WO2000041279A1 - A method and apparatus for pumping optical fibers - Google Patents

A method and apparatus for pumping optical fibers Download PDF

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Publication number
WO2000041279A1
WO2000041279A1 PCT/US2000/000258 US0000258W WO0041279A1 WO 2000041279 A1 WO2000041279 A1 WO 2000041279A1 US 0000258 W US0000258 W US 0000258W WO 0041279 A1 WO0041279 A1 WO 0041279A1
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WO
WIPO (PCT)
Prior art keywords
optical
optical fiber
fiber
annular wall
pump
Prior art date
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PCT/US2000/000258
Other languages
French (fr)
Inventor
Stanislav Igor Ionov
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Hrl Laboratories, Llc
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Priority to US22669199A priority Critical
Priority to US09/226,691 priority
Application filed by Hrl Laboratories, Llc filed Critical Hrl Laboratories, Llc
Publication of WO2000041279A1 publication Critical patent/WO2000041279A1/en

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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06Construction or shape of active medium
    • H01S3/063Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067Fibre lasers
    • H01S3/06704Housings; Packages
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09Processes or apparatus for excitation, e.g. pumping
    • H01S3/091Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09Processes or apparatus for excitation, e.g. pumping
    • H01S3/091Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/094003Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
    • H01S3/094019Side 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

Abstract

A method and apparatus to couple optical power into an optical fiber. A helically wound optical fiber (30) is provided for carrying optical information signals. The helically wound optical fiber includes: a core, the core having dopants to amplify the optical information signals and having an ncore refractive index; an input fiber portion for inputting the optical information signals to the helically wound optical fiber; an output fiber portion for outputting the optical information signals from the helically wound optical fiber, and cladding surrounding the core, the cladding having an n¿cladding? refractive index less than the ncore refractive index. An optical resonator chamber (25) is provided for housing the helically wound optical fiber within the optical resonator chamber wherein the input fiber portion and the output fiber portion are located external to the optical resonator chamber. Optical pump power is transmitted at an optical pump wavelength into optical resonator chamber externally therefrom at one or more window locations to further amplify the optical information signals. The optical resonator chamber can also include a medium enclosed therewithin, the medium having a refractive index matching the n¿cladding? refractive index.

Description

A METHOD AND APPARATUS FOR PUMPING OPTICAL FIBERS

FIELD OF THE INVENTION

This invention relates to the field of fiber optics, and, more particularly, to the field of pumping optical fibers to increase the output power of fiber optic based devices.

BACKGROUND

In the field of fiber optic systems, fiber optic guides transmit light power from a light source to a utilization device. Fiber optic guides ("fibers") typically have at least two essential parts. One part is the core where light propagates. The other part is cladding surrounding the core which creates conditions whereby the light propagates only in the core. These fibers are capable of transmitting single mode optical signals in the core without amplification, and produce a small amount of background loss. These can be considered "regular" fibers.

Referring to Fig. 1, light source 10 transmits light signal Ps at wavelength λs through fiber 12 to utilization device 14. Couplings between light source 10, utilization device 14 and fiber 12 are well known in the art and are not shown. Fiber 12 includes core 16, cladding 18 and protective covering 20. Light source 10 typically provides the optical signals carrying information which propagates in the core. This fiber is considered a single-clad fiber. There are also double-clad fibers. A double-clad fiber has a core, a first cladding, a second cladding and the protective coating. In the double-clad case, while a single-mode signal can propagate in the core, a multi- mode signal can be coupled into the inner cladding, whereupon the inner cladding acts as a core for the second cladding. As such, the double-clad fiber can be useful when coupling power into a fiber, as described in more detail below.

Those skilled in the art can appreciate that there are many applications requiring the generation and amplification of optical signals. For example, fiber optics systems used in a large variety of commercial and military applications such as in telecommunications, inter-satellite optical communications, and for missile radar tracking systems require the generation and amplification of optical signals.

