CA2239619C - Method and apparatus for side pumping an optical fiber - Google Patents
Method and apparatus for side pumping an optical fiber Download PDFInfo
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- CA2239619C CA2239619C CA002239619A CA2239619A CA2239619C CA 2239619 C CA2239619 C CA 2239619C CA 002239619 A CA002239619 A CA 002239619A CA 2239619 A CA2239619 A CA 2239619A CA 2239619 C CA2239619 C CA 2239619C
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims abstract description 23
- 238000005086 pumping Methods 0.000 title description 5
- 239000000835 fiber Substances 0.000 claims abstract description 132
- 230000003287 optical effect Effects 0.000 claims abstract description 19
- 230000008878 coupling Effects 0.000 claims abstract description 18
- 238000010168 coupling process Methods 0.000 claims abstract description 18
- 238000005859 coupling reaction Methods 0.000 claims abstract description 18
- 239000011248 coating agent Substances 0.000 claims abstract description 6
- 238000000576 coating method Methods 0.000 claims abstract description 6
- 238000005253 cladding Methods 0.000 claims description 45
- 230000003321 amplification Effects 0.000 claims description 16
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 16
- 239000000463 material Substances 0.000 claims description 14
- 238000010521 absorption reaction Methods 0.000 claims description 13
- 239000002019 doping agent Substances 0.000 claims description 7
- 238000013459 approach Methods 0.000 abstract description 3
- 238000002347 injection Methods 0.000 abstract description 3
- 239000007924 injection Substances 0.000 abstract description 3
- 238000002310 reflectometry Methods 0.000 abstract description 3
- 238000010276 construction Methods 0.000 abstract description 2
- 238000004519 manufacturing process Methods 0.000 abstract description 2
- 239000011162 core material Substances 0.000 description 105
- 230000001902 propagating effect Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 3
- 238000003491 array Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 239000003365 glass fiber Substances 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000003467 diminishing effect Effects 0.000 description 1
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- 239000010409 thin film Substances 0.000 description 1
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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
- G02B6/2817—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 reflective elements to split or combine optical signals
-
- 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
- H01S3/05—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
- H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
-
- 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
-
- 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)
-
- 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
- H01S3/094069—Multi-mode pumping
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- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optical Couplings Of Light Guides (AREA)
- Lasers (AREA)
Abstract
A technique for the efficient coupling of pump light into a fiber (19) by injecting the light through the side of a fiber leaving the fiber ends accessible to input and output coupling. This technique relies on the fabrication of a groove (18) or a microprism into the side of the fiber. The groove shape is adapted effective to the variables of light wavelength, orientation of the source and visible relating to fiber construction so as to allow the efficient injection of pump light. Light emerging from a laser diode or other suitable means (16) for launching light placed on the opposite side of the fiber, and in proximity to the fiber wall, propagates laterally through the fiber and impinges on the sides of the groove (18). The vertical rays impinging on the groove facets are specularly reflected and directed along the horizontal fiber axis of the outer core. By employing a reflective coating on the groove (18), the reflectivity of the groove facets approach 100% for a wide range of incidence angle. In this manner one can launch external optical signals into an optical fiber (19).
Description
METHOD AND APPARATUS FOR SIDE PUMPING AN OPTICAL FIBER
Field of the Invention BACKGROUND OF THE INVENTION
The present invention relates generally to a technique of coupling pump light into a fiber waveguide through the side of the fiber cladding and to fiber optic amplifiers and lasers particularly.
Description of the Related Art Launching an optical signal into an optical fiber is one of the most basic problems confronting scientist and engineers who design, build, and employ fiber optic systems. The manipulation of optical signals once propagating in an optical fiber represents an equally challenging problem to those attempting to use optical fibers to transmit information or other signals. It is generally accepted that an optical signal propagating in an optical fiber may be manipulated by launching or coupling light of differing wavelengths into the same fiber.
These fibers are often coupled to laser light sources which act as pumps for the information coded therein. Of the methods used to couple pump light to optical fibers, pigtailing is a preferred method. Typically single spatial mode, diffraction limited laser diodes with an emission aperture of approximately 1 x 3 Irm are used to achieve efficient diode to fiber coupling. Pump light is injected into the fiber core by proximity coupling into the polished face of the fiber, or by using small lenses between the laser aperture and the input face of the fiber. This fiber pigtailing process is expensive because of the sub,um alignment and mechanical stability required to achieve efficient and stable laser to fiber coupling.
The use of optical fibers with doped cores has become an indispensable tool in building optical systems for the transmission and amplification of optical information signals. Doping these fibers with different ions produces optical gain for light propagating in the fiber core at various wavelength ranges.
Optical gain for a signal propagating in the doped fiber core occurs when population inversion in the inner core material is induced by the absorption of pump light. For the majority of systems, pump light is coupled directly into the inner core via a wavelength selected fused fiber coupler. However, these fused fiber couplers, which allow the pump light coupling and constitute wavelength division multiplexers, add complexity and expense.
A current development in the art is the use of an active fiber configuration with a double cladded structure. The double dadded structure consists of a single mode fiber inner core, an outer core and an outer cladding. The refractive index is highest in the inner core and lowest in the outer cladding, so that both the fiber S inner-core and the outer core function as optical waveguides. The important feature of the double cladded structure is th~it light can be injected into the outer core where it propagates until it is absorbed by the active dopant in the fiber inner core.
