arXiv subjects

Shankar Kumar Selvaraja

Publications and source records attributed to Shankar Kumar Selvaraja.

At least 19 recordsLinked to original sources

arXiv2024

Purcell Enhancement of Spontaneous Emission of a Quantum Emitter on a Waveguide

We investigate the effect of a waveguide on an emitter spontaneous emission in its vicinity. The impact of various possible orientations of an emitter with respect to the waveguide surface is studied through simulations and compared with experimental demonstration. Quantum emitters are dip coated on waveguides and Purcell enhancement and a decrease in the lifetime of the emitter are observed. This study serves as a proof of concept for the Purcell effect offered by waveguides and helps ineffectively estimate the efficiency of waveguide-based evanescent sensors and quantum photonic applications

physics.optics↗

arXiv2023

Highly Oriented PZT Platform for Polarization-Independent Photonic Integrated Circuit and Enhanced Efficiency Electro-Optic Modulation

We demonstrate, for the first time, sputtered PZT as a platform for the development of Si-based photonic devices such as rings, MZI, and electro-optic modulators. We report the optimization of PZT on MgO(002) substrate to obtain highly oriented PZT film oriented towards the (100) plane with a surface roughness of 2 nm. Si gratings were simulated for TE and TM mode with an efficiency of -2.2 dB/coupler -3 dB/coupler respectively with a polarization insensitive efficiency of 50% for both TE and TM mode. Si grating with an efficiency of around -10 dB/coupler and a 6 dB bandwidth of 30 nm was fabricated. DC Electro-optic characterization for MZI yielded a spectrum shift of 71 pm/V at the c-band.

physics.optics↗

arXiv2023

3-D poling and drive mechanism for high-speed PZT-on-SOI Electro-Optic modulator using remote Pt buffered growth

In this work, we have demonstrated a novel method to increase the electro-optic interaction in an intensity modulator at the C-band by optimizing the growth methodology of PZT with the metal (Ti/Pt) as a base material and the PZT poling architecture. Here, we have used a patterned Pt layer for PZT deposition instead of a buffer layer. By optimizing the PZT growth process, we have been able to do poling of the fabricated PZT film in an arbitrary direction as well as have achieved an enhanced electro-optic interaction, leading to a DC spectrum shift of 304 pm/V and a Vπ Lπ value of 0.6 V-cm on a Si-based MZI. For an electro-optic modulator, we are reporting the best values of DC spectrum shift and Vπ Lπ using perovskite as an active material. The high-speed measurement has yielded a tool-limited bandwidth of > 12GHz. The extrapolated bandwidth calculated using the slope of the modulation depth is 45 GHz. We also show via simulation an optimized gap of 4.5 μm and a PZT thickness of 1 μm that gives us a less than 1 V-dB.

physics.optics↗

arXiv2023

DFT analysis and demonstration of enhanced clamped Electro-Optic tensor by strain engineering in PZT

We report $\approx$400\% enhancement in PZT Pockels coefficient on DFT simulation of lattice strain due to phonon mode softening.The simulation showed a relation between the rumpling and the Pockels coefficient divergence that happens at -8\% and 25\% strain developed in PZT film.The simulation was verified experimentally by RF sputter deposited PZT film on Pt/SiO$_2$/Si layer.The strain developed in PZT varied from -0.04\% for film annealed at 530\degree C to -0.21\% for 600\degree C annealing temperature.The strain was insensitive to RF power with a value of -0.13\% for power varying between 70-130 W. Pockels coefficient enhancement was experimentally confirmed by Si Mach Zehnder interferometer loaded with PZT and probed with the co-planar electrode.An enhancement of $\approx$300\% in Pockels coefficient was observed from 2-8 pm/V with strain increasing from -0.04\% to -0.21\%. To the best of our knowledge, this is the first time study and demonstration of strain engineering on Pockels coefficient of PZT using DFT simulation, film deposition, and photonic device fabrication.

physics.optics↗

arXiv2023

Polarization Independent Grating in GaN-on-Sapphire Photonic Integrated Circuit

In this work, we report the realization of a polarization-insensitive grating coupler, single-mode waveguide, and ring resonator in the GaN-on-Sapphire platform. We provide a detailed demonstration of the material characterization, device simulation, and experimental results. We achieve a grating coupler efficiency of -5.2 dB/coupler with a 1dB and 3dB bandwidth of 40 nm and 80 nm, respectively. We measure a single-mode waveguide loss of -6 dB/cm. The losses measured here are the lowest in a GaN-on-Sapphire photonic circuit. This demonstration provides opportunities for the development of on-chip linear and non-linear optical processes using the GaN-on-Sapphire platform. To the best of our knowledge, this is the first demonstration of an integrated photonic device using a GaN HEMT stack with 2D electron gas.

physics.optics↗

arXiv2023

Sputter-deposited PZT-on-Silicon Optimization for C-band Electro-Optic Modulation

