Modular, high energy, widely-tunable ultrafast fiber source

• US 20050163426A1
• Filed: 03/09/2005
• Published: 07/28/2005
• Est. Priority Date: 05/23/2000
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Galvanauskas, Almantas, Harter, Donald J., Fermann, Martin E.
• Granted Patent: US 7,167,300 B2
• Time in Patent Office: Days
• US Class Current: 385/37
• 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. Modularity is ensured by the implementation of interchangeable amplifier components. System compactness is ensured by employing efficient fiber amplifiers, directly or indirectly pumped by diode lasers. Peak power handling capability of the fiber amplifiers is expanded by using optimized pulse shapes, as well as dispersively broadened pulses. Dispersive broadening is introduced by dispersive pulse stretching in the presence of self-phase modulation and gain, resulting in the formation of high-power parabolic pulses. In addition, dispersive broadening is also introduced by simple fiber delay lines or chirped fiber gratings, resulting in a further increase of the energy handling ability of the fiber amplifiers. The phase of the pulses in the dispersive delay line is controlled to quartic order by the use of fibers with varying amounts of waveguide dispersion or by controlling the chirp of the fiber gratings. After amplification, the dispersively stretched pulses can be re-compressed to nearly their bandwidth limit by the implementation of another set of dispersive delay lines. 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. A particularly compact implementation of the whole system uses fiber oscillators in conjunction with fiber amplifiers. Additionally, long, distributed, positive dispersion optical amplifiers are used to improve transmission characteristics of an optical communication system. Finally, 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 counterpropogates within the Raman amplifier fiber with respect to the pump pulses.

Claims

1. A high power nonlinear fiber amplification system comprising:

a seed source producing pulses with a pulse width shorter than 1 ns.

a nonlinear fiber amplifier, said amplifier spectrally broadening said seed pulses in the presence of positive dispersion, gain, and self-phase modulation, to generate substantially linearly chirped pulses with a spectral bandwidth larger than a spectral bandwidth of said seed pulses.

2. A high power nonlinear fiber amplification system according to claim 1, further comprising a pulse stretcher, configured to stretch the pulses provided by the seed source.

3. A high power nonlinear fiber amplification system according to claim 1, wherein the fiber amplifier temporally broadens said seed pulses by means of fiber dispersion.

4. A high power nonlinear fiber amplification system according to claim 1, further comprising a pulse compressor following said nonlinear amplifier.

6. A high power nonlinear fiber amplification system according to claim 1, wherein said seed source comprises a modelocked fiber laser.

8. A high power nonlinear fiber amplification system according to claim 1, wherein said seed source comprises a directly modulated semiconductor laser.

10. A high power nonlinear fiber amplification system according to claim 1, wherein said seed source produces pulses with a pulse width shorter than 20 ps

14. A high power nonlinear fiber amplification system according to claim 1, wherein the nonlinear fiber amplifier generates output pulse energies greater than 1 nJ

17. A high power nonlinear fiber amplification system according to claim 1, wherein said nonlinear amplifier has a nonlinear phase shift>

π

.

18. A high power nonlinear fiber amplification system according to claim 2, wherein said pulse stretcher comprises a holey fiber.

24. A high power nonlinear fiber amplification system according to claim 1, wherein said self-phase modulation in said nonlinear amplifier is used to control the higher-order chirp in said amplified pulses.

5. (canceled)

7. (canceled)

9. (canceled)

11-13. -13. (canceled)

15-16. -16. (canceled)

19-23. -23. (canceled)

25. A nonlinear chirped pulse fiber amplification system comprising:

a seed source producing seed short pulses,

a pulse stretcher,

a nonlinear fiber amplifier, said amplifier inducing a substantial level of self-phase modulation which produces deterministic levels of n-th order dispersion,

and a pulse compressor selected to compensate substantially for said n-th order dispersion.

26. A nonlinear chirped pulse fiber amplification system according to claim 25, wherein n is one of 2, 3 and both of 2 and 3.

27. A nonlinear chirped pulse fiber amplification system according to claim 25, further comprising an amplitude filter inserted before said nonlinear amplifier.

28. 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 Yb;

or Nd;

fiber amplifier for broad bandwidth pulses which inputs and amplifies said pulses, and outputs amplified pulses; and

a pump laser for providing laser energy to said fiber amplifier.

