OPTICAL FIBER LASERS

• US 20140023098A1
• Filed: 05/13/2011
• Published: 01/23/2014
• Est. Priority Date: 01/24/2011
• Status: Active Grant

• Current Assignee: University of Southampton
• Original Assignee: University of Southampton
• Inventors: Clarkson, William, Cieslak, Rafal
• Granted Patent: US 9,627,839 B2
• Time in Patent Office: Days
• US Class Current: 372/3
• CPC Class Codes: G02F 1/3542 Multipass arrangements, i.e. arrangements to make light pass multiple times through the same element, e.g. using an enhancement cavity
• CPC Class Codes: H01S 3/0604 in the form of a plate or disc
• 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 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/07 consisting of a plurality of parts, e.g. segments H01S3/067 takes precedence
• CPC Class Codes: H01S 3/08 Construction or shape of optical resonators or components thereof
• CPC Class Codes: H01S 3/08022 Longitudinal modes mode suppression using a plurality of resonators H01S3/082
• CPC Class Codes: H01S 3/0826 using a diffraction grating
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/094084 with pump light recycling, i.e. with reinjection of the unused pump light, e.g. by reflectors or circulators
• CPC Class Codes: H01S 3/1083 using parametric generation
• CPC Class Codes: H01S 3/1086 using scattering effects, e.g. Raman or Brillouin effect
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation

Abstract

A fiber gain medium provided by a rare-earth doped fiber (10) is contained in a first resonant cavity by end reflectors (12, 18). The reflector (12) is wavelength selective to limit the frequency band of the first resonant cavity. The first resonant cavity also contains a second resonant enhancement cavity (16) with multiple transmission bands lying within the first resonant cavity'"'"'s frequency band. Multiple standing wave modes of the first resonant cavity lie within both the frequency band of the first resonant cavity and the transmission bands of the second resonant cavity, and it is these standing wave modes that support laser action when the rare-earth doped fiber is suitably pumped by pump lasers (40).

Claims

1. A device comprising:

a portion of optical fiber providing an amplifying medium;

a first resonant cavity containing the portion of optical fiber and having a frequency selective element which limits the frequency band of the first resonant cavity to cover a subset of standing wave modes of the first resonant cavity;

a second resonant cavity arranged in the first resonant cavity and having a transmission response that includes a plurality of transmission bands within the frequency band of the first resonant cavity, so that there are a plurality of standing wave modes which lie within both the frequency band of the first resonant cavity and at least two of the transmission bands of the second resonant cavity; and

a pump source having an output directed to excite optical emission within the first frequency band from the amplifying medium and induce lasing at multiple ones of said plurality of standing wave modes that lie within both the frequency band of the first resonant cavity and the transmission bands of the second resonant cavity.

2. A device according to claim 1, wherein the first resonant cavity is a linear cavity bounded by a first reflector and a second reflector.

3. A device according to claim 1, wherein the first resonant cavity is a ring cavity.

4. A device according to claim 2, wherein the frequency selective element comprises a grating.

5. A device according to claim 2, wherein the frequency selective element comprises a filter.

6. A device according to claim 1, wherein the optical fiber is single mode.

7. A device according to claim 1, wherein the optical fiber is multi-mode comprising a fundamental mode and at least one higher order mode.

8. A device according to claim 7, wherein the first resonant cavity is a linear cavity bounded by a first reflector and a second reflector, the first reflector being a fiber Bragg grating written into the optical fiber and having a mode-dependent effective period, and the second reflector being a volume Bragg grating having a period matched to the effective period of the fiber Bragg grating for the fundamental mode so that lasing is restricted to the fundamental mode.

9. A device according to claim 7, wherein the multi-mode output of the optical fiber at the end optically adjacent to the second resonant cavity is spatially matched to the fundamental transverse mode TEM₀₀ of the second resonant cavity so that the first resonant cavity is resonant for multi-mode amplification in the optical fiber.

10. A device according to claim 1, wherein the second resonant cavity has arranged therein a non-linear optical medium which supports a frequency mixing process in the second resonant cavity.

11. A device according to claim 1, wherein the second resonant cavity has arranged therein a laser medium having the property of absorbing light in the frequency band of the first resonant cavity, wherein, for light in the frequency band of the first resonant cavity, the round trip loss in the second resonant cavity—

including absorption by the laser medium—

is matched to the proportion of light coupled into the second resonant cavity.

12. A device according to claim 1, wherein each transmission band of the second resonant cavity has a width greater than the separation between the standing wave modes of the first resonant cavity.

13. A device according to claim 1, wherein the optical fiber is doped with active laser ions, thereby to provide the amplifying medium.

14. A device according to claim 1, wherein the optical fiber has a vibrational mode with a Stokes energy bridging the energy difference between the pump frequency band and the first frequency band, so that stimulated Raman scattering generates gain in the first frequency band, thereby to provide the amplifying medium.

15. A device according to claim 14, comprising a further pump source which acts as a pump for said pump source.