at the extremities of the optical waveguides is less than one-tenth of the optical fiber core diameter. This value is sufficiently accurate to realize passive alignment. And this result creates new possibilities for boosting the yield of optical modules in mass-production.

A focused 375 nm laser diode module is used to fabricate optical channel waveguides on Si wafers using commercially available inorganic-organic hybrid polymers. The fabrication process eliminates all the complex steps associated with the definition of structures using photolithographic techniques, making rapid prototyping of integrated optic devices possible. Channel waveguides with smooth side-walls are fabricated and characterized. The losses, measured using cutback loss measurement method, are typically less than 1dB/cm, making them especially applicable to Si based optical interconnects applications.

This paper reports recent advances in photonic functional devices based on silica planar lightwave circuit technology for advanced optical networks. After briefly summarizing the progress on circuits, this work describes dynamic devices designed to compensate for unwanted fiber characteristics with respect to high-speed wavelength division multiplexing transmissions, mainly focusing on a tunable chromatic dispersion compensator. The paper then describes optical signal processing devices, namely a spectrum synthesis device, an optical encoder/decoder for time-spreading/wavelength-hopping optical code division multiple access, and a label processor for a phase modulated signal.

In the field of optical interconnect technology, many works are in progress for polymer material that is more inexpensive in terms of material and processes than conventional quartz optical waveguides. We had developed a novel type of material for optical waveguides consisting polysilane, silicone and photosensitizer. This material named "GlasiaWG (TM) can decrease its refractive index by UV irradiation. Using this photobleaching phenomenon, we can fabricate optical waveguides that have flat surfaces by simple process without chemical etching. In this work, we have developed multilayered optical waveguides that enable to make two-dimensional multichannel connectors for multimode optical interconnects. To fabricate multilayered optical waveguides, we prepare glass substrates whose thickness are 150μm and two kinds of GlasiaWG (TM) having different refractive indexes respectively. At first GlasiaWG (TM) having a higher refractive index is coated on the glass substrate, and then the coated film is irradiated by UV-light with a photomask to create core and side cladding parts. After baking the core layer at 250 degrees C another GlasiaWG(TM) with a lower refractive index is coated on the core layer and baked at 250 degrees C. One-layer optical waveguide is completed for one unit. After accuracy alignment, four units of optical waveguides are laminated by heating at 80 degrees C and pressing with 50kg/cm2, and diced to proper size pieces. Eventually four-layered optical waveguides are fabricated. Flat surfaces made by photobleachig process and adhesive properties with glass enable to fabricate multilayered optical waveguides. This fabrication is a feature of GlasiaWG^TM.

The finite difference beam propagation method (FD-BPM) is an effective model for simulating a wide range of optical waveguide structures. The classical FD-BPMs are based on the Crank-Nicholson scheme, and in tridiagonal form can be solved using the Thomas method. We present a different type of algorithm for 3-D structures. In this algorithm, the wave equation is formulated into a large sparse matrix equation which can be solved using iterative methods. The simulation window shifting scheme and threshold technique introduced in our earlier work are utilized to overcome the convergence problem of iterative methods for large sparse matrix equation and wide-angle simulations. This method enables us to develop higher-order 3-D wide-angle (WA-) BPMs based on Pade approximant operators and the multistep method, which are commonly used in WA-BPMs for 2-D structures. Simulations using the new methods will be compared to the analytical results to assure its effectiveness and applicability.

We report thorough investigations of photonic crystal waveguide properties in the slow light regime. The transmission and the group index near the cutoff wavelengths oscillate in phase in close analogy with the 1D photonic crystal behavior. The influence of having a finite number of periods in the photonic crystal waveguide is addressed to explain the spiky character of both the transmission and group index spectra. The profile of the slow-light modes is stretched out into the first and second rows of the holes closest to the waveguide channel. One of our strategies to ameliorate the design of photonic crystal devices is to engineer the radii of holes in these rows. A topology optimization approach is also utilized to make further improvements. The results of the numerical simulations and the optical characterization of fabricated devices such as straight waveguides with bends and couplers are presented. A nice match is found between theory and experiment.