"Special" fibers, i.e., those that have their cores doped with rare earth atoms, for example., Erbium (Er), Ytterbium (Yb), Erbium- Ytterbium (ErYb), Neodium (Nd), Tulium (Tu), etc., are utilized in such applications requiring the generation and amplification of optical signals. When subjected to optical signals (typically 800 - 1400nm wavelength, depending on the dopants) these special fibers have their rare earth atoms excited to their upper lasing level. These excited atoms form a gain medium which is capable of amplifying optical signals. The special fibers providing the gain medium may be easily spliced to regular fibers to provide fiber systems with minimal losses in power.

A typical fiber amplifier has a source of optical signal coupled to a rare earth doped "special" fiber gain medium. Coupled also to the gain medium is an optical "pump" source to input optical power into the gain medium and a utilization device to receive an amplified optical signal as output from the gain medium. Referring to Fig. 2, in a typical fiber optic amplification system gain medium 22 is coupled with fiber 12 to permit light signal Ps at wavelength λs to be amplified when combined with pump light signal PP at wavelength λP to provide amplified signal APS at wavelength λs for use by utilization device 14. Those skilled in the art can appreciate that the more pump power that is coupled into the rare earth doped fiber, the more optical signal output is provided by the gain medium.

There are various ways to couple pump power into the rare earth doped special fiber. In a single- mode low power pump source where the special fiber has a core and a single cladding, direct end pumping, or a Wavelength Division Multiplexer (WDM) which combines the pump and optical signal, can be utilized. One form of gain medium 22 is described in PCT Publication WO 96/20519, entitled "A Coupling Arrangement Between A Multimode Light Source and An Optical Fiber Through An Intermediate Optical Fiber Length", wherein a progressively tapered fiber portion is fused to the inner cladding of a double clad fiber carrying an optical information signal in its core. This fused system is shown schematically in Fig. 3 of the present application. However, while the spliced coupling allows the ability to have multiple locations available to input the pump power into a single fiber and achieve power scalability with unrestricted access to both fiber ends, such fused fiber couplers, however, are somewhat difficult to manufacture.

Also, it is generally known to those skilled in the art that it is somewhat difficult to manufacture a powerful semiconductor laser at the lowest transverse mode that can be coupled into the fiber core, typically 100 - 200 mW being the maximum power levels. Unfortunately, there are applications which require much higher levels of pumping, namely, at the multi-watt level, such as for space communication applications. As such, efficient optical pumping of a single-mode fiber laser or an amplifier presents a serious challenge when high output powers are required. While end pumping has also been utilized for such pumping, it requires high-brightness-pump sources, limits scalability to higher powers and restricts access to fiber ends. In such systems, fiber lasers and amplifiers are end-pumped by single-mode diode lasers whose output is coupled directly into the core of the fiber. The maximum output power achieved with such pumping scheme is currently limited to 100 mW. On the other hand, higher output powers have been achieved with double-cladding fibers. Tens of watts of output power have been demonstrated at specific wavelengths. However, the maximum output power of such devices is limited by the brightness of available pump diodes. Further, the other drawbacks of such configurations include limited accessibility of fiber ends and difficulties in scaling to higher powers.

Therefore, there exists a need for an effective, easy to manufacture method and apparatus for use in pumping fiber lasers and amplifiers, namely, how to put more "pump" into the fiber that will translate into higher output of the fiber. The present invention and it's embodiments as described herein provide a solution which has unrestricted access to both fiber ends, enables scalability to high output powers and can be put together easily with relatively minor manufacturing expense.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus to couple optical power into a single fiber from the side and achieves an efficient and scalable fiber pumping with an unrestricted access to both fiber ends.

In accordance with the present invention a helically wound optical fiber is provided for carrying optical information signals. The helically wound optical fiber includes: a core, the core having dopants to amplify the optical information signals; an input fiber portion for inputting the optical information signals to the helically wound optical fiber; an output fiber portion for outputting the optical information signals from the helically wound optical fiber; and cladding surrounding the core, the cladding having an ncladdιn„ refraction index less than the ncore refraction index. The helically wound optical fiber is housed within the optical resonator chamber, wherein the input fiber portion and the output fiber portion are located external to the resonator chamber. Optical pump power is transmitted at an optical pump wavelength into the resonator chamber at one or more window locations to further amplify the optical information signals propagating through the fiber core. The optical resonator chamber can also include a medium enclosed therewithin, the medium having a refractive index matching the ndaddιng refractive index.

