Method and apparatus for controlling wavelength and dominant mode in fiber lasers

• US 20040175081A1
• Filed: 03/06/2003
• Published: 09/09/2004
• Est. Priority Date: 03/06/2003
• Status: Active Grant

• Current Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Original Assignee: Evans & Sutherland Computer Corp. (Elevate Entertainment, Inc.)
• Inventors: Elkins, Dennis, Grapov, Yuri, Owen, David, Tanner, Allen, DeWitte, Jeannie, McAllister, Aaron
• Granted Patent: US 6,868,212 B2
• Time in Patent Office: Days
• US Class Current: 385/123
• CPC Class Codes: G02B 6/022 using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper G02B6/02204 takes precedence; optical modulation using photo-elastic effect G02F1/0131
• CPC Class Codes: H01S 3/06704 Housings; Packages
• CPC Class Codes: H01S 3/102 by controlling the active medium, e.g. by controlling the processes or apparatus for excitation H01S3/13 takes precedence

Abstract

A method for adjusting the wavelength and dominant mode of a laser fiber prior to installation in a laser assembly includes the steps of linearly stretching the laser fiber so as to modify its output wavelength, axially twisting the laser fiber so as to modify its dominant mode, and affixing the laser fiber to a laser assembly in its linearly stretched and axially twisted condition. The laser assembly includes a dynamic tuning mechanism for wavelength adjustment during use. The twisted and stretched fiber has an unadjusted wavelength and dominant mode that are within a selected range before adjustment by the dynamic tuning mechanism.

Claims

1. A method for adjusting output characteristics of a laser fiber prior to installation in a laser assembly, comprising the steps of:

a) linearly stretching the laser fiber;

b) axially twisting the laser fiber; and

c) affixing the laser fiber to a laser assembly in its linearly stretched and axially twisted condition.

2. A method in accordance with claim 1, further comprising the step of monitoring the output of the laser fiber while being linearly stretched.

3. A method in accordance with claim 2, wherein the step of monitoring the output of the laser fiber more specifically comprises the steps of:

d) operatively coupling a laser driving device to a first end of the laser fiber, so as to activate the laser fiber; and

e) operatively coupling a wavelength meter to a second end of the laser fiber, so as to monitor the output wavelength of the laser fiber while being linearly stretched.

4. A method in accordance with claim 1, wherein the output characteristics include wavelength and dominant mode.

5. A method in accordance with claim 1, wherein the steps of linearly stretching the fiber and axially stretching the fiber are performed substantially simultaneously.

6. A method in accordance with claim 1, wherein the steps of linearly stretching and axially twisting the fiber further comprise the steps of:

a) affixing a first end of the fiber to a base;

b) affixing a second end of the fiber to a rotatable device;

c) rotating the rotatable device to axially twist the fiber; and

d) causing a distance between the base and the rotatable device to increase, so as to linearly stretch the fiber.

7. A method in accordance with claim 6, wherein the rotatable device comprises a gear assembly, the laser fiber being affixed to an axle thereof.

8. A method in accordance with claim 7, wherein the step of rotating the rotatable device comprises manually rotating a gear assembly knob configured to rotate gears of the gear assembly.

9. A method in accordance with claim 8, wherein the gear assembly comprises a reduction gear assembly, such that rotation of the gear assembly knob a full turn causes less than ¼

turn of the axle.

10. A method in accordance with claim 6, wherein the step of causing a distance between the base and the rotatable device to increase more specifically comprises adjusting a wedge device to move the base linearly away from the rotatable device.

11. A method in accordance with claim 10, wherein the step of adjusting the wedge device more specifically comprises manually rotating a micrometer drive, such that highly accurate small adjustments may be made in the distance between the base and the rotatable device.

12. A method in accordance with claim 1, wherein the step of linearly stretching the fiber more specifically comprises stretching the fiber within a range of from about 0 to about 500 μ

m, and the step of axially twisting the fiber more specifically comprises twisting the fiber within a range of from about −

360°

to about +360°

.

