Optical fibre precision positioning at cryogenic conditions

Abstract

Single photon detectors are an important optical sensing tool in many industries. However, these highly efficient detectors suffer from variations in the size of an optical cavity when cooling down to 3K. An active positioning system is therefore required to correct the relative position of the fibre to the detector, so an optimal and reproducible cavity size can be achieved, thereby maximizing their efficiency. The literature study performed on cryogenic precision actuators showed that a stepper motor in combination with a motion reduction mechanism is the most feasible design. A stepper motor and a precision screw were two fundamental components of the preliminary design, so their lubrication was removed and were proven to work cryogenically. The rest of the design was based around these fundamental components. Room temperature tests were done to show the functionality of the design and it showed a positioning resolution between 10 nm and 30nm with just a 100nm loss of motion when unloading and loading the system. Cryogenic tests achieved similar results and it showed that the reflected power of a detector was reduced from 8.8% to 3.6%, indicating that the maximum achievable detector efficiency increased from 91.2% to 96.4%.