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Photonic integrated circuits are applied on a broad range of technologies, from communication to computing and sensing. With the increasing interest on quantum technologies, quantum photonic integrated circuits became subjects of additional attention.
Several material platforms have been investigated, keeping in mind that the following elements are strictly necessary [1]: efficient sources of quantum light, single-mode low-loss waveguiding elements, beamsplitters, phase-shifters and single-photon detectors. So far, while several systems showed interesting perspectives, no platform has clearly emerged as winner of this race. This stimulated the use of hybrid approaches [2], where different complementary platforms are brought together in order to benefit from their respective strengths, furthermore foregoing the weaknesses.
In this work we report on the efficient interface of telecom quantum dots to low-loss silicon-nitride circuitry. In(Ga)As QDs emitting at telecom wavelength thanks to strain engineering, are embedded into etched microlenses. The use of laser-written photonic wire bonding enables the funnelling of single photons into a Si3N4 single-mode waveguide (average efficiency of ~ 29%) being this the input of a 50:50 beamsplitter. The light is then out-coupled with additional laser-written elements to increase the coupling into single-mode fibers connected to single-photon detectors. The on-chip element is used as beamsplitter into a Hanbury-Brown and Twiss experiment which results in a g^{(2)}(0) = 0.11 ± 0.2, clearly showing injection of single photons in the silicon-nitride chip. Several devices are fabricated to verify the scalability of the process as well as to quantify the efficiency of the photonic wire bonding interface.
These results set the basis for the up-scaling of photonic integrated circuits complexity.
[1] E. Knill, R. Laflamme G. J. Milburn, Nature 2001, 409, 46–52.
[2] A. W. Elshaari, W. Pernice, K. Srinivasan, O. Benson V. Zwiller, Nature Photonics 2020, 14(5), 285–298.
