US 5,848,205 AGranted

Polarization independent non-linear optical mirror

AssigneeAlcatel

InventorSebastien Bigo

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Abstract

The invention relates to a non-linear optical mirror comprising an optical fiber loop that operates independently of the polarizations of the signals of respective wavelengths .lambda..sub.s and .lambda..sub.c present on its signal and control inputs. The loop of the NOLM is made up of four polarization-maintaining fiber segments having equivalent optical lengths. These four segments are optically optically interconnected by three splices at three locations. At the first and third splices, the neutral propagation axes of the polarization-maintaining fibers are turned through 90.degree.. According to the invention, a mode converter is inserted in the loop at the second splice, the converter comprising an optical demultiplexer and an optical multiplexer together with two polarization-maintaining optical paths inter-connecting them. The demultiplexer separates the two optical signals present at its input and applies them respectively to said two paths. On the path conveying the control signal, .lambda..sub.c, there is a splice including 90.degree. rotation of the polarization-maintaining neutral axes. On the other path, there is no rotation of the axes. The multiplexer then recombines the two signals. The invention is applicable to long distance telecommunications by optical fiber.

Claims8

Dependent claims

A non-linear optical loop mirror (NOLM), said NOLM comprising an optical fiber loop, said loop having a signal output and a signal input for injecting a first optical signal characterized in part by a first wavelength, and a first signal input/output optical coupler with a coupling coefficient of .xi./(1-.xi.) for coupling said input and said output to said loop, where 0.gtoreq..xi..gtoreq.1, said NOLM also having a first control input via a control fiber and a second optical coupler for coupling said first control input to said loop to enable a "control" second optical signal characterized in part by a second wavelength to be injected into said loop via the control fiber, said optical fiber loop having an even number, 2i>2, i integer, of segments of polarization-maintaining fiber having two neutral propagation axes, said segments having equivalent optical lengths and being optically interconnected via 2i-1 splices at 2i-1 locations, said neutral propagation axes of the fiber being turned through 90.degree. at the 2i-2 splices other than the splice in the middle of the loop, with the i-th splice including a mode converter, wherein said mode converter comprises an optical polarization-maintaining demultiplexer and an optical polarization-maintaining multiplexer together with first and second optical paths interconnecting them for conveying said first and second wavelengths respectively, said optical paths being implemented by polarization-maintaining fiber, and wherein the neutral axes of said second path are turned through 90.degree. while the neutral axes of said first path are not turned.

Dependencies are inferred from the claim text.