Papers by Bijoy Krishna Das
Springer Proceedings in Physics, 2019
Single-mode silicon p-in waveguides with varying cross-sections have been studied experimentally ... more Single-mode silicon p-in waveguides with varying cross-sections have been studied experimentally for on-chip photodetection at an operating wavelength k * 1550 nm. It has been shown that the quantum efficiency increases with decreasing waveguide cross-section. The performance of such a photodetector can be modelled in terms of density of surface states, bulk two photon absorption coefficient , and waveguide loss parameters.
2018 3rd International Conference on Microwave and Photonics (ICMAP), 2018
Polarization dependent plasma dispersion effect is investigated for single-mode SOI waveguides (λ... more Polarization dependent plasma dispersion effect is investigated for single-mode SOI waveguides (λ ∼ 1550 nm) with laterally diffused p-n junction. The lateral p-n junction of desired length is formed initially in 1.5 μm thick SOI layer (BOX-2 μm) by diffusion doping and then the single-mode waveguides with appropriate design parameters (width W, height H, and slab height h) is defined along the junction for simulations studies to estimate Vπ and Lπ. It is observed that the device becomes more and more polarization sensitive as the device layer thickness (H) decreases, which is justified appropriately by calculating polarization dependent confinement factors as well as free carrier overlaps with the corresponding guided modes.
This paper reports a novel design of compact tunable resonance filter with a highly extinguished ... more This paper reports a novel design of compact tunable resonance filter with a highly extinguished and ultra-broad out-of-band rejection in CMOS compatible silicon photonics technology platform. The proposed device is designed with two identically apodized distributed grating structures for guided Fabry-Pérot resonant transmissions in a silicon on insulator rib waveguide structure. The device design parameters are optimized by theoretical simulation for a low insertion loss singly-resonant transmission peak at a desired wavelength. However, devices were fabricated (using in-house facilities) to demonstrate multiple resonant transmission peaks along with a singly-resonant one. We observed that a device length of as low as ∼35 𝜇m exhibits a rejection band as large as ∼60 nm with an extinction of ∼40 dB with respect to the resonant wavelength peak at 𝜆𝑟∼1550 nm (FWHM ∼80 pm, IL∼2 dB). The experimental results have been shown to be closely matching to our theoretical simulation and modell...
This paper presents an integrated optical signal processor (OSP) design using CMOS-compatible sil... more This paper presents an integrated optical signal processor (OSP) design using CMOS-compatible silicon photonics technology, offering a tunable RF bandpass filter (5G/6G frequency range) with a programmable bandwidth and symmetric out-of-band rejection. The OSP is comprised of two identical microring resonators cascaded with a common bus waveguide, in 220 nm silicon-on-insulator substrate. The ring resonators are designed with low-loss rib waveguide structures (supporting fundamental and first-order TE-like modes) to ensure relatively lower propagation losses and to obtain high-Q resonances. The single-mode bus waveguide is designed to facilitate the desired range of coupling strengths via thermo-optic tuning. Four thermo-optic phase shifters are integrated to tune the resonant wavelengths and the Q-values of the individual microring resonators. The four phase shifters could be programmed to obtain desired optical filter characteristics of the fabricated OSP chip. The RF filter exper...
Optical Fiber Communication Conference, 2017
A filter device with a flat-top passband of Δλ<inf>pb</inf> > 40 nm is demonstrate... more A filter device with a flat-top passband of Δλ<inf>pb</inf> > 40 nm is demonstrated using multi-mode SOI waveguide with a side-wall grating. The passband is bounded by highly extinguished sidebands of Δλ<inf>sb</inf> > 10 nm.
Silicon Photonics VIII, 2013
Polarization dependencies and dispersions are the two major bottlenecks in waveguide based silico... more Polarization dependencies and dispersions are the two major bottlenecks in waveguide based silicon photonic devices for various applications-especially in DWDM systems. In this paper, we present the design and experimental demonstration of a 2×2 integrated optical MZI that shows both polarization-independent and dispersion-free response over a wide wavelength range (C+L optical band) in SOI platform-for the first time to our knowledge. The entire device footprint (W×L) is ~ 0.8 mm × 5.2 mm; which is comprised of optimally designed single-mode waveguides (for input/output and interferometer arms) and a pair of MMI based 3-dB power splitters. To monitor the wavelength dependent performance, unbalanced arm lengths (L ~ 3037 µm, L+ΔL ~ 3450 µm) were introduced to construct the MZI. The differential arm length (ΔL ~ 412 µm) has been specifically chosen to provide alternate ITU channel transmission peaks at both the output ports alternatively. Accordingly, the fabricated device separates 100 GHz DWDM channel wavelengths alternatively into two output ports and is nearly insensitive to the polarization of the guided light. We have observed a uniform channel extinction of ~ 10 dB (~ 6 dB) at both ports with a 3-dB bandwidth of ~ 110 GHz (~120 GHz) for TM (TE) polarization over the wavelength range of 1520 nm to 1600 nm. The lower extinction for TE polarization is due to its relatively higher bending loss in the longer arm of the MZI. This can be adjusted by introducing identical bends in both the arms.
