Optoelectronics as applied to telecommunications, data communications, CATV, et. al. is characterized by prodigious global growth and spectacular technological innovations. During the next decade we will not only observe wide usage but also technological obsolescence and price erosion. We will review the systems, subsystems and components roadmaps into the next decade. While the technical performance requirements will continue to escalate, the reliability and cost criteria will be paramount. The requirements for design and performance of various active, passive and hybrid components and subsystems will be reviewed. Various new and exciting enabling technologies to yield the required components and subsystems will be described.

A review of the single-mode designs and their progress in the last few years will be given. Important design variables, their interactions and the trade-offs will be discussed. Current status of various designs for Terabit/s throughput on a single fiber will be presented. Emerging applications of single-mode fibers and waveguides will be described.

MCVD and VAD are the most commonly used fiber production processes in the world. A review of recent patents issued in USA for these two processes will be used to establish state of the art of the processes. Production cost of single mode fibers will be modeled based on the assumed state of the art and the relevance of the results will be discussed in the context of suitability of use in developing nations.

New optical fibers for high bit rate and high capacity transmission, which were developed for future all optical transmission line and submarine cable, are introduced. These fibers are designed not to have dispersion dependence against wavelength in total link transmission.

Refractive-index nonlinearities have negligible effect on the performance of short-haul fiber-optic communication links utilizing electronic repeaters. However, in long optical fiber links, nonlinearities can cause severe signal degradations. To mitigate nonlinear effects, new generation of fibers, referred to as large effective-area fibers, have been introduced in recent years. This paper reviews the latest research and development work on these fibers conducted by several research groups around the world. Attention is focused on a class of large effective-area fibers that are based on a depressed-core multiple-cladding design. Transmission properties, including dispersion, dispersion slope, effective area, mode-field diameter, bending loss, polarization-mode dispersion, and cutoff wavelength are discussed. Dispersion-shifted, non-zero dispersion-shifted, and dispersion-flattened designs are addressed. Design optimization, particularly with regard to effective area, bending loss, and polarization-mode dispersion, is elaborated upon. The trade-off between effective-area and bending loss is emphasized. Results for dispersion-shifted and non-zero dispersion-shifted large effective-area fibers with zero polarization-mode dispersion and low bending loss at 1.55 micrometer wavelength are presented.

We present here a refractive index profile design which can enable us to obtain a flat modal field (FMF) around the center. The design can be used to obtain FMF both for planar waveguides as well as for fibers. The design can be useful in reducing non-linear effects in fibers.

We show that an earlier proposed efficient dispersion compensating fiber (DCF) design based on a coaxial fiber structure can also provide dispersion compensation over a broad wavelength region matching that of an erbium doped fiber amplifier gain spectrum. The design can provide dispersion coefficient almost double those of existing DCF designs. Due to the basic nature of the dispersion curve of this design, the total link dispersion cannot only be compensated but also be flattened.

Using modified chemical vapor deposition (MCVD) process and the solution doping technique germania doped single mode fibers with additives of Ce, Pb, Al, Y, Er and Nd in concentration of 1000 - 2000 ppm either singly or in combination were fabricated in long lengths. The fibers were exposed to gamma radiation from ⁶⁰Co source at a dose rate of 300 - 400 rad/min for a total cumulative dose of 8 - 10 kilo rads at ambient temperature with on-line recording of the induced loss at 1300 nm. It was observed that the presence of minor quantities of dopants considerably influences the loss characteristics of the fibers recording highest radiation sensitivity in Nd doped ones while the co-doped fibers with Al+Y, Al+Pb and Al+Er have close range of sensitivity around 0.01 dB/Km.Rad.

It has been twenty years since the first fused fiber optic coupler was made and remarkable progress has been achieved during this period on the production, performance, and reliability of these devices. Several million fused couplers have now been produced and placed into service. Applications have included test instrumentation, both outside plant and central office telephony applications, cable TV systems, sensors, optical amplifiers, DWDM systems, and submarine repeaters, to mention a few. To meet the increased production requirements, significant work has been done to make the process more flexible and thereby more amenable to automation and computerization. Modern fused coupler operations are highly automated and can make a large variety of products by simply changing a computer file. Similar improvements have also been made in high volume testing so that sophisticated tests of a number of parameters can be performed in a matter of minutes. As the volume and variety of the products have increased over the years, so has the performance. Improvements have been made in reducing excess loss, polarization effects, and wavelength dependence. In addition, higher port count devices (1 X 3, 1 X 4, etc.) have been developed. Numerous studies have been conducted over the years to determine the reliability of these devices. The introduction of glass-to-glass sealing techniques to isolate the fused region by bonding the fibers directly to the quartz substrate significantly improved the stability and long term reliability of these devices. The state-of-the-art production, performance, and reliability of fused coupler technology will be reviewed in this paper.

We report here the fabrication of a single to dual mode evanescent field directional coupler for the first time. Experimental results are presented to show that such a coupler can be used to couple light into or to take out energy from the two modes of a two mode fiber (TMF) through a single-mode fiber (SMF). Such a coupler should be useful in the practical implementation of a two-mode fiber sensor making it compatible with the single mode fiber networks.

We report in-house development of a real time monitoring system with programmable fabrication parameters for fabricating fused-fiber coupler based branching components. A number of branching components of varied specifications and with fibers of different make have been fabricated; these exhibited low excess loss and other features akin to commercially available couplers. Fabricated WDM couplers for operation at 1310/1550 nm exhibited high degree of isolation, large isolation bandwidth and reasonably low excess loss. Characteristics of the fabricated couplers have been investigated for optimizing design and fabrication parameters with regard to channel isolation and excess loss in the device. An equivalent planar waveguide (EPG) model has also been used to model these couplers and to correlate with the experimental findings.

Experimental measurement of in-band Four-Wave-Mixing (FWM) power in non-zero dispersion fiber is presented. A comparison with known methods shows how the proposed procedure is more accurate in frequently interesting cases.

A method for polarization-resolved optical fiber Bragg grating characterization is reported on. The complete reflectance Jones matrix was measured interferometrically. Local dichroic reflectivity and birefringence of a sampled grating were derived from this data. Knowledge of these quantities should allow improvement of the UV illumination process and to effectively correct phase mask error by longitudinally selective UV light postprocessing.

Fiber Bragg gratings (FBGs) are finding a number of applications in fiber optic communication and sensing. For the best performance of a device/system employing an FBG, it is very important to choose FBGs with characteristics that are optimum for the particular application. Thus it is essential to have knowledge of the various characteristics of the FBG. In this paper we report on the estimation of the characteristic parameters of a given FBG by a measurement of the reflection spectrum and the far field of the fiber mode. Results of a coupled-mode analysis is then used to extract the FBG parameters from the measurements.

