# US 5,706,125 A · Optical signal amplifying circuit

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- Number: US 5,706,125 A
- Document ID: US5706125A
- Status: Granted
- Kind: A
- Application number: 08/666,845
- Filed: 1996-06-19
- Granted: 1998-01-06
- Earliest claimed: 1995-06-28
- Assignees: Hitachi, Ltd.
- Inventors: Hiroyuki Nakano
- Web page: https://patentgrep.com/patent/US5706125A

## CPC

- H04B 10/2912: {characterised by the medium used for amplification or processing}
- H01S 3/10023: {by functional association of additional optical elements, e.g. filters, gratings, reflectors}
- H04B 10/291: in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B 10/2941: {using an equalising unit, e.g. a filter (H04B10/296 takes precedence)}
- H04B 2210/003: Devices including multiple stages, e.g., multi-stage optical amplifiers or dispersion compensators
- 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

A wide-band optical signal amplifying circuit having gain exhibiting less wavelength dependency for amplifying optical signal and analogue-modulated optical signal. The optical signal amplifying circuit includes one or a plurality of optical amplifiers for amplifying en bloc optical signal components of respective wave-lengths of a wavelength-multiplexed optical signal and a multi-cavity type or the like dielectric multilayer interference filter disposed at an input or output side of the optical amplifier or therebetween. The dielectric multilayer interference filter is stable over a wide band and exhibits a steep cut-off characteristic. The multi-cavity type dielectric multilayer interference filter has a center wavelength for transmission which is variable.

## Claims

### Claim 1

An optical signal amplifying circuit using an optical fiber amplifier, comprising:
at least one optical amplifier for amplifying en bloc optical signal components of respective wavelengths contained a wavelength-multiplexed optical signal;
a multi-cavity type dielectric multilayer interference filter disposed at an input side or alternatively at an output side of said optical amplifier or alternatively between said optical amplifiers when a plurality of said optical amplifiers are employed;
an optical level detector for detecting a level of light inputted to the optical signal amplifying circuit; and
an optical filter controller, connected to said multi-cavity type dielectric multilayer interference filter and said optical level detector, for controlling said optical multi-cavity type dielectric multilayer interference filter in accordance with the detected input light level so as to have an optimum center wavelength for transmission.

### Claim 2

An optical signal amplifying circuit using an optical filter amplifier, comprising:
at least one optical amplifier for amplifying an optical signal modulated by an analog signal;
a multi-cavity type dielectric multilayer interference filter disposed at an input side or alternatively at an output side of said optical amplifier or alternatively between said optical amplifiers when a plurality of said optical amplifiers are employed;
an optical level detector for detecting a level of light inputted to the optical signal amplifying circuit; and
an optical filter controller, connected to said multi-cavity type dielectric multilayer interference filter and said optical level detector, for controlling said optical multi-cavity type dielectric multilayer interference filter in accordance with the detected input light level so as to have an optimum center wavelength for transmission.