Tunable laser and tuning method using the same

1. A tunable laser, comprising:

a) a gain section;

b) a multi-channel splitter section; and

c) a multi-channel reflection section, the multi-channel reflection section comprising multiple arms of unequal lengths;

wherein

the gain section, the multi-channel splitter section, and the multi-channel reflection section are sequentially connected in that order;

the gain section is configured to provide an optical gain for lasing; a facet of the gain section away from the multi-channel splitter section is an optical output facet of the laser;

the multi-channel splitter section is configured to split an input signal into multiple outputs;

the multi-channel reflection section is configured to provide an optical feedback and a mode selection function for the laser to work; and

when arranging the multiple arms of the multi-channel reflection section in an order according to their lengths, length difference between adjacent arms are unequal; facets of the multiple arms away from the multi-channel splitter section are coated with reflection films; arm phase sections are disposed on each of the multiple arms of unequal lengths for adjusting phases of the arms individually; and a number of the multiple arms is equal to or greater than 3.

2. The laser of claim 1 , further comprising a common phase section configured to change a wavelength of a longitudinal mode of the laser and connected between the gain section and the multi-channel splitter section.

3. The laser of claim 2 , wherein a reflection spectrum dominated by a single main reflection peak is generated by aggregated reflections from the multi-channel reflection section to achieve single mode working.

4. The laser of claim 3 , wherein in use, the length difference between adjacent arms are determined as follows:

adjusting the length difference ΔL i between adjacent arms according to that when an average value of the length difference ΔL i tends to enlarge, a full width half maximum of the main reflection peak reduces thus suppression of the adjacent longitudinal modes is enhanced, while suppression of the other minor random reflection peaks is weakened, and that when the average value of the length difference ΔL i tends to reduce, suppression of the other minor random reflection peaks is enhanced, while the full width half maximum of the main reflection peak enlarges thus weakening suppression of the adjacent longitudinal modes; and

optimizing the length difference between adjacent arms so as to suppress both the adjacent longitudinal modes and the other minor random reflection peaks to an appropriate level.

5. The laser of claim 4 , wherein the lengths of the multiple arms are determined as follows:

choosing one arm as a reference arm and setting an appropriate length for the reference arm;

setting lengths of other arms according to the length difference.

6. The laser of claim 1 , wherein the multi-channel splitter section adopts multi-mode interferometers, Y branches, or a star coupler.

7. The laser of claim 6 , wherein a reflection spectrum dominated by a single main reflection peak is generated by aggregated reflections from the multi-channel reflection section to achieve single mode working.

8. The laser of claim 7 , wherein in use, the length difference between adjacent arms are determined as follows:

adjusting the length difference ΔL i between adjacent arms according to that when an average value of the length difference ΔL i tends to enlarge, a full width half maximum of the main reflection peak reduces thus suppression of the adjacent longitudinal modes is enhanced, while suppression of the other minor random reflection peaks is weakened, and that when the average value of the length difference ΔL i tends to reduce, suppression of the other minor random reflection peaks is enhanced, while the full width half maximum of the main reflection peak enlarges thus weakening suppression of the adjacent longitudinal modes; and

optimizing the length difference between adjacent arms so as to suppress both the adjacent longitudinal modes and the other minor random reflection peaks to an appropriate level.

9. The laser of claim 8 , wherein the lengths of the multiple arms are determined as follows:

choosing one arm as a reference arm and setting an appropriate length for the reference arm;

setting lengths of other arms according to the length difference.

10. The laser of claim 1 , wherein a reflection spectrum dominated by a single main reflection peak is generated by aggregated reflections from the multi-channel reflection section to achieve single mode working.

11. The laser of claim 10 , wherein in use, the length difference between adjacent arms are determined as follows:

adjusting the length difference ΔL i between adjacent arms according to that when an average value of the length difference ΔL i tends to enlarge, a full width half maximum of the main reflection peak reduces thus suppression of the adjacent longitudinal modes is enhanced, while suppression of the other minor random reflection peaks is weakened, and that when the average value of the length difference ΔL i tends to reduce, suppression of the other minor random reflection peaks is enhanced, while the full width half maximum of the main reflection peak enlarges thus weakening suppression of the adjacent longitudinal modes; and

optimizing the length difference between adjacent arms so as to suppress both the adjacent longitudinal modes and the other minor random reflection peaks to an appropriate level.

12. The laser of claim 11 , wherein the lengths of the multiple arms are determined as follows:

choosing one arm as a reference arm and setting an appropriate length for the reference arm;

setting lengths of other arms according to the length difference.

13. A method of tuning using the laser of claim 1 , the method comprising coarse tuning of a working wavelength of the laser, and the coarse tuning comprising:

choosing one arm as a reference arm; and

adjusting phases of other arms and enabling the phases of the other arms to be the same as a phase of the reference arm at a selected wavelength to locate a main reflection peak of a reflection spectrum at the selected wavelength and allow the laser to work in the vicinity of the selected wavelength.

14. The method of claim 13 , further comprising fine tuning of the working wavelength of the laser, and the fine turning comprising:

adjusting the phase of the reference arm; and

readjusting the phases of other arms and enabling the phases of the other arms to be the same as the phase of the reference arm at the same selected wavelength to maintain a position of the main reflection peak of the reflection spectrum and align a position of the longitudinal mode position with the main reflection peak and to allow the laser to work at the wavelength selected.

15. The method of claim 14 , wherein adjustments of phases of the arm phase sections and the phase of the common phase section are fulfilled by injecting currents into corresponding phase sections.

16. The method of claim 13 , further comprising adjusting a phase of the common phase section to align the position of the longitudinal mode with the reflection peak at the selected wavelength to achieve fine tuning of working wavelength of the laser.

17. The method of claim 16 , wherein adjustments of phases of the arm phase sections and the phase of the common phase section are fulfilled by injecting currents into corresponding phase sections.

18. The method of claim 13 , wherein adjustments of phases of the arm phase sections and the phase of the common phase section are fulfilled by injecting currents into corresponding phase sections.