In accordance with a preferred embodiment of the present invention a circularly wound helical optical fiber is provided for carrying the optical information signals. The circularly wound helical optical fiber includes: a core, the core having dopants to amplify the optical information signals and having an ncore refractive index; an input fiber portion for inputting the optical information signals to the helically wound optical fiber; an output fiber portion for outputting the optical information signals from the helically wound optical fiber; and cladding surrounding the core. An optical resonator chamber is provided containing a non-absorbing fluid medium enclosed therewithin, the non-absorbing fluid medium having a refractive index matching the n addιn„ refractive index. The circularly wound helical optical fiber is housed within the non-absorbing fluid medium, wherein the input fiber portion and the output fiber portion are located external to the resonator chamber. The resonator chamber includes: an inner annular wall; an outer annular wall concentric with the inner annular wall. The volume between the inner annular wall and the outer annular wall provides a gap region. The resonator chamber has a bottom cover and a top cover. The inner annular wall, the outer annular wall, the bottom cover and the top cover enclose the non-absorbing fluid medium within the gap region. The circularly wound helical optical fiber is concentrically positioned within the gap. Optical pump power is transmitted at an optical pump wavelength into the medium externally from the resonator chamber at one or more window locations to further amplify the optical information signals. The one or more window locations are situated in the outer annular wall. Pump fibers are provided at each location to transmit the optical pump power into the medium.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows in schematic form a partial cross-section of an optical fiber, light source and utilization device of the prior art.

Fig. 2. shows in schematic form a fiber optics system of the prior art wherein a fiber, light source and utilization device has a gain medium employing an optical pump.

Fig. 3 depicts in schematic form a tapered pump fiber connection with an information carrying fiber.

Fig. 4 shows in partial section and cutaway perspective schematic form a resonator system in accordance with an embodiment of the present invention.

Fig. 5 shows in partial top section and schematic form the outer annular cylinder, the inner annular cylinder and pump fibers of a resonator embodiment of the present invention. Fig. 6 shows in partial front section and schematic form a resonator system in accordance with an embodiment of the present invention.

Fig. 7 depicts a partial perspective view in schematic form of the fiber column and outer annular cylinder of an embodiment of the present invention.

Fig. 8 shows in partial top section and schematic form an alternative window arrangement in the resonator wall for launching pump power directly into the resonator without involving pump- guiding fibers.

Fig. 9 depicts in schematic form a top plan view of an alternative rectangular resonator chamber embodiment.

DETAILED DESCRIPTION

A preferred embodiment of the present invention utilizes a guiding "donut-shaped" resonator for pumping optical fibers. The signal carrying fiber is coiled inside the guiding resonator while optical pump radiation is launched into the resonator via a number of ports. The pumping configuration in accordance with the present invention ensures good overlap between the pump beam and the dopants in the fiber core, resulting in efficient utilization of the available pump power.

The optical resonator in a preferred embodiment utilizes two concentric annular cylinders with a coiled optical fiber situated within a gap between the outer surface of the inner cylinder and the inner surface of the outer cylinder. The fiber is stripped of its protective coating, leaving its cladding and core, and is concentrically coiled inside the gap. The core has a refractive index ncore. Surrounding the core is a cladding having a refractive index nd.lddιπg The refractive index nculc is greater than refractive index nchlddina Preferably, the space between the signal carrying fiber and the resonator walls is filled with a non-absorbing material with the same refractive index as that of the fiber cladding (e.g., such as a liquid having a refractive index comparable to ncl.,ddin , which is generally referred to as an index-matching fluid. The pump action is launched from the sides of the resonator via small windows so that the pump light is guided along the signal carrying fiber.

Referring collectively to Figs. 4 to 7, there is shown a preferred embodiment of resonator 25, wherein rectangular fiber 30 is wound in one cylindrical column inside the resonator. The cylindrical shape of the proposed resonator ensures a good overlap between the pump beam and the fiber core, resulting in an efficient utilization of the available pump power. (Please note that the proportions of items depicted are not to scale and that relative dimensions, e.g, gap 32, have been depicted as such merely for clarity of component purposes.)

