The acousto-optically tuned devices are becoming quite popular in dense wavelength division multiplexing (DWDM)
applications due to low insertion loss, less cross talk and freedom from the grating wavelength drift due to thermal
variations. Acousto-optic cell diffracts the optical beam depending on the wavelengths and acoustic frequency. This
property is used to exploit acousto-optic cell array (AOCA) for multiplex/demultiplex (MUX/DEMUX) and cross-connect
applications in DWDM in optical communication. Acousto-optic diffraction grating is preferred over other
systems as the directions of the deflected light beams can be controlled by changing the frequency of the drive signal and
the light intensity of the beams can be adjusted by changing the power of the drive signal. This paper presents the
analysis and performance of three-dimensional acousto-optic cell array system based on generalized equations.
Numerical results have been obtained for optical wavelengths vs deflection angles, incident angles vs deflection angles
in different directions for several stages. The wavelengths under consideration range between 1500-1600 nm and the
effects of acoustic wave velocity variations have also been considered.
The interaction of a fiber Bragg grating point like soliton with local defects has been thoroughly analyzed. The stability
of trapped solitons has also been discussed. The main finding reveals the reversal of the sign of interaction from
attraction to repulsion. It is also observed that the attraction depends on the accuracy of the numerical simulations.
Two dimensional multistage AOCA system based on generalized equations has been analyzed. Numerical results for
Bragg angle as a function of acoustic frequency, deflection angles for different wavelengths, normalized power and
diffraction efficiency with and without phase shift between consecutive arrays having different channel spacing based on
generalized equations have been obtained.
One of the most promising devices for high speed optical signal processing is the Nonlinear Directional Coupler (NLDC). In this paper an asymmetric nonlinear directional coupler controlled by an external laser beam focused on the surface of the coupler has been analyzed. The analysis is based on couple-mode theory using rigorous perturbation technique and enables one to obtain asymptotically correct coupled-mode equations. The effects of various parameters such as plasma density, waveguide width, laser beam frequency and laser spot position on the coupling of power have been investigated and presented.
An optical switch based on micro electro mechanical systems (MEMS) technology has been analyzed and designed. In the proposed switch the collimating lenses as commonly used in MEMS switches have been eliminated thus making the switch smaller in size. The switch characteristics based on theoretical analysis and experimental results have been compared.
Current optical networks mainly serve very high data rates and long distances while short reach communication and low data rates is dominated by electrical interconnects. In this work, we examine and evaluate optical backplane technology based on substrate guided interconnects.
The information capacity of dense wavelength division multiplexing (DWDM) optical systems is reviewed. The effect of optical beat interference of closely spaced optical carriers sets the limit on the allowed channel spacing even in the absence of nonlinear effects. Present DWDM networks operating at 10.7 Gb/s in the C and L bands region have channel spacing no less than 25 GHz. We show that this limit is a constraint and smaller spacing may not be allowed without further optical and electrical pulse shaping.
A two dimensional acousto-optic cell array (AOCA) to be used as an optical MUX/DEMUX in DWDM systems has been analyzed. The diffraction efficiency, deflection angle and RF frequency required for the system have been determined.
Polarization-mode-dispersion (PMD) tolerance of a duobinary modulation format is investigated. With the use of 2.5 Gb/s Mack Zehnder modulator for modulation and optical pulse shaping of a 64 channels (10.7 Gb/s) dense wavelength division multiplexing metro networks, the electrical filter needed in conventional duobinary is no longer needed. The proposed method cut down in the complexity and cost of the duobinary transceiver. This technique allows the use of 10 Gb/s MZ modulator for 40 Gb/s duobinary transmission. We also used electronic compensation to adaptively compensate for PMD/GVD.
The possible improvement in the performance of networks without electro/optical conversion has been investigated by introducing optical memories. In particular, different buffering methods are presented, where optical signal is stored in the memory blocks. The need to process signals at electrical level limits the performance of transmission links or computing systems. This limit can be overcome through the introduction of all optical processing, thus avoiding the electro/optical conversion.
A computerized optical fiber variable pressure sensing system has been developed. The approach is based on the birefringence effect on a single mode fiber and uses a computer data collection system with 486 DX PC computer, a DAS 1600 A/D converter, linear amplifier and the GUI software for graphic processing. The system works very well over a wide temperature range from -50°C to 150°C.
An approach for modeling the saturated single-pass gain in an Ytterbium doped fiber amplifier has been proposed. This approach accounts for both two- and three-level schemes, as well as coupled spectral and power effects. A simple approximation considering an average value of depleted pump power over the fiber length allows to obtain analytic expressions for input and output pump, amplified spontaneous emission (ASE) and signal power in the fiber.
A unique graduate program in optical engineering by combining optical and microwave courses has been developed in the University of Nevada, Reno. The advantage of such a hybrid program is better job opportunities in a tight job market as these students are suitable for both RF/microwaves and Optical industries.
A Digital Scan Converter (DISC) has been developed which accepts input from a non-standard IR camera configured around 2nd Generation 288 X 4 element linear MCT-FPA and generates CCIR-B signal. The open-ended architecture of DISC allows it to be used with minor modifications for any other non-standard IR/visible cameras. The input for DISC is 288 X 576 pixels frame data available as two channels of 8 bit digital data (compensated for CDS and NUC) at 10 MSPS; the frame update rate being 25 Hz. The DISC architecture is based on Ping-Pong concept wherein input frame data gets written on one set of SRAMs and data for display read at CCIR-B rate from another set of SRAMs. The design takes care of camera specific signal processing requirement such as (1) providing delays between odd and even pixel data which arises due to staggered configuration of the detector. (2) Sequencing of pixels in vertical columns from a pseudo random sequence which arises due to off-focal plane multiplexing of detector outputs. (3) Interpolation of image in elevation. The CCIR-B sync generation is implemented using PLDs. Provision for symbology/RS422 interface is kept in design. Parallel and pipelined processing makes the DISC suitable for real time implementation of image processing algorithms. Entire design hardware has also been implemented using XILINX FPGA.
The analysis of an efficient, low-loss curved
single mode optical fiber coupler has been presented.
Numerical results for coupling coefficients, effective
interactive length and normalized power as a function of
minimum spacing, wavelength and offset have been obtained. The coupling effects due to vertkal offset of the
fibers have also been determined. This provides an
additional design flexibility for the coupler.
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