Electro-optic microwave phase modulators

Photonic components are in microwave systems because they can have extremely wideband frequency coverage and are immune to electromagnetic interference. The rationale for using optics also indudes very low losses in transmission and splitting, lightweight transmission lines, and the absence of crosstalk between microwave circuits. We describe a robust photonic microwave phase shifter that can be integrated economically into microwave systems. This phase shifter is based on commercially available lithium niobate technology. Two single frequency Nd:YAG lasers are offset phase locked at 10 GHz (100 MHz) from a 9.9 GHz synthesizer. Their outputs are combined with orthogonal polarizations in polarization maintaining fiber. The signals then pass from fiber into an optical waveguide in lithium niobate