An Optical System For Providing Short Laser-Pulses

• US 20060209908A1
• Filed: 03/23/2006
• Published: 09/21/2006
• Est. Priority Date: 10/24/2003
• Status: Active Grant

• Current Assignee: NKT Photonics A/S (NKT A/S)
• Original Assignee: Crystal Fibre A/S (NKT A/S), NKT Research & Innovation A/S
• Inventors: Pedersen, Claus Friis, Skovgaard, Peter M.W.
• Granted Patent: US 7,813,387 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: G02B 6/02214 tailored to obtain the desired dispersion, e.g. dispersion shifted, dispersion flattened
• CPC Class Codes: G02B 6/02261 Dispersion compensating fibres, i.e. for compensating positive dispersion of other fibres
• CPC Class Codes: G02B 6/02328 Hollow or gas filled core
• CPC Class Codes: G02B 6/02333 Core having higher refractive index than cladding, e.g. solid core, effective index guiding
• CPC Class Codes: G02B 6/02347 Longitudinal structures arranged to form a regular periodic lattice, e.g. triangular, square, honeycomb unit cell repeated throughout cladding
• CPC Class Codes: G02B 6/2552 reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
• 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 3/06725 Fibre characterized by a specific dispersion, e.g. for pulse shaping in soliton lasers or for dispersion compensating [DCF]
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06741 Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• CPC Class Codes: H01S 3/06745 Tapering of the fibre, core or active region
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/08009 using a diffraction grating
• CPC Class Codes: H01S 3/08059 Constructional details of the reflector, e.g. shape mirrors in general G02B5/08; mountings for mirrors G02B7/18
• CPC Class Codes: H01S 3/094076 Pulsed or modulated pumping H01S3/1024 takes precedence
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/1063 using a solid state device provided with at least one potential jump barrier
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/1118 Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
• CPC Class Codes: H01S 3/115 : using intracavity electro-optic devices
• CPC Class Codes: H01S 3/1611 : neodymium
• CPC Class Codes: H01S 3/1618 : ytterbium
• CPC Class Codes: H01S 3/1695 : germanium
• CPC Class Codes: H01S 3/2308 : Amplifier arrangements, e.g. MOPA

Abstract

The present invention deals with optical systems for providing short laser pulses. An object of the invention is to provide an optical system providing compact and cost-effective short laser-pulses using fibers with anomalous dispersion and high non-linear thresholds. The object is achieved by a short pulse optical system for generating or processing short laser-pulses, said optical system comprises an optical fiber in the form of a photonic crystal fiber arranged to provide guidance of light in the core region due to the photonic bandgap effect (PBG), where light propagates in a hollow or solid core surrounded by a Silica cladding comprising a substantially periodic distribution of micro-structural elements, and where the refractive index of the core is lower than the effective refractive index of the cladding. The invention may be useful in applications such as laser-based micromachining, thin-film formation, laser cleaning, in medicine and biology.

Claims

1. A short pulse optical system for generating or processing short laser-pulses, said optical system comprises a laser cavity and an optical fiber in the form of a photonic bandgap fiber (PBG), where light propagates in a core surrounded by a Silica cladding and where the refractive index of the core is lower than the effective refractive index of the cladding, wherein the optical system comprises an intra cavity dispersion compensating fiber constituted by said PBG fiber.

2. A short pulse optical system according to claim 1 wherein said intra-cavity PBG fiber is a solid core PBG fiber.

3. A short pulse optical system according to claim 1, said optical system further comprising an intra cavity modulator and an active medium.

4. A short pulse optical system according to claim 3 further comprising a pulsed laser for providing laser pulses wherein the pulsed laser is optically connected to said active medium to provide launching of said pulses into said active medium.

5. A short pulse optical system according to claim 3 wherein the modulator being selected from the group of active modulators, such as acousto-optic, LiNbO3 crystal, semiconductor and passive modulators, such as saturable absorber, APM, coupled cavity.

6. A short pulse optical system according to claim 3 wherein the modulator is a semiconductor saturable absorber mirror (SESAM) modulator.

7. A short pulse optical system according to claims 3 wherein the active medium is a waveguide or an actively doped semiconductor wafer.

8. A short pulse optical system according to claim 7 wherein the active medium is a doped fiber, such as a Nd—

, Yb—

Er—

, Pr—

or a Tm-doped fiber.

9. A short pulse optical system according to claim 8 wherein the active medium is a Large Mode Area actively doped photonic crystal fiber.

10. A short pulse optical system according to claim 9 wherein the Large Mode Area actively doped photonic crystal fiber is used within a SESAM based laser cavity e.g. to provide gain in a medium with high non-linear thresholds.

11. A short pulse optical system according to claim 3 wherein the dispersion compensating fiber and the active medium are coupled to each other, optionally with one or more intermediate light transmitting elements.

12. A short pulse optical system according to claim 1 wherein the PBG fiber is angle spliced to an index guiding fiber to provide a low back reflection combination of the two fibers.

13. A short pulse optical system according to claim 12 wherein the index guiding fiber is a standard fiber or a PCF.

14. A short pulse optical system according to claim 1 comprising an intra-cavity large mode area photonic crystal fiber wherein the large mode area photonic crystal fiber is spliced to an index guiding and mode expanded fiber to provide a low loss combination of the two fibers.

15. A short pulse optical system according to claim 14 wherein the index guiding and mode expanded fiber is a standard fiber or a PCF.

