arXiv subjects

Parul Sharma

Publications and source records attributed to Parul Sharma.

11 recordsLinked to original sources

arXiv2026

Deterministic Single-Photon Emitter Arrays in Hexagonal Boron Nitride by Carbon-Assisted Focused Ion Beam Engineering

The realization of on-chip photonic circuits requires scalable and deterministic single-photon emitters (SPEs) at room temperature, which remain a challenge in van der Waals materials. In this work, we report a novel three-step fabrication process for the generation of spatially controlled SPE arrays in hexagonal boron nitride (hBN). The process comprises site-selective gallium (Ga) focused ion beam milling, nanoscale conformal carbon deposition over the patterned regions, and subsequent thermal annealing. The synergistic combination of these steps resulted in a site-correlated emitter yield of ($\sim 89\%$) across 100 fabrication sites. Second-order autocorrelation measurements revealed pronounced three-level emitter dynamics where the best emitters exhibited high purity ($g^{(2)}(0)=0.15 \pm 0.09$).To the best of our knowledge, this is the first lithography-free, direct-write approach combining Ga-ion milling, selective carbon engineering, and thermal annealing to deterministically generate \hBN{} \SPE{}s. The reproducibility of the method is validated across multiple independently fabricated samples. These results establish a scalable, lithography-free pathway toward on-demand SPE arrays relevant to integrated quantum photonics.

physics.optics↗

arXiv2026

Active Control of Topological Exceptional Points in Non-Hermitian Metasurfaces

Active control and ultrafast switching of non-Hermitian photonic systems are essential for next-generation reconfigurable optical technologies. Here, we demonstrate dynamic temporal manipulation of EPs in the terahertz (THz) regime using optically excited germanium (Ge) as an active medium. By exploiting pump-probe delay as a continuous tuning parameter, we achieve sub-picosecond eigenmode switching (~0.5 ps) and realize a complete time-resolved EP encirclement within ~2 ps, enabling direct observation of topological phase accumulation. At EP, the metasurface exhibits highly asymmetric transmission for circularly polarized light, characteristic of chiral mode response. Furthermore, we observe ultrafast eigenmode switching and topological phase evolution within ~1 ps, achieving >99% cross-polarization modulation depth. The measured results show strong agreement with theoretical modeling, with a high Petermann factor of approximately 10^3, confirming the effectiveness of the design. Our work establishes pump-probe delay time as a dynamical control parameter for EP topology, introducing a new regime of ultrafast non-Hermitian photonics for high-speed switching, enhanced sensitivity, and tunable polarization control in the THz domain.

physics.optics↗

arXiv2025

From Atomic Defects to Integrated Photonics: A Perspective on Solid-State Quantum Light Sources

Single-photon emitters (SPEs) constitute a foundational resource for quantum technologies, including secure communication, photonic quantum computing, and emerging quantum network architectures. A wide range of quantum materials, from atom-like point defects in bulk crystals to excitonic states in low-dimensional semiconductors, now provide bright, coherent, and scalable sources of non-classical light. Meanwhile, advances in photonic integration have enabled efficient routing, filtering, and on-chip manipulation of these emitters. From this perspective, we survey and discuss the technological landscape in which solid-state emitters interface with quantum sensing, quantum communication, quantum computation, and emerging photonic AI platforms. Further, we discuss the materials landscape underpinning modern single-photon sources from the zero-dimensional, one-dimensional, two-dimensional and three-dimensional materials. Lastly, we highlight key integration pathways for these single-photon emitters into scalable quantum photonic systems.

physics.optics↗

arXiv2025

Protected Ion Beam Fabrication of Two-Dimensional Transition Metal Dichalcogenides based Photonic Devices

