Gain Equalizer
A gain equalizer using a lattice optical circuit with a smaller polarization-dependent loss is provided. The gain equalizer includes: 2M optical waveguide circuits formed on a substrate, wherein M is an integer of 1 or more, including M pairs of optical waveguide circuits, each pair of optical waveguide circuits having the same gain equalization spectrum; and a folding connection structure that connects input/output waveguides of a pair of optical waveguide circuits, the folding connection structure rotating a polarization direction of propagating light by 90 degrees,
1 . A gain equalizer comprising:
2M optical waveguide circuits formed on a substrate, wherein M is an integer of 1 or more, comprising M pairs of optical waveguide circuits, each pair of optical waveguide circuits having the same gain equalization spectrum; and
a folding connection structure that connects input/output waveguides of a pair of optical waveguide circuits, the folding connection structure rotating a polarization direction of propagating light by 90 degrees.
2 . The gain equalizer according to claim 1 , wherein
each of the optical waveguide circuits includes:
a first input/output waveguide;
N 2-input 2-output optical multiplexing/demultiplexing circuits, wherein N is an integer of 3 or more;
N−1 arm waveguides each consisting of two waveguides connecting between the optical multiplexing/demultiplexing circuits; and
a second input/output waveguide,
wherein a loaded phase shifter is provided in at least one of the arm waveguides.
3 . A gain equalizer comprising:
an optical waveguide circuit formed on a substrate, which is configured by an input waveguide; N 2-input 2-output optical multiplexing/demultiplexing circuits, wherein N is an integer of 3 or more; N−1 arm waveguides each consisting of two waveguides connecting between the optical multiplexing/demultiplexing circuits; and an output waveguide, the optical waveguide circuit further including a loaded phase shifter provided in at least one of the arm waveguides; and
an optical folding unit that outputs the light input from the output waveguide to the output waveguide again, and rotates a polarization direction of propagating light by 90 degrees.
4 . The gain equalizer according to claim 1 , wherein the folding connection structure includes:
an optical waveguide that connects the input/output waveguides; and
a groove formed along a part of the optical waveguide on one side in the part of the optical waveguide with respect to a plane of the substrate.
5 . The gain equalizer according to claim 1 , wherein the folding connection structure includes:
an optical waveguide that connects the input/output waveguides; and
a wavelength plate inserted into the optical waveguide.
6 . The gain equalizer according to claim 1 , wherein the folding connection structure includes a polarization-maintaining fiber that connects the input/output waveguides.
7 . The gain equalizer according to claim 3 , wherein the optical folding unit includes:
a second 2-input 2-output optical multiplexing/demultiplexing circuit connected to the output waveguide;
a folding optical waveguide that connects two output ports of the second optical multiplexing/demultiplexing circuit; and
a groove formed along a part of the folding optical waveguide on one side in the part of the folding optical waveguide with respect to a plane of the substrate.
8 . The gain equalizer according to claim 3 , wherein the optical folding unit includes:
a second 2-input 2-output optical multiplexing/demultiplexing circuit connected to the output waveguide;
a folding optical waveguide that connects two output ports of the second optical multiplexing/demultiplexing circuit; and
a wavelength plate inserted into the folding optical waveguide.