A 55-GHz Bandwidth PAM-4 InP DHBT Photoreceiver Based on PD–TIA Co-Design for >112-GBd Optical Transceivers

We present a photoreceiver assembly optimized through comprehensive modeling of the photodiode (PD), the transimpedance amplifier (TIA), and their interconnection. This allows an early and accurate optical signal-to-noise ratio (OSNR) prediction during the TIA design. Fabricated in a 0.5-μm InP DHBT technology, the standalone TIA achieves a 59-dBΩ transimpedance gain and a 70-GHz electrical bandwidth, supporting PAM-4 operation up to 100 GBd without digital signal processing. When wire-bonded to a 50 GHz PD, the photoreceiver exhibits a flat electro-optical response with 55 GHz of bandwidth. Open PAM-4 eye diagram is demonstrated up to 112 GBd with a 1.56 pJ/bit efficiency, using a 6-tap off-line feed-forward equalizer. High linearity is obtained, with a 1-dB gain compression point reached at 3.5 dBm input optical power, corresponding to a 650-mV electrical output swing. These results pave the way to beyond-112-GBd direct-detection optical transceivers.