Tunable laser

1. A wavelength tunable laser comprising:

a gain region comprising a gain medium;

a comb mirror disposed at one side of the gain region, the comb mirror having a plurality of reflection peaks;

a broadband mirror disposed at another side of the gain region, a laser cavity formed by the comb mirror and the broadband mirror having a plurality of cavity modes; and

a phase section configured to introduce a change in optical path of an optical signal in the laser cavity, wherein the phase section is configured to be electrically or thermally controlled such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes,

wherein the comb mirror is configured to be electrically or thermally controlled such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes,

wherein the comb mirror comprises one or more regions comprising gain medium, and

wherein the one or more regions comprising gain medium are separate from the gain region.

2. The tunable laser of claim 1 , wherein the gain region, the comb mirror and the broadband mirror are disposed on a substrate comprising at least one waveguide.

3. The tunable laser of claim 2 , wherein the substrate comprises a crystalline material.

4. The tunable laser of claim 2 , wherein the gain region comprises a multi-quantum well semiconductor heterojunction.

5. The tunable laser of claim 1 , configured as a semiconductor laser.

6. The tunable laser of claim 1 , wherein the comb mirror comprises one or more regions that are devoid of the gain medium.

7. The tunable laser of claim 1 , wherein the gain region comprises the comb mirror.

8. The tunable laser of claim 1 , wherein a gain bandwidth of the gain region comprises two or more reflection peaks of the comb mirror.

9. The tunable laser of claim 1 , wherein a length of the laser cavity is configured such that a non-integer number of cavity modes are between two consecutive reflection peaks of the comb mirror.

10. The tunable laser of claim 1 , wherein the broadband mirror comprises a cleaved facet.

11. A wavelength tunable laser comprising:

a crystalline substrate;

a waveguide on the crystalline substrate;

a comb mirror at one end of the waveguide, the comb mirror comprising a plurality of reflective regions, the comb mirror having a plurality of reflection peaks in a wavelength range;

a broadband reflector at another end of the waveguide, the broadband reflector having substantially uniform reflectivity for wavelengths in the wavelength range; and

a gain region in a cavity formed by the comb mirror and the broadband reflector, the gain region comprising a gain medium, the gain region having a gain peak in the wavelength range, the gain peak having:

a maximum gain; and

a gain bandwidth equal to a width of the gain peak at 50% of the maximum gain;

wherein the cavity formed by the comb mirror and the broadband reflector has a plurality of cavity modes, and

wherein a length of the cavity is configured such that a non-integer number of cavity modes are present in a free spectral range of the comb mirror, wherein the free spectral range of the comb mirror is between 0.05 nm and 50 nm, and

wherein the comb mirror is configured to be electrically or thermally controlled such that at least one of the plurality of reflection peaks overlaps with one of the plurality of cavity modes to output a laser signal having a side mode suppression ratio (SMSR) between about 10 dB and about 150 dB.

12. The laser of claim 11 , wherein the wavelength range is between about 650 nm and about 1950 nm.

13. The laser of claim 12 , wherein the wavelength range comprises at least one of a first range from about 1250 nm and about 1360 nm, a second range from about 1500 nm and about 1580 nm, or a third range from about 1600 nm and about 1700 nm.

14. The laser of claim 11 , further comprising one or more electrodes configured to provide electrical current or voltage to move the reflection peaks of the comb mirror with respect to the cavity modes to select a desired lasing wavelength.

15. The laser of claim 11 , wherein two or more reflection peaks of the comb mirror are within the gain bandwidth.