Fiber Coupling Onto Small Detector Area - THORLABS APD110 Series Operation Manual

APD110x/120x

5.7 Fiber Coupling onto Small Detector Area

When coupling an optical fiber into the APD110x/120x, please consider the beam divergence
out of the fiber tip and the active detector area.
For detectors with an active area diameter of 1.0 mm, a Thorlabs S120-xx fiber adapter is re-
commended. In this case, the detector area will not be overfilled by the diverging beam out of
the fiber tip.
For detectors with an active area smaller than 1 mm, the beam divergence out of the fiber
needs to be compensated by using a collimator and a focusing lens. Below is a possible ar-
rangement:
The assembly in front of the APD110x/120x 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 onto the detector. The X-Y translation mount allows the focused
beam to be aligned with the center of the sensor.
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