Diffraction gratings were fabricated both in optical slab waveguides and in optical fibers by irradiation with KrF excimer-laser pulses. Preliminary results are presented for the waveguide gratings, written in germano-silicate glasses and films. Arrays of in-fiber Bragg gratings were produced by using the phase mask method and an improved stretch-and-write technique. A purposely designed apparatus is described, which allows us to write spectrally well separated as well as concatenated grating arrays: both these kinds of structures can find applications as passive components in telecommunication systems.

A transfer matrix method is developed for the analysis of nonlinear waveguides with Bragg gratings. In our numerical model, the nonlinear refractive-index change resulting from the optical field along a grating structure is taken into consideration. This method can be applied to the study of a wide range of nonlinear phenomena in different grating structures. We have analyzed the nonlinear responses of optical signals at the Bragg wavelength as well as other wavelengths. We show that a small change in the refractive index can cause a significant change in the optical-field distributions along the grating and also the transmission response.

We present the reflection characteristics of Bragg gratings using the collocation method and the effect of various parameters such as grating profile, duty cycle of periodic variation, index change and strain on the spectra. Comparisons with the coupled mode theory have also been included.

Silica-based planar lightwave circuits (PLCs) have provided several key components for optical wavelength-division- multiplexing (WDM) systems and subscriber systems. This paper reviews recent work on silica-based PLCs and their applications, for example as an arrayed-waveguide grating multiplexer. Hybrid integrated PLCs are also described including high-speed optical wavelength selector.

The problem of improving the effectiveness of the single- sideband modulator and a special application of the modulator for measuring the deviation from the linear frequency superposition by transition to the rotating frame is considered.

A 4-stage spectral polarimeter based on Ti:LiNbO₃ acousto- optical TE-TM converters has been realized. It has about 20 dB stopband suppression and can measure polarimetric spectra as well as the time evolution of the state of polarization. A simple optical spectrum analyzer is also proposed.

A study of the fabrication process and optical characterization of Ni indiffusion into x and y cut LiNbO₃ substrate. The formation of waveguides in air ambient is clean and fast with the diffusion time well away from the T_c and out-diffusion regime of LiNbO₃. Optical characterization of the planar waveguides uses prism measurement technique and IWKB method, to establish the diffusion depth, d and the changed in refractive index, (Delta) n. The derived normalized dispersion relation satisfies the Gaussian refractive index profile dispersion for n_e (TE) mode along the optical axis and n_o (TM) mode along both the optical and non-optical axis. For the samples studied, the profile attains that of the Gaussian in the initial waveguide formation and retains the profile for long annealing time and high temperature. The acquired value of (Delta) n_e less than or equal to 0.04 and (delta) n_o less than or equal to 0.02 along the optical axis are comparable to that of Ti:LiNbO₃ and the anomaly, (Delta) n_e/(Delta) n_o less than 1, is valid for the non- optical axis only for high temperature annealing and thick Ni samples. The above measurements lead to a derivation for a simple model for the index profile of the channel waveguide, given the film thickness, diffusion time and temperature.

We present an experimental observation and numerical simulation of the evolution of the mode field profile in a Periodic Segmented Waveguide. A good agreement between the experimental and the numerical results is observed.

A wide range of photonic guided-wave devices may be modelled by using rigorous numerical approaches based on the finite element method (FEM). In this work, representative modal solutions for linear, nonlinear, anisotropic, passive and active waveguides are discussed. Photonic devices incorporating several butt-coupled uniform waveguide sections, such as optical modulators, switches, filters, polarizers, and duplexers, are shown by incorporating the least squares boundary residual (LSBR) method and the FEM. The FEM-based beam propagation method (BPM) is used to characterize photonic devices incorporating arbitrarily nonuniform guided wave sections or optical devices with second and third order material nonlinearity.

A numerical approach for three-dimensional optical waveguides using periodic boundary conditions in both transverse directions is presented. Expanding the electric and magnetic fields in a double Fourier series of complex trigonometric functions, Maxwell's equations are reduced to the eigenvalue problem of a linear system for the Fourier coefficients. The solutions yield the vectorial eigenmode fields for guided and radiation modes, both propagating in forward and backward directions. The method is used to analyze the junction of a fiber to an embedded waveguides and the power transfer between two parallel embedded waveguides.

The 2D and 3D beam propagation method (BPM) which is now widely used for the design of fiber-optic and integrated-optic components is highly computer-intensive. The matrix method, which is computationally much simpler and faster, was used to analyze 2D planar multi-layer structures. The method has now been applied to 3D channel waveguides by transforming the 2D refractive index profile over the cross-section of the channel waveguide to a 1D effective index profile and discretizing the profile into thin layers. The effective index based matrix method (EIMM) has been used to compute the guided-mode propagation constants, the coupling length of directional couplers and the bending loss in curved waveguides for Ti- indiffused LiNbO₃ channel waveguides. The computed results agree closely with available experimental results. The method may also be used to compute field profiles in single and coupled waveguides. A versatile computer software is being developed to implement the above method for the design of optical waveguides and related components/devices on different substrates realized by in-diffusion, ion exchange and other techniques.

The optical properties of titanium-indiffused lithium niobate (Ti:LiNbO₃) waveguides can be analyzed by various methods like effective index method, WKB method, finite element method, matrix method, BPM method, variational method, etc. Among these, the variational method offers a great advantage in estimating the important characteristics of Ti:LiNbO₃ optical waveguides by direct use of controllable fabrication parameters with less computing time. The present work deals with the assessment of optical properties of Ti:LiNbO₃ waveguide, typically at 1.53 and 1.3 micrometer wavelengths, although the method can be extended for other communication wavelengths within the range 0.6 - 1.6 micrometer. Our simulated results on mode profile have been verified with the experimental data.

It was noticed in the past that, to avoid physical inconsistencies, in Marcatili's lossless tapers through- flowing waves must be drastically different from standing waves. First, we reconfirm this by means of numerical results based on an extended BPM algorithm. Next, we show that this apparently surprising behavior is a straightforward fallout of Maxwell's equations. Very similar remarks apply to Gaussian beams in a homogeneous medium. As a consequence, Gaussian beams are shown to carry reactive powers, and their active power distributions depart slightly from their standard pictures. Similar conclusions hold for free-space modes expressed in terms of Bessel functions.

