Patent ID: 7899279
Filing Date: 2011-03-01
Classification: G02B,H04B

Abstract:
1. An optical delay line interferometer, comprising: an optical splitter that divides an input modulated optical signal into two optical signals; a first optical divider and a second optical divider that receive, respectively, one of the two optical signals divided by the optical splitter, and that each output N divided output lights; N short arm waveguides connected to the first optical divider, and configured to propagate N first divided output lights from the first optical divider therethrough, respectively; N long arm waveguides connected to the second optical divider, and configured to propagate N second divided output lights from the second optical divider therethrough, respectively; N optical combiners that combine one of the N first divided output lights propagating through the N short arm waveguides, with one of the N second divided output lights propagating through the N long arm waveguides and corresponding to the one of the N first divided output lights, thereby to cause interference of the one first divided output light and the one second divided output light, the optical combiners each outputting two interfering output lights, the optical combiners forming N interferometers corresponding to the N optical combiners, respectively; N pairs of output waveguides connected to the N optical combiners, respectively, each of the N pairs of the output waveguides being configured to propagate the corresponding two interfering output lights and including a first output waveguide and a second output waveguide; a polarization converter disposed across the N short arm waveguides and the N long arm waveguides, the polarization converter being placed in such a location that a difference between an integral value of birefringence of a path from the optical splitter to the polarization converter on each of the short arm waveguides and an integral value of birefringence of a path from the optical splitter to the polarization converter on the corresponding one of the long arm waveguides is half of a difference between an integral value of birefringence of an entire path from the optical splitter via the short arm waveguide to the corresponding one of the optical combiners and an integral value of birefringence of an entire path from the optical splitter via the long arm waveguide to the corresponding one of the optical combiner, the polarization converter performing conversion from one to another of TE and TM polarizations; two optical delay lines disposed on both sides of the polarization converter of the long arm waveguides, the two optical delay lines each producing a corresponding delay time between the entire paths from the optical splitter via the long arm waveguides to the optical combiners and the entire paths from the optical splitter via the short arm waveguides to the optical combiners, the corresponding delay time being equivalent to a time of 0.5 symbols of the input modulated optical signal; and a pair of phase shifters disposed on both sides of the polarization converter, respectively, in at least either the short arm waveguides or the long arm waveguides, the pair of phase shifters having the same phase shift elements before and after the polarization converter, the pair of the phase shifters being configured so that optical path length differences of the N interferometers each has a phase difference of π/N at a carrier optical frequency of the input modulated optical signal, and that the optical path length difference of the N interferometers taken as a whole has a phase difference of π(N−1)/N.