The index difference between the outer <:ore and the outer cladding is made .
relatively large, so that the effective numerical aperture (critical angle) of the outer core waveguide is very large, typically above 0.3. The large diarx~eter-and numerical aperture of the outer core waveguide make it possible to efficiently couple spatially incoherent emission from hiigh power, large aperture, broad area laser diodes or laser diode arrays. These pump lasers typically generate t-2 W
from an emission area of fpm by 100,vm, or a factor of ten greater power than is available frofn single mode laser diodes pigtailed into a single mode fiber: -An important advantage of the broad area laser diodes is that their cost is approximately'ten times smaller than that of pigtailed single mode laser diodes.
High power, double core fiber amplifiers: and Lasers can be constructed by ~hd-puimping using multiple large active area dicxles. However, this configuration does not~provide access to both ends of the fiber, thus diminishing flexibility in source placement:' ~ The double core design fibers can also in principle be pumped at multiple points by using special types of fused fiber couplers which allow pump tight transfer from a., multimode fiber into the outer core but do not disturb the signal, propagating in the fiber inner core. This however, is accomplished at the expense of efficiency, complexity and cost.
SUMMARY OF THE INVENTION
It is anvbject of this invention to efficiently couple pump light from a purr~p laser into an optical fiber waveguide.
'Another object of the present invention is to.provide a means for coupling ii~ht from multiple pump lasers into a single fiber to achieve high output in optical fiber amplifiers, and fiber lasers.
Field of the Invention BACKGROUND OF THE INVENTION
The present invention relates generally to a technique of coupling pump light into a fiber waveguide through the side of the fiber cladding and to fiber optic amplifiers and lasers particularly.
Description of the Related Art Launching an optical signal into an optical fiber is one of the most basic problems confronting scientist and engineers who design, build, and employ fiber optic systems. The manipulation of optical signals once propagating in an optical fiber represents an equally challenging problem to those attempting to use optical fibers to transmit information or other signals. It is generally accepted that an optical signal propagating in an optical fiber may be manipulated by launching or coupling light of differing wavelengths into the same fiber.
These fibers are often coupled to laser light sources which act as pumps for the information coded therein. Of the methods used to couple pump light to optical fibers, pigtailing is a preferred method. Typically single spatial mode, diffraction limited laser diodes with an emission aperture of approximately 1 x 3 Irm are used to achieve efficient diode to fiber coupling. Pump light is injected into the fiber core by proximity coupling into the polished face of the fiber, or by using small lenses between the laser aperture and the input face of the fiber. This fiber pigtailing process is expensive because of the sub,um alignment and mechanical stability required to achieve efficient and stable laser to fiber coupling.
The use of optical fibers with doped cores has become an indispensable tool in building optical systems for the transmission and amplification of optical information signals. Doping these fibers with different ions produces optical gain for light propagating in the fiber core at various wavelength ranges.
Optical gain for a signal propagating in the doped fiber core occurs when population inversion in the inner core material is induced by the absorption of pump light. For the majority of systems, pump light is coupled directly into the inner core via a wavelength selected fused fiber coupler. However, these fused fiber couplers, which allow the pump light coupling and constitute wavelength division multiplexers, add complexity and expense.
A current development in the art is the use of an active fiber configuration with a double cladded structure. The double dadded structure consists of a single mode fiber inner core, an outer core and an outer cladding. The refractive index is highest in the inner core and lowest in the outer cladding, so that both the fiber S inner-core and the outer core function as optical waveguides. The important feature of the double cladded structure is th~it light can be injected into the outer core where it propagates until it is absorbed by the active dopant in the fiber inner core.
The index difference between the outer <:ore and the outer cladding is made .
relatively large, so that the effective numerical aperture (critical angle) of the outer core waveguide is very large, typically above 0.3. The large diarx~eter-and numerical aperture of the outer core waveguide make it possible to efficiently couple spatially incoherent emission from hiigh power, large aperture, broad area laser diodes or laser diode arrays. These pump lasers typically generate t-2 W
from an emission area of fpm by 100,vm, or a factor of ten greater power than is available frofn single mode laser diodes pigtailed into a single mode fiber: -An important advantage of the broad area laser diodes is that their cost is approximately'ten times smaller than that of pigtailed single mode laser diodes.
High power, double core fiber amplifiers: and Lasers can be constructed by ~hd-puimping using multiple large active area dicxles. However, this configuration does not~provide access to both ends of the fiber, thus diminishing flexibility in source placement:' ~ The double core design fibers can also in principle be pumped at multiple points by using special types of fused fiber couplers which allow pump tight transfer from a., multimode fiber into the outer core but do not disturb the signal, propagating in the fiber inner core. This however, is accomplished at the expense of efficiency, complexity and cost.
SUMMARY OF THE INVENTION
It is anvbject of this invention to efficiently couple pump light from a purr~p laser into an optical fiber waveguide.
'Another object of the present invention is to.provide a means for coupling ii~ht from multiple pump lasers into a single fiber to achieve high output in optical fiber amplifiers, and fiber lasers.
Yet another object of the present invention is to provide a means for efficient coupling of pump light from spatially incoherent, large active area, high power laser diode arrays or broad stripe diode lasers into the fiber.
A further object of this invention is to eliminate the need for wavelength division multiplexing fiber couplers.
Yet a further object of the present invention is to provide a means for injecting pump light through the side of the fiber leaving the fiber ends access-ible for input and output coupling of the signal light.
Yet another objective is to reduce the cost of the overall system by permitting efficient coupling with less expensive lasers.
