Realization of high-speed avalanche photodiodes (APDs) requires the use of thin avalanche regions to reduce carrier transit time. A systematic investigation on the effect of dead space on the current impulse response and bandwidth of short APDs was carried out using a random path length model assuming a constant carrier velocity. The results indicate that, although dead space suppresses large multiplication values in a short device to give low excess noise, the number of impact ionization a carrier can undergo in a single transit is reduced. Consequently, multiple carrier feedback processes are necessary to achieve a given multiplication value. This results in an increase in the response time and reduces the bandwidth of short APDs. Conventional local models that take no account of the dead space effect will tend to overestimate the operating speed of these devices.

Thin film optical position sensitive detectors (PSDs) based on novel hydrogenated amorphous silicon Schottky barrier (SB) structures are compared in this work. The three structures reported here have been tested under different light sources to measure their linear properties and wavelength response characteristics. The sputtered a-Si sensors were configured as layered structures of platinum, a-Si and indium tin oxide, forming SB-i-n devices and exhibited linear properties similar to multi-layer a-Si p-i- n devices produced by complex chemical vapor deposition procedures, which involve flammable and toxic gases. All structures were test4ed as possible configurations for 2D sensors. The devices were tested under white light, filtered white light and also a red diode laser. Each of the three structures responded quite differently to each of the sources. Results, based on the correlation coefficient, which measures the linearity of output and which has a maximum value of 1, produced r values ranging between 0.992 to 0.999, in the best performances.

The photocurrent analysis of a metal-semiconductor-metal photoconductors (MSM-PD) with interdigitated electrodes fabricated on silicon-ion-implanted Borosilicate glass substrate is reported. The dark- and photo-current of the SiO₂:Si⁺ MSM-PD with finger width and spacing of 5 micrometers are 72 pA and 447 pA at bias of 50 volts, which corresponds to a photocurrent gain of 5.2 and a responsivity of 0.38 (mu) A/W as measured under the injection power of 25mW at 514.5 nm. The decreasing trend in photocurrent response versus wavelength reveals that the absorption coefficient of the SiO₂:Si⁺ becomes smaller at longer wavelengths.

A P-I-i-I-N GaAs/AlGaAs phase modulator with selective phase change only for TE mode is presented. TE-selective phase modulation can be achieved by utilizing the linear electro-optic (LEO) effect, which is polarization-dependent, and limiting contributions from polarization-independent effects. Separate confinement of optical and applied electric fields in the P-I-i-I-N structure and selection of an operating wavelength far from the bandgap enable this operation to be optimized. TE phase shift efficiencies of 4.0 ~ 6.5 degrees/V mm can be achieved with maintaining the ratio of TM to TE phase shift to be less than 10 percent. TE selectivity can be increased at the cost of reduction of phase shift efficiency and vice versa.

An accurate and yet simple simulation technique for optical modulators operating at multi-GHz region and optical modulators are critical for Tera-bps optical communications. This paper describes a simple, efficient and accurate analysis of the traveling wave electrodes for high speed optical modulation and the implementation of these electrodes in interferometric optical modulators. A finite difference approach is employed in modeling the traveling wave electrodes for efficient electro-optic interaction in interferometric optical modulators. Electrode configurations such as symmetric and asymmetric co-planar waveguide or strip structures and shielded electrode systems can be modeled. Simulated results demonstrate the efficiency of the presented method as compared with other methods such as the Green's function, conformal mapping, method if images, spectral domain analysis etc. Tilted and thick practical electro-plated electrodes are modeled and confirmed with implemented modulators operating up to 26 GHz in diffused LiNbO3 optical interferometric optical waveguide structures. The fabrication of optical waveguides and traveling wave electrodes are described for implementation of the electro-optic interferometric modulators.

Erbium oxalate and neodymium oxalate nanoparticles/titania/organically modified silane composite sol-gel thin films for photonic applications have been prepared by combining an inverse microemulsion technique and the sol-gel technique at low temperature. Transmission electron microscopy observation shows that the size of these oxalate nanoparticles is in the range from 10 to 40 nm. Up- conversion emission properties of these composite thin films on silicon substrates have been studied. A relatively strong room-temperature green up-conversion emission at 544 nm has been measured for the composite films dispersed with erbium oxalate nanoparticles upon excitation at 993 nm. An up- conversion emission in violet color from neodymium oxalate nanoparticles upon excitation with a yellow light emission, two UV emissions at 341 nm and 376 nm and a weak blue emission at 467 nm have been obtained. The mechanism of the up-conversion emission has been explained by means of an energy level diagram. The lifetimes of the violet emissions have been measured.

We took a step forward on the basis of existing deduction, the formula of net gain coefficient of amplification of spontaneous emission of Er-doped fiber was given. Based on the data, which were provided by the reference, we calculated the net gain coefficients for different fiber length pumped at different pump power. Then theoretical curves were drawn. ASE spectra obtained experimentally were in excellent qualitative agreement with the ones obtained from theory. At last, the calculated optimal fiber lengths were given according to several common used wavelengths at the same pump power.

