Ge p-i-n Photodiode as 60-Gbit/s Optical NRZ-OOK Data Receiver

Abstract

By the pulsed, heterodyned, and modulated laser illuminations, the impulse and noise responses of O-band germanium (Ge) p-i-n waveguide photodetector (WPD) with different transmission-line designs are characterized for receiving the NRZ-OOK data beyond 60 Gbit/s. The Ge lateral p-i-n WPD reveals an optical responsivity of 0.63-0.74 A/W at 1327.5 nm under −1.8 V bias.The noise equivalent power (NEP) is increased from 0.11 to 0.2 pW/√Hz by shrinking the transmission-line contact electrode length from 280 to 80 μm. After optimizing the transmission-line designs with shorter length and less right corner number (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> #) between PD and bonding pad, the Ge lateral p-i-n WPD improves its RLC response to suppress its switching time with broadened receiving bandwidth. Shrinking the connecting transmission-line length from 280 μm to 80 μm extends the flattened S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> spectral response from 51 to 57 GHz by up-shifting the inductor inductor-induced frequency notch from 58 to 61 GHz, as confirmed by the shrank spiral curve in the Smith chart with the decreased inductance by shortening the transmission-line electrode. The dual-wavelength optical heterodyne analysis demonstrates that the Ge p-i-n WPD significantly improves its analog receiving bandwidth from 29.5 to 44.3 GHz measured at 6-dB decay. The sub-ps laser pulse illumination observes that the Ge p-i-n WPD response shortens its impulse response from 23.14 to 19.92 ps by reducing the contact inductor length (by 200 μm) and right corner number (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> #) from 4 to 2) of its electrode. When receiving the optical NRZ-OOK data stream, the long-electrode (L = 280 μm, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> # = 4) device reveals only 53-Gbit/s receiving performance. The short-electrode (L = 80 μm, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> # = 2) Ge lateral p-i-n WPD with significantly reduced inductance successfully receives the NRZ-OOK data beyond 56 Gbit/s and 60 Gbit/s under error-free communication criterion of BER<10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> and BER<10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> , respectively.