A generalization of Talbot effect to the case of a tapered GRIN medium for non-uniform illumination is considered and an analogy with the conventional lens-imaging formula is presented. Self-imaging positions are evaluated. Results on Talbot effect are applied to a particular case of a tapered GRIN medium with divergent linear taper function in order to show the dependence of self-image distances on taper function, illumination and periodic object a well as the variation of the transverse magnification with self-image number.

A general modeling and simulation strategy suitable for the theoretical analysis of wavelength division multiplexed (WDM) fiber-optical systems is presented. We give a detailed explanation of component models and algorithms of different complexity and accuracy which can be used throughout the simulation. Transmitter chirp and noise, fiber dispersion and nonlinearity, imperfect filter and multiplexer characteristics, amplified spontaneous emission noise of the optical amplifiers, crosstalk in network elements such as optical add/drop multiplexers or optical cross-connects, and the polarization-dependence of the components are taken into account. Methods for a performance evaluation by means of eye patterns, spectral power densities, the optical signal-to- noise ratio, the Q-factor and the bit error rate are also addressed. Based on this work, a complete design environment consisting of a graphical network editor and an independent simulation engine (FOCUSS, Fiber Optic CommUnication System Simulator) has been implemented in C++. Simulation examples are presented here e.g. for wavelength-routed networks.

The concept of a sending-mode patch antenna array with an optical feeder and beamforming network is discussed. We describe the design of the patch antennas, and we present measured results for the impedance, the far- and the near- fields. Data for an integrated photoreceiver are given. Finally, we review some essential aspects of optical beamforming networks.

In this paper we present the analysis of optically controlled microstrip slow wave MIS (silicon oxide on silicon) structure. First, a rigorous multilayer wave analysis for the approximate parallel plate waveguide model is presented and results obtained by a complex capacitance circuit model shown to compare well in the dielectric mode to slow wave region. Next, a capacitance formulation based on the single layer reduction (SLR) method along with the variational method in the Fourier domain is presented to examine the actual optically controlled microstrip structure of finite conductor width.

New methods for integration of dissimilar components and optical inputs/outputs are expected to mass-produce photonic micro-systems at reduced levels of difficulty and therefore reduced cost. These methods involve monolithic and hybrid approaches, the latter at both wafer-to-wafer and chip-to- wafer levels. Broadly, these are called 'heterogeneous integration' and encompass technologies as diverse as wafer- fusion and DNA-assisted micro-assembly. This review summarizes the associated micro-assembly techniques and discusses their possible influence upon cost- and yield-benefits to industry.

SELFOC gradient-index glass lens has revolutionalized the industries of fiber optic communications. According to the recent development of DWDM system and high-speed computer networking, SELFOC micro lens is used more and more accordingly. This paper introduces present technical specifications of SELFOC lenses with emphasizing new development for applications in DWDM and optical data links.

The effect of illumination on the Schrodinger's wave function and related device characteristics has been studied in the quantum well of a n-AlGaAs/GaAs MODFET. Partial depletion of the active region of the MODFET has been considered. At the heterojunction interface, the quantum well has been considered as a modified triangular potential well of finite depth. The potential energy and the subband energy are calculated by solving the Poisson's equation. The wave function, sheet concentration and the I-V characteristics of the MODFET under dark and illuminated conditions have been calculated and discussed.

Optical constants of hexagonal AlN in the range 6-20 eV and 6H-SiC in the range 1-30 eV for the component perpendicular to the c axis are modeled using modified Adachi's model of the optical properties of semiconductors. Model parameters are determined by acceptance-probability-controlled simulated annealing. Main distinguishing feature of the model employed here is the use of variable broadening instead of the conventional Lorentzian one. In such a manner, broadening function can vary over a range of functions with similar kernels but different wings. Therefore, excessive absorption inherent to Lorentzian broadening can be reduced so that better agreement with experimental data can be achieved. Relative rms errors for the real and imaginary parts of the index of refraction, respectively, equal 3.5% and 5.2% for 6H- SiC and 1.5% and 1.9% for AlN.

Intermixed quantum well structures created by both impurity- induced and impurity-free or vacancy-promoted processes have recently attracted much attention. The full integration of photonics devices like tunable lasers, modulators and photodetectors has been attained and can be obtained using the quantum well intermixing technology. The advantage of being able to tune the material properties allows the realization of higher-performance devices, such as lasers, photodetectors and modulators. This bandgap modification is a powerful technique for monolithically integrating optoelectronic devices of varying functionalities on a single wafer. This paper will explore the wavelength tunability using different quantum well intermixing techniques. In addition, this paper will place a strong emphasis on the very recent device applications of intermixing technology. Attractive distributed-feedback laser and modulators have been developed as a result of some unique devices of quantum well intermixing. In particular, this allows a multi-section integrated structure to be fabricated for wide band-width and multi-wavelength applications. The use of such structure in wavelength division multiplexing (WDM) in high bit rate communication systems is a good example. Several state-of-the-art results of the intermixed quantum wells will be summarized, with an emphasis on the directions for future development.

A theoretical study of the polarization independent quantum- well gain using interdiffusion is presented here. Group V sublattice interdiffusion in InGaAs/InP quantum wells is used to produce polarization independent optical gain. The reverse bias and carrier effects on the subband structures, transition energy and optical gain of the interdiffused quantum well are discussed. The interdiffused quantum well structures are optimized in terms of their subband structure, carrier density, structural parameters and properties of optical gain spectra. The results show that an optimized interdiffused quantum well structure can produce polarization independent optical gain over a range of operation wavelengths around 1.5 micrometer, although the differential gain and linewidth enhancement factor are slightly degraded. The required tensile strain for the polarization independence of a lattice-matched quantum well structure is generated here using interdiffusion. These results suggest that polarization independent optical devices can be fabricated using interdiffusion using a lattice-matched InGaAsP quantum well structure.

Using semiclassical time-dependent perturbation approach, we have analyzed one of the important optical coherent transient effects viz., the Stark shift and Stark broadening (also known as self energy correction) by incorporating the higher excitonic states in GaAs/GaAlAs quantum well structures irradiated by an ultrashort pulsed laser. It has been found that both Stark shift as well as Stark broadening get modified when we take into account multiple excitonic states.