In this paper, we describe low-noise Er-doped optical fiber amplifiers (EDFAs) achieved by exploring novel long period fiber gratings (LPFG) fabrication technique is based on the thermal shock effect of high-frequency CO₂ laser pulses at several kHz. By inserting such a LPFG in the Er-doped fiber, the ASE noise of the EDFA has been reduced considerably. Two low-noise EDFAs have been constructed and demonstrated. The ASE noise of the two EDFAs used as a pre- amplifier and an in-line amplifier has been successfully reduced from 4.0dB to approximately 3.5dB and from approximately 4.8dB to approximately 4.3dB with a small- signal gain increase of approximately 7dB for the in-line amplifier, respectively.

Both government and industry have a long-standing interest in developing low-cost high-power semiconductor lasers for a variety of applications. These include material processing, long range sensing, and long-range communications. Key development goals are high brightness and high efficiency. This paper will review some of the applications, key laser performance features desired, and some of the past accomplishments in high power diode lasers form the High Power Semiconductor Laser Technology program. One of the primary outgrowths of HPSLT was the Grating Coupled Surface Emitting Laser (GCSEL). GCSEL progress will be highlighted.

Wavelength stability with respect to temperature for Fiber grating external cavity semiconductor lasers (FG-ECL) is analyzed theoretically. It is found that the use of temperature insensitive fiber grating can decrease the thermal induced wavelength shift, but simultaneously, reduce the temperature interval of mode hopping. Furthermore, a method is proposed to suppress the thermal induced mode hopping and wavelength shift in FG-ECL.

An electron-beam sensitive inorganic-organic hybrid SiO₂TiO₂ glass was synthesized for the fabrication of structures with sub-micron sized features. The sensitivity of the sol-gel material was characterized with the electron beam dosage and the optimized doses were found to cross-link the material for sub-micron structures. Due to its properties of low thermal expansion, good mechanical strength and chemical durability, the sol-gel material can be used as resistance in the dry etching process in optoelectronics fabrications. For micro-optical elements, the diffractive optical elements can be fabricated directly into the sol-gel glass without etching.

A new type of gain-flattening filter using long-period fiber gratings (LPFGs) based on periodic microbends is presented. The fabrication and characterization of the device are described and its use in an erbium-doped fiber amplifier (EDFA) to flatten the ASE spectrum is demonstrated. This filter, which is simple and inexpensive, exhibits the unique advantages of being tunable, erasable, and reconfigurable. The result shows that the gain variation over the wavelength range 1525 to 1560nm is less then 1dB when pumped with 45mW and 40mW of pump power at 980nm from a laser diode.

We address a genetic algorithm (Gas) to achieve optimization design for diffractive optical elements (DOEs) for the laser beam shaping. A laser beam shaping system is investigated using genetic algorithm, in which an incident Gaussian profile laser beam is converted into a zero-order Bessel beam. This algorithm exploits the global nature of the genetic algorithms. High-quality DOEs can be achieved by use of the optimization procedure we proposed.

We review an optical technique which is capable of detecting damage in semiconductors in a broad range of defect densities, and can be used to determine the distribution of damage on and below the sample surface. Using this contactless, room temperature technique, which is based on differential reflectance spectroscopy, we have been able to generate relief maps that show the spatial distribution of damage in a number of III-V compounds and Si, as well as the depth profile of damage in ion-implanted semiconductors.

GaAs epitaxial layers were grown using MOCVD on oriented Si substrates 2 degrees off towards direction. Growth runs were performed using 2 differential temperature cycles such as 300 degrees C - 950 degrees C and 300 degrees C - 950 degrees C + 750 degrees C - RT - 750 degrees C. Grown samples were characterized using X-ray diffractometer, time resolved photoluminescence (TRPL), Atomic Force Microscopy (AFM) and Photoluminescence (PL). The XRD results show that the G2 growth conditions results in the FWHM of 150 arc-sec. TRPL studies were also show longer minority carrier lifetime of 0.168 ns for G2 grown samples. Improved morphology was observed by AFM. The results were indicating that the G2 growth condition is able to improve the crystalline quality and surface morphology than the G1 growth condition. The substrates were also used further to grow In_0.30Ga_0.70As quantum dots.

In order to achieve controlled degree of intermixing in selected areas (CISA), SiO₂ gratings are checked first to be able to influence the degree of intermixing during high-temperature rapid thermal annealing of InGaAs/GaAs quantum wells. Subsequently, SiO₂/MgF₂ gratings with different periods are used to cover different parts of MWQ sample and found to be suitable for achieving CISA after only a single annealing procedure.

