Abstract
Superconducting-nanowire single photon detectors (SNSPDs) are able to reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 µm, in excellent agreement with simulations.
Highlights
The demand for reliable and efficient single photon detectors has significantly increased during the last years, driven by emerging applications in the domains of quantum cryptography, space-to-ground communication, integrated circuit testing, etc
We report on the reduction of the polarization sensitivity obtained by capping NbN-based Single-photon detectors based on superconducting nanowires (SNSPD) with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area
This strategy can be combined with more advanced microcavity designs [16] for the fabrication of near-unity efficiency, polarization-insensitive and fiber-coupled Single-photon detectors based on superconducting nanowires (SNSPD)
Summary
The demand for reliable and efficient single photon detectors has significantly increased during the last years, driven by emerging applications in the domains of quantum cryptography, space-to-ground communication, integrated circuit testing, etc. Redaelli et al have introduced a more flexible approach, for which only one side of the nanowire (top or bottom) is in contact with a highindex dielectric material such as Si3N4, TiO2, or semiconductors such as GaAs or Si [16][15] Following this approach, reduced polarization sensitivity has been reported for an SNSPD using amorphous silicon as permittivity-matching cap layer [16][16]. For an optimized thickness of the SiNx cap, we demonstrate a strong reduction of the polarization sensitivity, without compromising the detector efficiency for TE polarization This improvement is due to the decrease of the permittivity mismatch between the nanowire and the surrounding area, which leads to an enhancement of the electric field inside the nanowire, and of the absorption coefficient for TM-polarized light
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