polarisation maintaining fibre

8/10/2019 polarisation maintaining fibre

1/21

Delhi Technological University

(Formerly Delhi College of Engineering, Delhi)

Department of Electronics & CommunicationEngineering

&

Department of Applied Physics

M. Tech (Microwave and Optical Communication)


2/21


3/21

Overview :

Polarization.

PMF(polarization maintaining fiber).

Principle of operation.

Designs.Classification of PM fiber.

Dispersive effect(PMD).

Applications.Limitation of PM fiber.


4/21

What Is Polarization?

Light is a type of electromagnetic wave. It consistsof oscillating electrical fields, denoted by E, and

magnetic fields, denoted by B. Its properties can be

described by studying its electrical field E, although

we could just as well describe light and its effects interms of the magnetic field.


5/21

Light wave can vibrate in many directions.

Those that are vibrating in one direction

ina single plane such as up and down are

called polarized light.

Those that are vibrating in more than one

direction

in more than one plane such as

both up/down and left/right are called

unpolarized light.


6/21

How to Achieve Single Polarization:

The most common method of achievingsingle polarization is using a polarization

filter. Polarization filters are made of special

materials that are capable of blocking one

of the two planes of vibration of anelectromagnetic wave.


7/21

Polarization's effect on optical

fibers: Polarization does not really matter in multimode fibers but it

can be crucial in single mode fibers especially for long

distance and high speed rate fiber communications.

single mode fibers actually have two modes traveling in it.

These two modes have orthogonal polarization and perfect

single mode fibers cannot differentiate between them. Thesetwo modes are functionally identical and light energy can shift

easily between these two polarization modes.

Optical fibers always exhibit some degree of birefringence,

even if they have a circularly symmetric design, because in

practice there is always some amount of mechanical stress orother effect which breaks the symmetry. As a consequence,

the polarization of light propagating in the fiber gradually

changes in an uncontrolled (and wavelength-dependent) way,

which also depends on any bending of the fiber and on its

temperature.


8/21

Polarization Maintaining Fibers

Come To The Rescue! Polarization maintaining fibers are special kinds of

single mode fibers, they are also commonly called

PM fibers or Panda PM fibers.

PM fibers have built-in asymmetry which is also

called birefringence. The refractive index of PMfiber differs for the two polarizations and this effect

prevent light energy from coupling between two

polarizations.

PM fibers can transmit light in a single polarizationif the input light polarization is aligned to one of its

two birefringence axes. And that is why they are

called polarization maintaining fibers.


9/21

Polarization-maintaining Optical

Fiber:

Definition:In fiber optics, polarization-maintaining optical fiber(PMF or PM fiber) is a single-mode optical fiber in whichlinearly polarized light, if properly launched into thefiber, maintains a linear polarization during propagation,exiting the fiber in a specific linear polarization state;there is little or no cross-coupling of optical powerbetween the two polarization modes.


10/21

Principle Of Operation:

Polarization-maintaining fibers work byintentionally introducing a systematic linear

birefringence in the fiber, so that there are

two well defined polarization modes which

propagate along the fiber with very distinct

phase velocities.

The beat length Lb of such a fiber (for a

particular wavelength) is the distance overwhich the wave in one mode will experience

an additional delay of one wavelength

compared to the other polarization mode.


11/21

Birefringence:

Birefringence is the optical property of amaterial having a refractive index thatdepends on the polarization andpropagation direction of light. These

optically anisotropic materials are said to bebirefringent (or birefractive).

Birefringence is responsible for thephenomenon of double refraction whereby

a ray of light, when incident upon abirefringent material, is split by polarizationinto two rays taking slightly different paths.


12/21


13/21

Designs:

Several different designs are used to create

birefringence in a fiber.

The fiber may be geometrically asymmetric.

fiber have a refractive index profile which is

asymmetric such as the design using anelliptical cladding

Alternatively, stress permanently induced in

the fiber will produce stress birefringence by

using rods of another material included withinthe cladding.


14/21

The stress rods are two circles in the Panda

PM fiber, a elliptical clad in elliptical-clad PM

fiber and two bow-ties in the Bow-Tie type PM

fiber.


15/21

Classification Of Polarization-

maintaining Fibers:


16/21

More Pictures Of PM Fibers:


17/21

Dispersive Phenomena:

The performance of high-speed, digital fiber opticcommunications systems depends upon how

reliably the receiver is able to distinguish closely

spaced bits of information. Dispersive effects

physical mechanisms that broaden transmittedpulses degrade this process.

There are three fundamentally different dispersive

phenomena in optical fiber.

Modal dispersion. Chromatic dispersion.

polarization mode dispersion (PMD) is the most

complex.


18/21

A li i Of P l i i


19/21

Applications Of Polarization

Maintaining Fibers:

In special applications, such as fiber optic sensing,interferometer and slab dielectric waveguides.

Coherent optical transmission systems or long

distance bidirectional optical transmission systems.

In transmission applications where the polarization

plane of the optical signal is important, such as

transmission lines for optical sensors and coupling for

optical electrical integrated circuits.

In lithium niobate modulators, Raman amplifiers, and

other polarization sensitive systems


20/21

What limits PM fiber performance?

In the most common optical fiber telecommunicationsapplications, PM fiber is used to guide light in a linearly

polarized state from one place to another. To achieve

this result, several conditions must be met.

Input light must be highly polarized to avoid launching

both slow and fast axis modes.

The electric field of the input light must be accurately

aligned with a principal axis (the slow axis by industry

convention).

Connectors must have been installed on the PM fibersin such a way that internal stresses do not cause the

electric field to be projected onto the unintended axis of

the fiber.


21/21

polarisation maintaining fibre

Documents