For decades, precisely machining silicon has been critical for the success of the semiconductor industry. This has traditionally been done through wet chemical etching, but in the pursuit of integrating photonics devices on a single chip, other techniques are worth exploring. This quest opens up interest in finding a non-wet, non-contact, arbitrary-shape milling technique for silicon. In this paper, we present our latest work in the laser micromachining of silicon. A kilohertz-repetition-rate diode-pumped Nd:YLF laser (in infrared, green or ultraviolet modes) is focused on the surface of silicon wafers in a chlorine atmosphere for an enhanced magnitude and control of the etching rate. In the chlorine atmosphere, much less debris is deposited on the surface around the cut, sub-damage threshold machining is achieved for a better control of the etching depth, and etching rates ranging from 20-300,000 micron-cube/s have been measured. In particular, the use of an infrared laser beam is singled out, along with the advantages that it holds. Results of simulations highlight the particular characteristics of the various wavelength chosen for the machining.

A single layer sol-gel derived TiO₂ thin films and 6 periods SiO₂/TiO₂ multilayer coating were designed and prepared on GaAs substrates as anti-reflection coating or near-IR-reflective coating for high power semiconductor laser applications. Crack free TiO₂ thin films having thickness of 80-150 nm, and refractive indices of 1.8-2.1 have been obtained by simply sol-gel method upon heating at different temperatures. The obtained TiO₂ thin films on GaAs substrates have shown reflectance of <EQ 1 percent in the wavelength of about 808 nm. Thin films of TiO₂ and SiO₂ were also used to fabricate near IR reflector ion GaAs substrates. The reflector consisted of 6 SiO₂/TiO₂ bi-layers, designed with a high-reflective band in the wavelength of 1064 nm. A minimum transmittance of <EQ 2 percent in the wavelength range between 950 and 1100 nm has been obtained in the present multilayer SiO₂/TiO₂ coating.

A numerical model is presented for computing the out-of- plane losses of a general class of row-defect waveguides formed by the superposition of a 2D photonic crystal onto a slab confinement structure. The usefulness of this model is demonstrated here by calculating the propagation loss of a single-row-defect waveguide composed of hexagonal air holes etched into two different slab structures. The results are interpreted in terms of a simple coupled-mode-theory picture in which loss is due to coupling by the waveguide corrugation between the fundamental and certain radiative slab modes. These calculations show that low-loss photonic crystal waveguides should be possible by carefully engineering the radiation modes of the slab waveguide.

Linear as well as nonlinear optical responses of periodic array of semiconductor in a waveguide structure are reviewed. The period is chosen in the scale of optical wavelength. Such structures can be demonstrated by imbedding an inorganic-organic perovskite compound into quartz grating grooves. By virtue of its large excitonic oscillator strength, strong coupling regime is realized even at room temperature. Polraritonic effect, directional photoluminescence and ultrafast optical switching operation are discussed.

We report the fast and slow decay lifetimes of multi- component photoluminescence (PL) intensity decays in the time-resolved photoluminescence measurements at the room temperature and a low temperature. The fast decay component was essentially due to carrier dynamics, that is, carrier flow between strongly localized and weakly localized states. Such a carrier relaxation process results in extremely long PL decay time for strongly localized states at the low temperature. At room temperature, because of thermal energy and hence carrier escape form strongly localized states, effective lifetimes becomes stronger.

In this paper, the deep level defects in (pi)-GaN Schottky and the p/(pi)GaN diodes have been studied using digital deep level transient spectroscopy (DLTS). The alternative isothermal technique offered by the DL8000 system is used in complement to conventional temperature scan technique. Electron trap levels at Ec -Et ~ (0.23 - 0.27 eV) are detected for p/(pi) diode and (pi)-type Schottky diodes by both techniques. Although similar activation energy is obtained, it appears that the traps are associated with different defects, based on the observation of different capture cross-sections (10-16cm2 for (pi)-type Schottky and 10-19cm2 for p/(pi) diodes) and different capture kinetics (exponential for (pi)-type Schottky and logarithmic for p/(pi) diodes). In addition, three other electron traps are found for the (pi)-type Schottky diode at higher temperatures with Ec -Et ~ 0.56 eV, Ec -Et ~ 0.82 eV and Ec-Et~ 1.07 eV. The Ec -Et ~ 0.56 eV and Ec -Et ~ 0.82 eV traps in (pi)-type Schottky and the Ec -Et ~ 0.23 eV trap level in p/(pi)diode are attributed to extended defects. For the p /(pi) diode, a minority carrier (hole) trap level is also identified under minority carrier injection, with an energy position at Et -Ev ~ 0.85eV and a capture cross-section of 8.129x10-14 cm2. This level might be related to the same defects that gives rise to yellow luminescence detected in (pi)-GaN layer.

We report on optically pumped mid-IR semiconductor lasers that are based on type-II wells. A systematic study of the effect of increasing the In-content in the In_xGa_1-xSb hole-well suggests that improved hole confinement results in improved power conversion efficiency at elevated temperatures that is also accompanied by a reduction in threshold power and a reduction in T₀, the characteristics for threshold.

