Some 50 years ago it was clear that existing electrical communication systems were leading to a severe bottleneck in bandwidth due to the limited carrier frequencies available. Various optical techniques were examined with little success until the most unlikely one, glass fiber transmission lines, were taken up almost as a last resort. These have turned out to be remarkably successful by increasing transmission distance by a factor X10 and bandwidth by X10⁶. The paper reviews progress in passive and active fiber techniques, concluding that fiber technology will produce many further major advances.

In this paper we propose various applications of guided wave optics to quantum optics experiments. As quantum optics moves on to multiparticle and multiport configurations, guided wave optics, incorporating both integrated optics and fiber optics, could provide a realistic means of constructing experiments and devices.

This paper presents the basic principles of the laser generation of ultrasound (LGU) through thermal conversion and illustrates the approaches to its use in material evaluation using the broadband features of the source. Traditional LGU involves high energy optical pulse irradiation which often induces surface damage, especially in carbon or glass fiber composites. We therefore expand the concept into low power excitations using laser diode sources. This enables excitation without damage but requires coded temporal signals. Arrays of semiconductor laser sources can also produce very broadband acoustic signals, both temporally and spatially. Piezoelectric sources are usually the opposite constrained in both space and time. This basic observation opens new avenues of material investigation, some of which feature in this paper.

A highly dispersive fiber behaves like a Fourier transformer with respect to the complex envelope of the input signal. It follows that the best pulse shape for transmission on a dispersive fiber is that one of the most concentrated in frequency and time, and thus related to the prolate spheroidal wave functions. This is used to devise line coding schemes highly insensitive to chromatic dispersion. However, the greater the dispersion, the more complex these schemes become. The effect of filtering and chirping is also taken into account and it is shown that chirping over a bit time is not useful for bit rates greater than 10 Gb/s.

There is a need to develop reliable, low cost and efficient semiconductor sources at mid and far IR. The sources at mid- IR using II-VI and Iv-Vi compounds suffer from some limitations. There are proposals to develop THz emitters using novel concepts, but their practical realization is not imminent at present. Quantum Cascade Lasers based on intersubband transitions in coupled Quantum Wells and Superlattices have recently been the subject of intensive research. In this paper the basic mechanisms of these lasers using III-V compound based type I and II structures are mentioned and some recent results are mentioned. The possibility of obtaining population inversion in Si based QWs is then explored. The calculated values of transparency current density and gain in coupled triple QW structures using Si and SiGe are reported.

Generation of wide tunable laser radiation from 188 nm in UV til 7.7 micrometers in IR is reported in our laboratory using a single commercially available Nd:YAG laser as basic pump. Techniques employed are sum-frequency mixing and harmonic generation for the UV while for the IR we employ difference- frequency mixing. The nonlinear crystal used include BBO, LBO, CLBO, LB4, KTP, RTP, KTA and LiIO₃. A maximum conversion efficiency over 2-0 percent is realized for both in UV and IR generation. We have obtained some spectra of DNA, RDX in the UV while those of polystrene film and Methane gas in the IR with the generated radiation.

We study two coupled planar waveguides with Gaussian profile of dielectric constant and compare the results with equivalent uniform transverse profile, we show qualitative differences in the modes of the two structures.

The radiation characteristics of nonlinear dielectric waveguide with rectangular grating structure is analyzed by FDTD method. Dispersive linear and nonlinear polarizations are evaluated by making use of Z-transform technique. The dependency for optical wavelength and its electric field amplitude is shown. Possibility of the waveguide as an optical demultiplexing switch for WDM system is also discussed.

With the emergence of new services mixing data, voice and video, the expected increase of the traffic volume together with the modification of its profile creates a need for a high throughput multimedia network. In addition, quality-of- service (QoS) management is currently widely debated at the convergence between ATM and IP communities. In the meantime, WDM is widely deployed, giving access to large transport capacities together with a new dimension for routing purposes. This paper present alternatives for a multi- service optical network infrastructure in this Internet world, where WDM is used not only to increase the throughput but also to differentiate the traffic, to alleviate contention issues and to provide cost-effective solutions. On the same optical infrastructure under a self-sufficient management yet, would coexist different logical sub-networks where different routing techniques are used according to QoS and client protocol requirements. The main objective is to save on the transport cost by optimizing through packet switching techniques the resource utilization according traffic characteristics, while providing enough flexibility to adapt the resources to the evolution of the demand, and maintaining a high transmission quality, as provided by SONET today. This work, capitalizes on InP-based fast optical switching technologies demonstrated within the European ACTS KEIPS project. In this paper, the network concepts, packet format considerations, preferred routing techniques and system architecture will be reported and illustrated through physical and logical analysis. Finally, t < o introduction scenario will be presented: one for the backbone and one for the metro.