Recently, optical communication networks, such as FTTH (Fiber-To-The-Home), are spreading rapidly to the end-user. And the expectation of replacing electrical signal lines in the body of mobile devices by optical lines is growing based on the recent increase of communication density and the need of smaller mobile devices, also. But, the business fields are facing directly to the consumers, therefore, the serious cost reduction and higher productivity for large-scale production are expected toward the optical communication devices. In order to achieve these expectations, many efforts are given to develop the replicated polymer optical waveguide, SPICA (Stacked Polymer optical IC/Advanced). SPICA is based our unique replication technology which realizes both low cost and large-scale production. And we already realized the single mode polymer optical waveguide by adopting this original technology. And, we evolved this technology to fabricate the V-groove integrated optical waveguide and the film optical waveguide. The V-groove integrated optical waveguide realizes cost reduction at the optical fiber alignment and assembling processes by introducing the optical fiber self-alignment for further cost reduction as a optical link module. The film optical waveguide which is as flexible as electrical cables and is durable of many bending cycle test are realized. In this paper, the technology of SPICA and the applications are discussed.

Optical frequency standards are being developed worldwide to lead a new definition of the unit of time. We are developing broadband optical frequency combs, which aims to count the laser frequency highly stabilized to the resonance of atomic reference and generate a rf frequency standard directly converted from the optical frequency. The developed frequency combs was successfully operated with a measurement accuracy of 3×10^-14 at the averaging time of 1 s. From the primary demonstration, it was confirmed to be available for the frequency stability measurement of a clock laser used in an optical frequency standards. The frequency combs will be key components for the development of optical atomic clock.

All optical XOR, AND, OR, and, NOR functionality has been demonstrated experimentally using semiconductor optical amplifier (SOA) based devices at 40 Gb/s, 80 Gb/s. The performance of the optical logic operations has been analyzed by solving the rate equation of the SOA numerically. The high-speed operation is limited by the gain and phase recovery times in the SOA. In order to solve these limitations, a differential scheme for XOR operation has been experimentally investigated. This scheme is potentially capable of XOR operation to > 100 Gb/s.

One of the key challenges for the next-generation light sources such as X-FELs is to implement a timing stabilization and distribution system to enable ~ 10 fs synchronization of the different RF and laser sources distributed in such facilities with distances up to a few kilometers. These requirements appear to be beyond the capability of traditional RF distribution systems based on temperature-stabilized coaxial cables. A promising alternative is to use an optical transmission system: A train of pulses generated from a laser with low timing jitter is distributed over length-stabilized fiber links to remote locations. The repetition frequency of the pulse train and its higher harmonics contain the synchronization information. At the remote locations, RF signals are extracted simply by using a photodiode and a suitable bandpass filter to pick the desired harmonic of the laser repetition rate. Passively mode-locked Er-doped fiber lasers provide excellent long-term stability. The laser must have extremely low timing jitter, particularly at high frequencies (>1 kHz). Ultimately, the timing jitter is limited by quantum fluctuations in the number of photons making up the pulse and the incoherent photons added in the cavity due to spontaneous emission. The amplitude and phase noise of a home-built laser, generating 100-fs, 1-nJ pulses, was characterized. The measured phase noise (timing jitter) is sub-10 fs, from 1 kHz to Nyquist frequency. In addition to synchronization of accelerators, the ultra-low timing jitter pulse source can find applications in next-generation telecommunication systems.