16. A short pulse optical system according to claim 1 comprising extra-cavity light transmission element(s) coupled to the laser cavity to receive an output beam there from.

17. A short pulse optical system according to claim 16 wherein the extra-cavity light transmission element(s) comprises one or more fibers.

18. A short pulse optical system according to claim 16 wherein the light transmission element(s) comprises elements for chirped pulse amplification, said elements comprising elements for chromatically dispersing the optical pulses, amplifying the temporally broadened pulses, and recompressing them in a first dispersive medium with the reciprocal chromatic dispersion, the first dispersive medium preferably being selected from the group of a pair of diffraction gratings, an optical fiber, or a fiber Bragg grating.

19. A short pulse optical system according to claim 18 wherein the extra-cavity first dispersive medium is a PBG fiber.

20. A short pulse optical system according to claim 19 wherein the dispersive PBG fiber of the extra-cavity first dispersive medium is a hollow core PBG fiber.

21. An optical system according to claim 18 wherein the extra-cavity element for amplifying the temporally broadened pulses being a Large Mode Area actively doped photonic crystal fiber.

22. A short pulse optical system according to claim 18 wherein the extra-cavity light transmission element(s) comprise(s) elements for non-linear spectral pulse broadening and pulse compression in a second dispersive medium, the extra-cavity second dispersive medium preferably being selected from the group of a pair of diffraction gratings, an optical fiber, or a fiber Bragg grating.

23. A short pulse optical system according to claim 22 wherein the extra-cavity second dispersive medium is a PBG fiber.

24. A short pulse optical system according to claim 23 wherein the dispersive PBG fiber of the extra-cavity second dispersive medium is a standard fiber.

25. A short pulse optical system according to claim 22 wherein the extra-cavity non-linear spectral broadening mechanism is Self Phase Modulation in an optical fiber.

26. A short pulse optical system according to claim 17 wherein the one or more extra-cavity fibers comprises a PBG fiber for compressing the width of the pulses launched from the system.

27. A short pulse optical system according to claim 26 wherein said extra-cavity pulse-compressing PBG fiber is a hollow core PBG fiber.

28. A short pulse optical system for generating or processing short laser-pulses, said optical system comprises a laser cavity and an optical fiber in the form of a photonic bandgap fiber (PBG), where light propagates in a core surrounded by a Silica cladding and where the refractive index of the core is lower than the effective refractive index of the cladding, wherein the optical system comprises extra-cavity light transmission element(s) coupled to the laser cavity to receive an output beam there from, the extra-cavity light transmission element(s) comprising one or more fibers, including said PBG fiber for compressing the width of the pulses launched from the system.

29. A short pulse optical system according to claim 28 wherein said pulse compressing extra-cavity PBG fiber is a hollow core PBG fiber.

30. A short pulse optical system according to claim 28 wherein the extra-cavity light transmission element(s) comprise(s) elements for chirped pulse amplification, said elements comprising elements for chromatically dispersing the optical pulses, amplifying the temporally broadened pulses, and recompressing them in a first dispersive medium with the reciprocal chromatic dispersion, the first dispersive medium preferably being selected from the group of a pair of diffraction gratings, an optical fiber, or a fiber Bragg grating.

31. A short pulse optical system according to claim 30 wherein the first dispersive medium is a PBG fiber.

32. A short pulse optical system according to claim 31 wherein the dispersive PBG fiber of the first dispersive medium is a hollow core PBG fiber.

33. An optical system according to claim 30 wherein the extra-cavity element for amplifying the temporally broadened pulses being a Large Mode Area actively doped photonic crystal fiber.

34. A short pulse optical system according to claim 28 wherein the extra-cavity light transmission element(s) comprise(s) elements for non-linear spectral pulse broadening and pulse compression in a second dispersive medium, the second dispersive medium preferably being selected from the group of a pair of diffraction gratings, an optical fiber, or a fiber Bragg grating.

35. A short pulse optical system according to claim 34 wherein the second dispersive medium is a PBG fiber.

36. A short pulse optical system according to claim 35 wherein the dispersive PBG fiber of the second dispersive medium is a standard fiber.

37. A short pulse optical system according to claim 34 wherein the non-linear spectral broadening mechanism is Self Phase Modulation in an optical fiber.

38. A short pulse optical system according to claim 28 wherein the PBG fiber for compressing the width of the pulses launched from the system is angle spliced to an index guiding fiber to provide a low back reflection combination of the two fibers.

39. A short pulse optical system according to claim 38 wherein the index guiding fiber is a standard fiber or a PCF.

40. A short pulse optical system according to claim 28 comprising a large mode area photonic crystal fiber wherein the large mode area photonic crystal fiber is spliced to an index guiding and mode expanded fiber to provide a low loss combination of the two fibers.

41. A short pulse optical system according to claim 40 wherein the index guiding and mode expanded fiber is a standard fiber or a PCF.

42. A short pulse optical system according to claim 28 wherein the pulse compressing PBG fiber is characterized by mode field diameters above 5 μ

m.

43. A short pulse optical system according to claim 29 wherein the pulse compressing hollow core PBG fiber is characterized by at least 50% of the energy propagating outside of silica (i.e. in “

air”

).

44. A short pulse optical system according to claim 28 wherein the pulse compressing PBG fiber is characterized by a dispersion >

+100 ps*nm<sup>−

1</sup>*km<sup>−

1</sup> in selected parts of the wave guiding band.