In Fig. 4 there is shown a cutaway partial section perspective view of outer annular cylinder housing 26, including a non-section view of inner cylinder housing 28 and non-section view of coiled rectangular fiber 30 wound in gap 32 between inner cylinder surface 34 of outer cylinder housing 26 and outer cylinder surface 36 of inner cylinder housing 28. Fiber 30 has an input port at location 31 receptive of light signal Ps at wavelength λs and an output port 33 outputting amplified light signal APS at wavelength λs . hi the embodiment depicted in Fig. 4 the input port is at the lower portion of the resonator, while the output port is at the upper portion of the resonator. However, it can be appreciated that the input port could be at the upper portion of the resonator while the output port is at the lower portion of the resonator. Base 40 and cover 42, shown partially cut away in Fig. 4, fully enclose the respective lower and upper surfaces of outer cylinder housing 26, inner cylinder housing 28 and gap 32 as can be best seen in Fig. 6. Base 40 and cover 42 each have respective inner surfaces 41, 43.

The resonator typically would have one of two approaches to allow propagation of light pumped into the resonator. One approach would involve reflective (e.g. mirror-like) surfaces of the walls of the resonator. When the surfaces (including coatings on the walls) are mirror-like, light propagates by bouncing along the mirror walls. The other approach would involve having interfaces with different indexes of refractive to provide propagation by total internal reflection (TIR). When launching pump light into the resonator through a wall opening, wherein the walls of the resonator have indexes of refractive less than the medium within the walls, pump light would propagate within the resonator by TIR . In either case, as the pump light propagates within the resonator, a portion of the pump light can be coupled into the core. Pump radiation can be guided into the resonator by special pump fibers that are molded into the resonator surfaces as shown in Figs. 5 and 7, or by focusing the output of pump diode lasers directly into special windoes cut through the resonator surfaces, as shown in Fig. 8.

As such, referring back to Figs. 4 - 7, inner surface 34, outer surface 36, base inner surface 41 and cover inner surface 43 are considered collectively to be the resonator walls which help provide pump guiding. When using the reflective surfaces approach high-reflection (HR) coating may be deposited on the resonator walls to provide the mirror-like surfaces. Alternatively, when using the TIR approach inner cylinder 28, outer cylinder 26, base 40 and cover 42 could be made of MgF2, or covered by a transparent optical material whose refractive index is lower than that of fiber cladding 18 and of index-matching fluid 44, thereby providing guiding by TIR.

Pump fibers 38 can be molded into resonator 25 at any number of locations to launch pump light PPat wavelength λPinto the resonator. As an example, four pump fibers are shown in Figs, 4 and 5. However, in a preferred embodiment multiple pump fibers are located symmetrically in a column along the length of inner cylinder surface 34, as shown in Fig. 7.

In the case of an HR-coated resonator, pump light PPat wavelength λPis launched through small openings or windows 46 in the HR coating. The ends of the pump fibers may be polished flush with the resonator surface for reducing the unused volume, as shown in Fig. 5, or left dangling inside the gap to minimize cost. Since any opening used for launching pump power can reduce the lifetime of pump radiation in the resonator, therefore, the total area of the windows for the pump fibers is minimized for optimizing the efficiency of the device. The total area of the opening(s) for pump launching would be determined such that pump scattering losses on the openings per round-trip are below the pump power absorbed by the dopant atoms

An alternative way to launch pump power into the resonator via pump fibers is to focus the pump beam, such as from a diode laser focused onto a small window into the resonator Such windows may be made by removing HR coatings from small areas on the HR-coated reflective walls In the case of TIR guiding, small notches can be cut on the inner (and, maybe outer) walls Such a notch window is depicted in Fig 8 The notches enable the light to be efficiently launched at a wall that is perpendicular to the pump beam to provide optical pump power along the helically wound optical fiber