Clock recovery using self pulsating semiconductor laser structure is a sophisticated signal processing inside the device, involving optical injection locking, gain and index modulation, self pulsation, radiofrequency oscillation synchronization, and phase noise filtering. The mutual injection of the longitudinal mode and the passive mode locking leading to self pulsation is analyzed by using multimode rate equations. Self pulsation is easily achievable and is characterized by a large reduction of the RF spectral line width, as compared to those of the optical modes involved in the beating process. When they are injected by a power modulated optical signal, the self pulsating laser structures act as all-optical clock recovery devices. The self pulsation line width is found to be determinant to fulfill the high bit-rate optical communications and optical signal processing clock recovery property requirement.

We investigated the heteroepitaxial growth of GaSb on Si(001) substrates. High-quality GaSb films were grown on Si substrates by using an AlSb initiation layer. When small AlSb islands were formed on the Si substrate before the GaSb growth, two-dimensional GaSb film was grown. In contrast, without small AlSb islands, large GaSb islands formed on the substrate. Therefore, the AlSb islands played an important role in preventing excessive surface diffusion of Ga atoms on the Si surface and promoting two-dimensional growth of GaSb. A narrow X-ray diffraction rocking curve (around 200 arcsec) was obtained by optimizing the growth temperature and the thickness of the AlSb initiation layer. High-quality GaSb/AlGaSb and InGaSb/AlGaSb MQW samples were also grown on a Si substrate by using this method. At room temperature, these samples gave a strong emission at 1.55 μm, which is a wavelength used by fiber optic communications systems. Furthermore, we could control the emission wavelength by simply changing the well width. The emission energy was in good agreement with the theoretical curve. The temperature dependence of the PL intensity indicated a large activation energy (~77.6 meV) from the GaSb QWs. These results indicate that the fabricated QW structure had high crystalline quality and that GaSb quantum wells can be fabricated on Si for optical devices operating above room temperature.

In this paper, we employ a simple theory based on driven damped oscillators to clarify the physical basis for message extraction in optical chaos communications using injection-locked semiconductor lasers. The receiver laser is optically driven by injection from the transmitter laser. We have numerically investigated the response characteristics of the receiver when it is driven by periodic (message) and chaotic (carrier) signals. It is thereby revealed that the response of the receiver laser in the two cases is quite different. For the periodic drive, the receiver exhibits a response depending on the signal frequency, while the chaotic drive provides a frequency-independent synchronous response to the receiver laser. CPF can be clearly understood in the difference between the periodic and chaotic drives. Message extraction using CPF is also examined, and the validity of our theoretical explanation for the physical mechanism underlying CPF is thus verified.

In this paper we will present innovative design approach for UV Focal Plane Array for Photon Counting Applications. This Focal Plane includes the building a large area silicon micro-channel plate (MCP) using GaN photocathode. In this paper, we will present the design and simulation of silicon micro-channel plate with GaN photocathode with large area array with 2 micron pores and 3 micron pitch. We will also present results for the ICP-RIE process to fabricate 2 micron pores, and Growth of high conductivity GaN photocathodes using MOCVD to produce 40% QE. We will also discuss approaches for development of readout architecture and circuit for Silicon based MCP 4096x4096 UV FPA. The readout architecture scheme uses a series of charge sensitive amplifiers (CSA) to boost the charge received on each anode. The signal from each CSA is then passed into a shaping amplifier (SA) that produces a smooth waveform. The peak of the smoothed waveform is captured by a sample and hold (S/H) circuit that holds the signal until an analog to digital (A/D) converter can sample it. Details of the ROIC circuit will be presented.

Link reliability is a significant issue for free space optical links. Inclement weather, such as fog, can seriously reduce the transmission of light through the atmosphere. However, this effect, for some types of fog, is wavelength-dependent. In order to improve link availability in both metro and hostile environments, mid- and far-wavelength infrared diode lasers can be of use. This paper will discuss some of the recent advances in high-power, uncooled quantum cascade lasers and their potential for use in long range and/or highly reliable free space communication links.

