WO2002099471A2 - Method and apparatus for optical fiber side coupling - Google Patents

Method and apparatus for optical fiber side coupling Download PDF

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Publication number
WO2002099471A2
WO2002099471A2 PCT/US2002/018051 US0218051W WO02099471A2 WO 2002099471 A2 WO2002099471 A2 WO 2002099471A2 US 0218051 W US0218051 W US 0218051W WO 02099471 A2 WO02099471 A2 WO 02099471A2
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Prior art keywords
waveguide
fiber
prism
cladding
groove
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PCT/US2002/018051
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French (fr)
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WO2002099471A3 (en
Inventor
Hong Po
Leonard Wan
Dapeng Yan
Xiaojun Li
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Optical Power Systems Inc.
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Publication date
Application filed by Optical Power Systems Inc. filed Critical Optical Power Systems Inc.
Priority to AU2002314964A priority Critical patent/AU2002314964A1/en
Publication of WO2002099471A2 publication Critical patent/WO2002099471A2/en
Publication of WO2002099471A3 publication Critical patent/WO2002099471A3/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
    • G02B6/2852—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using tapping light guides arranged sidewardly, e.g. in a non-parallel relationship with respect to the bus light guides (light extraction or launching through cladding, with or without surface discontinuities, bent structures)
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02061—Grating external to the fibre and in contact with the fibre, e.g. evanescently coupled, gratings applied to the fibre end
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
    • G02B6/4214—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms the intermediate optical element having redirecting reflective means, e.g. mirrors, prisms for deflecting the radiation from horizontal to down- or upward direction toward a device
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H01S3/094019—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2383—Parallel arrangements