We report on controlled group V intermixing in a compressively strained In0.76Ga0.24As0.85P0.15/In0.76Ga0.24As0.52P0.48 multi-quantum well laser structure using different encapsulating layers followed by rapid thermal annealing, and the two-section tunable laser made by using this technique. The sample used is a laser structure with emission wavelength at 1.55micrometers . The active region consisting of three In0.76Ga0.24As0.85P0.15 quantum wells with In0.76Ga0.24As0.52P0.48 barriers grown by metal organic chemical vapor deposition. At the same thermal treatment, the blueshift of band gap energy was enhanced most efficiently by capping the sample with an InP layer grown at low temperature and less efficiently by a SiO2 film. While the blueshift was suppressed by a SixNy film with a refractive index of about 2.1. The suppression effect was independent of the SixNy film thickness from 30 nm to 2400 nm. Time of flight secondary ion mass spectra showed that the quantum well intermixing was caused by the interdiffusion of group V atoms between the wells and barriers that have the same group III compositions. A group V interstitial diffusion model was proposed to be responsible for the enhanced intermixing. A 1.55 micrometers two section ridge waveguide laser was fabricated using this technique. The energy transition level of the phase tuning section was tuned to be transparent to the emission wavelength of the active section. A tuning range of about 10 nm can be achieved by simply tuning the bias current for the phase tuning section.

Broad-area InGaAs/GaAs/AlGaAs double-quantum-well graded- index separate-confinement heterostructure diode lasers with non-intermixed and intermixed active regions were fabricated and characterized. Their light-current characteristics were used to extract information about the effects of impurity- free vacancy diffusion intermixing process on threshold current density, internal optical loss, internal quantum efficiency, material gain, etc. Comparison between these parameters indicates comparable device performance, even though lasers with intermixed active region underwent annealing at 1000 degrees C for 30 s and showed 42 nm wavelength blue shift.

The realization of single-mode Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers, based on surface grating structures is of considerable interest. Such devices offer a relatively simple grating fabrication process without complicated multistep-epitaxial growth or regrowth, as required in more conventional devices. This simplified processing could potentially reduce the fabrication cost for these lasers. A key concern for the surface grating lasers is designing the structure to provide sufficient feedback to achieve single mode operation with high yield and high quality as compared to conventional buried-grating DFB and DBR lasers. This paper reports numerical modelling of surface grating DFB and DBR lasers based on 1.55 micrometers wavelength InGaAs/InGaAsP/InP with graded-index separate confinement heterostructure multiple quantum well (GRINSCH-MQW) structures. Bragg wavelength operation of the DFB and DBR lasers may be satisfied by deeply etching fine surface gratings on both side portions and along top of the ridge stripe respectively. Sufficiently strong optical coupling between the corrugated structure and evanescent field can be achieved by controlling various parameters such as ridge width, etch depth, and grating width. The numerical results obtained allow optimum grating geometries to be developed to provide the desired feedback effect. Furthermore, the model has been used to investigate the influence on the device performance of fabrication errors and processing effects on the grating structures, prior to fabrication.

A non-fusional fiber coupler is demonstrated for the high power double clad fiber lasers with optical adhesive technique. The fiber coupler is constructed by polishing a non-doped single-clad fiber at a bevel angle and then adhere to the doped double-clad fiber with an optical adhesive. The pump light is launched through the single-clad fiber to the doped double-clad fiber. The polished angle for the optimal coupling depends on the fiber numerical aperture and coupling efficiency of 90 percent can be achieved. The bend effects on the coupling efficiency is investigated and find that the degrade of coupling efficiency is very sensitive to distance between the bend to the coupling point. Finally, laser radiation is demonstrate with a Nd-doped double clad fiber in low pump regime.

A wideband wavelength tunable Erbium-doped fiber laser using a unidirectional traveling-wave fiber ring combined with a novel switchable fiber Bragg grating (FBG) array is presented. The switchable FBG array consists of a 1 by 3 optical switch and three parallel discrete FBGs. The central reflection wavelengths of these three discrete FBGs are 1534 nm, 1549.15 nm and 1559.4 nm, respectively. The corresponding reflectivities are 90 percent, 99 percent and 99.8 percent, respectively. The wavelength of each grating can be continuously tuned in a range of over 16 nm by stretching (7 nm) and compressing (8 nm) the FBG. Therefore a fiber ring laser with a very large wavelength tuning range has been successfully demonstrated. In our experiment, the wavelength tuning range of the Erbium-doped fiber ring laser is 38 nm, from 1527 nm to 1565 nm. Within this tuning range, the total output power is about 7-8 dBm, the 3-dB linewidth is 0.01 nm, and the side mode suppression ratio is more than 48 dB. This tunable fiber ring laser can also work in the mode-locking mode when an amplitude modulator is inserted in the cavity. By applying the driving frequency matching the round-trip frequency or its multiples to the modulator, active mode-locking is realized. The highest harmonic order achieved is 125, the repetition rate and pulse-width of the mode-locked pulses are 1.00475 GHz and 539 ps, respectively.

10 GHz repetition rate soliton-like pulses with duration of 29.85 ps have been obtained in an actively mode-locked fiber ring laser. 20 GHz rational harmonic mode-locked soliton-like pulses were also observed. A piezoelectric transducer driven cavity length feedback system was employed to realize the long-term stability of the laser source.