As a practical example of the preferred embodiment of the resonator consider a high-power Er/Yb amplifier A high power 1 55 μm amplifier is made of 75 m of single mode Er/Yb-doped fiber The fiber may be cut into two or three pieces with Faraday isolators spliced between them In this case, the isolators are kept outside of the resonator attached to the Er/Yb fiber by un-doped single-mode fiber The diameter of the fiber core and cladding are 10 μm and 70 μm, respectively, and pump absorption length in the core is 10= 0 7 cm at 980 nm Fiber 30 would then be coiled and molded together by heating or by filling the voids with an index-matching compound The molded coil is polished, if necessary, and coated with a low index polymer, e g , Teflon AF 1600 from DuPont

Resonator outer cylinder housing 26 has an inner surface 34 of 31 cm diameter and small numeπcal aperture NA - 0 2 Fiber 30 is wound in one column, as shown in Fig 6, making ~ 75 turns (Note only a portion of the turns are shown for clarity) In this configuration, the height of the column is 75x70 μm = 5 25 mm and the width of the gap approaches the fiber cross-section width, l e , to 70 μm Pump fibers 38 (42 total in the preferred embodiment) are arranged in a column, as shown in Fig 7, delivering up to PP = 126 W of pump power The core and cladding diameters of the pump fibers are 100 μm and 125 μm, respectively, have a numerical aperture (NA) = 0 2, and up to 3 W of 980 nm pump radiation is delivered by each fiber The pump absorption length in the resonator is L0 = l0xAres/75Aco ~ 43 cm, where Ares and Aco are the cross sectional areas of the resonator and fiber coie, lespectively Under these conditions, the amount of pump powei absorbed per round tup is Pp (l-exp(-πD/Lo) = 0 9 PP = 113 W Assuming 40% optical-to-optical conversion efficiency, 45 W of output power is anticipated from the amplifier at 1.55 um. This number is considerably higher than that achieved cuirently (~ 10 W). The resonator housings aie constiucted from the fiber cladding material. Low-index polymer is applied around the molded cores, utilizing TIR guiding of pump power within the resonator. No index-matching fluid is needed in this case.

In the above example, the small NA of the lesonatoi lestncts the maximum number of pump fibers to one column only. This lestnction denves horn a consideiable loss oi the un-absoibed pump radiation on the fibei launch ports, which aie polished flush with the resonator suiface at a sharp angle. Pump launching at high angles is possible into lesonators with high NA. This will reduce the pump absorption length, allowing for seveial launch ports along the perimeter. Up to 4 W of pump radiation can be launched thiough a 10 μm x 500 μm window. The short side of the window is oriented along the dnection of pump propagation for minimizing resonator loss. Pump losses on such windows typically do not exceed a few percent, permitting a large number of windows to be situated along the perimeter.

It should be noted that in the described embodiment of the present invention the fiber's protective coating is removed to prevent pump power scattering and absorption by the coating material and to minimize the volume of the lesonatoi The coie and first cladding are situated in the resonatoi, whose walls act as a cladding foi the entne tibei The lesonator piefeiably has minimum excess volume, i.e., it is filled with coiled fiber to the utmost extent, to allow maximum absorption by the doped atoms in the core and minimum losses. As a lesult of efficient pump powei absorption between the successive launch windows, less pump power is lost by scattering while propagating along the next to launch window.

It should be further noted that when the fibei is stripped of its protective coating it is very fi agile and can be cracked easily. It is therefore preferable to wind the fiber in one column to avoid breakage. Unnecessary excess housing/fiber volume can be eliminated by stacking the windings one above the other.

The present invention has been described in its preferred and alternative embodiments. It is clear, however, that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art. Thus, it should be understood that various changes in form and usage of the present invention may be made without departing from the spirit and scope of this invention.

For example, the resonator chamber, rather than having a gap region formed by two concentric walls, can be a rectangular, cylindrical or the like volume, with a medium enclosed therewithin and the optical fiber randomly coiled within the resonator chamber. Fig. 9 depicts a top plan view of such an alternative rectangular resonator chamber. Chamber 60 has pump windows 62 situated in the chamber walls. Pump fibers 64 input optical pump power PPat wavelength λP . Optical fiber 66 is coiled within the medium and has an input portion 68 and an output portion 70 external to the chamber. Information carrying optical input signal Ps at wavelength λs is inputted at input portion 68 and amplified information carrying optical input signal APS at wavelength λs is outputted at output portion 70. The chamber inner walls have reflective surfaces such that input optical pump power PP at wavelength λP is reflected, as indicated by direction arrows 72. The resonator depicted in Fig. 9 operates in the same manner as the donut-shaped resonator described in the preferred embodiment. Pump radiation enters the optical resonator through the series of windows. A fraction of the pump radiation is absorbed in the first pass by the fiber coils. The remaining pump power is reflected by the walls of the resonator, and a part of it is absorbed by the fiber in the second pass. After a number of passes, the pump power is either absorbed by the fiber or lost on the imperfections of the optical resonator.