Definitions

  • This invention relates to couplers for pumping an optical fiber from the side (side couplers), and systems containing such side couplers (e.g., fiber lasers and fiber amplifiers).
  • side couplers e.g., fiber lasers and fiber amplifiers.
  • Fiber amplifiers and fiber lasers require high optical pump levels to be injected within the region of the fiber that includes the active medium that provides the optical gain.
  • the output power from fiber amplifiers and fiber lasers is limited by the amount of optical power that can be injected into the active medium of the fiber, a limitation arising in part from the approaches used to couple optical pump power into such fibers.
  • End pumping One common approach for injecting optical pump power into a double-clad fiber is end pumping. End pumping an optical fiber has several disadvantages, however. End pumping provides at most only two input ends through which all the injected optical pump power enters the fiber. This physically constrains the number and type of pump sources that can be used to inject the optical power, and limits applications which require access to one or both ends of the optical fiber.
  • optical side pumping techniques for double-clad fiber. Such techniques enable energy from a greater number and type of optical pump sources to be coupled into a double-clad fiber.
  • a number of side coupling techniques have been attempted.
  • One method for side coupling pump light is to cut grooves or gratings into the cladding of a double-clad fiber. The cutting of grooves or gratings into a double-clad fiber, however, can weaken the fiber.
  • Another approach for side pumping is to couple light into a double-clad fiber through a prism or other device that is placed against an exposed cladding surface.
  • the present invention provides highly efficient, highly power-scalable side couplers for optically pumping a double-clad fiber such as those used in fiber lasers and amplifiers.
  • This invention is adaptable for coupling an individual laser source, such as an individual diode laser, multiple laser sources, such as multiple individual diode lasers, and laser source arrays, such as diode laser bars.
  • the pumping light is easy to align and adjust.
  • the pumping light can be a focused, diverged or collimated beam.
  • the pumping light can be injected into one or more sides of a double-clad fiber.
  • high coupling efficiency can be achieved without damaging the fiber.
  • the invention relates to couplers for pumping an optical fiber from the side (side couplers), and systems containing such side couplers (e.g., fiber lasers and fiber amplifiers).
  • side couplers e.g., fiber lasers and fiber amplifiers.
  • This invention provides new methods and apparatus for coupling pump light into a double-clad fiber.
  • An object of the present invention is to provide methods and apparatus to pump light into the side of a double-clad fiber without damaging the fiber.
  • Another object of the present invention is to provide methods and apparatus for efficiently coupling light from one or more pump sources into a double-clad fiber to achieve a high output fiber laser or amplifier.
  • Yet another object of present invention is to provide methods and apparatus for coupling multispatial mode laser output into a double-clad fiber to achieve a single mode output fiber laser or amplifier.
  • a further object of present invention is to provide a method and apparatus for coupling pump light from an individual laser source, multiple laser sources or a laser source array through the side of a double-clad fiber while leaving a fiber end accessible for another use.
  • Still another object of the present invention is to provide methods and apparatus for pumping double-clad fiber in the form of a wound pack.
  • FIG. 1 is a schematic view of a double-clad fiber.
  • FIG. 2 is a schematic view of an embodiment of a side coupler according to the present invention.
  • FIG. 3A is a front elevational view of an embodiment of a side coupler according to the present invention.
  • FIG. 3B is an isometric view of the side coupler shown in FIG. 3A.
  • FIG. 4 is a schematic view of an additional embodiment of a side coupler according to the present invention.
  • FIG. 5 is a schematic view of an additional embodiment of a side coupler according to the present invention.
  • FIG. 6 is a schematic view of an additional embodiment of a side coupler according to the present invention.
  • FIG. 7 is a schematic view of an additional embodiment of a side coupler according to the present invention.
  • FIG. 8 is a schematic view of an additional embodiment of a side coupler according to the present invention.
  • Double-clad fiber 10 includes a single-mode core 12, an inner cladding 14 and an outer cladding 16.
  • Single-mode core 12 and inner cladding 14 have a high refractive index
  • outer cladding 16 has a lower refractive index relative to the inner cladding and core, so as to enable the pump light to travel within the inner cladding.
  • Double-clad fibers are disclosed, for example, in U.S. Patent No. 4,815,079.
