High Performance Electro-optic Modulator Designed for Military Aircraft

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Integrated Sensing and Cyber;Microelectronics OBJECTIVE: Design a high performance electro-optic modulator that can maintain its required performance over the expected environmental operating envelope when mounted directly to the antenna of a military aircraft. DESCRIPTION: The current advancements in Thin Film Lithium Niobate Mach-Zehnder low Vp (halfwave voltage) electro-optic modulators have resulted in compelling performance improvements for airborne receivers. The performance improvements compared to radio frequency (RF) sensors are in sensitivity, bandwidth, electromagnetic interference (EMI) protection, and cable weight. For STTR-developed modulators to be deployed on a military aircraft, they will need to maintain their performance over the appropriate military aircraft environmental envelope. The mounting locations with the most stressing environment will be the modulator attached directly an antenna mounted at the wingtip. This effort will meet generic target performance specifications for this application. The two largest areas of concern for this STTR topic are temperature and electromagnetic vulnerability. The challenge to operations over temperature is the interferometric bias control. Low Vp modulators require a bias controller with more sensitivity than previous large Vp modulators. Errors in bias control can degrade the second-order intercept point (IP2) and create unwanted harmonics. Most current modulator designs use thermal tuning for bias control. Thermal tuning may be difficult to maintain during thermal shock conditions. One possible alternative is to use electrical tuning, but this is not currently used because defects in the crystal structure of the waveguides create areas for charge accumulation, which can affect electrical bias control. This topic is looking for creative solutions to meet the thermal operational requirement. Electromagnetic vulnerability requirements will focus on transient susceptibility: This requirement specifies the maximum level of EM radiation that the system can tolerate without experiencing permanent damage. The requirements include transient sources, such as lightning, electrostatic discharge, and loud nearby transmitters. While the crystal of the modulator is impervious to high voltage, care must be taken with the design to prevent arcing between the electrodes or the case and to properly size the termination for power handling. Designs with internal terminations are unlikely to meet the requirements. The topic expects successful testing of thermal and electrostatic discharge (ESD) requirements (Threshold (T)) Altitude and shock/vibration (Objective(O)). Key Test Parameters (KTPs) for this effort are: Modulator Performance: Frequency = 10Mhz - 20Ghz Vp = 1V at 10Ghz (T), 0.5 volts at 10Ghz (O) Max optical input power = 27dBm Optical Insertion loss = < 6dB Bias Control = +-3 (T), +-2 (O) Operating Environment: Operational Temperature= -55C to 70C Continuous, +85C for 10 min Thermal Shock= 70C to -55C at a rate of 35C /min Electromagnetic Susceptibility: High power signals = 450V, 4GHz, 5us PW, 3.5% Duty cycle ESD: 0-4,000 V as discharged from a 100-pF capacitor through a 1.5kO resistor Max Altitude: 50K feet Shock/Vibration: (to be provided) The bias controller is preferred to be located with the modulator in a same or separate package and will meet the same environmental requirements. PHASE I: Develop a modulator and bias controller design. If feasible, demonstrate the core bias control technology concept at a bench top level. Insert data from the demonstration into the model and predict the modulator performance. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Build 4 packaged modulators and bias controllers and demonstrate the performance over the required thermal and EMS conditions (T). Also test over altitude and vibration (O). PHASE III DUAL USE APPLICATIONS: Support the DoD in transitioning the proposed receiver, to include working with a program office to develop a final packaging design that meets the platform's space, weight and power (SWAP) and environmental requirements plus systems specifications for the associated analog photonic links. Development of this receiver has widespread commercial applications for commercial radar and 5G/6G receivers. REFERENCES: 1. Wang, Mengke; Li, Junhui; Yao, Hao; Li, Xuepeng; Wu, Jieyun; Chiang, Kin Seng and Chen, Kaixi. "Thin-film lithium-niobate modulator with a combined passive bias and thermo-optic bias." Opt. Express 30, 2022, pp. 39706-39715. https://opg.optica.org/oe/fulltext.cfm?uri=oe-30-22-39706&id=509847 2. Celik, Oguz Tolga; Ammar, Nancy Yousry; Park, Taewon; Stokowski, Hubert S.; Multani, Kevin, K.S.; Hwang, Alexander Y.; Gyger, Samuel; Guo, Yudan; Fejer, Martin M. and Safavi-Naeini, Amir H. "Roles of temperature, materials, and domain inversion in high-performance, low-bias-drift thin film lithium niobate blue light modulators." Opt. Express 32, 2024, pp. 36160-36170. doi: 10.1364/OE.538150 https://pubmed.ncbi.nlm.nih.gov/39573516/ 3. Greenblatt, A. S.; Bulmer, C. H.; Moeller, R. P. and Burns, W. K. "Thermal stability of bias point of packaged linear modulators in lithium niobate." Journal of Lightwave Technology, vol. 13, no. 12, December 1995, pp. 2314-2319. doi: 10.1109/50.475569. https://ieeexplore.ieee.org/document/475569 4. Xu, Yuntao; Shen, Mohan; Lu, Juanjuan; Surya, Joshua B.; Al Sayem, Ayed and Tang, Hong X. "Mitigating photorefractive effect in thin-film lithium niobate microring resonators." Opt. Express 29, 2021, pp. 5497-5504. https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-4-5497&id=447430 KEYWORDS: Modulator; Fiber; radio frequency; RF; Receiver; Photonics; Terraform Linter; TFLint