Yet a further object of the present invention is to provide a means for injecting pump light from multiple lasers through the side of the fiber leaving the fiber ends accessible for input and output coupling of the signal light.
In accordance with these and other objects made apparent hereafter, the invention concerns a technique for the efficient coupling of pump light into a fiber by injecting the light through the side of a fiber leaving the fiber ends accessible to input and output coupling. This technique relies on the fabrication of a groove or a micro-prism into the side of the fiber. The groove shape is adapted effective to the variables of light wavelength, orientation of the source and variables relating to fiber construction so as to allow the efficient injection of pump light. Light emerging from a laser diode or other suitable means for launching light placed on the opposite side of the fiber, and in proximity to the fiber wall, propagates laterally through the fiber and impinges on the sides of the groove. The vertical rays impinging on the grove facets are reflected and directed along the horizontal fiber axis of the outer core. By employing a reflective coating on the groove, the reflectivity of the groove facets approach 100% for a wide range of incidence angles. In this manner one can launch external optical signals into an optical fiber.
The invention provides according to a first aspect, for an optical fiber suitable for amplification of light. The optical fiber comprises a cladding; a core disposed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency, into the outer core. In the optical fiber accord-ing to this first aspect, the light that passes through the cladding is reflected by the groove surface and propagates down the outer core facilitating absorption of the light into the inner core. .
According to a second aspect, the invention provides for a method of injecting light of a preselected frequency into an optical fiber which comprises a cladding, an inner core and an outer core, the inner core being doped with a preselected gain material which is suitable for light amplification. The method comprises: providing a groove in the fiber, the groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected fre-quency, into the outer core; and directing light of the preselected frequency onto the groove, wherein the light passes through the cladding, is reflected by the groove surface and propagates down the outer core.
According to a third aspect, the invention provides for an optical fiber suitable for amplification of light. The optical fiber comprises a cladding; a core disposed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to provide total internal reflection of injected light from a preselected direction and of a preselected frequency into the outer core.
In the optical fiber according to this third aspect, the light that passes through the cladding is reflected by the groove surface and propagates down the outer core, facilitating absorption of the light into the inner core.
According to a fourth aspect, the invention provides for a method of injecting light of a preselected frequency into an optical fiber. The method comprises: providing a groove in the fiber, the groove extending through a cladding into an outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected -3a-frequency into the outer core, the fiber having an inner core disposed within the outer core, the inner core comprising an optically active gain material suitable for light amplification; and directing light of the preselected frequency onto the groove from the preselected direction. In the method according to this fourth aspect, the directing of the light is effective to excite the gain material by optical overlap of the light in the outer core with the inner core, the light in the inner core being amplified.
According to a fifth aspect, the invention provides for an optical fiiber amplifier comprising an optical fiber which comprises: a cladding; a core dis-posed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into the outer core, facilitating absorption of the light into the inner core. In the optical fiber amplifier according to this fifth aspect, the light absorbed into the inner core is amplified and propagates unperturbed through the inner core.
These and other objects, features and advantages of the invention will become better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein like reference numerals and symbols designate identical or corresponding parts throughout the several views, while equivalent elements bear a prime designation.
-3b-i ~ i i BRifF DESCRIPTfON Oh THE DRAW1NCS
FIG 1, is art elevational view of an optical fiber according to the invention.
FIG 2. is a cross sectional view in the direction of 2-2 of FIG 7.
FiG 3. is a side elevationai view in the direction indicated as 3-3 in. FIG 1.
FIG 4. is a top elevational view in the direction indicated as 4-4 in F1G 1.
FIG 5. is a front end view of the fiber in 'the direction of lines 5-5 in FIG
1.
FIG 6, is a xhematic view of one configuration for pumping light from multiple lasers.
FIG 7. is a schematic illustration of one configuration for coupling multiple sources into a cladded fiber.
DETAILED DFS<:RIPTION
tteferring now to the drawings, and in particulaf to FIGS 1-2, which shows an optical fiber 19 and laser light source 16. Fiber 19 has an inner core 14, an outer core 12 disposed about the inner core, and an outer cladding 10 disposed about the. outer core 12. The outer tore and outer claddings 10, 12 have groove 18 and facets 22 disposed thereon. Laser light source 16 is disposed opposite groove and facets 22 to direct light 30 across interfa~~e 20 into the fiber 19, and transverse to inner core 14 and outer core 12 and -outer cladding 10. Groove 18 and facets 22 are selected so that light incident thereon from laser 16 will undergo specular reflection, for reasons discussed below.
FIG 2 is a cross sectional view of the optical fiber. The refraction index is usually lowest in outer cladding 10, with the highest index of refraction located in inner core 14. A lower -index of refraction in. outer cladding 10; allows outer core 12 and inner core i4 to function as optical v~raveguides, efficiently propagating light within the fiber 19, minimizing energy loss through the outer cladding 10.
V1%ith reference to F1.G 3, groove 18 is fabricated into fiber outer core 12 and outer cladding l0. Groove l8 extends through outer cladding 10, and into outer core 12. A broad area laser diode 16 is the I:aser light source lf~; however other tight sources which launch light 30 at useful wavelengths and intensities are suitable.
In operation laser light diode 16 launches light 30 through fiber outer cladding 10, and outer core 12 and onto faceted surfa~~e 22 of groove 18. The light 30, emitted by diode 16. impinges on faceted surface 22 of groove 18 and -is specularly reflected into fiber 19. Specular reflection, ensures maximum reflection into outer core 12, because this minimizes further divergence of the incident light 30.