Collocation method has been developed as a method which can treat the modal field computation as well as the total field propagation with equal ease and efficiency. The method, based on the orthogonal collocation principle, converts the Helmholtz equation into a matrix ordinary differential equation. This equation termed as the collocation equation can be solved either by using direct numerical techniques or by special techniques based on the matrix operator algebra. In the present paper, we outline the basic principle of the method and the implementation of the perfectly matched layer technique to overcome the reflections from the edge of the numerical window. In addition, we discuss its applications to Bragg waveguides and to soliton propagation which ave lately assumed great significance.

A rigorous approach to wave propagation in circularly bent planar waveguides is proposed. Open bent planar waveguide such as slab waveguide, H-guide and NRD waveguide are transformed into the bounded one by placing the concentric electric walls in radial direction. As the normal modes of the bounded bent waveguide are numerically obtained, it is possible to apply the standard modal matching approach to the analysis of the propagation along a bent waveguide connecting two straight waveguides. To verify the accuracy of the present method, numerical results for slab waveguide are shown and compared with the results by the conventional methods. Numerical results for circularly bent slab, H and NRD waveguides are shown.

Optical fiber has been used to develop various sensors such as temperature, pressure, magnetic field, stress, moisture, etc. A recent development in optical fiber technology due to fiber communication has drawn lot of interests in developing new optical fiber sensor. It has several advantages over conventional sensors. This paper will describe some of our works on the application of optical fiber sensors for the measurement of strain and moisture.

The paper discusses the analytical investigation of the occurrence of coherent optical transient processes such as dynamic Stark effect and free induction decay in direct-gap semiconductor quantum wires with thickness and width smaller than the bulk Wannier-Mott exciton Bohr radius. The role of a moderately strong magnetic field has been critically evaluated in the occurrence of the transient processes. The analysis is based upon the time dependent perturbation treatment of the coherent radiation-semiconductor interaction model under near band gap resonant excitation regime. The excitation intensity is kept below the Mott transition regime. Numerical estimates made for a GaAs/AlGaAs quantum wire irradiated by femtosecond pulse Ti:Sapphire laser establishes that the Stark shift, Stark broadening as well as free induction decay are all considerably influenced by the magnetic field. Moreover, the wire width also affects Stark splittings.

Starting from the discussion of the simple expression of the waveguide dispersion, it is shown that fibers with three novel index profiles allow to easily control the chromatic dispersion.

In this paper, we review the inverse WKB method for refractive-index profiling of graded-index planar waveguides with emphasis on the recent developments on profiling of single-mode waveguides.

Coherent, passive, linear optical signal processing networks, built with 2 by 2 couplers, gratings, mirrors and waveguides are discussed. The signal processing function is accomplished by the interference of coherent signals. Through the artifice of a generalized coupler complex network topologies are reduced to cascaded four-port and feedback-assisted cascaded four-port circuits, which are then treated by standard network analysis techniques. A wide range of configurations can thus be evaluated through a single numerical code. Several applications relevant to telecommunication, measurement and sensing are enumerated.

For fiber-optic communications at 1.3 micrometers , and 1.55 micrometers , materials lattice-matched to InP substrate are exploited to fabricate high performance photodetectors (PDS). Various types of novel structures are used for fabricating high- performance PDs. In this review, the roles of heterojunctions, resonant cavity structures and the edge- coupled structures on the bandwidth, quantum efficiency and noise performance of PDs are discussed. Their potential for the fabrication of integrated photo receivers for applications in optoelectronic integrated circuits is mentioned. Different possible structures and materials for PDs, and other important considerations for high performance PDs are also briefly discussed.

We evaluate the mode-coupling mechanisms for short- and long-period gratings based on the propagation constant differences between the various spatial modes of the optical fiber. The properties of these photoinduced devices such as strain and temperature response and spectral behavior are also reviewed. Short-period fiber gratings have applications to adding and dropping WDM channels, flattening the grain spectrum of optical amplifiers and compensating chromatic dispersion. The applications of long-period gratings to gain equalization, ASE suppression and sensor are summarized.

