arXiv subjects

Andrew J. Leenheer

Publications and source records attributed to Andrew J. Leenheer.

15 recordsLinked to original sources

arXiv2026

Micro-electromechanical photonic integrated memristors

Programmable optical memristors embedded in photonic integrated circuits (PICs) are emerging as an important technology for high-speed optical storage and in-memory optical computing applications. These devices provide multi-level, non-volatile storage of optical phases that can be interrogated at the speed of light, enabling parallel data readout or energy-efficient multiply-accumulate operations in artificial neural networks. However, there remains several outstanding challenges with existing optical memristor technology including durability, material-induced optical losses, large-scale reconfigurability, or fabrication yield for realistic applications. Here we introduce an analog-programmable photonic memristor based on photonic integrated micro-electromechanical (MEMS) cantilevers produced in a CMOS foundry. The memristor consists of low-loss silicon nitride waveguides, requires no additional back-end materials integration, and is all electrically programmed with electrostatic-piezoelectric forces. We demonstrate up to 5-bit phase storage levels, 50 kbit/s programming speeds, strain-assisted non-volatility lifetimes >1 hour, >1 billion cycle endurance, and stress-tested millions of write-read cycles with pseudorandom bit sequences. We further extend the memory lifetime to several days with simple electronic refresh circuits in a portable battery-powered module, demonstrating a proof-of-concept optical random-access memory in static or dynamic configurations. Our MEMS-photonics technology represents an important step toward practical optical memristors.

physics.optics↗

arXiv2026

Monolithic Integration of Piezo-Optomechanical Photonics and CMOS Electronics

Next-generation photonic architectures for AI, sensing, and quantum computing require thousands to millions of reprogrammable photonic devices on a chip[1]. The monolithic integration of Electronically-backed Photonic Integrated Circuits (EPICs) allows for very high density electrical interconnection and electronic drivers that can scale with photonics. Piezo-optomechanical photonic integrated circuits (POMPICs) offer low power consumption, high speed modulation, cryogenic compatibility and broadband optical transparency from ultraviolet to infrared wavelengths[2,3], but have not been demonstrated with monolithically integrated CMOS electronics. Here, we show a fully monolithic, all-CMOS fabricated platform for POMPICs co-fabricated with commercial control electronics. 200 millimeter photonic wafers are constructed directly on completed CMOS driver wafers by back-end-of-line processing, connecting integrated piezoelectric actuators under broadband silicon nitride waveguides to a high-density digital backplane comprising >2 million electrical connections per die with 6.4x6.4 micron electrode pitch. We introduce segmented POMPIC components as Photonic Digital-to-Analog converters (PDACs) that convert low-voltage digital electronic signals to multi-bit analog optical phase and amplitude modulation, and we demonstrate parallel control of optical phase shifters, Mach-Zehnder interferometers, optical routing trees, and tunable ring resonators using a standard HDMI interface to program CMOS electronics. We test multiple reticles and perform electronic and photonic characterization across the entire wafer to establish uniformity and yield, demonstrating wafer-scale integration of POMPICs on an electronic backplane and enabling dense, scalable electronic control of piezo-optomechanical circuits.

physics.optics↗

arXiv2025

Hybrid electrostatic-piezo MEMS photonic integrated modulators

Programmable photonic integrated circuits (PICs) have recently emerged as an important technology for quantum information science and artificial neural networks. In particular, PICs with MEMS-based modulators have the advantages of voltage-based control, ultra-low-energy consumption, cryogenic compatibility, and CMOS-foundry support. Here we report a cantilever optical modulator that utilizes hybrid piezoelectric and electrostatic tuning forces together on a monolithic silicon nitride (SiN) PIC platform. The device achieves actuation of visible-wavelength light with quasi-static tuning up to 10 kHz at 1.5 Vπ-cm as well as high-speed (>20 MHz) AC modulation with dynamically adjustable (25 - 40 MHz) mechanical resonances. We report the physics of how geometric nonlinearities such as capacitive pull-in give rise to suspended and contacted cantilever modes. These reversible operating regimes generate different strain profiles and boundary conditions which are responsible for the active tuning of the mechanical resonances. Our proof-of-concept electrostatic-piezo modulator shows promising potential in large-scale programmable PICs applied to high-speed optical switching and optomechanical sensing.

