Efficient Synthesis of Broadband Linear Frequency-Modulated Quadrature Signals for Coherent Electro-Optical Sensor Systems

• Published in: 2024 IEEE/MTT-S International Microwave Symposium - IMS 2024 pp. 257 - 260
• Main Authors: Schmidt, Marius, Carlowitz, Christian
• Format: Conference Proceeding
• Language: English
• Published: IEEE 16.06.2024
• Subjects: Bandwidth; Electro-optic modulators; electro-optical modulation; FMCW radar; Frequency modulation; frequency synthesis; Frequency synthesizers; microwave photonics; Optical fiber sensors; Optical variables measurement; Synthesizers
• ISSN: 2576-7216
• DOI: 10.1109/IMS40175.2024.10600286

This paper presents a novel approach to efficiently generate broadband, complex baseband, linear, frequency-modulated quadrature signals for driving quadrature mach-zehnder-modulators. In contrast to conventional approaches based on high sampling rate arbitrary waveform generators, cost and complexity is significantly reduced, while coherent distance and motion sensing is retained through single-sideband optical modulation. By using two FMCW synthesizers with contrary sweep rates and frequency crossing at half sweep duration, a zero-IF frequency ramp with unlimited relative bandwidth can be generated through I/Q-downconversion. Furthermore, sweep rate and bandwidth of the frequency ramp are doubled with this method compared to a single synthesizer. For experimental verification, an FMCW signal with 10 GHz bandwidth and a ramp duration of 32 μs has been generated using two 13-18 GHz PLL-based synthesizers. Coherent optical frequency domain ranging measurements at 1550 nm with different fiber lengths exhibit similar performance in terms of resolution and sensitivity compared to a two-channel 12 GS/s laboratory-grade AWG.