Recently, the technologies of optical fibers have been advanced and the special fibers, such as highly nonlinear fibers and photonic crystal fibers have been demonstrated. As the light sources, passively mode-locked ultrashort pulse fiber lasers have been commercialized and attracted a lot of attentions in several fields. The group of author has been working on the development and applications of high performance ultrashort pulse fiber lasers. In this paper, the recent progress of widely wavelength tunable ultrashort pulse and ultra wideband super continuum generation by use of ultrashort pulse fiber laser are described. In 1999, the widely wavelength tunable ultrashort soliton pulse generation has been demonstrated in the wavelength region of 1.55 - 2.0 um. In this light source, it was difficult to generate the ideal ultrashort pulses in the wavelength region around 1.55 um. Recently, we have demonstrated 1.0 - 1.7 um widely wavelength tunable ultrashort pulse generation system by use of Yb doped fiber laser and photonic crystal fibers. Using this source, we can cover the whole wavelength band used in optical communications. In 2001, 1.0 - 2.0 um ultra wideband super continuum generation has been reported using ultrashort pulse fiber laser and highly nonlinear fibers. In terms of the applications, the large noise and the fine structures become serious problems. We have also analyzed the characteristics of super continuum generation and clarified the origin of noise and fine structures. Recently, we have successfully generated the ultra wideband, low noise, ultraflat, and highly coherent super continuum without any fine structures for the first time. Another novel super continuum generations are also discussed.

Multi-Quantum Well (MQW) modulators have been demonstrated with a high contrast ratio of of 5:1 in an InGaAs/InAlAs p-i-n structure at 1.55 μm. Additionally, it was found that modulators that exploit the optical properties of resonant cavities can achieve contrast ratios at least three times larger than those that don't. The devices fabricated were measured to have modulation rates of greater than 30 MHz. Lastly, quantum efficiencies and responsivity measurements show that modulator would be able to detect incident light and coupled with electronics would "know" when to modulate.

Fiber tapers have found a wide range of important applications in communication and sensing, including narrow-band filters, mode-matching between waveguides, evanescent mode-coupling and fused couplers. Applying these taper-based technologies to air-core photonic bandgap fibers (PBFs) is very appealing because it would enable creating these same components directly in air-core fibers. Although there have been several studies of tapers in solid-core microstructured fibers, the transmission properties of tapered air-core photonic-bandgap fibers have not yet been studied. In this work, we report on the fabrication and testing of tapered air-core photonic-bandgap fibers. Our motivation in this work was to study the basic transmission properties of PBF bitapers in the bandgap region, and in particular, to see how the overall transmission was impacted by the taper, e.g., whether the taper induced resonant coupling to one or more cladding modes. Our experimental results indicate that air-core PBFs are highly sensitive to tapering, and unlike conventional single-mode telecommunication fibers, even a small tapering ratio results in significant modal interference in the transmission spectrum. Furthermore, we found out that the mechanical silica support surrounding the holey region of the PBF contributes as a lossy Fabry-Perot resonator to the observed transmission properties.

The effects of design parameters on the modulating voltage and optical bandwidth are reported for lithium niobate, GaAs and polymer electro-optic modulators by using rigorous numerical modelling techniques. It is shown that by etching lithium niobate, the switching voltage can be reduced and the bandwidth improved. For a GaAs-based modulator using higher aluminium content in the buffer layer, the device length can be shortened for a given optical loss. It is also observed that the dielectric loss and impedance matching play a key role in velocity-matched high-speed modulators with low conductor loss. It is also indicated in the work that by using tantalium pentoxide coating, velocity matching can be achieved for GaAs modulators. The effects of a non-vertical side wall on the polarisation conversion and single mode operation and the bending loss of polymer rib waveguide for electro-optical modulators are also reported.

