Superconducting nanowire single photon detectors (SNSPDs) deliver superior performance over their competitors in the near-infrared regime. However, these detectors have an intrinsic polarization dependence on the incident wave because of their one-dimensional meander structure. In this paper, we propose an approach to eliminate the polarization sensitivity of SNSPDs by using near-field optics to increase the absorption of SNSPDs under transverse magnetic (TM) illumination. In addition, an optical cavity is added to our SNSPD to obtain nearly perfect absorption of the incident wave. Numerical simulations show that the maximum absorption of a designed SNSPD can reach 96% at 1550 nm, and indicate that the absorption difference between transverse electric (TE) and TM polarization is less than 0.5% across a wavelength window of 300 nm. Our work provides the first demonstration of the possibility of designing a polarization-insensitive and highly efficient SNSPD without performing device symmetry improvements.
Superconducting nanowire single photon detectors (SNSPDs) deliver superior performance over their competitors in the near-infrared regime. However, these detectors have an intrinsic polarization dependence on the incident wave because of their one-dimensional meander structure. In this paper, we propose an approach to eliminate the polarization sensitivity of SNSPDs by using near-field optics to increase the absorption of SNSPDs under transverse magnetic (TM) illumination. In addition, an optical cavity is added to our SNSPD to obtain nearly perfect absorption of the incident wave. Numerical simulations show that the maximum absorption of a designed SNSPD can reach 96% at 1550 nm, and indicate that the absorption difference between transverse electric (TE) and TM polarization is less than 0.5% across a wavelength window of 300 nm. Our work provides the first demonstration of the possibility of designing a polarization-insensitive and highly efficient SNSPD without performing device symmetry improvements.
Superconducting nanowire single photon detector (SNSPD) has been widely used in many fields such as quantum communication due to its extremely high detection efficiency, low dark count rate, high count rate, and low timing jitter. Compared with conventional single-photon detectors with planar structure, SNSPD is typically made a periodical meandering structure consisting of parallel straight nanowires. However, owing to its unique linear structure, the detection efficiency of SNSPD is dependent on the polarization state of incident light, thus limiting SNSPD’s applications in unconventional fiber links or other incoherent light detection. In this paper, a polarization-insensitive SNSPD with high detection efficiency is proposed based on the traditional meandering nanowire structure. A thin silicon film with a high refractive index is introduced as a cladding layer of nanowires to reduce the dielectric mismatch between the nanowire and its surroundings, thereby improving the optical absorption efficiency of nanowires to the transverse-magnetic (TM) polarized incident light. The cladding layer is designed as a sinusoidal-shaped grating structure to minimize the difference in optical absorption efficiency between the transverse electric (TE) polarized incident light and the TM polarized incident light in a wide wavelength range. In addition, the twin-layer nanowire structure and the dielectric mirror are used to improve the optical absorption efficiency of the device. Our simulation results show that with the optimal parameters, the optical absorption efficiency of nanowires to both of the TE polarized incident light and TM polarized incident light has a maximum of over 90% at 1550 nm, and the corresponding polarization extinction ratio is less than 1.22. The fabricated device possesses a maximum detection efficiency of 87% at 1605 nm and a polarization extinction ratio of 1.06. The measured detection efficiency exceeds 50% with a polarization extinction ratio less than 1.2 in a wavelength range from 1505 nm to 1630 nm. This work provides a reference for high-efficiency polarization-insensitive SNSPD in the future.
Superconducting nanowire single-photon detectors (SNSPDs) struggle to balance high system detection efficiency (SDE) and low polarization dependence. This work proposes a co-design of the NbN films, α -Si anti-reflection coating (ARC), and SiO 2 /Ta 2 O 5 distributed Bragg reflector (DBR) to reduce the polarization-dependent optical response of the nanowires. Simulations based on rigorous coupled-wave analysis (RCWA) and the finite-element method show absorptance above 99% for both transverse-electric (TE) and transverse-magnetic (TM) polarizations and absorptance above 90% over the wavelength range from 1530 to 1640 nm. Experimentally, the device achieves 97% SDE at 1530 nm (polarization sensitivity, PS = 1.1), PS < 1.3 over 1490–1640 nm, 39.5 ns recovery time, and 63.5 ps timing jitter. Retaining a conventional single-layer meander nanowire geometry, this design unifies high efficiency and polarization insensitivity, advancing SNSPD applications in quantum communications, free-space links, and single-photon imaging.
We designed a low-filling-factor and polarization-sensitive superconducting nanowire single photon detector (SNSPD), which can achieve a high absorption efficiency and counting rate simultaneously. Numerical simulations show that high absorption efficiency can be achieved by low-filling-factor SNSPDs with a silicon slot and silver reflector. The absorptance of the NbN nanowire for a transverse magnetic (TM) wave at the wavelength of 1550 nm can be 84.4% when the filling factor is only 16.5%, and the corresponding polarization extinction ratio (PER) is 562.9; the absorptance of the NbN nanowire for a transverse electric (TE) wave can be 67.0% when the filling factor is only 11.7%, and the PER is 7.4.
A highly efficient single-photon detector with strong polarization sensitivity is an important device in the field of quantum communication. Here, we present the design of a kind of superconducting-nanowire single-photon detector (SNSPD), in which the superconducting nanowire is embedded in a resonant cavity covered by a metasurface made of a coupled asymmetric split-ring resonator (CASRR). When illuminated by an incident light with different polarizations, CASRR will show totally different optical responses, which is used to obtain high polarization contrast in SNSPDs. Our simulation results show that an NbN nanowire meander with a filling factor of 0.2 can achieve an absorption efficiency of 84.3% at a wavelength of 1550 nm, when the electric field of the incident light is parallel to the NbN nanowire. Moreover, the polarization extinction ratio, i.e., the ratio of absorption rates between cases, where the electric fields are parallel and perpendicular to the NbN nanowire, is 522. Comparing with the results reported before, our SNSPD design demonstrates a much better performance.
This study proposed what we believe to be a novel method for fabricating superconducting nanowire single-photon detectors (SNSPDs) with high efficiency, polarization insensitivity, and ultrafast response. To achieve these properties in niobium nitride (NbN) SNSPDs, the periodic four-split rings (PFSR) were positioned above the nanowires. This design uses the localized surface plasmon resonance to enhance the electric field around nanowires. For an incident light with a wavelength of 1550 nm, the PFSR-SNSPD structure achieved a polarization extinction ratio of 1.0064 and absorptions of 88.94% and 88.37% under TE and TM polarizations, respectively. The nanowire length was reduced by 85% using a meandering nanowire arrangement with a fill factor of 0.074.
Polarization sensitivity is an intrinsic characteristic of the superconducting nanowire single-photon detector (SNSPD). It is caused by the periodical meander structure of the SNSPD, and may severely limit the scope of the SNSPD's applications. In this study, we have designed and fabricated a SNSPD with much reduced polarization sensitivity, based on a previously published theoretical result that involves high refractive index compensation materials. Using a home-built broadband automatic measurement system, the device detection efficiencies of the fabricated SNSPD have been measured for wavelengths ranging from 1200 to 1700 nm. The measurement results show that the polarization sensitivity of the fabricated device is greatly reduced, with the device detection efficiencies at 1550 nm being 61% and 56% for cases of parallel and perpendicular polarizations, respectively. The measurement results are in good agreement with the numerical simulations.