Various shapes of fiber can be utilized for both the coiled fiber and the pump fibers, namely circular, rectangular, elliptical, etc. Other arrangements of the fiber inside a donut shape resonator are possible, e.g. fiber wound in elliptical loops, helical loops with varying orbit lengths along the helical translation line. Additional improvements may be gained by fusing the wound fiber so that the softened fiber cladding fills all the voids between the fiber and the resonator walls. The output power can be scaled by increasing the number of optical pump sources, e.g., the pump semiconductors and corresponding access windows.

Therefore, in accordance with the present invention, there is provided an effective method and apparatus for use in pumping fiber lasers and amplifiers, enabling more pump to be put into the information carrying fiber that will translate into higher output of the fiber, while having unrestricted access to both fiber ends, enables scalability to high output powers and can be put together easily with relatively minor manufacturing expense.

Claims

1. A method of pumping an optical fiber carrying optical information signals comprising the steps of:
providing a helically wound optical fiber for carrying the optical information signals, the helically wound optical fiber having:
a core, the core having dopants to amplify the optical information signals and having an ncore refractive index;
an input fiber portion for inputting the optical information signals to the helically wound optical fiber,
an output fiber portion for outputting the optical information signals from t h e helically wound optical fiber, and
cladding surrounding the core, the cladding having an nC|.,ϋdill„ refractive index less than the ncore refractive index;
providing an optical resonator chamber for housing the helically wound optical fiber within the optical resonator chamber, wherein the input fiber portion and the output fiber portion are located external to the optical resonator chamber; and
transmitting optical pump power at an optical pump wavelength into the optical resonator chamber at one or more window locations to further amplify the optical information signals.
2. The method for pumping an optical fiber of Claim 1, wherein the step of providing an optical resonator chamber for housing the helically wound optical fiber includes the steps of: providing an optical resonator chamber which has:
an inner annular wall,
an outer annular wall concentric with the inner annular wall, the volume between the inner annular wall and the outer annular wall providing a gap region,
a bottom cover and a top cover, and
the inner annular wall, the outer annular wall, the bottom cover and the top cover enclosing the gap region; and
concentrically positioning the helically wound optical fiber within the gap region.
3. The method for pumping an optical fiber of Claim 1 , wherein the helically wound optical fiber is circularly wound.
4. The method for pumping an optical fiber of Claim 3, wherein the helically wound optical fiber is circularly wound with windings stacked one above the other.
5. The method for pumping an optical fiber of Claim 2, wherein the inner annular wall, the outer annular wall, the bottom cover and the top cover have reflective surfaces.
6. The method for pumping an optical fiber of Claim 2, wherein the inner annular wall, the outer annular wall, the bottom cover and the top cover are of a material having a refractive index less than the ncladdιng refractive index to provide total internal reflection.
7. The method for pumping an optical fiber of Claim 2, wherein the width of the gap region approaches the cross-section width of the helically wound optical fiber.
8. The method for pumping an optical fiber of Claim 2. wherein the step of transmitting optical pump power includes the steps of:
situating the one or more window locations in the outer annular wall; and
providing pump means to transmit the optical pump power into the gap region.
9. The method for pumping an optical fiber of Claim 8, wherein the pump means include a pump fiber located at each window location.
10. The method for pumping an optical fiber of Claim 9, wherein the pump fibers are located such that each pump fiber has a pump fiber end which interfaces with the gap region.
11. The method for pumping an optical fiber of Claim 10, wherein each pump fiber end is polished flush with the outer annular wall.
12. The method for pumping an optical fiber of Claim 6, wherein the outer annular walls have notches at the window location for providing optical pump power along the helically wound optical fiber.
13. The method for pumping an optical fiber of Claim 1, wherein the optical resonator chamber contains a medium enclosed therewithin, the medium having a refractive index matching the ncl ddιn„ refractive index.
14. The method for pumping an optical fiber of Claim 13, wherein the medium is a non- absorbing fluid.
15. A method of pumping an optical fiber carrying optical information signals, comprising the steps of:
providing a circularly wound helical optical fiber for carrying the optical information signals, the circularly wound helical optical fiber having:
a core, the core having dopants to amplify the optical information signals and having an ncore refractive index;,
an input fiber portion for inputting the optical information signals to the helically wound optical fiber,
an output fiber portion for outputting the optical information signals from t h e helically wound optical fiber, and
cladding surrounding the core, the cladding having an nC|.lddιn„ refractive index less than the ncore refractive index;
providing an optical resonator chamber for housing the circularly wound helical optical fiber within the optical resonator chamber, the input fiber portion and the output fiber portion being located external to the optical resonator chamber, the optical resonator chamber having:
an inner annular wall and an outer annular wall concentric with the inner annular wall, the volume between the inner annular wall and the outer annular wall providing a gap region, a bottom cover and a top cover,
the inner annular wall, the outer annular wall, the bottom cover and the top cover enclosing the gap region; and
concentrically positioning the circularly wound helical optical fiber within the gap region; and