The strain introduced at the junction of two lattice mismatched semiconductors reshapes the valence band reducing the density of states, intervalence band absorption, Auger recombination and temperature sensitivity. In the present study, a strained ternary system Cd_xZn_1-xTe on ZnTe substrate has been investigated. The effect of x on critical thickness, effective mass, band gap, optical gain and current density has been calculated. This system was chosen as it is useful in blue emission, emission at high temperature etc. and also it can be grown on Silicon substrate directly. The optical gain increases with x whereas current density decreases. The laser cavity length and number of quantum wells have been optimized for different temperatures and for Cd compositions of 0.1 and 0.2 and well widths of 50 A and 60 A. Further, intersubband transitions in symmetric - (ZnTe-Cd_xZn_1-xTe-ZnTe) square quantum well have been studied. The effect of barrier height and well width on absorption coefficient and detectivity, which have a large bearing on the performance of a detector, have been studied. Absorption coefficient ((alpha) ) and detectivity (D_(lambda )) are calculated for different frequencies (w) for the given x and well width. The maximum value of (alpha) and D_(lambda ) are picked up from the (alpha) versus w, and D_(lambda ) versus w curves, and are plotted as the functions of Cd composition (x) and well width. Both (alpha) and D_(lambda ) increases with x and decreases with well width.

A quarter of a century ago, the lightwave envelope in an optical fiber was shown to be described by the nonlinear Schrodinger Equation. A localized stationary and stable optical pulse (optical soliton) found as its solution was suggested as a carrier of ultra-high speed data transmission. Now the soliton based ultra-high speed communication is vigorously pursued around the world. Furthermore, the nonlinear Schrodinger equation model is widely used as the simulator of information transmission in fibers in general not limited to solitons. Looking back the historical development of optical soliton research is an interesting case study of how an abstract mathematical concept is put into practical use. This development is a consequence of combined efforts of prominent scientists and engineers around the world. However the most significant factor that has contributed to this success is the appropriateness of the god given physical parameters in fibers. Thus it is a sin not to take advantage of this rear opportunity. History of application of optical solitons for high speed signal transmission in fibers may be divided into five stages, (1) historical background and the discovery of the optical soliton, (2) idea and demonstration of all optical soliton transmission systems, (3) identification of possible problems, (4) demonstration of soliton control and (5) Discovery of Dispersion Managed Optical Solitons. In addition, other application of solitons such as modulational instability, dark solitons, spatial solitons are currently vigorously pursued.

We present a review of known and new theoretical results on short-pulse propagation in optical systems with either slow or fast saturable absorbers. The analysis is based on using a modified complex Ginzburg-Landau equation. We show that in addition to the normal 'plain pulse' solutions, various other types of composite pulse solutions can exist. These composite solutions are formed from simpler solutions and may be considered as bound states of plain solitons or plain solitons and fronts. In the former case the bound states can be analyzed using the 'interaction plane' and balance equations.

We review recent experimental, theoretical and numerical results dealing with the generation and the interaction of solitary waves in second-order nonlinear crystals. Particular emphasis is devoted to the issues related to the collisions between two-dimensional type II second-order solitons of orthogonal polarization in a KTP crystal. We report the experimental evidence that both quasi elastic and inelastic collision (when two solitons at input merge into a single one at output) are feasible, depending on the relative transverse velocity of the interacting beams.

A whole family of waveguide lasers (fixed frequency, acousto- optically tunable, modelocked, Q-switched) has been developed in Er-diffusion doped LiNbO₃ substrates. By periodically poling the Ti:Er:LiNbO₃ waveguides quasi-phase-matched nonlinear interactions can be achieved in the same structure. In this way the development of self-frequency doubling lasers, of laser/difference frequency generator combinations, and of optical parametric oscillators with intracavity pump laser becomes possible.

Recent developments in high-concentration erbium-doped fiber (EDF) and waveguide devices for integrated optical circuits applications are reviewed. The uniform upconversion and pair- induced quenching mechanisms that limit the maximum usable erbium ion concentration are discussed. We also present the performance of erbium-doped fiber amplifiers based on high- concentration fibers. The performance of a laser based on a highly-doped EDF and fiber grating is reported.

In this work we have generated widely-tunable continuous-wave (CW) red light by second-harmonic generation (SHG) of the output of a Cr⁴⁺:forsterite laser, tunable from 1.206 to 1.320 micrometer, using quasi-phasematching (QPM) in periodically-poled lithium niobate (PPLN). For a given grating period in the PPLN, a combination of Cr⁴⁺:forsterite pump wavelength tuning and PPLN temperature tuning up to 200 degrees Celsius provided continuous SHG tuning over a wavelength range of approximately 14 nm in the red. By translating the PPLN crystal to other periods, we have demonstrated SHG over the entire tuning range of the pump laser, yielding tunable CW output from 603 to 660 nm with maximum output powers of approximately 5 mW for a typical Cr⁴⁺:forsterite pump power of 500 mW.

Erbium is doped into z-cut Lithium Niobate (LiNbO₃) substrate by thermal diffusion from thin Er film. XPS, PL and reflection studies have been carried out in order to characterize the doped sample and to test the suitability for amplifying signal at the wavelength 1530 nm. Straight waveguides of different widths (10, 15 and 100 micrometer) have been fabricated on the Er-doped sample by Ti diffusion. Loss measurements for the Er:Ti:LiNbO₃ waveguides have been done by using lasers of wavelengths 633 and 1300 nm.

A stable, passively mode-locked erbium-doped fiber resonator is developed to generate tunable optical pulses with durations of 270 - 325 fs in the soliton regime. The lasing wavelength is tuned continuously over a wavelength range of 60 nm by rotating a bulk band-pass filter inserted in the resonator with a repetition frequency of 45.4 MHz. We reduced the timing jitter by minimizing the intensity fluctuation of the pump source using a feedback loop and by controlling the influence of airflow and temperature fluctuation of the resonator in a sealed box.

In this paper, we first define a complex refractive index profile for the pumped Erbium Doped Fiber which depends on radial distance, pump and signal powers and Er-doping profile in order to obtain modal gain/loss of the propagating signal/pump power by a Rayleigh Ritz Variational analysis. This provides a novel way of looking at the gain characteristics of EDFAs. Next, we use this to estimate the total signal gain in fiber lengths for given input pump power levels.

The use of time-dependent transfer matrix and wide-angle beam propagation method is proposed to improve the computational speed and accuracy of a recently developed time-domain traveling-wave model of vertical cavity surface emitting lasers. With suitable utilization of the transfer matrix, significant reduction of the total execution time of the traveling-wave model can be obtained. In addition, the use of wide-angle beam propagation method can minimize the calculation error of the traveling-wave model due to the diffraction of light from small aperture of laser cavity.

The given work is devoted to a problem of numerical simulation and analysis of the vertical cavity lasers parameters with the purpose of numerical simulation methods improving. The analysis of the VCSEL with the help of the mathematical model, based on beam propagation method, are presented. The dependence of the VCSEL dynamic behavior on the temperature dependence of the gain coefficient is submitted. With the help of extended system of the rate equations for VCSEL the modulation characteristics are obtained. Analysis of the lasing wavelength dependence on thermal gain coefficient is carried out.