A new technique based on logarithmic Hilbert transform processing of Maker-fringe (MF) curves to characterize second-order optical nonlinear depth profile of thin films is described. Such characterization methods are important for several fields, for example to characterize the nonlinear coefficient profile of poled glass samples, which hold an important potential for fiber based nonlinear devices in telecommunication links. In the classical MF measurement system, a laser beam is focused onto the nonlinear film and the generated second-harmonic power is recorded vs. the laser incidence angle. The resulting MF curve is proportional to the square of the magnitude of the Fourier transform of the spatial profile d(z) of the nonlinear coefficient, where z is perpendicular to the film surface. Our new analytical method requires only the measurement of the MF curve of the nonlinear sample alone. It is based on the computation of the logarithmic Hilbert transform of the measured MF curve of the sample. Being analytical, this approach provides speed advantage over its iterative alternative. This new technique is verified experimentally with two germanosilicate-Infrasil structures, thermally poled at ~5 kV and 280° C in air. This choice of material was primarily made because germanosilicate films form excellent waveguides with a refractive index close to that of silica, which makes them compatible with fiber-optic technology. This is the first time that a Hilbert transform based analytical tool has been applied to uniquely characterize nonlinear thin films.

We investigated ultrafast optical signal processing schemes utilizing mode-locked semiconductor laser diodes (MLLDs) for optical time-division multiplexing (OTDM) transmission at over 100 Gbit/s and developed a polarization-insensitive all-optical clock recovery scheme for an optical-electrical hybrid phase-locked loop (PLL) operating at 160 Gbit/s. In this scheme, the MLLD functions as a voltage-controlled oscillator to which the error signal is fed back by forming a closed loop with a semiconductor optical amplifier (SOA) used as a phase comparator and with a low-frequency component used as a filter. Cross-gain modulation in the SOA enables high-frequency PLL operation at 160 Gbit/s. A bulk active layer in the SOA with small polarization dependency is the origin of the polarization insensitive clock extraction. Testing of all-optical clock extraction on an OTDM transmission test bed of 254-km field-installed fibers (Dojima-Keihanna, 63.5 km, and four spans) at 160 Gbit/s showed that the measured root-mean-square timing jitter of the recovered clock signal was as low as 240 fs. This clock extraction scheme is thus practical for use in OTDM systems operating at over 100 Gbit/s.

Planar lightwave circuit (PLC) chips based on III-V semiconductor MQW rib waveguide promise to be not only a solution to information access, but also direct the issues of bandwidth, pin count, reliability and complexity. Nanopositioning and precision alignment addresses vital importance in high-efficient connectivity between PLC chips and fiber arrays. Refractive-index mismatching between fused silica and III-V compound is one of the most serious problem which remains unsolved on one hand as well as mode field mismatching which can be mitigated in other hand through gradient geometry structure such as tapered spot size converter (SSC) and specialty fibers such as wedge-shaped fiber (WSF). Spherical gradient refractive-index (SGRIN) media intervened between WSF and MQW rib waveguide is put forward. The GRIN media virtually eliminates the reflection losses associated with the fused silica-air interface and III-V semiconductor-air interface. The beam spot emitted from WSF are observed by digital camera and the fundamental mode of MQW rib waveguide was calculated out. Lightwave propagation and mode field evolution in the WSF-SGRIN-PLC system is simulated by FDTD method with the coupling loss of 8.54dB at a wavelength of 1.55μm. An LED signal is injected into WSF, transmitted along GRIN media and PLC waveguide and output through single mode fiber (SMF). Optical power meter-based measurement verifies the whole system coupling loss to be consistent with the numeric estimation. The approach provides an experimental prototype for coupling and packaging technique of integrated photonic devices, hence supplying foundation for photonic network.

A novel FSR tunable Fabry-Perot Filter scheme with a superimposed fiber Bragg grating has been proposed. And a cantilever beam-based tuning setup has been demonstrated to obtain large linear chirp to a superimposed uniform fiber Bragg grating without central wavelength shift. Finally, as an example, an FPF with a continuously tunable FSR of 0.1-0.5nm is obtained.