transmitting optical pump power at an optical pump wavelength into the medium externally from the optical resonator chamber at one or more window locations to further amplify the optical information signals, by situating the one or more window locations in the outer annular wall and providing pump fibers at each window location to transmit the optical pump power into the gap region.
16. The method of pumping an optical fiber carrying optical information signals of Claim 15, wherein the gap region contains a non-absorbing fluid medium enclosed therewithin, the non- absorbing fluid medium having a refractive index matching the n addmg refractive index.
17. An optical fiber pumping system comprising:
a helically wound optical fiber for carrying optical information signals, the helically wound optical fiber having:
a core, the core having dopants to amplify the optical information signals having an ncore refractive index;,
an input fiber portion for inputting the optical information signals to the helically wound optical fiber, an output fiber portion for outputting the optical information signals from t h e helically wound optical fiber, and
cladding surrounding the core, the cladding having an ndaddm„ refractive index less than the ncore refractive index;
an optical resonator chamber for housing the helically wound optical fiber within optical resonator chamber, wherein the input fiber portion and the output fiber portion are located external to the optical resonator chamber; and
optical pump power transmission means coupled with the optical resonator chamber to transmit at an optical pump wavelength optical pump power into the optical resonator chamber at one or more window locations to further amplify the optical information signals.
18. The optical fiber pumping system for pumping an optical fiber of Claim 17, wherein the optical resonator chamber includes:
an inner annular wall,
an outer annular wall concentric with the inner annular wall, the volume between the inner annular wall and the outer annular wall providing a gap region,
a bottom cover and a top cover, and
the inner annular wall, the outer annular wall, the bottom cover and the top cover enclosing the gap region,
the helically wound optical fiber being positioned concentrically within the gap region.
19. The optical fiber pumping system of Claim 17, wherein the helically wound optical fiber is circularly wound.
20. The optical fiber pumping system of Claim 18, wherein the helically wound optical fiber is circularly wound with windings stacked one above the other.
21. The optical fiber pumping system of Claim 18, wherein the inner annular wall, the outer annular wall, the bottom cover and the top cover have reflective surfaces.
22. The optical fiber pumping system of Claim 18, wherein the inner annular wall, the outer annular wall, the bottom cover and the top cover are of a material having a refractive index less than the n adding refractive index to provide total internal reflection.
23. The optical fiber pumping system of Claim 18, wherein the width of the gap region approaches the cross-section width of the helically wound optical fiber.
24. The optical fiber pumping system of Claim 18, wherein the one or more window locations are situated in the outer annular wall, each location having a pump fiber to transmit the optical pump power into the medium.
25. The optical fiber pumping system of Claim 24, wherein the pump means include a pump fiber located at each window location.
26. The optical fiber pumping system of Claim 25 wherein the pump fibers are located such that each pump fiber has a pump fiber end which interfaces with the gap region.
27. The optical fiber pumping system of Claim 26, wherein each pump fiber end is polished flush with the outer annular wall.
28. The optical fiber system of Claim 22, wherein the outer annular walls have notches at the window location for providing optical pump power along the helically wound optical fiber.
29. The optical fiber pumping system for pumping an optical fiber of Claim 17, wherein the optical resonator chamber contains a medium enclosed therewithin, the medium having a refractive index matching the ncl ddm„ refractive index.
30. The optical fiber pumping system of Claim 29, wherein the medium is a non-absorbing fluid.
31. An optical fiber pumping system, comprising:
a circularly wound helical optical fiber for carrying the optical information signals, the circularly wound helical optical fiber having:
a core, the core having dopants to amplify the optical information signals and having an ncore refractive index,
an input fiber portion for inputting the optical information signals to the helically wound optical fiber,
an output fiber portion for outputting the optical information signals from t h e helically wound optical fiber, and
cladding surrounding the core, the cladding having an n addlll„ refractive index less than the ncore refractive index;
an optical resonator chamber for housing the circularly wound helical optical fiber within the optical resonator chamber, wherein the input fiber portion and the output fiber portion are located external to the optical resonator chamber, the optical resonator chamber having:
an inner annular wall,
an outer annular wall concentric with the inner annular wall, the volume between the inner annular wall and the outer annular wall providing a gap region, and a bottom cover and a top cover, the inner annular wall, the outer annular wall, the bottom cover and the top cover having reflective surfaces, the inner annular wall, the outer annular wall, the bottom cover and the top cover enclosing the gap region;
the circularly wound helical optical fiber being concentrically positioned within the gap region; and
optical pump power transmission means coupled with the optical resonator chamber for transmitting at an optical pump wavelength into the gap region externally from the optical resonator chamber at one or more window locations to further amplify the optical information signals, the one or more window locations being situated in the outer annular wall, each location having a pump fiber to transmit the optical pump power into the gap region.
32. The optical fiber pumping system for pumping an optical fiber of Claim 31 , wherein the gap region contains a medium enclosed therewithin, the medium having a refractive index matching the n .lddιπε refractive index.
33. The optical fiber pumping system of Claim 32, wherein the medium is a non-absorbing fluid.
PCT/US2000/000258 1999-01-07 2000-01-06 A method and apparatus for pumping optical fibers WO2000041279A1 (en)

