External cavity tunable laser with provisions for intracavity optical reflection suppression

• US 20050036534A1
• Filed: 08/12/2003
• Published: 02/17/2005
• Est. Priority Date: 08/12/2003
• Status: Active Grant

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Baney, Douglas M.
• Granted Patent: US 6,993,051 B2
• Time in Patent Office: Days
• US Class Current: 372/106
• CPC Class Codes: H01S 3/08004 incorporating a dispersive element, e.g. a prism for wavelength selection H01S3/0811, H01S3/08022 take precedence
• CPC Class Codes: H01S 3/08031 Single-mode emission
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/1066 using a magneto-optical device

Abstract

An external cavity laser system includes an in-line optical filter and a reflection suppressor that efficiently suppresses back-reflected light while allowing light to resonate within the laser cavity. The reflection suppressor may include a polarizer that polarizes light within the cavity and polarization rotators that rotate the polarization state of the polarized light such that back-reflected light is suppressed by the polarizer. Because back-reflected light is suppressed, use of an in-line filter becomes viable in an external cavity laser system.

Claims

1. An external cavity laser system, comprising:

a laser cavity;

a light source that provides light to said laser cavity;

an in-line optical filter, within said laser cavity, which filters said light within said laser cavity; and

a reflection suppressor, within said laser cavity, which suppresses back-reflected light within said laser cavity while allowing light to resonate within said laser cavity.

2. The system of claim 1, wherein said in-line optical filter is tunable to establish an optical frequency for the system.

3. The system of claim 1, wherein said in-line optical filter is a micro-electromechanical (MEM) filter.

4. The system of claim 1, wherein said in-line optical filter is a Fabry-Perot filter.

5. The system of claim 1, wherein said reflection suppressor includes:

a polarizer, within said laser cavity, which polarizes the light within said laser cavity; and

polarization rotators, within said laser cavity, which rotate the polarization state of the light such that said polarizer suppresses back-reflected light.

6. The system of claim 5, wherein said polarizer is a first polarizer for suppressing back-reflected light in a first direction from said in-line optical filter, and further including:

a second polarizer for suppressing light back-reflected in a second direction from said in-line optical filter.

7. The system of claim 5, wherein said polarization rotators include multiple unidirectional polarization rotators.

8. The system of claim 5, wherein said polarization rotators include:

a first polarization rotator that rotates the polarization state of light incident on the first polarization rotator by 45 degrees, wherein light that passes through the polarizer, that is rotated by the first polarization rotator, and that is back-reflected, is rotated again by the first polarization rotator and suppressed by the polarizer.

9. The system of claim 8, wherein said polarization rotators include:

a second polarization rotator that rotates the polarization state of light incident on the second polarization rotator by 45 degrees, wherein light passes through the polarizer, is rotated by the first polarization rotator, is not back-reflected, is rotated by the second polarization rotator, is reflected by a first mirror of the laser cavity back to the second polarization rotator, is rotated by the second polarization rotator, is rotated by the first polarization rotator, passes through the polarizer, and is reflected by a second mirror of the laser cavity, thereby completing a laser cavity round trip.

10. The system of claim 1, wherein said laser cavity includes:

a fixed mirror; and

a theta mirror opposite said fixed mirror such that said light source and said reflection suppressor are between said fixed mirror and said theta mirror, wherein

laser output is through said theta mirror.

11. The system of claim 10, wherein the laser output power and frequency are established by settings of said light source, said in-line optical filter, and said theta mirror.

12. A method for operating an external cavity laser, comprising:

providing light in a laser cavity;

filtering the light; and

suppressing back-reflected light while allowing the filtered light to resonate within the laser cavity.

13. The method of claim 12, further comprising:

polarizing the light; and

rotating the polarization state of the light to a first polarization state.

14. The method of claim 13, wherein said suppressing further comprises:

rotating the polarization state of back-reflected light to a second polarization state; and

suppressing the back-reflected light in response to the polarization state of the back-reflected light.

15. The method of claim 14, further comprising:

filtering the light in-line; and

rotating the polarization state of the filtered light such that it is not suppressed because of the polarization state of the filtered light.

16. The method of claim 14, further comprising:

filtering the light in-line;

rotating the polarization state of the filtered light to a second polarization state;

reflecting the filtered light off of the laser cavity;

rotating the polarization state of the filtered light to a third polarization state;

rotating the polarization state of the filtered light to a fourth polarization state, wherein the fourth polarization state is parallel to the polarization state of light after polarizing but before rotating the polarization state of the light to a first polarization state; and

polarizing the filtered light.

17. The method of claim 13, further comprising:

rotating the polarization state of back-reflected light to a second polarization state, wherein the second polarization is orthogonal to the polarization state of the light after polarizing but before rotating the polarization state of the light to a first polarization state; and

polarizing the back-reflected light, thereby suppressing the back-reflected light

18. An external cavity tunable laser system, comprising:

a laser cavity including a first mirror and a second mirror;

an in-line optical filter, within said laser cavity, for filtering light to set an optical frequency for the system;

an optical amplifier, between said first mirror and said in-line optical filter, which provides light to said in-line optical filter;

a polarizer, between said in-line optical filter and said optical amplifier, for polarizing light with said laser cavity;

a first polarization rotator, between said in-line optical filter and said polarizer, for rotating the polarization state of light;

a second polarization rotator, between said in-line optical filter and said second mirror, for rotating the polarization state of light, wherein back-reflected light is suppressed by the polarizer.

19. The system of claim 18, wherein said in-line optical filter is a Fabry-Perot filter.

20. The system of claim 18, wherein said first unidirectional polarization rotator and said second unidirectional polarization rotator are Faraday rotators that rotate the polarization state of light by 45 degrees.

21. The system of claim 18, wherein said polarizer is aligned to a high gain axis of said optical amplifier.