It is important to know the spectral characteristics of light sources for optical coherence systems. From experimental view, this paper systematically investigates the spectral characteristics of two kinds of laser diodes whose structures are buried heterostructure (BH) and transverse junction stripe (TJS), and they are modulated directly by low-frequency sinusoidal current signal. The modulation frequency is less than 100 kHz. From our experiment results, we find that, under the low frequency modulation, when the modulation depth is over some values, the spectra of these laser diodes which originally are single longitudinal mode will become multi- longitudinal modes. This results are different from the general idea. Besides, we find that, under the same operating conditions, for those laser diodes which have greater sidemode suppression ratio, or when the modulation frequency is increased, it must increase the modulation depth for getting multi-longitudinal modes. Moreover, we find that TJS laser diodes are easier to appear sidemodes than BH laser diodes. To the authors' knowledge, these phenomena have not yet been reported.

Self pulsation in laser diodes results from the non uniform distribution of the carrier lifetime along the cavity, and can be used for short optical pulse generation. A large signal electrical equivalent circuit for an absorptive multi quantum well bistable laser diode has been developed from the rate equations. The dc and transient analysis are carried out using PSPICE circuit simulator. The dc simulation shows hysterisis characteristics. In transient analysis, the gain section is excited with an electrical pulse and the optical output exhibits self pulsation phenomenon in which short optical pulses of width 30 ps (FWHM) are generated.

This paper presents a brief overview of some of the common high-speed and high-sensitivity photodetectors. These devices are the key components in long-haul, high bit-rate fiber optic communication systems. In this paper, while we describe several types of photodetectors, we concentrate on avalanche photodiodes since they are the current preferred candidates for high bit-rate long-haul fiber optic communication systems. We describe and compare some analytical and stochastic modeling results with experimental data and conclude with a discussion of some state-of-the-art results on photodetectors.

We have fabricated InGaAs/InP PIN diodes with a coplanar waveguide design. The diodes have been integrated in a two- chip wavelength-selective Fabry-Perot filter for the use as wavelength-selective PIN receivers for dense wavelength division multiplex systems.

APD/FET optical receivers are preferred choice over PIN/FET for high data rate, high sensitivity applications mainly because of APDs combine detection of optical signal with internal amplification of photo current. However, there are number of critical issues such as device and preamplifier design, circuitary required to keep the Avalanche photodetector (APD) biased at optimum gain and temperature compensation of bias being applied to it etc., have to be addressed to realize an optical receiver with desired performance. This paper deals with the design and fabrication of 622 Mbps optical receiver front-end using Separate Absorption Graded Multiplication (SAGM) APD for photodetection and combination of MESFET and BJT for transimpedance amplifier design. AIMSPICE has been extensively used to simulate appropriate biasing of the active and passive devices taking into account various parasitics like miller capacitances, lead inductance etc. in order to optimize DC and AC performance of the circuit. Cr/Cu/Au thin film technology and solderable surface mount devices (SMD) have been used for its fabrication. Also included are the optical receiver performance in terms of Sensitivity and Dynamic range.

We demonstrate a new CMOS synchronized photoreceiver for conversion of optical input pulses to digital output signals. A combination of two p-n-p vertical CMOS BJTs controlled by an external clock is designed to achieve the first clocked photoDarlington structure. This clocked photoDarlington is used as a detector of input light. The generated photocurrent is reflected by a current-mirror comparator and digitized by a buffer. The synchronized photoreceiver, in its return-to- zero (RZ) format, has been implemented in a standard digital 0.7-micrometer, 5-V n-well CMOS technology with an effective area of 100 X 60 micrometer². It was measured to operate at 100 MHz with an external input light of -18.8 dBm/beam.

There is a considerable interest in recent years on microbolometer infrared detectors, due to the possibility of operating them at room temperature and the compatibility with CMOS fabrication process. In this work, we have fabricated bolometers with Ti and a:Ge as the sensing elements using a CMOS compatible process. Noise measurements indicate that detectivity D* of over 1.5 X 10⁹ cmHz^-1/2W^-1 and 4 X 10⁹ cmHz^-1/2W^-1 at 30 Hz could be realized for a:Ge and Ti bolometers, respectively. With further improvements in design and processing, it is estimated that bolometer focal plane arrays (FPAs) with noise equivalent temperature difference (NETD) of less than 50 mK are realizable using the above materials.

For low cost fiber-to-the-home (FTTH) passive optical networks (PON), we have studied the delivery of broadcast digital video as an overlay to baseband switched digital services on the same fiber using a single transmitter and a single receiver. We have multiplexed the baseband data at 155.52 Mbps with digital video QPSK channels in the 270 - 1450 MHz range with minimal degradation. We used an additional 860 MHz carrier modulated with 8 Mbps QPSK as a test-signal. An optical to electrical (O/E) receiver using an APD satisfies the power budget needs of ITU-T document G983.x for both class B and C operations (i.e., receiver sensitivity less than -33 dBm for a 10^-10 bit error rate) without any FEC for both data and video. The PIN diode O/E receiver nearly satisfies the need for class B operation (-30 dBm receiver sensitivity) of G983 with FEC in QPSK FDM video. For a 155.52 Mbps baseband data transmission and for a given bit error rate, there is approximately 6 dBo¹ optical power penalty due to video overlay. Of this, 1 dBo penalty is due to biasing the laser with an extinction ratio reduced from 10 dBo to approximately 6 dBo, and approximately 5 dBo penalty is due to receiver bandwidth increasing from approximately 100 MHz to approximately 1 GHz. The penalty due to receiver is after optimizing the filter for baseband data, and is caused by the reduced value of feedback resistor of the first stage transimpedance amplifier. The optical power penalty for video transmission is about 2 dBo due to reduced optical modulation index.

Copper based wired local loop has served us well for over 100 years. However much we may decry the copper for its bottlenecks today, it has served us so long due to the following: (1) it is a passive network, which does not fail unless cable is cut; (2) it carries power for subscriber terminals; (3) it carries voice signals both ways; (4) 56 kbps data can be carried in 4 kHz copper loop; (5) n-isdn, HDSL, ADSL, VDSL is enabling tens of Mbps data to be carried on the copper loop. It is such a loop that one wishes to replace with Fiber. How does fiber handle these issues? While fiber finds it difficult to provide one to one replacement of copper loop, and is still struggling to make a mark in the Access Network of developed world, a certain kind of Fiber Access Networks is suddenly becoming the way of deploying new telecom networks in developing countries. Fiber in the Loop today provides the most cost-effective solution for new deployment in urban areas; most Basic Services Operators in India plan to use this in major way. It is likely that in the next three to four years, more Fiber in Access Network will be deployed in India than in any other country in the world. This paper examines the issues involved in use of Fiber in the Access Network and suggest solutions which are likely to make it the technology of choice for new operators.