From infrared absorption spectra, the present authors elucidated behaviors of the structural relaxation in silica glass doped with various elements, and claim that sub-relaxation process exists besides the main-relaxation given by the viscous flow. Light scattering measurement also suggested the existence of such an additional relaxation channel. The sub- and main-structural relaxations are in general greatly accelerated by a proper dopant. And, the sub-relaxation, which extends below the glass transition temperature, gives a breakthrough to bring silica glass to a more stable structure even below the glass transition temperature. The sub-relaxation then reduces the Rayleigh scattering, a predominant component of the optical loss in the glass. Fluorine and chlorine seem to greatly accelerate the relaxations in silica glass.

In Ge-doped SiO₂ defect centers induced by an ArF laser irradiation are investigated by electron spin resonance (ESR) measurements. Isochronal annealing have been carried out after the irradiation at 77~K in order to observe the formation and the relaxation processes of defects. Thermally induced decay of self-trapped hole (STH) and the formation of so-called 'Ge(2) centers are observed with increasing the temperature. The result suggests that holes are transferred from STH to Ge(2). It is observed that the relative concentration of germanium electron center (GEC) and GeE' do not change in the relaxation process from 210~K to 280~K.

The modeling and design of single-mode planar waveguides and devices for silica-on-silicon technology is a crucial factor in both the quantification of the functionality of novel and innovative light-processing devices, and also in the design stages of any planar fabrication process for device production. There is a range of analytical techniques and an increasing number of numerical techniques readily available to help in this process, and particularly for more complex light processing devices such as arrayed waveguide gratings. However, a good physical understanding of the qualitative behavior of any device is a prerequisite to a full interpretation of the quantitative results. In this paper, a number of existing and novel planar waveguides and devices are discussed from both the qualitative and quantitative viewpoints.

Existing optical fiber and fiber-device fabrication techniques have been complemented recently by the development of new processes for the fabrication of planar optical waveguides and devices. These processes rely on new forms of plasma reactors and diagnostic systems which allow in-situ control of optical parameters such as refractive index. Recent technical developments in the micro- electronics industry now allow the fabrication of very compact and highly complex optical circuitry which can be produced on a single photonic chip. They also offer the potential to integrate photonic devices with semiconductor sources and detectors to realize a compact, hybrid photonic- optoelectronic chip, complete with fiber pig-tailing. Because of their compactness and potential low cost, these types of photonic chips are attractive components for future high-capacity optical telecommunications and other networks now being planned. This paper presents the general techniques used in the plasma processing of thin films of silicate glasses including Plasma Enhanced Chemical Vapor Deposition and Reactive Ion Etching.

A general method for analyzing the multilayer optical waveguide with nonlinear cladding and substrate is presented. This method can also be used to analyze the multi branch waveguide. Numerical simulation results show that the analysis is correct.

Different frequency generation (DFG) and the cascaded second-order nonlinear interaction () based wavelength conversions in 5-mol MgO doped LiNbO3 QPM waveguides are studied and compared both experimentally and theoretically for the first time. It is shown that DFG based wavelength conversions have a higher conversion efficiency; while the cascaded based wavelength conversions have a wider 3-dB signal conversion bandwidth. It is also exhibited that the simulations are consistent well with the experimental results. Tolerance of pump wavelength for the cascaded based wavelength conversion is twice as large as that of DFG based devices. These results are very helpful in choosing suitable wavelength converters for practical optical communication systems according to the system requirements.

Cascaded (chi) ⁽²) based wavelength conversions in quasi phase-matched periodically poled LiNbO₃ waveguide were theoretically analyzed by the step-by-step method. The analytic expressions were obtained and analyzed in detail to reveal the physical insight of the wavelength converters based on the cascaded (chi) ⁽²) process. In addition, the phase shift of the converted light was studied using the obtained analytic expressions. Some of the simulated results were compared with our experimental results.

Optical polymers which exhibit no birefringence with any orientation of polymer chains are desirable to realize high performance optical devices that handle polarized light. We defined such polymers as 'zero-birefringence polymer' and demonstrated two methods for synthesizing the zero- birefringence polymers: the random copolymerization method and the anisotropic molecule dopant method. Orientational birefringence is compensated by random copolymerization using a positive and a negative birefringence monomers at specified ratio in the random copolymerization method. Poly(methyl methacrylate-co-benzyl methacrylate) synthesized by this method showed no orientational birefringence with any orientation degree. In the anisotropic molecule dopant method, orientational birefringence of polymers is compensated by doping with 3 wt percent of trans-stilbene as the anisotropic molecule. Furthermore, we demonstrated the isotropic particle dopant method to reduce orientational birefringence of polymers. Orientation birefringence for polymethyl methacrylate film was decreased by approximately 20 percent by doping with 2 wt percent of silica particle with an average diameter of 7 nm as the isotropic particle dopant.

