MODULAR, HIGH ENERGY, WIDELY-TUNABLE ULTRAFAST FIBER SOURCE

• US 20140036939A1
• Filed: 08/05/2013
• Published: 02/06/2014
• Est. Priority Date: 05/23/2000
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: FERMANN, Martin E.
• Granted Patent: US 9,819,142 B2
• Time in Patent Office: Days
• US Class Current: 372/18
• 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 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/094019 Side pumped fibre, whereby pump light is coupled laterally into the fibre via an optical component like a prism, or a grating, or via V-groove coupling
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1616 thulium
• CPC Class Codes: H01S 3/1618 ytterbium
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

A modular, compact and widely tunable laser system for the efficient generation of high peak and high average power ultrashort pulses. Peak power handling capability of fiber amplifiers is expanded by using optimized pulse shapes, as well as dispersively broadened pulses. Dispersive pulse stretching in the presence of self-phase modulation and gain results in the formation of high-power parabolic pulses. To ensure a wide tunability of the whole system, Raman-shifting of the compact sources of ultrashort pulses in conjunction with frequency-conversion in nonlinear optical crystals can be implemented, or an Anti-Stokes fiber in conjunction with fiber amplifiers and Raman-shifters are used. Positive dispersion optical amplifiers are used to improve transmission characteristics. An optical communication system utilizes a Raman amplifier fiber pumped by a train of Raman-shifted, wavelength-tunable pump pulses, to thereby amplify an optical signal which counterpropagates within the Raman amplifier fiber with respect to the pump pulses.

Claims

1. A passively modelocked fiber laser, comprising:

a laser cavity comprising at least one Yb or Nd doped gain fiber; and

a pump diode to pump said laser cavity,

wherein said laser cavity is configured for operation in a positive dispersion regime without negative dispersion cavity components.

2. The passively modelocked fiber laser according to claim 1, further comprising a saturable absorber disposed in said laser cavity to initiate mode locking.

3. The passively modelocked fiber laser according to claim 1, wherein said doped gain fiber is a Yb doped gain fiber configured as polarization maintaining fiber.

4. The passively modelocked fiber laser according to claim 1, wherein said cavity comprises a polarizer to select a polarization state.

5. The passively modelocked fiber laser according to claim 1, wherein said pump diode and said Yb or Nd doped gain fiber are arranged for cladding pumping.

6. The passively modelocked fiber laser according to claim 1, wherein said laser cavity comprises an unchirped fiber Bragg grating, and wherein pulses oscillating in said cavity are positively chirped.

7. The passively modelocked fiber laser of claim 1, wherein said cavity is configured such that an oscillation bandwidth of intracavity pulses is small compared to the gain bandwidth of Yb.

8. The passively modelocked fiber laser or claim 1, wherein said cavity comprises a fiber grating arranged as a cavity end mirror, said fiber grating having a reflection bandwidth smaller than a gain bandwidth of said Yb or Nd doped gain fiber.

9. An optical pulse source, comprising:

a passively modelocked fiber laser according to claim 1, and

a Yb amplifier disposed downstream from said passively modelocked fiber laser and configured to amplify an output of said passively mode locked fiber laser.

10. The optical pulse source according to claim 9, wherein said Yb amplifier is configured to generate parabolic pulses.

11. The optical pulse source according to claim 9, further comprising a saturable absorber disposed in said fiber laser cavity to initiate mode locking.

12. A passively mode locked fiber laser, comprising:

a laser cavity comprising at least one Yb or Nd doped gain fiber;

a pump diode to pump said laser cavity; and

a negative dispersion fiber configured to control intra-cavity dispersion inside the cavity.

13. A passively mode locked fiber laser according to claim 12, wherein said negative dispersion fiber comprises holey fiber.

14. A passively mode locked fiber laser according to claim 13, wherein said holey fiber is spliced to at least one fiber component in said cavity.

15. A passively mode locked fiber laser according to claim 12, wherein said cavity comprises a length of polarization maintaining fiber.

16. A passively mode locked fiber laser according to claim 12, further comprising a saturable absorber to initiate modelocking.

17. A passively mode locked fiber laser according to claim 12, further comprising a polarizer.

18. The passively modelocked fiber laser according to claim 12, wherein said pump diode and said Yb or Nd doped gain fiber are arranged for cladding pumping.

19. An optical pulse source, comprising:

a passively modelocked fiber laser according to claim 12, and

a Yb amplifier disposed downstream from said passively modelocked fiber laser and configured to amplify an output of said passively mode locked fiber laser.

20. A laser system producing output in the 3-5 μ

m wavelength region, comprising;

a femtosecond pulse source;

a fiber having an infrared absorption edge longer than that of silica.

21. A tunable laser system producing wavelength tunable pulses, comprising:

a seed module producing femtosecond pulses in the spectral range from about 1.5-2.2 μ

m; and

an infrared transmitting fiber having an infrared absorption edge longer than that of silica, said infrared transmitting fiber capable of frequency shifting pulses produced with said seed module to longer wavelengths, up to the spectral range from about 3-5 μ

m.

22. A laser system comprising:

a fiber laser source generating pulses in the 1-1.15 um wavelength region which have a spectral bandwidth larger than 0.3 nm and a pulse width between 50 fs and 1 ns, said laser system comprising;

a frequency-shifting fiber which outputs an anti-Stokes, blue-shifted output.

23. An optical pulse source comprising:

a diode-pumped passively modelocked fiber laser including a saturable absorber and capable of generating femtosecond pulses in the 1-1.15 μ

m wavelength region;

a Yb;

fiber amplifier for amplifying an output of said fiber laser; and

an optical modulator disposed between said passively modelocked fiber laser and said Yb;

amplifier, said modulator being controllable to reduce the repetition rate of pulses emitted from said modelocked fiber laser, to increase the available pulse energy of pulses amplified with said Yb;

amplifier, and to provide for selection of pulses for amplification with said Yb;

amplifier.

24. A fiber-based chirped pulse amplification system comprising:

the optical pulse source according to claim 23; and

a combination of a pulse stretcher and pulse compressor optically coupled to said optical pulse source.

25. A laser system comprising:

a seed source generating pulses in the 1-1.15 μ

m wavelength region which have a spectral bandwidth larger than 0.3 nm and a pulse width between approximately 50 fs and 1 ns;

a cladding-pumped fiber amplifier for broad bandwidth pulses which receives, amplifies and outputs said pulses, wherein the fiber amplifier is operated with at least one forward and one backward pass; and

a pump laser for providing laser energy to said fiber amplifier, and

an optical modulator located between the one forward and one backward pass of said amplifier.

26. A laser system according to claim 25, further comprising:

a plurality of additional fiber amplifiers, wherein at least one of the fiber amplifier and the plurality of additional fiber amplifiers is operated with at least one forward and one backward pass.

27. A laser system according to claim 26, further comprising at least one pulse picker located between the at least one forward and one backward pass.

28. A laser system according to claim 25, wherein the seed source produces pulses which induce the formation of parabolic pulses within said fiber amplifier.

29. A laser system according to claim 25, further comprising:

a coupler between the seed source and the fiber amplifier, which couples the seed source to the fiber amplifier, and which further comprises an optical fiber with a length less than 1 km.

30. A laser system according to claim 25, further comprising:

an optical delivery fiber coupled to the output of the fiber amplifier.

31. A laser system according to claim 30, wherein said optical delivery fiber is selected from the group consisting of:

a holey fiber, a length of few-moded fiber and a length of few-moded fiber spliced together with one or two lengths of single-mode fiber.