arXiv subjects

Alexander D. White

Publications and source records attributed to Alexander D. White.

13 recordsLinked to original sources

arXiv2025

Quantum critical electro-optic and piezo-electric nonlinearities

Electro-optics, the tuning of optical properties of materials with electric fields, is key to a multitude of quantum and classical photonics applications. However, a major obstacle preventing many emerging use cases is inefficient modulation in cryogenic environments, as traditional tuning mechanisms degrade at low temperatures. Guided by the connection between phase transitions and nonlinearity, we identify the quantum paraelectric perovskite SrTiO$_3$ (STO) as the strongest cryogenic electro-optic photonic material. As a result of the unique quantum paraelectric phase of STO, we demonstrate a dynamically tunable linear Pockels coefficient ($r_{33}$) exceeding 500 pm/V at $T=5$ K, and study its full temperature and bias dependence. We also measure an enhanced piezo-electric coefficient ($d_{33}$) above 90 pC/N. Both of these coefficients exceed all previously reported values for cryogenic materials, including lithium niobate ($r_{33}\approx24$ pm/V) and barium titanate ($r_{42}\approx170$ pm/V). Furthermore, by tuning STO towards \textit{quantum criticality} with oxygen isotope substitution we more than double the optical and piezo-electric nonlinearities, demonstrating a linear Pockels coefficient above 1100 pm/V. Our results probe the link between quantum phase transitions, dielectric susceptibility, and optical nonlinearities, unlocking opportunities in cryogenic optical and mechanical systems, and provide a framework for discovering new nonlinear materials.

cond-mat.mtrl-sci↗

arXiv2024

Rigorous Bound on the Violation of Dynamic Reciprocity Induced by Four-Wave Mixing

Dynamic reciprocity imposes stringent performance constraints on nonlinear optical devices such as isolators and circulators. The seminal result by Shi et al. establishes that nonlinear optical devices relying on the intensity-dependent refractive index obey dynamic reciprocity for small signals with spectrally distinct fields. However, it has also been recognized that it is possible to violate dynamic reciprocity by exploiting frequency mixing processes. In this paper, we establish a rigorous upper bound on this violation that is independent of device geometry. We demonstrate that this bound captures the parameter scalings of realizable physical systems, and that under some conditions dynamic reciprocity violation can grow unbounded to achieve arbitrary nonlinear isolation. These results provide an analytically robust version of dynamic reciprocity, as well as theoretical guidance for the development of power efficient nonlinear optical isolators and circulators.

physics.optics↗

arXiv2024

Unified laser stabilization and isolation on a silicon chip

Rapid progress in photonics has led to an explosion of integrated devices that promise to deliver the same performance as table-top technology at the nanoscale; heralding the next generation of optical communications, sensing and metrology, and quantum technologies. However, the challenge of co-integrating the multiple components of high-performance laser systems has left application of these nanoscale devices thwarted by bulky laser sources that are orders of magnitude larger than the devices themselves. Here we show that the two main ingredients for high-performance lasers -- noise reduction and isolation -- currently requiring serial combination of incompatible technologies, can be sourced simultaneously from a single, passive, CMOS-compatible nanophotonic device. To do this, we take advantage of both the long photon lifetime and the nonreciprocal Kerr nonlinearity of a high quality factor silicon nitride ring resonator to self-injection lock a semiconductor laser chip while also providing isolation. Additionally, we identify a previously unappreciated power regime limitation of current on-chip laser architectures which our system overcomes. Using our device, which we term a unified laser stabilizer, we demonstrate an on-chip integrated laser system with built-in isolation and noise reduction that operates with turnkey reliability. This approach departs from efforts to directly miniaturize and integrate traditional laser system components and serves to bridge the gap to fully integrated optical technologies.

physics.optics↗

arXiv2023

Titanium:Sapphire-on-insulator for broadband tunable lasers and high-power amplifiers on chip

