The high speed analog optical readout system designed for low temperature experiments

TL;DR

The paper presents a low-temperature analog optical readout for cryogenic LXe detectors, replacing traditional coaxial feedthroughs with fiber-coupled optical transmission to reduce attenuation and crosstalk. The authors design a cryogenic transmitter that linearly converts electrical signals to optical power, coupled with a room-temperature receiver to recover the waveform, and they demonstrate a $-3$ dB bandwidth around $150$–$200$ MHz and a dynamic range above $500$ mV, with per-channel cryogenic power near $70$ mW. They extend the approach with wavelength-division multiplexing (WDM) to achieve four-channel transmission on a single fiber at −100 °C and validate the concept through commissioning with a PMT, showing SPE SNRs around 4–5. This work offers a scalable, low-power, and simpler alternative to digital or conventional readouts for large LXe experiments, potentially enabling higher channel counts with preserved signal integrity. $-3$ dB bandwidth and dynamic range figures illustrate competitive performance for timing and waveform preservation in cryogenic environments.

Abstract

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.

Figures (11)

• Figure 1: The multiplexed analog optical readout diagrams.
• Figure 2: (Left) The schematic diagram of one of the channels of the optical transmitter. The laser diodes are LSCDLDX-4-S-0-2-fJKFC, produced by Beijing Lightsensing Technologies Ltd, where X is the corresponding wavelength. (Right) The Spice simulation result of a 100 mV SPE-like signal input, with a simulation time step of 0.01 ns.
• Figure 3: The schematic diagram of one of the channels of the optical receiver. The photodiodes are the LSIPD-A75-B-2JKFC produced by Beijing Lightsensing Technologies Ltd.
• Figure 4: (Left) The test diagram of the analog optical readout system performance evaluation. (Right) The receiver output (yellow) as a SPE-like waveform (blue) is injected by a waveform generator.
• Figure 5: The Bode plot of the analog optical readout system, and the -3 dB frequency is around 170 MHz at room temperature and increases to about 190 MHz at -40 $^{\circ}$C, -60 $^{\circ}$C, and -80 $^{\circ}$C, and 200 MHz at -100 $^{\circ}$C and -120 $^{\circ}$C.