arXiv subjects

Aditya Bahulikar

Publications and source records attributed to Aditya Bahulikar.

4 recordsLinked to original sources

arXiv2026

Optimizing Finite Structures to Suppress the Photonic Density of States

We propose a topology-optimization framework for optimizing finite structures of arbitrary shape by combining density-based methods with level-set approaches. We first optimize regular polygonal structures to suppress the photonic density of states and find that the best performing polygon is consistent with a tiling of space with hexagonal unit cells. We next show that introducing cavities into hexagonal structures further suppresses the photonic density of states, particularly when the cavity is also hexagonal. Such a result would find application in the design of fiber-optic cables. We then describe an approach for optimizing arbitrary x-simple or y-simple designs that can recover finite supercells of a hexagonal unit cell. Our approach can therefore discover the symmetry of photonic-crystal primitive unit cells that significantly suppress the photonic density of states for a given set of material parameters within a single optimization.

physics.optics↗

arXiv2025

Structure-Adaptive Topology Optimization Framework for Photonic Band Gaps with TE-Polarized Sources

Leveraging our structure-adaptive topology optimization framework based on the integration of the photonic density of states over a frequency window for the TM polarization of light [see A. Bahulikar et al., arXiv:2411.09165 (2025)], we show that the $\Gamma$-point and full Brillouin zone integration schemes can also recover two-dimensional photonic crystals for TE polarization. For the $\Gamma$-point formalism, we employ the scalar magnetic field formulation of the electromagnetic wave equation with independent sources polarized in the x and y directions. For the full Brillouin zone formalism, we employ the vector electric field formulation of the electromagnetic wave equation, again with independent sources polarized in the x and y directions. This work can simultaneously treat frequency-dependent optical response, allow for targeted optimization for a given frequency and reciprocal lattice vector pair, and inherently encourage binarized designs.

physics.optics↗

arXiv2024

Theoretical Investigation of Yield-Enhancing Equilibrium Negatively Ionized Tin-Vacancy Center Preparation Pathways in N-Doped Diamond

The elucidation of the mechanism of Sn$V^-$ formation in diamond is especially important as the Sn$V^-$ color center has the potential to be a superior single-photon emitter when compared to the N$V$ and to other Group IV color centers. The typical formation of the Sn$V$ involves placing Sn in diamond by ion implantation, but the formation of a charged Sn$V$ species requires an additional complication. This complication is related to the energy cost associated with electronic transitions within the host diamond. Effectively, producing the Sn$V^-$ charge state using an electron obtained from a band edge of the host diamond is less energetically favorable than having the Sn$V^-$ receive an electron from a neighboring donor dopant. Among donor dopants, substitutional N (N$_\text{C}$) is always present in even the purest synthetic or natural diamond sample. The mechanism of electron donation by N$_\text{C}$ has been proposed by Collins for charging the N$V$ in diamond and it has been used to interpret many experimental results. Therefore, in this paper we use DFT to explore the pathways for the formation of the Sn$V^-$ charge state due to electron donation arising from the presence of N$_\text{C}$ in the host diamond. Explicitly, defect concentrations are calculated in equilibrium in each of the explored pathways to determine the yield of the Sn$V^-$ throughout each of the pathways. The importance of our work is to suggest experimental ways of enhancing the yield of charged states like the Sn$V^-$ in diamond for transformative applications in optoelectronics and quantum information.

cond-mat.mtrl-sci↗

arXiv2024

Structure-Adaptive Topology Optimization Framework for Photonic Band Gaps with TM-Polarized Sources

We present a structure-adaptive topology optimization framework for engineering photonic band gaps with TM-polarized sources based on computation of the photonic density of states with a uniform source substituting for the standard Dirac delta function sources in formalisms analogous to $\Gamma$-point integration and to integration over a full Brillouin zone. We generalize the limiting uniform and Dirac delta function sources to more general collections of sources, such that the union of the sources in a given collection is hyperuniform. The uniform-source approach necessarily leads to the fastest computations. We also demonstrate how our approach can be generalized to the treatment of the frequency-dependent optical response of materials. Finally, we show that we can recover known two-dimensional photonic crystals for the TM polarization. A key advantage of our work is its ability to optimize for a specific midgap frequency and band gap in a structure-adaptive manner. Our work leverages the insight that the determination of the minimum supercell size and the minimum precision to which the frequencies within the photonic band gap must be sampled will lead to the observation of photonic-crystal structures when the $\Gamma$-point formalism for the uniform-source approach is employed. Additionally, our $\Gamma$-point and full Brillouin zone formalisms for the uniform-source approach inherently encourage binarized designs even in gradient descent.

physics.optics↗