arXiv subjects

Nils T. Otterstrom

Publications and source records attributed to Nils T. Otterstrom.

At least 19 recordsLinked to original sources

arXiv2026

Acoustoelectrically enhanced acousto-optic modulation in an integrated silicon nitride and thin film lithium niobate platform

Acoustoelectric interactions in piezoelectric-semiconductor heterostructures allow the propagation characteristics of microwave frequency phonons in piezoelectric media to be controlled and radically enhanced, providing electrically controllable phonon gain, large velocity tuning, isolation, and circulation, as well as extremely large electron-mediated phononic nonlinearities. Here, for the first time, we create such a piezoelectric-semiconductor heterostructure with lithium-niobate-on-insulator and InGaAs that also supports guided optical modes through the addition of a silicon nitride waveguide and modification of the acoustic materials to provide an optical lower cladding. We use this new architecture to demonstrate acoustoelectrically enhanced acousto-optic modulation, where 1 GHz phonons are piezoelectrically generated and acoustoelectrically amplified on-chip by up to 60 dB before impinging on the optical waveguide, providing pure phase modulation with a $V_πL$ figure-of-merit of 0.077 V-cm while only consuming 3.77 mW of DC electrical power to provide the amplification. We then consider future applications enabled by these functionalities and describe a novel tunable optical delay and an optoelectronic oscillator (OEO) analog---an acoustoelectrically enhanced opto-acoustic oscillator (AE-OAO). We show that using Brillouin optomechanical transduction and acoustoelectrically lossless acoustic time delay, the AE-OAO could replace kilometers of optical fiber delay used in OEOs but on a single, centimeter-scale chip.

physics.optics↗

arXiv2026

Mode-selective acousto-electric modulation of phonons in a silicon photonic platform

Acousto-electric (AE) interactions enable electrical control of acoustic propagation through piezoelectric media. Bringing AE control onto integrated photonic platforms provides a powerful on-chip control mechanism to reconfigure both the acoustic propagation through piezoelectric media. Bringing AE control onto integrated photonic platforms provides a powerful on-chip control mechanism to reconfigure both the acoustic delay line response and the effective photon-phonon interaction by electrically tuning the phonon propagation. Here we report a mode-selective AE modulation effect in a scalable aluminum nitride on silicon-on-insulator (AlN-on-SOI) platform. An applied DC field is seen to modulate the phonon dissipation via changes in carrier concentration in a mode-selective fashion, producing up to 20 dB forward transmission suppression of non-fundamental modes within an acoustic delay line while maintaining the fundamental Rayleigh mode, a phenomenon not captured by conventional AE treatments. To probe these dynamics, we integrate an optical waveguide along the acoustic delay line, providing a broadband, non-destructive interface between the acoustic and optical domains. Leveraging both this optical interface and the underlying mode selectivity, we demonstrate proof-of-concept multi-domain transduction and Rayleigh-mode filtering on this hybrid platform, outlining a scalable path toward electrically reconfigurable mode engineering and microwave-photonic functionality.

physics.optics↗

arXiv2026

Resonant multi-harmonic acousto-optics for programmable frequency control of visible light in a CMOS platform

Scaling quantum control for atoms, ions, and solid-state emitters requires gigahertz-frequency spectral control of high-power visible light in a volume-manufacturable platform. Silicon nitride photonics provides high power handling and CMOS-foundry compatibility but has no intrinsic mechanism for high-speed modulation. Integration with piezoelectric materials enables acousto-optic phase modulation, and mechanical resonant enhancement has made it efficient at gigahertz frequencies. However, a single resonance restricts the modulation waveform to a single tone, imposing Bessel-function sideband amplitudes and limiting frequency-shifting efficiency to 33.9%. Here we engineer a silicon nitride acousto-optic microstructure to support harmonically spaced resonances at 1.14 GHz and 2.28 GHz, each strongly optomechanically coupled to a 730 nm guided optical mode, so that tailored non-sinusoidal modulation waveforms can be resonantly synthesized. By piezoelectrically controlling the two mechanical amplitudes and their relative phase, we demonstrate 50% conversion to one sideband (1.5x the single-tone theoretical maximum), a flat seven-line comb, and a frequency shift with 60 dB carrier and 53 dB image suppression - to our knowledge the highest reported for an integrated modulator. The devices are fabricated in a 200 mm CMOS foundry, and we measure 91.7% yield without post-fabrication tuning across 36 devices from three wafers. We also show how the technique can be straightforwardly scaled to three or more harmonics. This result overcomes the trade-off between resonant enhancement and spectral programmability, with important consequences including improved single-qubit gate efficiency for hyperfine qubits.