The.
light 30 is reflected by faceted surface Z2 of groove 18 and injected into outer fore 12 of the fiber 19. 1n this manner, one can inject any optical signal into an optical fiber 19 having a groove such as 18. In an embodiment employing a cladded fiber -19, inner .core 14, may contain an acaive medium, such as an fr or other dopant, which at a selected wavelength absorbs the light 30 propagating in the inner core 14', activating the Er and permitting it to-function as an amplifier for any other optical signal propagating in inner care 14.
For example, assume a typical outer core 12 diameter of 125~um and inner core 14 diameter of lOpm. Further assuming the angle ~ of groove 78 is 90°, a maximum groove 18 depth and width of 52.5Nm and-105pm, respectively is suggested. This provides for Sum clearance between groove 18 and inner core 14, disposing groove 18's apex slightly above inner core 14, allowing unobstructed propagation of an optical signal in inner care 14. Light 30 emerging from laser diode 16 or other type pump laser, placed on the opposite side of the fiber 19; and in proximity to fiber outer cladding 10, propagates laterally through fiber 16, impinges on the sides of groove 18, underl;oes specular reflection, and is injected into outer core 12.
If the above exampled embodiment employs a glass fiber with a refractive index of 1.5, the critical angle required for total intema) reflection is 41 ° relative to the surface normal, and vertical rays impinging at 4S ° on air-to-glass groove facets 24 are totally reflected and directed along the horizontal fiber axis. For a typical broad area laser diode 16, the emission divergence angle in the junction plane is 10 ° FWHM in air or 6.6 ° inside fiber 19, so that substantially all of the pump emission would undergo total internal reflection at groove facets 22 thus launching fight 30 in outer core 12 with very high efficiency. For an outer core t2 numerical aperture of 0.3 outer core waveguide 12 acceptance angle is 17.5 °, thus virtually all of the laser's emission would be captured by outer core waveguide t 2. The reflectivity of groove.facets 22 can approach 100'k for a wide range of incidence angles when thin film reflective coating 55 is placed on groove surface 22.
Although the foregoing dimensions are merely exemplary, the dimensions involved are not atypical of commonly use~~ optical fibers. Thus, one can see that, a groove such as 18 permits injection of lif;ht from broad area laser diodes (i:e:
A further object of this invention is to eliminate the need for wavelength division multiplexing fiber couplers.
Yet a further object of the present invention is to provide a means for injecting pump light through the side of the fiber leaving the fiber ends access-ible for input and output coupling of the signal light.
Yet another objective is to reduce the cost of the overall system by permitting efficient coupling with less expensive lasers.
Yet a further object of the present invention is to provide a means for injecting pump light from multiple lasers through the side of the fiber leaving the fiber ends accessible for input and output coupling of the signal light.
In accordance with these and other objects made apparent hereafter, the invention concerns a technique for the efficient coupling of pump light into a fiber by injecting the light through the side of a fiber leaving the fiber ends accessible to input and output coupling. This technique relies on the fabrication of a groove or a micro-prism into the side of the fiber. The groove shape is adapted effective to the variables of light wavelength, orientation of the source and variables relating to fiber construction so as to allow the efficient injection of pump light. Light emerging from a laser diode or other suitable means for launching light placed on the opposite side of the fiber, and in proximity to the fiber wall, propagates laterally through the fiber and impinges on the sides of the groove. The vertical rays impinging on the grove facets are reflected and directed along the horizontal fiber axis of the outer core. By employing a reflective coating on the groove, the reflectivity of the groove facets approach 100% for a wide range of incidence angles. In this manner one can launch external optical signals into an optical fiber.
The invention provides according to a first aspect, for an optical fiber suitable for amplification of light. The optical fiber comprises a cladding; a core disposed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency, into the outer core. In the optical fiber accord-ing to this first aspect, the light that passes through the cladding is reflected by the groove surface and propagates down the outer core facilitating absorption of the light into the inner core. .
According to a second aspect, the invention provides for a method of injecting light of a preselected frequency into an optical fiber which comprises a cladding, an inner core and an outer core, the inner core being doped with a preselected gain material which is suitable for light amplification. The method comprises: providing a groove in the fiber, the groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected fre-quency, into the outer core; and directing light of the preselected frequency onto the groove, wherein the light passes through the cladding, is reflected by the groove surface and propagates down the outer core.
According to a third aspect, the invention provides for an optical fiber suitable for amplification of light. The optical fiber comprises a cladding; a core disposed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to provide total internal reflection of injected light from a preselected direction and of a preselected frequency into the outer core.
In the optical fiber according to this third aspect, the light that passes through the cladding is reflected by the groove surface and propagates down the outer core, facilitating absorption of the light into the inner core.
According to a fourth aspect, the invention provides for a method of injecting light of a preselected frequency into an optical fiber. The method comprises: providing a groove in the fiber, the groove extending through a cladding into an outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected -3a-frequency into the outer core, the fiber having an inner core disposed within the outer core, the inner core comprising an optically active gain material suitable for light amplification; and directing light of the preselected frequency onto the groove from the preselected direction. In the method according to this fourth aspect, the directing of the light is effective to excite the gain material by optical overlap of the light in the outer core with the inner core, the light in the inner core being amplified.
