# US 5,706,124 A · Rare earth element-doped optical fiber amplifier

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- Number: US 5,706,124 A
- Document ID: US5706124A
- Status: Granted
- Kind: A
- Application number: 08/629,593
- Filed: 1996-04-09
- Granted: 1998-01-06
- Earliest claimed: 1995-11-13
- Assignees: Hitachi Cable, Ltd.
- Inventors: Katsuyuki Imoto; Kazuo Koya; Jun Abe
- Web page: https://patentgrep.com/patent/US5706124A

## CPC

- H04B 10/2912: {characterised by the medium used for amplification or processing}
- H01S 3/06737: {Fibre having multiple non-coaxial cores, e.g. multiple active cores or separate cores for pump and gain}
- H01S 3/06754: {Fibre amplifiers (H01S3/06708 takes precedence)}
- H04B 10/291: in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B 10/294: in a multiwavelength system, e.g. gain equalisation
- H01S 3/094096: {Multi-wavelength pumping}
- H01S 3/1608: {erbium}
- H01S 2301/02: ASE (amplified spontaneous emission), noise; Reduction thereof
- H01S 2301/04: Gain spectral shaping, flattening
- H04B: TRANSMISSION
- 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

An Er-doped multiple-core optical fiber amplifier has an Er-doped multiple-core optical fiber. A signal light of 1.5 .mu.m wavelength band is input through an optical isolator at front stage, and excitation lights of 0.98 .mu.m or 1.48 .mu.m wavelength emitted from excitation light sources are injected through a WDM coupler at front stage and a WDM coupler at rear stage, respectively. An amplified signal light is output through optical isolator at rear stage. A length L.sub.M of the Er-doped multiple-core optical fiber is set to obtain a substantially maximum saturated output power of the amplified signal light.

## Claims

### Claim 1

A rare earth element-doped optical fiber amplifier, comprising:
an optical fiber provided with plural cores, each core being doped with at least one rare earth element; and
a light source for emitting an excitation light which is injected into said optical fiber to amplify a signal light transmitted through said optical fiber;
wherein a length of said optical fiber is set to obtain a substantially maximum saturated output power of an amplified signal light, said length being different from a fiber length set for obtaining a maximum gain, said amplified signal light being obtained by amplifying said signal light;
whereby the flat characteristics of gain to wavelength and noise figure to wavelength are wider compared to an optical fiber length where maximum gain is obtained.

### Claim 2 (depends on 1)

A rare earth element-doped optical fiber amplifier, according to claim 1, wherein:
each of said cores is doped with a concentration of at least 300 ppm of Er and a concentration of at least 8000 ppm of Al.

### Claim 3 (depends on 1)

A rare earth element-doped optical fiber amplifier, according to claim 1, wherein:
said signal light has a wavelength band of 1.5 .mu.m, and said excitation light has a wavelength of one or both of 0.98 .mu.m and 1.48 .mu.m.

### Claim 4

A rare earth element-doped optical fiber amplifier comprising:
an optical fiber provided with plural cores, each core being doped with at least one rare earth element;
a light source for emitting an excitation light which is injected into said optical fiber to amplify a signal light transmitted through said optical fiber, thereby providing an amplified signal light;
an optical isolator at front stage of said optical fiber for suppressing a reflected signal light to retrograde into a light source for said signal light, and an optical isolator at rear stage of said optical fiber for suppressing a reflected signal light of said amplified signal light to retrograde into said optical fiber; and
at least one WDM coupler at said front or rear stage of said optical fiber for injecting said excitation light emitted from said light source to said optical fiber;
wherein a length of said optical fiber is set to obtain a substantially maximum saturated output power of said amplified signal light, said length being different from a fiber length set to obtain a maximum gain;
whereby the flat characteristics of gain to wavelength and of noise figure to wavelength are wider compared to an optical fiber length where maximum gain is obtained.

### Claim 5 (depends on 4)

A rare earth element-doped optical fiber amplifier, according to claim 4, wherein:
each of said cores is doped with a concentration of at least 300 ppm of Er and a concentration of at least 8000 ppm of Al.

### Claim 6 (depends on 4)

A rare earth element-doped optical fiber amplifier, according to claim 4, wherein:
said signal light has a wavelength band of 1.5 .mu.m, and said excitation light had a wavelength of one or both of 0.98 .mu.m and 1.48 .mu.m.