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Method for a differential modal dispersion emulator

IP.com Disclosure Number: IPCOM000032569D
Publication Date: 2004-Nov-08
Document File: 3 page(s) / 77K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a differential modal dispersion (DMD) emulator. Benefits include improved functionality and improved performance.

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Method for a differential modal dispersion emulator

Disclosed is a method for a differential modal dispersion (DMD) emulator. Benefits include improved functionality and improved performance.

Background

              Conventionally, measurements of transmission performance over multimode glass optical fiber (MMF) channels are taken using specified lengths of a fiber sample. As many variations of these fibers are available and installed in legacy applications, the results of individual experiments produce widely varying results. A common reference for comparisons of component performance is difficult to compile.

              DMD results from the fact that individual optical modes within a multimode fiber propagate at different velocities. After propagating over a distance of MMF, the different arrival times of each mode begin to cause eye closure, which results in transmission errors.

Description

              The disclosed method is a channel emulator for DMD in MMF. The method includes a device used as test equipment to emulate a multimode fiber communications channel where DMD is one of the signal degradations that limits the performance of the channel.

              The channel emulator is based on single-mode fiber (SMF) based components to provide stability that is not inherent to multimode systems. An optical waveform is launched into an SMF, where it is split into a number of fibers, designated as N (for example, N=16). Each fiber has a unique true-time delay and attenuation. The delayed and weighted waveforms are recombined into a single fiber. The delays and attenuation factors on each individual channel can be varied to emulate waveforms that result from a channel with various levels of DMD. The delays and attenuation values can be continually or discreetly varied. In the illustrated implementation, the delays are fixed and the attenuation values are varied discreetly (see Figure 1).

              An optical gain element compensates for various losses throughout the system, although this is not required for...