Measurement of beat length in Hi-Bi fiber using Faraday magneto-optic effect

The polarization maintaining capability of the birefringent fiber can be described in terms of its modal birefringence or beat length. The minimum length of fiber over which the state of polarization (SOP) comes back to its original value is called the beat length and the beat length of the PM fiber can be measured by altering the SOP of the light in the fiber by external means. One technique is to apply a strong magnetic field to the fiber to alter the SOP of the light. This technique is based on Faraday magneto-optic effect, discovered in 1845 by Michael Faraday. This technique is non-destructive. Simple and efficient and beat lengths of 2 mm and less have been measured which fulfil the requirements for currently available PM fibers. The experimental results are very comprehensive and promising and it has been proven that this technique has significant advantages over other techniques in terms of simplicity, versatility, productivity and practicality