Graded-Grown-Gate oxide involves a 2-step synthesis of growing an oxide at a temperature above the viscoelastic temperature onto a pre-grown SiO₂ layer. The cooling rate is carefully modulated near T_ve-925 degrees C to enhance growth induced stress relaxation. This new ultra- thin gate oxide process is manufacturable and delivers significant improvement in transistor performance and exceptional reliability. These improvements are a consequence of a planar and stress-free Si/SiO₂ generated by this novel process.

The one dominant characteristic of our times is the significant increase in the density of communication. Popularity of WWW has skyrocketed and so has the need for the bandwidth. The advent of fiber optics and WDM technology has appeared as a savior for solving these problems. In this paper, an overview of the WDM technology and its marriage with IP networking will be presented.

Optical information processing techniques offer many advantages for data security applications. Optics offers many degrees of freedom like phase, spatial frequency and polarization to encode data more securely. Being inherently 2D, optical systems can process and relay 2D information in parallel resulting in higher through put rate compared to the electronic systems. The above advantages offered by optical information processing systems, coupled with advancements in enabling technologies like photorefractive crystals, spatial light modulators, charge coupled device cameras, and smart pixel technology have led to the increasing use of optoelectronic data processing techniques for security applications. This article reviews some of the optoelectronic techniques used for data encryption with an emphasis on the research in this area being done in the Photonics Group at the Indian Institute of Technology, Delhi.

Alignment tolerance can be improved if instead of a large photodetector an array of several photodetectors is used to receive the power in each light beam used for interconnection. The design formulae for optically selecting the number of photodetectors, the center-to-center spacing between the photodetectors, and the radii of the photodetectors in a focal plane array are derived as a function of the spot sizes and diffraction patterns of the beams. Since photocurrents generated by several smaller photodiodes are summed together it is possible to enhance the signal to noise ratio without suffering a degradation in the overall bandwidth in the interconnect.

This paper reveals performance capabilities of critical fiber optic components and photonic devices, which have potential applications in industrial, commercial and military systems and equipment. These devices are widely used in battlefield, space surveillance, medical diagnosis, crime fighting, and detection of terrorist activities. Performance capabilities of fiber optic components for possible applications in WDM and DWDM systems are summarized. Photonic devices and sensor for forward battlefield applications are identified with emphasis on performance and reliability. Performance parameters of Erbium-doped fiber amplifiers, Erbium doped waveguide amplifiers, and optical hybrid amplifiers comprising of EDFAs and Raman amplifiers are discussed withe emphasis on bandwidth, gain-flatness, data handling capability, channel capacity and cost-effectiveness.

We survey optical solutions to the communications bottleneck which is becoming a growing problem in high-performance electronic systems as on-chip clock speeds increase. A variety of optical interconnects will be presented including highly parallel free-space optical systems and flexible fiber image guide and fiber array links.

Development of a novel multifunctional acrylate based photo- polymer for photonic integration is presented. A 325 nm He:Cd laser has been used for direct writing of 50 micrometers square core multi-mode waveguides, compliant bumps for flip- chip bonding and 45 degrees total internal reflection mirrors for out of plane coupling. The transmission losses are measured to be 0.17 dB/cm at 850 nm and 0.5 dB/cm at 1300 nm by cutback method. Partially halogenated versions show losses around 1dB/cm at 1550 nm. DTA-TG analysis shows that this multifunctional acrylate co-polymer is thermally stable up to a temperature of 270 degrees C.

Erbium doped fiber amplifier has revolutionalized the optical signal amplification technology and becomes a critical component when used to amplify wavelength division multiplexed signals in optical networks. In the dense WDM technology the different channels are multiplexed in wavelength domain with inter-channel spacing of 0.8 nm. When these different channels propagate through the EDFA for signal amplification, they suffer from inter channel crosstalk resulting in degradation of signal to noise ratio due to uneven gain spectra of EDFA. In this paper we discuss the experimental and uneven gain spectra of EDFA. In this paper we discuss the experimental and simulation results of EDFA pumped at 980 nm.

One of the most common interface for communications specified is RS 232C standard. Though widely accepted, RS232 has limited transmission speed, range and networking capabilities. RS 422 standard overcomes limitations by using differential signal lines. In automation of the operation of gas discharge lasers, multiple processors are used for control of lasers, cooling system, vacuum system etc. High EMI generated by lasers interfere through galvanic transmission or by radiation over the length of cables, and hang up operation of processors or control PC. A serial communications link was designed eliminating copper transmission media, using plastic optical fiber cables and components, to connect local controllers with the master PC working on RS232 protocols. The paper discusses the design and implementation of a high ly reliable EMI harden serial communications link.

