Optical pulse generator for return-to-zero signaling

• US 20040005110A1
• Filed: 07/08/2002
• Published: 01/08/2004
• Est. Priority Date: 07/08/2002
• Status: Active Grant

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Zhang, Liming, Wei, Xing, Leuthold, Juerg
• Granted Patent: US 7,076,120 B2
• Time in Patent Office: Days
• US Class Current: 385/15
• CPC Class Codes: G02B 6/29355 Cascade arrangement of interferometers
• CPC Class Codes: H04B 10/505 using external modulation
• CPC Class Codes: H04B 10/5051 using a series, i.e. cascade, combination of modulators
• CPC Class Codes: H04B 10/508 Pulse generation, e.g. generation of solitons

Abstract

The specification describes an optical pulse generator in a return-to-zero format in which a phase-modulated (PM) optical signal is converted to intensity-modulated (IM) optical pulses using chromatic dispersion. Compared with Mach-Zehnder-modulator-based pulse generators, this scheme is potentially more efficient (lower insertion loss). The pulse generator of the invention is suitable for very high data rates, e.g. 40 Gb/s. The structure of the pulse generator is a phase-modulated pulse source combined with a dispersive element having the required dispersion.

Claims

1. An optical pulse generator comprising:

a. a phase modulated light source, and

b. a dispersive element to convert the phase-modulated light signal to a periodic light pulse train.

2. The optical pulse generator of claim 1 wherein the phase-modulated light source has a modulation frequency Ω

/2π

exactly equal to the desired pulse repetition rate R.

3. The optical pulse generator of claim 1 wherein the phase-modulated light source has a phase modulation depth Δ

φ

_p-p in the range from 0.3π

to 0.9π

.

4. The optical pulse generator of claim 1 wherein the phase modulated light source comprises a CW laser and a phase modulator coupled to the CW laser.

5. The optical pulse generator of claim 4 wherein the CW laser and the phase modulator are integrated on one substrate.

6. The optical pulse generator of claim 4 wherein the phase modulator and the dispersive element are integrated on one substrate.

7. The optical pulse generator of claim 1 wherein the phase modulated light source is a directly frequency-modulated laser.

8. The optical pulse generator of claim 7 wherein the directly frequency-modulated laser and the dispersive element are integrated on one substrate.

9. The optical pulse generator of claim 1 wherein the dispersive element is a length of optical fiber.

10. The optical pulse generator of claim 9 wherein the total group velocity dispersion of the fiber is:

|DL|=c/2λ

²R²±

20%

where c is the speed of light, λ

is the wavelength of the CW laser, and R is the pulse repetition rate.

11. The optical pulse generator of claim 1 wherein the dispersive element comprises Bragg gratings.

12. The optical pulse generator of claim 1 wherein the dispersive element is a tunable fiber grating.

13. The optical pulse generator of claim 1 wherein the dispersive element is a Fourier filter comprising three optical couplers linked by two differential delays.

14. The Fourier filter of claim 13 wherein one of the two differential delays is equal to one half of the pulse period within an accuracy of ±

20%, and the other one is in the range between ⅕

to ⅗

of the pulse period.

15. The optical pulse generator of claim 1 further including a data modulator coupled to the dispersive element.

16. An optical transmission system comprising an optical pulse generator according to claim 1, a data modulator, an optical path comprising a length of fiber optically coupled to the data modulator, and a receiver optically coupled to the optical path.