Method and system for hybrid integration of a tunable laser and a phase modulator
A tunable laser includes a substrate comprising a silicon material and a gain medium coupled to the substrate. The gain medium includes a compound semiconductor material. The tunable laser also includes an optical modulator optically coupled to the gain medium, a phase modulator optically coupled to the optical modulator, and a waveguide disposed in the substrate and optically coupled to the gain medium. The tunable laser further includes a first wavelength selective element characterized by a first reflectance spectrum and disposed in the substrate, a second wavelength selective element characterized by a second reflectance spectrum and disposed in the substrate, an optical coupler disposed in the substrate and joining the first wavelength selective element, the second wavelength selective element, and the waveguide, and an output mirror.
1. A tunable pulsed laser comprising:
a substrate comprising a silicon material and a recess region having an interface;
a gain medium coupled to the substrate and having a facet spatially separated from the interface by an index matching region, wherein the gain medium includes a compound semiconductor material;
an optical modulator optically coupled to the gain medium;
a phase modulator optically coupled to the optical modulator;
a waveguide disposed in the substrate and optically coupled to the gain medium;
a first wavelength selective element characterized by a first reflectance spectrum and disposed in the substrate;
a second wavelength selective element characterized by a second reflectance spectrum and disposed in the substrate;
an optical coupler disposed in the substrate and joining the first wavelength selective element, the second wavelength selective element, and a phase adjustment section disposed in the silicon material substrate between the waveguide and the optical coupler, the phase adjustment section having a heating element; and
an output mirror.
2. The tunable pulsed laser of claim 1 wherein:
the first wavelength selective element comprises a first modulated grating reflector; and
the second wavelength selective element comprises a second modulated grating reflector.
3. The tunable pulsed laser of claim 2 wherein the first modulated grating reflector comprises a superstructure grating characterized by a first wavelength spacing between modes.
4. The tunable pulsed laser of claim 3 wherein the second modulated grating reflector comprises a superstructure grating characterized by a second wavelength spacing between modes different than the first wavelength spacing between modes.
5. The tunable pulsed laser of claim 1 wherein the silicon material comprises a silicon on insulator wafer.
6. The tunable pulsed laser of claim 5 wherein the silicon on insulator wafer comprises a silicon substrate, an oxide layer disposed on the silicon substrate, and a silicon layer disposed on the oxide layer, wherein the first wavelength selective element and the second wavelength selective element are disposed in the silicon layer.
7. The tunable pulsed laser of claim 1 wherein the optical modulator and the phase modulator comprise external cavity optical elements.
8. The tunable pulsed laser of claim 1 wherein:
the first wavelength selective element comprises a first index of refraction adjustment device; and
the second wavelength selective element comprises a second index of refraction adjustment device.
9. The tunable pulsed laser of claim 8 wherein:
the first index of refraction adjustment device comprises a thermal device; and
the second index of refraction adjustment device comprises a thermal device.
10. The tunable pulsed laser of claim 9 further comprising:
a controlled index layer over the waveguide having a higher refractive index than the silicon material waveguide, the controlled index layer broadening a mode in the waveguide; and
an encapsulant layer disposed between a metal of at least one of the thermal devices and the controlled index layer.
11. The tunable pulsed laser of claim 10 wherein a portion of the controlled index layer is disposed within the index matching region to form an index matching layer within the index matching region.
12. The tunable pulsed laser of claim 8 wherein
the first wavelength selective element further comprises a first temperature sensor; and
the second wavelength selective element further comprises a second temperature sensor.
13. The tunable pulsed laser of claim 1 wherein the optical modulator comprises a Mach-Zehnder modulator.
14. The tunable pulsed laser of claim 1 further comprising a second phase adjustment section operable to modify an optical phase in at least one of the first wavelength selective element or the second wavelength selective element.
15. The tunable pulsed laser of claim 1 further comprising a controlled index layer over the waveguide having a higher refractive index than the silicon material waveguide, the controlled index layer broadening a mode in the waveguide.
16. The tunable pulsed laser of claim 1 further comprising an encapsulant layer disposed over the first and second wavelength selective elements.
17. A method of operating a tunable pulsed laser, the method comprising:
tuning, using a first resistive thermal device, a first modulated grating reflector, wherein the first modulated grating reflector is characterized by a first reflectance spectra including a first plurality of reflectance peaks;
tuning, using a second resistive thermal device, a second modulated grating reflector, wherein the second modulated grating reflector is characterized by a second reflectance spectra including a second plurality of reflectance peaks;
generating optical emission from a gain medium comprising a compound semiconductor material;
adjusting a phase of the optical emission from the gain medium through a phase adjustment section integrated in a silicon layer using a heating element;
waveguiding the phase adjusted optical emission to pass through an optical waveguide in the silicon layer to an optical coupler;
reflecting a portion of the optical emission having a spectral bandwidth defined by an overlap of one of the first plurality of reflectance peaks and one of the second plurality of reflectance peaks;
transmitting the portion of the optical emission through an index matching region disposed between the optical waveguide in the silicon layer and the gain medium;
amplifying the portion of the optical emission in the gain medium;
transmitting a portion of the amplified optical emission through an output mirror;
optically modulating the transmitted optical emission to form a pulsed optical output; and
phase modulating the pulsed optical output.
18. The method of claim 17 wherein the first modulated grating reflector and the second modulated grating reflector are disposed in a silicon on insulator wafer.
19. The method of claim 18 wherein the silicon on insulator wafer comprises a silicon substrate, an oxide layer disposed on the silicon substrate, and a silicon layer disposed on the oxide layer, wherein the first modulated grating reflector and the second modulated grating reflector are disposed in the silicon layer.
20. The method of claim 18 wherein phase modulating the pulsed optical output comprises producing a time varying phase profile.
21. The method of claim 17 wherein the first modulated grating reflector comprises a superstructure grating characterized by a first wavelength spacing between modes.
22. The method of claim 21 wherein the second modulated grating reflector comprises a superstructure grating characterized by a second wavelength spacing between modes different than the first wavelength spacing between modes.
23. The method of claim 17 wherein:
the first and second modulated grating reflectors are integrated into the silicon layer; and
the first and second resistive thermal devices have been integrated onto the silicon layer by vacuum deposition.