This PDF file contains the front matter associated with SPIE Proceedings Volume 7158, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We propose a different pulse pair Brillouin optical time domain analysis (DPP-BOTDR) for centimeter or sub-centimeter spatial resolution using meter equivalent pulses. It is based on a pair of different pulses with small pulse width difference (much smaller than each of the pulse width). The process is analogous to the high pass filter which amplifies short stress section and provides high spatial resolution for the distributed Brillouin sensor using the large pulses (tens of nanoseconds) and extinction ratio of more than 30dB. This new approach achieves the centimeter spatial resolution over fiber length of kilometers with low pump and probe power. Using a pair of 50ns and 48ns pulses we achieve the spatial resolution of 2ns equivalent spatial resolution for two stress section of 50cm and separated by 1m fiber over 1km sensing length. The strain resolution is equivalent to 2.6MHz Brillouin frequency shift. The spatial resolution is determined by the convolution of the bandwidth of the detection system and pulse width difference. The signal to noise ratio of the sensor difference is also related to the pulse width difference.

The lithography ion-exchange method of producing the gradient index micro-cylinder lens with gradual focus is presented. The lens is developed for the coupled shaping of the pump beam of side-pumped disk fiber laser, its main purpose is to make the LD beam which coupled into the ring disk container and the radial of the ring disk container have a certain angle, and ensure that all the pump beams couple into the interior of the ring disk container through the thin slit of the side. The micro-cylinder lens with different shapes can be obtained by the special designs of ion-exchange windows. The focused spot of the parallel beam passed through the lens is a special curve with required setting. Consequently, the lens also adapt to other applies with gradual focus. The experimental results coincide with the design.

According to the preparation of tapered fiber hemispherical micro-lens by hybrid etching and melting, a geometric calculation model for fabricating hemispherical micro-lens at the end of optical fiber by melting tapered flat fiber end into hemispherical fiber end has been developed. If the taper diameter and taper angle are obtainable, the radius of hemispherical micro-lens of the fiber taper after melting can be calculated. Particularly, hemi-spherical micro-lenses of optical fibers with various radii can be fabricated by etching-cleaving-melting method. According to the linear relationship between etching fiber diameter and etching time, as well as the characteristic of fiber volume maintaining constant before and after electric arc melting, the relationship between the radius of fiber hemispherical micro-lens and etching time was deduced in this paper. Through controlling the etching time precisely after calculating the etching rate, which is determined by the sampling and analysis of the etched fiber, the hemi-spherical micro-lenses with different radius at the fiber ends can be produced. The experiments were conduct to test the operability of this method. The results showed that radii of micro-lenses fabricated by the etching-cleaving-melting method made a good coincidence with the designed radius values of 10µm and 20µm.

The method of producing the orthogonal micro-cylinder lens arrays on the two surfaces of the glass substrate with ion-exchange is presented. The former and latter arrays are used for beam shaping of the fast-axis and slow-axis of LD respectively. In this paper, the ray transfer matrices of the optical system have been obtained, the numerical calculation results coincide with the experimental results. This numerical calculation results have a good role in guiding the design of micro-cylinder lens arrays and the optimization of ion-exchange process.

Microcavity lasers with whispering-gallery modes (WGMs) are potential light sources for photonic integrated circuits. However, the direction emission and output power are greatly limited for microdisks with the WGMs confined by total internal reflection. Deformed microdisk with chaos mode light rays or evanescently coupled waveguide were used to realize directional emission microlasers. Different from the microdisk with traveling wave WGMs, confined modes in triangle and square microcavities are standing wave WGMs. So the confined modes can still have high Q-factors if an output waveguide is directly connected to triangle and square microcavities at the position with weak mode field distribution. Based on theoretical analysis and numerical simulation of the mode characteristics, we fabricate directional emission triangle and square InGaAsP/InP microcavity lasers with an output waveguide directly connected to the resonators by standard photolithography and inductively coupled plasma etching technique. Continuous-wave (CW) electrically injected InGaAsP triangle and square microlasers are realized at room temperature for the triangle microlasers with side length from 10 to 30 μm and the square microlaser with the side length of 20 μm.

We present the 1.3-μm InAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) with novel planar electrodes configuration. The lasing wavelength is around 1274 nm. The lowest threshold current of wafer level device is ~1 mA, which corresponds to a low threshold current density of ~1.3 kA/cm² or 76 A/cm² per QD layer. The maximum output power of 1 mW can be obtained at room temperature. High temperature stability can be seen in temperature dependence L-I characteristics of InAs QD VCSEL 3-dB modulation frequency response of 1.7 GHz can be obtained in the small signal response measurements.

HgCdTe infrared detector is designed to operate at cryogenic temperatures, so vacuum baking is a required process for out-gassing in packaging of devices. As HgCdTe material, as well as ZnS passivation layer is sensitive to heat induced changes, this process may be problematical for HgCdTe devices even at relatively low temperatures. We try to solve the problems of heat instability by the fabrication of CdTe/ZnS double passivation layers. The effect of vacuum baking is investigated through current-voltage (I-V) characteristics. We have compared the effects on devices with different passivation layers. We have also compared the photodiodes fabricated on MBE grown HgCdTe on GaAs substrates and LPE grown HgCdTe on CdZnTe. The devices were passivated with electron beam evaporated CdTe and ZnS and the p-n junction was formed by ion-implantation. Through the analysis of I-V characteristics, we found that the devices passivated with ZnS cannot afford vacuum baking even at 70°C, while the CdTe/ZnS- passivated devices can afford up to 110°C temperature and the performance improved. After only 4 hours baking, the dynamic resistance of ZnS passivation devices began to decrease and 10 hours later the zero-bias dynamic resistance (R0) decreased nearly 3 times. Further baking of 110°C sees the maximum dynamic resistance of CdTe/ZnS passivation devices increase 2 to 4 times. An insight into the mechanisms and parameters that are affected by vacuum baking is also gained by resistance-voltage (R-V) curve fitting. The results also indicated the baking effects on LPE grown HgCdTe devices are almost same to MBE grown HgCdTe devices.

