POLARIZATION-INSENSITIVE ELECTROABSORPTION MODULATORS FOR HIGH-SPEED OPTICAL GATING

Polarization insensitive discrete electroabsorption modulators have be en designed as an optical gating device. It reveals the first finding, to our knowledge, that the ratio of the optical confinement Factor (G amma) to the differential of the values (Delta Gamma) between TE and T M polarized lights decides polarization dependence of attenuation. The ratio Delta Gamma/Gamma is significantly reduced by increasing core t hickness. Large optical confinement structures combining a thick InGaA sP bulk absorption layer and polyimide-buried mesa-ridge waveguide hav e Fabricated. The ratio Delta Gamma/Gamma of the high-mesa structure w as estimated to be less than 0.05 in the gain-region of an erbium-dope d fiber amplifier (EDFA), which enable us extremely low polarization s ensitivity less than 1 dB up to 20 dB extinction. Proper waveguide len gth of the structure allowed low insertion loss (<9.3 dB), small loss- change (<1.8 dB) and sufficient modulation depth (>30 dB) simultaneous ly in the EDFA's gain region. The low-mesa structure provided low inse rtion loss around 7 dB with small deviation in the wavelength region. High modulation band width and a polarization-insensitive optical gati ng waveform have also demonstrated.