Fiber Coupling Onto Small Detector Area - THORLABS APD450C Operation Manual

5 Appendix

5.7 Fiber Coupling onto Small Detector Area

When coupling an optical fiber into the APD450C, please consider the beam divergence out of
the fiber tip and the active detector area.
For APD450C we recommend to compensate for possible beam divergence out of the fiber by
using a collimator and a focusing lens. Below is a possible arrangement, shown on the example
of the APD430A2/M. The arrangement is identical for all Thorlabs Avalance Photodiodes.
The assembly in front of the detector comprises of a fiber collimator (dependent on fiber), a
lens tube collimator adapter (AD11F or AD12F, dependent on collimator), a SM1L1 lens tube
with aspheric lens inside (not visible above) and a LM1XY X-Y translation mount.
The beam out of the fiber is collimated (transferred into a nearly parallel beam) and afterwards
focused by the aspheric lens. In the case of the APD450C, the beam should be focused onto
the focal plane of the integrated ball lens. The X-Y translation mount allows the focused beam
to be aligned with the center of the sensor.
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