High-directivity fibre optic multimode couplers

6th April 2021
Alex Lynn

LASER COMPONENTS offers SEDI-ATI’s special multimode coupler series for optical metrology and sensing, where the dynamic range of the sensor is a key parameter. The unique manufacturing technology of these couplers is based on wavefront division. The main benefits of this technique, other than high directivity, are mode insensitivity and achromaticity.

The optical signal is input through the injection port of the 1x2 coupler (the light source) onto a measured surface.  The light can be backscattered by an object to be analysed, either as it is, or with a shifted wavelength.  The reflected light is gathered back through the common fibre (port 3) followed by redirection towards the second port of the coupler to the detector.

High directivity is a great advantage to minimise the light that can directly pass from the injection port to the output port.  Also, the insertion loss from port 1 to port 2 is < 6.5dB with a total reflection at the common port. This way, a minimal mismatch between the input and the reflected signal is achieved.

Key features:

  • High Directivity > 55dB (with GI 50/125µm).
  • Achromaticity and mode insensitivity over the wavelength range 400-1625nm.
  • Low insertion loss in round trip configuration ≤ 6.5dB (can be lower than 6dB if not used at fully filled stage).


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