This review details the approaches adopted to implement classical code division multiple access (CDMA) principles directly in the optical domain, resulting in all optical derivatives of electronic systems. There are a number of ways of realizing all-optical CDMA systems, classified as incoherent and coherent based on spreading in the time and frequency dimensions. The review covers the basic principles of optical CDMA (OCDMA), the nature of the codes used in these approaches and the resultant limitations on system performance with respect to the number of stations (code cardinality), the number of simultaneous users (correlation characteristics of the families of codes), concluding with consideration of network implementation issues. The latest developments will be presented with respect to the integration of conventional time spread codes, used in the bulk of the demonstrations of these networks to date, with wavelength division concepts, commonplace in optical networking. Similarly, implementations based on coherent correlation with the aid of a local oscillator will be detailed and comparisons between approaches will be drawn. Conclusions regarding the viability of these approaches allowing the goal of a large, asynchronous high capacity optical network to be realized will be made.

A hybrid incoherent optical fiber code-division multiple- access (CDMA) scheme is presented in which encoding is based on the Kronecker product of two short component sequences of relatively large weight. The first short sequence permits realistic electronic encoding of each data bit. The 'chips' of this sequence are then all-optically encoded at substantially higher speed but the all-optical encoder remains practical by virtue of the shortness of the sequences. It is shown that by judicious selection of component sequences the network can accommodate a large number of simultaneous users without sacrificing BER performance due to multiple-access interference.

An all-optical ATM (packet) switch that utilizes Fiber-Optic Code Division Multiple Access (FO-CDMA) to achieve fast, asynchronous switching of ATM cells is proposed. An 8 port, OC-12 configuration is chosen for a feasibility study and simulations are used to characterize its performance with respect to two metrics -- cell loss ratio and average latency. The significant features of the proposed architecture include high switch throughput, scaleability and multicast-capable switching.

We present the bit-error-rate (BER) analysis of an ultrashort light pulse code-division multiple access (CDMA) communication system, which employs a practical nonlinear detector. The system considered here assumes a CDMA network, in which M user stations are connected via a star coupler and a common fiber channel. The transmitter at each station consists of a mode locked femtosecond fiber laser at 1550 nm whose ultrashort pulses are encoded by a spectral phase encoder and uses an on- off-keying scheme. The receiver consists of a decoder, a nonlinear detector, and an integrate and dump data circuit. In this work, we develop an efficient Monte Carlo simulation using importance sampling scheme to estimate the error probabilities of the system in addition to the analytical technique. The simulation results are found to be in good agreement with the analytical results.

The rapid growth of thor required information bandwidth due to new services in the communication society forces network providers to increase the bit rate and to use wavelength and time division multiplex, both for new systems and upgrading existing lightwave systems. One economic way for system layout is the extensive use of reliable numerical simulations. Therefore we focus on new and more accurate simulation tools for lightwave systems including all key components As with increasing channel numbers the accumulated optical power increases dramatically, too, nonlinear effects become significant. Here we present our extended erbium-doped fiber amplifier (EDFA) model that includes phase modulation in the EDFA due to signal and pump-induced change of the refractive index. We assume an intensity modulated-direct detection (IM- DD) system operating at 193 THz (1552.5 nm) with a bit rate of 10 Gbit/s in the anomalous dispersion regime and a total fiber length of 500 km. The fibers are assumed to be dispersion shifted one and EDFAs are used to compensate for the fiber loss. It turns out by numerical simulation that in the anomalous dispersion regime on omission of the signal and pump-induced change of the refractive index strongly underestimates the Q-factor. Therefore our extended EDFA model can be used for more reliable system simulations.

In this work we show the potentiality of numerical modelling in evaluating and optimizing the performance of optically amplified communication systems. The reliability of the developed numerical coded has been successfully tested in the framework of European projects in the telecommunications area (COST and ACTS projects) by comparison with analytical theories and experimental measurements. We present also a survey of the main strategies proposed to achieve very high capacity transmission systems, trying to draw some general guidelines for different systemistic solutions.

This paper investigates the various restoration control architectures for photonic transport networks. A comparison of the centralized, distributed and quasi-centralized control schemes is made, while highlighting their respective advantages. An analytical comparison of their real-time span restoration times is performed using a study network, in which the distributed control architectures offering the fastest restoration times. An additional performance metric is proposed, and together with the mean restoration time a further search is made for an optimum control architecture for networks of different sizes and connectivity.

For realizing wavelength routing algorithm, hierarchy management architecture is designed basing on the TMN logical layered architecture. Information model for managing different network elements and logical resources was established, comportable features should be considered for wavelength routing management.

Polarization mode dispersion (PMD) hampers development of greater than or equal to 10 Gb/s trunk lines but can be compensated by endless polarization controllers and birefringent fiber. We demonstrate automatic 10 Gb/s PMD compensation using three deformed-helix ferroelectric liquid crystal cells.

Gas spectroscopy based upon fiber optic systems is emerging as an important contributor to the art of remote measurement. To date two generic application sectors have emerged. The first is to make measurements in difficult and hazardous environments for which an integrated and passive optical source is extremely attractive. An optical fiber equipped with suitable collimation optics can furnish such a source. These systems have been utilized to measure gas flow and concentration in gas turbine engines and in hazardous chemical processes. The second applications sector lies in monitoring geographically widely spread locations at which the same measurement is continuously required. These occur for example in oil and gas exploration and processing systems and petrochemical plant. In this case it is the transmission capabilities of the optical fiber which are especially attractive. The optical fiber transmission medium implies that any optical signals which are used in the spectroscopic measurement lie in the near infra red with the absorption line strengths for most interesting species are relatively weak. However, modern source: detector combinations lead to very useful performance despite the weaker line strengths. This paper presents an analysis of the principal factors which determine system performance and illustrates these with some specific applications examples. Finally, we briefly explore the prospects offered by non-linear systems to produce remote spectroscopic measurements operating in the mid infra red but interohated and energized in the near infra red.