physics.optics↗

arXiv2026

Ultra-low loss piezo-optomechanical low-confinement silicon nitride platform for visible wavelength quantum photonic circuits

Realizing photonic quantum computing at scale requires integrated circuits that combine ultra-low loss with fast, low-power, low-hysteresis, and low-crosstalk reconfiguration. These requirements are particularly challenging at visible wavelengths, where many quantum resource-state generators, including single-photon sources and quantum memories, naturally operate. Low-confinement silicon nitride waveguides offer the requisite loss performance, but conventional thermo-optic modulators dissipate significant static power, driving thermal crosstalk and precluding cryogenic operation. Visible-wavelength piezo-optomechanical circuits avoid these drawbacks, but existing demonstrations rely either on high-confinement waveguides with propagation losses of 35-100 dB/m, or on low-confinement platforms using foundry-incompatible PZT. Here we combine piezo-optomechanical actuation with a CMOS-foundry-fabricated, low-confinement silicon nitride platform, achieving 2.6 dB/m propagation loss at 780 nm, megahertz-scale modulation bandwidth, a half-wave voltage-length product of 2.8 Vm, and negligible hysteresis. We demonstrate reconfigurable Mach-Zehnder interferometers with 0.63 dB loss per spiral phase shifter, enabling deep, actively reconfigurable visible-wavelength quantum photonic circuits.

physics.optics↗

arXiv2026

A heterogeneously integrated coupled-cavity frequency beam splitter

Frequency encoded photonic qubits promise a scalable path towards high-dimensional quantum information processing, but require efficient components for coherently mixing frequency modes. Coupled cavity modulators provide this functionality by using only a single driving microwave tone to couple hybridized optical supermodes. Here, we demonstrate a heterogeneously integrated thin-film lithium-niobate-on-silicon coupled-cavity modulator that realizes tunable bidirectional frequency mode transformations, including $50/50$ beam splitting and near complete frequency swapping with $>20~\mathrm{dB}$ pump extinction at a $10~\mathrm{GHz}$ supermode splitting. Because the electro-optic film is bonded onto a foundry fabricated silicon photonics platform, the approach is compatible with co-integration of photon pair sources, spectral filters, active tuning elements, and single photon detectors. We also bond thin-film lithium tantalate onto the same coupled-cavity platform, demonstrating material flexibility for scalable integrated frequency bin quantum photonic circuits.

quant-ph↗

arXiv2026

Noise factor of Brillouin amplifiers

Stimulated Brillouin scattering (SBS), an optical nonlinearity arising from photon-phonon interactions, has formed the basis for a large class of optical signal processing devices, including Brillouin amplifiers. A limiting factor of such amplifiers is the noise due to thermal-mechanical fluctuations that the phonons imprint on the optical signal. Prior work has either inferred or experimentally observed a noise factor ($F$) that depends only on the thermal occupation of the phonons ($F\approx 1+n_{th}$). We show that this noise factor results naturally from a Hamiltonian-based spatio-temporal coupled mode treatment in the limit of large Brillouin amplification and when phonon propagation is neglected. Moreover, this theoretical framework allows us to extend our treatment to a much larger and more representative parameter space for emerging SBS systems; specifically, this analysis accounts for the forward or backward nature of the scattering process and the effects of phonon propagation, optical loss, and small Brillouin gains. Our results demonstrate that the noise factor can deviate radically from $F\approx 1+n_{th}$ for a host of modern SBS devices, especially those in which phonon propagation significantly changes the coupled mode dynamics.

physics.optics↗

arXiv2026

Noise and dynamics in acoustoelectric waveguides

We present a quantum field theoretic formulation of acoustoelectric interactions in waveguide-like systems of arbitrary cross-section. Building on an open quantum systems approach, we derive a unified description of plasmon-phonon coupling that incorporates dissipation, noise, and the influence of drift currents. Our analysis captures both bulk and surface plasmon modes, highlighting how drift currents Doppler-shift plasmonic resonances and reshape the phonon noise spectrum. The resulting Heisenberg-Langevin equations yield closed-form expressions for frequency shifts, gain, and noise power spectra, enabling direct evaluation of performance metrics such as the noise factor in acoustoelectric amplifiers and oscillators. In the appropriate limits, this framework reproduces known results while extending them to complex geometries.

physics.optics↗

arXiv2026

Frequency-Time Multiplexing for Near-Deterministic Generation of n-Photon Frequency-Bin States