Bistability in silicon microring resonator is electrically controlled for maximizing gain in four... more Bistability in silicon microring resonator is electrically controlled for maximizing gain in four wave mixing. The proposed technique can be used in designing actively controlled efficient photon sources for quantum photonic chips operating at λ~1550nm. © 2020 The Author(s)
Springer Proceedings in Physics
Conference on Lasers and Electro-Optics
A single-stage distributed Bragg filter in silicon waveguide has been demonstrated with a rejecti... more A single-stage distributed Bragg filter in silicon waveguide has been demonstrated with a rejection bandwidth of 7-nm and ultra-high extinction of ∼ 55-dB; suitable towards silicon quantum photonic chip operating at λ ∼ 1.55 μm for on-chip pump rejection.
, for the award of the degree of Master of Science, is a bona fide record of the research work do... more , for the award of the degree of Master of Science, is a bona fide record of the research work done by him under my supervision. The contents of this thesis, in full or in parts, have not been submitted to any other Institute or University for the award of any degree or diploma.
The combined mathematical representation of Gauss’ laws of electricity and magnetism, Ampere’s ci... more The combined mathematical representation of Gauss’ laws of electricity and magnetism, Ampere’s circuital law, and Faraday’s law is known as ”Maxwell’s Equations”. It is one of the important milestones in the human history and was championed by the great Scottish Scientist James Clerk Maxwell in 19th Century (1860 -1871). In this note, we will quickly discuss about the important terms used in Maxwell’s Equations, their role in understanding electromagnetism and its versatile applications.
Bistability in silicon microring resonator is electrically controlled for maximizing gain in four... more Bistability in silicon microring resonator is electrically controlled for maximizing gain in four wave mixing. The proposed technique can be used in designing actively controlled efficient photon sources for quantum photonic chips operating at λ~1550nm. © 2020 The Author(s)
OSA Continuum
A detailed theoretical and experimental study of metal-microheater integrated silicon waveguide p... more A detailed theoretical and experimental study of metal-microheater integrated silicon waveguide phase-shifters has been carried out. It has been shown that the effective thermal conductance gw and the effective heat capacitance hw evaluated per unit length of the waveguide are two useful parameters contributing to the overall performance of a thermo-optic phase-shifter. Calculated values of temperature sensitivity, SH = 1/gw and thermal response time, τth = hw/gw of the phase-shifter are found to be consistent with the experimental results. Thus, a new parameter ℱH = SH/τth = 1/hw has been introduced to capture the overall figure of merit of a thermo-optic phase-shifter. A folded waveguide phase-shifter design integrated in one of the arms of a balanced MZI switch is shown to be superior to that of a straight waveguide phase-shifter of the same waveguide cross-sectional geometry. The MZI switches were designed to operate in TE-polarization over a broad wavelength range (λ ∼ 1550 nm).
13th International Conference on Fiber Optics and Photonics, 2016
IEEE Journal of Selected Topics in Quantum Electronics, 2017
It is shown that the dispersion in transmission characteristics of a ring resonator designed with... more It is shown that the dispersion in transmission characteristics of a ring resonator designed with silicon-on-insulator waveguides in all-pass configuration can be enhanced significantly by increasing interaction length of the directional coupler. This in turn helps to single-out highly extinct resonance(s) at and around the critically coupled wavelength. Such a device is found to be useful for a wide range of refractive index sensing for the cladding materials/analytes (1.0 <; nc ≤ 2.0). As a proof of concept, the sensor devices were fabricated and characterization results are shown to be consistent with theoretical prediction. The fabricated devices have been also used successfully to determine unknown refractive index of a given analyte (Newport F-IMF-150) with an error limit of δn ~ 1.67 × 10-2 RIU. Analyzing experimental results, it is shown that the limit of detection can be further reduced (≪10-3 RIU), if the perimeter of the ring is increased without compromising the round-trip waveguide loss. The superiority of such a sensor device lies in its simpler design rule, easier operation, wider range, and nearly accurate detection mechanism.
