arXiv subjects

Awanish Pandey

Publications and source records attributed to Awanish Pandey.

7 recordsLinked to original sources

arXiv2026

Geometric Criteria for Complete Mode Conversion in Detuned Systems via Piecewise-Coherent Modulation

Static phase detuning fundamentally constrains coherent state transfer in asymmetric classical and quantum systems. We introduce a Bloch-sphere formulation for piecewise-coherent modulation that recasts coupled-mode dynamics as geometric trajectories, transforming algebraic control into path optimization. The approach reveals a cone of inaccessibility at the target pole and yields exact geodesic criteria for complete mode conversion in detuned systems. Leveraging this framework, we break time-reversal symmetry to realize a magnet-free optical isolator with near-unity contrast. Furthermore, for detuning larger than coupling between modes, we develop a recursive multi-step protocol enabling deterministic transfer for arbitrary detunings and derive a universal geometric lower bound on the required number of coupling-switching events.

quant-ph↗

arXiv2024

Backscattering-Immune Floquet Conversion in Ring Modulators

Backscattering in micro-ring cavities induces mode mixing and limits device performance. Existing methods to mitigate backscattering often involve complex fabrication processes or are insufficient for complete suppression. In this work, we introduce a novel method to eliminate backscattering by operating the cavity at an exceptional point (EP). By engineering non-conservative coupling between degenerate clockwise (CW) and counter-clockwise (CCW) modes, we achieve chiral transmission that prevents degeneracy lifting and suppresses unwanted mode coupling. Unlike previous approaches that rely on precise gain-loss balance or complex structures, our method utilizes non-conservative coupling between the counterpropgating cavity modes. Using this method, we further show significant enhancement in the cavity performance in Floquet mode conversion efficiency at the EP. Our highly adaptable approach enables seamless integration into various photonic platforms with electro-optic modulators. This advancement mitigates backscattering and improves the precision of light-matter interactions, offering promising applications in quantum communication and information processing.

physics.optics↗

arXiv2022

Dynamics of a ring resonator under simultaneous index and loss modulation

We report a complete steady-state solution to the time rate equations governing the dynamics of a sinusoidally driven ring modulator. Compared to previous works that provide comprehensive solutions for pure index (phase) or loss (loss) modulation, this work presents an exact solution with their simultaneous modulation. Furthermore, the optimum modulation parameters for efficient microwave-to-optical conversion are discussed under such concurrent modulation. As an application, we report selective downward frequency conversion from the ring modulator which is not possible from pure loss or index modulation. The work allows for more accurate modeling of the ring modulator. It provides an insight to explore the interplay between phase and amplitude modulation in MRMs for unique applications, and fully understand the limitations of such devices.

physics.optics↗

arXiv2021

Light modulation in Silicon photonics by PZT actuated acoustic waves

Tailoring the interaction between light and sound has opened new possibilities in photonic integrated circuits (PICs) that ranges from achieving quantum control of light to high-speed information processing. However, the actuation of sound waves in Si PICs usually requires integration of a piezoelectric thin film. Lead Zirconate Titanate (PZT) is a promising material due to its strong piezoelectric and electromechanical coupling coefficient. Unfortunately, the traditional methods to grow PZT on Silicon are detrimental for photonic applications due to the presence of an optical lossy intermediate layer. In this work, we report integration of a high quality PZT thin film on a Silicon-on-insulator (SOI) photonic chip using an optically transparent buffer layer. We demonstrate acousto-optic modulation in Silicon waveguides with the PZT actuated acoustic waves. We fabricate inter digital transducers (IDTs) on the PZT film with a contact photo-lithography and electron-beam lithography to generate the acoustic waves in MHz and GHz range respectively. We obtain a V$_{\pi}$L $\sim$ 3.35 V$\cdot$cm at 576 MHz from a 350 nm thick gold (Au) IDT with 20 finger-pairs. After taking the effect of mass-loading and grating reflection into account, we measured a V$_{\pi}$L $\sim$ 3.60 V$\cdot$cm at 2 GHz from a 100 nm thick Aluminum (Al) IDT consisting of only 4 finger-pairs. Thus, without patterning the PZT film nor suspending the device, we obtained figures-of-merit comparable to state-of-the-art modulators based on SOI, making it a promising candidate for broadband and efficient acousto-optic modulator for future integration.

physics.optics↗

arXiv2021

Input Validation with Symbolic Execution

Symbolic execution has always been plagued by the inability to handle programs that require highly structured inputs. Most often, the symbolic execution engine gets overwhelmed by the sheer number of infeasible paths and fails to explore enough feasible paths to gain any respectable coverage. In this paper, we propose a system, InVaSion, that attempts to solve this problem for forking-based symbolic execution engines. We propose an input specification language (ISL) that is based on a finite-state automaton but includes guarded transitions, a set of registers and a set of commands to update the register states. We demonstrate that our language is expressive enough to handle complex input specifications, like the Tiff image format, while not requiring substantial human effort; even the Tiff image specification could be specified in our language with an automaton of about 35 states. InVaSion translates the given program and the input specification into a non-deterministic program and uses symbolic execution to instantiate the non-determinism. This allows our tool to work with any forking-based symbolic execution engine and with no requirement of any special theory solver. Over our set of benchmarks, on an average, InVaSion was able to increase branch coverage from 24.97% to 67.84% over baseline KLEE.

cs.PL↗

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

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↗