According to a fifth aspect, the invention provides for an optical fiiber amplifier comprising an optical fiber which comprises: a cladding; a core dis-posed within the cladding, the core comprising an outer core and an inner core, the inner core being disposed within the outer core, the inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through the cladding into the outer core, the groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into the outer core, facilitating absorption of the light into the inner core. In the optical fiber amplifier according to this fifth aspect, the light absorbed into the inner core is amplified and propagates unperturbed through the inner core.
These and other objects, features and advantages of the invention will become better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein like reference numerals and symbols designate identical or corresponding parts throughout the several views, while equivalent elements bear a prime designation.
-3b-i ~ i i BRifF DESCRIPTfON Oh THE DRAW1NCS
FIG 1, is art elevational view of an optical fiber according to the invention.
FIG 2. is a cross sectional view in the direction of 2-2 of FIG 7.
FiG 3. is a side elevationai view in the direction indicated as 3-3 in. FIG 1.
FIG 4. is a top elevational view in the direction indicated as 4-4 in F1G 1.
FIG 5. is a front end view of the fiber in 'the direction of lines 5-5 in FIG
1.
FIG 6, is a xhematic view of one configuration for pumping light from multiple lasers.
FIG 7. is a schematic illustration of one configuration for coupling multiple sources into a cladded fiber.
DETAILED DFS<:RIPTION
tteferring now to the drawings, and in particulaf to FIGS 1-2, which shows an optical fiber 19 and laser light source 16. Fiber 19 has an inner core 14, an outer core 12 disposed about the inner core, and an outer cladding 10 disposed about the. outer core 12. The outer tore and outer claddings 10, 12 have groove 18 and facets 22 disposed thereon. Laser light source 16 is disposed opposite groove and facets 22 to direct light 30 across interfa~~e 20 into the fiber 19, and transverse to inner core 14 and outer core 12 and -outer cladding 10. Groove 18 and facets 22 are selected so that light incident thereon from laser 16 will undergo specular reflection, for reasons discussed below.
FIG 2 is a cross sectional view of the optical fiber. The refraction index is usually lowest in outer cladding 10, with the highest index of refraction located in inner core 14. A lower -index of refraction in. outer cladding 10; allows outer core 12 and inner core i4 to function as optical v~raveguides, efficiently propagating light within the fiber 19, minimizing energy loss through the outer cladding 10.
V1%ith reference to F1.G 3, groove 18 is fabricated into fiber outer core 12 and outer cladding l0. Groove l8 extends through outer cladding 10, and into outer core 12. A broad area laser diode 16 is the I:aser light source lf~; however other tight sources which launch light 30 at useful wavelengths and intensities are suitable.
In operation laser light diode 16 launches light 30 through fiber outer cladding 10, and outer core 12 and onto faceted surfa~~e 22 of groove 18. The light 30, emitted by diode 16. impinges on faceted surface 22 of groove 18 and -is specularly reflected into fiber 19. Specular reflection, ensures maximum reflection into outer core 12, because this minimizes further divergence of the incident light 30.
The.
light 30 is reflected by faceted surface Z2 of groove 18 and injected into outer fore 12 of the fiber 19. 1n this manner, one can inject any optical signal into an optical fiber 19 having a groove such as 18. In an embodiment employing a cladded fiber -19, inner .core 14, may contain an acaive medium, such as an fr or other dopant, which at a selected wavelength absorbs the light 30 propagating in the inner core 14', activating the Er and permitting it to-function as an amplifier for any other optical signal propagating in inner care 14.
For example, assume a typical outer core 12 diameter of 125~um and inner core 14 diameter of lOpm. Further assuming the angle ~ of groove 78 is 90°, a maximum groove 18 depth and width of 52.5Nm and-105pm, respectively is suggested. This provides for Sum clearance between groove 18 and inner core 14, disposing groove 18's apex slightly above inner core 14, allowing unobstructed propagation of an optical signal in inner care 14. Light 30 emerging from laser diode 16 or other type pump laser, placed on the opposite side of the fiber 19; and in proximity to fiber outer cladding 10, propagates laterally through fiber 16, impinges on the sides of groove 18, underl;oes specular reflection, and is injected into outer core 12.
If the above exampled embodiment employs a glass fiber with a refractive index of 1.5, the critical angle required for total intema) reflection is 41 ° relative to the surface normal, and vertical rays impinging at 4S ° on air-to-glass groove facets 24 are totally reflected and directed along the horizontal fiber axis. For a typical broad area laser diode 16, the emission divergence angle in the junction plane is 10 ° FWHM in air or 6.6 ° inside fiber 19, so that substantially all of the pump emission would undergo total internal reflection at groove facets 22 thus launching fight 30 in outer core 12 with very high efficiency. For an outer core t2 numerical aperture of 0.3 outer core waveguide 12 acceptance angle is 17.5 °, thus virtually all of the laser's emission would be captured by outer core waveguide t 2. The reflectivity of groove.facets 22 can approach 100'k for a wide range of incidence angles when thin film reflective coating 55 is placed on groove surface 22.
Although the foregoing dimensions are merely exemplary, the dimensions involved are not atypical of commonly use~~ optical fibers. Thus, one can see that, a groove such as 18 permits injection of lif;ht from broad area laser diodes (i:e:
inexpensive laser diodes) with high efficiency. This is equally so for the examples given below.
