Optical regeneration circuit for regenerating signal with deteriorated signal to noise ratio by means of saturable absorption element

• US 6,504,637 B1
• Filed: 03/10/1999
• Issued: 01/07/2003
• Est. Priority Date: 03/13/1998
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Ishii, Satoshi, Yokoyama, Ryu
• Primary Examiner(s): Pascal, Leslie
• Assistant Examiner(s): TRAN, DZUNG D
• Application Number:
  US09/266,069
• Time in Patent Office: 1,399 Days
• Field of Search: 359/176, 359/179, 359/339, 359/244, 359/161
• US Class Current: 398/97
• CPC Class Codes: H04B 10/291 in which processing or amplification is carried out without conversion of the main signal from optical form
• CPC Class Codes: H04B 2210/258 treating each wavelength or wavelength band separately

Abstract

An optical transmission system having an optical regeneration circuit for regenerating a signal with a deteriorated signal to noise ratio. A signal light at wavelength λ1 which includes a noise light is composed with a continuous light at wavelength λ2 outputted from a light source to obtain a composed signal light in an optical coupler. The composed signal light is passed through a saturable absorption type optical element which transmits only the signal light having a light intensity equal to or greater than a threshold value, thereby removing the included noise light. From the signal light, only the signal at the same wavelength λ2 as the wavelength of the continuous light is extracted by a wavelength divider and data signal of the incident signal light is replicated in the continuous light and outputted. Thus, a signal light having no deterioration of the signal to noise ratio at wavelength λ2 can be regenerated from the signal light having the deteriorated signal to noise ratio.

Claims

1. An optical regeneration circuit comprising:

optical wavelength selecting means for passing therethrough, from an incident signal light which includes a noise light, only a component at a wavelength of the signal light;

a light source for outputting a continuous light at a certain constant wavelength;

a saturable absorption type optical element having a saturable absorption region, for adding a light intensity of the continuous light received from said light source at one terminal and a light intensity of the signal light received at another terminal, for absorbing almost all the continuous light and the signal light when the added value is lower than a threshold value of the saturable absorption region, and for passing therethrough transmit the continuous light to output the passed light as a regenerated signal light at the other terminal when the added value is equal to or greater than said threshold value; and

optical dividing means including a first terminal connected to said optical wavelength selecting means, a second terminal connected to said saturable absorption type optical element and an output terminal through which the regenerated signal light is outputted to the outside, for outputting the signal light received from said optical wavelength selecting means at the first terminal to said saturable absorption type optical element at the second terminal, and for outputting to the output terminal the regenerated signal light received from said saturable absorption type optical element at the second terminal.

2. The optical regeneration circuit according to claim 1, wherein a wavelength of the signal light and a wavelength of the continuous light are substantially equal to each other.

3. The optical regeneration circuit according to claim 1, wherein said optical dividing means is an optical circulator.

4. The optical regeneration circuit according to claim 1, wherein said wavelength selecting means is an optical band pass filter.

5. An optical regeneration device comprising:

wavelength separating means for composing a wavelength multiplexing signal light in which a plurality of signal lights having different wavelengths are composed for each wavelength;

a plurality of optical regeneration circuits according to claim 1, for receiving the respective signal lights divided by said wavelength separating means to output regenerated signal lights; and

wavelength multiplexing means for composing the respective regenerated signal lights outputted by said respective optical regeneration circuits to output the composed signal as a wavelength multiplexing signal light.

6. The optical regeneration device according to claim 5, further comprising optical amplifying means at an input terminal of said wavelength separating means, at input terminals and output terminals of said respective optical regeneration circuits, and at an output terminal of said wavelength multiplexing means.

7. An optical transmission system comprising:

an optical transmitter for wavelength-multiplexing a signal light, and for outputting the wavelength composed signal light;

an optical receiver for receiving the wavelength composed signal light;

an optical fiber for connecting between said optical transmitter and said optical receiver;

optical amplifying means provided on the path of said optical fiber, for amplifying a light intensity of the signal light passing through the optical fiber; and

an optical regeneration circuit according to claim 5, provided on the path of said optical fiber.

8. An optical transmission system comprising:

an optical transmitter for outputting a signal light;

an optical receiver for receiving the signal light;

an optical fiber for connecting between said optical transmitter and said optical receiver;

optical amplifying means provided on the path of optical fiber, for amplifying a light intensity of the signal light passing through the optical fiber; and

an optical regeneration circuit according to claim 1 provided on the path of said optical fiber.