Event
Ph.D. Research Proposal Exam: Neelesh Kumar Vij
Wednesday, October 7, 2026
11:00 a.m.
AVW 2460
Souad Nejjar
301 405 8135
snejjar@umd.edu
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Neelesh Kumar Vij
Committee:
Professor Edo Waks (Chair)
Professor Ron Walsworth
Professor Carlos Rios Ocampo
Date/time: Wednesday, October 7 at 11:00 AM
Location: AVW 2460
Title: Inverse design of photonic crystal cavity
Abstract: Photonic crystal cavities confine light to subwavelength volumes, which results in enhanced light-matter interaction. This property can be used for applications in low-power photonics, opto-electronics, nonlinear optics, and quantum information. Crucial to these applications are cavities that combine high quality factors (Q), low mode volumes, and efficient optical coupling. However, optimizing across these metrics requires exploring a design space that grows exponentially with the number of parameters, rendering manual and heuristic optimization impractical, thereby motivating different design strategies such as inverse design. Previous inverse design efforts targeted low mode volumes and high Q, compromising the coupling efficiency of the cavity in the process. However, several applications demand finer control of the far-field and achieving such precise control of the cavity far-field emission remains a significant challenge.
We present a novel inverse design framework that simultaneously optimizes cavity quality factor and far-field numerical aperture, both specified as design targets. Using this method, we design L3 photonic crystal cavities, with varying far-field numerical apertures, in the visible wavelength regime and fabricate them in silicon nitride. Photoluminescence measurements confirm experimental control of the far-field numerical aperture and reveal a 27.4-fold and 3.4-fold (Q ~ 3700) simultaneous improvement in the coupling efficiency and quality factor respectively when compared to the standard L3 cavity. We further propose integrating these inverse designed cavities with colloidal halide perovskite quantum dots that are emerging as promising light emitters. With the high measured quality factors of our inverse designed cavities, optical nonlinearity and low-threshold power nanolasers can be realized.