Ferroelectric materials exhibit interesting electric, mechanical and optical properties. Particularly,tin-film lead zirconium titanate (PZT) has been used as a standard piezo-electric material in micro-electro-mechanical systems. Interestingly, it has one of the highest electro-optic properties that can be exploited to make high-speed on-chip light modulators. In this work, we demonstrate sputter-deposited PZT on silicon-on-insulator wafers. Desired phase and film morphology is achieved through process and buffer layer engineering. We present results on buffer layer screening between MgO, TiO2 and Pt. MgO is identified as a suitable buffer layer from an optical and film growth perspective. We achieve a measured coercive field for PZT/MgO and PZT/Pt film is 50 kV/cm and 30 kV/cm, respectively. We use a PZT-loaded ring modulator with an electro-optic response of 14 pm/V.

cond-mat.mtrl-sci↗

arXiv2023

Sandwiched Hybrid Waveguide Platform for Integrated Photonics Application

We propose and demonstrate a hybrid waveguide platform using layered amorphous silicon and silicon nitride. The waveguide offers more degrees of freedom to design waveguides with desired confinement, effective index and polarization birefringence. Unlike single core material, the proposed waveguide offers design flexibility, and light confinement in the layers is polarization-dependent. We present a detailed waveguide design and analysis of efficient fiber-chip grating couplers with a coupling efficiency of -3.27 dB and -8 dB for $TE$ and $TM$ polarization, respectively. The couplers offer a 3dB bandwidth of 100 nm. Furthermore, we demonstrate excitation of TE and TM modes exploiting the polarization-dependent confinement using thermo-optic characteristics of a ring resonator.

physics.optics↗

arXiv2023

On-Chip Chemical Sensing Using Double-slot Silicon Waveguide

In this paper, we present refractive index measurement using a double-slot silicon waveguide-based Mach Zehnder interferometer. We present a double-slot waveguide that offers the best sensitivity and limit of detection compared to wire and single-slot waveguides. We demonstrate ultra-low loss coupling between a single-mode waveguide and a double-slot waveguide and experimental proof for double-slot excitation. The double-slot waveguide is used to demonstrate a highly sensitive concentration sensor. An unbalanced Mach-Zehnder is used as the sensor device to demonstrate concentrations of Potassium Chloride in deionized water. A sensitivity of 700 nm/RIU and a limit of detection (LOD) of 7.142e^-6 RIU are achieved experimentally. To the best of our knowledge, the demonstrated sensitivity is the highest for an on-chip guided waveguide sensing scheme.

physics.optics↗

arXiv2020

Compact Ring Resonator Enhanced Silicon-MSM Photodetector in SiN-on-SOI Platform

We present a compact on-chip resonator enhanced silicon-MSM photodetector in $850$ $nm$ wavelength band for communication and lab-on-chip bio-sensing applications. We report the highest responsivity of 0.81 A/W for a 5 $μm$ long device. High responsivity is achieved by integrating the detector in a silicon nitride ring resonator. The resonance offers 100X responsivity improvement over a single-pass photodetector due to cavity enhancement. We also present a detailed study of the high-speed response of the cavity and single-pass detector. We report an electro-optic bandwidth of 7.5 GHz measured using a femtosecond optical excitation. To the best of our knowledge, we report for the first time silicon nitride resonator integrated Si-MSM detector in SiN-SOI platform.

physics.app-ph↗

arXiv2019

Alignment Tolerant Broadband Compact Taper for Low-Loss Coupling to a Silicon-on-Insulator Photonic Wire Waveguide

We experimentally demonstrate a broadband, fabrication tolerant, CMOS compatible compact silicon waveguide taper (34.2 um) in silicon-on-insulator wire waveguides. The taper works on multi-mode interference along the length of the taper. A single taper design has a broadband operation with coupling efficiency >70% over 700 nm that can be used in O, C and L-band. The compact taper is highly tolerant to fabrication variations; >100 nm change in the taper and end waveguide width varies the taper transmission by <5%. The footprint of the device i.e. taper along with the linear gratings is ~ 442 m2; i.e. 11.5X smaller than the adiabatic taper. The taper with linear gratings provides comparable coupling efficiency as standardly used focusing gratings. We have also compared the translational and rotational alignment tolerance of the focusing grating with the linear grating.

physics.app-ph↗

arXiv2019

Mitigation of carrier induced optical bistability in silicon ring resonators

We present a detailed study of electrical and optical generated free carrier on the spectral characteristics of a silicon microring modulator. The spectral distortion generated due to thermal and free carriers is presented, and the mechanism for mitigation is also presented. We observed that two-photon induced nonlinearity could be addressed by operating the modulator at suitable bias points. Furthermore, by applying small-signal drive the spectral distortion can be restored. We also present the effect of optical power and drive signal limit on the spectral characteristics. The study allows one to identify suitable device performance and operating conditions to utilize silicon ring modulator for optical signal processing.

physics.optics↗

arXiv2019

High-speed waveguide integrated silicon photodetector on a SiN-SOI platform for short reach datacom

