# US 5,703,987 A · Rare earth element-doped multiple-core optical fiber and optical systems using the same field of the invention

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- Number: US 5,703,987 A
- Document ID: US5703987A
- Status: Granted
- Kind: A
- Application number: 08/695,493
- Filed: 1996-08-12
- Granted: 1997-12-30
- Earliest claimed: 1996-02-22
- Assignees: Hitachi Cable, Ltd.
- Inventors: Katsuyuki Imoto
- Web page: https://patentgrep.com/patent/US5703987A

## CPC

- G02B 6/03666: {arranged - + - +}
- C03B 37/01222: {for making preforms of multiple core optical fibres (preforms of multifibres C03B37/01214)}
- G02B 6/02042: {Multicore optical fibres}
- G02B 6/03611: {Highest index adjacent to central axis region, e.g. annular core, coaxial ring, centreline depression affecting waveguiding}
- G02B 6/03644: {arranged - + -}
- G02B 6/04: formed by bundles of fibres (G02B6/24 takes precedence)
- H01S 3/06708: {Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering (optical fibres as passive waveguides G02B6/02)}
- C03B 2201/02: Pure silica glass, e.g. pure fused quartz
- C03B 2201/31: doped with germanium
- C03B 2201/34: doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers
- C03B 2201/36: doped with rare earth metals and aluminium, e.g. Er-Al co-doped
- C03B 2203/22: Radial profile of refractive index, composition or softening point
- C03B 2203/34: Plural core other than bundles, e.g. double core
- G02B 6/02004: {characterised by the core effective area or mode field radius}
- G02B 6/03694: {Multiple layers differing in properties other than the refractive index, e.g. attenuation, diffusion, stress properties}
- G02B 6/29377: {controlling dispersion around 1550 nm, i.e. S, C, L and U bands from 1460-1675 nm}
- H01S 3/06729: {Peculiar transverse fibre profile}
- H01S 3/06737: {Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- C03B: MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- 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

## Abstract

A rare earth element-doped multiple-core optical fiber 31 has a bundle of cores 32-1.about.32-7 co-doped with Er and Al, primary cladding layers 33 covering each core, and an outer cladding layer 34 covering all cores 32-1.about.32-7, wherein one core 32-1 being positioned substantially on a central axis of the outer cladding layer and surrounded by other six cores 32-2.about.32-7. A core diameter Dc of the center core 32-1 is smaller than a core diameter Do of each peripheral core 32-2.about.32-7. The power of both signal light (1.53 .mu.m.about.1.57 .mu.m wavelength bands) and pumping light (0.98 .mu.m or 1.48 .mu.m band) propagating through the center core 32-1 becomes lower and the power propagating through each core 32-1.about.32-7 is equalized, and the flatter characteristics of gain to wavelength are obtained.

## Claims

### Claim 1

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each having a refractive index of nW doped with at least one rare earth element therein; and
an outer cladding layer having a refractive index of nC (nW>nC), and covering said cores;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores having a larger core diameter than said surrounded core.

### Claim 2 (depends on 1)

A rare earth element-doped multiple-core optical fiber, according to claim 1, wherein said surrounded core is a center core, and said remaining cores are peripheral cores surrounding said center core symmetrically.

### Claim 3 (depends on 2)

A rare earth element-doped multiple-core optical fiber, according to claim 2, wherein an outer diameter of primary cladding layer of said surrounded core is the same as those of said remaining cores.

### Claim 4 (depends on 2)

A rare earth element-doped multiple-core optical fiber, according to claim 2, wherein a thickness of primary cladding layer of said surrounded core is the same as those of said remaining cores.

### Claim 5

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each having a refractive index of nW doped with at least one rare earth element and Al therein;
a plurality of primary cladding layers each having a refractive index of nP (nP<nW), and covering each of said cores; and
an outer cladding layer having a refractive index of nC (nW>nC and nP.ltoreq.nC), and covering said plurality of cores each covered by said primary cladding layer;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores having a larger core diameter than said surrounded core.

### Claim 6

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each having a refractive index of nW doped with at least one rare earth element and Al therein;
a primary cladding layer having a refractive index of nP (nP<nW), and covering said plurality of cores; and
an outer cladding layer having a refractive index of nC (nW>nC and nP.ltoreq.nC), and covering said primary cladding layer;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores having a larger core diameter than said surrounded core.

### Claim 7

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each doped with at least one rare earth element therein; and
an outer cladding layer having a lower refractive index than said cores, and covering said cores;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores having a higher refractive index than said surrounded core.

### Claim 8 (depends on 7)

A rare earth element-doped multiple-core optical fiber, according to claim 7, wherein said surrounded core is a center core, and said remaining cores are peripheral cores surrounding said center core symmetrically.

### Claim 9

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each doped with at least one rare earth element and Al therein;
a plurality of primary cladding layers each having a lower refractive index than said cores, and covering each of said cores; and
an outer cladding layer having a lower refractive index than said primary cladding layers or the same refractive index as said primary cladding layers, and coveting said plurality of cores each covered by said primary cladding layer;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores having a higher refractive index than said surrounded core.

### Claim 10

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each doped with at least one rare earth element therein; and
an outer cladding layer having a lower refractive index than said cores, and covering said cores;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores containing a larger amount of rare earth element than said surrounded core.

### Claim 11 (depends on 10)

A rare earth element-doped multiple-core optical fiber, according to claim 10, wherein said surrounded core is a center core, and said remaining cores are peripheral cores surrounding said center core symmetrically.

### Claim 12

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each doped with at least one rare earth element and Al therein;
a plurality of primary cladding layers each having a lower refractive index than said cores, and covering each of said cores; and
an outer cladding layer having a lower refractive index than said primary cladding layers or the same refractive index as said primary cladding layers, and covering said plurality of cores each covered by said primary cladding layer;
wherein said cores are positioned substantially on a central axis of said outer cladding layer, at least one of which is surrounded by remaining cores containing a larger amount of rare earth element than said surrounded core.

### Claim 13

A rare earth element-doped multiple-core optical fiber, comprising:
a plurality of cores each having a first refractive index doped with at least one rare earth element; and
a cladding layer having a second refractive index lower than said first refractive index for surrounding said plurality of cores, said plurality of cores being positioned in a central region of said cladding layer;
wherein said plurality of cores comprises a first group of one or more cores, and a second group of cores, such that said second group of cores surrounds a periphery of said first group of one or more cores to equalize powers propagated through each core of said first and second groups.