Modular, high energy, widely-tunable ultrafast fiber source

• US 20070103765A1
• Filed: 12/22/2006
• Published: 05/10/2007
• Est. Priority Date: 05/23/2000
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Harter, Donald, Galvanauskas, Almantas, Fermann, Martin
• Granted Patent: US 7,688,499 B2
• Time in Patent Office: Days
• US Class Current: 359/337.500
• 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 comprising a solid state laser, 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, wherein said seed source comprises a directly modulated semiconductor laser.

3. A high power nonlinear fiber amplification system according to claim 1, wherein said non-linear fiber amplifier is multi-mode.

4. 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.

5. A laser system according to claim 4, wherein the seed source comprises a passively modelocked fiber laser.

6. A laser system according to claim 5, further comprising a fiber pulse stretcher upstream of said fiber amplifier and having a 2nd order dispersion of a first sign and a 3rd order dispersion of opposite sign.

7. A laser system according to claim 6, further comprising:

a pulse compressor downstream of said fiber amplifier and temporally compressing said amplified pulses;

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

8. A laser system according to claim 7, wherein said pulse compressor comprises a bulk grating pulse compressor having second order dispersion with a sign opposite to the sign of said fiber stretcher, and having non-zero values of third and fourth order dispersion

9. A laser system according to claim 8, wherein said fiber pulse stretcher has third-order dispersion of a sign which partially compensates for third order dispersion of said bulk grating compressor.

10. A laser system according to claim 6, where said pulse stretcher comprises a multi-clad fiber pulse stretcher,

11. A laser system according to claim 10, wherein said multi-clad fiber pulse stretcher has a W refractive index profile.

12. A laser system according to claim 6, wherein said pulse stretcher comprises a holey fiber pulse stretcher,

13. A laser system according to claim 5, further comprising a plurality of fiber pulse stretchers, and a bulk compressor, said stretchers compensating n orders of dispersion of said grating compressor, where 1<

n<

7.

14. An optical pulse source comprising, a seed laser, an Yb fiber amplifier for amplifying said seed laser, and generating output pulses;

an optical fiber configured to receive said output pulses, said optical fiber subjecting said output pulses to large levels of self-phase modulation.

15. An optical pulse source according to claim 14, where said seed laser is a modelocked fiber laser.

16. An optical pulse source according to claim 14, where said seed laser is a modelocked Yb or Nd fiber laser.

17. An optical pulse source comprising,

a fiber seed laser,

a fiber amplifier for amplifying said seed laser, and generating output pulses;

said output pulses being characterized in having a spectral emission in a first spectral window;

an optical fiber configured to receive the output from said source, said optical fiber characterized in having a small core diameter;

said optical fiber generating spectral output at wavelengths in a 2^nd spectral window wavelength-blue-shifted from said first spectral window by as much as 500 nm.

18. An optical system comprising,

a pulse source comprising a fiber seed laser, and a high power Yb fiber amplifier for amplifying said seed laser;

and

an optical fiber configured to have said pulse source at its input, and subjecting said pulse source to large levels of self-phase modulation.

19. An optical system, comprising,

a pulse source comprised of an Yb fiber seed laser operating in the positive dispersion regime, and a high power fiber amplifier for amplifying said seed laser, and

an optical fiber configured to have said pulse source at its input, and subjecting said pulse source to large levels of self-phase modulation.

20. An optical pulse source comprising:

a passively modelocked fiber laser and;

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

21. An optical pulse source according to claim 20, wherein said passively modelocked fiber laser comprises an Yb fiber laser.

22. An optical pulse source according to claim 20, wherein said passively modelocked fiber laser comprises a Nd fiber laser.

23. An optical pulse source according to claim 20, said passively modelocked fiber laser containing a saturable absorber.