Two-dimensional (2D) transition metal dichalcogenides are pivotal for next-generation photonic devices due to their exceptional optical properties and strong light-matter interactions. However, their atomic thinness renders them susceptible to damage during nanoscale fabrication. Focused ion beam technology, while offering precise defect engineering for tailoring optoelectronic properties, often induces collateral damage far beyond the target region, compromising device performance. This study addresses the critical challenge of preserving the intrinsic optical characteristics of 2D TMDCs during FIB patterning. We demonstrate that conventional dielectric encapsulation fails to protect 2D TMDCs from gallium ion-induced damage, leading to persistent defects and quenched optical responses in patterned microstructures. In contrast, polymeric encapsulation with PMMA (polymethyl methacrylate) effectively mitigates damage by acting as a sacrificial layer that absorbs ion impact, thereby preserving the optical properties of the underlying TMDC. Furthermore, we leverage XeF2-assisted Ga ion beam direct patterning, which significantly reduces collateral damage, minimizes Ga ion implantation, and enables precise anisotropic material removal, yielding ultra-smooth sidewalls critical for high-quality photonic resonators. This combined approach of PMMA encapsulation and XeF2-assisted FIB patterning offers a robust, cost-effective, and scalable single-step fabrication route for integrating 2D TMDCs into high-performance photonic devices, thereby maintaining their intrinsic optical functionality essential for advancing quantum technologies and compact optical circuits.

physics.optics↗

arXiv2025

Sensing with Broken Symmetry: Revisiting Bound States in the Continuum

Metasurface with bound states in the continuum (BICs) offer exceptional potential for optical sensing due to their inherently high quality (Q) factors. However, the detection of symmetry-protected BICs remains experimentally challenging due to their non-radiative nature. Introducing slight asymmetry makes these resonances observable, though it reduces the Q-factor. In real devices, intrinsic material losses further affect the resonance behavior and sensing performance. While it is often assumed that sensing is optimized at the critical coupling when radiative and non-radiative losses are balanced, the precise conditions for achieving the best limit of detection (LOD) and figure-of-merit (FOM) remain under active discussion. In this work, we experimentally and theoretically investigate BIC-based sensing in the terahertz (THz) range. We demonstrate that the LOD exhibits a non-monotonic dependence on asymmetry, reaching an unexpected optimum where radiative and non-radiative losses are not equal. Moreover, we show that this optimum differs between reflection and transmission sensing schemes. Our results provide practical guidelines for optimizing Q-factor, sensitivity, and signal amplitude together, and contribute to a deeper understanding of the fundamental limits of BIC-based sensing.

physics.optics↗

arXiv2024

Focused ion beam polishing based optimization of high-Q silica microdisk resonators

Whispering gallery mode (WGM) microdisk resonators are promising optical devices that confine light efficiently and enable enhanced nonlinear optical effects. This work presents a novel approach to reduce sidewall roughness in SiO\textsubscript{2} microdisk resonators using focused ion beam (FIB) polishing. The microdisks, with varying diameter ranging from 5 to 20 $\mu$m are fabricated using a multi-step fabrication scheme. However, the etching process introduces significant sidewall roughness, which increases with decreasing microdisk radius, degrading the resonators' quality. To address this issue, a FIB system is employed to polish the sidewalls, using optimized process parameters to minimize Ga ion implantation. White light interferometry measurements reveal a significant reduction in surface roughness from 7 nm to 20 nm for a 5 $\mu$m diameter microdisk, leading to a substantial enhancement in the scattering quality factor (Qss) from $3\times 10^2$ to $2\times 10^6$. These findings demonstrate the effectiveness of FIB polishing in improving the quality of microdisk resonators and open up new possibilities for the fabrication of advanced photonic devices.

physics.optics↗

arXiv2023

Exceptional point sensing via energy loss profile in a non-Hermitian system

The heightened sensitivity observed in non-Hermitian systems at exceptional points (EPs) has garnered significant attention. Typical EP sensor implementations rely on precise measurements of spectra and importantly, for real time sensing measurements, the EP condition ceases to hold as the perturbation increases over time, thereby preventing the use of high sensitivity at the EP point. In this work, we present an new approach to EP sensing which goes beyond these two traditional constraints. Firstly, instead of measuring the spectra, our scheme of EP based sensing is based on the observation of decay length of the optical mode in finite size gratings, which is validated via coupled mode theory as well as full wave electrodynamic simulations. Secondly, for larger perturbation strengths, the EP is spectrally shifted instead of being destroyed -- this spectral shift of the EP is calibrated and using this look-up table, we propose continuous real time detection by varying the excitation laser wavelength. As a proof of principle of our technique, we present an application to the sensing of coronavirus particles, which shows unprecedented limit of detection. These findings will contribute to the expanding field of exceptional point based sensing technologies for real time applications beyond spectral measurements.