Visible fiber lasers and amplifiers have potential applications in the fields of optical data storage, spectroscopy, biomedical, and optical local area networks. A spectroscopic analysis has been performed on a borosilicate glass, codoped with Tb³⁺ and Yb³⁺, to assess this material as a green laser and amplifier medium. The rare-earth ion concentration effect on thermal, absorption, and emission properties of the glasses were investigated using differential scanning calorimetry, UV/VIS/NIR absorption, and luminescence measurements, respectively. These materials were found to have good glass-forming ability, and show a high thermal stability, indicating the potential to facilitate low-loss fiber fabrication. Judd-Oflet analysis was performed for Tb³⁺ doped in the borosilicate glasses. The radiative lifetime of the ⁵D₄ level was found to be 2.6 ms, and was almost constant in 0.5-15 wt.% concentration range. The peak cross section for stimulated emission by the ⁵D₄->⁷F₅ transition was found to be 0.8×10^-21 cm² at λ = 542 nm. In the Tb³⁺-Yb³⁺-codoped glasses, the green emission resulting from the cooperative energy transfer between doped ions was observed under infrared excitation (λ_ex = 0.98 μm). This upconversion emission increased with doping ion concentration. These results suggested that the Tb³⁺-Yb³⁺-codoped borosilicate glass is a promising candidate for an all-solid-state upconversion green laser and amplifier.

Free space optical (FSO) communications technology has potential applications in the military sector to provide a secure, high speed communication channel, and in the civilian sector as a "last mile" carrier solution. It was proposed by other researchers that a multi-rate communication system that utilizes Meyer wavelets would achieve the greatest bandwidth and highest reliability possible for an FSO system. In order to generate Meyer wavelets from femtosecond laser pulses, filtering must be performed optically to produce the desired pulse shape. One of the simplest ways to produce an arbitrary pulse shape from a laser pulse is with a tunable liquid-crystal spatial light modulator (LC-SLM) in a zero-dispersion pulse compression system. The simplest approach to determine the correct mask pattern for an LC-SLM is to utilize adaptive, global optimization methods. Since it takes several milliseconds to adjust the attributes of each pixel of an LC-SLM and there are typically over one-thousand pixels, it is important to determine the fastest algorithm for determining the optimum mask pattern. Several global optimization methods, including simulated annealing, exhaustive search, and random search, a hybrid of the other two algorithms, were characterized. It was found that exhaustive search can be used to form waveforms with negligible inaccuracies at rates of about 5 times faster than simulated annealing and about 3 times faster than random search, but that simulated annealing provides the highest accuracy. However, the difference in accuracy between all of these algorithms is less than 10^-5.

The Michelson interferometer based interleaver has been widely used in dense wavelength-division multiplexing (DWDM) systems. It possesses advantages such as compact size, low material costs, etc. However, the Michelson interferometer based interleaver can not be designed as a constant group delay filter due to its infinite impulse response filter nature. In this article, a Michelson interferometer design algorithm based on all-pass filter phase approximation is proposed. It is demonstrated that, with the proposed algorithm, it is straightforward to design an interleaver with respect to different requirements such as bandwidth utilization, isolation, etc. More importantly, it is also demonstrated that, with the proposed algorithm, the group delay variation of the Michelson interferometer based interleaver can be minimized while given magnitude spectrum specifications are satisfied.

A broad near-infrared emission of Bi-doped lithium alumino silicate glasses has been investigated. It was found that the peak wavelength and width of the emission from the glasses could be controlled drastically by the excitation wavelength. The emission spectrum had the broadest full width of half maximum (FWHM) of more than 500 nm under the 900 nm excitation. The emission consisted of two Gaussian peaks and the stimulated emission cross sections at the peaks were calculated as 7.3×10^-21 and 2.3×10^-20 cm². The lifetime was almost independent of temperature up to 350 K, indicating that the emission from the Bi-doped lithium alumino silicate glass has strong resistance to the thermal quenching. It was found that the peak wavelength and the width of the emission from the glasses depend on both the excitation wavelength and the Bi content for the first time. The emission covered a spectral range from 920 to wavelengths over 2000 nm. The bandwidth exceeded 1000 nm. The quantum efficiency of the emission was obtained as 11% when the glass was excited at 974 nm.