13. A method of tuning an output wavelength and dominant mode of a fiber laser disposed in a laser assembly comprising a substrate and a dynamic tuning assembly, the method comprising the steps of:

a) rough-tuning the laser to an approximate target wavelength and isolating a dominant mode during manufacture, by the steps of;

a. linearly stretching the laser fiber so as to modify an output wavelength;

b. axially twisting the laser fiber so as to isolate the dominant mode of oscillation;

c. monitoring the output wavelength and dominant mode of the fiber laser during stretching and twisting until the desired characteristics of wavelength and dominant mode are reached; and

d. connecting the laser fiber to the laser assembly in its linearly stretched and axially twisted condition; and

b) fine-tuning the laser to a substantially exact wavelength during normal operation, by manipulating the dynamic tuning assembly to modify a length of the laser fiber.

14. A system for tuning the output wavelength and dominant mode of a fiber laser, comprising:

a) a moveable bed, configured to receive an elongate fiber laser assembly having a first end and a second end, and a laser fiber secured to the first end thereof, the laser fiber having a long axis;

b) an axle, having an axis of rotation, configured to securely hold a second end of the laser fiber substantially collinearly with the axis of rotation and beyond the second end of the fiber laser assembly; and

c) an adjustment mechanism, configured to (i) move the bed linearly away from the rotatable axle, so as to linearly stretch the laser fiber between the axle and the secured first end of the fiber, and (ii) rotate the axle to twist the laser fiber along its long axis, so as to allow rough adjustment of an output wavelength and dominant mode of the laser fiber prior to permanently affixing the laser fiber to the second end of the fiber laser assembly.

15. A system in accordance with claim 14, wherein the adjustment mechanism further comprises:

a) a wedge assembly, configured to push the bed away from the rotatable axle; and

b) a reduction gear assembly, configured for rotating the axle.

16. A system in accordance with claim 15, further comprising a base having a linear track, the bed being slidably disposed on the track, and the wedge assembly and reduction gear assembly being disposed on the base.

17. A system in accordance with claim 15, further comprising a fiber aperture extending through the axle substantially collinearly with the axis of rotation, and configured to allow the laser fiber to extend therethrough.

18. A system in accordance with claim 17, further comprising:

a) a first fiber slot, disposed in the gear assembly; and

b) a second fiber slot extending from a side of the axle to the fiber aperture, the second fiber slot being alignable with the first fiber slot, such that the laser fiber may be laterally inserted through the gear assembly and the axle to a position within the fiber aperture.

19. A system in accordance with claim 15, further comprising:

a) a micrometer drive, associated with the wedge assembly, configured for accurately adjusting the distance between the axle and the bed; and

b) a gear assembly knob, configured for actuating the reduction gear assembly.

20. A system in accordance with claim 19, wherein the micrometer drive and the gear assembly knob are manually actuable.

21. A system in accordance with claim 14, wherein the adjustment mechanism is configured to linearly stretch the fiber within a range of from about 0 to about 500 μ

m, and to axially twist the fiber within a range of from about −

360°

to about +360°

.

22. A system in accordance with claim 14, further comprising:

a) a laser driving device operatively coupled to a first end of the laser fiber, so as to activate the laser fiber; and

b) a wavelength meter operatively coupled to a second end of the laser fiber, so as to monitor the output wavelength of the laser fiber while being axially stretched.

23. A fiber laser for emitting a laser beam, comprising:

a) a substrate;

b) a laser fiber, coupled to the substrate, having a length, an unadjusted output wavelength and dominant mode, and an adjusted output wavelength;

c) a dynamic tuning mechanism associated with the substrate, configured to modify the adjusted output wavelength of the laser fiber by adjusting the length of the fiber, the laser fiber being coupled to the substrate in a linearly stretched and axially twisted condition, such that the unadjusted wavelength and dominant mode are within a selected range before adjustment by the dynamic tuning mechanism.