Referring to FiG 4, and once again to FIG 3, and assuming, for example, a typical emission aperture of 100,um for a 1.0-2.0w broad area laser diode 16, the output light cone in the junction plane diverges to a width of 1 l2,um at the opposite side of fiber 19 cross section. For a 105~rm wide groove 18, substantially all of pump fight 30 would therefore be intercepted and coupled into fiber 19.
Fibers with large outer core diameters can be used to allow larger groove width.
Of course, lenses could be placed, if one desired, in between laser diode 16 and fiber 19 to decrease the beam divergence or to project a reduced image of the laser emission aperture on the groove. Laser 16 can also be oriented as shown in FIG
3, or rotated by 90 °, so that the emitting area is parallel to the apex of groove 18.
Referring now to FIG. 5, similar considerations to those of the above example apply in the plane perpendicular to the junction 20 (i.e. the plane perpendicular to the page containing FIG 5), where the laser diode emission area 21 is approximately l,um, and the pump light 30 diverges much faster than in FIG 3, with a typical divergence angle of 40° in air or 25° in glass.
With laser diode 16 placed in proximity to fiber wall 10, the emission spreads out to approximately 50~rm after propagation of a distance of one fiber diameter. Since the total length of groove 18 would typically be 100,um at the apex, the beam spread in this plane is sufficiently small so that substantially all of pump light 30 is intercepted by groove facets 22.
The cylindrical fiber to air interface 99 provides a tensing effect which can be used to collimate or focus light 30 propagating in the plane perpendicular to the Laser diode function. For example, for a glass fiber with a refractive index of 1.5, the effective cylindrical (ens focal length is given by 1/3 R, where R is the fiber radius. For a 125,um fiber OD, this corresponds to a focal length of 2lErm.
Collimation is achieved with the laser diode facet placed approximately 2l~.rm from the fiber side-wall 10, whereas greater distances result in a converging beam.
In an embodiment which employs a doped fiber inner core pump light 30 is injected into outer core 12 where it propagates until it is absorbed by the dopant in fiber inner core 14. More efficient absorption of pump light 30 is made possible via the use of special outer core 12 shapes and off center inner core 14 placement which assure that light injected into the outer core waveguide 12 will spatially _ 6 _ overlap with fiber inner core 14 and insure absorption of the pump light 30 by the inner core 14. On skilled in the art knows how to accomplish this once instructed on the reasons for so doing in the text of this specification. An example of such is fiber with a rectangular shaped outer core 12 with a centrally disposed inner core.
Of course, if one has a fiber geometry which gives rise to modes disposed about the fiber's periphery (as is frequently the case with cylindrical fibers), one could effect spatial overlap by simply placing the inner core nearer the fiber's periphery.
With reference to FIG 6, a pair of lasers 16, 16' are disposed on opposite sides of fiber 19 so as to direct light beams 30, 30' to groove 18 from opposite directions along the length of fiber 19. To accomplish this face 60 is preferably disposed at about 45 ° to each of beams 30, 30'. Face 62 is preferably disposed at about 45° to face 60 (90° to direction 64) so that the angle at which beam 30' is incident on face 62 is as close to 90° as possible, to ensure that little of beam 30 is reflected from face 62.
Referring now to FlG 7. which illustrates one embodiment in which multiple grooves 18 are appropriately spaced along fiber 19 to couple light from multiple lasers 16 into fiber outer core 12. This embodiment of the side pumping technique can be used to increase the total pump power in fiber 19 and scale up the fiber laser output or fiber amplifier saturation power. For a 4-level atomic transition, the spacing of grooves 18 is such that almost all of the pump light injected from one groove 18 is absorbed by the gain medium before it reaches the ' adjacent groove 18'. For exponentially decaying pump light intensity, characterized by an absorption coefficient a, this corresponds to a spacing of approximately 2/a.
For example, in a typical Nd doped or a 3-level Er/Yb co-doped fiber, the absorption lengths are in the range of 1-10 m, while passive transmission losses for the single mode guided light are few dB/km. Multiple pump diodes 16 are multiplexed along fiber 19 with active fiber lengths of 10-100 m. in the case of a 3-level atomic transition, such as that occurring in the Er /Yb doped fiber, the pump intensity must be of sufficient magnitude to achieve gain or transparency everywhere, including regions of low pump power. fncompiete absorption of the pump power injected by one groove 18 results in coupling a portion of the residual pump out of fiber 19 by adjacent groove 18', causing a small drop in overall laser efficiency. This effect is somewhat reduced by the fact that pump _ 7 _ intensities from two grooves overlap, resulting in a more uniform pump distribution than would be the case for end-fire pumping from a single fiber facet.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
r
Referring to FiG 4, and once again to FIG 3, and assuming, for example, a typical emission aperture of 100,um for a 1.0-2.0w broad area laser diode 16, the output light cone in the junction plane diverges to a width of 1 l2,um at the opposite side of fiber 19 cross section. For a 105~rm wide groove 18, substantially all of pump fight 30 would therefore be intercepted and coupled into fiber 19.
Fibers with large outer core diameters can be used to allow larger groove width.
Of course, lenses could be placed, if one desired, in between laser diode 16 and fiber 19 to decrease the beam divergence or to project a reduced image of the laser emission aperture on the groove. Laser 16 can also be oriented as shown in FIG
3, or rotated by 90 °, so that the emitting area is parallel to the apex of groove 18.
Referring now to FIG. 5, similar considerations to those of the above example apply in the plane perpendicular to the junction 20 (i.e. the plane perpendicular to the page containing FIG 5), where the laser diode emission area 21 is approximately l,um, and the pump light 30 diverges much faster than in FIG 3, with a typical divergence angle of 40° in air or 25° in glass.
