Understanding Optical Fiber Polarization Mode Dispersion

While they travel along with fiber, Dispersion with polarization maintaining splitter is the fact that light pulses spread out. Because the speed of light in the fiber depends on the propagation mode and its wavelength i.e. the light color, this fact occurs.

A small range of wavelengths (colors) constitutes the light pulses in optical fibers. Practically, a pure single colored light can be generated by no light source. In either a relatively broad range as a LED or a narrow wavelength range as a semiconductor laser, they generate light always.

Various light wavelengths travel at different speeds in optical fibers. This means as compared to others, at the receiver, some might arrive a bit later. As compared to that of the transmitter side, this fact offers broader received light pulses. Dispersion is this pulse broadening.

By the dependence of refractive index on wavelength, the transmission of two different polarizations of light (PMD), multimode transmission (different mode travels at a different speed), and variations in waveguide (optical fiber) properties with wavelength, Dispersion with polarization maintaining isolator can also be caused through single-mode fibers. In a fiber-optic digital communication system, Dispersion's impact on bit rate is present.

Dispersion can limit the distance a lightwave signal can travel through an optical fiber like power loss in a fiber optic link. But it makes the signal blurry; dispersion does not weaken a signal different than attenuation. For example, at the end of the fiber, the pulse spreads to 10 milliseconds if you send out a 1-millisecond width pulse but then in time that the signal becomes unintelligible, signals blur together.

Impact of PMD on single-mode fiber optic systems

Only a few years ago, Getting significant when high-speed fiber-optic digital communication systems came to play, such as the 40Gbit/s systems, the potential effects of polarization mode dispersion occurs. In magnitude, Polarization mode dispersion (PMD) with polarization maintaining circulator is smaller than other types of dispersions, but at least until now, it is tougher to compensate for. With data rates higher than 2.5Gbit/s, PMD becomes a problem in systems. To sending higher data rates, PMD makes more challenges over long distances.

Know about the Polarization Maintaining Fibers

Polarization

A type of electromagnetic wave is Light. Denoted by E, It consists of oscillating electrical fields, and denoted by B, magnetic fields. By studying its electrical field E, Its properties can be described although, in terms of the magnetic field, we could just as well describe light and its effects. The polarization maintaining splitter is very useful.

Light-is-a-electromagnetic-wave and in many directions, Light waves can vibrate. Those that are vibrating in a single plane and one direction such as up and down are known as polarized light. Those that are vibrating in more than one plane and more than one direction such as both left/right and up/down are called unpolarized light.

Using a polarization filter is the most common method of achieving single polarization. Capable of blocking one of the two planes of vibration of an electromagnetic wave, Polarization filters are made of special materials.

Polarization maintaining fiber

A special type of single-mode fiber is Polarization maintaining fiber (PM Fiber). Normal single-mode fibers can carry randomly polarized light. However, to propagate only one polarization of the input light, PM fiber is designed.

With no or little cross-coupling of optical power between the polarization modes, the polarization of linearly-polarized light waves launched into the fiber is maintained during propagation in polarization-maintaining fiber. For some fiber optic components such as external modulators and polarization maintaining isolator that require a polarized light input, this polarization-maintaining feature is extremely crucial.

By inducing stresses in the material itself, this characteristic is achieved during the manufacturing process. Circular polarization-maintaining fiber and linear polarization-maintaining fiber are the two categories of polarization maintaining fiber (PMF) available.

Polarization maintaining fibers applications

In special applications, such as slab dielectric waveguides, interferometry, and fiber optic sensing, PM optical fibers are used in long-distance bidirectional optical transmission systems, polarization maintaining patch cable or coherent optical transmission systems, PM fibers are expected to be used.

Where the polarization plane of the optical signal is important, they may also be used in transmission applications such as coupling for optical-electrical integrated circuits and transmission lines for optical sensors. To keep cross-coupling between polarization modes at minimum PM fibers and maintain the polarization of the incoming light is used in lithium niobate modulators, polarization-sensitive systems and amplifiers are used.