Optical system for providing short laser-pulses

• US 7,813,387 B2
• Filed: 03/23/2006
• Issued: 10/12/2010
• Est. Priority Date: 10/24/2003
• Status: Expired due to Fees

• Current Assignee: NKT Photonics A/S (NKT A/S)
• Original Assignee: NKT Photonics A/S (NKT A/S)
• Inventors: Pedersen, Claus Friis, Skovgaard, Peter M. W.
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): King; Joshua
• Application Number:
  US11/277,252
• Publication Number:
  US 20060209908A1
• Time in Patent Office: 1,664 Days
• Field of Search: 372/10, 372/25
• US Class Current: 372/10
• 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 short laser-pulses, said optical system being in the form of a modelocked laser, and comprising;

an optical pump; and

a laser cavity, comprising;

an intracavity modulator;

an intracavity dispersion compensating photonic bandgap (PBG) fiber, comprising a solid core that is substantially homogeneous and an all solid cladding, wherein the solid core has a refractive index that is lower than a refractive index of the cladding;

a polarizing component adapted to provide the cavity with a single polarization; and

an active medium optically coupled to said PBG fiber and said optical pump, wherein said PBG fiber is connected to said laser cavity via at least one splice;

wherein any non-polarization maintaining fibers in the laser cavity are kept substantially straight.

2. A short pulse optical system according to claim 1, wherein said optical pump is a laser diode.

3. A short pulse optical system according to claim 1, wherein the intra cavity modulator is selected from the group consisting of an acousto-optic modulator, a LiNbO3 crystal, a semiconductor modulator, a saturable absorber, an APM, or coupled cavity modulators.

4. A short pulse optical system according to claim 1, wherein the intra cavity modulator is a semiconductor saturable absorber mirror (SESAM) modulator.

5. A short pulse optical system according to claim 1 wherein the active medium is a waveguide or an actively doped semiconductor wafer.

6. A short pulse optical system according to claim 5 wherein the active medium is a doped fiber.

7. A short pulse optical system according to claim 6 wherein the active medium is a Large Mode Area actively doped photonic crystal fiber.

8. A short pulse optical system according to claim 7 wherein the laser cavity further comprises a semiconductor saturable absorber mirror (SESAM).

9. A short pulse optical system according to claim 1, wherein the intracavity dispersion compensating PBG fiber and the active medium are coupled to each other with one or more intermediate light transmitting elements.

10. A short pulse optical system according to claim 7, wherein the large mode area actively doped photonic crystal fiber is spliced to an index guiding and mode expanded fiber to provide a low loss combination of the two fibers.

11. A short pulse optical system according to claim 10 wherein the index guiding and mode expanded fiber is a standard fiber or a PCF.

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

13. A short pulse optical system according to claim 12 wherein the extra-cavity light transmission element(s) comprises one or more extra-cavity fibers.

14. A short pulse optical system according to claim 12 wherein the extra-cavity light transmission element(s) comprises elements for chirped pulse amplification, said elements comprising one or more elements for chromatically dispersing the optical pulses, one or more elements for amplifying the temporally broadened pulses, and one or more elements for recompressing.

15. A short pulse optical system according to claim 14 wherein the one or more extra-cavity elements for recompressing is a PBG fiber.

16. A short pulse optical system according to claim 15 wherein said PBG fiber for recompressing is a hollow core PBG fiber.

17. A short pulse optical system according to claim 14 wherein the extra-cavity element for amplifying the temporally broadened pulses is a Large Mode Area actively doped photonic crystal fiber.

18. A short pulse optical system according to claim 13, wherein the extra-cavity comprises a PBG fiber.

19. A short pulse optical system according to claim 18, wherein the PBG fiber of the extra-cavity is a hollow core PBG fiber.

20. A short pulse optical system according to claim 1, wherein the intra cavity modulator is an active modulator.

21. A short pulse optical system according to claim 1, wherein the intra cavity modulator is a passive modulator.

22. A short pulse optical system according to claim 8, wherein said active medium has a high non-linear thresholds.

23. A short pulse optical system according to claim 14, wherein said one or more elements for chromatically dispersing the optical pulses is selected from a pair of diffraction gratings, an optical fiber, or a fiber Bragg grating.

24. A short pulse optical system according to claim 6, wherein the doped fiber is a Nd-, Yb—

Er-, Pr- or a Tm-doped fiber.

25. A short pulse optical system according to claim 1, wherein said solid core PBG fiber is coupled within the cavity via at least one splice to a fiber having a cladding without microstructures.

26. A short pulse optical system according to claim 12, wherein the extra-cavity light transmission element(s) comprises elements for amplification and pulse compression.

27. A short pulse optical system according to claim 26, wherein pulse compression is performed in a PBG fiber.

28. A short pulse optical system according to claim 1, wherein said laser-pulses are in the range from 10 picoseconds (10*10⁻

12 s) to femtoseconds (10¹⁵ s).