arXiv subjects

Andrew S. Greenspon

Publications and source records attributed to Andrew S. Greenspon.

3 recordsLinked to original sources

arXiv2025

Nanophotonic waveguide chip-to-free-space beam scanning at 68 Million Spots/(s$\cdot$mm$^{2}$)

A seamless chip-to-world photonic interface enables wide-ranging advancements in optical ranging, display, communication, computation, imaging, and light-matter interaction. An optimal solution allows for 2D scanning of a diffraction-limited beam from anywhere on a photonic chip over a large number of beam-spots in free-space. Currently, devices with direct PIC integration rely on tiled apertures with poor mode qualities, large footprints, and complex control systems. Micro-mechanical beam scanners have good beam quality but lack direct PIC integration and are inertially-limited due to the use of bulk optical components or structures in which the optical aperture and actuator sizes are inextricably linked, resulting in trade-offs among resolution, speed, and footprint. Here, we overcome these limitations with the photonic "ski-jump": a nanoscale optical waveguide monolithically integrated atop a piezoelectrically actuated cantilever which passively curls ~90$^{\circ}$ out-of-plane in a footprint of <0.1 mm$^{2}$, emits sub-micron diffraction-limited optical modes, and exhibits kHz-rate mechanical resonances with quality factors exceeding 10,000. This enables two-dimensional beam-scanning with footprint-adjusted spot-rates of 68.6 mega-spots/(s$\cdot$mm$^{2}$) at CMOS-level voltages, which is equivalent to a 1 megapixel display at 100 Hz from a 1.5 mm$^{2}$ footprint, and exceeds the performance of state-of-the-art MEMS mirrors by >50$\times$. Using this device, we demonstrate image projection, video projection, and the initialization and readout of single photons from silicon vacancy centers in diamond waveguides. Based on current performance, we identify pathways for achieving >1 giga-spots at kHz-rates in a ~1 cm$^{2}$ area to provide a seamless, scalable optical pipeline between integrated photonic processors and the free-space world.

physics.optics↗

arXiv2024

Scalable construction of hybrid quantum photonic cavities

Nanophotonic resonators are central to numerous applications, from efficient spin-photon interfaces to laser oscillators and precision sensing. A leading approach consists of photonic crystal (PhC) cavities, which have been realized in a wide range of dielectric materials. However, translating proof-of-concept devices into a functional system entails a number of additional challenges, inspiring new approaches that combine: resonators with wavelength-scale confinement and high quality factors; scalable integration with integrated circuits and photonic circuits; electrical or mechanical cavity tuning; and, in many cases, a need for heterogeneous integration with functional materials such as III-V semiconductors or diamond color centers for spin-photon interfaces. Here we introduce a concept that generates a finely tunable PhC cavity at a select wavelength between two heterogeneous optical materials whose properties satisfy the above requirements. The cavity is formed by stamping a hard-to-process material with simple waveguide geometries on top of an easy-to-process material consisting of dielectric grating mirrors and active tuning capability. We simulate our concept for the particularly challenging design problem of multiplexed quantum repeaters based on arrays of cavity-coupled diamond color centers, achieving theoretically calculated unloaded quality factors of $10^6$, mode volumes as small as $1.2(λ/n_{eff})^3$, and maintaining >60 percent total on-chip collection efficiency of fluorescent photons. We further introduce a method of low-power piezoelectric tuning of these hybrid diamond cavities, simulating optical resonance shifts up to ~760 GHz and color center fluorescence tuning of 5 GHz independent of cavity tuning. These results will motivate integrated photonic cavities toward larger scale systems-compatible designs.

physics.optics↗

arXiv2020

Enhanced cavity coupling to silicon monovacancies in 4-H Silicon Carbide using below bandgap laser irradiation and low temperature thermal annealing

The negatively charged silicon monovacancy $V_{Si}^-$ in 4H-silicon carbide (SiC) is a spin-active point defect that has the potential to act as a qubit or quantum memory in solid-state quantum computation applications. Photonic crystal cavities (PCCs) can augment the optical emission of the $V_{Si}^-$, yet fine-tuning the defect-cavity interaction remains challenging. We report on two post-fabrication processes that result in enhancement of the $V_1^{'}$ optical emission from our 1-dimensional PCCs, indicating improved coupling between the ensemble of silicon vacancies and the PCC. One process involves below bandgap illumination at 785 nm and 532 nm wavelengths and above bandgap illumination at 325 nm, carried out at times ranging from a few minutes to several hours. The other process is thermal annealing at $100^o C$, carried out over 20 minutes. Every process except above bandgap irradiation improves the defect-cavity coupling, manifested in augmented Purcell factor enhancement of the $V_1^{'}$ zero phonon line at 77K. The below bandgap laser process is attributed to a modification of charge states, changing the relative ratio of $V_{Si}^0$ (dark state) to $V_{Si}^-$ (bright state), while the thermal annealing process may be explained by diffusion of carbon interstitials, $C_i$, that subsequently recombine with other defects to create additional $V_{Si}^-$s. Above bandgap radiation is proposed to initially convert $V_{Si}^{0}$ to $V_{Si}^-$, but also may lead to diffusion of $V_{Si}^-$ away from the probe area, resulting in an irreversible reduction of the optical signal. Observations of the PCC spectra allow insights into defect modifications and interactions within a controlled, designated volume and indicate pathways to improve defect-cavity interactions.

physics.optics↗