High power short pulse fiber laser

• US 9,640,940 B2
• Filed: 04/13/2015
• Issued: 05/02/2017
• Est. Priority Date: 03/31/2004
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Gu, Xinhua, Bendett, Mark, Cho, Gyu Cheon, Fermann, Martin E.
• Primary Examiner(s): VAN ROY, TOD THOMAS
• Application Number:
  US14/685,320
• Publication Number:
  US 20150325977A1
• Time in Patent Office: 750 Days
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108
• CPC Class Codes: H01S 3/0064 Anti-reflection devices, e.g. optical isolaters absorbing layers for marking or protecting purposes in laser working B23K26/50; magneto-optical non-reciprocal devices G02F1/093, G02F1/0955
• CPC Class Codes: H01S 3/0078 Frequency filtering
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06741 Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/0941 of a laser diode
• CPC Class Codes: H01S 3/1028 by controlling the temperature
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1305 Feedback control systems
• CPC Class Codes: H01S 3/1618 ytterbium
• CPC Class Codes: H01S 3/1698 rare earth

Abstract

A pulsed laser comprises an oscillator and amplifier. An attenuator and/or pre-compressor may be disposed between the oscillator and amplifier to improve performance and possibly the quality of pulses output from the laser. Such pre-compression may be implemented with spectral filters and/or dispersive elements between the oscillator and amplifier. The pulsed laser may have a modular design comprising modular devices that may have Telcordia-graded quality and reliability. Fiber pigtails extending from the device modules can be spliced together to form laser system. In one embodiment, a laser system operating at approximately 1050 nm comprises an oscillator having a spectral bandwidth of approximately 19 nm. This oscillator signal can be manipulated to generate a pulse having a width below approximately 90 fs. A modelocked linear fiber laser cavity with enhanced pulse-width control includes concatenated sections of both polarization-maintaining and non-polarization-maintaining fibers. Apodized fiber Bragg gratings and integrated fiber polarizers are included in the cavity to assist in linearly polarizing the output of the cavity. Very short pulses with a large optical bandwidth are obtained by matching the dispersion value of the fiber Bragg grating to the inverse of the dispersion of the intra-cavity fiber.

Claims

1. A pulsed fiber laser comprising:

a modelocked fiber oscillator comprising a gain fiber and a pair of reflective optical elements disposed with respect to said gain fiber to form a resonant cavity, said modelocked fiber oscillator comprising a semiconductor saturable absorber (SAM) optically connected and in close contact with an end of said gain fiber and operably arranged to induce modelocking, said modelocked fiber oscillator producing a train of optical pulses having an average pulse width, said modelocked fiber oscillator comprising a wedge-shaped area between said SAM and said end of said gain fiber, wherein said wedge-shaped area is operably arranged to limit the finesse of an etalon formed with surfaces of said SAM and said gain fiber;

a fiber amplifier optically connected to said modelocked fiber oscillator such that said optical pulses can propagate through said amplifier, said fiber amplifier amplifying said optical pulses; and

one or more optical pump sources optically connected to said modelocked fiber oscillator and said fiber amplifier to pump said fiber oscillator and fiber amplifier.

2. The pulsed fiber laser of claim 1, further comprising a pulse compressor optically coupled to receive said amplified optical pulses output from said fiber amplifier, said pulse compressor shortening the pulse width of said optical pulses output by said fiber amplifier.

3. The pulsed fiber laser of claim 2, further comprising a pre-compressor disposed in an optical path between said modelocked fiber oscillator and said fiber amplifier, said pre-compressor shortening the duration of said optical pulses introduced into said fiber amplifier such that said pulse duration of said optical pulses output by said fiber amplifier can be further shortened by said pulse compressor.

4. The pulsed fiber laser of claim 3, wherein said pre-compressor comprises a photonic crystal fiber, a photonic bandgap fiber, or a holey fiber.

5. The pulsed fiber laser of claim 3, wherein said pre-compressor is operably arranged to reduce a spectral bandwidth of said optical pulses.

6. The pulsed fiber laser of claim 3, wherein said pre-compressor comprises a dispersive optical element to differentiate between spectral components and to introduce different phase shifts to said different spectral components.

