Light Instead of Wires: How to Send a Signal Out of a Freezer express
A thermos of liquid xenon cooled to minus 100 degrees Celsius. Inside are sensitive sensors that catch rare signals from dark matter particles. To bring these signals out, copper cables are usually used. But over the long haul, the signal weakens, and adjacent cables start 'cross-talking' — that's called crosstalk.
The new method works like a translator from the language of electricity to the language of light. An electrical signal from the sensor makes a laser shine brighter or dimmer — strictly proportional to the signal's strength. This light travels along a thin optical fiber to the outside, where a photodetector converts it back into an electrical pulse. The signal shape is preserved, as if you had transcribed the notes from one score to another without losing a single rest.
At minus 100 degrees, the system passes signals with frequencies up to 150 megahertz — tens of times faster than needed for the fastest events in the detector. The amplitude range reaches half a volt, and each channel consumes only 70 milliwatts — less than a bulb in a string of holiday lights. All this promises that future dark matter detectors will become more compact and reliable.
Original abstract
as written by the authors arXiv:2602.10596
For low-temperature experiments such as liquid xenon dark matter detectors, it is crucial to read out detector signals from cryostats. Traditionally, photoelectrical signals are transmitted from the cryogenic region to the outside using coaxial cables through vacuum feedthroughs on the cryostats. In this paper, we investigate an analog optical transmission method in which the raw electrical signals are converted into optical signals with light intensity linearly proportional to the electrical amplitude, transmitted out of the cryogenic environment through optical fiber, and subsequently converted back into electrical signals by photoelectric devices while preserving the signal waveform. This new approach offers advantages, including low attenuation over long-distance transmission and reduced crosstalk across the feedthroughs. Additionally, the low-temperature optical wavelength multiplexing scheme has been investigated and applied, increasing the transmission capability of a single fiber. At -100 degree Celsius, the proposed analog optical readout system achieves a -3dB bandwidth of larger than 150MHz, a dynamic range of up to 500mV, and a low cryogenic-region power consumption of 70mW per channel, demonstrating its strong potential for low-temperature experiments.
Optical fiber barely heats up and creates no interference, so it can be routed right through the cryostat wall — the sealed cold vessel — without risking the thermal insulation.
In the movie 'Interstellar', data from sensors near a black hole was transmitted to the ship via radio; in real experiments, light through optical fiber carries signals from icy depths.