High-responsivity and low-operation-voltage edge-illuminated refracting-facet photodiodes with large alignment tolerance for single-mode fiber

We demonstrate a novel edge-illuminated refracting-facet photodiode (RFPD), in which the incident light parallel to the up-side surface is refracted at an angled facet and absorbed in a thin absorption layer. Although the absorption layer is thin, the absorption length is effectively increased by making the light transit at a certain angle to the absorption layer, resulting in an increase in internal quantum efficiency. The fabricated RFPD's with an absorption layer thickness of 1.5 μm have a responsivity as high as 0.95 A/W even at a bias voltage of 0.5 V for a flat-ended single-mode fiber. The 1-dB-down misalignment tolerances for vertical and horizontal directions are as large as 9.5 and 33 μm, respectively. The 3-dB bandwidth of more than 6 GHz is obtained.