Aircraft in active service are mostly made of aluminum alloy. On line health monitoring of these structures is becoming more important as the older aircraft reach the end of their design life. At the same time newer aircraft made of new materials such as composites need monitoring since the design methodology for these materials is still under development. While conventional NDT methods are improving, an on-line monitoring system would provide regular check-ups without significant downtime. Fiber optic sensors embedded into or mounted on the surface of materials or structures to monitor the integrity of members has been discussed widely in recent years. Among them the Fiber Optic Polarimetric Sensor (FOPS) has the advantage of long sensing gauge length. In this paper, FOPS are mounted on the surface of aluminum specimens as well as embedded within composites to demonstrate its ability to monitor the development of cracks and predict residual load of structure.

Strain measurements on synthetic fiber rope constructions of the type used in marine applications are reported. The ropes are of a novel construction by virtue of incorporation of fiber-optic sensors for strain measurement. Two instrumentation approaches -- a Brillouin strain measuring system and a RF sub-carrier strain measuring system -- have been utilized to interrogate the fiber sensors.

This paper discusses the technique of sensing the roughness of a surface in terms of slope of its microelements, based on reflection and scattering of electromagnetic wave from such elements of the continuous surface. An array of fibers collects the optical power reflected from the surface due to illuminating optical energy launched onto it through the central fiber of the array. The tilt and orientation of the illuminated pixel can be estimated from the measurement of reflected and scattered power captured by different fibers in the array. Theoretical developments to compute the tilt and orientation of the illuminated area -- by the shape of the illuminated spot of the incident beam, analyzing the reflected or scattered beam, and the reflected beam intensity available at different fibers of the array -- is presented. The intensity profile so derived shows close agreement to that obtained experimentally. A number of different types of array packing structures have been suggested and analyzed to evaluate their comparative efficiencies. The results obtained demonstrate that such a sensor can be used to measure surface roughness over a wide range, by employing different etching techniques like analyzing total integrated scattering (TIS), angle resolved light scattering (ARLS), specular reflection, etc.

The problem concerning excitation of an elliptically birefringent fiber is dealt with by the variably coupled mode theory under the slowly varying condition. A composite fiber element is structured in a one-step fabrication process, comprising an extra spun hi-bi section whose spin-pitch varies from zero to a value equal to the constant spin-pitch of the main spun hi-bi fiber section. Meanwhile, the magnetic field strength distribution along the tapered portion of the fiber is made to taper simultaneously. Theoretical analysis indicates that such a composite tapered fiber architecture is capable of supporting transmission of a single elliptical eigenmode, and moreover, responding analytically to an applied magnetic-field. Practical aspects of the fiber architecture are discussed on the basis of a preliminary experimental investigation.

Design, fabrication and application of twisted fiber for polarized light transmission and electric current sensor are presented in the paper. A characterization parameter of twist fiber is proposed for the design of twisted fiber for linearly or circularly polarized light transmission. The problem of employing twisted fiber in current sensor, e.g., the temperature or polarization perturbation induced sensor bias drifting, is overcome by a novel signal processing method with a modified optical arrangement for ac current detection. Experimental results show the compensation method is effective to arbitrary bias phase drifting in electrical current sensor using twisted fiber.

In Brazil several groups develop Optical Fiber Sensors based on Wavelength Division Multiplexed Optical Bragg Gratings. We present a review of recent results obtained at our groups in the development of Optical Fiber Sensors to measure deformation (strain) or temperature in high voltage power transmission lines.

Fiber Bragg Gratings (FBG) have been applied to a wide range of systems both in telecommunication and sensors systems. For sensors the main advantages in using FBG are the ease of multiplexing and the reliability of measurements due to spectral encoding. Although many different ways of analyzing the spectral response of a FBG have been proposed and demonstrated, most of them involve sophisticated electronics and do not take into account practical problems. We describe a simple, robust and low cost technique in which a reference grating is used as a spectral filter for the sensing grating. In our prototype a 1550 nm pig-tailed LED is used as broad band source. As the system is proposed for strain measurements, special attention is paid to field calibration and long term measurements. Two calibration methods are demonstrated. One uses the digitalized reflection spectra of sensor and filter grating and numerically predicts the sensor output. The other method is based on the application of a controlled opposite strain on the filter grating. Both methods were compared with conventional resistance strain gage and the measuring accuracy is estimated. We also point out applications where FBG strain sensor can have significant advantages over conventional electric counterparts.

The optical fiber, as a dielectric and flexible medium capable of guiding with low attenuation the light of the visible and near-infrared spectral regions, is an excellent tool for performing spectral measurements at selected wavelengths or in combination with conventional spectrometers. This paper shows some applications for absorption spectroscopy by citing optical fiber sensors currently being experimented at IROE- CNR. Senors for the monitoring of Chromium in sewage water and for the colorimetry of gasoline samples are presented, together with sensors for radiation dosimetry in radiotherapy and for lighting control in museum environments.

In recent years investigation and understanding of the interaction between brain activity and human hemodynamics is receiving much attention. Such investigations are generally confined to few select premier research institutions where expensive and sophisticated facilities like PET, NMRI, etc. are available. Actual advancement in optoelectronics and computer technology have accelerated the development of new measuring systems and methodologies for use in this medical field. Specifically, transcutaneous assessment of skin perfusion changes (blood volumetric measurement) through optical sensor based Photoplethysmography (PPG) has rapidly gained an important role. This basically noninvasive measuring procedure is devoid of harmful radiation and ionizing phenomena, simple in construction and connection to the measuring setup and is easy to use in all areas of human body. The relatively low cost of these sensors have resulted in their use in varied medical fields for extensive clinical applications. In the past, the application of PPG had been limited by technical difficulties involving calibration of the data. The development of quantitative PPG technique based on computer-aided data processing has removed this obstacle. In co-operation between Indian Institute of Technology at Chennai and Aachen University of Technology an Indo-German Project was initiated in 1996 for advanced studies in this research area. Measuring system design, experimental details and some preliminary results obtained so far within the framework of this project are presented in this paper. From the investigations carried out so far using the PPG sensors in conjunction with breathing sensors, it has been possible to monitor the 0.125 to 0.15 Hz rhythms in the arterial volumetric changes and to study the influence of breathing on them. These rhythms, which according to medical experts have relevance to psychosomatic conditions e.g. stress or relaxation, can also be addressed to by ancient Indian practices like yoga and meditation.

A new sensing technique for the in situ monitoring of the rate of pulsed laser deposition of metal thin films has been developed. This optical fiber based sensor utilizes the evanescent wave penetration of waveguide modes into the uncladded portion of a multimode fiber. The utility of this optical fiber sensor is demonstrated in the case of pulsed laser deposition (PLD) of silver thin films obtained by a Q- switched Nd:YAG laser which is used to irradiate a silver target at the required conditions for the preparation of thin films. In the present paper we describe the performance and characteristics of this sensor and show how this device can be an effective tool for the monitoring of the deposition rate of silver thin films.