Experiment of a lateral semi-insulating GaAs photoconductive semiconductor switch (SI-GaAs PCSS) with different electrode gaps triggered by 900nm semiconductor laser is reported. With the biased voltage of 0.2KV~3.0KV, the linear electrical pulse is outputted by SI-GaAs PCSS. When laser energy is very low, the semi-insulating GaAs PCSS with 1.5mm electrode gap is triggered by laser pulse, the output electrical pulse samples is instable. When the energy of the laser increases, the amplitude and the width of the electrical pulse also increase. It indicates that a stable electrical pulse is obtained while laser energy is high. With the biased voltage of 2.8kV, the SI-GaAs PCSS with 3mm electrode gap is triggered by laser pulse about 10nJ in 200ns at 900nm. The SI-GaAs PCSS switches a electrical pulse with a voltage up to 80V. The absorption mechanism by Franz-Keldysh effect under high-intensity electric field and EL2 deep level defects is discussed.

The optical waveguide switch utilizing the principle of total internal reflection (TIR) is a promising structure since its merits such as compact size, digital response characteristic, insensitivity to wavelength and polarization, and so on. In this paper the TIR switch is studied both in theory and in experiment. At first, we give a comprehensive analysis about reflection mechanism in the TIR switch from the following three issues: the grazing incidence of a narrow beam in the free space, the beam reflection in a bounded space, and the beam expansion induced by the reflection in a two-dimensional gradient field of the refractive index decrease. Then based on the analytical works, we successfully fabricate practical TIR switches by utilizing the thermo-optical effect of polymer and the carrier injection effect of GaAs (both the current injection and the photon injection manners are employed). The testing results show that: the extinction ratio of the thermo-optical TIR switch exceeds 35 dB at an power consumption of 80 mW; for the carrier injection TIR switch utilizing the current injection manner, its operation speed is faster than 20 ns and its operation current is about 70 mA.

Study of bend loss of curved optical waveguides is a fundamental subject in field of curved optical waveguides design and fabrication. In order to decrease the bend loss of curved optical waveguides efficiently, a number of strategies are proposed. In this paper, we give out a new strategy to reduce bend loss of curved optical waveguides by modifying its cross section. The principle of this strategy was discussed and the simulations using beam propagation method was given. This new method is useful and practical in design of curved optical waveguides. Especially, it is more effective in situations that the radius of curvature of the waveguides and the refractive index of materials were set beforehand.

With the development of the infrared focal plane detectors, the internal noises in the infrared focal plane arrays (IRFPAs) CMOS readout integrated circuit gradually became an important factor of the development of the IRFPAs. The internal noises in IRFPAs CMOS readout integrated circuit are researched in this work. Part of the motivation for this work is to analyze the mechanism and influence of the internal noises in readout integrated circuit. And according to the signal transporting process, many kinds of internal noises are analyzed. According to the results of theory analysis, it is shown that 1/f noise, KTC noise and pulse switch noise have greater amplitude in frequency domain. These noises have seriously affected the performance of output signal. Also this work has frequency test on the signals of a readout integrated circuit chip which is using DI readout mode. After analyzing the frequency test results, it is shown that 1/f noises and pulse switch noises are the main components of the internal noises in IRFPAS CMOS readout integrated circuit and they are the noises which give a major impact to the output signal. In accordance with the type of noise, some design methods for noise suppression are put forward. And after the simulation of these methods with EDA software, the results show that noises have been reduced. The results of this work gave the referenced gist for improving the noise suppression design of IRFPAs CMOS readout integrated circuit.

Using the birefringence properties and the electro-optic effect of LiNbO₃ crystal, an optical 90°-hybrid with 2 input ports and 4 output ports is designed in this paper. The new optical hybrid consists mainly of two pairs of LiNbO₃ crystal plates with the same sizes, the modulating electrodes and a polarization analyzer. One pair of LiNbO₃ crystal plates split incoming signal beam E_S and local oscillator beam E_LO into four light beams and the other mix them into two synthetic beams. By adjusting applied voltage on the LiNbO₃ crystal plates, 4 output ports from the polarization analyzer give the narrow mixed beams with a relative phase shift 90°. The optical hybrid has the advantage of low losses and good stability of the phase shift. It has the great potential for wide applications in free-space coherent laser communications and laser radar.

A novel lensed fiber for side-coupling of a single-mode(SM) optical fiber and the corresponding fabrication method were proposed, which makes the coupling assembly more compact and easy to integrate and package. The novel lensed fiber mainly composes of a portion of SM optical fiber and a portion of coreless optical fiber. The two fibers are jointed by fusing splicing. The end of the coreless fiber is shaped to have a 45 degree angled end face and polished to form a contoured curved surface. Then the contoured surface is coated so it acts as a curved reflective surface. Besides, the cylindrical surface of the coreless fiber acts as a second curved surface. The two curved surfaces compose a pair of equivalent cylindrical lens. After being focused by the equivalent cylindrical lens pair, the output spot size is comparable to the mode field radius of the SM optical fiber. Matrix optics was used to analyze the output beam parameters of the proposed lensed fiber structure. Simulation results showed that the proposed lensed fiber can bend the beam with 90 degree and make a focused spot on its side with a small spot size close to 6µm, which is suitable for fiber to photodetector chip side-coupling applications.

Using chirped phase mask to fabricate chirped fiber Bragg gratings (CFBG) is a very important method. In this paper, a linearly chirped phase mask with the period of 1000nm in the center, ruled area 100×10mm2 and 1nm/mm chirp rate has been fabricated by a new technique, which combines holographic-ion beam etching and reactive ion beam etching. This involves two main steps: formation of a grating mask by holographic interference exposure and development, and transferring it into the substrate to form a permanent phase mask by both ion beam etching and reactive ion beam etching. Experimental measurements show that the zero order diffraction efficiency is less than 2% and the plus and minus first-order diffraction efficiency is more than 35%; the nonlinear coefficient is 1.6%. Theoretical analysis also indicates that these phase masks can be used to fabricate the UV written CFBG.

