Tunable laser with polarization anisotropic amplifier for fabry-perot filter reflection isolation

• US 6,339,603 B1
• Filed: 10/25/2000
• Issued: 01/15/2002
• Est. Priority Date: 10/25/2000
• Status: Expired due to Term

• Current Assignee: Axsun Technologies Incorporated
• Original Assignee: Axsun Technologies Incorporated
• Inventors: Flanders, Dale C., Kuznetsov, Mark E.
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US09/696,055
• Time in Patent Office: 447 Days
• Field of Search: 372/20, 372/43, 372/27, 372/32, 372/98, 372/99, 372/101, 372/102, 372/703
• US Class Current: 372/20
• CPC Class Codes: H01S 5/02325 Mechanically integrated components on mount members or optical micro-benches
• CPC Class Codes: H01S 5/0264 for monitoring the laser-output
• CPC Class Codes: H01S 5/0617 using memorised or pre-programmed laser characteristics
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/142 which comprises an additional resonator

Abstract

A semiconductor tunable laser system includes a tunable Fabry-Perot cavity and a cavity length modulator, which controls an optical length of the cavity at least over a distance corresponding to the spacings between the longitudinal modes of the laser cavity. Thus, the tunable Fabry-Perot cavity allows the laser cavity to have gain at the desired wavelength of operation while the cavity length modulator tunes the cavity length such that a longitudinal cavity mode exists at the desired wavelength of operation. Also, in one embodiment, a wavelength locker system is further provides that has a differential wavelength filter, e.g., stepped etalon, and a multi-element detector, e.g., a quad-detector. The controller then modulators the Fabry-Perot cavity to control the wavelength in response to the signal received from the multi-element detector.

Claims

1. A semiconductor tunable laser system, comprising:

a front reflector and a back reflector defining a laser cavity;

a semiconductor chip functioning as a laser gain medium within the laser cavity, the semiconductor chip being polarization anisotropic to only amplify light of an amplification polarization;

a filter within the laser cavity having a tunable passband for selecting a wavelength of operation of the laser system;

a first polarization rotator between semiconductor chip and the tunable filter that rotates a polarization of light that is emitted from the semiconductor chip and that is outside of the passband of the tunable filter such that a polarization of the rejected light is substantially orthogonal to the amplification polarization upon returning to the semiconductor chip; and

a second polarization rotator in the laser cavity that cooperates with the first polarization rotator to rotate a polarization of light that is emitted from the semiconductor chip and that is within a passband of the tunable filter such that a polarization of the passed light is substantially parallel to the amplification polarization upon returning to the semiconductor chip.

2. A semiconductor tunable laser system as claimed in claim 1, wherein the front reflector is formed on one facet of the semiconductor chip and has a power reflectivity of less than 15%.

3. A semiconductor tunable laser system as claimed in claim 1, wherein the back reflector is formed on a deflectable membrane.

4. A semiconductor tunable laser system as claimed in claim 3, further comprising a controller that tunes the tunable filter to a desired wavelength of operation and controls the deflectable membrane so that longitudinal mode of the cavity resides at the desired wavelength of operation.

5. A semiconductor tunable laser system as claimed in claim 1, wherein the semiconductor chip comprises a semiconductor optical amplifier chip with a reflective front facet.

6. A semiconductor tunable laser system as claimed in claim 1, wherein the filter is a Fabry-Perot filter and comprises serial first and second partial reflectors and means for changing an optical distance between the reflectors.

7. A semiconductor tunable laser system as claimed in claim 1, wherein the filter is a Fabry-Perot filter and comprises a stationary partial reflector, a movable partial reflector including a reflector electrode and a stationary electrode, wherein a controller modulates an electric field between the reflector electrode and the stationary electrode to change a distance between the stationary partial reflector and the movable partial reflector and thereby select the passband of the filter.

8. A semiconductor tunable laser system as claimed in claim 1, wherein the first polarization rotator comprises a Faraday rotator.

9. A semiconductor tunable laser system as claimed in claim 1, wherein the first polarization rotator comprises a quarterwave plate.

10. A semiconductor tunable laser system as claimed in claim 1, wherein the first polarization rotator comprises a subwavelength period grating.

11. A semiconductor tunable laser system as claimed in claim 1, wherein the second polarization rotator comprises a Faraday rotator.

12. A semiconductor tunable laser system as claimed in claim 1, wherein the second polarization rotator comprises a quarterwave plate.

13. A semiconductor tunable laser system as claimed in claim 1, wherein the second polarization rotator comprises a subwavelength period grating.

14. A semiconductor tunable laser system as claimed in claim 1, wherein the first polarization rotator is optically interposed between the semiconductor chip and the filter;

and the second polarization rotator is optically positioned between the filter and the back reflector.

15. A semiconductor tunable laser system as claimed in claim 1, further comprising:

an hermetic package;

an optical bench sealed within the package, the semiconductor chip, the tunable filter, the first polarization rotator, and the second polarization rotator are attached to the optical bench.

16. A semiconductor tunable laser system as claimed in claim 15, further comprising a fiber pigtail entering the package via a fiber feed-through to connect to the bench and terminate above the bench to receive a laser beam from the laser cavity.

17. A semiconductor tunable laser system as claimed in claim 16, further comprising an output-focusing lens for coupling the laser beam into the fiber pigtail.

18. A semiconductor tunable laser system as claimed in claim 15, further comprising focusing lenses installed on the bench at either end of the semiconductor chip to couple optical energy into and out of the chip.

19. A semiconductor tunable laser system, comprising:

means defining a laser cavity;

polarization anisotropic amplification means for amplifying light of an amplification polarization;

filter means in the laser cavity having a tunable passband;

first polarization rotating means for rotating light that is outside of a passband of the filtering means to be orthogonal to the amplification polarization; and

second polarization rotating means for rotating a polarization of light that is within the passband of the filter means such that a polarization of the passed light is substantially parallel to the amplification polarization.

20. A method for generating tunable laser light, comprising:

amplifying light within a cavity in a gain medium;

changing the polarization of light within the cavity in response to whether a wavelength of the light is outside or inside of a passband;

coupling light that is in the passband and outside of the passband into the gain medium; and

preventing amplification of the light in the gain medium that is outside of the passband using the different polarizations.