Integrated high-power tunable laser with adjustable outputs

1. A laser having a laser cavity comprising:

a first reflector at a first end of the laser cavity;

an intracavity N×M coupler arranged to receive light from the first reflector at a first port and distribute the light to N output ports, where N and M are both greater than 1;

Q optical amplifiers arranged to amplify light from at least some of the N output ports to produce amplified light, where Q≧2; and

at least one second reflector arranged to reflect the amplified light back to the N×M coupler, wherein the first reflector is located on a first photonic integrated circuit chip that includes a coherent optical receiver and an optical modulator arranged to receive power from the laser and the at least one second reflector is located on a second chip.

2. The laser of claim 1 , further comprising at least one phase shifter in at least one optical path between the N×M coupler and the Q optical amplifiers.

3. The laser of claim 2 , wherein the at least one phase shifter comprises at least one thermo-optic phase shifter.

4. The laser of claim 2 , further comprising M−1 power ports connected to the N×M coupler, wherein the at least one phase shifter is adjustable to alter an amount of laser power from at least one of the M−1 power ports.

5. The laser of claim 4 , further comprising:

a detector arranged to sense an optical power from one of the M−1 power ports; and

a feedback circuit arranged to receive a power signal from the detector and alter a phase of a phase shifter responsive to the received power signal.

6. The laser of claim 1 , further comprising a tunable wavelength filter in the laser cavity and coupled to the N×M coupler.

7. The laser of claim 6 , wherein the tunable wavelength filter comprises at least one ring resonator coupled to a waveguide.

8. The laser of claim 6 , wherein the tunable wavelength filter is configured to tune a wavelength of the laser over a range of wavelengths, the range of wavelengths lying between 1200 nm and 1700 nm.

9. The laser of claim 1 , wherein the N×M coupler is integrated on the first photonic integrated circuit chip and the Q optical amplifiers are integrated on the second chip.

10. The laser of claim 9 , further comprising:

first microfabricated waveguides on the first photonic integrated circuit chip and second microfabricated waveguides on the second chip arranged to couple the N output ports of the N×M coupler to the Q optical amplifiers; and

mode-size adapters located between the first microfabricated waveguides and the second microfabricated waveguides.

11. The laser of claim 10 , wherein the first microfabricated waveguides are butt-coupled to the second microfabricated waveguides.

12. The laser of claim 9 , wherein the first photonic integrated circuit chip comprises a silicon photonics chip and the second chip comprises indium-phosphide.

13. The laser of claim 12 , further comprising:

M−1 power ports connected to the N×M coupler,

wherein a first of the M−1 power ports is connected to the coherent receiver, and

wherein a second of the M−1 power ports is connected to the optical modulator.

14. A method of generating coherent light, the method comprising:

reflecting light from a first reflector located on a first photonic integrated circuit chip;

distributing the light, with an N×M coupler, to N optical paths, where N and M are both greater than 1;

producing amplified light by amplifying light in at least some of the N optical paths with Q optical amplifiers, where Q ≧2;

returning the amplified light to the N×M coupler and first reflector with at least one second reflector located on a second chip;

receiving power from the N×M coupler at a coherent optical receiver located on the first photonic integrated circuit chip; and

receiving power from the N×M coupler at an optical modulator located on the first photonic integrated circuit chip.

15. The method of claim 14 , wherein producing amplified light by amplifying light in at least some of the N optical paths comprises amplifying the light with indium-phosphide semiconductor optical amplifiers.

16. The method of claim 14 , wherein returning the amplified light comprises returning the amplified light from a first semiconductor material to a second semiconductor material in which the N×M coupler is fabricated, wherein the first semiconductor material is different from the second semiconductor material.

17. The method of claim 16 , wherein the first semiconductor material comprises indium phosphide and the second semiconductor material comprises silicon.

18. The method of claim 14 , further comprising adjusting a tunable filter to select a wavelength of the light reflected from the first reflector, wherein the wavelength is between approximately 1200 nm and approximately 1700 nm.

19. The method of claim 14 , further comprising:

providing portions of the coherent light out M−1 power ports connected to the N×M coupler; and

adjusting a phase of light in at least one of the N optical paths to alter an amount of power in at least one of the M−1 power ports.

20. The method of claim 19 , further comprising:

providing a first signal from a first power port of the M−1 power ports to the coherent optical receiver; and

providing a second signal from a second power port of the M−1 power ports to the optical modulator, wherein the N×M coupler is located on the first photonic integrated circuit chip.

21. The method of claim 20 , further comprising:

mixing the first signal as a local oscillator with a received optical signal; and

modulating the second signal as a carrier wave to encode at least a portion of a transmitted optical signal.