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FR2815181A1 (en) * 2000-10-06 2002-04-12 Thomson Csf Guided propagation optical amplifier having doped flat spiral waveguide circular flat disc embedded with optical pump around outer periphery
US6515794B2 (en) 2000-03-15 2003-02-04 Corning Incorporated Techniques for making an insertion loss correction in an optical fiber amplifier
EP1612895A2 (en) * 2004-07-01 2006-01-04 Toyoda Koki Kabushiki Kaisha Fiber laser oscillators

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EP0840411A2 (en) * 1996-10-31 1998-05-06 Kenichi Ueda Optical fiber laser device
EP0840410A2 (en) * 1996-10-31 1998-05-06 Kenichi Ueda Laser apparatus

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EP0840410A2 (en) * 1996-10-31 1998-05-06 Kenichi Ueda Laser apparatus

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US6515794B2 (en) 2000-03-15 2003-02-04 Corning Incorporated Techniques for making an insertion loss correction in an optical fiber amplifier
FR2815181A1 (en) * 2000-10-06 2002-04-12 Thomson Csf Guided propagation optical amplifier having doped flat spiral waveguide circular flat disc embedded with optical pump around outer periphery
EP1612895A2 (en) * 2004-07-01 2006-01-04 Toyoda Koki Kabushiki Kaisha Fiber laser oscillators
EP1612895A3 (en) * 2004-07-01 2006-04-05 Toyoda Koki Kabushiki Kaisha Fiber laser oscillators
US7457327B2 (en) 2004-07-01 2008-11-25 Jtekt Corporation Fiber laser oscillators

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