Searcharxiv⌕ Search

arXiv subjects

Rishi Maiti

Publications and source records attributed to Rishi Maiti.

At least 19 recordsLinked to original sources
arXiv2026

A Passive Daytime Colored Radiative Cooler with DBR-Engineered Color Selectivity

Passive daytime colored radiative cooling (PDCRC) offers an attractive approach to thermal management while enabling structural coloration. However, achieving both strong daytime cooling and vivid, stable colors remains challenging. Here, we propose a lithography-free PDCRC comprising a polydimethylsiloxane (PDMS) emitter, SiC/SiO2 distributed Bragg reflector (DBR), MgF2 spacer, and Ag back reflector. The DBR and MgF2 spacer enable selective visible-spectrum reflection for cyan, magenta, and yellow (CMY) color generation, while the PDMS layer provides strong thermal emission within the atmospheric transparency window (8-14 micrometers). Finite-difference time-domain (FDTD) simulations, validated using the transfer matrix method (TMM), yield an average emissivity of 92% in the atmospheric window and an average reflectivity of 93.3% over 0.75-6 micrometers. CIE 1931 chromaticity analysis confirms high-contrast CMY colors with low color differences from standard subtractive primary colors. Under daytime conditions with a heat-transfer coefficient of 6 W m-2 K-1, the proposed cooler achieves cooling powers of approximately 140-145 W m-2 and a temperature reduction of about 12 degrees C below ambient. The color characteristics remain stable over a broad range of incidence angles, with only a gradual reduction in color intensity at larger angles, while the spectral response remains nearly insensitive to TE and TM polarizations. Simulations using meteorological conditions from different global cities further demonstrate robust cooling performance under diverse environmental conditions. The combination of high cooling performance, vivid coloration, simple multilayer architecture, and fabrication feasibility makes the proposed PDCRC promising for energy-efficient thermal management in buildings, vehicle coatings, wearable devices, and other outdoor applications.

physics.app-ph↗
arXiv2026

2D GaSe-Based Single-Pixel Spectrometer via Electro-Optical Barrier Co-Modulation

Driven by the growing demand for miniaturized spectrometers for in-situ analysis, and point-of-care diagnostics, conventional spectrometers are often constrained by bulky architectures and pathlength-limited spectral resolution. Achieving high-resolution, single-pixel computational spectrometers is therefore critical for the realization of compact, on-chip systems. Here, we report a single-pixel spectrometer enabled by a single 2D material; few-layer GaSe-based photodetector, in which the Schottky barrier height modulation, governed jointly by applied bias and optical excitation, provides an efficient mechanism for spectral encoding without the need for bulky dispersive elements. The device exhibits a high peak-wavelength accuracy of ~0.78 nm across a broad operational bandwidth (300-700 nm) within a compact footprint of ~100 um^2 and resolves closely spaced spectral features with separations down to ~5 nm. The device operates at low bias (+/- 4V) with an ultralow dark current density ~0.3 pA/um^2 at 4V bias. These results establish a simple, scalable route toward compact, cost-effective spectroscopic systems for on-chip spectral sensing and portable hyperspectral imaging applications.

physics.optics↗
arXiv2023

Unravelling the room temperature growth of two-dimensional h-BN nanosheets for multifunctional applications

Room temperature growth of two-dimensional van der Waals (2D-vdW) materials is indispensable for state-of-the-art nanotechnology. The low temperature growth supersedes the requirement of elevated growth temperature accompanied with high thermal budgets. Moreover, for electronic applications, low or room temperature growth reduces the possibility of intrinsic film-substrate interfacial thermal diffusion related deterioration of functional properties and consequent device performance. Here, we demonstrated the growth of ultrawide-bandgap boron nitride (BN) at room temperature by using the pulsed laser deposition (PLD) process and demonstrated various functionalities for potential applications. Comprehensive chemical, spectroscopic and microscopic characterization confirms the growth of ordered nanosheet-like hexagonal BN. Functionally, nanosheets show hydrophobicity, high lubricity (low coefficient of friction), low refractive index within the visible to near-infrared wavelength range, and room temperature single-photon quantum emission. Our work unveils an important step that brings a plethora of applications potential for room temperature grown h-BN nanosheets as it can be feasible on any given substrate, thus creating a scenario for h-BN on demand at frugal thermal budget.

