Quasi-phase-matched Electro-Optic Modulators for High-Speed Signal Processing

摘要

This paper reports on the design, fabrication and testing of quasi-phase-matched (QPM) lithium niobate electro-optic modulators optimized for the 40-60 GHz frequency range. The device used a single-drive, coplanar-waveguide (cpw) electrode structure that provided a good balance between impedance and RF loss, and a DC VπL product of approximately 10 Vcm. Ferroelectric domain engineering enabled push-pull operation with a single drive, while achieving low chirp. A custom developed pulsed poling process was used to fabricate periodic domain QPM structures in lithium niobate. QPM periods were in the range of 3 mm to 4.5 mm, depending on the design frequency. The pulse method enabled precise domain definition with a minimum of overpoling. Low-loss diffused optical waveguides were fabricated by an annealed proton exchange (APE) process. By operating in both co-propagating and counter-propagating modes, the QPM devices can be used to implement dual band RF bandpass filters simultaneously covering both 10-20 GHz and 40-60 GHz frequency bands. Arrays of QPM device structures demonstrated in this work form the basis for a reconfigurable RF photonic filter. The RF photonic QPM technology enables efficient concurrent antenna remoting and filtering functionality.