  • a groove 18 is fabricated into one side of a trapezoidal prism 19.
  • the refractive index of prism 19 is the same as that of the inner cladding.
  • Groove 18 is preferably V-shaped.
  • a side of prism 19 is in contact with a portion of double- clad fiber 10.
  • a portion of the outer cladding of the double-clad fiber is removed and prism 19 is then adhered to the surface of the double-clad fiber by, e.g., a refractive index matching cement or other adhesive adapted to reduce the reflection loss at the interface of the prism and fiber.
  • Pumping light 22 which may be emitted from a laser source such as an individual diode laser, enters the two surfaces of groove 18.
  • Light 22 impinges on faceted surfaces 24 and 24 of groove 18 and is reflected and injected into the two wedges of prism 19.
  • Pumping light 22 is then transmitted through the fiber after multi-reflection between wedge surface 26 and inner cladding 28.
  • the angle a ⁇ ( 1; ⁇ 2 , and ⁇ 3 ) between the incident light and the side of inner cladding 28 must satisfy the following requirements:
  • n mner _ claddmg and n outer _ claddms are the refractive index of the inner cladding and outer cladding respectively
  • N is the number of multi-reflections
  • ⁇ is the angle of the wedge of the dove prism
  • ⁇ is the incident angle of pumping light on the surfaces of the groove
  • ⁇ is the angle between the double-cladding fiber and groove hypotenuse.
  • the incident angle of pumping light on the surfaces of the groove ⁇ also must satisfy the following requirement:
  • n the refractive index of the prism.
  • the length of bottom side L of the prism is determined by:
  • h is the height of the groove
  • h is the distance between the apical angle of the groove and the surface of the prism for incident light.
  • the length h and D must be designed to protect the broken portion of the prism due to the fabrication of the groove in its side.
  • Pumping light 22 can be a focused beam, diverged beam or collimated beam, provided equations (1) to (4) are satisfied.
  • Fig. 3 shows an example of a side coupler in accordance with the present invention.
  • Fig. 4 illustrates an embodiment of the present invention in which multiple prisms 19 are appropriately connected along double-clad fiber 10 to couple pumping light from multiple lasers 28 into the fiber inner cladding.
  • This embodiment of the side pumping technique can be used to increase the total pump power in double-clad fiber 10 and scale up the fiber laser output or fiber amplifier saturation power.
  • Fig. 5 illustrates an embodiment of the present invention in which prism 19 has a square shape.
  • the pumping light is reflected by the two surfaces 24 and 24' of groove 18, focused and injected into the fiber.
  • a pumping light from a laser source array such as a diode laser bar, can be coupled into a double-clad fiber in the form of a wound pack by using a prism in accordance with the present invention.
  • Such a wound pack 30 is shown in Fig. 6.
  • Wound pack 30 may be side pumped with a pumping laser bar, lens elements (not shown in the figure) and the prism with a groove disclosed herein. Referring to Fig. 6, wound pack 30 may have only one layer of wound turns or multiple layers.
  • Light from the diode laser bar may be introduced into opposite sides of fiber 10 defining the wound pack 30 at a plurality of turns thereon.
  • a prism with a groove may be used to direct pump light from the diode laser bar into opposite sides of the fiber inner cladding.
  • the width of the prism preferably spans several fibers, as does the diode laser bar.
  • the portion of the wound pack designed to contact the prism may be made as shown in Fig. 7.
  • Fibers with inner cladding only (no outer cladding) can be placed in contact, e.g., side by side, and lower refractive index material can be applied to the other side with a complimentary shape to that of the inner cladding.
  • a grating 20 is placed in contact with the inner cladding 14 of a double-clad fiber 10.
  • the grating may be adhered to the surface of the inner cladding or written into the cladding using any of a number of known methods for preparing gratings including, e.g., lithographic, holographic, and mechanical processes.
  • Grating 20 is preferably a diffraction grating having a blazed groove profile, but could be another type of grating, e.g. a reflection grating, and could have any other groove profile, e.g. rectangular, triangular, sinusoidal, trapezoidal, etc.
  • Grating 20 is preferably prepared lithographically on a ZnSe plate and adhered to the fiber using, e.g., a UV curable polymer, although any of a number of other preparation techniques and substrate materials, e.g. Al, Ag, Au, etc., may be used.
  • a reflector 32 e.g. a Fresnel mirror, is placed opposite grating 20 to capture light in the inner cladding 14 of double- clad fiber 10. While certain embodiments of the invention have been disclosed herein, the invention is not limited to these embodiments. Other fiber arrangements and double- clad fiber laser/amplifier configurations are possible within the spirit of the current invention. Other embodiments are in the claims.

