arXiv subjects

Anne R. Kroo

Publications and source records attributed to Anne R. Kroo.

8 recordsLinked to original sources

arXiv2026

Polarization vector conjugation in a photonic integrated circuit

We show how to perform polarization conjugation of light in a simple apparatus without any nonlinear optical materials, based on self-configuring Mach-Zehnder interferometers fed by a polarization splitter. This allows us to completely and automatically remove the polarization variations on a single beam or mode propagating through an optical system with arbitrary birefringence, such as a conventional optical fiber, and compensate polarization variations experienced in the forward direction by propagating the conjugated beam back through the system and recreating the original polarization at the source. We demonstrate this polarization conjugation in an optical fiber setup in different orientations with a measured polarization extinction ratio of -30 dB for the returned beam.

physics.optics↗

arXiv2026

Separating partially coherent light

Recent advances in optical imaging and communication increasingly involve high-dimensional, partially coherent light, creating a growing need for scalable tools to measure and manipulate coherence. Here, we demonstrate the automatic separation of spatially partially coherent light into "coherence modes" -- its orthogonal and mutually incoherent components. To make this separation possible, we exploit variational processing in layered self-configuring interferometer architectures in a silicon photonic circuit. This process formally finds and measures the eigenvectors and eigenvalues of the coherency matrix, hence measuring the partially coherent state, while leaving it intact and separated after optimization. Furthermore, we show that mutually incoherent beams, if spatially orthogonal, can be automatically separated even if they are completely overlapped, hence separating unknown laser beams based only on their mutual incoherence. Our experiment finds and separates the two strongest coherence modes starting from a nine-mode sampling of the partially or fully overlapping fields from two independent lasers. The method requires a number of physical components that scales linearly with the rank $r$ of the coherency matrix and operates through a sequence of $r$ in situ gradient-based optimizations enabled by electronic drive frequency multiplexing of interferometer phase shifters. We benchmark its performance against a mixture-based tomographic method, also implemented on chip. These results establish a scalable framework for programmable coherence analysis and control in imaging, communication, and photonic information processing.

physics.optics↗

arXiv2026

Integrated Photonic Polarization Synthesizer and Analyzer

Polarization-resolved control and measurement of the optical field are essential for a wide range of photonic systems, including coherent communication, polarimetric sensing, and quantum information processing. We present a photonic integrated circuit that enables the generation and analysis of arbitrary polarization states. The device provides reconfigurable access to the full polarization degree of freedom of coherent light within a single integrated platform. We experimentally demonstrate arbitrary polarization state generation spanning the Poincare sphere, as well as Stokes vector measurement on chip. Unlike conventional Stokes measurements that rely on direct detection, polarization analysis utilizing this architecture is intrinsically non-destructive, preserving the optical signal for further optical domain processing. The devices are fabricated in a commercial foundry using CMOS-compatible processes, enabling scalable and reproducible integration. By combining polarization generation and analysis in a compact and stable photonic circuit, this work eliminates the need for external polarization optics and provides a foundation for robust, polarization-enabled photonic integrated systems.

physics.optics↗

arXiv2025

Programmable Optical Filters Based on Feed-Forward Photonic Meshes

We demonstrate an integrated photonic circuit based on feed forward photonic meshes that can be programmed and reconfigured to perform arbitrary spectral filter functions. We investigate a subset of the available filter functions, demonstrating that a N = 4 input triangular mesh with M = 3 layers may be operated via self-configuration algorithms to filter M arbitrary wavelengths from a given input spectrum. The tunable nature of the architecture enables preconfigured filter functions to be swept in the spectral domain continuously over the free spectral range of the device. This removes any strict requirements between the design parameters of the architecture and the center wavelength of a desired filter function. With this architecture, we experimentally demonstrate arbitrary wavelength rejection filters with contrasts as deep as 40 dB. Further, by intentionally selecting the center wavelengths of each filter function to lie along a wavelength grid we demonstrate deep wavelength division demultiplexing (DWDM) with inter-channel crosstalk between -25 dB and -40 dB. Unlike typical DWDM systems, in this architecture the center wavelength of each channel is not fixed at fabrication and instead may be swept or reordered arbitrarily. This device demonstrates advantages over typical methods for DWDM, Raman spectroscopy, and correlation spectroscopy as well as other applications.

physics.optics↗

arXiv2025

Three-Wave Interaction Grating Coupler with Sub-Decibel Insertion Loss at Normal Incidence

We report the design, fabrication in a commercial foundry, and experimental results of high-efficiency, normal incidence grating couplers for silicon photonics. We observe a maximum coupling efficiency of 85.4% (-0.69 dB) with a 1 dB bandwidth of 20 nm at a central wavelength of 1546 nm. These experimental results verify earlier theoretical and simulation results and pave the way for the use of perfectly vertical grating couplers, as an alternative to edge coupling, in silicon photonics applications that are sensitive to input coupling loss. Further, these results enable the use of grating couplers for vertically oriented elements, such as multicore fibers and VCSELs, and address challenges associated with coupling to free space beams.

physics.optics↗

arXiv2025

Diffractive Retroreflector for Distributed Sensing

We introduce a modified corner cube reflector that encodes information from passive optical sensors in its retroreflected diffraction pattern, enabling remote sensor-state measurement over a single-ended optical link. The design interferes a reference path and a sensor-modulated path within the retroreflected beam to produce an interferometric signal suitable for reading out phase and amplitude variations with a squarelaw camera. This enables sensor-state determination in arbitrarily oriented passive nodes, extending coherent interferometric read out of chemical, biological, and physical sensors to scalable, robust, and inert field deployments.

physics.optics↗

arXiv2025

High Contrast Nulling in Photonic Meshes Through Architectural Redundancy

We demonstrate a silicon photonic architecture comprised of Double Mach-Zehnder Interferometers (DMZIs) designed for high-contrast photonic applications. This configuration significantly enhances the achievable extinction ratio of photonic integrated circuits (PICs), reaching levels exceeding 80 dB. By leveraging the tunable properties of DMZIs and implementing a systematic configuration algorithm, the proposed mesh effectively compensates for fabrication imperfections and mitigates non-idealities such as back reflections. Experimental validation on a silicon-on-insulator platform demonstrates the potential of this approach for applications requiring high contrast nulling such as astronomical sensing.

physics.optics↗

arXiv2025

Universal programmable and self-configuring optical filter

We propose an approach to integrated optical spectral filtering that allows arbitrary programmability, can compensate automatically for imperfections in filter fabrication, allows multiple simultaneous and separately programmable filter functions on the same input, and can configure itself automatically to the problem of interest, for example to filter or reject multiple arbitrarily chosen frequencies. The approach exploits splitting the input light into an array of multiple waveguides of different lengths that then feed a programmable interferometer array that can also self-configure. It can give spectral response similar to arrayed waveguide gratings but offers many other filtering functions, as well as supporting other structures based on non-redundant arrays for precise spectral filtering. Simultaneous filtering also allows, for the first time to our knowledge, an automatic measurement of the temporal coherency matrix and physical separation into the Karhunen-Loève expansion of temporally partially coherent light fields.

physics.optics↗