Bragg fibers in systems for the generation of high peak power light

• US 20060126679A1
• Filed: 04/22/2005
• Published: 06/15/2006
• Est. Priority Date: 12/13/2004
• Status: Active Grant

• Current Assignee: Rayd LLC
• Original Assignee: Raydiance, Inc. (Coherent Corp.)
• Inventors: Brennan, James F. III, Mielke, Michael, Vaissie, Laurent
• Granted Patent: US 7,349,452 B2
• Time in Patent Office: Days
• US Class Current: 372/30
• CPC Class Codes: G02B 6/02266 Positive dispersion fibres at 1550 nm
• CPC Class Codes: G02B 6/02304 Core having lower refractive index than cladding, e.g. air filled, hollow core
• CPC Class Codes: G02B 6/02357 Property of longitudinal structures or background material varies radially and/or azimuthally in the cladding, e.g. size, spacing, periodicity, shape, refractive index, graded index, quasiperiodic, quasicrystals
• CPC Class Codes: G02B 6/02361 Longitudinal structures forming multiple layers around the core, e.g. arranged in multiple rings with each ring having longitudinal elements at substantially the same radial distance from the core, having rotational symmetry about the fibre axis
• CPC Class Codes: G02B 6/02371 Cross section of longitudinal structures is non-circular
• 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 3/08013 Resonator comprising a fibre, e.g. for modifying dispersion or repetition rate the active medium being a fibre H01S3/067
• CPC Class Codes: H01S 3/235 Regenerative amplifiers

Abstract

The present invention generally concerns the use of Bragg optical fibers in chirped pulse amplification systems for the production of high-pulse-energy ultrashort optical pulses. A gas-core Bragg optical fiber waveguide can be advantageously used in such systems to stretch the duration of pulses so that they can be amplified, and/or Bragg fibers can be used to compress optical signals into much shorter duration pulses after they have been amplified. Bragg fibers can also function as near-zero-dispersion delay lines in amplifier sections.

Claims

1. A method of producing an ultrashort high-energy optical pulse, comprising:

generating a chirped optical signal;

amplifying the chirped optical signal; and

compressing the amplified optical signal to an ultrashort duration optical pulse, wherein at least some of the compression is performed by introducing the optical signal into a Bragg-fiber waveguide, the waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region.

4. The method of claim 1, wherein the step of compressing the amplified optical signal further comprises introducing the optical signal into a Bragg-fiber waveguide having increased dispersion characteristics and an index of refraction in the core of less than 1.4.

2. A method of producing an ultrashort high-energy optical pulse, comprising:

generating an optical signal;

stretching the optical signal by introducing the optical signal into a Bragg-fiber waveguide, the waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region;

amplifying the stretched optical signal; and

compressing the amplified optical signal to an ultrashort duration optical pulse.

5. The method of claim 2, wherein the step of stretching the optical signal further comprises introducing it into a Bragg-fiber waveguide having increased dispersion characteristics and an index of refraction in the core of less than 1.4.

6. The method of claim 2, wherein at least one of the steps of stretching or compressing the optical signal further comprises introducing the optical signal into a diffraction grating.

3. A method of producing a high-energy ultrashort optical pulse, comprising:

generating a chirped optical signal;

amplifying the chirped optical signal; and

compressing the amplified optical signal to an ultrashort optical pulse,

wherein at least one of the steps of generating the chirped optical signal and compressing the optical signal further comprises introducing the optical signal into a Bragg-fiber waveguide, the waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region.

7. The method of claim 3, wherein at least one of the steps of generating the chirped optical signal or compressing the amplified optical signal further comprises introducing the optical signal into a diffraction grating.

8. The method of claim 3, wherein the Bragg-fiber waveguide has a waveguide dispersion at least three times larger than the fiber'"'"'s material dispersion.

9. The method of claim 3, further comprising the step of delivering the ultrashort optical pulse to a work surface through a second Bragg-fiber waveguide.

10. The method of claim 3, wherein a bilayer comprised of two of the plurality of substantially concentric annular regions of distinct refractive indices in the Bragg-fiber waveguide has a different thickness or refractive index from another bilayer comprised of a different two of the plurality of substantially concentric annular regions.

11. The method of claim 3, wherein the Bragg-fiber waveguide is a multi-mode Bragg-fiber waveguide.

12. The method of claim 3, wherein the optical signal is introduced into the Bragg-fiber waveguide from a diffractive element which matches the polarization and spatial profiling of the optical signal to a mode of the Bragg fiber.

13. The method of claim 3, further comprising the step of passing the optical signal through a second Bragg-fiber waveguide having minimal dispersion characteristics such that the optical signal is subjected to a time delay.

14. The method of claim 3, wherein the step of compressing the optical signal to an ultrashort optical pulse further comprises compressing the optical signal to a pulse having a duration of less than 10 picoseconds.