Recent progress in research on polymer photonics is reviewed in this paper, including new concepts of polymer-based photonic materials, components and devices. Novel polymer photonic materials developed in our photonic research group, polysiloxanes (named as PSQ-Ls), are reported, including two kinds of PSQ-Ls, named as PSQ-LL and PSQ-LH. These polymer photonic materials are of a liquid and can be cured by UV light irradiation or by heat. The characterization of the optical films and waveguides based on the novel polymer materials, including refractive index, birefringence, optical loss and thermal stability, is given in detail. By blending PSQ-LL and PSQ-LH, the refractive indexes can be tuned linearly from 1.4482 to 1.5212 at 1310nm and from 1.4478 to 1.5198 at 1550nm. The birefringence is below 0.0005 with the variation of PSQ-LL content. These materials exhibit low optical losses of 0.31dB/cm at a wavelength of 1310nm and 0.70dB/cm at 1550nm, and high thermal stability with 1% decomposition temperatures of 297°C (in air) and 340°C (in N₂) for PSQ-LH, and 313°C (in air) and 370°C (in N₂) for PSQ-LL. Optical waveguide components such as micro-ring resonators and waveguide gratings based on PSQ-Ls are fabricated by photolithography-etching method and by UV imprint technology, respectively. The experimental measurements show that the polymer-based micro-ring resonators exhibit an excellent resonant filtering function. Potential applications of the polymer-based micro-ring resonators for optical communications and optical sensing are discussed.

The properties of truly confined modes of a 2D hex horizontal photonic crystal slot slab waveguide are analyzed. Then the dispersion of liner defect waveguide is calculated. In addition, what influence the slots with different height have over the band structure and the group velocity dispersion of the defect mode waveguide are analyzed. Based on these studies, an ultra-compact silicon-based Mach-Zehnder amplitude modulator is proposed. For a design with almost negligible first order chromatic dispersion in an optical bandwidth of 1THz, we predict a modulation bandwidth of 40GHz and a length of about 80µm. This is achieved by infiltrating an electro-optic polymer into a slotted photonic crystal waveguide, the strong field confinement in slotted waveguides and the slow light interaction enhancements provided by the photonic crystal waveguide, where group velocity and dispersion may be controlled.

A new time domain sensing scheme using a compact single abrupt taper-based standard single mode fiber Mach- Zehnder interferometer is proposed, tested and simulated. The interferometer consists of cascaded symmetrical abrupt 3 dB taper regions separated by a middle interfering section. After the interfering middle section, the cladding modes are converted back into core mode. Due to the external stimuli applied to the interferometer, change of refractive index and the optical path length are induced, resulting in phase difference of core and cladding modes, and hence, the output optical signal in the time domain. The proposed scheme promises a simple and sensitive approach to optical sensing.

Using a short optical pulse with finite extinction ration (ER) in Brillouin optical time domain analysis (BOTDA) system can achieve high spatial resolution and frequency resolution at the same time. However, the fluctuation after the pulse generated by the pulse generator can result in a same fluctuation to the optical pulse modulated by electro-optic modulator (EOM). Theoretical and experimental results demonstrate that this fluctuation can result in a reverse peak which has a 60MHz dip in the detected Brillouin spectrum. This makes it impossible to perform the sensing successfully when the Brillouin frequency shift (BFS) induced by the strain or temperature is within the dip. By adjust the DC bias of the EOM and the power of the electrical pulse, the influence of the fluctuation is eliminated successfully. A 15MHz BFS induced by strain on 20cm section over a 50m fiber is successfully detected with a frequency error of 0.8MHz.

In this paper, a design of demodulation system applied to Fiber Bragg Grating sensor will be illustrated. This system is based on the principle of Fiber Bragg Grating strain sensing; therefore this applied system has the following characteristics: high sensitivity, high precision, low cost and so on. Demodulation system bases on the traditional matching method, and uses the two matched Fiber Bragg Grating parallel mode. Just because of this, it improves on a certain extent compared with the traditional one. The two Fiber Bragg Gratings are pasted on Hollow Aluminum Cantilever respectively so as to realize the high precision and the large scale strain demodulation. This paper proves the following theory through the academic analyses and experimentation, that is: pasting Fiber Bragg Grating on Hollow Aluminum Cantilever can improve the response sensitivity. During the process of matching, increasing the load on the Hollow Aluminum Cantilever, when the qualities of load cannot beyond the limited quality, there is a good linearity relation between the change of load's quality and the change of wavelength. The limited quality comes from the experimentation. The experimentation proves that the structure of two matched Fiber Bragg Grating parallel can increase the range of strain which can be measured largely, and at the same time this structure can solve double-value problem which exists in the ordinary matching method. The strain sense signal through the two parallel demodulation Fiber Bragg Gratings into data processing circuit. The single chip processes the data from the data processing circuit and works out the strain which is detected by Fiber Bragg Grating sensor.

Sampled and linearly chirped fiber Bragg gratings provide multiple wavelength responses and linear group delays (constant dispersions) within each of the wavelength channels. We show that the sampled and chirped fiber Bragg gratings can be used to perform multiwavelength signal processing. In particular, we demonstrate, by numerical simulation, their use for performing real-time Fourier transform (RTFT) and for pulse repetition rate multiplication (PRRM) simultaneously over multiple wavelength channels. To present how the sampled fiber Bragg gratings perform the multichannel optical signal processing, a 9-channel sampled fiber grating with 100GHz channel spacing was designed and the effect of ripples in both amplitude and the group delay channel on the performance of the signal processing was examined and discussed.

