Method of evaluating fiber pmd using potdr trace

Abstract

A method for screening fiber polarization mode dispersion using a polarization optical time domain reflectometer is disclosed. A pulse radiation is emitted into an end of the fiber under test, and the backscattered radiation is measured by the POTDR and used to obtain an OTDR trace. A pulse radiation is emitted into an opposite end of the fiber under test, and the backscattered radiation is measured by the POTDR and used to obtain another OTDR trace. Either one or both traces are analyzed to compare the variation of intensity of signals along the length of the fiber, the variation in signals relating to the PMD along the length of the fiber.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates generally to optical fibers, and particularly to a method for identifying optical fibers which exhibit elevated polarization mode dispersion (PMD). [0003] 2. Technical Background [0004] PMD is an important factor in the design of state-of-art fiber optic transmission systems. The effect of PMD in fiber systems is evident when, after propagating a sufficient distance in the network, one digital pulse may spread in the time domain and become indistinguishable from a nearby pulse. The pulse spreading from PMD can introduce errors into the data transmission, effectively limiting the transmission rate of the pulses or the maximum distance of the concatenated fiber medium. Polarization mode dispersion (PMD) can be a major limitation for high data rate optical communications systems and is thus an important fiber attribute that fiber manufacturers monitor closely. One notorious aspect of fiber...

AI Technical Summary

Benefits of technology

[0020] Thus, we have found that backscatter intensity traces from large linewidth pulses allow an analysis which reveals the existence of elevated PMD in an optical fiber, and moreover allow the detection of relatively short length sections of the optical fiber having elevated PMD. We have found that higher linewidths of the pulses permits the detection of lower PMD. This method is effective even when the section of fiber with elevated PMD is as short as a few meters.

Problems solved by technology

The pulse spreading from PMD can introduce errors into the data transmission, effectively limiting the transmission rate of the pulses or the maximum distance of the concatenated fiber medium.

Although fiber outliers usually represent a very small percentage of the whole population of newly made fibers, the effect of such fibers can be very detrimental.

Fiber PMD failure identified at a cable plant can also incur significant financial loss to the fiber makers.

However, a common feature of the above known methods is that they are effective only when the fiber has elevated PMD over a sufficiently long length to permit detection by those schemes.

In some instances, PMD failures have been detected and linked to gas bubbles or air lines, sometimes called seeds, in the fiber perform, between the interfaces of different preform manufacturing steps, which can occur more often in the manufacture of fibers with complex refractive index profiles made with multiple steps, although similar conditions can occur in the manufacture of relatively simple step index fibers.

Images