One of the primary challenges of photonic quantum information processing is the on-demand preparation of multiple single-photon-level quantum states from probabilistic photon pair sources. Motivated by recent developments in frequency-bin-encoded photonic quantum information processing, here we consider active time multiplexing to generate n-photon states, where n single photons with n distinct frequencies occupy the same spatiotemporal mode. We devise an approach that uses optical quantum memories to manipulate the temporal mode of heralded single photons and an array of fiber Bragg grating reflectors to jointly manipulate the frequency and temporal modes of the photons, overlapping n photons in n separate frequency bins into a single spatiotemporal mode. We calculate multiphoton state generation rates that, accounting for loss, are realistically achievable with commercially available hardware. Using only a single free-space switchable delay loop for an optical quantum memory, this scheme could feasibly produce 8-photon states at an average rate of 1 kHz.

quant-ph↗

arXiv2026

Modeling integrated frequency shifters and beam splitters

Photonic quantum computing is a strong contender in the race to fault-tolerance. Recent proposals using qubits encoded in frequency modes promise a large reduction in hardware footprint, and have garnered much attention. In this encoding, linear optics, i.e., beam splitters and phase shifters, is necessarily not energy-conserving, and is costly to implement. In this work, we present designs of frequency-mode beam splitters based on modulated arrays of coupled resonators. We develop a methodology to construct their effective transfer matrices based on the SLH formalism for quantum input-output networks. Our methodology is flexible and highly composable, allowing us to define $N$-mode beam splitters either natively based on arrays of $N$-resonators of arbitrary connectivity or as networks of interconnected $l$-mode beam splitters, with $l<N$. We apply our methodology to analyze a two-resonator device, a frequency-domain phase shifter and a Mach-Zehnder interferometer obtained from composing these devices, a four-resonator device, and present a formal no-go theorem on the possibility of natively generating certain $N$-mode frequency-domain beam splitters with arrays of $N$-resonators.

quant-ph↗

arXiv2026

A paradigm for universal quantum information processing with integrated acousto-optic frequency beamsplitters

Frequency-bin encoding offers tremendous potential in quantum photonic information processing, in which a single waveguide can support hundreds of lightpaths in a naturally phase-stable fashion. This stability, however, comes at a cost: arbitrary unitary operations can be realized by cascaded electro-optic phase modulators and pulse shapers, but require nontrivial numerical optimization for design and have thus far been limited to discrete tabletop components. In this article, we propose, formalize, and computationally evaluate a new paradigm for universal frequency-bin quantum information processing using acousto-optic scattering processes between distinct transverse modes. We show that controllable phase matching in intermodal processes enables 2$\times$2 frequency beamsplitters and transverse-mode-dependent phase shifters, which together comprise cascadable FRequency-transverse-mODe Operations (FRODOs) that can synthesize any unitary via analytical decomposition procedures. Modeling the performance of both random gates and discrete Fourier transforms, we demonstrate the feasibility of high-fidelity quantum operations with existing integrated photonics technology, highlighting prospects of parallelizable operations achieving 100\% bandwidth utilization. Our approach is realizable with CMOS technology, opening the door to scalable on-chip quantum information processing in the frequency domain.

quant-ph↗

arXiv2025

In situ quantum verification of polarization-stabilized optical channels

The active stabilization of polarization channels is a task of growing importance as quantum networks move to deployed demonstrations over existing fiber infrastructure. However, the uniquely strict requirements for high-fidelity qubit transmission complicate the extent to which classical solutions may apply to future quantum networks, particularly in terms of recognizing noise sources present in low-flux, nonunitary channels. Here we introduce a novel in situ benchmarking approach that augments a classical polarization tracking system, limited to unitary correction, with simultaneously transmitted quantum light for ancilla-assisted process tomography of the full quantum map. Implemented in a local-area quantum network, our method uses the reconstructed map both to validate the classical compensation and to expose noise sources it fails to capture. A sliding measurement window that continuously updates the estimated quantum process further increases sensitivity to rapid channel fluctuations. Our results should unlock new opportunities for in situ channel characterization in quantum-classical coexistence networks.

quant-ph↗

arXiv2025

Gigahertz-Frequency, Acousto-Optic Phase Modulation of Visible Light in a CMOS-Fabricated Photonic Circuit