physics.app-ph↗
arXiv2022

Unzipping hBN with ultrashort mid-infrared pulses

Manipulating the nanostructure of materials is critical for numerous applications in electronics, magnetics, and photonics. However, conventional methods such as lithography and laser-writing require cleanroom facilities or leave residue. Here, we describe a new approach to create atomically sharp line defects in hexagonal boron nitride (hBN) at room temperature by direct optical phonon excitation in the mid-infrared (mid-IR). We term this phenomenon "unzipping" to describe the rapid formation and growth of a <30-nm-wide crack from a point within the laser-driven region. The formation of these features is attributed to large atomic displacements and high local bond strain from driving the crystal at a natural resonance. This process is distinguished by (i) occurring only under resonant phonon excitation, (ii) producing highly sub-wavelength features, and (iii) sensitivity to crystal orientation and pump laser polarization. Its cleanliness, directionality, and sharpness enable applications in in-situ flake cleaving and phonon-wave-coupling via free space optical excitation.

cond-mat.mtrl-sci↗
arXiv2021

An ITO Graphene hybrid integrated absorption modulator on Si-photonics for neuromorphic nonlinear activation

The high demand for machine intelligence of doubling every three months is driving novel hardware solutions beyond charging of electrical wires given a resurrection to application specific integrated circuit (ASIC)-based accelerators. These innovations include photonic ASICs (P-ASIC) due to prospects of performing optical linear (and also nonlinear) operations, such as multiply-accumulate for vector matrix multiplications or convolutions, without iterative architectures. Such photonic linear algebra enables picosecond delay when photonic integrated circuits are utilized, via on-the-fly mathematics. However, the neurons full function includes providing a nonlinear activation function, knowns as thresholding, to enable decision making on inferred data. Many P-ASIC solutions performing this nonlinearity in the electronic domain, which brings challenges in terms of data throughput and delay, thus breaking the optical link and introducing increased system complexity via domain crossings. This work follows the notion of utilizing enhanced light-matter-interactions to provide efficient, compact, and engineerable electro-optic neuron nonlinearity. Here, we introduce and demonstrate a novel electro-optic device to engineer the shape of this optical nonlinearity to resemble a rectifying linear unit (ReLU) - the most-commonly used nonlinear activation function in neural networks. We combine the counter-directional transfer functions from heterostructures made out of two electro-optic materials to design a diode-like nonlinear response of the device. Integrating this nonlinearity into a photonic neural network, we show how the electrostatics of this thresholders gating junction improves machine learning inference accuracy and the energy efficiency of the neural network.

physics.app-ph↗
arXiv2020

Heterogeneously Integrated ITO Plasmonic Mach-Zehnder Interferometric Modulator on SOI

Densely integrated active photonics is key for next generation on-chip networks for addressing both footprint and energy budget concerns. However, the weak light-matter interaction in traditional active Silicon optoelectronics mandates rather sizable device lengths. The ideal active material choice should avail high index modulation while being easily integrated into Silicon photonics platforms. Indium tin oxide (ITO) offers such functionalities and has shown promising modulation capacity recently. Interestingly, the nanometer-thin unity-strong index modulation of ITO synergistically combines the high group-index in hybrid plasmonic with nanoscale optical modes. Following this design paradigm, here, we demonstrate a spectrally broadband, GHz-fast Mach-Zehnder interferometric modulator, exhibiting a high efficiency signified by a miniscule VpL of 95 Vum, deploying an one-micrometer compact electrostatically tunable plasmonic phase-shifter, based on heterogeneously integrated ITO thin films into silicon photonics. Furthermore we show, that this device paradigm enables spectrally broadband operation across the entire telecommunication near infrared C-band. Such sub-wavelength short efficient and fast modulators monolithically integrated into Silicon platform open up new possibilities for high-density photonic circuitry, which is critical for high interconnect density of photonic neural networks or applications in GHz-fast optical phased-arrays, for example.

