Figure eight fiber laser for ultrashort pulse generation

• US 20100061407A1
• Filed: 09/05/2008
• Published: 03/11/2010
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: Furukawa Electric Company Limited
• Original Assignee: Furukawa Electric North America Incorporated (Furukawa Electric Company Limited)
• Inventors: Nicholson, Jeffrey W.
• Granted Patent: US 7,940,816 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• 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 3/106 by controlling devices placed within the cavity H01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1061 using a variable absorption device
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1608 erbium

Abstract

A polarization-maintaining figure eight (PMFE) fiber laser is configured to generate ultrashort (femtosecond) output pulses by intentionally inserting asymmetry (in the form of a phase bias) into the bi-directional loop of the fiber laser. The introduction of asymmetry (via an asymmetric coupler, splice, attenuator, fiber bend, multiple amplifying sections, or the like) allows for an accumulation of phase difference within the bi-directional loop sufficient to create modelocking and generate ultrashort output pulses.

Claims

1. A mode-locked, polarization-maintaining figure-eight fiber laser for generating ultrashort optical output pulses, the laser comprising

a bi-directional loop comprising polarization maintaining optical fiber;

a unidirectional loop comprising polarization maintaining fiber;

a first section of a polarization-maintaining amplifying medium inserted along either one of the bi-directional loop and the unidirectional loop, the amplifying medium responsive to an incoming optical pump signal to generate an amplified version of a propagating optical signal;

a polarization maintaining directional coupler disposed between and coupled to both the bi-directional and unidirectional loops of polarization maintaining fibers, the maintained polarization state of the propagating optical signal providing a stable and constant mode-locking state thereof; and

an optical loss element disposed along the bi-directional loop to create an accumulation of a phase difference between the propagating signals sufficient to generate an ultrashort optical output pulse.

2. A fiber laser as defined in claim 1 where the polarization-maintaining amplifying medium comprises a polarization-maintaining fiber amplifier.

3. A fiber laser as defined in claim 2 wherein the polarization-maintaining fiber amplifier comprises an erbium-doped fiber amplifier.

4. A fiber laser as defined in claim 1 wherein the polarization-maintaining amplifying medium comprises a semiconductor optical amplifier.

5. A fiber laser as defined in claim 1 wherein the laser further comprises

an external perturbation source for introducing a perturbation into the propagating optical signal and initiating mode locking.

6. A fiber laser as defined in claim 5 wherein the external perturbation source comprises

a polarization-maintaining modulation element for introducing a modulation perturbation to the propagating optical signal;

and

an external driver coupled to the modulation element for supplying an input modulation signal thereto.

7. A fiber laser as defined in claim 1 wherein the optical loss element comprises a non-symmetric directional coupler disposed between the bi-directional loop and the unidirectional loop.

8. A fiber laser as defined in claim 1 wherein the optical loss element comprises an optical attenuator inserted along the bi-directional loop to provide a sufficient amount of attenuation to create a modelocking condition.

9. A fiber laser as defined in claim 8 wherein the optical attenuator comprises a variable optical attenuator.

10. A fiber laser as defined in claim 1 wherein the optical loss element comprises at least one fiber bending element.

11. A fiber laser as defined in claim 1 wherein the optical loss element comprises at least one fiber splice along or between the bi-directional fiber loop and the unidirectional fiber loop.

12. A fiber laser as defined in claim 1 wherein the optical loss element comprises an output directional coupler inserted along the bi-directional loop.

13. A fiber laser as defined in claim 1 wherein the optical loss element comprises a second section of polarization-maintaining amplifying medium disposed along the fiber laser, where the gains of the first and second sections of polarization-maintaining amplifying medium are adjusted to create a phase difference sufficient to create modelocking and generate ultrashort optical output pulses.

14. A fiber laser as defined in claim 1 wherein the bi-directional loop and the unidirectional loop comprise single mode fiber.

15. A fiber laser as defined in claim 1 wherein the bi-directional loop and the unidirectional loop comprise multimode fiber.