In this work, a new subscriber access network architecture has been proposed. It uses optical add-drop multiplexer and wavelength division multiplexing. In order to alleviate the limitation on supportable number of users use of OAS has been investigated. It is found that with all the degradation in OAs, the number o users for a typical network is limited to 384.

A novel frequency domain simulator is developed for simulation of large size WDM system considering the spectrum evolution of each of the WDM channel impaired by the simultaneous effect of group velocity dispersion, self-phase modulator and cross-phase modulation. The frequency domain approach has been made possible by linearly the relationship p between Fourier transform of input and output power profile and phase over small step size.

In this paper, forward error correction schemes are discussed for application in the multigigabit-per-second optical channel. The proposed schemes, based on specific convolutional codes which allow simple decoding techniques, represent a valid alternative, in terms of performance and complexity, to the recommended Reed-Solomon codes.

Three different first order polarization mode dispersion compensation techniques are compared in terms of outage probability, calculated for a fixed value of sensitivity penalty at the receiver, with the purpose of evaluating their impact on 10 Gbit/s communication system performance. A numerical approach is followed for different conditions of polarization mode dispersion and for varying compensation parameters, looking for the best operating point of compensation.

Deep dry etching of silica is used for patterning of waveguides for optoelectronic applications. We report on the use of Electron Cyclotron Resonance/Reactive Ion Etching process for deep reactive ion etching of silica glass films using different fluorocarbons as etch gases. 1 by 8 splitter has been used as test structure for the optimization of the etch process. The optimized process parameters like RF/Microwave power, pressure and gas composition etc. for the above have been presented.

We report the fabrication and packaging of 1 by 8 power splitter on BK-7 glass. The single mode waveguide structures at 1.31 and 1.55 micrometers have been fabricated using K⁺- Ag⁺-Na⁺ ion exchange at 340 degrees followed by the reverse ion exchange at the same temperature. The power splitter is first tested on the optical test bench and then fiber pigtailed using an automated alignment system and packaged in a compact housing. The total insertion loss for 1 by 8 power splitter after packaging is 5.6 dB at 1.31 micrometers and 4.8 dB at 1.55 micrometers wavelength. The uniformity of power in the output ports is < 1.5 dB while the directivity is measured to be > 40 dB.

Finite element-based modal and beam propagation and the least squares boundary residual methods are used to optimize compact low-loss optical bends. Important optical parameters such as the radiation, transition, and transmission efficiencies, and the reflection coefficients of compact optical waveguide bends are presented.

Graded-index optical channel waveguides rare fabricated by diffusion of Ti in LiNbO₃. A model has been developed for calculating the mode profiles of the same, by first finding the effective refractive index profile along the lateral direction, and then discretizing the profile and applying the matrix method. This effective-index-based matrix method has been presented in this paper and established as a computationally fast, analytical method to computer modal electric field and intensity profiles in single and coupled graded-index channel waveguides. The method can be used in coupled systems consisting of three or more waveguides where the input power may be launched to any of the waveguides. Some of the computed intensity profiles have been compared with experimental data. Although computation and measurements have been performed only for TE and TM polarizations, the method has the inherent capability of handling arbitrary polarization.

A convenient, reliable and fast computation scheme for evaluating the carrier induced change in the optical propagation characteristics in semiconductor rib waveguide structures is presented. The modes of the unperturbed waveguide are computed by the Spectral Index Method while Perturbation analysis is used to evaluate the modal characteristic following barrier injection. Macroscopic carrier transport equations combined with appropriate approximations provide the basis for obtaining almost analytic solutions for the injected carrier profile. The modeled operational characteristics of injection current controlled deep ridge waveguide couplers are presented to illustrate the attractive features of this computational scheme.

The optical gain spectra of inhomogeneously distributed semiconductor Quantum dots embedded in a di-electric matrix has been examined theoretically using density matrix treatment. The expression for the threshold field required to obtain optical gain has been obtained. We have examined the role of excitons and biexcitons in gain mechanism and found that the gain arising due to excitonic nonlinearity enhances in presence of biexcitons. A detailed numerical analysis established strong dependence of optical gain on size distribution function and it is found that an increased size distribution width yields larger gain and increased gain band width. The nonlinear gain is also found to increase in a matrix possessing larger dielectric constant.

