In polarization maintaining components, there is a huge rule of polarization as it influences the performance of these components, the quality of the signal transmitted across the network, and their desirability in certain applications. So, if you wonder about what this polarization means in optical fiber communication networks, this blog is a must-read for you.
What is the meaning of polarization in optical fiber communication?
A light beam is composed of two electrical vector field components that are orthogonal to each other. These components vary in terms of frequency and amplitude. We call a light beam polarized when these two components vary in amplitude (or phase).
Polarization in optical fibers has been extensively researched and studied, and now, we have a variety of ways to either minimize this polarization or maximize it to take advantage of polarization, depending on our requirements.
Meaning, in polarization maintaining components, components are designed using optical fibers to maintain polarization to take advantage of this phenomenon.
When talking about polarization, there is another term that you should know about for better understanding.
Birefringence
This phenomenon occurs in certain types of materials that can split a light beam into two different paths. It happens because these materials have different indices of refraction based on the polarization direction of the light. This phenomenon is also seen in optical fibers because of the slight asymmetry in the cross-section of the fiber core and external stresses exerted on fiber due to bending. In general, birefringence is induced more often by external stresses than the geometry of the fiber.
A specialty fiber that maintains polarization creates a consistent birefringence pattern along its length intentionally, and thereby prevents the coupling between two orthogonal polarization patterns. In any fiber design, the geometry of the fiber and materials used in the formation of fiber creates a lot of stress in one direction and hence produces higher birefringence as compared to the random one.
In the market, a number of designs with stress-inducing architectures, such as Panda and Bow Tie PM Fibers with different cut-off wavelengths are available for commercial use.
Did you know polarization is characterized by some measurable properties? We have enlisted some of these properties below:
- Extinction Ratio: It is expressed in dB and refers to the ratio of minimum polarized power and maximum polarized power.
- Polarization Dependent Loss: Also expressed in dB, it is the maximum peak-to-peak variation in insertion loss.
- Polarization Mode Dispersion: It is another form of material dispersion.
Since the fiber core is not perfectly circular in general and it is exposed to mechanical stresses that induce birefringence in the fiber, it causes one of the orthogonal polarization modes to travel faster than the other. This, in turn, causes dispersion of the optical pulse.
The maximum difference in the times of the mode propagation caused by dispersion is known as differential group delay, which is typically expressed in picoseconds.