High dynamic range coherent RF/photonic links and related device technologies

Analog photonic links have emerged as a promising solution to the ever-increasing demands of next generation wireless systems such as high bandwidth, low loss, low weight, flexibility, and immunity to electromagnetic interference (EMI). By leveraging the properties of optical fiber, radio frequency (RF) signals can be generated, distributed, and processed for applications such as radar, communications, and sensors. Despite its advantage over traditional electronic links, RF photonic links still suffer from poor spur-free dynamic range (SFDR) due to the nonlinear properties and noise contributions of devices used in the electrical-to-optical (E/O) and optical-to-electrical (O/E) conversion processes. Furthermore, to make full use of the electromagnetic (EM) spectrum, frequency down-conversion is still required for compatibility with high performance digital signal processors available in today’s market. The need for frequency down-conversion adds to the complexity of achieving a high dynamic range link as existing methods also rely on nonlinear mechanisms. To fully address this challenge, new approaches are needed to overcome technology limitations encountered at both the link and component level. In this work, multiple coherent RF photonic links architectures and their respective components are investigated as a means to overcome these challenges. The architectures include a phase modulated (PM) link with an optical phased-locked loop (OPLL) receiver, and an amplitude-modulated (AM) link with an optical superheterodyne receiver. To improve the performance of the PM a link, a novel hybrid OPLL receiver based on thin-film lithium niobate (TFLN) integrated with a III-V photodetector is also proposed as an enabler for high dynamic range, small footprint, and large-scale integration. The novel contributions of this works include: • Proposed AM link with optical superheterodyne receiver and digital linearization. Demonstrated record breaking (RF-to-Bits) link performance, SFDR > 120 dB∙Hz2/3 at 15GHz. • First comprehensive theoretical studies of noise performance of PM link configurations, including Sagnac loop PM link. • Proposed a novel integration scheme of hybrid OPLL receiver for PM link based on optical contact between TFLN modulator and Mesa structure photodetector. Validated the integration scheme using a well-established photonic simulator. • First comprehensive study of TFLN phase modulator nonlinearities. • Demonstrated the first directly-etched TFLN modulator platform using i-line stepper photolithography for mass production and low cost.