A new type of the intelligent real-time protection device is developed, which is supposed to better adapt to the physical layer protection of the mesh optical network. By means of converting the optical signal into the electric ones, the real-time online optical power data of the optical fibers are sampled and processed by the protection device, so the working state of the mesh optical network is obtained. By communicating with each other, the protection devices placed at each node of the mesh optical network can figure out the backup lightpath of each primary fiber in advance, and then a backup lightpath route table will be dynamically established and maintained by each protection device. Whenever the failure of the primary fiber occurs, the protection device will immediately switch to the backup lightpath by driving the optical switch matrix according to its backup lightpath route table. The intelligent real-time protection device for mesh optical network is a kind of real unattended intelligent real-time online monitoring and protection device for the physical layer of optical network, which is enabled to meet the requirement of the development of the mesh optical network. So the transparent uninterrupted communication of the mesh optical network could be achievable by applying the proposed intelligent real-time protection device.

Passive phase locking of multiple fiber lasers by using a common all-fiber ring cavity is proposed and demonstrated. The cavity is chiefly composed of multiple 2×2 fiber couplers, which are insets of component fiber lasers of an array. The common ring cavity not only acts as a ring filter for mode selection and stabilization of component fiber lasers, but also provides a common channel for mutual injection coupling among them. We have demonstrated efficient phase locking of multiple Erbium-doped fiber lasers with linear and ring resonators based on the common ring cavity configuration, and obvious interference patterns and stable coherent output have been observed in experiment. The power transmission and resonance properties of the ring cavity are investigated theoretically by the intensity and amplitude addition methods. The research results indicate that increasing the coupling ratio of fiber couplers can increase the coupling strength, and decreasing the loss of the common ring cavity can increase both the coupling strength and combining efficiency. Finally, the phase locking mechanism of the presented scheme is discussed, and we believe that the phase locking array forms a composite resonator on account of the common ring cavity, and the array achieves phase locking states through mutual injection coupling among component lasers.

Double-clad rare-earth-doped fiber laser is a new generation of high power solid-state lasers. The numerical simulation is an important approach in the configuration design and parameter optimization for the high power fiber lasers (HPFLs). In this paper, we report our user-friendly high-power fiber laser simulation software system, which integrates the design, analysis and optimization functions together. The numerical simulations of the software are with the HPFL model based on the rate-equation theory. By using the theoretical model, for specific laser cavity configuration, doped fiber parameters and pump conditions, the distributions of the population inversion, forward and backward pump, and circulating lasing intensity along the doped fiber can be calculated, and thus, the main output characteristics, such as cavity gain, output power and laser efficiency, can be achieved accordingly. On the basis of the simulation results, the software supplies the functions developed for designs and optimizations of the pump configuration, doped fiber length and the reflectivity of output mirror. By combining the calculated mode-field distribution in doped fibers with the mechanism of curvature loss to suppress the higher-order modes, the software also supplies the function for optimizing the beam quality. With graphical user interface (GUI), all the functions of the software are provided function tools in menu options, especially for those which may be used frequently, toolbar buttons, shortcut keys and pop-up menus are also provided. The software is with single-document interface (SDI) and coded in C++ in the integrated development environment of Visual C++ 6.0. We believe it would be very helpful for the investigation and development of HPFLs.

Laser imaging radar has the unique capability to generate 3D images of objects, which is widely used in the civilian and military fields concerning target detection and identification. The imaging simulation for 3-D laser radar is presented to help in the design of the future laser radar systems and gauge their performances. Each stage from the laser source to the 3D image generation has been modelled, including the models of the laser emitted pulse, atmospheric effects, reflection properties of the target surface, discrimination methods and the returned signal. Moreover, the three-dimensional CAD description of the target is established for imaging simulation. The simulation produces the simulated 3D images for a pulsed laser radar and allows to understand the influences of the phenomena leading to the final image under a variety of conditions. Finally, a collection of imaging simulations with one changing parameter at a time is implemented to illustrate the good possibilities of the simulation.

We present a phase feature extraction technique for weakly polarized organic compounds in THz-RTDS by taking the second derivative of the phase of the signal beam with respect to frequency. In nitrogen purged environment this method doesn't require any reference. In real scenarios, a reference beam is applied only to remove the influence of atmospheric attenuation. This method offers a straightforward and speedy way to retrieve the absorption features in the reflection spectrum without the presence of the amplitude of the THz pulse or the settlement of a reference surface. It opens the pathways for the application of a more un-conventional THz emission mechanism and extends the capability of THz sensing technology into more practical sensing and imaging situations.

In this paper, the imaging ability of terahertz wave in time-domain spectroscopy (THz-TDS) imaging system is assessed by using the step-by-step scan imaging method to four small structures: thread, dots, round hole, and square on the focus of the imaging system. We utilize THz-TDS energy imaging model to acquire the energy distribution of terahertz wave passing through the different small structure, which can be use as a criterion of imaging ability. Theoretically, terahertz imaging technology possesses highly spatial resolution because the size of spot is inversely proportional to the frequency. Our experimental results also show that THz-TDS technology has a preferable spatial resolution on the millimeter scale. In addition, a more delicate and smooth image can be obtained by means of the nearest neighbor interpolation algorithm. A method to measure the size of target is provided. These results are important references for the further terahertz spectroscopy imaging research.

The terahertz(THz) fingerprint spectra of Ephedrine Hydrochloride and Papaverine Hydrochloride have been measured using THz time-domain Spectroscopy (THz-TDS) system in the region of 0.2~2.6 THz. To explain the spectra, both gas-phase simulation methods and solid-state simulation methods were performed in the efforts to extract pictures of the molecular interior vibrational modes. By comparing the results of various gas-phase simulation methods, It was found that using the semi-empirical theory is more applicable than the density functional theory (DFT) for some chemical compounds. In the solid-state calculations, solid-state density functional theory (DFT) was employed to obtain the vibration frequencies and Difference-Dipole Method (DDM) was used to calculate the corresponding infrared (IR) intensity. In the process of calculating the IR intensity of Papaverine Hydrochloride in terahertz range, we found that the results by Hirshfeld partitioning method agree better with the experiments than the ones derived from Mulliken atomic charges. Moreover, the accuracy of simulation results depends on the basis sets and grid size being chosen.

