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Lindell M. Williams

Publications and source records attributed to Lindell M. Williams.

5 recordsLinked to original sources

A generative pre-trained transformer with Kerr-soliton attention

Artificial intelligence systems, particularly through generative pre-trained transformers (GPTs), have enabled capability-rich language models, but their operation incurs substantial costs in digital computation, memory, and data movement. Attention is a core operation in GPTs that computes context-dependent weights for input tokens. Since deep-learning models are defined by compositions of nonlinear transformations, identifying physical systems that can realize them offers a pathway to higher efficiency. Here, we introduce Kerr-soliton attention, harnessing driven-dissipative nonlinear dynamics in a resonator to realize, execute, and validate a deep-learning attention operation in physical hardware. We train a transformer language model using an analytic Kerr-soliton attention response and explore generative inference by streaming model-produced inputs through the experimental system. We observe high-fidelity agreement between the experimentally produced nonlinear weights and those predicted by the analytic Kerr-soliton model. Computation proceeds through streaming-in-time excitation of an ensemble of Kerr solitons, with inputs encoded as temporal signals that evolve under nonlinear dynamics. Our approach maps memory and compute onto the same physical dynamics, relaxing the need for intermediate digital storage and reducing data movement. This work points toward hybrid digital-physical learning systems in which Kerr solitons provide physical memory and high-bandwidth streaming nonlinear processing within deep-learning models.

physics.optics

Second-harmonic stabilization of a bulk photonic resonator

The resonant modes of optical cavities provide a powerful resource for laser-frequency stabilization, underpinning high-precision metrology and coherent signal generation. Photonic resonators in which the optical mode propagates through material offer a compact alternative to vacuum Fabry-Perot cavity systems, but their performance is limited by sensitivity of the material to the ambient environment. In this work, we explore second-harmonic (SH) stabilization, which exploits the interplay of a dispersive mode structure against the strict energy conservation of second-harmonic generation. Operationally, we use two, 1550 nm lasers to PDH-detect octave-spaced resonant modes of an ultra-high-Q photonic resonator with one laser frequency-doubled to 775 nm. Under SH stabilization, the microwave frequency offset between the 1550 nm lasers, which we refer to as the SH signal ($f_{SH}$) maps the absolute frequency of the 1550 nm laser to an electronic signal. We characterize this mapping through comparison of the absolute optical frequency inference provided by $f_{SH}$ to an out-of-loop optical measurement, and our results suggest $f_{SH}$ accurately proxies frequency drift. We evaluate the sensitivity and noise floor of this technique, considering contributions from laser locking and bulk material properties, and conclude that $f_{SH}$ is sufficiently sensitive to enhance long-term laser-frequency stability with respect to the resonator. These results demonstrate SH stabilization as a useful technique that infers absolute drift, thereby enabling the increased stability of future compact, precision frequency references.

physics.optics

Monolithic 3D integration of tantalum pentoxide photonics on arbitrary substrates

The photonics landscape encompasses a wide scope of material platforms, each optimized for specific functionalities, yet no platform meets the demands of all current and evolving photonic applications. While combining integrated photonics materials enhances overall capability - such as unifying nonlinear optics, low-loss passive devices, and electro-optics - material and process compatibility remains a major challenge. We introduce full-wafer, monolithic 3D integration of tantalum pentoxide (Ta$_2$O$_5$, hereafter tantala) photonics onto arbitrary substrates, which we explore here with thin-film lithium niobate (LN) on silicon. Tantala's unique properties, importantly room-temperature deposition, low-temperature annealing, and low stress in thick films optimized for phase matching, make it well suited for monolithic 3D integration without compromising substrate performance or compatibility. We demonstrate low-loss, high-quality-factor microresonators and nanophotonics in tantala, robust quasi-phase-matching in poled LN waveguides, and efficient 3D interlayer routing. This enables us to demonstrate a rich palette of nonlinear frequency conversion processes, including $χ^{(3)}$ optical parametric oscillation (OPO) and soliton microcomb generation in tantala microresonators and photonic-crystal resonators, $χ^{(2)}$ second-harmonic generation (SHG) in periodically poled LN, and combinations thereof. Monolithic 3D integration with tantala opens a new paradigm for scalable, multifunctional photonic systems, enabling visible, near-IR, and nonlinear operation into existing photonic infrastructure.

physics.optics

Activating high-power parametric oscillation in photonic-crystal resonators

By engineering the mode spectrum of a Kerr microresonator, we selectively activate nonlinear phase matching amongst broadband parametric gain. At threshold, optical parametric oscillators (OPOs) emerge from vacuum fluctuations in the presence of a pump laser, and above threshold, OPOs seed the formation of intraresonator patterns and states, such as chaos and solitons. These competing nonlinear processes hinder an important application of OPOs as wavelength-variable, low-noise sources. Recently, nanopatterned microresonator OPOs have leveraged photonic crystal bandgaps to enable universal phase matching and control of nonlinear interactions. Here, we explore a design paradigm optimized for high-output power that uses geometric dispersion to suppress nonlinear interactions and a photonic crystal bandgap to activate only a single OPO interaction. Our devices convert an input pump laser to output signal and idler waves with powers exceeding 40 mW while maintaining spectral purity and side-mode suppression ratios greater than 40 dB. We show that this approach suits custom wavelengths by measuring four independent oscillators that vary only photonic crystal parameters to select output waves. Our experiments demonstrate that microresonators functionalized by photonic crystals offer a versatile and lossless palette of controls for nonlinear laser conversion.

physics.optics

Heterogeneous tantala photonic integrated circuits for sub-micron wavelength applications

Atomic and trapped-ion systems are the backbone of a new generation of quantum-based positioning, navigation, and timing (PNT) technologies. The miniaturization of such quantum systems offers tremendous technological advantages, especially the reduction of system size, weight, and power consumption. Yet, this has been limited by the absence of compact, standalone photonic integrated circuits (PICs) at the wavelengths suitable for these instruments. Mobilizing such photonic systems requires development of fully integrated, on-chip, active components at sub-micrometer wavelengths. We demonstrate heterogeneous photonic integrated circuits operating at 980 nm based on wafer-scale bonding of InGaAs quantum well active regions to tantalum pentoxide passive components. This high-yield process provides > 95 % surface area yield and enables integration of > 1300 active components on a 76.2 mm (3 inch) silicon wafer. We present a diverse set of functions, including semiconductor optical amplifiers, Fabry-Perot lasers, and distributed feedback lasers with 43 dB side-mode suppression ratio and > 250 GHz single-mode tuning range. We test the precise wavelength control and system level functionality of the on-chip lasers by pumping optical parametric oscillation processes in microring resonators fabricated on the same platform, generating short-wavelength signals at 778 nm and 752 nm. These results provide a pathway to realize fully functional integrated photonic engines for operation of compact quantum sensors based on atomic and trapped-ion systems.

physics.optics