A polarization maintaining filter coupler splits the light from an input PM fiber between 2 output PM fibers or combines light signals from 2 input fibers into a single PM output. Basically, the device is used to split high-power linearly polarized light into multiple paths without perturbing the linear state of polarization or SOP. Other than this, the device is used as a power tap to monitor signal power in a PM fiber system without disturbing the linear SOP of the light propagating in the PM filter.
In the applications, you will find PM fiber interferometers, power sharing in polarization-sensitive systems, and signal monitoring in PM fiber systems. The package consists of rugged stainless steel, which is designed for high optical performance and stability.
The polarization maintaining filter coupler features low excess insertion loss, low back reflection, and high extinction ratio.
In this post, we will discuss one of the features of polarization maintaining filter coupler i.e. the extinction ratio, and why it should be high.
Extinction ratio
The extinction ratio quantifies the cross-coupling in regards to birefringent fiber. It indicates the amount of light that can mix between the two polarization axes. The value of the extinction ratio is important because it measures the polarization maintaining the performance of an optical fiber.
Mostly, the extinction ratio is misunderstood by many people, leading to lots of problems in the future.
The value of the extinction ratio depends on the length of the fiber and the environmental conditions in which you use it. If the fiber is subject to high mechanical stress and small-diameter bends, then internal disruption is possible, reducing the extinction ratio significantly.
What’s the impact of extinction ratio on the system performance and other parameters?
With a high extinction ratio, the bit-error ratio or BER improves. And when the bit-error ratio improves, it reduces the number of errors and the amount of error correction required. The high data rates are pushed through materials, loss, and dispersion close the eye and errors increase.
What happens if the extinction ratio is low or poor?
If the extinction ratio is low or poor, the polarization-maintaining filter coupler will increase its power penalty (PP), worsen its Bit-error ratio (BER) and diminish its benefit of increased power.
When does the extinction ratio become significant?
If you want quality and successful performance of the maintaining polarization filter coupler, the extinction ratio becomes significant.
Sometimes, the measured values between manufacturers and designers are very different. Even the end users obtain different values than the manufacturers. If this happens, the device will be rarely productive. So, the value of the extinction ratio should be determined before buying a polarization-maintaining filter coupler. And undoubtedly, it should be high.