With laser diode 16 placed in proximity to fiber wall 10, the emission spreads out to approximately 50~rm after propagation of a distance of one fiber diameter. Since the total length of groove 18 would typically be 100,um at the apex, the beam spread in this plane is sufficiently small so that substantially all of pump light 30 is intercepted by groove facets 22.
The cylindrical fiber to air interface 99 provides a tensing effect which can be used to collimate or focus light 30 propagating in the plane perpendicular to the Laser diode function. For example, for a glass fiber with a refractive index of 1.5, the effective cylindrical (ens focal length is given by 1/3 R, where R is the fiber radius. For a 125,um fiber OD, this corresponds to a focal length of 2lErm.
Collimation is achieved with the laser diode facet placed approximately 2l~.rm from the fiber side-wall 10, whereas greater distances result in a converging beam.
In an embodiment which employs a doped fiber inner core pump light 30 is injected into outer core 12 where it propagates until it is absorbed by the dopant in fiber inner core 14. More efficient absorption of pump light 30 is made possible via the use of special outer core 12 shapes and off center inner core 14 placement which assure that light injected into the outer core waveguide 12 will spatially _ 6 _ overlap with fiber inner core 14 and insure absorption of the pump light 30 by the inner core 14. On skilled in the art knows how to accomplish this once instructed on the reasons for so doing in the text of this specification. An example of such is fiber with a rectangular shaped outer core 12 with a centrally disposed inner core.
Of course, if one has a fiber geometry which gives rise to modes disposed about the fiber's periphery (as is frequently the case with cylindrical fibers), one could effect spatial overlap by simply placing the inner core nearer the fiber's periphery.
With reference to FIG 6, a pair of lasers 16, 16' are disposed on opposite sides of fiber 19 so as to direct light beams 30, 30' to groove 18 from opposite directions along the length of fiber 19. To accomplish this face 60 is preferably disposed at about 45 ° to each of beams 30, 30'. Face 62 is preferably disposed at about 45° to face 60 (90° to direction 64) so that the angle at which beam 30' is incident on face 62 is as close to 90° as possible, to ensure that little of beam 30 is reflected from face 62.
Referring now to FlG 7. which illustrates one embodiment in which multiple grooves 18 are appropriately spaced along fiber 19 to couple light from multiple lasers 16 into fiber outer core 12. This embodiment of the side pumping technique can be used to increase the total pump power in fiber 19 and scale up the fiber laser output or fiber amplifier saturation power. For a 4-level atomic transition, the spacing of grooves 18 is such that almost all of the pump light injected from one groove 18 is absorbed by the gain medium before it reaches the ' adjacent groove 18'. For exponentially decaying pump light intensity, characterized by an absorption coefficient a, this corresponds to a spacing of approximately 2/a.
For example, in a typical Nd doped or a 3-level Er/Yb co-doped fiber, the absorption lengths are in the range of 1-10 m, while passive transmission losses for the single mode guided light are few dB/km. Multiple pump diodes 16 are multiplexed along fiber 19 with active fiber lengths of 10-100 m. in the case of a 3-level atomic transition, such as that occurring in the Er /Yb doped fiber, the pump intensity must be of sufficient magnitude to achieve gain or transparency everywhere, including regions of low pump power. fncompiete absorption of the pump power injected by one groove 18 results in coupling a portion of the residual pump out of fiber 19 by adjacent groove 18', causing a small drop in overall laser efficiency. This effect is somewhat reduced by the fact that pump _ 7 _ intensities from two grooves overlap, resulting in a more uniform pump distribution than would be the case for end-fire pumping from a single fiber facet.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
r
Claims (22)
1. ~An optical fiber suitable for amplification of light, comprising:
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency, into said outer core, wherein said light that passes through said cladding is reflected by said groove surface and propagates down said outer core facilitating absorption of said light into said inner core.
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency, into said outer core, wherein said light that passes through said cladding is reflected by said groove surface and propagates down said outer core facilitating absorption of said light into said inner core.
2. ~The fiber of claim 1, wherein said groove comprises a pair of faces disposed generally opposite of one another along the length of said fiber, said faces intersecting one another at about a 45° angle.
3. ~The fiber of claim 2, wherein one of said faces is disposed at about 45° to said length of said fiber, and the other of said faces is disposed at about 90° to said length.
4. ~The fiber of claim 3, wherein said fiber further comprises a reflective coating disposed on said one of said faces.
5. ~The fiber of claim 1, wherein said fiber comprises at least one additional groove, said at least one additional groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said core.
6. ~The optical fiber of claim 1 further comprising at least one groove extending through said cladding into said outer core, said at least one groove having at least one surface disposed effective to specularly reflect light from preselected directions and of preselected frequencies, into said outer core facilitating absorption of said light into said inner core.
7. ~A method of injecting light of a preselected frequency into an optical fiber which comprises a cladding, an inner core and an outer core, said inner core being doped with a preselected gain material which is suitable for light amplifi-cation, said method comprising:
providing a groove in said fiber, said groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected fre-quency, into said outer core; and directing light of said preselected frequency onto said groove, wherein said light passes through said cladding, is reflected by said groove surface and propagates down said outer core.
providing a groove in said fiber, said groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected fre-quency, into said outer core; and directing light of said preselected frequency onto said groove, wherein said light passes through said cladding, is reflected by said groove surface and propagates down said outer core.
