What is it about?
Detecting single photons – the fundamental units of light – is challenging because the energy of a single photon is very small. The detectors we use convert the small energies of a photon and generate a signal. To do so, we pass a current through a thin wire made of a superconducting material. At a temperature close to absolute zero, the current passes through the wire without a resistance, which is called superconduction. If a photon is absorbed, it heats up the wire with its energy. The superconduction of the wire will then break down, and as a result a resistance is measured. This mechanism can detect single photons with very high efficiencies: over 90% of the photons absorbed will generate a signal. To achieve superconducting temperatures in the wire, the detector must be cooled to near absolute zero. These temperatures are typically reached by specialised refrigerator, called a cryostat. Unfortunately, the electronic connection from the coldest part of the cryostat to the rest the experiment at room temperatures conducts a considerable amount of heat. This heat conduction of the electronic connection limits the maximal number of single photon detectors which can be operated in one cryostat. Our method shows an alternative for the operation of superconducting single photon detectors in a cryostat. To deliver the supply power to the superconducting detector, we replace the electrical input by an optical fibre and photodiode. Light is guided by an optical fibre from the outside to the photodiode, which converts the light into electrical power and provides the current for the superconducting detector. This has the added benefit of being less prone to noise and interference.
Photo by John Adams on Unsplash
Why is it important?
We show with our method that we can provide the electrical power inside a cryostat for superconducting single photon detectors via an optical connection. In this configuration, the photodiode acts as a current source at cryogenic temperatures. The power for the photodiode is then guided through a single mode fibre. In contrast, a coaxial cable has a larger thermal conduction when providing the input power for the detector in the cryostat. In addition, the single mode fibres are poor electrical conductors such that no electrical noise can be picked up or transmitted through the connection.
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This page is a summary of: Opto-electronic bias of a superconducting nanowire single photon detector using a cryogenic photodiode, APL Photonics, August 2022, American Institute of Physics, DOI: 10.1063/5.0097506.
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