physics.app-ph↗
arXiv2020

Strain Induced Modulation of Local Transport of 2D Materials at the Nanoscale

Strain engineering offers unique control to manipulate the electronic band structure of two-dimensional materials (2DMs) resulting in an effective and continuous tuning of the physical properties. Ad-hoc straining 2D materials has demonstrated novel devices including efficient photodetectors at telecommunication frequencies, enhanced-mobility transistors, and on-chip single photon source, for example. However, in order to gain insights into the underlying mechanism required to enhance the performance of the next-generation devices with strain(op)tronics, it is imperative to understand the nano- and microscopic properties as a function of a strong non-homogeneous strain. Here, we study the strain-induced variation of local conductivity of a few-layer transition-metal-dichalcogenide using a conductive atomic force microscopy. We report a novel strain characterization technique by capturing the electrical conductivity variations induced by local strain originating from surface topography at the nanoscale, which allows overcoming limitations of existing optical spectroscopy techniques. We show that the conductivity variations parallel the strain deviations across the geometry predicted by molecular dynamics simulation. These results substantiate a variation of the effective mass and surface charge density by .026 me/% and .03e/% of uniaxial strain, respectively. Furthermore, we show and quantify how a gradual reduction of the conduction band minima as a function of tensile strain explains the observed reduced effective Schottky barrier height. Such spatially-textured electronic behavior via surface topography induced strain variations in atomistic-layered materials at the nanoscale opens up new opportunities to control fundamental material properties and offers a myriad of design and functional device possibilities for electronics, nanophotonics, flextronics, or smart cloths.

cond-mat.mes-hall↗
arXiv2020

Low Dimensional Material based Electro-Optic Phase Modulation Performance Analysis

Electro-optic modulators are utilized ubiquitously ranging from applications in data communication to photonic neural networks. While tremendous progress has been made over the years, efficient phase-shifting modulators are challenged with fundamental tradeoffs, such as voltage-length, index change-losses or energy-bandwidth, and no single solution available checks all boxes. While voltage-driven phase modulators, such as based on lithium niobate, offer low loss and high speed operation, their footprint of 10's of cm-scale is prohibitively large, especially for density-critical applications, for example in photonic neural networks. Ignoring modulators for quantum applications, where loss is critical, here we distinguish between current versus voltage-driven modulators. We focus on the former, since current-based schemes of emerging thin electro-optical materials have shown unity-strong index modulation suitable for heterogeneous integration into foundry waveguides. Here, we provide an in-depth ab-initio analysis of obtainable modulator performance based on heterogeneously integrating low-dimensional materials, i.e. graphene, thin films of indium tin oxide, and transition metal dichalcogenide monolayers into a plurality of optical waveguide designs atop silicon photonics. Using the fundamental modulator tradeoff of energy-bandwidth-product as a design-quality quantifier, we show that a small modal cross section, such as given by plasmonic modes, enables high-performance operation, physically realized by arguments on charge-distribution and low electrical resistance. An in-depth design understanding of phase-modulator performance, beyond doped-junctions in silicon, offers opportunities for micrometer-compact yet energy-bandwidth-ratio constrained modulators with timely opportunities to hardware-accelerate applications beyond data communication towards photonic machine intelligence.

physics.app-ph↗
arXiv2020

Roadmap for Gain-Bandwidth-Product Enhanced Photodetectors

Photodetectors are key optoelectronic building blocks performing the essential optical-to-electrical signal conversion, and unlike solar cells, operate at a specific wavelength and at high signal or sensory speeds. Towards achieving high detector performance, device physics, however, places a fundamental limit of the achievable detector sensitivity, such as responsivity and gain, when simultaneously aimed to increasing the detectors temporal response, speed, known as the gain-bandwidth product (GBP). While detectors GBP has been increasing in recent years, the average GBP is still relatively modest (~10^6-10^7 Hz-A/W). Here we discuss photodetector performance limits and opportunities based on arguments from scaling length theory relating photocarrier channel length, mobility, electrical resistance with optical waveguide mode constrains. We show that short-channel detectors are synergistic with slot-waveguide approaches, and when combined, offer a high-degree of detector design synergy especially for the class of nanometer-thin materials. Indeed, we find that two dimensional material-based detectors are not limited by their low mobility and can, in principle, allow for 100 GHz fast response rates. However, contact resistance is still a challenge for such thin materials, a research topic that is still not addressed yet. An interim solution is to utilize heterojunction approaches for functionality separation. Nonetheless, atomistically- and nanometer-thin materials used in such next-generation scaling length theory based detectors also demand high material quality and monolithic integration strategies into photonic circuits including foundry-near processes. As it stands, this letter aims to guide the community if achieving the next generation photodetectors aiming for a performance target of GBP = 10^12 Hz-A/W.