Abstract

This invention relates to couplers (19) for pumping an optical fiber (10) from the side, side couplers, and systems containing such side couplers e.g., fiber lasers and fiber amplifiers.

Description

Method and Apparatus for Optical Fiber Side Coupling
TECHNICAL FIELD
This invention relates to couplers for pumping an optical fiber from the side (side couplers), and systems containing such side couplers (e.g., fiber lasers and fiber amplifiers).
BACKGROUND
Fiber amplifiers and fiber lasers require high optical pump levels to be injected within the region of the fiber that includes the active medium that provides the optical gain. The output power from fiber amplifiers and fiber lasers is limited by the amount of optical power that can be injected into the active medium of the fiber, a limitation arising in part from the approaches used to couple optical pump power into such fibers.
One common approach for injecting optical pump power into a double-clad fiber is end pumping. End pumping an optical fiber has several disadvantages, however. End pumping provides at most only two input ends through which all the injected optical pump power enters the fiber. This physically constrains the number and type of pump sources that can be used to inject the optical power, and limits applications which require access to one or both ends of the optical fiber.
The limitations of end pumping have led to the development of optical side pumping techniques for double-clad fiber. Such techniques enable energy from a greater number and type of optical pump sources to be coupled into a double-clad fiber. A number of side coupling techniques have been attempted. One method for side coupling pump light is to cut grooves or gratings into the cladding of a double-clad fiber. The cutting of grooves or gratings into a double-clad fiber, however, can weaken the fiber. Another approach for side pumping is to couple light into a double-clad fiber through a prism or other device that is placed against an exposed cladding surface. Although such techniques avoid cutting into the fiber cladding, light injected through such a device must be prevented from re-entering the device again or the coupling efficiency will be compromised. Approaches that require removal of a portion of the fiber cladding can compromise the strength and integrity of the fiber. Yet prior coupling schemes that do not require cutting into the fiber are inefficient, complex, not scalable to higher power levels and/or not easily adaptable for coupling pump light from a laser source array, such as a diode laser bar, into an optical fiber.
The present invention provides highly efficient, highly power-scalable side couplers for optically pumping a double-clad fiber such as those used in fiber lasers and amplifiers. This invention is adaptable for coupling an individual laser source, such as an individual diode laser, multiple laser sources, such as multiple individual diode lasers, and laser source arrays, such as diode laser bars. The pumping light is easy to align and adjust. The pumping light can be a focused, diverged or collimated beam. The pumping light can be injected into one or more sides of a double-clad fiber. In addition, high coupling efficiency can be achieved without damaging the fiber.
SUMMARY
In general, the invention relates to couplers for pumping an optical fiber from the side (side couplers), and systems containing such side couplers (e.g., fiber lasers and fiber amplifiers).
This invention provides new methods and apparatus for coupling pump light into a double-clad fiber.
An object of the present invention is to provide methods and apparatus to pump light into the side of a double-clad fiber without damaging the fiber.
Another object of the present invention is to provide methods and apparatus for efficiently coupling light from one or more pump sources into a double-clad fiber to achieve a high output fiber laser or amplifier.
Yet another object of present invention is to provide methods and apparatus for coupling multispatial mode laser output into a double-clad fiber to achieve a single mode output fiber laser or amplifier.