We have studied optical nutation and Stark splitting in a GaAs/AlGaAs quantum well with multi valence band structure using effective semiconductor Bloch equations. The individual roles of light and heavy holes in optical nutation have been examined. The analysis shows that both Rabi oscillation frequency and Stark splitting increase with rising electric field strength as observed experimentally. Also it is seen that light hole species dominates over heavy hole species in the transmission characteristics of quantum wells.

In this paper, the VOPc film was prepared on KBr substrate by OMBD. After that, it was treated in organic gas. The thickness of VOPc film was 96 nm. The morphologies of VOPc film before and after the gas treatment were characterized with optical absorption spectra and SEM image. The third- harmonic generation of VOPc film before and after the gas treatment were also measured by Maker fringe method using a Nd:YAG laser.

The effect of enhancing nonlinear generation of entangled photons in the process of interaction of the external coherent electromagnetic field with nonlinear dispersive medium is studied in this paper. Taking into account the second and third order of the susceptibility tensor of the crystal, it is demonstrated that in good cavity approximation the bistable behavior of the two photon generation coefficient as a function of intensity of the pump laser field is possible. This effect is stimulated by decreasing the detuning between the frequency of the cavity mode and pump frequency as a function of an harmonicity terms in polarization.

The cooperative two-photon spontaneous decay of an excited atomic system in a micro-cavity is investigated. We demonstrate that the presence of a small number of thermalized photons in the microcavity mode stimulate the cooperative generation rate of the coherent entangled photon pairs.

For photodiode bias-Ts in optoelectronic ICs > 20dB isolation is essential at 2.5-10 GHz for the photodiode to work at both 2.5 and 10 Gbit/s. Designed micro strip and suspended substrate GaAs bias-Ts show 30-140 dB isolation and measured values are approximately 30 dB in the 2.5-10 Ghz range.

Stable ultrashort pulses have applications in ultrafast laser spectroscopy, biology, medicine, and fiber optic communication. Fiber lasers are capable of producing femtosecond duration pulses at 1.55 micrometers . In the present paper we report our simulations on effect of higher order dispersion parameters on pulse generation and propagation in figure of eight laser.

Distributed feedback dye laser technique gives a small, compact design and reduces the duration of the output pulses significantly compared to that of the pump. In the represent paper, we report our theoretical simulations and experiments on laser action in Rhodamine 6G upon pumping with various input parameters.

A study of the performance of an Avalanche Photodiode (APD) at low bias using time-domain modeling has been conducted. Three important considerations in this range of bias voltages are: the emission of holes from the interface-trap at the valence-band discontinuity; the diffusion of photogenerated holes from the undepleted region of the absorption layer; and the velocity of carriers at low electric fields. A new recurrence relation has been obtained for the emission of holes from the valance-band trap. The time-delays due to the diffusion of holes photogenerated in the undepleted region of the absorption layer has been taken into account in computing the impulse response of the APD in time-domain. The effect of velocity of the carriers at low- bias has been considered by using a field-dependent formulation for velocity. The frequency response of the device has been obtained by using the fast Fourier Transform of the impulse response in time-domain. The result on the gain-bias and bandwidth-gain characteristics show good agreement with the published experimental data on InP/InGaAs APDs.

Si/Si_1-x-yGe_xC_y/Si quantum well heterostructures grown by UHVCVD have been characterized in terms of structural and optical properties. The Schottky barrier height (SBH) and ideality factor of PtSi/p-Si_1-x-yGe_xC_y/Si diodes have been investigated using the current-voltage characteristics. The valence band offsets of Si/Si_0.795Ge_0.2C_0.005 and Si/Si_0.79Ge_0.2C_0.01 have been extracted using the Schottky diode measurements. A lower value of SBH has been observed in the ternary alloy compared to those in fully strained-Si_1-xGe_x films indicating the potential of former for long wavelength IR detection.

Thin films of binary chalcogenide synthesized on quartz and silicon single crystal substrates by CW argon ion laser and pulsed third harmonic of Nd:YAG laser irradiation of separate sandwiched Ge/Se and Sn/Se films. The alloy formation and crystalline states are characterized by observing photomicrographs, scanning electron micrographs, optical absorption and reflection spectra. EDAX measurements manifest near stoichiometric proportion of Sn and Se.

