Direct coupling of a laser-written photonic integrated circuit to a SPAD array

To date, several experiments in integrated quantum photonics exploit single-photon detectors operating at cryogenic temperatures coupled to photonic integrated circuits (PICs) through single-mode optical fibers. In this scenario, the complexity of the detection part represents an obstacle for the scalability of the entire setup. Here, we propose an alternative approach in which a programmable PIC fabricated by femtosecond laser writing (FLW) is interfaced directly to a silicon single-photon avalanche diode (SPAD) array. Each of the two components is realized by taking advantage of fully custom technologies able to provide state-of-the-art performance to the final application. The effectiveness of this solution is preliminary demonstrated by measuring a coupling efficiency as high as 93.2%, along with a system detection efficiency of 36.3% at 561 nm. These values, which are best in class, have the potential to unlock a new perspective in terms of scalability in quantum photonics experiments.