A further object of present invention is to provide a method and apparatus for coupling pump light from an individual laser source, multiple laser sources or a laser source array through the side of a double-clad fiber while leaving a fiber end accessible for another use.
Still another object of the present invention is to provide methods and apparatus for pumping double-clad fiber in the form of a wound pack. Features, objects and advantages of the invention are in the description, drawings and claims.
DESCRIPTION OF DRAWINGS The above and other objects and features advantages of the present invention will become apparent from the following description given in conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic view of a double-clad fiber.
FIG. 2 is a schematic view of an embodiment of a side coupler according to the present invention.
FIG. 3A is a front elevational view of an embodiment of a side coupler according to the present invention.
FIG. 3B is an isometric view of the side coupler shown in FIG. 3A. FIG. 4 is a schematic view of an additional embodiment of a side coupler according to the present invention.
FIG. 5 is a schematic view of an additional embodiment of a side coupler according to the present invention.
FIG. 6 is a schematic view of an additional embodiment of a side coupler according to the present invention. FIG. 7 is a schematic view of an additional embodiment of a side coupler according to the present invention.
FIG. 8 is a schematic view of an additional embodiment of a side coupler according to the present invention.
DETAILED DESCRIPTION
Fig. 1 shows a typical double-clad fiber for use with the disclosed invention. Double-clad fiber 10 includes a single-mode core 12, an inner cladding 14 and an outer cladding 16. Single-mode core 12 and inner cladding 14 have a high refractive index, and outer cladding 16 has a lower refractive index relative to the inner cladding and core, so as to enable the pump light to travel within the inner cladding. Double-clad fibers are disclosed, for example, in U.S. Patent No. 4,815,079.
Referring now to Fig. 2, an apparatus for optically pumping an optical fiber from the side is disclosed. A groove 18 is fabricated into one side of a trapezoidal prism 19. The refractive index of prism 19 is the same as that of the inner cladding. Groove 18 is preferably V-shaped. A side of prism 19 is in contact with a portion of double- clad fiber 10. Preferably, a portion of the outer cladding of the double-clad fiber is removed and prism 19 is then adhered to the surface of the double-clad fiber by, e.g., a refractive index matching cement or other adhesive adapted to reduce the reflection loss at the interface of the prism and fiber. Pumping light 22, which may be emitted from a laser source such as an individual diode laser, enters the two surfaces of groove 18. Light 22 impinges on faceted surfaces 24 and 24 of groove 18 and is reflected and injected into the two wedges of prism 19. Pumping light 22 is then transmitted through the fiber after multi-reflection between wedge surface 26 and inner cladding 28. In order to ensure the light is transmitted through the inner cladding and does not escape the outer cladding, the angle a^ ( 1; α2, and α3) between the incident light and the side of inner cladding 28 must satisfy the following requirements:
Figure imgf000006_0001
where nmner_claddmg and nouter_claddms are the refractive index of the inner cladding and outer cladding respectively, and
an ^ a^ 2 N ~l)γ ( 2 )
l = -&+ω-90° ( 3 )
where N is the number of multi-reflections, γ is the angle of the wedge of the dove prism, ϋ is the incident angle of pumping light on the surfaces of the groove and ω is the angle between the double-cladding fiber and groove hypotenuse. The incident angle of pumping light on the surfaces of the groove ϋ also must satisfy the following requirement:
Figure imgf000007_0001
where n is the refractive index of the prism. The length of bottom side L of the prism is determined by:
L r = h + h + D π ( 5 ) tgγ tgγ