15. The method of claim 12, wherein the diffractive element further comprises a subwavelength diffractive grating.

16. The method of claim 15, wherein the subwavelength-diffractive grating further comprises a subwavelength metal-wire grating.

17. The method of claim 12, wherein the diffractive element converts a linearly polarized beam to a circularly polarized beam.

18. The method of claim 3, wherein the optical signal is introduced into the Bragg-fiber waveguide from an optical element comprising a beam-shaping optical element and a diffractive element which matches the polarization and spatial profiling of the optical signal to a mode of the Bragg fiber.

19. The method of claim 18, wherein the beam-shaping optical element is a refractive lens.

20. The method of claim 18, wherein the beam-shaping optical element is a diffractive lens.

21. The method of claim 18, wherein the beam-shaping optical element is another diffractive element.

22. The method of claim 18, wherein the optical element comprising a beam-shaping optical element and a diffractive element is fabricated on a single substrate.

23. The method of claim 12, wherein the diffractive element is a spatially varying half-wave plate.

24. The method of claim 12, wherein the diffractive element is a spatially varying quarter-wave plate.

25. The method of claim 12, wherein the diffractive element is a spatially varying polarizer.

26. The method of claim 12, wherein the diffractive element is fabricated by etching the structure into a dielectric substrate.

27. The method of claim 12, wherein the diffractive element is fabricated by etching the structure into a semiconductor substrate.

28. The method of claim 27, wherein the diffractive element is etched into a transparent dielectric substrate with an antireflective coating on the substrate'"'"'s backside.

29. The method of claim 27, wherein the diffractive element is etched into a transparent dielectric substrate with an antireflective subwavelength structure on the substrate'"'"'s backside.

30. The method of claim 12, further comprising the step of introducing the output from the Bragg-fiber waveguide into a diffractive element to convert the polarization and spatial profile of the Bragg fiber mode to a different mode.

31. The method of claim 3, wherein the Bragg-fiber waveguide further comprises a bilayer comprised of two materials of distinct refractive indices which is wound around the core such that the bilayer is in a spiral configuration.

32. A method of producing a high-energy ultrashort optical pulse, comprising

generating a chirped optical signal;

amplifying the chirped optical signal; and

compressing the amplified optical signal to an ultrashort optical pulse,

wherein at least one of the steps of generating the chirped optical signal and compressing the optical signal further comprises introducing the optical signal into a Bragg-fiber waveguide, the waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of alternating solid material and gas surrounding the inner core region.

33. A method of producing a high-energy ultrashort optical pulse, comprising

generating a chirped optical signal;

amplifying the chirped optical signal; and

compressing the amplified optical signal to an ultrashort optical pulse,

wherein at least one of the steps of generating the chirped optical signal and compressing the optical signal further comprises introducing the optical signal into a photonic crystal fiber waveguide, the waveguide comprising;

an inner core region in which the optical signal is confined; and

a plurality of substantially concentric annular regions surrounding the inner core region, each comprising a first substantially annular region having holes of a first size surrounded by a second substantially annular region having holes of a second size.

34. A method of delivering an ultrashort optical pulse to a surface, comprising:

generating a chirped optical signal;

amplifying the chirped optical signal;

compressing the optical signal into an ultrashort duration optical pulse; and

delivering the ultrashort optical pulse to a work surface with a Bragg-fiber waveguide, the waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region.

35. A system for ablating material from a surface with an ultrashort pulse having an energy greater than 1 μ

J, comprising;

means for generating an optical signal;

a first fiber waveguide for stretching the optical signal;

means for amplifying the stretched optical signal;

a second fiber waveguide for compressing the amplified optical signal to an untrashort duration optical pulse; and

means for delivering the ultrashort pulse to the surface to be ablated;

wherein at least one of the first and second fiber waveguides comprises an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region.

36. The system of claim 35, wherein the means for delivering the ultrashort pulse to the surface is the second fiber waveguide.

37. The system of claim 35, wherein the means for delivering the ultrashort pulse to the surface is a third fiber waveguide comprising an inner core region in which the optical signal is confined, and a plurality of substantially concentric annular regions of differing refractive indices surrounding the inner core region.

38. The system of claim 35 wherein the second fiber waveguide is a photonic crystal fiber.

39. The system of claim 35 wherein the means for amplifying the stretched optical signal is an Erbium doped fiber waveguide, a co-doped fiber waveguide or a Bragg fiber waveguide.

40. An amplifier for amplifying optical signals, the signals having energy in a band of wavelengths and characterized by a center wavelength, comprising:

An optical cavity;

a gain medium in said resonant cavity characterized by a gain bandwidth that at least partially overlaps the band of wavelengths of the optical signals;

a delay line to circulate the optical signals through the gain medium several times, comprised of a Bragg-fiber waveguide and an optical switch to couple light into and out of the Bragg-fiber waveguide;

an input port for injecting the optical signals into the resonant cavity; and

an output port for extracting the amplified signals from the resonant cavity.