The last decade has seen tremendous advances in the field of semiconducting-polymer optoelectronics as a result of a concerted chemistry, physics and engineering effort. For example, ink-jet-printed full-color active-matrix thin-film display prototypes with semiconducting polymers as the active layers have already been demonstrated. The key advantages of this technology lie in its full-color capability, scalability to both large-area and micro- displays, as well as low-cost associated with simplicity and solution processability. In a number of related inorganic device technologies, the control of optical properties using photonic structures has ben crucial to the performance of the devices. In principle, polymer devices can also benefit from such control if appropriate polymer optical building blocks that retain the processing advantages can be found. Here we will show that the refractive index of poly(p- phenylenevinuylene) (PPV) can be tuned over remarkable ranges from 1.6 to 2.7 at 550-nm wavelength by dispersing 50-angstrom-diameter silica nanoparticles into its matrix. This is achieved without incurring significant optical scattering losses. Using these semiconducting-polymer composites, we have demonstrated efficient distributed Bragg reflectors in the green spectral region from relatively few periods of quarterwave stacks of the high- and low-index materials. Controlled chemical doping of these photonic structures fabricated polymer microcavity light-emitting diodes in which current is injected through the polymer DBR with adequate confinement of photons and electron-hole pairs. We have also fabricated photo pumped all-polymer microcavity structures.

Two oligobipyridly derivatives (L1, L2) which belong to partially conjugated oligomers in structure, were synthesized and found to show strong photoluminescence. In its as-obtained powder states, L1 shows an emission at 403 nm under the excitation of 365 nm; while when mixed with KBr, it shows one emission peak at 402 nm and one shoulder at 389 nm; and in its chloroform solution, it emits with two peaks at 344 nm and 356 nm. The as-obtained powder state of L2 emits with a peak at 418 nm under the excitation of 367 nm, while its doped state in KBr plate has two emissions at 403 nm and 423 nm; in its chloroform solution, two peaks at 393 nm and 414 nm appear under the excitation of 364 nm light. Films of L2 fabricated by vacuum evaporation emit at 406 nm and 428 nm. Both compounds show emission in the range of deep blue or violet color. It is proposed that one way to obtain blue emitting materials is to shorten the conjugation length in the polymeric and oligomeric structures. Silver complex of L1 show emission at 445 nm under the excitation of 348 nm. EL properties of L2 were studied preliminarily.

A bilayer is used as an electrode for organic light-emitting devices. The bilayer consists of a Sn layer adjacent to Alq layer and an Al outerlayer. The effects of a controlled Sn buffer layer on the behavior of ITO/CuPc/NPB/Alq/Sn/Al light-emitting devices are described. It is found that both electron injection efficiency and electroluminescence are significantly enhanced when the thickness of Sn layer is suitable. The enhancement is believed to be due to increased electron density of Sn layer near the Sn/Al interface .

A graded doping technique was presented to fabricate high brightness and high efficiency OLEDs, in which a copper phthalocyanine(CuPc) film acts as buffer layer (alpha) -naphthylphenybiphenyl amine(NPB) film as hole-transport layer and a tris(8-hydroxyquinolinolate)aluminum(Alq3) film as the electron-transport layer.The luminescent layer consists of the mixture of NPB,Alq3 and an emitting dopant 5,6,11,12-petraphenylnaphthacene(Rubrene), where the concentration of NPB raised while the concentration of Alq3 was declined gradually in the deposition process. The graded doping device exhibited the maximum emission of 50000cd/m2 at 35v and the maximum efficiency of about 8cd/A at 9v, respectively, which have been improved by four times in comparison with the conventional doped devices.

The single layer of organic optical microcavity with 1D distributed Bragg reflectors (DBRs) was fabricated. The PL emission properties of the microcavity were explored at the two sides, which show different characteristics due to the asymmetric structure. The PL emission peak of Alq film is at 5113 nm with a half width of 78nm. Compared with the Alq film, the emission of microcavity from the top DBR side shows a narrow peak at 494nm with a half width of 4.6nm and an enhanced factor of 11, and 606nm with a half width of 6.6nm.

Organic Metal microcavities were fabricated by using full- reflectivity metal film and semi-transparent metal film as cavity mirrors. Compared with the conventional organic microcavity, the typical structure of which is Glass/DBR/organic layers/metal mirror, a short cavity-length microcavity can be obtained by using metal mirrors. Red, green and blue emission of the microcavities were realized under photoexcitation due to the change of the thickness of the Alq₃ layer. The measured microcavity emission spectra were shown to be roughly in agreement with the theoretical calculation spectra using the characteristic matrix method. The results implied that organic metal microcavity has some advantages in realizing the pure single mode RGB emission.