physics.app-ph↗
arXiv2019

A semi-empirical integrated microring cavity approach for 2D material optical index identification at 1.55 μm

Atomically thin two-dimensional (2D) materials provide a wide range of basic building blocks with unique properties, making them ideal for heterogeneous integration with a mature chip platform for advances in optical communication technology. Control and understanding of the precise value of the optical index of these materials, however, is challenging, due to the small lateral flake dimension. Here we demonstrate a semi-empirical method to determine the index of a 2D material (nMoTe2 of 4.36+0.011i) near telecommunication-relevant wavelength by integrating few layers of MoTe2 onto a micro-ring resonator. The placement, control, and optical-property understanding of 2D materials with integrated photonics paves a way for further studies of active 2D material-based optoelectronics and circuits.

physics.app-ph↗
arXiv2019

A Guide for Material and Design Choices for Electro-Optic Modulators and recent 2D-Material Silicon Modulator Demonstrations

Electro-optic modulation performs a technological relevant functionality such as for communication, beam steering, or neuromorphic computing through providing the nonlinear activation function of a perceptron. Wile Silicon photonics enabled the integration and hence miniaturization of optoelectronic devices, the weak electro-optic performance of Silicon renders these modulators to be bulky and power-hungry compared to a single switch functionality known from electronics. To gain deeper insights into the physics and operation of modulators hetero-generous integration of emerging electro-optically active materials could enable separating light passive and low-loss light routing from active light manipulation. Here we discuss and review our recent work on a) fundamental performance vectors of electro-optic modulators, and b) showcase recent development of heterogeneous-integrated emerging EO materials into Si-photonics to include an ITO-based MZM, a Graphene hybrid-plasmon and the first TMD-MRR modulator using a microring resonator. Our results indicate a viable path for energy efficient and compact Silicon photonic based modulators.

physics.app-ph↗
arXiv2019

A Lateral MOS-Capacitor Enabled ITO Mach-Zehnder Modulator for Beam Steering

Here, we experimentally demonstrate an Indium Tin Oxide (ITO) Mach-Zehnder interferometer heterogeneously integrated in silicon photonics. The phase shifter section is realized in a novel lateral MOS configuration, which, due to favorable electrostatic overlap, leads to efficient modulation (VπL = 63 Vum). This is achieved by (i) selecting a strong index changing material (ITO) and (ii) improving the field overlap as verified by the electrostatic field lines. Furthermore, we show that this platform serves as a building block in an endfire silicon photonics optical phased array (OPA) with a half-wavelength pitch within the waveguides with anticipated performance, including narrow main beam lobe (<3°) and >10 dB suppression of the side lobes, while electrostatically steering the emission profile up to plus/minus 80°, and if further engineered, can lead not only towards nanosecond-fast beam steering capabilities in LiDAR systems but also in holographic display, free-space optical communications, and optical switches.

physics.app-ph↗
arXiv2018

Compact Graphene Plasmonic Slot Photodetector on Silicon-on-insulator with High Responsivity

Graphene has extraordinary electro-optic properties and is therefore a promising candidate for monolithic photonic devices such as photodetectors. However, the integration of this atom-thin layer material with bulky photonic components usually results in a weak light-graphene interaction leading to large device lengths limiting electro-optic performance. In contrast, here we demonstrate a plasmonic slot graphene photodetector on silicon-on-insulator platform with high-responsivity given the 5 um-short device length. We observe that the maximum photocurrent, and hence the highest responsivity, scales inversely with the slot gap width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 15-times higher responsivity per unit device-length compared to photonic graphene photodetectors. Furthermore, we reveal that the back-gated electrostatics is overshadowed by channel-doping contributions induced by the contacts of this ultra-short channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously-unseen offset between the maximum photovoltaic-based photocurrent relative to graphenes Dirac point and the observed non-ambipolar transport. Such micrometer compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being an ideal testbed to study short-channel carrier physics in graphene optoelectronics.

physics.app-ph↗
arXiv2018

Loss and Coupling Tuning via Heterogeneous Integration of MoS2 Layers in Silicon Photonics