7. The pulsed fiber laser of claim 1, wherein said gain fiber comprises an angle polished core portion disposed in an angled polished housing.

8. The pulsed fiber laser of claim 7, wherein said angle polished housing is attached to said SAM.

9. The pulsed fiber laser of claim 1, wherein said gain fiber comprises a core with an expanded portion proximate to said SAM.

10. A Yb-based pulsed fiber laser amplification system comprising:

a Yb passively modelocked fiber oscillator configured to output optical pulses, said Yb passively modelocked fiber oscillator comprising a saturable absorber, and an oscillator pump configured to optically pump said Yb passively modelocked fiber oscillator, wherein said saturable absorber exhibits a multi-temporal lifetime and is configured such that Q-switched mode-locking evolves at a low oscillator pump power followed by cw mode locking at a higher operational pump power that exceeds a threshold pump power for operation of said mode locked laser;

a fiber Bragg grating configured to control intra-cavity dispersion and configured as a mirror of said Yb passively modelocked fiber oscillator;

a fiber amplifier optically connected to said modelocked fiber oscillator via a first optical path, said fiber amplifier configured to amplify said optical pulses; and

an optical pump source optically connected to said fiber amplifier.

11. The Yb-based pulsed fiber laser amplification system of claim 10, wherein said fiber Bragg grating is further configured as an output mirror of said passively modelocked fiber oscillator.

12. The Yb-based pulsed fiber laser amplification system of claim 10, wherein said saturable absorber comprises multiple quantum wells or bulk semiconductor films, and wherein said saturable absorber is configured with non-uniform ion-implantation which, in combination with one or more implantation parameters, achieves said multi-temporal lifetime in the presence of optical excitation with short optical pulses.

13. The Yb-based pulsed fiber laser amplification system of claim 10, further comprising an optical tap arranged to receive a portion of an output from said modelocked fiber oscillator.

14. The Yb-based pulsed fiber laser amplification system of claim 10, further comprising an optical tap arranged to receive a portion of an output from said fiber amplifier.

15. The Yb-based pulsed fiber laser amplification system of claim 10, wherein said saturable absorber comprises:

a film of a semiconductor material implanted with high energy ions at a penetration depth which differs from the penetration depth of optical signals reflected from said saturable absorber mirror, said semiconductor material having an ion implantation depth profile selected to provide saturable absorption having a multi-temporal carrier relaxation.

16. The Yb-based pulsed fiber laser amplification system of claim 10, wherein said saturable absorber is configured with depth selective ion implantation.

17. The Yb-based pulsed fiber laser amplification system of claim 10, wherein said Yb passively modelocked fiber oscillator comprises a gain fiber, wherein an end of said gain fiber is in close contact with said saturable absorber.

18. The Yb-based pulsed fiber laser amplification system of claim 17, wherein the end of said gain fiber is butt-coupled to said saturable absorber.

19. The Yb-based pulsed fiber laser amplification system of claim 17, wherein the end of said gain fiber is disposed in a housing that is attached to said saturable absorber.

20. The Yb-based pulsed fiber laser amplification system of claim 17, wherein the end of the gain fiber and the housing are angle-polished.

21. A pulsed fiber laser comprising:

a modelocked fiber oscillator comprising a gain fiber and a pair of reflective optical elements disposed with respect to said gain fiber to form a resonant cavity, said modelocked fiber oscillator comprising a semiconductor saturable absorber (SAM) optically connected to said gain fiber and arranged such that said modelocked fiber oscillator comprises a wedge-shaped area between said SAM and said gain fiber, wherein said wedge-shaped area is operably arranged to limit the finesse of an etalon formed with surfaces of said SAM and said fiber, said modelocked fiber oscillator producing a train of optical pulses having an average pulse width;

a fiber amplifier optically connected to said modelocked fiber oscillator such that said optical pulses can propagate through said amplifier, said fiber amplifier amplifying said optical pulses; and

one or more optical pump sources optically connected to said modelocked fiber oscillator and said fiber amplifier to pump said fiber oscillator and fiber amplifier.

22. The pulsed fiber laser of claim 21, wherein said gain fiber comprises an angle-polished portion disposed in an angle-polished housing.

23. The pulsed fiber laser of claim 22, wherein said angle-polished housing is attached to said SAM.