Erbium doped optical glasses are effective media for active lasers generating eye safe radiation of a wavelength 1.53 divided by 1.55 micrometers . Development of erbium glass laser systems requires investigations aimed at improvement in glass properties and increase in effectiveness of laser radiation generation. Phosphate glass samples with various Cr₂O₃, Yb₂O₃ and Er₂O₃ contents based upon P₂O₅-Al₂O₃-BaO-PbO- K₂O oxide system were prepared. The obtained phosphate glasses are characterized by advantageously low thermal expansion coefficient what is important for increase of glass resistance to thermal shock, especially when they are applied as rods for lamp pumped lasers. The effect of changing concentrations of Er³⁺ and sensitizes Cr³⁺, Yb³⁺ as well as glass base compositions on luminescence properties were investigated. The spectral and spectroscopic properties were measured for these glasses. Absorption spectra of these Er³⁺, Yb³⁺ and Cr³⁺-doped glasses were measured in spectral range 190 nm divided by 25 micrometers at room temperature. The excitation and luminescence spectra were also recorded at room temperature on a spectro fluorometer using a diode laser as an excitation source. The presence of hydroxyl groups is an important factor influencing glass structure. In glasses having high concentration of hydroxyl ions, strong attenuation of a lifetime of excited Er³⁺ ions was stated. In such a case the absorption band around 3.3 micrometers was observed. Concentration of OH groups was reduced due to adequate special melting process of glass. Carried out investigations on thermal, optical, and spectroscopic properties of the obtained glasses showed their good quality, ensuring possibility of their application in laser systems.

Based on the theory of artificial material index and state- of-the-art electron beam lithographic nano-structure technique, a phase-only polarization-selective form- birefringent-computer-generated-hologram generated by the combination of two independent phase-only binary-computer- generated-hologram can be implemented as an optical switch to reconstruct two different images by either TE or TM polarization.

The characteristic of 2D grating optical low-pass filter (GOLF) was compared to that of birefringent low-pass filter (BLF). The modulation transfer function (MTF) of the optical system that consists of lens and GOLF is theoretically derived by taking all orders of diffracted beams into consideration. MTF of a 2 phase chess-board type GOLF and a 3-phase GOLF was compared to that of BLF. The 3 phase GOLF with 9 center beams of equal strength has the best filtering characteristic, and thus removes most moire fringe, but resolution degradation is severe compared to BLF. The two- phase GOLF with phase difference of 180 degrees that is similar to BLF in terms of beam distribution has medium characteristic of 3-phase GOLF and BLF. And, 3 phase GOLF of phase difference of 90 degrees has similar characteristics, too. These three GOLF's are made and experimented by attaching them to a digital camera. The experimental result coincides with the theoretical development.

The grating optical low-pass filter (GOLF) has lots of advantages over traditional birefringent low-pass filter. But, one disadvantage of it is that the shadow image of the grating is visible, especially when the numerical aperture of a camera is large. We found that we can reduce the visibility of a grating image, if we adopted a multi-phase grating instead of a two-phase grating. First, from the simulation of the Fresnel diffraction pattern of a 1D multi- phase grating, we found the optimum width and phase of each grating step that minimizes the modulation of the Fresnel diffraction. And then, we designed a 2D multi-phase GOLF by extrapolating 1D structure. Four types of GOLF, four-phase, seven-phase, eight-phase, and also two-phase GOLF were manufactured with a semiconductor process. Finished GOLF samples were installed to a digital camera to take pictures of a test target and compare them with each other. Experiment results show that as the number of phase step increase, the gratin image becomes more indistinctive.

The relation between the fictive temperature and concentration of electron-trapped centers in Ge-doped silica glass (Ge: SiO2) associated with fourfold coordinated Ge ion (GEC) and GeE' is examined in this study. The fictive temperature of Ge:SiO2, Tf, is determined by monitoring peak positions of 1970 cm-1 and 1870 cm-1 infrared absorption bands. After ArF-laser beam irradiation, ESR spectra of Ge:SiO2 glasses with changing the fictive temperature between 950 and 1250íC were obtained. The concentration of paramagnetic centers increases with increasing Tf. Supposing two kinds of GEC, Ge(1) and Ge(2) depending on the number of nearest-neighbor Ge ions, and GeE' center, ESR spectrum was simulated to estimate the concentration of each paramagnetic center. It has been found that the concentrations of Ge(1) and GeE' increase with increasing Tf, while that of Ge(2) is almost constant.

ZnSe and phosphorus doped ZnSe have been grown by Physical Vapour Transport (PVT) and Chemical Vapour Transport (CVT). In chemical vapour transport iodine is used as the transport agent where as in the physical vapour transport no transport agent is used. The largest crystal measures a size of 9 x 5 x 5 mm3. The Hall mobility is measured at room temperature and found to be 510 (cm2 / V.Sec) for pure ZnSe and 340 (cm2 / V.Sec) for doped ZnSe. The variance of mobility with temperature is also measured. The results are compared with the existing data and the advantages of this procedure over the existing experiments are discussed.

The combination of Microwave-Hydrothermal techniques has been used in the last few years to synthesis of nanocrystalline powders. The Microwave assisted synthesis is generally much faster, cleaner and more economical than the conventional methods. We present here, a versatile process of Novel Microwave-Solvothermal technique for synthesizing nanocrystalline CdS particles. The effect of different parameters such as time, temperature, solvents and molar ratio of Cd²⁺ to thiourea on the phase(s) formation of nanocrystalline Cadmium Sulphide under Microwave- Solvothermal conditions using Microwaves of 2.45 Ghz frequency are investigated. The obtained CdS are characterized by the Optical properties, powder x-ray diffraction and SEM.