physics.optics↗

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

Piezoelectrically actuated high-speed spatial light modulator for visible to near-infrared wavelengths

Advancements in light modulator technology have been driving discoveries and progress across various fields. The problem of large-scale coherent optical control of atomic quantum systems-including cold atoms, ions, and solid-state color centers-presents among the most stringent requirements. This motivates a new generation of high-speed large-scale modulator technology with the following requirements: (R1) operation at a design wavelength of choice in the visible (VIS) to near-infrared (NIR) spectrum, (R2) a scalable technology with a high channel density (> 100mm-2 ), (R3) a high modulation speed (> 100MHz), and (R4) a high extinction ratio (> 20 dB). To fulfill these requirements, we introduce a modulator technology based on piezoelectrically actuated silicon nitride resonant waveguide gratings fabricated on 200mm diameter silicon wafers with CMOS compatible processes. We present a proof-of-concept device with 4 x 4 individually addressable 50 {mu}m x 50 {mu}m pixels or channels, each containing a resonant waveguide grating with a ~ 780 nm design wavelength, supporting > 100MHz modulation speeds, and a spectral response with > 20 dB extinction.

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

High-speed photonic crystal modulator with non-volatile memory via structurally-engineered strain concentration in a piezo-MEMS platform

Numerous applications in quantum and classical optics require scalable, high-speed modulators that cover visible-NIR wavelengths with low footprint, drive voltage (V) and power dissipation. A critical figure of merit for electro-optic (EO) modulators is the transmission change per voltage, dT/dV. Conventional approaches in wave-guided modulators seek to maximize dT/dV by the selection of a high EO coefficient or a longer light-material interaction, but are ultimately limited by nonlinear material properties and material losses, respectively. Optical and RF resonances can improve dT/dV, but introduce added challenges in terms of speed and spectral tuning, especially for high-Q photonic cavity resonances. Here, we introduce a cavity-based EO modulator to solve both trade-offs in a piezo-strained photonic crystal cavity. Our approach concentrates the displacement of a piezo-electric actuator of length L and a given piezoelectric coefficient into the PhCC, resulting in dT/dV proportional to L under fixed material loss. Secondly, we employ a material deformation that is programmable under a "read-write" protocol with a continuous, repeatable tuning range of 5 GHz and a maximum non-volatile excursion of 8 GHz. In telecom-band demonstrations, we measure a fundamental mode linewidth = 5.4 GHz, with voltage response 177 MHz/V corresponding to 40 GHz for voltage spanning -120 to 120 V, 3dB-modulation bandwidth of 3.2 MHz broadband DC-AC, and 142 MHz for resonant operation near 2.8 GHz operation, optical extinction down to min(log(T)) = -25 dB via Michelson-type interference, and an energy consumption down to 0.17 nW/GHz. The strain-enhancement methods presented here are applicable to study and control other strain-sensitive systems.

physics.optics↗

arXiv2023

Electrically interfaced Brillouin-active waveguide for multi-domain transduction

New strategies to convert signals between optical and microwave domains could play a pivotal role in advancing both classical and quantum technologies. Through recent studies, electro-optomechanical systems have been used to implement microwave-to-optical conversion using resonant optical systems, resulting in transduction over limited optical bandwidth. Here, we present an optomechanical waveguide system with an integrated piezoelectric transducer that produces electro-optomechanical transduction over a wide optical bandwidth through coupling to a continuum of optical modes. Efficient electromechanical and optomechanical coupling within this system enables bidirectional optical-to-microwave conversion with a quantum efficiency of up to $-$54.16 dB. When electrically driven, this system produces a low voltage acousto-optic phase modulation over a wide ($>$100 nm) wavelength range. Through optical-to-microwave conversion, we show that the amplitude-preserving nature inherent to forward Brillouin scattering is intriguing and has the potential to enable new schemes for microwave photonic signal processing. We use these properties to demonstrate a multi-channel microwave photonic filter by transmitting an optical signal through a series of electro-optomechanical waveguide segments having distinct resonance frequencies. Building on these demonstrations, such electro-optomechanical systems could bring flexible strategies for modulation, channelization, and spectrum analysis in microwave photonics.