Titanium:Sapphire (Ti:Sa) lasers have been essential for advancing fundamental research and technological applications. Ti:Sa lasers are unmatched in bandwidth and tuning range, yet their use is severely restricted due to their large size, cost, and need for high optical pump powers. Here, we demonstrate a monocrystalline Ti:Sa-on-insulator (Ti:SaOI) photonics platform which enables dramatic miniaturization, cost-reduction, and scalability of Ti:Sa technology. First, through fabrication of low-loss whispering gallery mode resonators, we realize a Ti:Sa laser operating with an ultra-low lasing threshold of 290 $μ$W. Then, through orders-of-magnitude improvement in mode confinement in Ti:SaOI waveguides, we realize the first integrated solid-state (i.e., non-semiconductor) optical amplifier operating below 1 $μ$m, with an ultra-wide bandwidth of 700 - 950 nm and peak gain of 64 dB/cm. We demonstrate unprecedented 17 dB distortion-free amplification of picosecond pulses to up to 2.3 nJ pulse energy, corresponding to a peak power of 1.0 kW. Finally, we demonstrate the first tunable integrated Ti:Sa laser, featuring narrow linewidths and a 24.7 THz tuning range, which, for the first time, can be pumped with low-cost, miniature, off-the-shelf green laser diodes. This opens doors to new modalities of Ti:Sa lasers (now occupying a footprint less than 0.15 mm$^2$), such as massively-scalable Ti:Sa laser array systems for a variety of applications. As a proof-of-concept demonstration, we employ a Ti:SaOI laser array as the sole optical control for a cavity quantum electrodynamics experiment with artificial atoms in silicon carbide. This work is a key step towards the democratization of Ti:Sa technology through a three orders-of-magnitude reduction in cost and footprint, as well as the introduction of solid-state broadband amplification of sub-micron wavelength light.

physics.optics↗

arXiv2023

An inverse-designed nanophotonic interface for excitons in atomically thin materials

Efficient nanophotonic devices are essential for applications in quantum networking, optical information processing, sensing, and nonlinear optics. Extensive research efforts have focused on integrating two-dimensional (2D) materials into photonic structures, but this integration is often limited by size and material quality. Here, we use hexagonal boron nitride (hBN), a benchmark choice for encapsulating atomically thin materials, as a waveguiding layer while simultaneously improving the optical quality of the embedded films. When combined with photonic inverse design, it becomes a complete nanophotonic platform to interface with optically active 2D materials. Grating couplers and low-loss waveguides provide optical interfacing and routing, tunable cavities provide a large exciton-photon coupling to transition metal dichalcogenides (TMD) monolayers through Purcell enhancement, and metasurfaces enable the efficient detection of TMD dark excitons. This work paves the way for advanced 2D-material nanophotonic structures for classical and quantum nonlinear optics.

physics.optics↗

arXiv2023

Tunable vector beam decoder by inverse design for high-dimensional quantum key distribution with 3D polarized spatial modes

Spatial modes of light have become highly attractive to increase the dimension and, thereby, security and information capacity in quantum key distribution (QKD). So far, only transverse electric field components have been considered, while longitudinal polarization components have remained neglected. Here, we present an approach to include all three spatial dimensions of electric field oscillation in QKD by implementing our tunable, on-a-chip vector beam decoder (VBD). This inversely designed device pioneers the "preparation" and "measurement" of three-dimensionally polarized mutually unbiased basis states for high-dimensional (HD) QKD and paves the way for the integration of HD QKD with spatial modes in multifunctional on-a-chip photonics platforms.

physics.optics↗

arXiv2022

Platform-agnostic waveguide integration of high-speed photodetectors with evaporated tellurium thin films

Many attractive photonics platforms still lack integrated photodetectors due to inherent material incompatibilities and lack of process scalability, preventing their widespread deployment. Here we address the problem of scalably integrating photodetectors in a photonic platform-independent manner. Using a thermal evaporation and deposition technique developed for nanoelectronics, we show that tellurium (Te), a quasi-2D semi-conductive element, can be evaporated at low temperature directly onto photonic chips to form air-stable, high-responsivity, high-speed, ultrawide-band photodetectors. We demonstrate detection at visible, telecom, and mid-infrared wavelengths, a bandwidth of more than 40 GHz, and platform-independent scalable integration with photonic structures in silicon, silicon nitride and lithium niobate.

physics.optics↗

arXiv2022

Integrated Passive Nonlinear Optical Isolators

Fiber and bulk-optical isolators are widely used to stabilize laser cavities by preventing unwanted feedback. However, their integrated counterparts have been slow to be adopted. While several strategies for on-chip optical isolation have been realized, these rely on either integration of magneto-optic materials or high frequency modulation with acousto-optic or electro-optic modulators. Here, we demonstrate an integrated approach for passively isolating a continuous wave laser using the intrinsically non-reciprocal Kerr nonlinearity in ring resonators. Using silicon nitride as a model platform, we achieve single ring isolation of 17-23dB with 1.8-5.5dB insertion loss, and a cascaded ring isolation of 35dB with 5dB insertion loss. Employing these devices, we demonstrate hybrid integration and isolation with a semi-conductor laser chip.