physics.optics↗

arXiv2023

Polaritons in photonic hypercrystals of van der Waals materials

In-plane Hyperbolic Phonon polaritons (HPhPs) are quasiparticles formed via coupling of photons and optical phonons in in-plane hyperbolic materials and offer unique applications in sensing, thermal emitters and high resolution imaging. However, the large momentum mismatch between photons and these in-plane HPhPs has restricted their technological potential as most experimental demonstration rely on sophisticated and expensive near field detection schemes. In this work, using the example of $\alpha-$MoO$_3$, we demonstrate that by constructing photonic hypercrystals of this material, one can not only excite these in-plane HPhPs in the far field but also tune the far field response via twisting the hypercrystal lattice with respect the lattice of $\alpha-$MoO$_3$. Our findings will pave the way for the development of practical in-plane HPhP devices as well as provide access to new fundamental physics of such materials via conventional and well developed far field measurement techniques.

physics.optics↗

arXiv2023

Controllable Emphasis with zero data for text-to-speech

We present a scalable method to produce high quality emphasis for text-to-speech (TTS) that does not require recordings or annotations. Many TTS models include a phoneme duration model. A simple but effective method to achieve emphasized speech consists in increasing the predicted duration of the emphasised word. We show that this is significantly better than spectrogram modification techniques improving naturalness by $7.3\%$ and correct testers' identification of the emphasized word in a sentence by $40\%$ on a reference female en-US voice. We show that this technique significantly closes the gap to methods that require explicit recordings. The method proved to be scalable and preferred in all four languages tested (English, Spanish, Italian, German), for different voices and multiple speaking styles.

eess.AS↗

arXiv2022

A universal and stable metasurface for photonic quasi bound state in continuum coupled with two dimensional semiconductors

Strong coupling of excitons to optical cavity modes is of immense importance to understanding the fundamental physics of quantum electrodynamics at the nanoscale as well as for practical applications in quantum information technologies. There have been several attempts at achieving strong coupling between excitons in two dimensional semiconductors such as transition metal dichalcogenides (TMDCs) and photonic quasi-bound states in the continuum (BICs). We identify two gaps in the platforms for achieving strong coupling between TMDC excitons and photonic quasi-BICs: firstly, in the studies so far, different cavity architectures have been employed for coupling to different TMDCs. This would mean that typically, the fabrication process flow for the cavities will need to be modified as one moves from one TMDC to the other, which can limit the technological progress in the field. Secondly, there has been no discussion of the impact of fabrication imperfections in the studies on strong coupling of these subsystems so far. In this work, we address these two questions by optimizing a cavity with the same architecture which can couple to the four typical TMDCs (MoS$_2$, WS$_2$, MoSe$_2$, WSe$_2$) and perform a detailed investigation on the fabrication tolerance of the associated photonic quasi-BICs and their impact on strong coupling.

physics.optics↗

arXiv2014

Security concerns of ipv6-slaac and security policies to diminish the risk associated with them

Though, IPv6 has presented a long list of features that will actually change the entire networking environment, it still represents a very small proportion of Internet traffic. One of the major reasons behind its partial acceptance is its security, as these features were incorporated in IPv6 just to enhance its overall performance and quality of service, thereby neglecting its security part. One such feature is Stateless Address Auto Configuration or simply SLAAC, which have undoubtedly reduced a lot of overhead in configuring networks, but on the same time it has challenged the security of IPv6 networks. This research work, therefore targets at proposing some security policies to mitigate the risks associated with SLAAC, by understanding its working scenario and trying to create the possible attack vector to highlight its security concerns. Hence, the implementation of these policies will directly add security to networks and make them resistant to SLAAC based attacks.

cs.CR↗