where h is the height of the groove, h is the distance between the apical angle of the groove and the surface of the prism for incident light. The length h and D must be designed to protect the broken portion of the prism due to the fabrication of the groove in its side.
Pumping light 22 can be a focused beam, diverged beam or collimated beam, provided equations (1) to (4) are satisfied.
For example, if a right angle groove is selected, and a collimated pumping light is used, then θ = 45° and ω =45°. If an =16° ( nιnner_claddmg =1.38 and nouter_daddms =1.435),
N = 3, then γ = 4°. This means that the angle of the wedge of the prism is 4°, and the pumping light injected on and reflected by the surface of the groove and entered into the wedge of the prism will be multi-reflected three times between the inner cladding and the wedge's surface, and finally transmitted through the fiber with an incident angle of 74°. Fig. 3 shows an example of a side coupler in accordance with the present invention.
Fig. 4 illustrates an embodiment of the present invention in which multiple prisms 19 are appropriately connected along double-clad fiber 10 to couple pumping light from multiple lasers 28 into the fiber inner cladding. This embodiment of the side pumping technique can be used to increase the total pump power in double-clad fiber 10 and scale up the fiber laser output or fiber amplifier saturation power.
Fig. 5 illustrates an embodiment of the present invention in which prism 19 has a square shape. In this embodiment, the pumping light is reflected by the two surfaces 24 and 24' of groove 18, focused and injected into the fiber. A pumping light from a laser source array, such as a diode laser bar, can be coupled into a double-clad fiber in the form of a wound pack by using a prism in accordance with the present invention. Such a wound pack 30 is shown in Fig. 6. Wound pack 30 may be side pumped with a pumping laser bar, lens elements (not shown in the figure) and the prism with a groove disclosed herein. Referring to Fig. 6, wound pack 30 may have only one layer of wound turns or multiple layers. Light from the diode laser bar may be introduced into opposite sides of fiber 10 defining the wound pack 30 at a plurality of turns thereon. A prism with a groove may be used to direct pump light from the diode laser bar into opposite sides of the fiber inner cladding. The width of the prism preferably spans several fibers, as does the diode laser bar.
In order to efficiently couple pump light from the diode laser bar into the fiber wound pack, the portion of the wound pack designed to contact the prism may be made as shown in Fig. 7. Fibers with inner cladding only (no outer cladding) can be placed in contact, e.g., side by side, and lower refractive index material can be applied to the other side with a complimentary shape to that of the inner cladding.
Referring now to Fig. 8, an alternative apparatus for optically pumping an optical fiber from the side is disclosed. A grating 20 is placed in contact with the inner cladding 14 of a double-clad fiber 10. The grating may be adhered to the surface of the inner cladding or written into the cladding using any of a number of known methods for preparing gratings including, e.g., lithographic, holographic, and mechanical processes. Grating 20 is preferably a diffraction grating having a blazed groove profile, but could be another type of grating, e.g. a reflection grating, and could have any other groove profile, e.g. rectangular, triangular, sinusoidal, trapezoidal, etc. Grating 20 is preferably prepared lithographically on a ZnSe plate and adhered to the fiber using, e.g., a UV curable polymer, although any of a number of other preparation techniques and substrate materials, e.g. Al, Ag, Au, etc., may be used. A reflector 32, e.g. a Fresnel mirror, is placed opposite grating 20 to capture light in the inner cladding 14 of double- clad fiber 10. While certain embodiments of the invention have been disclosed herein, the invention is not limited to these embodiments. Other fiber arrangements and double- clad fiber laser/amplifier configurations are possible within the spirit of the current invention. Other embodiments are in the claims.

