# US 5,706,113 A · Phase lock loop circuit using optical correlation detection

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- Number: US 5,706,113 A
- Document ID: US5706113A
- Status: Granted
- Kind: A
- Application number: 08/658,414
- Filed: 1996-06-05
- Granted: 1998-01-06
- Earliest claimed: 1994-02-23
- Assignees: Nippon Telegraph and Telephone Corporation
- Inventors: Satoki Kawanishi; Osamu Kamatani; Masatoshi Saruwatari
- Web page: https://patentgrep.com/patent/US5706113A

## CPC

- H04B 10/60: Receivers
- H04L 7/0075: {with photonic or optical means}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

It is an object of the present invention to provide an optical clock phase lock loop capable of a higher operational speed than the conventional technology by utilizing high-speed optical phenomena other than gain modulation. In an optical clock phase lock loop for conducting locking control by means of obtaining the correlation of an optical signal and optical clock, after combining an optical clock of a short pulse containing a harmonics component with an optical signal by means of an optical coupler 102, and providing the resultant light to traveling-wave semiconductor laser amplifier 103, the correlation signal of the optical signal and optical clock included in the output signal of this traveling-wave semiconductor laser amplifier 103 is detected by means of optical bandpass filter 104.

## Claims

### Claim 1

Optical correlation detecting circuit comprising:
optical combining means for combining an optical signal pulse and an optical clock pulse possessing a sufficiently narrow pulse width including nth harmonics, n being a natural number, component of a repetition frequency;
optical non-linear loop mirror means for outputting a product of intensities of said optical signal pulse and said optical clock pulse; and
optical splitting means for extracting from an optical output signal of said optical non-linear loop mirror means only a correlation component of said optical signal pulse and said optical clock pulse.

### Claim 2 (depends on 1)

Optical correlation detecting circuit as recited in claim 1, wherein said optical signal pulse and said optical clock pulse are lights of wavelengths that coherently interfere with each other.

### Claim 3 (depends on 1)

Optical correlation detecting circuit as recited in claim 1, wherein said optical signal pulse and said optical clock pulse are lights of wavelengths that coherently interfere with each other; and a correlation component of a coherent light is generated.

### Claim 4 (depends on 1)

Optical correlation detecting circuit as recited in claim 1, wherein a gain with respect to an optical signal pulse of said optical non-linear loop mirror means is modulated using the intensity of an optical clock; and said correlation component being an optical signal undergoing intensity modulation.

### Claim 5 (depends on 1)

Optical correlation detecting circuit as recited in claim 1, wherein said correlation component of said optical signal pulse and said optical clock pulse is a four-wave mixing light generated in said optical non-linear loop mirror means.

### Claim 6

Optical correlation detecting circuit comprising:
optical combining means for combining an optical signal pulse and an optical clock pulse possessing a sufficiently narrow pulse width including nth harmonics, n being a natural number, component of a repetition frequency;
optical fiber for outputting a product of intensities of said optical signal pulse and said optical clock pulse; and
optical splitting means for extracting from an optical output signal of said optical fiber only a correlation component of said optical signal pulse and said optical clock pulse;
wherein, said optical signal and said optical clock respectively possess wavelengths in a vicinity of a zero dispersion wavelength of said optical fiber.

### Claim 7

Optical correlation detecting circuit comprising:
optical combining means for combining an optical signal pulse and an optical clock pulse possessing a sufficiently narrow pulse width including nth harmonics, n being a natural number, component of a repetition frequency;
optical fiber for outputting a product of intensities of said optical signal pulse and said optical clock pulse; and
optical splitting means for extracting from an optical output signal of said optical fiber only a correlation component of said optical signal pulse and said optical clock pulse;
wherein a loop is formed by optically coupling said optical combining means, said optical fiber, and said optical splitting mean, and wherein said optical combining means separately includes a means for receiving said optical signal pulse and means for receiving said optical clock pulse.