physics.optics↗

arXiv2022

Gradient-Based Optimization of Optical Vortex Beam Emitters

Vortex beams are stable solutions of Maxwell's equations that carry phase singularities and orbital angular momentum, unique properties that give rise to many applications in the basic sciences, optical communications, and quantum technologies. Scalable integration and fabrication of vortex beam emitters will allow these applications to flourish and enable new applications not possible with traditional optics. Here we present a general framework to generate integrated vortex beam emitters using photonic inverse design. We experimentally demonstrate generation of vortex beams with angular momentum spanning -3$\hbar$ to 3$\hbar$. We show the generality of this design procedure by designing a vortex beam multiplexer capable of exciting a custom vortex beam fiber. Finally, we produce foundry-fabricated beam emitters with wide-bandwidths and high-efficiencies that take advantage of a multi-layer heterogeneous integration.

physics.optics↗

arXiv2022

Superradiance in dynamically modulated Tavis-Cumming model with spectral disorder

Superradiance is the enhanced emission of photons from quantum emitters collectively coupling to the same optical mode. However, disorder in the resonant frequencies of the quantum emitters can perturb this effect. In this paper, we study the interplay between superradiance and spectral disorder in a dynamically modulated Tavis-Cummings model. Through numerical simulations and analytical calculations, we show that the effective cooperativity of the superradiant mode, which is always formed over an extensive number of emitters, can be multiplicatively enhanced with a quantum control protocol modulating the resonant frequency of the optical mode. Our results are relevant to experimental demonstration of superradiant effects in solid-state quantum optical systems, wherein the spectral disorder is a significant technological impediment towards achieving photon-mediated emitter-emitter couplings.

quant-ph↗

arXiv2021

Inverse-designed multi-dimensional silicon photonic transmitters

Modern microelectronic processors have migrated towards parallel computing architectures with many-core processors. However, such expansion comes with diminishing returns exacted by the high cost of data movement between individual processors. The use of optical interconnects has burgeoned as a promising technology that can address the limits of this data transfer. While recent pushes to enhance optical communication have focused on developing wavelength-division multiplexing technology, this approach will eventually saturate the usable bandwidth, and new dimensions of data transfer will be paramount to fulfill the ever-growing need for speed. Here we demonstrate an integrated intra- and inter-chip multi-dimensional communication scheme enabled by photonic inverse design. Using inverse-designed mode-division multiplexers, we combine wavelength- and mode- multiplexing and send massively parallel data through nano-photonic waveguides and optical fibres. Crucially, as we take advantage of an orthogonal optical basis, our approach is inherently scalable to a multiplicative enhancement over the current state of the art.

physics.app-ph↗

arXiv2021

Augmenting On-Chip Microresonator through Photonic Inverse Design

Recent advances in the design and fabrication of on-chip optical microresonators has greatly expanded their applications in photonics, enabling metrology, communications, and on-chip lasers. Designs for these applications require fine control of dispersion, bandwidth and high optical quality factors. Co-engineering these figures of merit remains a significant technological challenge due to design strategies being largely limited to analytical tuning of cross-sectional geometry. Here, we show that photonic inverse-design facilitates and expands the functionality of on-chip microresonators; theoretically and experimentally demonstrating flexible dispersion engineering, quality factor beyond 2 million on the silicon-on-insulator platform with single mode operation, and selective wavelength-band operation.

physics.optics↗

arXiv2020

Spectrally reconfigurable quantum emitters enabled by optimized fast modulation

The ability to shape photon emission facilitates strong photon-mediated interactions between disparate physical systems, thereby enabling applications in quantum information processing, simulation and communication. Spectral control in solid state platforms such as color centers, rare earth ions, and quantum dots is particularly attractive for realizing such applications on-chip. Here we propose the use of frequency-modulated optical transitions for spectral engineering of single photon emission. Using a scattering-matrix formalism, we find that a two-level system, when modulated faster than its optical lifetime, can be treated as a single-photon source with a widely reconfigurable photon spectrum that is amenable to standard numerical optimization techniques. To enable the experimental demonstration of this spectral control scheme, we investigate the Stark tuning properties of the silicon vacancy in silicon carbide, a color center with promise for optical quantum information processing technologies. We find that the silicon vacancy possesses excellent spectral stability and tuning characteristics, allowing us to probe its fast modulation regime, observe the theoretically-predicted two-photon correlations, and demonstrate spectral engineering. Our results suggest that frequency modulation is a powerful technique for the generation of new light states with unprecedented control over the spectral and temporal properties of single photons.

quant-ph↗