Here we present an efficient, visible-light, gigahertz-frequency acousto-optic modulator fabricated on a 200 mm wafer in a volume CMOS foundry. Our device combines a piezoelectric transducer and a photonic waveguide within a single microstructure that confines both a propagating optical mode and an electrically excitable breathing-mode mechanical resonance. By tuning the device's geometry to optimize the optomechanical interaction, we achieve modulation depths exceeding 2 rad with 15 mW applied microwave power at 2.31 GHz in a 2 mm long device. This corresponds to a modulation figure of merit of $V_π\cdot L$ = 0.26 Vcm in a visible-light, integrated acousto-optics platform that can be straightforwardly extended to a wide range of optical wavelengths and modulation frequencies. For the important class of gigahertz-frequency modulators that can handle hundreds of milliwatts of visible-light optical power, which are critical for scalable quantum control systems, this represents a 15x decrease in $V_π$ and a 100x decrease in required microwave power compared to the commercial state-of-the-art and existing work in the literature.

physics.optics↗

arXiv2024

A Terahertz Bandwidth Nonmagnetic Isolator

Integrated photonics could bring transformative breakthroughs in computing, networking, imaging, sensing, and quantum information processing, enabled by increasingly sophisticated optical functionalities on a photonic chip. However, wideband optical isolators, which are essential for the robust operation of practically all optical systems, have been challenging to realize in integrated form due to the incompatibility of magnetic media with these circuit technologies. Here, we present the first-ever demonstration of an integrated non-magnetic optical isolator with terahertz-level optical bandwidth. The system is comprised of two acousto-optic frequency-shifting beam splitters which create a non-reciprocal multimode interferometer exhibiting high-contrast, nonreciprocal light transmission. We dramatically enhance the isolation bandwidth of this system by precisely dispersion balancing the paths of the interferometer. Using this approach, we demonstrate integrated nonmagnetic isolators with an optical contrast as high as 28 dB, insertion losses as low as -2.16 dB, and optical bandwidths as high as 2 THz (16 nm). We also show that the center frequency and direction of optical isolation are rapidly reconfigurable by tuning the relative phase of the microwave signals used to drive the acousto-optic beam splitters. With their CMOS compatibility, wideband operation, low losses, and rapid reconfigurability, such integrated isolators could address a key barrier to the integration of a wide range of photonic functionalities on a chip. Looking beyond the current demonstration, this bandwidth-scalable approach to nonmagnetic isolation opens the door to ultrawideband (>10 THz) isolators, which are needed to shrink state-of-the-art imaging, sensing, and communications systems into photonic integrated circuits.

physics.optics↗

arXiv2023

Laser cooling of traveling wave phonons in an optical fiber

In recent years, optical control of mechanical oscillators has emerged as a critical tool for everything from information processing to laser cooling. While traditional forms of optomechanical cooling utilize systems comprised of discrete optical and mechanical modes, it has recently been shown that cooling can be achieved in a chip-based system that possesses a continuum of modes. Through Brillouin-mediated phonon-photon interactions, cooling of a band of traveling acoustic waves can occur when anti-Stokes scattered photons exit the system more rapidly than the relaxation rate of the mechanical waves -- to a degree determined by the acousto-optic coupling. Here, we demonstrate that a continuum of traveling wave phonons can be cooled within an optical fiber, extending this physics to macroscopic length scales. Leveraging the large acousto-optic coupling permitted within a liquid-core optical fiber, heterodyne spectroscopy reveals power-dependent changes in spontaneous Brillouin scattering spectra that indicate a reduction of the thermal phonon population by 21K using 120 mW of injected laser power.

physics.optics↗

arXiv2022

Intermodal strong coupling and wideband, low-loss isolation in silicon

Strong coupling enables a diverse set of applications that include optical memories, non-magnetic isolators, photonic state manipulation, and signal processing. To date, strong coupling in integrated platforms has been realized using narrow-linewidth high-Q optical resonators. In contrast, here we demonstrate wideband strong coupling between two photonic bands. The indirect interband photonic transition is controlled by electrically driving phonons in a linear silicon waveguide. Under large acoustic drive, the system features a Rabi-like energy exchange between two waveguide modes, demonstrating strong coupling. When tuned to unity energy conversion, our system unlocks a set of powerful applications, including optical modulators, routers and filters. In particular, we demonstrate a low loss (-2.08 dB) acousto-optic modulator (AOM) with pump suppression ratio > 55 dB. We also reconfigure our system to demonstrate a non-magnetic, low-loss (< 1 dB) and broadband (59 GHz 10 dB isolation bandwidth) optical isolator.

physics.optics↗

arXiv2021

Modulation of Brillouin optomechanical interactions via acoustoelectric phonon-electron coupling

