High power short pulse fiber laser

• US 9,071,037 B2
• Filed: 08/28/2013
• Issued: 06/30/2015
• 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:
  US14/012,508
• Publication Number:
  US 20150085885A1
• Time in Patent Office: 671 Days
• Field of Search: 372/6, 372/11, 372/26, 372/30
• US Class Current: 1/1
• 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 amplification system comprising:

a passively modelocked fiber oscillator outputting optical pulses, said passively modelocked fiber oscillator comprising a saturable absorber disposed in a temperature-controlled saturable absorber module and an oscillator pump that optically pumps said passively modelocked fiber oscillator, wherein said saturable absorber exhibits a multi-temporal lifetime and is configured in such a way 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 modelocked fiber oscillator;

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

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

an optical pump source optically connected to said fiber amplifier;

a pulse compressor optically coupled to receive said amplified optical pulses output from fiber amplifier via a second optical path; and

(i) a first optical tap in said first optical path between said modelocked fiber oscillator and said fiber amplifier, and

a first feedback loop from said first tap to control said modelocked fiber oscillator based on measurement of output from said first optical tap, said first feedback loop from said first tap controlling at least said oscillator pump, and

(ii) a second optical tap in said second optical path between said fiber amplifier and said compressor, and

a second feedback loop from said second tap to control said fiber amplifier based on measurement of output from said second optical tap.

2. The pulsed fiber laser amplification system of claim 1, further comprising a variable optical attenuator in the first optical path between said modelocked fiber oscillator and said fiber amplifier, said variable optical attenuator having an adjustable transmission such that optical energy coupled from the modelocked fiber oscillator to the fiber amplifier is reduced.

3. The pulsed fiber laser amplification system of claim 2, wherein said variable optical attenuator comprises a polarization selective optical component and provides an adjustable transmission such that an amplitude of said optical pulses that are coupled from said mode-locked fiber oscillator to said amplifier can be reduced.

4. The pulsed fiber laser amplification system of claim 1, further comprising a first isolator in said first optical path from said oscillator to said fiber amplifier, said first isolator comprising said first tap.

5. The pulsed fiber laser amplification system of claim 1, further comprising a second isolator in said second optical path from said fiber amplifier to said compressor, said second isolator containing said second tap.

6. The pulsed fiber laser amplification system of claim 1, further comprising a temperature controller in thermal contact with said modelocked fiber oscillator to adjust operation of said modelocked fiber oscillator, said first feedback loop from said first tap controlling said temperature controller.

7. The pulsed fiber laser amplification system of claim 1, further comprising a temperature controller in thermal contact with said fiber amplifier to adjust operation of said fiber amplifier, said second feedback loop from said second tap controlling said temperature controller.

8. The pulsed fiber laser amplification system of claim 1, wherein said second feedback loop from said second tap controls said optical pump source.

9. The pulsed fiber laser amplification system of claim 1, wherein said saturable absorber module comprises a polarizing optical component.

10. The pulsed fiber laser amplification system of claim 9, wherein said polarizing optical component comprises at least one of a polarization beamsplitter, a variable waveplate, a polarization maintaining fiber, and a rotatable optical fiber.

11. The pulsed fiber laser amplification system of claim 9, wherein a polarization extinction ratio of the saturable absorber module is above about 23 dB.

12. The pulsed fiber laser amplification system of claim 1, wherein said modelocked fiber oscillator comprises a cavity fiber assembly module optically coupled to said saturable absorber module.

13. The pulsed fiber laser amplification system of claim 12, wherein said cavity fiber assembly module is optically coupled to said saturable absorber module by an optical fiber pigtail.

14. The pulsed fiber laser amplification system of claim 13, wherein the modelocked fiber oscillator comprises a resonant cavity, and a length of said optical fiber pigtail can be varied to contribute to a desired group delay dispersion of the cavity.

15. The pulsed fiber laser amplification system of claim 12, wherein said cavity fiber assembly module is coupled to a temperature control component configured to adjust the temperature of a gain fiber in the cavity fiber assembly module to stabilize gain and reduce noise.

16. The pulsed fiber laser amplification system of claim 1, wherein said saturable absorber exhibits a multi-temporal lifetime with a response time of less than about 20 ps and a recovery time of greater than about 50 ps.

17. The pulsed fiber laser amplification system of claim 16, wherein said recovery time is greater than about 100 ps.

18. The pulsed fiber laser amplification system of claim 16, wherein said response time is less than about 5 ps.

19. The pulsed fiber laser amplification system of claim 1, 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.

20. The pulsed fiber laser amplification system of claim 1, wherein said passively modelocked fiber oscillator comprises a Yb-doped gain fiber.

21. The pulsed fiber laser amplification system of claim 1, wherein said passively modelocked fiber oscillator comprises Yb-doped polarization maintaining fiber.

22. The pulsed fiber laser amplification system of claim 1, wherein said fiber Bragg grating is configured as an output mirror of said passively modelocked fiber oscillator.

23. The pulsed fiber laser amplification system of claim 1, wherein said fiber Bragg grating is arranged such that the total intra-cavity dispersion is negative.

24. The pulsed fiber laser amplification system of claim 1, wherein said passively modelocked fiber oscillator comprises Yb-doped polarization maintaining fiber.

25. The pulsed fiber laser amplification system of claim 1, 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, said semiconductor material having an ion implantation depth profile selected to provide saturable absorption having a multi-temporal carrier relaxation.

26. The pulsed fiber laser amplification system of claim 1, further comprising:

a pulse stretcher disposed upstream from said fiber amplifier,

wherein said fiber amplifier is configured such that attenuating an amplitude of the optical pulses coupled from said mode-locked fiber oscillator to said amplifier reduces a pulse width at an output of said compressor.

27. The pulsed fiber laser amplification system of claim 1, further comprising:

a spectral filter disposed external to the modelocked fiber oscillator and between said oscillator and said amplifier, said spectral filter configured to receive said optical output of said modelocked fiber oscillator prior to reaching said amplifier, said spectral filter having a spectral transmission with a band edge that overlaps said spectral power distribution of said optical output of said modelocked fiber oscillator to attenuate a portion of said spectral power distribution and thereby reduce the spectral bandwidth, the pulse width of said optical pulses coupled from said modelocked fiber oscillator to said amplifier thereby being reduced, wherein said spectral filter reduces the spectral bandwidth to less than about 12 nanometers.

28. The pulsed fiber amplification system of claim 27, wherein said spectral filter comprises a fiber Bragg grating.

29. The pulsed fiber amplification system of claim 27, wherein said spectral filter has a spectral bandwidth of between about 5 and 12 nm.

30. The pulsed fiber laser amplification system of claim of claim 1, wherein compressed high-power short laser pulses at an output of said pulse compressor comprise an optical power of at least about 200 mW and a pulse duration of about 200 femtoseconds or less.

31. The pulsed fiber laser amplification system of claim 1, further comprising a pre-compressor in the first optical path between said modelocked fiber oscillator and said fiber amplifier.

32. The pulsed fiber laser amplification system of claim 31, wherein said pre-compressor comprises a spectral filter or a dispersive optical element.