physics.optics↗

arXiv2023

Synchronous micromechanically resonant programmable photonic circuits

Programmable photonic integrated circuits (PICs) are emerging as powerful tools for the precise manipulation of light, with applications in quantum information processing, optical range finding, and artificial intelligence. The leading architecture for programmable PICs is the mesh of Mach-Zehnder interferometers (MZIs) embedded with reconfigurable optical phase shifters. Low-power implementations of these PICs involve micromechanical structures driven capacitively or piezoelectrically but are limited in modulation bandwidth by mechanical resonances and high operating voltages. However, circuits designed to operate exclusively at these mechanical resonances would reduce the necessary driving voltage from resonantly enhanced modulation as well as maintaining high actuation speeds. Here we introduce a synchronous, micromechanically resonant design architecture for programmable PICs, which exploits micromechanical eigenmodes for modulation enhancement. This approach combines high-frequency mechanical resonances and optically broadband phase shifters to increase the modulation response on the order of the mechanical quality factor $Q_m$, thereby reducing the PIC's power consumption, voltage-loss product, and footprint. The architecture is useful for broadly applicable circuits such as optical phased arrays, $1$ x $N$, and $N$ x $N$ photonic switches. We report a proof-of-principle programmable 1 x 8 switch with piezoelectric phase shifters at specifically targeted mechanical eigenfrequencies, showing a full switching cycle of all eight channels spaced by approximately 11 ns and operating at >3x average modulation enhancement across all on-chip modulators. By further leveraging micromechanical devices with high $Q_m$, which can exceed 1 million, our design architecture should enable a new class of low-voltage and high-speed programmable PICs.

physics.optics↗

arXiv2023

Multiplexed control of spin quantum memories in a photonic circuit

A central goal in many quantum information processing applications is a network of quantum memories that can be entangled with each other while being individually controlled and measured with high fidelity. This goal has motivated the development of programmable photonic integrated circuits (PICs) with integrated spin quantum memories using diamond color center spin-photon interfaces. However, this approach introduces a challenge in the microwave control of individual spins within closely packed registers. Here, we present a quantum-memory-integrated photonics platform capable of (i) the integration of multiple diamond color center spins into a cryogenically compatible, high-speed programmable PIC platform; (ii) selective manipulation of individual spin qubits addressed via tunable magnetic field gradients; and (iii) simultaneous control of multiple qubits using numerically optimized microwave pulse shaping. The combination of localized optical control, enabled by the PIC platform, together with selective spin manipulation opens the path to scalable quantum networks on intra-chip and inter-chip platforms.

quant-ph↗

arXiv2023

Modular chip-integrated photonic control of artificial atoms in diamond nanostructures

A central goal in creating long-distance quantum networks and distributed quantum computing is the development of interconnected and individually controlled qubit nodes. Atom-like emitters in diamond have emerged as a leading system for optically networked quantum memories, motivating the development of visible-spectrum, multi-channel photonic integrated circuit (PIC) systems for scalable atom control. However, it has remained an open challenge to realize optical programmability with a qubit layer that can achieve high optical detection probability over many optical channels. Here, we address this problem by introducing a modular architecture of piezoelectrically-actuated atom-control PICs (APICs) and artificial atoms embedded in diamond nanostructures designed for high-efficiency free-space collection. The high-speed 4-channel APIC is based on a splitting tree mesh with triple-phase shifter Mach-Zehnder interferometers. This design simultaneously achieves optically broadband operation at visible wavelengths, high-fidelity switching ($> 40$ dB) at low voltages, sub-$μ$s modulation timescales ($> 30$ MHz), and minimal channel-to-channel crosstalk for repeatable optical pulse carving. Via a reconfigurable free-space interconnect, we use the APIC to address single silicon vacancy color centers in individual diamond waveguides with inverse tapered couplers, achieving efficient single photon detection probabilities (15$\%$) and second-order autocorrelation measurements $g^{(2)}(0) < 0.14$ for all channels. The modularity of this distributed APIC - quantum memory system simplifies the quantum control problem, potentially enabling further scaling to 1000s of channels.

