Maziyar Milanizadeh

Optical mode-sorting and generation are used for a wide range of quantum, sensing and communication applications. High-speed switching between mode sets would allow photonics systems to react to changes in propagation channel in real time. Photonic-Integrated-Circuits (PICs) with phased arrays can rapidly reconfigure their function at MHz depending on installed modulators. As a reconfigurable photonic system, PIC can reconfigure significantly fast than spatial light modulators that are limited to less than 1 kHz. However, phased-arrays are bound by two-dimensional Nyquist-sampling limit and spacing between array elements leads to grating lobe formation, where many additional array elements are needed to mitigate these effects. We leverage a passive Multiple-Plane-Light-Converters (MPLC) as an Optical Mode-Selective Interface (OMSI), coupling a basis set of free-space Hermite Gaussian (HG) modes directly into an active optical mesh implemented on a PIC. The active mesh can generate or sort any free-space mode-set that can be created by a linear superposition of 15 HG modes. Without changing the physical system, we demonstrate the generation and sorting of four orthogonal mode groups, each with 15 modes, achieving a mean intermodal crosstalk for sorting of -22 dB. This approach can allow for rapidly reconfigurable mode-sorters that could be used for quantum or classical communications or sensing applications.

Photonic integration in a silicon nitride (SiN) platform enables low propagation losses and a wide transparency range, making it ideal for quantum applications. However, polarization control in SiN is challenging because of its low birefringence. This work demonstrates polarization beam splitters using asymmetric directional couplers in SiN, designed for 950 nm and 1300 nm wavelengths. These devices exhibit low insertion losses (<1 dB) and high polarization extinction ratios (20 dB–30 dB).

A generic antenna array design approach through multi-objective optimization is adopted to design a non-uniform optical thinned array (TA) satisfying a desired far-field pattern mask and minimizing the number of radiating elements. The proposed optical TA is integrated with a silicon photonic beam-forming network (BFN) made of a mesh of tuneable Mach-Zehnder interferometer to implement a self-adaptive beam transmitter/receiver for free-space optical (FSO) systems. Experimental results demonstrate the beam steering and shaping capability of the proposed architecture, which self-configures without any need for pre-calibration.

Programmable photonic circuits require an electronic control layer to configure and stabilize the optical functionality at run‐time. Such control action is normally implemented by supervising the status of the circuit with integrated light monitors and by providing feedback signals to integrated actuators. This paper demonstrates that the control action can be effectively performed with electrical signals that are time‐multiplexed directly on the photonic chip. To this aim, the necessary electronic functionalities are monolithically integrated in a conventional 220 nm silicon photonics platform with no changes to the standard fabrication process. By exploiting a non‐conventional structure to implement metal‐oxide–semiconductor field‐effect transistors, an electronic controller is co‐designed into a programmable photonic circuit to enable a time‐multiplexed readout of integrated photodetectors and sequential activation of thermal phase shifters with on‐chip electronic memory. The accuracy of the time‐multiplexed control, achieved on a time scale of less than 10 ms, is demonstrated by penalty‐free routing of 10 Gbit s⁻¹ modulated signals. This approach can be straightforwardly applied to large‐scale photonic chips to reduce the number of required electrical input/output connections.

Optical phase measurement is critical for many applications, and traditional approaches often suffer from mechanical instability, temporal latency, and computational complexity. In this paper, we describe compact phase sensor arrays based on integrated photonics, which enable accurate and scalable reference-free phase sensing in a few measurement steps. This is achieved by connecting multiple two-port phase sensors into a graph to measure relative phases between neighboring and distant spatial locations. We propose an efficient post-processing algorithm, as well as circuit design rules to reduce random and biased error accumulations. We demonstrate the effectiveness of our system in both simulations and experiments with photonics integrated circuits. The proposed system measures the optical phase directly without the need for external references or spatial light modulators, thus providing significant benefits for applications including microscope imaging and optical phased arrays.

Surface grating couplers are an important component for interfacing photonic integrated circuits with optical fibers. However, conventional coupler designs typically provide limited performance due to low directionality and poor fiber-to-grating field overlap. The efficiency can be improved by using non-uniform grating structures at the expense of small critical dimensions complicating the fabrication process. While uniform gratings can alleviate this constraint, they produce an exponentially decaying near-field with the Gaussian fiber mode overlap limited to a theoretical maximum of 80%. In this work, we propose a uniform grating coupler that circumvents this field overlap limitation. This is achieved by leveraging inter-layer mode interference through a virtual directional coupler effect in a hybrid amorphous-silicon (α-Si) on silicon nitride (Si₃N₄) platform. By optimizing the inter-layer gap and grating geometry, a near-Gaussian profile of the out-radiated beam is achieved, resulting in an unprecedented grating-to-fiber overlap of 96%. The full three-dimensional (3D) finite-difference time-domain (FDTD) simulations show a high directionality of 84% and a record coupling loss of −1.27 dB with a 1-dB bandwidth of 20 nm for the uniform grating coupler design. Our device is designed for a wavelength of 950 nm aimed for use in hybrid quantum photonic integrated circuits using III-V quantum dot single photon sources.

Integrated photonic neural networks provide a promising platform for energy-efficient, high-throughput machine learning with extensive scientific and commercial applications. Photonic neural networks efficiently transform optically encoded inputs using Mach-Zehnder interferometer mesh networks interleaved with nonlinearities. We experimentally trained a three-layer, four-port silicon photonic neural network with programmable phase shifters and optical power monitoring to solve classification tasks using “in situ backpropagation,” a photonic analog of the most popular method to train conventional neural networks. We measured backpropagated gradients for phase-shifter voltages by interfering forward- and backward-propagating light and simulated in situ backpropagation for 64-port photonic neural networks trained on MNIST image recognition given errors. All experiments performed comparably to digital simulations ( > 94% test accuracy), and energy scaling analysis indicated a route to scalable machine learning.

As blockchain technology and cryptocurrency become increasingly mainstream, photonic computing has emerged as an efficient hardware platform that reduces ever-increasing energy costs required to verify transactions in decentralized cryptonetworks. To reduce sensitivity of these verifications to photonic hardware error, we propose and experimentally demonstrate a cryptographic scheme, LightHash, that implements robust, low-bit precision matrix multiplication in programmable silicon photonic networks. We demonstrate an error mitigation scheme to reduce error by averaging computation across circuits, and simulate energy-efficiency-error trade-offs for large circuit sizes. We conclude that our error-resistant and efficient hardware solution can potentially generate a new market for decentralized photonic blockchain.

Continuously variable true-time optical delay lines are typically subject to a constraint of the bandwidth-delay product, limiting their use in several applications. In this Letter, we propose an integrated topology that breaks the bandwidth-delay product limit. The device is based on multiple Mach–Zehnder Interferometers (MZIs) arranged in parallel, providing easier control and a larger bandwidth compared to ring resonator-based solutions. The functionality of this architecture is demonstrated with a 4-stage delay line by performing measurements in both the time and frequency domains. The delay line introduces a delay of 90 ps over a bandwidth of more than 22 GHz with a negligible group delay distortion, operates on a wavelength range of about 60 nm, and is scalable to a higher number of MZI stages.

Multiple orthogonal free-space optical (FSO) communication channels are automatically established between photonic chips hosting programmable integrated processors. All-optical channel demultiplexing is achieved with a crosstalk < -30 dB even after co-propagation though arbitrary mode mixers.