The design, development and technological aspects of a fiber optic analog CATV receiver have been discussed vis-a-vis its conventional Silicon Hybrid counterpart. This provides an economical solution for the deployment of fiber optics in the trunk and feeder segments of the fiber based networks with superior characteristics and ease of compatibility with advanced multiplexed lightwave CATV and other futuristic systems based on digital transmission techniques.

In this work we propose a genetic algorithm for the design of reflective filters consisting of organic materials. The algorithm chooses the materials of the layers from the list of available materials and chooses their thickness in order to obtain optimal reflectance characteristics. The wavelength dependence of the refractive index and the coefficient of extinction of the layers is taken into account.

An efficient erbium doped fiber based superfluorescent source, which operates by reflection of the backward ASE in the forward direction, has been studied. Dependence of conversion efficiency on fiber length and amount of reflectance has been investigated. A simple reflecting device such as a Faraday rotating mirror can be used for this purpose so as to increase the conversion efficiency of the reflected forward ASE.

This paper presents the analysis of Erbium Doped Fiber Amplifier (EDFA) operated in the saturation regime for high output signal power. Results indicate that Er³⁺ doped silica fibers with higher numerical aperture and erbium ion concentration can be used as efficient, high gain power amplifiers in the 1.55micrometers region. It is also observed that the optimum fiber length in high power EDFA does not change appreciably with increasing pump power or signal power.

We present an analysis of fused fiber couplers by simultaneously considering the coupling of guided modes through the overlap of the evanescent fields in the weakly interacting 'taper transition' region as well as the beating of cladding modes in the strongly interaction 'taper waist' region. We have incorporated geometrical parameters to account for the 'degree of fusion' and the 'shape of taper', thus representing a realistic coupler structure. The results of our model are in very good agreement with the measured characteristics of coupler components fabricated in our laboratory.

Switching of bistable solitons in a recently proposed doubly and inhomogeneously doped fiber system is studied numerically. It is shown that both up-switching and down- switching of solitons between bistable states are realizable in the given model, if the amplification of the input soliton for up-switching and the extraction of energy from it for down-switching are suitably adjusted.

In this paper, we analyze and propose an exponentially modulated refractive index profile for large effective area fibers with non-zero dispersion characteristics. A linear finite element method is used for computing the modal propagation characteristics and modal field distributions of an optical fiber having an arbitrary refractive index profile. The core effective area and the dispersion characteristics are optimized by optimizing a constraint objective function in the profile parametric space. The optimum refractive index profile can give a core effective area of 110 micrometers ². The dispersion varies linearly from 2.5 ps/nm-km to 4.5 ps/nm-km with a dispersion slope of 0.065 ps/nm²-km over 1.53 micrometers -1.56 micrometers wavelength range. Manufacturing tolerance analysis for the designed fiber characteristics is also studied. The bending loss for the fiber is around 0.003 dB/m for a bend radius of 100mm.

We present the fabrication of long period fiber grating, in non-hydrogenated standard telecommunication fiber, using an electric discharge. We have obtained a gratin with low insertion loss, dynamic rejection of 37.5dB at 1530 nm and bandwidth of 16.3nm at -3 dB. The performances are competitive compared to literature. We have demonstrated the flexibility of the process by fabricating band pass and compact concatenated filters.

We present here the use of Berry's's topological phase for possible realization of fiber optic sensors and devices. Berry's phase is the phase change that can be effected on a light beam without changing the optical path length, but by changing the direction of propagation of light. This phase is not dependent on the material properties of the medium through which light is traveling and hence achromatic. A tunable reflectivity fiber loop mirror based on this phase is demonstrated.

The finite element method and the beam propagation method are demonstrated to be particularly suitable for precisely modeling the propagation into novel fibers such as transverse-Bragg-grating photonic-band-gap fibers or holey fibers. Modes patterns observed at the output end of each kind of fiber are described.

A method of determining the dielectric constant of slender cylindrical structures using an open resonator is presented. This method uses a perturbation analysis to determine the frequency shift due to the permits of the cylindrical structure and permits the measurement of very small, fiber- like, structures at a wavelength near 3 mm. The method is tested on glass optical fibers.

