What is a polarization maintaining filter coupler?

A polarization-maintaining filter coupler is an optical coupler that combines the light coming from the two input PM fibers into one output-PM fiber. This type of coupler supports the light wave of each polarization and doesn’t block any polarization. It also works as a splitter as it can also split the light typically into two ports. So, a PM filter coupler can work in both ways as a coupler and as a splitter.

It is basically designed to split high power linearly polarized light into multiple paths, without altering the state of polarization. You can also use it as a power tap for monitoring signal power flowing in a PM fiber system without affecting the linear SOP of the light traveling through the optical PM fiber.

 In a 1×2 PM filter coupler, the division of power occurs with a fixed proportion.

To suit the needs of different projects, there are various configurations available for polarization-maintaining filter couplers.

Different Configurations of PM Filter Couplers

The different configurations available for PM Filter couplers include but are not limited to:

  • 1×2 (one input/two outputs)
  • 2×2 (two inputs/two outputs)
  • 1×4 (one input/four outputs)
  • 2×3 (two inputs/three outputs)

How is the coupling ratio in PM Fiber couplers determined?

The coupling ratio of signals or splitting proportions depends on the PM Filter coupler’s configuration. A coupler ratio refers to the ratio in which input optical signals are divided between different outputs. For instance, with 50:50 coupling ratio in a 1×2 PM filter couplers, the optical signals are divided in equal proportion in two output-PM fibers. In such couplers, half of the input optical power is coupled to each port.

Other common coupling ratios include 90:10, 80:20, and 70:30. With these coupling ratios, a PM filter coupler doesn’t couple equal power to both the output-PM ports. For instance, in a PM filter coupling with an 80:20 coupling ratio, 80% percent of optical power is sent to one output PM fiber and 20 percent of the remaining optical power is directed to another output PM fiber.

Thus, you can easily design your optical fiber architecture as you have optical filter couplers with different configurations and can send optical power depending on whether you are sending it to the end-point or another device from where the optical power needs to be split further.

What should I know before choosing PM filter couplers?

First of all, you need to know the desired coupling ratio of PM filter couplers. Then, you need to check other parameters such as insertion losses, optical return loss (directivity), and excess loss. If an application involves differences in the polarization states, then you also need to analyze the polarization-dependent loss.

If you need polarization-maintaining filter couplers for applications such as PM fiber interferometers, power sharing in polarization-sensitive systems, signal monitoring in PM fiber systems, or fiber optic instruments, please get in touch with DK Photonics.