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Single photon detector

Performance improvement, increased detection efficiency, and reduced dark count rate can be achieved through the following methods:

Methods to improve detection efficiency

Material selection and preparation:

Choose materials with high superconducting transition temperature, low resistivity, and high critical current density, such as tungsten (W), niobium (Nb) nitrides (NbN), titanium (Ti) nitrides (TiN), or their alloys (such as NbTiN).

High quality nanowire structures are prepared through sophisticated thin film growth techniques such as molecular beam epitaxy and pulsed laser deposition, as well as nanofabrication techniques such as focused ion beam etching and electron beam lithography.

Optimize the size and shape of nanowires, such as reducing their width and optimizing their edge morphology, to improve their photon absorption efficiency and detection sensitivity.

Optical coupling and enhancement:

By using structures such as optical resonant cavities, optical waveguides, or optical antennas, incident photons are effectively coupled into nanowires, enhancing the interaction between photons and nanowires.

Directly deposit nanowires on the surface of optical resonators or waveguides, or enhance photon absorption efficiency by designing special optical antenna structures.

Multi pixel parallel operation:

By designing a multi pixel superconducting nanowire single photon detector array and achieving parallel operation, the counting rate and photon number resolution of the detector can be significantly improved.

Reduce working temperature:

Superconducting nanowire single photon detectors need to operate at extremely low temperatures (usually below a few Kelvin) to reduce thermal noise and improve detection efficiency.

The use of efficient refrigeration systems (such as GM refrigerators) and optimized thermal design can reduce the operating temperature of the detector.

Optimize bias current:

Adjusting the bias current of the detector appropriately can reduce the dark count and noise while ensuring high detection efficiency.

Through experiments and theoretical simulations, find the ideal bias current value to achieve optimal detection performance.

Improving quantum efficiency:

The use of back illuminated structures (such as Si3N4 microcavity enhancement structures) can increase the quantum efficiency of silicon-based detectors to 95% (@ 1550nm).

Methods to reduce the dark count rate

Electromagnetic shielding:

Adopting electromagnetic shielding measures to reduce the impact of external electromagnetic fields on detector performance.

By designing a reasonable electromagnetic shielding structure, the noise level of the detector can be effectively reduced.

Low noise circuit design:

Use low-noise electronic readout circuits and signal processing circuits to reduce the impact of circuit noise on detector performance.

Through precise circuit design and optimization, the signal-to-noise ratio and detection efficiency of the detector can be improved.

Active cooling:

Reduce detector temperature and suppress thermal excitation noise. For example, cooling APD to -40 ℃ can reduce the dark count rate to below 1cps.

Environmental light exclusion:

Use multi-layer metal vacuum chambers (shielding rate>60dB), cascaded interference filters (bandwidth<1nm) and other measures to eliminate environmental light interference.

Optimize signal discrimination threshold:

Using a dynamic discrimination circuit, set the optimal discrimination threshold based on the noise distribution curve (usually 5-10 times the noise peak).

Dead time control:

After triggering the signal, briefly turn off the detector (e.g. 80 μ s) to avoid additional noise caused by residual charges.