A. Bandyopadhyay

Bio: A. Bandyopadhyay is an academic researcher from University of Calcutta. The author has contributed to research in topics: Power dividers and directional couplers & Quantum well. The author has an hindex of 2, co-authored 3 publications receiving 13 citations.

Modeling of excitonic electrorefraction in InGaAsP multiple quantum wells

Abstract: The absorption spectra in an InGaAsP/InP multiple quantum well for different values of electric field, applied perpendicularly to the quantum well layer planes, are delineated by modifying the model given by P.J. Stevens et al. (IEEE J. Quantum Electron., vol.24, pp.2007-2015, 1988). The essential deviations in the present model lie in the inclusion of the additional broadening of excitons due to composition fluctuation in the quaternary, the forbidden transition between the second heavy hole subband and the first conduction subband, an improved excitonic envelope function dependent on both the in-plane and transverse separation of electrons and holes, and a modified calculation of oscillator strength. The modeled curve's are then used to calculate the values of Delta n, the change in refractive index due to field, and the ratio Delta n/ Delta k, where Delta k is the extinction coefficient, using Kramers-Kronig relations. The calculated values are found to agree with the experimental data for 1.537 mu m. >

Low-voltage vertical directional coupler switch with suppressed electroabsorption

Abstract: We have studied the performance of a vertical directional coupler in which a multiple quantum well and a bulk semiconductor material act as the cores of the two guides in two arms. The power output of the device is expected to be unaffected by the electroabsorption effect in a directional coupler based on quantum confined Stark effect even when operated very close to the excitonic absorption edge. The above principle is utilized in realizing low-voltage switching and almost equal power in bar and cross states in a multiple-quantum-well (MQW) vertical directional coupler. Our calculation for a vertical coupler composed of InGaAsP bulk and InGaAsP-InP MQWs show switching voltages comparable to that of a similar coupler composed of a more complex barrier reservoir and quantum well electron transfer (BRAQWET) structure, with a slightly lower value of power output.

A new variational method of incorporating loss in the analysis of coupled multiple-quantum well three-dimensional waveguides

Abstract: We have developed a simple method of calculating the imaginary part of the propagation constant in a lossy waveguide that closely follows the effective-index method of finding the real propagation constant of a rectangular dielectric guide. The method gives values much in agreement with the exact values obtained by the circular-harmonics method. The method has been used in the improved coupled-mode analysis of coupled-multiple-quantum-well waveguides developed by Tsang and Chuang. Three different configurations of coupled waveguides have been considered: slab, buried-channel, and strip-loaded waveguide directional couplers, where excitonic electrorefraction in multiquantum wells has been utilized to accomplish the switching. The output power-electric field curves calculated by using the above method agree closely in all three cases with similar curves obtained by using a complex propagation constant calculated by a numerical two-dimensional root-searching technique. The present method simplifies the design and optimization of coupled-waveguide devices and its application is illustrated in the case of multiple-quantum-well directional couplers. >

Comparison of effective /spl alpha/ parameters for multiquantum-well electroabsorption modulators

Abstract: A new effective /spl alpha/ parameter appropriate for evaluating the transmission performance of multiquantum-well electroabsorption (MQW-EA) modulators is proposed. It is defined by the ratio of the phase change to the loss change between the ON voltage and the voltage at which the exciton peak reaches the wavelength of the light source. Simulation reveals that along various effective /spl alpha/ parameters it has the best correlation with the equivalent /spl alpha/ parameter obtained from the transmission performance. >

Performance prediction of an electroabsorption modulator at 1550 nm using GeSn/SiGeSn Quantum Well structure

Abstract: The absorption spectra in strain-free Ge 0.992 Sn 0.008 /Si 0.3 Ge 0.61 Sn 0.09 Quantum Well structure due to direct gap excitons formed in Ge 0.992 Sn 0.008 wells reported by Chang and Chang are reproduced by an empirical expression. Two Gaussian distributions for heavy hole and light hole excitons and two exponential functions describing continuum transitions and The Sommerfeld factors are used for the fit. The expressions are then used to obtain the change in refractive index, Δ n , with field (electrorefraction) using the Kramers–Kronig relation. With the calculated changes in absorption and refraction with bias, other performance parameters of an Electro-Absorption Modulator (EAM), like extinction ratio, chirp parameter, and a figure of merit (FoM) defined as the ratio of extinction coefficient and insertion loss, are evaluated. The FoM takes the largest value for 1 μm length of the EAM with 2 V bias applied to the p–i–n structure. The parameters are also calculated for different wavelengths as well as detuning lengths. For applications as short pulse generation the transmission T as a function of bias V should be linear. We have evaluated the best value of bias voltage that makes the sum of second and third derivatives of T with V equal to zero so that the variation of T with V becomes maximally linear for optimum operation as a short pulse generator.

Coupler-multiplexer permutation switch

Abstract: A coupler-multiplexer permutation switch (CMPS) integrates multiplexng and switching functions on a single substrate. It has a single-mode/multi-mode backward coupler followed by a digital optical switch (DOS). In the CMPS, the single-mode waveguide channels are phase-matched through a grating with the corresponding, backward-propagating modes of a multi-mode waveguide. The different modes are subsequently separated in a digital optical switch. Different permutations are obtained by electronically controlling an effective-index distribution of DOS output waveguides.

Ge/Si photodetectors and group IV alloy based photodetector materials

Abstract: Photodetecctors using Si, Ge and other group IV alloys are of current interest for use at telecommunication wavelength 1550 nm We have presented in this paper our work on resonant cavity enhanced (RCE) Si/SiGe multiple Quantum Well (MQW) and Ge Schottky photodetectors Tensile strained Ge layers grown with suitable barriers show direct gap type I band alignment Predicted performance of photodetectors using strong Quantum Confined Stark Effect and Franz-Keldysh effects in these structures and properties related to photodetection using these new materials are also described

Integrated Inp Photonic Switches

Abstract: Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been