An experimental study of the fiber-optic evanescent field absorption sensor based on tapered sensing probe is presented. The influences of numerical aperture, core radius of the fiber and the taper ratio on the sensitivity of the sensor are investigated. Increase in the numerical aperture of the fiber increases the sensitivity of the sensor while the decrease in the core radius increases the sensitivity. In addition, for a given fiber, increase in taper ratio increases the sensitivity. The relationship has been found to be linear.

The present work describes an all-fiber hybridization assay sensor that relies on the evanescent field excitation of fluorescence from surface-bound fluorophores. The evanescent field is made accessible through the use of a long adiabatically tapered single-mode fiber probe. A semiconductor laser operating at 785 nm wavelength is used in a pulsed mode to excite fluorescence in the tapered region of a fiber probe using the near-infrared fluorophore IRD 41. We have carried out real-time hybridization tests for IRD 41-labeled oligonucleotide at various probe concentrations binding to complementary oligonucleotide cross-linked to the tapered fiber surface. Short oligonucleotides (20-mer) bound to the fiber surface have been used to detect near-infrared dye labeled complementary sequences at sub-nanomolar levels. Sandwich assays with total RNA were conducted to examine the capability of the biosensor for detecting bacterial cells using rRNA as the target. The results indicate that this fluorosensor is capable of detecting H. pylori in a sandwich assay at picomolar concentrations.

In this paper, the Mach-Zechnder interferometric all fiber hydrophones developed are introduced, and their unit-to-unit consistency performances are placed on emphasis. The considerations of the means such as the hydrophones design, laser stability, optical path difference, optical fiber selection and circuitry for achieving the performance consistence are made. The performances of unit optical fiber hydrophone and its measurement methods of underwater acoustical sensitivity including low frequency comparison and delay-frequency scanning are introduced. The experimental results are given.

This paper reports the outcome of research studies carried out by us in the area of Optical Pattern Recognition. We describe experimental realization of two kinds of all-optical nonlinear photorefractive (PR) joint transform correlators. One method uses a controllable beam-fanning nonlinearity and the other uses an incoherent erasure beam in PR wave-mixing. An experimental technique has been demonstrated to achieve high pattern discrimination using a bank of wavelet filters. Correlation technique has further been extended to real-time object motion measurement.

An optical wavelet processor for image feature analysis has been proposed using a JTC geometry. Haar wavelets are used in this study. Computer simulation studies are carried out to illustrate the principe of the processor using standard binary and gray-scale test images. An encoding technique has been discussed for the optical realization of the processor.

A Two-dimensional holographic memory for archival storage is described. Assuming a coherent transfer function, an A4 page can be stored at high resolution in an area of 1 mm². Recently developed side-chain liquid crystalline azobenzene polyesters are found to be suitable media for holographic storage. They exhibit high resolution, high diffraction efficiency, have long storage life, are fully erasable and are mechanically stable.

We report wavelength shifting (generation of a pulse at the wavelength (lambda) _p - (Delta) (lambda) from a signal at (lambda) _p + (Delta) (lambda) under the action of a pump at (lambda) _p) and parametric amplification through a cascaded second order process in a periodically poled lithium niobate crystal and also in an organic crystal N-(4-nitrophenyl)-L- prolinol (NPP). NPP could convert signal pulse (from 1.16 to 1.14 micrometer) with unit gain under the action of a pump pulse (at 1.15 micrometer) of peak intensity as low as 9 MW/cm². In the limit of negligible conversion, where the cascading effect can be described through an effective (chi) ⁽³), we derive for NPP(chi) _eff⁽³) approximately equals 2.4 X 10^-17 m²/V², which is approximately 10² larger than (chi) ⁽³) of conjugated polymers or semiconductors. In a 19 mm long PPLN sample, at (lambda) _p equals 1.8 micrometer and (Delta) (lambda) as large as 60 nm, we could obtain unit gain with a pump intensity of 6 MW/cm², while amplification by a factor of 10 requires 18 MW/cm². We also present a theoretical comparison between frequency mixing and cascading.

Near-field scanning optical microscopy (NSOM) allows simultaneous mapping of both the topography and optical properties of a surface with resolution below the diffraction limit. Second harmonic generation (SHG) always occurs at a surface, even for centro-symmetric media, because of symmetry breaking. By combining NSOM and SHG we can study local variations in symmetry breaking, caused for example by ferroelectric and ferromagnetic domains, and can correlate them with surface topography. We report NSOM/SHG measurements made on piezoelectric ceramics, ferromagnetic materials and periodic structures.

Based upon coherent radiation-semiconductor interaction, pulse propagation effects such as pulse break-up and pulse peak shifts in unmagnetized bulk narrow direct-gap semiconductors as well as pulse chirping and broadening in the above crystals in presence of a moderate magnetostatic field have been analyzed. The effect of externally applied magnetic field on the transient optical processes has been treated in terms of the Landau level splittings. Numerical analysis of nonlinear phase shift, pulse break-up, pulse chirping and broadening have been made in InSb duly irradiated by infrared pulsed lead-Salt (PbEuSeTe) or AgGaS₂ dye laser with photon energy in the vicinity of the crystal band gap. The results being in good qualitative agreement with the available experimental observations suggest the suitability of the narrow-gap semiconductors in all-optical processing devices.

Based upon the time dependent perturbation theory for coherent radiation-semiconductor interaction, the possibility of occurrence of the phenomenon of two-pulse photon echo has been investigated analytically in a bulk direct-gap semiconductor under near resonant transition regime below the absorption edge of the crystal. The excitation intensity is chosen to be in the low-to-moderate power regime such that the photoinduced electron-hole pair density remains below the Mott transition limit and the weakly bound Wannier-Mott excitonic structure of the crystal absorption edge is manifested. The band gap renormalization effect is also taken into account. Numerical estimation of the transmitted intensity has been made for electron-hole transition to the 1s excitonic states in the bulk CdS crystal. The analytical results demonstrate the occurrence of photon echo in direct-gap semiconductors.

We present here a perturbation approach to study the modes of a waveguide with sinusoidal variation of refractive index within or outside the guiding region; the sinusoidal term has been assumed to be the perturbation over the average refractive index profile. The results of the method have been tested by comparing them with numerical results and it has been shown that the perturbation method gives extremely accurate results for large number of oscillation in the guiding region even for a large perturbation. The method should be useful for the analysis of structures with sinusoidal variation of refractive index in the transverse direction, such as in multiple quantum wells.