Claims

1. A system, comprising: a waveguide having a gain medium; and a trapezoidal prism having a first surface and a second surface opposite the first surface and substantially parallel to the first surface, the second surface having a groove, wherein the trapezoidal prism is configured so that energy impinging upon the first surface of the trapezoidal prism is reflected by the groove into the waveguide.
2. The system of claim 1, wherein the waveguide is a fiber.
3. The system of claim 2, wherein the fiber has a cladding around the gain medium.
4. The system of claim 3, wherein the cladding has a substantially flat surface.
5. The system of claim 4, wherein the substantially flat surface of the cladding is substantially parallel to the second surface of the trapezoidal prism.
6. The system of any of the preceding claims, wherein the groove is substantially V-shaped.
7. The system of any of claims 1-5, wherein the groove has a curved surface.
8. The system of claim 7, wherein the curved surface is convex.
9. The system of claim 7, wherein the curved surface is concave.
10. The system of any of the preceding claims, further comprising additional trapezoidal prisms, at least one of the additional trapezoidal prisms having a third surface and a fourth surface opposite the third surface and substantially parallel to the third surface, the fourth surface having a groove, wherein at least one of the additional trapezoidal prisms is configured so that energy impinging upon the third surface is reflected by the groove into the waveguide.
11. The system of claim 10, wherein each of the additional trapezoidal prisms has a third surface and a fourth surface opposite the third surface and substantially parallel to the third surface, the fourth surface of each of the additional prisms has a groove, and each of the additional trapezoidal prisms is configured so that energy impinging upon the third surface of each of the additional trapezoidal prisms is reflected by the groove into the waveguide.
12. The system of claim 1, wherein the waveguide is in the form of a wound pack.
13. The system of any of the preceding claims, wherein an index of refraction of the trapezoidal prism is substantially the same as the index of refraction of the waveguide.
14. A system, comprising: a waveguide having a gain medium; and a prism having a first surface and a second surface opposite the first surface and substantially parallel to the first surface, the second surface having a V- shaped groove, wherein the prism is configured so that energy impinging upon the first surface of the prism is reflected by the V-shaped groove into the waveguide.
15. The system of claim 14, wherein the waveguide is a fiber.
16. The system of claim 15, wherein the fiber has a cladding around the gain medium.
17. The system of claim 16, wherein the cladding has a substantially flat surface.
18. The system of claim 17, wherein the substantially flat surface of the cladding is substantially parallel to the second surface of the prism.
19. The system of any of claims 14-18, wherein the prism is square-shaped or rectangular.
20. The system of any of claims 17-19, further comprising additional prisms, at least one of the additional prisms having a third surface and a fourth surface opposite the third surface and substantially parallel to the third surface, the fourth surface having a V-shaped groove, wherein at least one of the additional prisms is configured so that energy impinging upon the third surface is reflected by the V-shaped groove into the waveguide.
21. The system of claim 20, wherein each of the additional prisms has a third surface and a fourth surface opposite the third surface and substantially parallel to the third surface, the fourth surface of each of the additional prisms has a V-shaped groove, and each of the additional prisms is configured so that energy impinging upon the third surface of each of the additional prisms is reflected by the V-shaped groove into the waveguide.
22. The system of claim 14, wherein the waveguide is in the form of a wound pack.
23. The system of any of claims 14-22, wherein an index of refraction of the prism is substantially the same as the index of refraction of the waveguide.
24. A system, comprising: a waveguide having a gain medium; and a transmission grating having a first surface and a second surface opposite the first surface, wherein the grating is configured so that energy impinging upon the first surface of the grating passes through the second surface of the grating and is diffracted by the grating into the waveguide.
25. The system of claim 24, wherein the waveguide has a first cladding around the gain medium.
26. The system of claim 25, wherein the second surface of the grating is disposed adjacent a surface of the first cladding.
27. The system of claims 25 or 26, wherein the waveguide has a second cladding around the first cladding.
28. The system of any of claims 24-27, wherein the grating is a diffraction grating.
29. The system of claim 28, wherein the diffraction grating has a blazed profile.
30. The system of claim 28, wherein the diffraction grating has a rectangular profile, a triangular profile, a sinusoidal profile, or a trapezoidal profile.
31. The system of any of claims 24-30, further comprising a reflector disposed adjacent the surface of the cladding and opposite the grating.
32. The system of claim 31 , wherein the reflector is a Fresnel mirror.
33. The system of claim 31, wherein the reflector is a reflection grating.
34. The system of any of the preceding claims, further comprising a source of input energy into the waveguide.
5. The system of any of the preceding claims, further comprising a receiver ut energy from the waveguide.
PCT/US2002/018051 2001-06-07 2002-06-07 Method and apparatus for optical fiber side coupling WO2002099471A2 (en)

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US29657701P 2001-06-07 2001-06-07
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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3883221A (en) * 1974-02-01 1975-05-13 Bell Telephone Labor Inc Portable prism-grating coupler
US4861128A (en) * 1987-02-04 1989-08-29 Hitachi, Ltd. Optical pickup using a waveguide
US5105403A (en) * 1988-01-27 1992-04-14 Hitachi, Ltd. Optical information reading apparatus with waveguide and diffraction grating
US5418765A (en) * 1991-04-19 1995-05-23 Ricoh Company, Ltd. Apparatus for recording and reproducing optical information having an optical waveguide
US5420947A (en) * 1994-06-17 1995-05-30 Eastman Kodak Company Method for achromatically coupling a beam of light into a waveguide

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3883221A (en) * 1974-02-01 1975-05-13 Bell Telephone Labor Inc Portable prism-grating coupler
US4861128A (en) * 1987-02-04 1989-08-29 Hitachi, Ltd. Optical pickup using a waveguide
US5105403A (en) * 1988-01-27 1992-04-14 Hitachi, Ltd. Optical information reading apparatus with waveguide and diffraction grating
US5418765A (en) * 1991-04-19 1995-05-23 Ricoh Company, Ltd. Apparatus for recording and reproducing optical information having an optical waveguide
US5420947A (en) * 1994-06-17 1995-05-30 Eastman Kodak Company Method for achromatically coupling a beam of light into a waveguide

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