Optical time-domain reflectometers, laser ranging, fluorescence measurements, quantum optics experiments, and many other photonics applications can benefit from the sensitivity of single-photon detectors (SPDs).
: Experimental setup for heralded photon using (A) spatial multiplexing technique [18] and (B) temporal. Image Credit: Beijing University of Posts and Telecommunications
For fiber-optic QKD, near-infrared SPDs at the telecom wavelength of 1550 nm are essential. Two options are electrically-cooled InGaAs avalanche photodiodes (APDs) and cryogenic superconducting nanowire single-photon detectors (SNSPD). APDs are more advantageous than other options because they are more affordable, compact, and do not require refrigeration at extremely low temperatures.
To detect weak photon-induced avalanches, a purpose-designed readout circuit must reject the strong capacitive response of the APD to sub-nanosecond gating under the Geiger mode. Modularization and miniaturization are required to serve a wide range of applications but are made more difficult by rapid gating and readout circuits.
Recently, a research group realized exceptional performance for narrow-band rejection of the SPD capacitive response by developing a novel readout circuit known as the ultra-narrowband interference circuit (UNIC), which integrates a surface acoustic wave (SAW) filter into an asymmetric radio-frequency Mach-Zehnder interferometer. Advanced Devices & Instrumentation is the journal where the work has been published.
The UNIC interferometer can generate an ultra-narrrow band rejection with a manufacturing tolerance that is easily achievable in the RF track lengths because of the long group delay of the SAW filter.
The avalanche signal is not greatly distorted by the UNIC because it can offer a broad and continuous pass band in the frequency domain. The team describes how they developed an independent InGaAs SPD module that completely integrates temperature control and compensation and driving and readout electronics.
Measuring only 8.8 × 6 × 2 cm3, its volume is almost four times smaller than that of the most compact detector module currently in use, which makes use of a monolithically integrated readout circuit. In addition, there is no decline in performance as a result of this size reduction.
To achieve optimal performance over a wide range of ambient temperatures, the research team incorporates an automatic temperature compensation into their previously developed UNIC techniques for the APD signal readout.
The module’s performance with a 1.25 GHz clock input is said to be similar to that of its benchtop counterpart. With a net detection efficiency of 30% after a pulsing probability of 2.4% and a hold-off time of 3 ns, the UNIC-SPD performs exceptionally well. The UNIC-SPD module has enormous potential for high-speed quantum key distribution and single-photon imaging due to its compact size and cutting-edge performance.
Journal Reference:
Wang, H., et al.(2024) Progress on Chip-Based Spontaneous Four-Wave Mixing Quantum Light Sources. Advanced Devices & Instrumentation. doi.org/10.34133/adi.0032