We present waveguide integrated high-speed Si photodetector integrated with silicon nitride (SiN) waveguide on SOI platform for short reach data communication in 850 nm wavelength band. We demonstrate a waveguide couple Si pin photodetector responsivity of 0.44 A/W at 25 V bias. The frequency response of the photodetector is evaluated by coupling of a femtosecond laser source through SiN grating coupler of the integrated photodetector. We estimate a 3dB bandwidth of 14 GHz at 20 V bias, highest reported bandwidth for a waveguide integrated Si photodetector. We also present detailed optoelectronic DC and AC characterisation of the fabricated devices. The demonstrated integrated photodetector could enable an integrated solution for scaling of short reach data communication and connectivity.

physics.app-ph↗

arXiv2018

Generation of tunable, high repetition rate optical frequency combs using on-chip silicon modulators

We experimentally demonstrate tunable, highly-stable frequency combs with high repetition-rates using a single, charge injection based silicon PN modulator. In this work, we demonstrate combs in the C-band with over 8 lines in a 20-dB bandwidth. We demonstrate continuous tuning of the center frequency in the C-band and tuning of the repetition-rate from 7.5GHz to 12.5GHz. We also demonstrate through simulations the potential for bandwidth scaling using an optimized silicon PIN modulator. We find that, the time varying free carrier absorption due to carrier injection, an undesirable effect in data modulators, assists here in enhancing flatness in the generated combs.

physics.app-ph↗

arXiv2017

All-optical wavelength multicasting in quadruple resonance-split coupled Silicon microring cavity

We demonstrate an all-optical four-channel wavelength multicasting in a coupled Silicon microring resonator system. The scheme is based on two-photon absorption induced free carrier dispersion in Silicon. The coupled cavity facilitates resonance splitting that is utilized as individual channels for multicasting. Using the split resonances, we achieve an aggregate multicasted data rate of 48 Gbps (4X12 Gbps). Moreover, we also present a detailed analysis and performance of the multicasting architecture.

physics.optics↗

arXiv2017

Efficient and Tunable Strip-to-Slot Fundamental Mode Coupling

We present a novel photonic wire-to-slot waveguide coupler in SOI. The phase matching between a wire and slot mode is achieved using a mode transformer. The architecture consists of a balanced 50/50 power splitter and a tunable phase matched taper combiner forming a slot waveguide. We show a theoretical wire-to-slot coupling efficiency of 99 % is achievable and experimentally, we demonstrate a coupling efficiency of 99 % in the 1550 nm band. Based on the coupling scheme, we also show excitation of a slot mode in a slotted ring resonator and verified the excitation through the thermo-optic response of the rings. We show a nearly athermal behaviour of a PMMA filled slot ring with a thermo-optic response of 12.8 pm/C compare to 43.5 pm/C for an air clad slot waveguide.

physics.optics↗

arXiv2017

Compact Broadband Low-Loss Taper for Coupling to a Silicon Nitride Photonic Wire

We demonstrate an ultra-compact waveguide taper in Silicon Nitride platform. The proposed taper provides a coupling-efficiency of 95% at a length of 19.5 um in comparison to the standard linear taper of length 50 um that connects a 10 um wide waveguide to a 1 um wide photonic wire. The taper has a spectral response > 75% spanning over 800 nm and resilience to fabrication variations; >200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally demonstrate taper insertion loss of <0.1 dB/transition for a taper as short as 19.5 um, and reduces the footprint of the photonic device by 50.8% compared to the standard adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in Silicon Nitride.

physics.app-ph↗

arXiv2017

High-efficiency broad-bandwidth sub-wavelength grating based fibre-chip coupler in SOI

We report a comprehensive study on the performance of uniform and non-uniform based subwavelength grating couplers in Silicon-on-Insulator. The two performance metrics, coupling efficiency and bandwidth enhancement and trade-offs is presented. We also present, design parameters to achieve high-efficiency and broadband operation based on the detailed study of various loss mechanisms in the grating. Based on the detailed analysis subwavelength grating coupler designs with efficiency as high as 84 % with a 1 dB bandwidth of 50 nm and 98 % with a 44 nm 1 dB bandwidth is presented.

physics.app-ph↗

arXiv2017

Tunable coupling-induced resonance splitting in self-coupled Silicon ring cavity with robust spectral characteristics

We propose and demonstrate a self-coupled microring resonator for resonance splitting by mutual mode coupling of cavity mode and counter-propagating mode in Silicon-on-Insulator platform The resonator is constructed with a self-coupling region that can excite counter-propagating mode. We experimentally study the effect of self-coupling on the resonance splitting, resonance extinction, and quality-factor evolution and stability. Based on the coupling, we achieve 72% of FSR splitting for a cavity with FSR 2.1 nm with < 5% variation in the cavity quality factor. The self-coupled resonance splitting shows highly robust spectral characteristic that can be exploited for sensing and optical signal processing.

physics.optics↗