We present a terahertz (THz) imaging system with a Backward Wave Oscillator (BWO). BWO Continuous-Wave THz imaging is a new approach to non-destructive testing. Many materials that are opaque to visible and infrared light are transparent to THz radiation. THz wave image provides a higher spatial resolution than microwave image by having much shorter wavelength. It also poses no known harm to living organisms, making it a safe and powerful imaging technology. Unlike pulsed THz imaging, BWO THz imaging only yields intensity data without providing any depth, frequency-domain or time-domain information about the subject. However, in most cases the energy plots are sufficient for identification of targets. In exchange for the loss of depth, time-domain and frequency-domain information, BWO imaging offers a simple, fast and relatively low-cost system. In this work we show a simple Terahertz (THz) 2-dimentional scanning imaging system utilizing a BWO source tunable from 0.52 to 0.71 THz and a pyroelectric sensor detector operated in THz range. The sample is placed on an X-Z two-dimensional stage controlled by a computer. The intensity information of the terahertz wave after passing sample is collected. Two-dimensional image of the sample is obtained by raster scanning the sample in X and Z directions. A number of potential imaging applications are demonstrated using the 0.71 THz radiation, including nondestructive real-time testing for campus debit card and various articles contained in an envelop. And we present the digital image processing based on the result of the imaging system. This work reveals that a BWO THz imaging system is very practical, effective and promising in nondestructive identification and security inspections applications in future.

We present a reference-free transmission spectroscopy of two kinds of aminophenol (Tyrosine and Phenylalanine) using terahertz time domain spectroscopy (THz-TDS). The THz band, which refers to the spectral region between 0.1 to 10 THz, offers a plethora of fingerprints of many chemical and biological materials. Within the past few years, efforts have been focused on exploiting the broadband nature of the THz time domain spectroscopy (THz-TDS) system for material identification and characterization. The conventional spectroscopic sensing method involves measuring both the terahertz signal carrying the sample information and a reference terahertz signal. In transmission geometry measurement, the absorption peaks of the sample material are found by taking the logarithm of the power spectrum of the transmitted signal beam divided by a reference power spectrum. In this work, we propose a reference-free approach to extract the absorption feature in THz transmission spectroscopy. The samples are identified by their absorption peaks extracted from the negative first-order derivative of the sample signal phase divided by the frequency. Unlike in conventional transmission spectroscopy measurement, in this method, the amplitude spectrum of the terahertz signal is not considered at all. Instead, the absorption features are extracted exclusively from the phase information by taking advantage of the almost-linear phase spectrum of terahertz pulses and the correlation between dispersion and absorption. It is also noted that the spectral phase of the terahertz pulse can be determined with far greater accuracy than the amplitude, which makes this method even more favorable. We measured two kinds of aminophenol (Tyrosine and Phenylalanine), and calculated the absorbance spectrum of each by both methods: taking the ratio between the power spectra of the sample signal and the reference signal and the reference-free phase spectrum of each material. The agreement between the positions of the absorption lines calculated from both methods indicates that the reference-free method is valid.

We present a novel feature extraction technique for identification of explosive and biological materials using terahertz reflective time domain spectroscopy (THz-RTDS). The absorption signatures of the materials are extracted directly from the derivative of the amplitude reflectance without measuring the phase shift caused by the sample's height. This technique provides a straightforward and fast solution to solve the phase-retrieval problem in RTDS and will benefit the future development of standoff, large size focal-plane THz sensing and imaging system.

THz spectra of two pure materials and some mixed explosive materials and the theoretical analysis results are introduced. The refractive index and absorption coefficient of the samples are measured in the region of 0.2-2.5 terahertz by time-domain spectroscopy (THz-TDS). The absorption spectra are obtained correspondingly. The obtained results indicate the THz-TDS technology can identify the different explosives and roughly analysis the main ingredients of the mixed samples.

Waveguide ring resonators are key elemental devices for wavelength filters, optical switches, lasers and optical sensors. In order to control the finesse and notch depth of the resonator, the coupling ratio needs to be varied widely and accurately. A novel thermooptic polymer ring resonator integrated with a tunable directional coupler was theoretical analyzed. Polymer materials with different thermooptic coefficients were chosen as the core and cladding layers of waveguides. The structure of the directional coupler was optimized to achieve large tuning range of coupling ratio. The finesse, notch depth and the resonant frequency peak of the resonator can be controlled precisely by temperature. The coupled-mode theory (CMD) and beam propagation method (BPM) were used to simulate the characteristics of the tunable directional coupler. The transmission spectra and loss characteristic of the resonator are also discussed in detail. This device can be used to improve the performance of integrated optical gyroscope (IOG) and other resonator-based photonic integrated circuits.

A novel polycarbonate (PC) was introduced to apply in the optical waveguide devices. PC has following distinct merits than common polycarbonate: good processability, high thermal stability up to 293 C°; and high optical transparency. Optical properties of absorption behavior and propagation loss were investigated in slab waveguides, and low propagation losses of 0.335 dB/cm (@1550nm) and 0.197 dB/cm @632.8nm) have been achieved by using prismcoupler. Additionally, straight optical waveguide and MMI coupler of ring resonator were fabricated using ultraviolet (UV) cured resin Norland optical adhesive 61 (NOA61) as under or upper cladding layer and polycarbonate as waveguide core-layer material through conventional methods such as spin coating, photolithography and reactive ion etching (RIE). The process was studied in detail and the experimental results were given.

This paper reports the ray trajectory and coupling efficiency of a GRIN ball lens and the functions of the ray trajectory in the rectangular coordinate and coupling efficiencies are given. According to analyzing the ray trajectory and coupling efficiencies, the focus performances inside/outside and at the surface of GRIN ball lenses are explained and accordance with them of the Maxwell fisheye lens, the Luneburg lens, and the generalized Luneburg lens.

