Mach Zehnder lattice based generalized Mach Zehnder interferometer
An optical phase shift circuit can include: a first Mach Zehnder lattice and a second Mach Zehnder lattice. Each Mach Zehnder lattice can have a first waveguide and a second waveguide, with a set of active phase shifters disposed along one of the waveguides and a plurality of directional coupler regions disposed along both waveguides between the active phase shifters. A first passive phase shifter can be coupled between one output path of the first Mach Zehnder lattice and one input path of the second Mach Zehnder lattice, and a second passive phase shifter can be coupled between the other output path of the first Mach Zehnder lattice and the other input path of the second Mach Zehnder lattice. Optical phase shift circuits of this kind can be used to implement phase shifters in a Generalized Mach Zehnder interferometer.
1. A circuit comprising:
a first Mach Zehnder lattice having a first waveguide defining a first input path and first output path, a second waveguide defining a second input path and a second output path, the first Mach Zehnder lattice including a plurality of first active phase shifters disposed along the first waveguide and a plurality of directional coupler regions disposed along both waveguides between the first active phase shifters;
a second Mach Zehnder lattice having a first waveguide defining a first input path and first output path, a second waveguide defining a second input path and a second output path, the second Mach Zehnder lattice including a plurality of second active phase shifters disposed along the second waveguide and a plurality of directional coupler regions disposed along both waveguides between the second active phase shifters;
a first passive phase shifter coupled between the first output path of the first Mach Zehnder lattice and the first input path of the second Mach Zehnder lattice, the first passive phase shifter implementing a first phase shift; and
a second passive phase shifter coupled between the second output path of the first Mach Zehnder lattice and the second input path of the second Mach Zehnder lattice, the second passive phase shifter implementing a second phase shift that differs from the first phase shift by π radians.
2. The circuit of claim 1 wherein the plurality of first active phase shifters includes a number (S) of active phase shifters and the plurality of second active phase shifters also includes the number S of active phase shifters.
3. The circuit of claim 1 wherein:
the first Mach Zehnder lattice further includes a plurality of first dummy phase shifters disposed along the second waveguide at locations corresponding to the first active phase shifters; and
the second Mach Zehnder lattice further includes a plurality of second dummy phase shifters disposed along the first waveguide at locations corresponding to the second active phase shifters.
4. The circuit of claim 1 wherein each directional coupler region in the first Mach Zehnder lattice and each directional coupler region in the second Mach Zehnder lattice has a transmissivity equal to a transmissivity of each other directional coupler region in the first Mach Zehnder lattice and each directional coupler region in the second Mach Zehnder lattice.
5. The circuit of claim 1 wherein different directional coupler regions in the first Mach Zehnder lattice have different transmissivities.
6. The circuit of claim 5 wherein different directional coupler regions in the second Mach Zehnder lattice have different transmissivities.
7. The circuit of claim 1 wherein:
the first waveguide of the first Mach Zehnder lattice has an input port coupled to vacuum;
the second waveguide of the first Mach Zehnder lattice has an input port coupled to an upstream optical component capable of providing photons;
the first waveguide of the second Mach Zehnder lattice has an output port coupled to a downstream optical component capable of receiving photons; and
the second waveguide of the second Mach Zehnder lattice has an output port coupled to vacuum.
8. The circuit of claim 1 further comprising:
control logic coupled to the first active phase shifters and the second active phase shifters and configured to generate a first control signal to set a third phase shift for the first active phase shifters and a second control signal to set a fourth phase shift for the second active phase shifters, wherein the third phase shift and the fourth phase shift differ by π radians.
9. A circuit comprising:
a first Hadamard-type passive interferometer having a plurality of input paths and a plurality of output paths;
a second Hadamard-type passive interferometer having a plurality of input paths and a plurality of output paths; and
a plurality of phase shifter circuits, each phase shifter circuit coupled between one of the output paths of the first Hadamard-type passive interferometer and one of the input paths of the second Hadamard-type passive interferometer,
wherein each phase shifter circuit includes:
a first Mach Zehnder lattice having a first waveguide defining a first input path and first output path, a second waveguide defining a second input path and a second output path, the first Mach Zehnder lattice including a plurality of first active phase shifters disposed along the first waveguide and a plurality of directional coupler regions disposed along both waveguides between the first active phase shifters;
a second Mach Zehnder lattice having a first waveguide defining a first input path and first output path, a second waveguide defining a second input path and a second output path, the second Mach Zehnder lattice including a plurality of second active phase shifters disposed along the second waveguide and a plurality of directional coupler regions disposed along both waveguides between the second active phase shifters;
a first passive phase shifter coupled between the first output path of the first Mach Zehnder lattice and the first input path of the second Mach Zehnder lattice, the first passive phase shifter implementing a first phase shift; and
a second passive phase shifter coupled between the second output path of the first Mach Zehnder lattice and the second input path of the second Mach Zehnder lattice, the second passive phase shifter implementing a second phase shift different from the first phase shift.
10. The circuit of claim 9 wherein, in each phase shifter circuit:
the first waveguide of the first Mach Zehnder lattice has an input port coupled to vacuum;
the second waveguide of the first Mach Zehnder lattice has an input port coupled to an output port of the first Hadamard-type passive interferometer;
the first waveguide of the second Mach Zehnder lattice has an output port coupled to an input port of the second Hadamard-type passive interferometer; and
the second waveguide of the second Mach Zehnder lattice has an output port coupled to vacuum.
11. The circuit of claim 9 wherein, in each phase shifter circuit, the first phase shift and the second phase shift differ by π radians.
12. The circuit of claim 9 wherein, in each phase shifter circuit, the plurality of first active phase shifters includes a number (S) of active phase shifters and the plurality of second active phase shifters also includes the number S of active phase shifters.
13. The circuit of claim 9 wherein, in each phase shifter circuit:
the first Mach Zehnder lattice further includes a plurality of first dummy phase shifters disposed along the second waveguide at locations corresponding to the first active phase shifters; and
the second Mach Zehnder lattice further includes a plurality of second dummy phase shifters disposed along the first waveguide at locations corresponding to the second active phase shifters.
14. The circuit of claim 9 wherein, in each phase shifter circuit, each directional coupler region in the first Mach Zehnder lattice and each directional coupler region in the second Mach Zehnder lattice has a transmissivity equal to a transmissivity of each other directional coupler region in the first Mach Zehnder lattice and each directional coupler region in the second Mach Zehnder lattice.
15. The circuit of claim 9 wherein, in each phase shifter circuit, different directional coupler regions in the first Mach Zehnder lattice have different transmissivities.
16. The circuit of claim 9 wherein, in each phase shifter circuit, different directional coupler regions in the second Mach Zehnder lattice have different transmissivities.
17. The circuit of claim 9 further comprising:
control logic coupled to the first active phase shifters and the second active phase shifters in each phase shifter circuit and configured to generate a first control signal to set a third phase shift for the first active phase shifters and a second control signal to set a fourth phase shift for the second active phase shifters, wherein the third phase shift and the fourth phase shift differ by π radians.