Integratable High Linearity Compact Waveguide Coupled Tapered InGaAsP Photodetectors

We investigate high linear response tapered photodiodes composed of bulk and multiquantum-well absorption layers based on the integratable asymmetric twin waveguide architecture. The tapered shape reduces space-charge induced nonlinearities, enhancing the saturation current densities at high input optical powers. The 1-dB compression current density for an InGaAsP bulk active layer photodiode (BPD) is in excess of (2.8 plusmn 0.3) kA/cm², compared to quantum-well photo- diodes (QWPD) in the same materials system that saturate at (1.2 plusmn 0.1) kA/cm². We find that the limited density of states of QWPDs leads to the early onset of current saturation. The BPD has a polarization sensitivity of S_Pol = (1.0 plusmn 0.5) dB and responsivity R = (0.3plusmn0.03) A/W at a wavelength of 1.55 mum, whereas the QWPD has S_Pol = (7plusmn1) dB and R = (0.55plusmn0.05) A/W, while both have a bandwidth of (11 plusmn 1) GHz.