Optomechanical Brillouin nonlinearities -- arising from the coupling between traveling photons and phonons -- have become the basis for a range of powerful optical signal processing and sensing technologies. The dynamics of such interactions are largely set and limited by the host material's elastic, optical, and photo-elastic properties, which are generally considered intrinsic and static. Here we show for the first time that it is feasible to dynamically reconfigure the Brillouin nonlinear susceptibility in transparent semiconductors through acoustoelectric phonon-electron coupling. Acoustoelectric interactions permit a wide range of tunability of the phonon dissipation rate and velocity, perhaps the most influential parameters in the Brillouin nonlinear susceptibility. We develop a Hamiltonian-based analysis that yields self-consistent dynamical equations and noise coupling, allowing us to explore the physics of such acoustoelectrically enhanced Brillouin (AEB) interactions and show that they give rise to a dramatic enhancement of the performance of Brillouin-based photonic technologies. Moreover, we show that these AEB effects can drive systems into new regimes of fully-coherent scattering that resemble the dynamics of optical parametric processes, dramatically different than the incoherent traditional Brillouin limit. We propose and computationally explore a particular semiconductor heterostructure in which the acoustoelectric interaction arises from a piezoelectric phonon-electron coupling. We find that this system provides the necessary piezoelectric and carrier response ($k^2\approx 6 \%$), favorable semiconductor materials properties, and large optomechanical confinement and coupling ($|g_0|\approx8000$ (rad/s)$\sqrt{\text{m}}$) sufficient to demonstrate these new AEB enhanced optomechanical interactions.

physics.optics↗

arXiv2020

Electrically-driven Acousto-optics and Broadband Non-reciprocity in Silicon Photonics

Emerging technologies based on tailorable interactions between photons and phonons promise new capabilities ranging from high-fidelity microwave signal processing to non-reciprocal optics and quantum state control. While such light-sound couplings have been studied in a variety of physical systems, many implementations rely on non-standard materials and fabrication schemes that are challenging to co-implement with standard integrated photonic circuitry. Notably, despite significant advances in integrated electro-optic modulators, related acousto-optic modulator concepts have remained relatively unexplored in silicon photonics. In this article, we demonstrate direct acousto-optic modulation within silicon waveguides using electrically-driven surface acoustic waves (SAWs). By co-integrating SAW transducers in piezoelectric AlN with a standard silicon-on-insulator photonic platform, we harness silicon's strong elasto-optic effect to mediate linear light-sound coupling. Through lithographic design, acousto-optic phase and single-sideband amplitude modulators in the range of 1-5 GHz are fabricated, exhibiting index modulation strengths comparable to existing electro-optic technologies. Extending this traveling-wave, acousto-optic interaction to cm-scales, we create electrically-driven non-reciprocal modulators in silicon. Non-reciprocal operation bandwidths of >100 GHz and insertion losses <0.6 dB are achieved. Building on these results, we show that unity-efficiency non-reciprocal modulation, necessary for a robust acousto-optic isolator, is within reach. The acousto-optic modulator design is compatible with both CMOS fabrication and existing silicon photonic device technologies. These results represent a promising new approach to implement compact and scalable acousto-optic modulators, frequency-shifters, and non-magnetic optical isolators and circulators in integrated photonic circuits.

physics.optics↗

arXiv2020

Tunable RF-photonic filtering with high out-of-band rejection in silicon

The ever-increasing demand for high speed and large bandwidth has made photonic systems a leading candidate for the next generation of telecommunication and radar technologies. The photonic platform enables high performance while maintaining a small footprint and provides a natural interface with fiber optics for signal transmission. However, producing sharp, narrow-band filters that are competitive with RF components has remained challenging. In this paper, we demonstrate all-silicon RF-photonic multi-pole filters with $\sim100\times$ higher spectral resolution than previously possible in silicon photonics. This enhanced performance is achieved utilizing engineered Brillouin interactions to access long-lived phonons, greatly extending the available coherence times in silicon. This Brillouin-based optomechanical system enables ultra-narrow (3.5 MHz) multi-pole response that can be tuned over a wide ($\sim10$ GHz) spectral band. We accomplish this in an all-silicon optomechanical waveguide system, using CMOS compatible fabrication techniques. In addition to bringing greatly enhanced performance to silicon photonics, we demonstrate reliability and robustness, necessary to transition silicon-based optomechanical technologies from the scientific bench-top to high-impact field-deployable technologies.

physics.app-ph↗