We proposed N-channel power compensated and reconfigurable optical add/drop multiplexer (ROADM) based on the utilization of fiber Bragg gratings (FBGs). Both tunable and fixed fiber Bragg gratings are used in this ROADM. By using the dual-pass amplification scheme, an 8.0 dB optical net gain is achieved with gain variation under ±0.5 dB for each add/drop/pass-through channel. System demonstration bit error rate performance with only 1.2 dB of power penalty in a 10 Gb/sx 4 Ch, 100-km lightwave transmission.

We report on two types of wavelength conversion techniques that are based on gain saturation effect in semiconductor optical amplifier (SOA) and erbium doped fiber amplifier (EDFA). In these amplifiers the gain saturation occurs when the optical density at the gain medium is high enough to result in depletion of the population inversion by stimulated emission. In each case, the fiber ring laser is assembled using a variable fiber coupler, a narrowband optical filter and the gain medium. For external input power values higher than the determined threshold value of the ring resonator, the gain will be saturated. Because the wavelength of the external laser is different from the oscillating wavelength of the ring resonator, the optical power at the output of the resonator is drastically decreased (low-state). On the other hand, when the input of the external laser is below the threshold value the output power of the resonator increases (high-state). In our experiment the operating wavelengths of the ring resonators are 1314 nm and 1553 nm for the SOA and EDFA respectively. The input signal is modulated around the threshold value for frequencies of 20 MHz and 1 MHz and resonator lengths of around 8 m and 16 m for the SOA and EDFA cases respectively. Both systems exhibit high contrast modulation of 41 dB and 33 dB at the output port for the low/high states of the SOA and EDFA ring lasers respectively.

Photoinscription of superstructured Bragg gratings in Er-Yb codoped fiber is a promising and cost-effective approach to produce high-quality multi-wavelength fiber lasers for various applications like radio-over-fiber systems, fiber-optic sensors or low-cost WDM testing source. However, a good understanding of the noise properties of the laser source is required before these applications can be addressed. Previous modeling has shown that these devices are similar to compact cascades of single wavelength DFB fiber lasers in which the modes at each wavelength are almost nonoverlapping along the fiber. In this paper, we further examine the independence of each channel by performing relative intensity noise (RIN) measurements on a multi-wavelength fiber laser, a dual-polarization fiber laser and a dualwavelength fiber laser. In each case, we estimate the correlation between the laser lines. From RIN measurements performed on each channel of a multi-wavelength laser, as well as on the full spectrum, we compute an average degree of correlation between the RIN of neighboring lines and observed no correlation in most of the cases. Moreover, each channel displays a single relaxation frequency which is different from those of the other channels. On the other hand, we observed strong partition noise, with negative correlation, between polarization modes of a single wavelength fiber laser. Finally, we measured the RIN of the two modes of a dual-wavelength fiber laser with modes having a greater overlap than the multi-wavelength laser. The results show that the lines share two common relaxation frequencies, an indication of a dynamic link between them.

The impact of the cross-phase modulation (XPM) on the performance of NOLM in the single-wavelength channel and WDM channel is studied by using the split-step Fourier method (SSFM) that can solve the coupled nonlinear Schroedinger equation (CNLSE). The numerical simulation results show that the switching performance of NOLM is distorted by the XPM induced nonreciprocity when the splitting ratio of NOLM coupler 0.5 f ≠ and the distortion effect would be more serious with the increase of the working speed. The power transmission function of NOLM decreases in the range of f ∈ (0,0.5) and increases in the range of f ∈ (0.5,1). Furthermore, the impact of XPM induced by the crosstalk of wavelengths is far more than that of XPM induced by the overlap of counter-propagating optical components in the WDM channel. Pedestals are leaked from the main lobe appear and the pedestals of the middle wavelengths are larger than those of the edge wavelengths.

