SEDI has developed a so-called “high directivity (HD) coupler” especially for sensor applications. Crosstalk between port 1 and port 2 is referred to as directivity (see figure: red arrow). These products make it possible to couple a light source into port 1 (blue arrow) and collect the reflected signal in port 2 (green arrow). Here it is important that the crosstalk signal (red) not interfere with the signal being returned (green).
The established technology from SEDI, which is based on lateral polishing of the fibers, was optimized for relevant coupler parameters:
Directivity: The light reflected from the coupler must be minimal so as not to interfere with the measurement signal. The sources of interference are kept as small as possible. This includes assembly and packaging of the connectors.
Forward and Return Configuration: The design of these couplers is particularly well suited for sensor applications such as in refractometers or OTDRs in which the entire insertion loss plays a crucial role. For this reason the input of the coupler is marked. This input features a very low insertion loss.
One additional point in development is that a photodiode is integrated into the coupler to monitor the signal in operation!
