GAAS TRAVELING-WAVE OPTICAL MODULATOR USING A COPLANAR SLOW-WAVE ELECTRODE WITH PERIODIC OVERLAYS

A coplanar slow-wave electrode with periodic cross-tie overlays has been used to satisfy the essential phase velocity matching between the modulation and optical waves for wideband travelling-wave optical modulators. For an optimized modulator of 4 mm length at 1.3 mum light wavelength, the calculated halfwave modulation voltage (23 V) is slightly higher than that (20 V) of conventional coplanar modulators but the 3 dB bandwidth (100 GHz) is much wider than the bandwidth limit (30 GHz) of walkoff-limited conventional coplanar modulators. The measured effective index (4.61) of the modulation wave is much higher than that (2.65) of conventional coplanar electrodes and agrees very well with the calculated one (4.25).