Polarization beam splitter and optical device
A polarization beam splitter includes a demultiplexer, a multiplexer, a first waveguide at least partially formed of a rib waveguide, and a second arm waveguide at least partially formed of a channel waveguide. Waveguide widths of the first and second waveguides are configured to cause, with respect to a linear polarization component of an input light of the polarization beam splitter, 1) a first refractive index of the first arm waveguide and a second refractive index of the second arm waveguide to be the same, and 2) changes of the first and second refractive indexes, due to changes of the respective waveguide widths, to be the same.
1. A polarization beam splitter comprising:
a demultiplexer that demultiplexes input light into first input light and second input light;
a multiplexer that multiplexes the first input light and the second input light, the first input light and the second input light being obtained by demultiplexing the input light by the demultiplexer;
a first arm waveguide that guides the first input light to the multiplexer, at least a part of the first arm waveguide being formed of a rib waveguide; and
a second arm waveguide that guides the second input light to the multiplexer, at least a part of the second arm waveguide being formed of a channel waveguide, wherein
the first and second arm waveguides are formed with a first waveguide width and a second waveguide width respectively, such that:
in a first linear polarization components orthogonal to a second polarization component, a refractive index of the first arm waveguide with respect to the input light is the same as a refractive index of the second arm waveguide with respect to the input light, and a refractive index change of the first arm waveguide with respect to a change in the first waveguide width is the same as a refractive index change of the second arm waveguide with respect to a change in the second waveguide width, and
in the second orthogonal polarization component, a phase difference is generated between the first input light propagating through the first arm waveguide and the second input light propagating through the second arm waveguide.
2. The polarization beam splitter according to claim 1 , wherein the first and second waveguide widths are in a range from 1 to 4 μm.
3. The polarization beam splitter according to claim 1 , wherein the first and second arm waveguides have substantially the same length.
4. An optical device comprising:
polarization beam splitters connected in multiple sequential stages, each of the polarization beam splitters comprising:
a demultiplexer that demultiplexes input light into first input light and second input light;
a multiplexer that multiplexes the first input light and the second input light, the first input light and the second input light being obtained by demultiplexing the input light by the demultiplexer;
a first arm waveguide that guides the first input light to the multiplexer, at least a part of the first arm waveguide being formed of a rib waveguide; and
a second arm waveguide that guides the second input light to the multiplexer, at least a part of the second arm waveguide being formed of a channel waveguide, wherein
the first and second arm waveguides are formed with a first waveguide width and a second waveguide width respectively, such that:
in a first linear polarization components orthogonal to a second polarization component, a refractive index of the first arm waveguide with respect to the input light is the same as a refractive index of the second arm waveguide with respect to the input light, and a refractive index change of the first arm waveguide with respect to a change in the first waveguide width is the same as a refractive index change of the second arm waveguide with respect to a change in the second waveguide width, and
in the second orthogonal polarization component, a phase difference is generated between the first input light propagating through the first arm waveguide and the second input light propagating through the second arm waveguide.
5. The optical device according to claim 4 , wherein
the multiplexer of the polarization beam splitter at a first stage outputs first polarized light and second polarized light separately, the first polarized light and the second polarized light being linear polarization components orthogonal to each other,
the demultiplexer of the polarization beam splitter at a second stage subsequent to the first stage receives the first polarized light as the input light, and
the first and second arm waveguides of the polarization beam splitter at the second stage are formed with a third waveguide width and a fourth waveguide width respectively, such that in the first polarized light, a refractive index of the first arm waveguide with respect to the input light is the same as a refractive index of the second arm waveguide with respect to the input light and a refractive index change of the first arm waveguide with respect to a change in the third waveguide width is the same as a refractive index change of the second arm waveguide with respect to a change in the fourth waveguide width.