Abstract
Optical cavity with backside optical coupling is one of the prevalent optical structures for superconducting nanowire single photon detector. A single layer anti-reflection coating (ARC) on the backside of the substrate is often adopted to enhance the transmittance to the substrate. We here apply a multilayer ARC to further increase the transmittance from 94.5% to 99.5%. An NbTiN SNSPD made on such a substrate with cavity structure presents a system detection efficiency of 90.1% at a dark count rate (DCR) of 100 Hz, which is the best value reported for backside optical coupled SNSPD at 1550 nm. It shows a timing jitter of ∼40.7 ps and the recovery time constant of ∼22.9 ns.
Highlights
INTRODUCTIONSuperconducting nanowire single-photon detectors (SNSPDs) have undergone significant improvements and are attracting considerable attention because of their high detection efficiency (DE),[1,2] low timing jitter,[3,4] high count rate,[5,6] and low dark count rate (DCR).[7,8,9,10] These characteristics have enabled the key role in numerous impressive applications such as quantum key distribution in fiber,[11] space-ground laser communication,[12] depth imaging,[13,14] and singlet oxygen luminescence detection.[15]
The alignment was achieved using a homemade alignment system based on an inverted microscope, which may tune the relative position between detector and the fiber end face with an acceptable precision (∼2 μm in X-Y plane and ∼10 μm in Z plane)
The lensed fiber was designed to ensure that the beam waist of the light was smaller than the size of the meander structure, and its focus was located on the plane of the nanowire
Summary
Superconducting nanowire single-photon detectors (SNSPDs) have undergone significant improvements and are attracting considerable attention because of their high detection efficiency (DE),[1,2] low timing jitter,[3,4] high count rate,[5,6] and low dark count rate (DCR).[7,8,9,10] These characteristics have enabled the key role in numerous impressive applications such as quantum key distribution in fiber,[11] space-ground laser communication,[12] depth imaging,[13,14] and singlet oxygen luminescence detection.[15]. The SNSPDs with cavity structure were less affected since the mirror was deposited after the fabrication of the nanowire. One factor which limits SDE is the optical transmittance from the air to the substrate. A simple anti-reflection coating (ARC) layer has been utilized in the cavity SNSPDs,[17,18,21] the interface optical loss due to impedance mismatch still exists and it cannot be overlooked if one wants to further increase SDE. One efficient approach to further decrease the optical loss is to use the multilayer ARC, which was applied in the mirror based SNSPDs.[1] In this study, we replaced the simple ARC with a multilayer optical film for a SNSPD with the cavity structure. The SNSPD has a timing jitter of ∼ 40.7 ps, and a recovery time constant of ∼ 22.9 ns
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