High directivity fibre optic multimode couplers

SEDI-ATI is the company’s French based manufacturer of various fibre optical solutions. Their main area of expertise is the development of multimode fibre components.  Significant knowhow in this field, along with great experience in manufacturing allows us to introduce a high directivity fibre coupler.   

One of the application spaces for this coupler are optical metrology and sensing where the dynamic range of the sensor is a key parameter. Here, the optical signal is input through the injection port of the 1x2 coupler (the 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. Reflected light is gathered back through the common fibre (port 3) followed by redirection towards the second port of the coupler to the detector.

This is where high directivity is a great advantage since it is essential to minimize the light that can pass directly from the branch 1 to the branch 2. Main benefits of this technique, other than high directivity, are mode insensitivity and achromaticity.

In a round trip configuration (depending on the launch condition), 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.

The manufacturing technology of this couplers is based on wavefront division.

These couplers can be manufactured with any Graded Index fibre type such as GI50/125µm or GI62.5/125µm with directivity as high as >50dB. In case of high-power UV applications, additional to high directivity requirement, an improvement can be made with a solution which can handle as much as 2W at 420nm.

Bespoke coupling ratios and fibre lengths are available.