# US 5,353,146 A · Optical signal regenerator and optical communications system incorporating same

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- Number: US 5,353,146 A
- Document ID: US5353146A
- Status: Granted
- Kind: A
- Application number: 07/949,253
- Filed: 1992-11-23
- Granted: 1994-10-04
- Earliest claimed: 1990-05-08
- Assignees: British Telecommunications public limited company
- Inventors: Roderick P. Webb
- Web page: https://patentgrep.com/patent/US5353146A

## CPC

- H04L 7/027: extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
- H01S 5/5036: {the arrangement being polarisation-selective}
- H04L 7/0075: {with photonic or optical means}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- 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 optical signal regenerator has a semiconductor laser in a resonant cavity defined by a mirror and a semireflective facet of the laser to form a resonant, non-linear, optical amplifier. A polarization beam splitter allows resonance in one polarization mode only. A clock signal generator provides clock signals in the resonant polarization mode of a power just below the optical power bistable threshold of the amplifier. An information signal coupled to the laser by a lens and the beam splitter is in a non-resonant mode of the amplifier and will give rise to a regenerator output by triggering the bistability. Because the information signal is in a non-resonant mode its wavelength need not be controlled to lie near a resonance peak of the amplifier so reducing control requirements.

## Claims

### Claim 1

An optical signal regenerator comprising:
a resonant, non-linear, optical amplifier including gain material for providing optical gain, and capable of exhibiting bistability at a first wavelength with a power threshold between a first relatively low power output state and a second relatively high power output state;
a clock signal generator for generating optical clock pulses at the first wavelength and at an optical power just below the optical power bistability threshold of the amplifier at the first wavelength;
first coupling means for coupling the optical clock pulses to the resonant amplifier in a resonant mode thereof;
a source of information pulses; and
second coupling means for coupling the information pulses to the amplifier in a non-resonant mode thereof;
whereby bistable switching to one of said power states occurs upon an initial concurrent occurrence of an information pulse and a clock pulse, with subsequent bistable switching to the other of the power states occurring when the clock pulse is terminated.

### Claim 2 (depends on 1)

A regenerator as in claim 1 in which the amplifier comprises a semiconductor laser within a Fabry-Perot resonator cavity.

### Claim 3 (depends on 1)

A regenerator as in claim 1 in which the clock signals and the information signal have different frequencies.

### Claim 4 (depends on 1)

A regenerator as in claim 1 in which the first optical coupling means comprises an optical fibre.

### Claim 5 (depends on 1)

An optical communications system comprising an optical signal regenerator as in claim 1 disposed between an input optical transmission fibre and an output optical transmission fibre.

### Claim 6 (depends on 1)

A method of transmitting an information signal including the step of regenerating the information signal by use of a regenerator as in claim 1.

### Claim 7

A method of regenerating an optical information signal, comprising:
configuring a resonant, non-linear, optical amplifier including gain material for providing optical gain, to exhibit bistability with a power threshold between a first relatively low power output state and a second relatively high power output state;
generating optical clock pulses at an optical power just below the optical power bistability threshold of the amplifier;
coupling the optical clock pulses to the resonant amplifier in a resonant mode thereof; and
coupling information pulses to the amplifier in a non-resonant mode thereof;
whereby bistable switching to one of said power states occurs upon an initial concurrent occurrence of an information pulse and a clock pulse, with subsequent bistable switching to the other of the power states occurring when the clock pulse is terminated.

### Claim 8

An optical signal regenerator comprising:
a resonant, non-linear, optical amplifier including gain material for providing optical gain, and capable of exhibiting bistability at a first wavelength;
a clock signal generator for generating optical clock signals at the first wavelength and at an optical power just below the optical power bistable threshold of the amplifier at the first wavelength; and
a first and a second optical coupling means for coupling the optical clock signals and an information signal to the amplifier in a resonant mode and a non-resonant mode of the amplifier, respectively;
in which the clock signals and the information signal have different frequencies; and
in which the second optical coupling means comprises a frequency dependent polarising beam splitter located within the resonator cavity so that the amplifier cannot resonate at the frequency of the information wavelength.

### Claim 9

An optical signal regenerator comprising:
a resonant, non-linear, optical amplifier including gain material for providing optical gain, and capable of exhibiting bistability at a first wavelength;
a clock signal generator for generating optical clock signals at the first wavelength and at an optical power just below the optical power bistable threshold of the amplifier at the first wavelength; and
a first and a second optical coupling means for coupling the optical clock signals and an information signal to the amplifier in a resonant mode and a non-resonant mode of the amplifier, respectively;
in which the clock signals and the information signals are in orthogonal spatial modes.

### Claim 10 (depends on 9)

A regenerator as in claim 9 in which:
the amplifier comprises a twin-stripe semiconductor laser having end facets,
the first and second optical coupling means are arranged so that the clock signals and information signals overlap in the gain material but are spatially separated at the end facets, and
the end facets are selectively anti-reflection coated to reflect only the clock signals.

### Claim 11

An optical signal regenerator comprising:
a resonant, non-linear, optical amplifier including gain material for providing optical gain, and capable of exhibiting bistability at a first wavelength;
a clock signal generator for generating optical clock signals at the first wavelength and at an optical power just below the optical power bistable threshold of the amplifier at the first wavelength; and
a first and a second optical coupling means for coupling the optical clock signals and an information signal to the amplifier in a resonant mode and a non-resonant mode of the amplifier, respectively;
in which the clock signals and the information signal are in orthogonal polarisation modes.

### Claim 12 (depends on 11)

A regenerator as in claim 11 in which the second optical coupling means comprises a polarising beam splitter located within a resonator cavity so that the amplifier resonates in one polarisation mode only.

### Claim 13 (depends on 12)

A regenerator as in claim 12 in which the second optical coupling means further comprises a lens for collimating an information signal end-fired from an optical waveguide.