The High-Speed and High-Effieincy Photodetctors for 400/800 Gbit/Sec Ethernet

The construction of of data center and the fiber communication network as its backbone are both booming in the recent 10 years. This case is just similar with the birth of electrical network at 19th century, which results in the revolutionary change in human’s civilization. In the cabins of data center, the essential number of short reach (<2 km) optical interconnect (OI) channels is up to several millions. This drives us to develop the low power consumption, densely packaged, small form factor transreceiver modules to meet the above-mentioned requirements. Removing the lens inside ROSA package is one of the most effective ways to further minimize the size and reduce the cost of receiver optical sub-assembly (ROSA). However, in order to meet the bandwidth requirement in next generation 400 and 800 Gbit/sec Ethernet, the optical-to-electrical (O-E) bandwidth of photodetector (PD) inside ROSA must be over 30 GHz and have a responsivity value >0.7 A/W. These specifications seriously limit the enlarging of active area of photodetector and let the lens-free alignment become very difficult. Besides, in order to save the space of dc bias circuit in ROSA package, such kind of PD must be able to function under the low reverse bias voltage (< -2V), which is supplied by the integrated trans-impedance amplifier (TIA). 　 　 In this project, we will develop our newly demonstrated uni-traveling carrier photodiodes (UTC-PDs) to satisfy the above-mentioned requirements in PD. The traditional p-type In0.53Ga0.47As absorber inside UTC-PD is replaced by the Type-II p- GaAs0.5Sb0.5/i-In0.53Ga0.47As hetero-structure. Due to that the bandgap of type-II interface is narrower than that of In0.53Ga0.47As (0.5 vs. 0.75 eV) absorber, so it can effectively enhance the photo-absorption process and responsivity performance in a given absorption layer thickness. On the other hand, for the case of a desired responsivity, this novel design of absorber can reduce its thickness, shorten the carrier transit time, and enhance the speed performance. By combing such absorption layer with a thick InP collector layer with only electron as active carrier, we can thus increase the diameter of active window of PD for top-side alignment and minimize the degradations in O-E bandwidth and responsivity. Furthermore, we will consider the deformation of optical beam after passing the beveled optical fiber tip and further optimize the shape of active PD mesa to minimize the coupling loss. The approach of flip-chip bonding package integrated with a InP substrate lens for lens-free backside alignment will also be realized in such PD structure. Overall, by combing with the above-mentioned device technology with advanced package technology, which is supported by Source Photonic Company, we will demonstrate a high-linearity/-sensitivity-/ and reliable PD based photo-receiver module with low-cost for next-generation (400) 800 Gbit/sec Ethernet communication system.