38. A laser system according to claim 28, wherein the seed source comprises a passively modelocked fiber laser.

50. A laser system according to claim 28, further comprising

a pulse stretcher which receives the pulses from said seed source, dispersively stretches said pulses in time, and outputs said stretched pulses to said fiber amplifier.

51. A laser system according to claim 50, further comprising:

a pulse compressor for temporally compressing said amplified pulses;

wherein the dispersion of the pulse compressor is such that the pulse compressor outputs approximately bandwidth-limited pulses.

80. A laser system according to claim 28, wherein the seed source comprises an ND or Yb soliton oscillator comprising a negative dispersion cavity element.

81. A laser system according to claim 80, wherein the negative dispersion cavity element includes a chirped fiber grating.

82. A laser system according to claim 80, wherein the negative dispersion cavity element includes holey fiber.

83. A laser system according to claim 38, wherein the modelocked fiber laser contains polarization maintaining fiber.

29-34. -34. (canceled)

35. A laser system comprising

a pulse source, wherein the pulse source comprises:

a passively modelocked fiber laser; and

a Raman-shifter which inputs the output of said fiber laser;

wherein said Raman shifting fiber is a holey fiber

36. A laser system according to claim 35, wherein the seed source is a passively modelocked fiber laser, and further wherein said Raman shifting fiber is a holey fiber which is used to Raman-shift the frequency-doubled output of the nonlinear crystal from a wavelength range of approximately 750 nm to approximately 1050 nm.

37. A laser system according to claim 35, wherein the seed source is a passively modelocked fiber laser, and further wherein a range of non-amplifying fibers and amplifying fibers with different refractive index profiles and different rare-earth amplifier ions are used to Raman-shift the frequency-doubled output of said nonlinear crystal from the wavelength range of around 750 nm to around 5000 nm.

39-49. -49. (canceled)

52-54. -54. (canceled)

55. 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 pulse stretcher which receives said pulses, dispersively stretches said pulses in time, and outputs said stretched pulses;

a cladding-pumped fiber amplifier, having a gain larger than 10, for broad bandwidth pulses which receives, amplifies and outputs said stretched pulses; and

a pulse compressor which inputs said amplified stretched pulses and temporally compresses them to approximately their bandwidth limit.

58. A laser system according to claim 55, further comprising:

an plurality of additional fiber amplifiers connected between said pulse stretcher and said pulse compressor;

a fiber coupler coupling the seed source to a first one of the plurality of additional fiber amplifiers, said fiber coupler comprising an optical fiber with a length less than 1 km; and

a plurality of pulse picking means located either before the fiber amplifier, after the plurality of additional fiber amplifiers, or in-between any of the amplifiers.

56-57. -57. (canceled)

59-61. -61. (canceled)

62. A pulse source operating at an output wavelength greater than 1.8 microns, comprising:

a seed source outputting short pulse-width pulses; and

a first fiber Raman shifter inputting said pulses, and producing said output wavelength.

63. A pulse source according to claim 62, further comprising:

at least one additional fiber Raman shifter connected to said first fiber Raman shifter; and

a plurality of fiber amplifiers alternately connected between said fiber Raman shifters.

64. A pulse source according to claim 63, further comprising;

a non-linear crystal following the last one of said fiber Raman shifters, wherein the wavelength tuning curve of the nonlinear crystal is selected to be below the center wavelength of the Raman-spectral component of the Raman-shifted and amplified seed pulse.

65. An optical pulse source comprising:

a passively modelocked fiber laser; and

a Yb amplifier for amplifying an output of said fiber laser.

66. A optical pulse source according to claim 65, wherein said passively modelocked fiber laser comprises a Yb fiber laser.

67-69. -69. (canceled)

70. A pulse source comprising:

a fiber laser producing a pulse output;

a Raman-shifter which inputs the pulse output of said fiber laser; and

a nonlinear crystal which frequency-doubles the output of said Raman-shifter.

71. A laser system according to claim 70, wherein said Raman shifting fiber is a holey fiber

72. A seed source as claimed in claim 70, wherein said non-linear crystal comprises a periodically-poled ferroelectric optical material selected from the group consisting of PPLN, PP lithium tantalate, PP MgO:

LiNbO₃, PP KTP, and a periodically poled crystal of the KTP isomorph family.

73-79. -79. (canceled)