Mode-locked multi-mode fiber laser pulse source

• US 20050008044A1
• Filed: 05/20/2004
• Published: 01/13/2005
• Est. Priority Date: 11/25/1998
• Status: Abandoned Application

• Current Assignee: Donald J. Harter, Martin E. Fermann
• Original Assignee: Donald J. Harter, Martin E. Fermann
• Inventors: Harter, Donald J., Fermann, Martin E.
• Application Number:
  US10/850,509
• Publication Number:
  US 20050008044A1
• Time in Patent Office: Days
• US Class Current: 372/19
• CPC Class Codes: G02B 6/26 Optical coupling means G02B6/36, G02B6/42 take precedence
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/067 Fibre lasers
• CPC Class Codes: H01S 3/06704 Housings; Packages
• CPC Class Codes: H01S 3/06708 Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering optical fibres as passive waveguides G02B6/02
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06716 Fibre compositions per se C03C13/04or doping with active elements lasing materials in general H01S3/14
• 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 3/06733 Fibre having more than one cladding
• CPC Class Codes: H01S 3/06737 Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain
• CPC Class Codes: H01S 3/06745 Tapering of the fibre, core or active region
• CPC Class Codes: H01S 3/06783 Amplifying coupler
• CPC Class Codes: H01S 3/08045 Single-mode emission
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• 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 3/094069 Multi-mode pumping
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1109 : Active mode locking
• 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 3/1608 : erbium
• CPC Class Codes: H01S 3/1618 : ytterbium

Abstract

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity. To amplify and compress optical pulses in a multi-mode (MM) optical fiber, a single-mode is launched into the MM fiber by matching the modal profile of the fundamental mode of the MM fiber with a diffraction-limited optical mode at the launch end, The fundamental mode is preserved in the MM fiber by minimizing mode-coupling by using relatively short lengths of step-index MM fibers with a few hundred modes and by minimizing fiber perturbations. Doping is confined to the center of the fiber core to preferentially amplify the fundamental mode, to reduce amplified spontaneous emission and to allow gain-guiding of the fundamental mode. Gain-guiding allows for the design of systems with length-dependent and power-dependent diameters of the fundamental mode. To allow pumping with high-power laser diodes, a double-clad amplifier structure is employed. For applications in nonlinear pulse-compression, self phase modulation and dispersion in the optical fibers can be exploited. High-power optical pulses may be linearly compressed using bulk optics dispersive delay lines or by chirped fiber Bragg gratings written directly into the SM or MM optical fiber. High-power cw lasers operating in a single near-diffraction-limited mode may be constructed from MM fibers by incorporating effective mode-filters into the laser cavity. Regenerative fiber amplifiers may be constructed from MM fibers by careful control of the recirculating mode. Higher-power Q-switched fiber lasers may be constructed by exploiting the large energy stored in MM fiber amplifiers.

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59. A multi-mode fiber amplifier system providing discrimination between a fundamental mode and undesired higher-order modes, said amplifier system comprising:

a light source for producing a light beam, and

a linear multi-mode fiber amplifier for receiving said light beam and comprising a multi-mode doped optical fiber having a V-number equal to or higher than 2.41 with respect to an input signal, capable of supporting a fundamental mode and higher-order modes, having a radius of curvature such that the higher-order modes of said input signal experience substantially increased bend losses as compared with the fundamental mode of said input signal.

60. An amplifier system according to claim 59 wherein said fiber comprises a coiled fiber.

61. An amplifier system according to claim 60 wherein said coiled fiber has a constant radius of curvature.

62. An amplifier system according to claim 59 wherein said light source comprises a continuous wave light source.

63. An amplifier system according to claim 59 wherein said light source comprises a pulsed light source.

64. An amplifier system according to claim 59 wherein said multi-mode optical fiber comprises a double-cladding structure.

65. An amplifier system according to claim 59 wherein said multi-mode optical fiber comprises a core having a diameter of between 28 microns and 50 microns.

66. An amplifier system according to claim 59 wherein said multi-mode fiber amplifier has an M² value less than 2.0, where M²=1 denotes diffraction-limited beam quality.

67. An amplifier system according to claim 59 wherein the fiber amplifier is side pumped.

68. A linear multi-mode fiber amplifier comprising:

a cylindrical support member, and

a doped multi-mode optical fiber having a V-number equal to or higher than 2.4 with respect to an input signal, capable of supporting a fundamental mode and a plurality of higher-order modes, said fiber being wound onto said support with a radius such that said higher-order modes of said input signal experience substantially increased bend loss as compared with the fundamental mode of said input signal.

69. An amplifier system according to claim 68 wherein said wound fiber has a constant radius of curvature.

70. A multi-mode fiber amplifier according to claim 68 wherein said multi-mode optical fiber comprises a double-cladding structure.

71. A multi-mode fiber amplifier according to claim 68 wherein said multi-mode optical fiber comprises a core having a diameter of between 28 μ

m and 100 μ

m.

72. A multi-mode fiber amplifier according to claim 68 wherein said multi-mode fiber amplifier has an M² value less than 2.0, where M²=1 denotes diffraction-limited beam quality.

73. An amplifier system as in claim 68, further comprising a seed beam having a controlled launch condition for preferential excitation of the fundamental mode.