The long lasting phosphorescence glass spheres doped with Eu₂O₃ and Dy₂O₃ were prepared under the reducing atmosphere and characterized. XRD analysis indicated the glass spheres exhibited the typical diffraction peaks of SrAl₂O₄: Eu²⁺, Dy³⁺. The emission spectra of the glass spheres showed broad bands peaking at 510nm. The excitation spectra of the glass spheres showed broad bands ranging from 300 to 480nm. These are believed due to the 5d4f→4f transitions of Eu²⁺ in the SrAl₂O₄: Eu²⁺, Dy³⁺ phosphors. The afterglow luminescence of the glass spheres excited by a 40W fluorescence lamp for 30min can be observed in the dark for about 15h with the naked eye.

Utilizing terahertz time domain spectroscopy system, we have characterized the electromagnetic response of a planar array of split ring resonators (SRRs) fabricated upon a high resistivity GaAs substrate. We discuss the phenomena of resonant transmission and absorption experimentally, and analyze the factors that affect the frequency of the resonant transmission peak. Free charge in metal rings occurs directional moving with effects of electric and magnetic fields when terahertz wave is incident in split ring (SR). It makes transmission and absorption peaks at certain frequencies by electric and magnetic responses between metal rings. There is another kind of absorption which is made by its structure at natural frequency of SR. We demonstrate, SRR structure has anisotropic property. The directions of split will decide transmission mode of terahertz in samples. Different modes of dipole oscillating are made by changing electric wave vector, and its absorption is also affected. However, natural frequency of SRR is decided by lattice size, independent of transmission mode. Magnetic response occurs when magnetic wave vector has component which is normal to sample surface. It makes phenomenon of absorption more apparently. In addition, decreasing component of which is parallel to sample surface can make transmission peak move to low frequency. Infections to resonance properties of SRR by terahertz electric and magnetic wave vectors are discussed in this letter. It can be a reference for researching terahertz devices.

The terahertz (THz) emission properties of four kinds of bow-tie photoconductive antennas are studied. The characteristic of THz radiation generated by them is compared. The emission spectra of the photoconductive antennas are obtained by THz time domain spectroscopy (TDS) technology. The corresponding frequency domain spectra are obtained by Fast Fourier Transformation (FFT). The results show that when we increase the bias voltage, the peak value of THz radiation is increased and tends to saturation when the pump power is strong enough. Under the same bias voltage and the pump power, the properties of THz radiation generated by four bow-tie photoconductor antennas are compared. It shows that under low bias voltage, the full width of half maximum (FWHM) of frequency a domain spectrum which is generated by small-aperture bow-tie photoconductor antenna is broader than that of the large aperture one. The gap size of small-aperture photoconductive antenna is smaller, the FWHW is broader. On the other hand, under the high bias voltage, the intensity of THz radiation of the large aperture photoconductor antenna is much larger than the small aperture one. Our results provide a reference to investigate and fabricate the high efficient of THz emission source.

In recent years, negative refractive media as the representation of new electromagnetic medium has become the front and the very popular researching field, and the production of the flat lens is one of its major applications. In our study, the imaging behaviors by two-dimensional photonic crystal slabs have been investigated systematically. We suggest a ray-tracing technique to discuss the action of photonic crystal slab with negative refraction. The propagation of electromagnetic waves in two-dimensional hexagonal lattice photonic crystal slab is investigated through dispersion characteristics analysis and numerical simulation of field patterns. Imaging and focusing with effective negative refractive index of -1 have been observed in these systems for both polarized waves, that is TE- and TM-polarized point source be considered simultaneously. Based on the exact finite-difference time-domain method to perform numerical simulation and physical analysis, we have demonstrated that the two-dimensional photonic crystal we designed can realize nearly perfect imaging with TM-polarized point source in the near field and far field, and the results are consistent with the ray-tracing technique quite well, while to TE-polarized point source the imaging is not perfect although it have n_eff=-1 in the same direction.

We present the enhanced transmission spectrum of a copper foil with the sub-wavelength fractal structures by means of the terahertz time domain spectroscopy (THz-TDS) and FDTD simulation. In the view of experimental measurement and finite-difference-time-domain (FDTD) simulations, respectively, we studied the influence of the electric field and magnetic field on the enhanced transmission of THz wave through each level of fractal pattern generated by the repeated affine transformations of an H-shaped mother element on the copper foil. We simulate the incidence and transmission of the THz wave and show the propagation and distribution of the interior electromagnetic field by the software for electromagnetic design named CONCERTO. To compare with the experimental results, we simulate the cases that the certain levels of the pattern are deleted. The results of simulation agree with the experimental one. It is found that the transmission enhancement in the low frequency regime is caused by the radiation of electron resonance in the low fractal levels, and the transmission enhancement in the high frequency regime is caused by the radiation of electron resonance in the high fractal level, that is, the localization resonance of the fractal structures. These results indicate that the flat surface fractal structure like an ideal wave-guide. The vertically incident THz wave is confined on the surface and transmitted along the fractal slits. The controlling ability of fractal structures will offer a powerful tool for the design of THz photonic devices.

Experimental measurement and theoretical analysis of THz vibration spectra of four different kinds of vitamins are presented. The refractive index and absorbance of these vitamins are measured at room temperature by THz-TDS in the frequency region of 0.2-2.6 THz. The full-geometry optimizations and frequency calculations using the density functional theory (DFT) are applied to obtain the structure and vibration frequencies of these vitamins. The calculated results are in agreement with the experimental data. The simulation results show that the intermolecular interactions are considerably weak so that the gas-phase simulations spectra are closely to the solid-phase. The calculated results confirm that most of the absorption peaks result from the intra-molecular modes; the others have been ascribed to intermolecular interaction or phonon modes.

A novel 256×1 readout integrated circuit (ROIC) with simultaneous integration mode for two-color (MWIR/LWIR,MWIR/SWIR) n-p-P-P-N HgCdTe infrared detectors is presented in this paper. This ROIC features an input stage based on current mirror integration (CMI) structure, which separates MW (SW) photocurrent signal from mixed signals of LW and MW (MW and SW) and each waveband photocurrent signal is capable to be integrated in uncorrelated-simultaneous mode. A test chip of 256×1 ROIC is designed and fabricated with 0.6μm double poly double metal mixed signal technology. The chip test results prove right function of the circuit. It shows good performance of integration of MW and LW signals. The linearity of MW and LW output voltage- input current curve is over 99%. Power dissipation of the circuit is less than 50 mW. Readout clock frequency is up to 2 MHz.