With an energy gap of 1.34 eV, indium phosphide (InP) is an ideal material for solar energy conversion. Much work has been carried out on sputtered indium-tin-oxide (ITO)/InP solar cells but modeling of this structure has long been the subject of debate. The double-layer structure used in this work was originally devised to minimize the surface degradation of InP when exposed to normal heating steps during the fabrication process due to the low congruent temperature of InP. We deposited a thin protective layer of either ITO or indium-tin to protect the front surface of the InP before any heating stages took place. A second layer, ITO, was then deposited to compete the junction. Variation of film deposition conditions, thicknesses and annealing steps worked to improve device performances as well as provide insight into junction mechanisms.

Past works has demonstrated that both Phase- and Amplitude two-level Binary-Computer-Generated-Holograms would generally resolve identical reconstruction image profiles but with different diffraction efficiency. In this paper, we investigate and study the difference in diffraction efficiency and reconstruction image quality of a two-level binary and multi-level Amplitude- and Phase-CGH.

It is well known that two-phase CGH can only reproduce graphic images with rotational symmetric features. A multi- phase hologram is required to regenerate arbitrary shaped graphic patterns. Also, for the high fidelity reproduction of images, the computer program must be able to handle many pixels with multi phase. We devised a stochastic optimization program that can generate a multi-phase hologram. Since the algorithm and programming technique is so efficient that the program can be used to generate hologram of black and white pictures as well as graphic patterns. We used the CGH program to generate a portrait picture and some graphical patterns with four-phase holograms. The holograms were transferred onto a glass plate with the semiconductor manufacturing techniques

The rigorous and efficient FEM based beam propagation method is used to model SHG in semiconductor waveguides. The effect of material loss on the overall efficiency of SHG is also analyzed. It is shown that under certain conditions, GaAlAs based devices with a lower non-linear susceptibility tensor could be more efficient than GaAs with a higher non-linear susceptibility tensor due to their low material loss. Numerical results are also presented, of the effect of domain fabrication error, in the case of quasi phase matched devices on the efficiency of SHG. The finite element method is also extended to the study of cascaded second harmonic generation in optical waveguides. The accuracy of the method is demonstrated by comparison with previously published results. The effect of the second harmonic on the fundamental in the presence of an intense input beam is discussed, through application to a practical waveguide structure.

In this article it is shown that the plane wave propagation eigenpolarizations in a linear homogeneous time-independent anisotropic media without free sources, coincide with the extrema of the difference between stored electric and magnetic energies. It is demonstrated that at these stationary points the wave equation is satisfied, by showing that each of the Maxwell's curl equations may be obtained by inserting the other equation into the energy functional as a constraint. Furthermore, it is proved that the theorem holds for extrema of the stored electric energy independently, when the medium is magnetically isotropic. It is concluded that when at least one of the permittivity and permeability tensors are scalar, both the total and difference of electric and magnetic energies are extremized simultaneously. As an example, the eigenpolarizations in a non-magnetic anisotropic medium with optical activity are obtained by this approach.

Phase change optical recording disks using have been found to demonstrate long thermal stability of the amorphous recording marks. The thermal analysis of Ag-Sb-Te material was studied using DTA and structural analysis of the material were studied by x-ray diffraction, SEM and TEM respectively. The films were studied for both the cases: before and after annealing and it was concluded that the alloy could be used as a phase change optical memory material.

The optimization of the active region of ZnSe-based laser diodes for laser emission around a wavelength of 560 nm is reported. Two concepts are presented: quaternary CdZnSSe quantum wells with a high Cd content and CdSe quantum dots. With quantum well devices output powers of more than 1 W are realized. The first electrically pumped CdSe quantum dot laser is presented. The electroluminescence dynamics under current injection of these devices allow lasing operation only in pulsed-mode with pulse widths around 50 ns. Although the threshold current density of the quantum dot laser is around 7 kA/cm(superscript 2, lasing operation can be sustained up to 20 kA/cm(superscript 2 indicating a so far unexpected stability of II-VI material against current injection.

Continuous GaN films were grown on the top of cracked Si- doped n⁺-GaN epilayers by MOCVD techniques. Raman- scattering studies of the samples indicated strain-free top GaN film. The biaxial compressive stress estimated by using x-ray diffraction analysis was as low as 0.036 GPA for sample grown under optimized conditions. The results obtained show that the use of an intermediate relaxed n⁺-GaN:Si layer is perspective for growing high quality GaN films.

Photoluminescence)PL) spectra and time resolved PL form self-assembled Inas/GaAs quantum dots (QDS) grown by metal organic chemical vapor deposition are studied. A reduction in the emission linewidth with increasing temperature was observed that the variation of PL peak energy with temperature does not follow Varshni's equation. These anomalous behaviors of PL can be explained in terms of thermal redistribution of carriers. It was also found that the PL decay time increases with photon wavelength, which is due to the carrier transfer between laterally coupled QDs.