Crosstalk-free signal source for dense wavelength division multiplexed systems

• US 6,233,080 B1
• Filed: 08/26/1998
• Issued: 05/15/2001
• Est. Priority Date: 08/26/1998
• Status: Expired due to Term

• Current Assignee: Ciena Corporation
• Original Assignee: Ciena Corporation
• Inventors: Morton, Paul A., Brenner, Tomas, Zhu, Daniel Xiaoxing
• Primary Examiner(s): Pascal, Leslie
• Assistant Examiner(s): Phan, Hanh
• Time in patent office: 993 Days
• Field of Search: 359/161, 359/180, 359/181, 359/187
• US Class Current: 398/196
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/506 Multiwavelength transmitters
• CPC Class Codes: H04B 10/572 Wavelength control

Abstract

An optical device is provided which locks the wavelength output of a laser transmitter in an optical transmission system as well as preventing the propagation of unwanted signals generated by the laser transmitter prior to the transmitter reaching the desired operating wavelength thereby reducing crosstalk between channels within a wavelength division multiplexed communication system.

Claims

1. An optical device for reducing crosstalk associated with a plurality of optical channels in a communication system comprising:

a light source for generating a light signal at a particular wavelength, said light source having a ramp-up period in which said light source does not substantially emit the light signal at the particular wavelength; and

a light modulation element coupled to said light source, said light modulation element having an “

on” and

“

off”

state such that when said light modulation element is in said “

on”

state, said light signal generated by said light source at said particular wavelength is substantially allowed to propagate along an optical transmission path, and when said light modulation element is in said “

off”

state, said light modulation element substantially prevents said light signal from propagating along said optical transmission path,

said light modulation element being in the off state during the ramp-up period of said light source to substantially prevent the light signal at a wavelength other than the particular wavelength from propagating along said optical transmission path.

2. The optical device in accordance with claim 1 further comprising:

a filtering element coupled to said light modulation element, said filtering element having a transmissivity characteristic as a function of wavelength, said transmissivity characteristic defining a transmission band corresponding at or near said particular wavelength; and

a control circuit coupled to said filtering element and to said light source, said control circuit receiving a portion of said light signal at or near said particular wavelength transmitted by said filtering element, said control circuit generating a control signal, based on said portion of said light signal for controlling the wavelength and power outputted by said light source.

3. The optical device in accordance with claim 2 wherein said filtering element is an in-fiber Bragg grating.

4. The optical device in accordance with claim 2 wherein said light modulation element is a variable attenuator.

5. The optical device in accordance with claim 2 further comprising an optical splitting element coupled to said transmission path, said splitting element configured to tap said portion of said light signal at or near said particular wavelength.

6. The optical device in accordance with claim 2 wherein said control circuit further comprises a photodetector for receiving said portion of said optical signal and generating an electrical signal in response thereto.

7. The optical device in accordance with claim 6 wherein said control circuit comprises a processor for receiving and processing said electrical signal.

8. The optical device in accordance with claim 1 wherein said light modulation element is an electroabsorption modulator.

9. The optical device in accordance with claim 8 wherein said electroabsorption modulator and said light source are monolithically integrated.

10. The optical device in accordance with claim 1 wherein said light source is a distributed feedback laser.

11. An optical communication system comprising:

a light source generating a light signal at or near a particular wavelength when said light source is in a stabilized condition and at other wavelengths when said light source is not in the stabilized condition;

a modulation element optically communicating with said light source along a transmission path, said modulation element having a transmit condition and a nontransmit condition, wherein when said light source is in the stabilized condition said modulation element is in said transmit condition such that said light signal generated by said light source is allowed to propagate along said transmission path, and wherein when said light source is not in the stabilized condition said modulation element is in said nontransmit condition such that said modulation element substantially prevents said light signal at one of the other wavelengths from leaking into said optical transmission path;

a partially reflective element optically communicating with said modulation element; and

a control circuit optically communicating with said partially reflective element and said light source, said control circuit configured to detect a portion of said light transmitted through said partially reflective element and generating an output signal in response thereto, said output signal used to adjust said wavelength of said light signal.

12. The optical device in accordance with claim 11 wherein said output signal is used to adjust a power level associated with said light source.

13. The optical device in accordance with claim 11 wherein said modulator element is a semiconductor electroabsorption modulator.

14. The optical device in accordance with claim 11 wherein said partially reflective element is a Bragg grating.

15. The optical device in accordance with claim 11 wherein said light source is a first light source generating a first light signal at a first wavelength, said modulation element is a first modulation element, said transmission path is a second transmission path, said partially reflective element is a first partially reflective element and said control circuit is a first control circuit, said optical system further comprising:

a second light source generating a second light signal at or near a second particular wavelength;

a second modulation element optically communicating with said second light source along a second transmission path, said second modulation element having a transmit condition and a nontransmit condition such that when said second modulation element is in said transmit condition, said second light signal generated by said second light source is allowed to propagate along said second transmission path, and when said second modulation element is in said nontransmit condition, said second modulation element prevents said second light source from leaking into said second optical transmission path;

a second partially reflective element optically communicating with said second modulation element; and

a second control circuit optically communicating with said second partially reflective element and said second light source, said second control circuit configured to detect a second portion of said second light transmitted through said second partially reflective element and generating an output signal in response thereto, said output signal used to adjust said second wavelength of said second light signal.

16. The optical device in accordance with claim 15 wherein said first and second transmission paths optically communicating with an optical multiplexer configured to supply said first and second optical signals to an optical waveguide.

17. The optical device in accordance with claim 16 wherein said first light signal transmitted by said first modulation element at said first wavelength and said second light signal transmitted by said second modulation element at said second wavelength are such that said first signal at said first wavelength does not cause crosstalk with said second signal at said second wavelength along said optical waveguide.

18. The optical device in accordance with claim 15 wherein said second modulation element is a semiconductor electroabsorption modulator.

19. The optical device in accordance with claim 15 wherein said second partially reflective element is a Bragg grating.