Narrow linewidth fiber lasers have become more and more necessary in field of coherent communication, fiber optic sensor, and high resolutions optical spectrum analysis, especially long-range distributed fiber sensing system. In this paper, a simple and stable narrow linewidth Er³⁺ -doped ring fiber laser is first proposed and experimentally demonstrated. In the cavity, a passive fiber Bragg grating Fabry-Perot (FBG F-P) etalon acts as mode-selecting device to greatly reduce the longitudinal-mode density, while a section un-pumped Er³⁺ -doped fiber serves as a saturable absorber to ensure the single longitudinal-mode (SLM) operation. Meanwhile the stability of lasing frequency is further improved by controlling the temperature of the FBG F-P, and then through varying the temperature the lasing wavelength tuning is achieved also. Finally stable SLM laser at 1550nm with linewidth about 7.5 kHz, maximum output power 39 mW and the corresponding slope efficiency 30% is acquired.

Brillouin Optical Time-Domain Reflectometry (BOTDR) is attracting significant attention due to its immense potential applications in temperature or strain monitoring. Conventional BOTDR system based on Spontaneous Brillouin Scattering Spectrum(SBSS) narrow-band detection is not only time-consuming but also controlling complicated. To overcome the drawbacks of the conventional detection method, a new SBSS wideband detection method is proposed in this paper. In the new detection method, the whole SBSS is captured by use of a wideband receiver in a single measurement, and Discrete Fourier Transform (DFT) signal processing algorithm is used to obtain the SBSS. The configuration of a heterodyne detection BOTDR system based on SBSS wideband detection is presented, and the data processing method, the spatial resolution of the system and the measurement time is discussed. The BOTDR system based on SBSS wideband detection has been demonstrated, and a temperature resolution of 3°C and a spatial resolution of 2 m have been achieved. The measurement time is only about one-tenth that of conventional narrow-band detection method.

Symmetrical apodization technique of the chirped fiber Bragg grating has the advantages of suppressing the sidelobes of reflection spectra and smoothing the curves of group delay. However, it shortens the bandwidth of the reflection spectrum markedly. Compared with symmetrical apodization method, the asymmetric method can increase the 3dB bandwidth by 64.08% without the change of group delay curves. The apodization simulation is implemented by using a rised cosine function with different apodization length ratios at both ends of the grating. There is a compromise between the bandwidth and the group delay ripple. The result shows that the grating with 30% apodization at the long wavelength end and 20% apodization at the short wavelength side can improve the reflection bandwidth effectively and depress the group delay ripple within the range of ±2 ps.

A multi-channel tunable mechanically induced long-period fiber gratings (LPFGs) scheme is presented, which can induce several LPFGs with different resonance wavelengths simultaneously. LPFGs spectra characteristics are simulated to find the influence of these parameters such as grating length, tilt angle and the pressure on the fiber. The simulation results show that the transmission loss peak mainly depends on both the grating length and the pressure, while tilt angle factor dominates the resonant wavelength. The infuence of the pressure and tilt angles on the transmission spectra is experimentally studied. This multi-channel LPFGs module will have great potential applications in the fiber sensing field and flexible filter design region.

Hydrogen-based dry plasmas, generated in inductively coupled plasma reactors have been demonstrated to be very effective in fabricating high fill-factor mesa of Hg_1-xCd _xTe multi-layer hetero-structure material for infrared focal plane array applications. To obtain reasonable dry etching process for Hg _1-xCd _xTe, it is essential to investigate the physical, chemical, and electrical characteristics of the surface. This paper explores the effect of varying the plasma process parameters on the surface of Hg _1-xCd _xTe. The surface chemical analysis was carried out using spot X-ray photoelectron spectroscopy (XPS), the surface roughness was measured by atomic force microscopy (AFM), and p-to-n type conversion depth was assessed by a reliable current-voltage test of a designed structure basing on material-chip technology concept and a convenient technology of cross-section surface potential imaging (SPM). At last, Hg _1-xCd _xTe etched surfaces with roughness low and mechanical or electrical damage free were achieved.

By numerically solving the time-dependant Kohn-Sham equation with initial states obtained through self-consistent density-functional theory, we studied, in a numerical way, photoionization of a one-dimensional helium cluster model exposed to intense laser pulses. Enhanced ionization effect, which is similar to the CREI effect for small molecules, was observed and the associated mechanism was discussed. Our numerical results present good agreement with previous conclusions using different algorithms.

A detailed theoretical and experimental study of buried ion-exchanged waveguides is reported. The model of the ion concentration distribution in Ag⁺-Na⁺ ion exchanged glass, which is analyzed by numerical calculations, agrees well with our experiments showing that after the first ion-exchange, a half oval-shaped ion concentration distribution can be obtained in the substrate; and after the second ion-exchange, the radio-shaped ion concentration distribution presents. These results may be used to establish the necessary correlation between the ion-exchange process parameters and the waveguide characteristics.

Blood lead detecting can make certain valuation to human being health and environment problem. Traditional blood lead detecting instrument used only in laboratory analysis with long time and relatively expensive cost disadvantage. Based on small volume and strong anti-interference of fiber sensor, the paper designed fiber system, including fiber sensor and demodulate system, which can be used in blood lead measurement. Using compound environment fixed in fiber sensor, fiber transferred the reflected light with Pb consistency information, then the impatt diode receives modulated light intensity and demodulates to corresponding lead thickness. with designed fiber system, the paper measured some blood samples with 2.67% precision and 0.231 variance. The designed fiber system is very considerable and usable.

