Packaging and Demonstration of Optical-Fiber-Coupled Photodiode Array for Operation at 4 K

An optoelectronic module for operation at 4 K is developed, intended for use in pulse-driven Josephson arbitrary waveform synthesizer. Multiple InP/InGaAs photodiodes with customized optical fiber assembly were assembled on a single silicon carrier. Photodiodes were flip-chip bonded on the carrier using Au stud bumps, and laser-cut silicon fixtures were aligned and adhesively bonded to the carrier in order to attach pigtailed borosilicate ferrules. Optical simulations were performed to estimate the tolerance for fiber-chip misalignment. The photodiodes were bonded with an average misalignment of 8 μm, while the misalignment between the silicon fixture and the photodiodes after bonding was 13 μm. The electrical response to continuous-wave laser inputs was measured at room temperature and at 4 K by direct immersion in liquid helium. The results show that the assembly technique could facilitate a stable and efficient optical coupling. The individual photodiodes were able to deliver currents up to 12 mA at room temperature and 7 mA at 4 K.