Cu₂O microcrystallites of the size range 55-73 angstrom were embedded in the nano-zirconia thin film matrix if precursor contains zirconium oxychloride octahydrate and cupric nitrate trihydrate. Absorption and fluorescence spectra of the films annealed at different temperature, 200 degrees-1200 degrees C revealed that the microcrystallites are possessing both mono- and biexcitonic behaviors which are dependent on microcrystallite size. Maximum biexcitonic behavior has been predicted in the case of 450 degrees annealed sample which also showed phosphorescence possibly due to inter-crossing of potential energy curve (Gamma) ₁⁺ of Cu₂O exciton and 3D of free Cu⁺. The anisotropic nature of the excitonic transitions of Cu₂O was also observed due to electrical quadrupole transition which was authenticated by its emission and ESR spectral studies.

A comparative study of the photorefractive response of some commonly used ferroelectric, nonferroelectric and semiconducting crystals is presented. The figure-of-merit parameters such as steady-state change in refractive index, response time and photorefractive sensitivity tare evaluated for crystals of BaTiO₃, LiBnO₃, BSO, GaAs and InP on the basis of Kukhtarev's theory, using input parameters form reported data. These parameters are calculated as a function of the grating period with and without an application of 10kV/cm electric field. The results indicate that the choice of the ideal material for a given application can be made only after a careful comparison of the figure-of-merit parameters as trade-offs exist among the various parameters for any material.

Spatial confinement of electrons in ultrathin layers of indirect gap Si, SiGe and SiGeC leads to a spread in the momentum of electrons, so that the envelope function of electrons possesses a sizeable Fourier component at k₀, the wave vector for conduction band minima in the materials. Under this situation, the matrix elements for interband transition may be appreciably enhanced. In this work, the matrix elements for quasi-direct non phonon transitions have been evaluated for Si quantum wells, coupled Si/SiGe quantum wells and SiGeC/Si quantum wells. The absorption coefficient, (alpha) , for all these cases, are then calculated to examine the potential of the structures as emitters. The values of (alpha) are enhanced in quantum wells; however to achieve values of (alpha) , as large as in direct gap GaAs, quantum dots need be considered.

We have investigated a Fabry-Perot filter and a nonlinear fiber loop mirror (NFLM) for their suitability as photonic switching devices. In the light of new information available on chalcogenide glasses with respect to their nonlinear optical coefficients and attenuation levels, we have found from our analysis that fibers made of these doped glasses hold a lot of promise. The advantage is seen to be more in the case of FP filters than in NFLM, which is rather due to the fact that some of these glass compositions have very high losses at (Lambda) equals 1.55 micrometers . We have made a comparison between the use of Silica glass and Chalcogenide glass as the switching medium. We have also studied the effect of reducing the losses in Chalcogenide glass fibers.

A method for measurement of refractive index profile of a GRIN system is developed based on a longitudinal interferometer using a birefringent lens. The fringe pattern so generated is made to traverse through the sample under test. The modification of the fringes gives a measure of the refractive index profile. The fringe patterns both in presence and absence of the test samples are grabbed by a CCD camera and further processed by a computer. The basic software required for the same is being developed. Some experimental results are presented.

An integrated software package is built-up for simulation studies of optical fibers and fiber optic sensors. The FOSenSim is a user interactive menu driven software package developed as a central simulation tool for optical fibers and FO sensors. This package incorporates simulation modules for study of optical fiber based on wave theory and various FO sensors based on ray optics and analytical geometry. The detailed mathematical models are developed for liquid level detector, through beam and reflection type displacement sensor, and refractive index sensor. The simulant results are used as a feedback for sensor design and fabrication process. At present, FOSenSim supports these sensors. However, due to modularity in software programming, it can be easily upgraded to incorporate other FO sensors.

This paper describes the design, development and characterization of dual wavelength, phase modulated device in near IR region which can be used for real time monitoring of oxy- and deoxy-hemoglobin. The device measures amplitude and phase which can be employed in the diffusion equation for a homogeneous semi-infinite medium to obtain the concentration of oxy- and deoxy-hemoglobin of the sample.

A fiber optic strain sensor based on interference between LP₀₁-LP₀₂ modes of a circularly symmetric few mode fiber has been studied. Differential phase shift between the two modes is measured as a function of strain in the fiber with and without coating. A simple theoretical model to estimate the differential phase shift due to strain is also developed, the prediction of which matches well with the experimental results.

