Fiber laser apparatus and method of detecting failure of fiber laser apparatus

• US 9,985,407 B2
• Filed: 08/18/2016
• Issued: 05/29/2018
• Est. Priority Date: 02/25/2014
• Status: Active Grant

• Current Assignee: Fujikura Limited
• Original Assignee: Fujikura Limited
• Inventors: Matsuoka, Yuji
• Primary Examiner(s): Sohn, Seung C
• Application Number:
  US15/240,442
• Publication Number:
  US 20160359288A1
• Time in Patent Office: 649 Days
• Field of Search: 250553, 372 3809
• CPC Class Codes: G01J 1/4257 applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam monitoring arrangements for lasers in general H01S3/0014
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G02B 6/2804 forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
• CPC Class Codes: G02B 6/4286 Optical modules with optical power monitoring
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/094011 with bidirectional pumping, i.e. with injection of the pump light from both two ends of the fibre
• CPC Class Codes: H01S 3/09408 Pump redundancy
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

To provide a fiber laser apparatus capable of detecting a failure of an optical fiber within a wide range of the apparatus with an inexpensive configuration. The fiber laser apparatus 100 has a plurality of fiber laser units 110, a combiner 120 operable to optically combine output laser beams outputted from the fiber laser unit 110 to generate a combined laser beam, a laser emission portion 130 operable to emit the combined laser beam, output laser beam power detection parts 170 operable to detect a power of an output laser beam of each of the fiber laser units 110, a combined laser beam power detection part 140 operable to detect a power of the combined laser beam, and a failure detection part 160 operable to compare the total of detected powers of the output laser beams (total laser beam power) with the detected power of the combined laser beam and determine that a failure has occurred in the fiber laser unit 110 when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than a predetermined threshold T.

Claims

1. A fiber laser apparatus comprising:

a plurality of fiber laser units each having an amplifying optical fiber operable to amplify a laser beam, a pumping light source operable to supply pumping light to the amplifying optical fiber, and an optical cavity operable to oscillate the laser beam;

a combiner operable to optically combine output laser beams outputted from the plurality of fiber laser units to generate a combined laser beam;

a laser emission portion operable to emit the combined laser beam generated by the combiner;

a plurality of output laser beam power detection parts operable to detect a power of an output laser beam outputted from the optical cavity of each of the plurality of fiber laser units;

a combined laser beam power detection part operable to detect a power of the combined laser beam generated by the combiner; and

a failure detection part including an adder part operable to sum up the powers of the output laser beams detected by the output laser beam power detection parts of the plurality of fiber laser units to calculate a total laser beam power, a comparator part operable to compare the total laser beam power calculated by the adder part with a power of the combined laser beam detected by the combined laser beam power detection part, and a determination part operable to determine that a failure has occurred in at least one of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than a predetermined threshold T.

2. The fiber laser apparatus as recited in claim 1, wherein the predetermined threshold T is set to be (U−

1)/U where U is the number of the plurality of fiber laser units, and

the determination part of the failure detection part determines that a failure has occurred in one of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than the predetermined threshold T.

3. The fiber laser apparatus as recited in claim 1, wherein the predetermined threshold T is set to be (U−

n)/U where U is the number of the plurality of fiber laser units, and n is an integer that is equal to or greater than 1 but equal to or smaller than U, and

the determination part of the failure detection part determines that a failure has occurred in n of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than the predetermined threshold T.

4. The fiber laser apparatus as recited in claim 1, wherein the predetermined threshold T is set so as to meet the following inequality:

5. The fiber laser apparatus as recited in claim 1, wherein the predetermined threshold T is set so as to meet the following inequality:

6. The fiber laser apparatus as recited in claim 1, wherein the failure detection part includes a drive control part operable to control a current to be supplied to pumping light sources of the plurality of fiber laser units so as to operate at least one of the plurality of fiber laser units in sequence, and

the determination part of the failure detection part specifies a fiber laser unit in which the failure has occurred from the at least one of the plurality of fiber laser units that is being driven by the drive control part, based on a difference between the total laser beam power calculated by the adder part and the power of the combined laser beam that is detected by the combined laser beam power detection part.

7. The fiber laser apparatus as recited in claim 1, wherein the combined laser beam power detection part includes a photodetector operable to receive leakage light from a fusion splicing portion provided on an optical fiber connecting between the combiner and the laser emission portion, the photodetector being disposed on a downstream side of the fusion splicing portion.

8. A method of detecting a failure in a fiber laser apparatus operable to emit a combined laser beam into which output laser beams outputted from a plurality of fiber laser units are combined by a combiner, the plurality of fiber laser units each having an amplifying optical fiber operable to amplify a laser beam, a pumping light source operable to supply pumping light to the amplifying optical fiber, and an optical cavity operable to oscillate the laser beam, the method comprising:

detecting a power of the output laser beam outputted from the optical cavity of each of the plurality of fiber laser units;

detecting a power of the combined laser beam on a downstream side of the combiner;

summing up the detected powers of the output laser beams from the plurality of fiber laser units to calculate a total laser beam power;

comparing the total laser beam power with the detected power of the combined laser beam; and

determining that a failure has occurred in at least one of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than a predetermined threshold T.

9. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, further comprising setting the predetermined threshold T to be (U−

1)/U where U is the number of the plurality of fiber laser units,

wherein the determining comprises determining that a failure has occurred in one of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than the predetermined threshold T.

10. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, further comprising setting the predetermined threshold T to be (U−

n)/U where U is the number of the plurality of fiber laser units, and n is an integer that is equal to or greater than 1 but equal to or smaller than U,

wherein the determining comprises determining that a failure has occurred in n of the plurality of fiber laser units when a ratio of the power of the combined laser beam to the total laser beam power becomes lower than the predetermined threshold T.

11. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, further comprising setting the predetermined threshold T so as to meet the following inequality:

12. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, further comprising setting the predetermined threshold T so as to meet the following inequality:

13. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, further comprising:

controlling a current to be supplied to pumping light sources of the plurality of fiber laser units so as to operate at least one of the plurality of fiber laser units in sequence when it is determined that a failure has occurred in at least one of the plurality of fiber laser units; and

specifying a fiber laser unit in which the failure has occurred from the at least one of the plurality of fiber laser units that is being driven, based on a difference between the total laser beam power and the power of the combined laser beam.

14. The method of detecting a failure in a fiber laser apparatus as recited in claim 8, wherein the detecting the power of the combined laser beam comprises receiving leakage light from a fusion splicing portion on a downstream side of the fusion splicing portion, the fusion splicing portion being provided on a downstream side of the combiner.