Layered two-dimensional (2D) materials provide a wide range of unique properties as compared to their bulk counterpart, making them ideal for heterogeneous integration for on-chip interconnects. Hence, a detailed understanding of the loss and index change on Si integrated platform is a prerequisite for advances in opto-electronic devices impacting optical communication technology, signal processing, and possibly photonic-based computing. Here, we present an experimental guide to characterize transition metal dichalcogenides (TMDs), once monolithically integrated into the Silicon photonic platform at 1.55 um wavelength. We describe the passive tunable coupling effect of the resonator in terms of loss induced as a function of 2D material layer coverage length and thickness. Further, we demonstrate a TMD-ring based hybrid platform as a refractive index sensor where resonance shift has been mapped out as a function of flakes thickness which correlates well with our simulated data. These experimental findings on passive TMD-Si hybrid platform open up a new dimension by controlling the effective change in loss and index, which may lead to the potential application of 2D material based active on chip photonics.

physics.optics↗
arXiv2018

0.52 V-mm ITO-based Mach-Zehnder Modulator in Silicon Photonics

Electro-optic modulators transform electronic signals into the optical domain and are critical components in modern telecommunication networks, RF photonics, and emerging applications in quantum photonics and beam steering. All these applications require integrated and voltage-efficient modulator solutions with compact formfactors that are seamlessly integratable with Silicon photonics platforms and feature near-CMOS material processing synergies. However, existing integrated modulators are challenged to meet these requirements. Conversely, emerging electro-optic materials heterogeneously integrated with Si photonics open a new avenue for device engineering. Indium tin oxide (ITO) is one such compelling material for heterogeneous integration in Si exhibiting formidable electro-optic effect characterized by unity order index at telecommunication frequencies. Here we overcome these limitations and demonstrate a monolithically integrated ITO electro- optic modulator based on a Mach Zehnder interferometer (MZI) featuring a high-performance half-wave voltage and active device length product, VpL = 0.52 V-mm. We show, how that the unity-strong index change enables a 30 micrometer-short pi-phase shifter operating ITO in the index-dominated region away from the epsilon-bear-zero ENZ point. This device experimentally confirms electrical phase shifting in ITO enabling its use in multifaceted applications including dense on-chip communication networks, nonlinearity for activation functions in photonic neural networks, and phased array applications for LiDAR.

physics.app-ph↗
arXiv2018

Solution Processed CMOS compatible Carbon Nano-dots Based Heterojunction for Enhanced UV Detector

Carbon nanostructures technology has recently emerged as a key enabler for next-generation optoelectronic devices including deep UV detectors and light sources which is promising in health and environment monitoring. Here, we report the fabrication of solution processed Carbon nano-dots (CNDs)/n-Si heterojunction showing broadband spectral response with a peak responsivity of ~ 1.25 A/W in UV (~300 nm) wavelength. The surface topography and chemical information of synthesized CNDs via a facile synthesis route have been characterized showing the presence of surface chemical states resulting broad optical emission. The CNDs/n-Si photo diodes exhibit very low dark current (~500 pA), excellent rectification ratio (~5*10^3), and very good photo-modulation in UV region. Given the solution-processing capability of the devices and extraordinary optical properties of CNDs, the use of CNDs will open up unique opportunities for future high-performance, low-cost DUV photo detectors.

physics.ins-det↗
arXiv2018

Microring Resonators Coupling Tunability by Heterogeneous 2D Material Integration

Atomically thin 2D materials provide a wide range of basic building blocks with unique properties, making them ideal for heterogeneous integration with a mature chip platform. An understanding the role of excitons in transition metal dichalcogenides in Silicon photonic platform is a prerequisite for advances in optical communication technology, signal processing, and possibly computing. Here we demonstrate passive tunable coupling by integrating few layers of MoTe2 on a micro-ring resonator. We find a TMD-to-rings circumference coverage length ratio to place the ring into critical coupling to be about 10% as determined from the variation of spectral resonance visibility and loss as a function of TMD coverage. Using this TMD ring heterostructure, we further demonstrate a semi-empirical method to determine the index of an unknown TMD material (nMoTe2 of 4.36+.011i) near for telecommunication-relevant wavelength.

physics.optics↗