We examine now the p0owers coupled to LP₀₁ and LP₀₂ modes in a few mode optical fiber from axially aligned single mode fiber vary with fiber parameters. The study shows that by selecting the fiber parameters approximately it is possible to excite either only the LP₀₁ mode or both the modes with equal powers. The study should find applications in the design of recently demonstrated few mode fiber sensors.

The use of low coherence broad band optical source in Mach- Zehnder type optical fiber interferometric sensor is presented. The cross-sensitivity effect has been studied for simultaneous measurement of temperature strain. The DFTS technique has been used to retrieve the phase modulation from the interferogram.

In the work we consider certain optical properties of bio- membrane due to dichroism of polypeptides associated with membrane structures, shifting of polarization due to (pi) - electron transitions in the peptide groups and photo-induced changes in channels through which solute molecules pass. In respect of these optical characteristics, we have designed an optical fiber extrinsic sensor for measurement of permeability, particularly the Na and K diffusion through bio-membrane, based on the principle of attenuation of laser beam due to change in refractive index gradient of a liquid, induced by the variation of concentration gradient across the membrane.

A low-coherence Linnik interference microscope using high numerical aperture optics has been constructed. The system uses a tungsten halogen lamp and a Koehler illumination, with separate control over field and aperture stops, so that experiments can be conducted with a range of different geometric phase which is achieved by using a polarizing beam splitter, a quarter wave plate and a rotating polarizer. Image information is extracted from the visibility of the fringes, and the position of the visibility peak along the scanning axis, yielding the height of the test surface at the corresponding points.

In this paper a derivative spectrometer, utilizing an FFP tunable filter for the wavelength shift detection and an electronic device for the signal processing, was realized and tested for data acquisition and elaboration from a fiber-Bragg-grating strain sensor system for automotive applications. The result of measurements carried out both under static and dynamic conditions have been compared with those performed with a strain gauge.

This paper introduces optical fiber based a novel high speed sensing technique to measure angular displacement as well as slope of a smooth object. The scheme is based on the analysis of the directional intensity distribution of the reflected and scattered electromagnetic wave from the object. Theoretical predictions supported by the experimentally verified results are presented. A fairly good accuracy in the angular displacement and slope measurement in the range of 10^-1 radians to 10^-6 radians can be achieved by this proposed technique.

The design and fabrication of a fiber optic pH sensor working on the basis of evanescent wave absorption is presented. A pH sensitive dye is immobilized on the uncladed portion of the optic fiber by sol-gel route. The sensitivity of the device is found to increase when multiple sol-gel coatings are used as the cladding in the sensing region. The sensor response and its dynamic range are reported for two pH indicator dyes, viz. bromocresol purple and bromocresol green.

The design and fabrication of a fiber optic pH sensor working on the basis of evanescent wave absorption is presented. A pH sensitive dye is immobilized on the uncladded portion of the optic fiber by sol-gel route. The sensitivity of the device is found to increase when multiple sol-gel coatings are used as the cladding in the sensing region. The sensor response and its dynamic range are reported for two pH indicator dyes, vis. bromocresol purple and bromocresol green.

An optical matrix-vector multiplier has ben efficiently used for photonic implementation of Hopfield network model, which is used for binary pattern recognition. Training matrices are recorded on electrically addressed spatial light modulator, where each matrix is composed of the same row of each pattern, that the network is being trained with. After training, if an unknown pattern is presented to the network in the form of a vector, the output vector is obtained by the element that has the highest magnitude through a winner- take-all algorithm. Pattern can be recognized even if the input is noisy and distorted.

Recent advancement in the technology in integrated circuit fabrication and new smart sensors allow us to implement adaptive optics systems which is otherwise not possible to implement a few years back with limited resources or for those projects where cost factor is an important one. Our first aim is to understand the technologies of adaptive optics by experimenting with low cost adaptive optics components and implement a wavefront sensor to measure the aberrations in an optical telescope and mirror surface testing in an optical fabrication shop. The second aim is to design a low cost adaptive optics system for image quality improvement using tip-tilt and deformable mirrors. We describe our work to achieve this goal.

Some types of rough alignment system for pre-alignment of precise alignment is proposed. One is a system using wide pitch gratings, with narrow pitch gratings for precise alignment. The other is a system using only narrow pitch gratings with small slit number, which is simple in construction. The operations are discussed on the basis of the results of computer simulation.

A finite element-based beam propagation approach has been used for the design of a 4 by 4 multimode interference-based device on InP, for wavelength division multiplexing applications, using straight arrayed waveguide gratings with variable width difference.