A novel method of narrow line-width Er³⁺-doped fiber ring laser based on FBG F-P etalon and FBG Sagnac loop is presented in this paper. The all-fiber single frequency and narrow line-width Er³⁺-doped fiber ring laser has been designed in which two 976 nm laser diodes are used as the pump sources, the high concentration Er³⁺-doped fiber as the gain medium, the fiber Faraday rotator is adopted to eliminate the spatial hole burning effect, the FBG F-P etalon and FBG Sagnac loop filter can discriminate and select laser longitudinal modes efficiently. The experiment system using 3m long Er³⁺-doped fibers is presented, when the maximum pump power of two 976nm laser diodes is 146mW, the fiber laser exhibits 16mW threshold and stable single frequency 1550nm laser with the output powers of 45mW is acquired, and the slope efficiency is about 34.6%. The 3dB line-width is less than 9.3 kHz, measured by the delayed selfheterodyne method with 15km single-mode fiber, and no mode hopping is observed. The fiber laser has the advantages of simple structure, high efficiency and high reliability and it has great potential applications in the fields of optical fiber sensing system.

In this work, we demonstrate that the spectral self-imaging phenomenon is not restricted to phase-only sampled and linearly chirped fiber Bragg gratings(LCFBGs), rather they can be implemented in phase-only sampled fiber Bragg gratings (FBGs) with an arbitrarily chirped grating period. We derive the general conditions at which spectral Talbot phenomenon, namely, integer and fractional spectral self-imaging occurs. The multiplication of spectral channels, respectively in the linear, square and cubic chirp coefficient conditions, and/or together, are implemented and observed in phase-only sampled FBGs with both integer and fractional types using the transfer matrix method.

The multimode devices, which are also polarization-sensitive, have been widely used in modern optical communication system. In some cases, the modal properties, including the modal propagation constants and the modal fields of every order, must be given for the device design. The scalar finite difference beam propagation method (FD-BPM) is extended to solve this polarization-related problem. The different finite difference schemes corresponding to different polarized directions, which satisfy different boundary continual conditions, are formulized and the alternate directions implicit (ADI) FD-BPM were used to deal with the three dimensional (3D) waveguide. The guided modal properties of a 3D rib waveguide including the propagation constants and modal field distributions up to ten ranks were obtained and illustrated as an example.

An approximate explicit solution for Raman fiber lasers with arbitrary cascades is obtained. The solution is deduced without using depleted pump approximation. The proposed analytical solution shows excellent agreement with numerical simulation. Furthermore, optimal design of the cascaded Raman fiber lasers is carried out analytically. The optimal values of fiber length, reflectivity of output fiber Bragg grating and power conversion efficiency are obtained under different pump power. The optimal fiber length and reflectivity of output FBG decrease with increasing pump power. There exists a certain tolerance of the optimal cavity parameters, in which the conversion efficiency decreases only slightly. In addition, by the proposed solution one can readily determine whether pump power is depleted.

With the rapid development of micro optoelectronic device and integration techniques in PMMA fiber, micro-structure integration in PMMA fiber such as diffraction gratings graved by focusing fslaser inside the PMMA fiber is becoming popular. However, the white light induced by interaction of femtosecond pulse with PMMA has a property that is similar to laser beam has been founded, and generated a continuous spectrum from ultraviolet to infrared. Ti:sapphire femtosecond laser systems with 1kHz, 45fs, 1mJ were used to get the white continuum spectrum in PMMA . The white continuum spectrum from 440nm to1100nm has been recorded. Also White light filament induced by fslaser at lower thredhold power inside the PMMA than others , and this white light filaments will damage the PMMA fiber and induce refractive-index change so as to affect micro optoelectronic device and integration techniques application in PMMA fiber.

This paper reports the design and preparation of ultra-fast photoconductive (PC) switch made from a 500 nm thick low temperature grown GaAs (LT-GaAs) on a transparent quartz glass substrate. After the procedures of photolithography, etching, evaporation etc., coplanar strip (CPS) transmission lines of Au/Pt with width and spacing of 10 μm and thickness of 600 nm are evaporated on the substrate of LT-GaAs. The photoconductive switch has ideal dark resistance, good I-V performance and photoelectric linearity under an exposure of weak light. The dark current is about 0.1 pA at a bias voltage of 10 V. The typical risetime of the photoconductive switch is 1.3 ps measured by pump-probe technique with a mode-locked Ti: sapphire laser with pulse width of 100 fs, wavelength of 800 nm, and frequency of 100 MHz.

Monte Carlo simulation method has been used to study the linear mode of photoconductive semiconductor switches (PCSS). Its triggered source is a femtosecond laser pulse. The simulation results are well in agreement with experiment data, so the model is accurate. Based on the model, some important factors which influence the response time of PCSS have been analyzed by computer simulation. Then the sizes of these parameters that make an important contribution to get better response time have been deduced. From this simulation analysis, it is sure that some experiment conditions can be used more enough. In other words, the response time can be further shortened under the same experiment condition. Moreover, the transition from linear mode to non-linear mode has been analyzed using this model.

In this paper, the THz spectra of several weakly absorptive chemical materials are measured by a novel technology: reference-free THz transmission spectroscopy. We then introduce a new THz spectral feature recognition method by applying pattern recognition method in explosive spectra classification and identification. Two types of artificial neural networks (ANNs): self organized mapping (SOM) and multilayer perceptron (MLP) and are used through repetitive modeling and adequate training with high accuracy rate and low alarm rate. The results indicate that the reference-free technique is a viable and valid spectroscopic modality by replacing the conventional absorbance curves with phase curves as features for identification and classification. The phase spectroscopy method is especially favorable for long distance and large size THz sensing and imaging systems by ignoring the imperfect beam amplitude profile. We also show that it is feasible to apply these two ANNS on the identification of different types of explosives, amino acid and many other chemicals. It provides an effective method in material inspection and identification using THz-TDS.

The controllable focusing property of a flat lens is investigated by changing the external voltage. The tunability is introduced based on electro-optical effect. The flat lens is a slab of photonic crystal composed of air cylinders in electro-optic material background. The results demonstrate that focusing can be achieved by the flat photonic crystal slab. Moreover, the focal length of the flat lens can be tuned continuously by the applied voltage, which might have potential applications in photoelectric devices.