Tag: Polarization Maintaining Fibers

Why Do We Need Polarization Maintaining Fibers?

Polarization maintaining fibers has been around since the development of fiber optics in the mid 20th century.

In fact, these fibers are considered to be the next generation of fiber optic technology with capabilities such as high bandwidth, low loss, and high temperature stability.

In order to understand this concept, you must first have an understanding of what polarization is and how it works in fiber optics.

What is Polarization?

Polarization is a fundamental property of electromagnetic waves, which have oscillating electric and magnetic fields. This phenomenon occurs in light waves and radio waves, for example.

Light that is polarized can be described as having an electric field vibrating at right angles to its direction of travel, or an electric field vibrating parallel to its direction of travel.

Light with an uneven distribution of polarization (i.e., light that has both vertical and horizontal components) can be said to be unpolarized.

What is Polarization Maintaining Fibers?

A polarization-maintaining fiber (PM Fiber) is a specialty single-mode fiber. Normally, single-mode fibers can carry randomly polarized light. In contrast, PM fiber propagates a single polarization of light.

Polarization-maintaining fibers maintain linearly-polarized light waves during propagation and do not cross-couple optical power between polarizations.

Some fiber optic components require polarized light input, such as external modulators. This polarization-maintaining feature plays a crucial role in these components.

In order to achieve this characteristic, stresses are induced in the material during the manufacturing process. PMFs come in two types: linear polarization maintaining fibers (LPMFs) and circular polarization maintaining fibers (CPMFs)

Uses of Polarization Maintaining Fibers

A PMF fiber optic cable is used in many applications. In fact, a PMF fiber optic cable might be what you are using to read these words right now!

The most common applications of PMF optical cables include lightwave transmission, telecommunications, and medical equipment.

Many telecommunications companies use PMF optical cables to transmit information over long distances in order to support communication between different countries.

Common medical devices that utilize fiber optics are sonography devices and endoscopes.

Ways of Realizing Polarization-maintaining Fibers

First, a polarization preserving fiber (PPF) has three layers: core, clad, and coating. Inside an optical fiber is a cavity known as core that is surrounded by a cladding.

There are also two polarizations in fiber optics – linear and circular polarization. Circular polarization states that when light propagates through a medium with time-varying ellipticity, its direction rotates continuously around an axis parallel to the propagation direction.

Cross Section of Polarization Maintaining Fibers

Polarization-maintaining fibers (PMF) or polarization-maintaining optical fibers (PMOF) are optical fibers which have a property that preserves the polarization state of light as it travels through them.

This is an important feature for applications in areas such as telecommunications and fiber-optic gyroscopes, and is usually provided by intrinsic material properties (such as birefringence), by inner cladding layers, or by external polarization controllers.

Conclusion

Polarization-maintaining fibers are well known for their ability to allow different polarized components (vertical and horizontal) to be transmitted through the fiber simultaneously. Their applications range from fiber optic sensing to interferometry to slab dielectric waveguides.

Let’s Talk About Polarization Maintaining Fibers!!

When it comes to optical fibers always reveal some degrees of birefringence, regardless of having a circular symmetric design. This is because, in practice, there is usually some percentage of stress and other impacts that breaks down the symmetry. As an outcome, the polarization of light disseminating in the Fiber moderately changes in an unmanageable way which also bent the fiber and its temperature.

Principle Of polarization-maintaining Fibers

The mentioned issues can be repaired by utilizing a polarization-maintaining fiber component, which ain’t a fiber without birefringence; however, on the other hand, it is a specialty fiber with a powerful built-in birefringence. Considering that the polarization of light set in motion into the fiber is lined up to one of the axes of birefringent, no matter what comes in, this polarization phase will get properly preserved even if the fiber is in a bent state. Not to mention, the principle behind this can be comprehended as a mode coupling.

To your knowledge, the transmission sustains of the two polarization modes will always be varied because of the powerful birefringence. In this way, the relative phase of co-spreading modes will quickly bob away. Hence, any sort of hurdle along the fibers can efficiently couple all the two modes if only it has a dimensional Fourier component with wave digits that precisely go with the difference of the propagation constants of both the polarization modes. Just in case, if the variation is enormous enough, the usual disturbances, the poking in the fiber will do efficient mode coupling. To put it simply, the polarization beat length must be shorter than the typical length scale over which the parasitic birefringence varies.

Ways Of Realizing Polarization-maintaining Fibers Components

One of the most commonly utilized methods for introducing strong birefringence is to incorporate stress rods of altered glass composition (generally boron-doped glass, with a varied degree of thermal expansion) in the preform on different and opposite sides of the core. When a fiber is pinched from such kind of perform, it wouldn’t be wrong to say that the stress components lead to some mechanical stress with an accurate orientation. By making use of other methods, it is possible to make bow-tie fibers (where the stress elements have gotten a varied shape and go nearby to the fiber core) so that a stronger birefringence can be easily achieved. 

Single-mode and Few-mode Fibers: 

There is nothing wrong with stating that when it comes to polarization-maintaining fiber components, they are usually single-mode fibers. Having said that, however, only in seldom cases do polarization-maintaining components fibers come in few-mode fibers. The main reason behind this is- that it is arduous to manufacture strong and uniform birefringence in the fiberglass in comparison to the enormous core area where plenty of modes can be guided.

Applications: 

Polarization-maintaining fibers components are executed in devices where the polarization state isn’t permitted to drift, for example, as an outcome of temperature changes. Some examples are- fiber interferometers, fiber-optic gyroscopes, and certain fiber lasers.