Linear 0.20 GHz modulation with a 1*2 directional coupler

The design and performance of a traveling-wave 1*2 directional coupler modulator are described. A 0-20 GHz response (-4 dB/sub e/) was achieved for Ti:LiNbO/sub 3/ devices at the 1.3- mu m wavelength. From experimental determinations of coupling coefficient and interarm intrinsic phase-mismatch for several modulators, linear dynamic ranges of, on average, 78 dB and voltage sensitivities of down to 9 mu V are determined (for 1-mW detector power, 3-kHz bandwidth, 50- Omega detector load). The dependence of sensitivity on the coupling coefficient is described, and the effect of the buffer layer thickness on the optical bandwidth and sensitivity is demonstrated.<
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