Optical wavemeter

1. A photonic integrated circuit (PIC) for determining a wavelength of an input signal, the PIC comprising:

a substrate;

a first Mach-Zehnder Interferometer (MZI) disposed over the substrate, comprising first optical waveguides having a first effective index of refraction and configured to receive a first output optical signal from a light source; and

a second Mach-Zehnder Interferometer (MZI) disposed over the substrate, comprising second optical waveguides having a second effective index of refraction, which is greater than the first effective index of refraction, and configured to receive a second output optical signal from the light source, wherein the first MZI has a first optical path length (OPL) difference, and the second MZI has a second optical path length (OPL) difference, which is greater than the first OPL difference.

2. The PIC of claim 1 , wherein the first optical waveguides have a first core width, the second optical waveguides have a second core width, and the second core width is greater than the first core width.

3. The PIC of claim 1 , wherein the first optical waveguides have a first core height, the second optical waveguides have a second core height, and the second core height is greater than the first core height.

4. The PIC of claim 2 , wherein the first and second optical waveguides are each one of a strip optical waveguide, a rib optical waveguide, a slot optical waveguide, a photonic crystal optical waveguide, a subwavelength grating (SWG) optical waveguide, a slot SWG optical waveguide, and a surface plasmon polariton slot optical waveguide.

5. The PIC of claim 4 , wherein the first and second optical waveguides are different from one another.

6. The PIC of claim 3 , wherein the first and second optical waveguides are each one of a strip optical waveguide, a rib optical waveguide, a slot optical waveguide, a photonic crystal optical waveguide, a subwavelength grating (SWG) optical waveguide, a slot SWG optical waveguide, and a surface plasmon polariton slot optical waveguide.

7. The PIC of claim 6 , wherein the first and second optical waveguides are different from one another.

8. The PIC of claim 1 , wherein geometric length difference of the arms of the first MZI is not the same as the geometric length difference of the arms of the second MZI.

9. The PIC of claim 8 , wherein the first optical waveguides comprise a first core and a first cladding, the first core comprising one of silicon (Si) or germanium (Ge), and indium phosphide, and the first cladding comprising one of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), and indium phosphide (InP).

10. The PIC of claim 1 , wherein the second optical waveguides comprise a second core substantially surrounded by a second cladding, wherein an index of refraction of the second core is greater than an index of refraction of the second cladding.

11. The PIC of claim 10 , wherein the second core comprises silicon (Si) and the first cladding comprises one of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), and indium phosphide (InP).

12. The PIC of claim 1 , further comprising:

a first photodetector and a second photodetector, wherein a first difference signal is provided based on first outputs of the first MZI; and

a third photodetector and a fourth photodetector, wherein a second difference signal is provided based on second outputs of the second MZI, wherein the first and second difference signals are used to determine an output wavelength of the light source.

13. An optical wavemeter for determining an optical wavelength of a light source, the optical wavemeter comprising:

a substrate;

a first Mach-Zehnder Interferometer (MZI) disposed over the substrate, comprising first optical waveguides having a first optical path length difference, and configured to receive a first output optical signal from a light source; a second Mach-Zehnder Interferometer (WI) disposed over the substrate, comprising second optical waveguides having a second optical path length difference, which is greater than the first optical path length difference, and configured to receive a second output optical signal from the light source, wherein: the first optical waveguides have a first core width, the second waveguides have a second core width, and the second core width is greater than the first core width; or the first optical waveguides have a first core height, the second waveguides have a second core height, and the second core height is greater than the first core height;

a first photodetector and a second photodetector, wherein a first difference signal is provided based on first outputs of the first MZI;

a third photodetector and a fourth photodetector, wherein a second difference signal is provided based on second outputs of the second MZI; and

a controller comprising a memory that stores instructions, and a processor that executes the instructions, wherein, when executed by the processor, the instructions cause the controller to implement a process, comprising:

comparing the first and second difference signals with first and second difference values stored in the memory, and, based on the comparing, determining an output wavelength of the light source.

14. The system of claim 13 , wherein the first and second optical waveguides are each one of a strip optical waveguide, a rib optical waveguide, a slot optical waveguide, a photonic crystal optical waveguide, a subwavelength grating (SWG) optical waveguide, a slot SWG optical waveguide, and a surface plasmon polariton slot optical waveguide.

15. A photonic integrated circuit (PIC) for determining a wavelength of an input signal, the PIC comprising:

a substrate;

a first Mach-Zehnder Interferometer (MZI) disposed over the substrate, comprising first optical waveguides having a first optical path length difference, and configured to receive a first output optical signal from a light source; and

a second Mach-Zehnder Interferometer (MZI) disposed over the substrate, comprising second optical waveguides having a second optical path length difference, which is greater than the first optical path length difference, and configured to receive a second output optical signal from the light source wherein the first optical waveguides have a first index of refraction and the second waveguides have a second index of refraction, which is different than the first index of refraction.

16. The PIC of claim 15 , wherein the first optical waveguides have a first core width, the second optical waveguides have a second core width, and the second core width is greater than the first core width.

17. The PIC of claim 15 , wherein the first optical waveguides have a first core height, the second optical waveguides have a second core height, and the second core height is greater than the first core height.

18. The PIC of claim 17 , wherein the first and second optical waveguides are each one of a strip optical waveguide, a rib optical waveguide, a slot optical waveguide, a photonic crystal optical waveguide, a subwavelength grating (SWG) optical waveguide, a slot SWG optical waveguide, and a surface plasmon polariton slot optical waveguide.

19. The PIC of claim 15 , wherein the first optical waveguides each have a first core and a first cladding have first indices of refraction, and the second optical waveguides each have a second core and a second cladding have second effective indices of refraction, which are different than the first effective indices of refraction.