On-Chip Modulator for Cryogenic Electro-Optic (EO/IR) Sensors

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber;Microelectronics The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Develop and demonstrate a novel photonic integrated circuit (PIC)-compatible optical modulator for on-chip integration with cryogenically cooled electro-optical and infrared (EO/IR) sensors. DESCRIPTION: Emerging military EO/IR sensors are being developed with smaller pixels and larger array sizes to enable high spatial sampling (i.e., pixel pitch and frame size), high temporal sampling (i.e., frame rate), low latency, and greater bit-depth resolution for real time imaging. The data bandwidth required to enable such real-time imaging for the most advanced sensor designs is reaching the limits of conventional copper wire interconnects. Datalinks using optical interconnects offer a unique and commercially mature component solution that can obviate the copper bandwidth limitation, while offering additional advantages of lower power, lower cost, and on-chip integration [Refs 1,2]. However, mature PIC-compatible modulators may not perform well at cryogenic temperatures or lack full characterization at low temperatures. Common methods used for modulation in the photonic domain include thermo-optic and electro-optic mechanisms, but these were largely developed for room temperature telecommunications applications. For example, common disk and ring resonators are very sensitive to temperature variations. Stabilization is achieved using high-speed heating elements located along the resonator surface, which increase power dissipation, introduce jitter noise, and degrade in performance at low temperature, increasing bit error rate (BER) and reducing modulation bandwidth significantly. Moreover, large bandwidth bottlenecks can be imposed by the integration strategy, such as wire-bonding, whereas flip-chip or alternative integration schemes could offer better performance. Recently, an electro-absorption-based modulator (EAM) demonstrated > 30 Gbps bandwidth at cryogenic temperatures, which was limited by wire-bond integration, but eliminated the need to maintain resonant coupling [Ref 3]. The EAM is based on the Franz-Keldysh effect, which can provide a constant extinction ratio from room temperature down to 5K. Thin-film lithium niobate (TFLN) modulators, alternatives based on the Pockel's effect, are also candidates for PIC-compatible cryogenic modulators, becoming more efficient at low temperatures and being compatible with Si foundry processing lines. While these advances are promising, innovations in cryo-compatible modulator design and integration are needed to increase modulation bandwidth, improve operational stability, and to facilitate automated operation. The goal of this SBIR topic is to develop or advance a PIC-compatible optical modulator that can stably operate within the relevant cryogenic temperature range for EO-IR sensors (~77K-120K) and can enable on-chip integration with EO/IR sensors. PHASE I: Design a concept for a PIC-compatible photonic modulator that can provide stable high-speed modulation and tuning at cryogenic temperatures to enable high bandwidth readouts for EO/IR sensors. Establish proof of concept. Develop a modulator fabrication process and a modulator test plan for Phase II. PHASE II: Optimize electrical and optical design and fabricate a packaged modulator prototype. Demonstrate modulator electrical and optical performance for high speed, high frequency range, and high bandwidth cryogenic operation (77K-120K). Demonstrate single-mode fiber pigtailed electro-optic modulator packaging. Prepare a Phase III commercialization/transition plan. PHASE III DUAL USE APPLICATIONS: Transition the demonstrated modulator technology to EO/IR sensor systems onto Naval Surface and Expeditionary Platforms. Cryogenic PIC-based modulators can also be applied to quantum sensing/computing, free space optical communication, and electromagnetic warfare (EW) applications. REFERENCES: 1. Estrella, Steven; Renner, Daniel; Hirokawa, Takako; Maharry, Aaron; Dumont, Mario and Schow, Clint. High-Speed Optical Interconnect for Cryogenically Cooled Focal Plane Array. Government Microcircuit Applications & Critical Technology Conference, 2019. https://apps.dtic.mil/sti/tr/pdf/AD1075373.pdf 2. Fard, Erfan M.; Long, Christopher M.; Lentine, Anthony L. and Norwood, Robert A. "Cryogenic C-band wavelength division multiplexing system using an AIM Photonics Foundry process design kit." Opt. Express 28, 2020, pp. 35651-35662. https://opg.optica.org/oe/fulltext.cfm?uri=oe-28-24-35651&id=442545 3. Chansky, E. et al., "High-Speed SiGe EAMs at Cryogenic Temperatures." 2022 IEEE Photonics Conference (IPC), Vancouver, BC, Canada, 2022, pp. 1-2. doi: 10.1109/IPC53466.2022.9975738 KEYWORDS: Optical Modulator, Cryogenic, Electro-Optic Sensors; EO/IR