quant-ph↗

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↗

arXiv2022

Programmable photonic integrated meshes for modular generation of optical entanglement links

Large-scale generation of quantum entanglement between individually controllable qubits is at the core of quantum computing, communications, and sensing. Modular architectures of remotely-connected quantum technologies have been proposed for a variety of physical qubits, with demonstrations reported in atomic and all-photonic systems. However, an open challenge in these architectures lies in constructing high-speed and high-fidelity reconfigurable photonic networks for optically-heralded entanglement among target qubits. Here we introduce a programmable photonic integrated circuit (PIC), realized in a piezo-actuated silicon nitride (SiN)-in-oxide CMOS-compatible process, that implements an N x N Mach-Zehnder mesh (MZM) capable of high-speed execution of linear optical transformations. The visible-spectrum photonic integrated mesh is programmed to generate optical connectivity on up to N = 8 inputs for a range of optically-heralded entanglement protocols. In particular, we experimentally demonstrated optical connections between 16 independent pairwise mode couplings through the MZM, with optical transformation fidelities averaging 0.991 +/- 0.0063. The PIC's reconfigurable optical connectivity suffices for the production of 8-qubit resource states as building blocks of larger topological cluster states for quantum computing. Our programmable PIC platform enables the fast and scalable optical switching technology necessary for network-based quantum information processors.

quant-ph↗

arXiv2022

Piezo-optomechanical cantilever modulators for VLSI visible photonics

Visible-wavelength very large-scale integration (VLSI) photonic circuits have potential to play important roles in quantum information and sensing technologies. The realization of scalable, high-speed, and low-loss photonic mesh circuits depends on reliable and well-engineered visible photonic components. Here we report a low-voltage optical phase shifter based on piezo-actuated mechanical cantilevers, fabricated on a CMOS compatible, 200 mm wafer-based visible photonics platform. We show linear phase and amplitude modulation with 6 V$_π$-cm in differential operation, -1.5 dB to -2 dB insertion loss, and up to 40 dB contrast in the 700 nm - 780 nm range. By adjusting selected cantilever parameters, we demonstrate a low-displacement and a high-displacement device, both exhibiting a nearly flat frequency response from DC to a peak mechanical resonance at 23 MHz and 6.8 MHz respectively, which through resonant enhancement of Q~40, further decreases the operating voltage down to 0.15 V$_π$-cm.

physics.app-ph↗

arXiv2021

High-speed programmable photonic circuits in a cryogenically compatible, visible-NIR 200 mm CMOS architecture

Recent advances in photonic integrated circuits (PICs) have enabled a new generation of "programmable many-mode interferometers" (PMMIs) realized by cascaded Mach Zehnder Interferometers (MZIs) capable of universal linear-optical transformations on N input-output optical modes. PMMIs serve critical functions in photonic quantum information processing, quantum-enhanced sensor networks, machine learning and other applications. However, PMMI implementations reported to date rely on thermo-optic phase shifters, which limit applications due to slow response times and high power consumption. Here, we introduce a large-scale PMMI platform, based on a 200 mm CMOS process, that uses aluminum nitride (AlN) piezo-optomechanical actuators coupled to silicon nitride (SiN) waveguides, enabling low-loss propagation with phase modulation at greater than 100 MHz in the visible to near-infrared wavelengths. Moreover, the vanishingly low holding-power consumption of the piezo-actuators enables these PICs to operate at cryogenic temperatures, paving the way for a fully integrated device architecture for a range of quantum applications.

physics.optics↗