8. ~The method of claim 7, wherein:
said inner core is disposed within said outer core, said groove extends into said outer core, and said inner core comprises an optically active pre-selected gain material which comprises a dopant; and said reflecting of said light down said outer core is effective to excite said dopant by optical coupling of said light between said inner and said outer core.
said inner core is disposed within said outer core, said groove extends into said outer core, and said inner core comprises an optically active pre-selected gain material which comprises a dopant; and said reflecting of said light down said outer core is effective to excite said dopant by optical coupling of said light between said inner and said outer core.
9. ~The method of claim 7, wherein said fiber comprises a plurality of fibers.
10. ~An optical fiber suitable for amplification of light, comprising:
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to provide total internal reflection of injected light from a preselected direction and of a preselected frequency into said outer core, wherein said light that passes through said cladding is reflected by said groove surface and propagates down said outer core, facilitating absorption of said light into said inner core.
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to provide total internal reflection of injected light from a preselected direction and of a preselected frequency into said outer core, wherein said light that passes through said cladding is reflected by said groove surface and propagates down said outer core, facilitating absorption of said light into said inner core.
11. ~The fiber of claim 10, wherein said groove comprises a pair of faces disposed generally opposite of one another along the length of said fiber, said faces intersecting one another at about a 90° angle.
12. ~The fiber of claim 11, wherein one of said faces is disposed at about 45°
to said length of said fiber, and the other of said faces is disposed at about 90°
to said length.
to said length of said fiber, and the other of said faces is disposed at about 90°
to said length.
13. ~The fiber of claim 12, wherein said fiber further comprises a reflective coating disposed on at least one of said faces.
14. ~The fiber of claim 10, wherein said groove comprises a pair of faces disposed generally opposite of one another along the length of said fiber, said faces intersecting one another at about a 90° angle.
15. ~The fiber of claim 14, wherein one of said faces is disposed at about 45°
to said length of said fiber, and the other of said faces is disposed at about 90°
relative to said length.
to said length of said fiber, and the other of said faces is disposed at about 90°
relative to said length.
16. ~The fiber of claim 15, wherein said fiber further comprises a reflective coating disposed on at least one of said faces.
-11-~
-11-~
17. ~The fiber of claim 10, wherein said fiber further comprises at least one additional groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said inner core.
18. ~A method of injecting light of a preselected frequency into an optical fiber, said method comprising:
providing a groove in said fiber, said groove extending through a cladding into an outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said outer core, said fiber having an inner core disposed within said outer core, said inner core comprising an optically active gain material suitable for light amplification; and directing light of said preselected frequency onto said groove from said preselected direction, wherein said directing of said light is effective to excite said gain material by optical overlap of said light in said outer core with said inner core, said light in said inner core being amplified.
providing a groove in said fiber, said groove extending through a cladding into an outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said outer core, said fiber having an inner core disposed within said outer core, said inner core comprising an optically active gain material suitable for light amplification; and directing light of said preselected frequency onto said groove from said preselected direction, wherein said directing of said light is effective to excite said gain material by optical overlap of said light in said outer core with said inner core, said light in said inner core being amplified.
19. ~The method of claim 18, wherein:
said inner core is disposed within said outer core, said groove extends into said outer core, and said inner core comprises an optically active pre-~
selected gain material comprising a dopant and suitable for light amplification;
and said directing of said light is effective to excite said dopant by optical overlap of said light in said outer core, said light in said inner core being amplified.
said inner core is disposed within said outer core, said groove extends into said outer core, and said inner core comprises an optically active pre-~
selected gain material comprising a dopant and suitable for light amplification;
and said directing of said light is effective to excite said dopant by optical overlap of said light in said outer core, said light in said inner core being amplified.
20. ~An optical fiber amplifier comprising an optical fiber which comprises:
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said outer core, facilitating absorption of said light into said inner core, wherein said light absorbed into said inner core is amplified and propagates unperturbed through said inner core.
a cladding;
a core disposed within said cladding, said core comprising an outer core and an inner core, said inner core being disposed within said outer core, said inner core being doped with a preselected gain material suitable for light amplification; and a groove extending through said cladding into said outer core, said groove having a surface disposed effective to specularly reflect light from a preselected direction and of a preselected frequency into said outer core, facilitating absorption of said light into said inner core, wherein said light absorbed into said inner core is amplified and propagates unperturbed through said inner core.
21. The optical fiber amplifier of claim 20, wherein said preselected direction comprises a plurality of preselected directions and said preselected frequency comprises a plurality of preselected frequencies.
22. The optical fiber amplifier of claim 20, wherein said fiber comprises a plurality of fibers.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/568,859 | 1995-12-07 | ||
| US08/568,859 US5854865A (en) | 1995-12-07 | 1995-12-07 | Method and apparatus for side pumping an optical fiber |
| PCT/US1996/019452 WO1997021124A1 (en) | 1995-12-07 | 1996-12-09 | Method and apparatus for side pumping an optical fiber |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2239619A1 CA2239619A1 (en) | 1997-06-12 |
| CA2239619C true CA2239619C (en) | 2006-08-01 |
Family
ID=36764315
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002239619A Expired - Fee Related CA2239619C (en) | 1995-12-07 | 1996-12-09 | Method and apparatus for side pumping an optical fiber |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2239619C (en) |
-
1996
- 1996-12-09 CA CA002239619A patent/CA2239619C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2239619A1 (en) | 1997-06-12 |
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