To amplify a signal after a few kilometers, need an optical amplifier in optical communication systems. In this paper OSNR as a function of length of EDFA for physical model of EDFA is observed. Also measured the receive power for custom designed length at different wavelength and optimize the length of EDF (Erbium doped fiber). It is observed that at 980nm, EDFA with length 20 to 40m has highest OSNR and satisfactory power available. Similar results are found at wavelength 1550nm.

We investigated twenty channels at 80 Gb/s wavelength division multiplexing (WDM) transmission over 910 km single mode fiber & dispersion compensating fiber using cascaded in-line semiconductor optical amplifiers at span of 70 km for soliton RZ-DPSK (return zero differential phase shift keying) modulation format. With the narrow channel spacing i.e. 200 GHz, we obtained quality more than 15dB of the received signals after covering 910 km transmission distance without any power drop. We optimize the SOA model for in-line amplifier having low cross talk in multi channel WDM systems at zero power penalty with sufficient gain. We show that for the differential gain 200 atto cm² and length 750 mm of SOA has minimum SOA induced crosstalk. The impact of optical power received and Q factor at different differential gain, carrier lifetime and length has been illustrated. It is found that for transmission distance 700 km, as we decrease the channel spacing, there is increase in crosstalk among channels hence quality of signal goes on decreasing. We show clear eye diagram and good optical spectrum is observed at the transmission distance 910 km in soliton RZ-DPSK system.

We simulated, 40 Gb/s wavelength converter for non-return to zero differential phase shift keying (NRZ-DPSK) signal using four wave mixing in semiconductor optical amplifier (SOA), for the first time. Also optimize the signal-to-pump ratio for NRZ-DPSK. The optimum signal-to-pump ratio is 12 dB & 10 dB with Q-factor penalty of 0.685 dB & 0.663 dB. The dependence of four wave mixing efficiency and converted signal power with signal input power studied & it is evaluated that four wave mixing efficiency decrease with increase in input power. The impact of pump power, signal-to-pump ratio, SOA parameters with Q-factor penalty for 40 Gb/s has been illustrated. We show that converted signal power increase up to saturation power of semiconductor optical amplifier, then decreases. It is observed that for optimum pump power, OSNR varies small with signal input power. Investigation also made for transmission distance after conversion.

Mode-locking characteristic of hybrid soliton pulse source (HSPS) utilizing linearly chirped raised-cosine flat top apodized fiber Bragg grating (FBG) is investigated by using coupled-mode equations. It is found that the fundamental repetition frequency range of HSPS is significantly extended by using linearly chirped raised-cosine flat top apodized FBG instead of linearly chirped Gaussian apodized FBG. The range of repetition frequencies over which proper modelocking is obtained is 2-3.3 GHz with linearly chirped raised-cosine flat top apodized grating whereas this range is 2.1- 2.95 GHz with linearly chirped Gaussian apodized grating.

A DFB laser diode is forced to operate in feedback Regime V by omitting the laser isolator and using an extended cavity mode. The DFB laser diode is coupled to a Fiber Bragg Grating (FBG) that has a reflectivity based on parameters extracted from optical back-reflection measurements. A stable wavelength, narrow linewidth and low relative intensity noise (RIN) were obtained using the proposed configuration. A DFB diode laser coupled to the FBG achieved a RIN level of (-158.5 dB/Hz) at a 1 GHz frequency offset, comparable to results obtained for a DFB diode laser with an isolator (-157.9 dB/Hz), for the same average optical power (5.1 dBm) at 1310 nm.