Optical receiver circuit
An optical receiver circuit includes a polarization beam splitter configured to split input signal light into two different polarized wave components; two variable optical attenuators configured to respectively adjust attenuation of and output the signal light split by the polarization beam splitter according to polarization state; and a single planar optical waveguide on which the polarization beam splitter and the two variable optical attenuators are disposed.
1. An optical receiver circuit comprising:
a polarization beam splitter configured to split input signal light into two different polarized wave components;
two variable optical attenuators configured to respectively adjust attenuation of and output the signal light split by the polarization beam splitter according to polarization state; and
a single planar optical waveguide on which the polarization beam splitter and the two variable optical attenuators are disposed
a splitter-coupler configured to split input local light;
a half-wave plate disposed between the polarization beam splitter and one of the two variable optical attenuators, and configured to make the polarization state of a first component of the signal light split by the polarization beam splitter to coincide with the polarization state of a second component of the signal light; and
two 90-degree hybrid circuits each configured to receive a respective input of the local light split by the splitter-coupler and an optical signal for which attenuation has been adjusted by a respective one of the two variable optical attenuators.
2. The optical receiver circuit according to claim 1 , further comprising
a single variable voltage source that supplies equivalent voltage to the two variable optical attenuators to cause attenuation of the signal light.
3. The optical receiver circuit according to claim 2 , wherein
the two variable optical attenuators have arm waveguides of differing optical path lengths and correct a difference in attenuation of the signal light of different polarization states.
4. The optical receiver circuit according to claim 3 , wherein
the arm waveguides of the two variable optical attenuators have differing arm waveguide widths, or refractive indices.
5. The optical receiver circuit according to claim 2 , wherein
a corrective resistor is disposed between the variable voltage source and the two variable optical attenuators to correct with respect to applied voltage, a difference in attenuation of the two variable optical attenuators caused by a fabrication difference of resistance of thin film heaters disposed in the two variable optical attenuators.
6. The optical receiver circuit according to claim 2 , further comprising
a constant voltage source to correct with respect to applied voltage of the variable voltage source, a difference in attenuation caused by a fabrication difference of arm waveguides of the two variable optical attenuators, the constant voltage source being configured to supply constant voltage to a thin film heater for an arm waveguide, among thin film heaters disposed on two arm waveguides of the two variable optical attenuators.
7. The optical receiver circuit according to claim 1 , further comprising
two variable voltage sources configured to supply voltage to the two variable optical attenuators, respectively, to attenuate the signal light.
8. The optical receiver circuit according to claim 7 , further comprising
control circuitry configured to detect a level of the signal light after attenuation by the two variable optical attenuators and control attenuation of the two variable optical attenuators.
9. An optical receiver circuit comprising:
a polarization beam splitter configured to split input signal light into two different polarized wave components;
two variable optical attenuators configured to respectively adjust attenuation of and output the signal light split by the polarization beam splitter according to polarization state; and
a single planar optical waveguide on which the polarization beam splitter and the two variable optical attenuators are disposed
a splitter-coupler configured to split input local light;
a half-wave plate configured to change the polarization state of a first component of the signal light split by the splitter-coupler; and
two 90-degree hybrid circuits each configured to receive a respective input of the local light split by the splitter-coupler and an optical signal for which attenuation has been adjusted by a respective one of the two variable optical attenuators.