IEEE Journal of Selected Topics in Quantum Electronics
Resonance shift and bistability in a silicon microring resonator operating at higher optical powe... more Resonance shift and bistability in a silicon microring resonator operating at higher optical power levels pose serious difficulties, especially in nonlinear four wave mixing process. A solution of parking a laser wavelength around any of the resonances of a microring resonator and operating at any power levels is explored by integrating a microheater. We have shown with the existing theoretical model that the previous history of phase detuning in a silicon microring resonator determines the effective gain in stimulated four wave mixing process. The experimental results have been shown to be closely matching with the simulation results. For a microring resonator of radius 50 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m, an improved stimulated four wave mixing gain of <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 11.6 dB has been observed while thermo-optically blue-shifting resonances in comparison to that of red-shifting resonances, for a launched pump power of 8.4 mW operating at a slightly off-resonant wavelength <inline-formula><tex-math notation="LaTeX">$\lambda _p$</tex-math></inline-formula>. The proposed technique can be used in designing actively controlled efficient photon sources in a large-scale integrated quantum photonic circuit operating at <inline-formula><tex-math notation="LaTeX">$\lambda \sim$</tex-math></inline-formula> 1550 nm.
IEEE Journal of Selected Topics in Quantum Electronics
An ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pa... more An ultrabroadband add-drop filter/switch circuit is designed and demonstrated by integrating a pair of subwavelength grating waveguides in a <inline-formula><tex-math notation="LaTeX">$2\times 2$</tex-math></inline-formula> Mach–Zehnder interferometer configuration using silicon photonics technology. The subwavelength grating is designed such that its stopband and passband are distinguished by a band-edge wavelength <inline-formula> <tex-math notation="LaTeX">$\lambda _{\text{edge}} \sim$</tex-math></inline-formula> 1565 nm, separating <italic>C </italic> and <italic>L</italic> bands. The stopband (<inline-formula><tex-math notation="LaTeX">$\lambda < \lambda _{\text{edge}}$</tex-math></inline-formula>) is filtered at the drop port of the device, whereas the passband ( <inline-formula><tex-math notation="LaTeX">$\lambda >\lambda _{\text{edge}}$</tex-math></inline-formula>) is extracted either in cross port or in bar port. The device is designed to operate only in TE polarization. Experimental results exhibit a nearly flat-top band exceeding 40 nm for both stopband and passband. The stopband extinction at cross- and bar ports are measured to be <inline-formula><tex-math notation="LaTeX">$>$</tex-math></inline-formula> 35 dB with a band-edge roll-off exceeding 70 dB/nm. Wavelength independent directional coupler design and integrated optical microheaters at different locations of the Mach–Zehnder arms for thermo-optic phase detuning are the key for stopband filtering at the drop port and switching of passband between cross- and bar ports with flat top response. Though the insertion loss of fabricated subwavelength grating waveguides are negligibly small, the observed passband insertion loss is <inline-formula><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 2 dB, which is mainly due to the combined excess loss of two directional couplers. Experimental results also reveal that the passband switching between cross- and bar ports of the device has been possible with an extinction of <inline-formula><tex-math notation="LaTeX">$>$</tex-math></inline-formula>15 dB by an electrical power consumption of <inline-formula><tex-math notation="LaTeX">$P_\pi \sim$</tex-math></inline-formula> 54 mW. A switching time of 5 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s is estimated by analyzing the transient response of the device. The passband edge could also be detuned thermo-optically at a rate of 22 pm/mW.
IEEE Photonics Technology Letters
An integrated optical apodized sub-wavelength grating waveguide is designed and demonstrated exhi... more An integrated optical apodized sub-wavelength grating waveguide is designed and demonstrated exhibiting high-extinction edge-filter characteristics with a linear roll-off in the dB scale. For a given waveguide cross-sectional geometry with fixed grating duty cycle and period, it has been shown that the apodized device length <inline-formula> <tex-math notation="LaTeX">$L_{g}$ </tex-math></inline-formula> and width <inline-formula> <tex-math notation="LaTeX">$W_{m}$ </tex-math></inline-formula> are the two important parameters deciding the band-edge position, roll-off and broadband extinction around the Bragg wavelength. The experimental results from fabricated devices (<inline-formula> <tex-math notation="LaTeX">$L_{g} = 70\,\,\mu \text{m}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$W_{m} = 2.5\,\,\mu \text{m}$ </tex-math></inline-formula>) in silicon-on-insulator substrates (device layer ~ 220 nm and buried oxide layer <inline-formula> <tex-math notation="LaTeX">$\sim ~2~\mu \text{m}$ </tex-math></inline-formula>) show a smooth band-edge roll-off of > 3.5 dB/nm (<inline-formula> <tex-math notation="LaTeX">$\lambda _{edge} \sim ~1550$ </tex-math></inline-formula> nm) with a stopband (<inline-formula> <tex-math notation="LaTeX">$\Delta \lambda _{sb}>50$ </tex-math></inline-formula> nm) extinction of > 40 dB and a nearly flat-top passband (<inline-formula> <tex-math notation="LaTeX">$\Delta \lambda _{pb}>100$ </tex-math></inline-formula> nm) with negligible insertion loss of ~ 0.5 dB.
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Papers by Bijoy Krishna Das