Method and apparatus for recovering an optical clock signal

Details Method and apparatus for recovering an optical clock signal Method and apparatus for recovering an optical clock signal

1999-10-29

2003-04-01

Negash, Kinfe-Michael (Department: 2633)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S199200, C359S199200

Reexamination Certificate

active

06542274

ABSTRACT:

RELATED APPLICATIONS
Not applicable
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
MICROFICHE APPENDIX
Not applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to the field of communication systems, and in particular, to a system that recovers an optical clock signal.
2. Description of the Prior Art
Fiber optic communications require synchronization between the transmitter and receiver to derive the optical data. Fiber optic communication systems use an optical clock signal for this synchronization. The transmitter embeds the optical clock signal into an optical data signal. The receiver then extracts the optical clock signal from the optical data signal.
Fiber optic communication systems recover the clock signal from an optical domain, an electrical domain, or a combination of the optical and electrical domain. In the optical domain, the communication system recovers the optical clock signal directly from the optical data signal without any optical to electrical conversions. In the electrical domain, the communication system converts the optical data signal to an electrical data signal using an optical detector. The communication system then produces the electrical clock signal from the electrical data signal. In the combination of the optical and electrical domain, the communication system typically produces the electrical clock signal directly from the optical data signal without converting the optical clock signal to electrical. A solution to recover the optical clock signal in the optical domain with no electronic filtering of the optical clock signal is more transparent and advantageous.
In wavelength division multiplexing (WDM), the transmitter transmits different optical data signals at different wavelengths within the same fiber. Each optical data signal has the ability to carry an optical clock signal in WDM. Also, the data rates may vary between each wavelength in WDM.
Some prior systems recover the clock signal by injecting the optical data signal into a mode-locked fiber ring, a multi-segment mode-locked semiconductor laser, or a self-pulsating laser diode. However, each of these prior systems is data rate dependent and extracts the optical clock signal from only one wavelength.
Another system injects the optical data signal into an optical tank circuit. The optical tank circuit filters the data portion of the optical data signal leaving only the optical clock signal. Most optical tank circuits are data-rate and wavelength dependent. One exception is Brillouin tank circuits.
FIG. 1
depicts a prior solution using a Brillouin tank circuit that recovers an optical clock signal from the optical data signal. A laser transmitter
102
transmits an optical signal to a first modulator
104
. The first modulator
104
modulates the optical signal with data into an optical data signal in a return-to-zero format. An Erbium-doped fiber amplifier (EDFA)
106
then amplifies the optical data signal. A coupler
110
receives and splits the optical data signal into a first optical data signal and a second optical data signal. The coupler
110
propagates the first optical data signal clockwise and the second optical data signal counter-clockwise in opposite directions around a fiber loop
150
.
The coupler
110
transmits the first optical data signal clockwise to an isolator
120
. The isolator
120
isolates the first optical data signal from the second optical data signal to prevent any signals from returning to the coupler
110
. A first polarization controller
122
adjusts the polarization of the first optical data signal and transfers the first optical data signal to a second modulator
124
. The polarization controllers
122
,
126
, and
130
align the polarizations of the optical data signals so the first optical data signal and the second optical data signal will interact. The second modulator
124
modulates the first optical data signal at 10.9 GHz. A second polarization controller
126
adjusts the polarization of the first optical data signal and transfers the first optical data signal to a 2 Kilometer polarization maintaining fiber
128
.
The coupler
110
propagates the second optical data signal counter-clockwise in the direction of a third polarization controller
130
. The third polarization controller
130
adjusts the polarization of the second optical data signal and transfers the second optical data signal to the fiber
128
.
In the fiber
128
, the first optical data signal and second optical data signal interact in an effect known as stimulated Brillouin scattering. This effect acts as an active filter and amplifies the signals that are above a Brillouin power threshold in the first optical data signal. The amplification occurs through a kinetic energy transfer from the second optical data signal to the fiber
128
and from the fiber
128
to frequency components of the first optical data signal that are above the Brillouin power threshold. The optical clock signal in the first optical data signal is above the Brillouin power threshold. Therefore, the Brillouin scattering effect amplifies the optical clock signal. Thus, the coupler
110
receives the optical clock signal from the fiber
128
and transmits the optical clock signal over an outgoing link
140
.
The problem with this Brillouin optical tank system is the system does not operate for WDM signals. There is not enough gain in the EDFA
106
to be effective for WDM signals. There is a need for a system that recovers the optical clock signals from the optical data signals from each wavelength that are at different data rates.
SUMMARY OF THE INVENTION
The invention solves the above problem by recovering an optical clock signal from an optical data signal. A clock recovery system splits the optical data signal into a first optical data signal and a second optical data signal. The clock recovery system then transmits the first optical data signal and the second optical data signal in opposite directions around a fiber loop. In the fiber loop, the clock recovery system modulates and amplifies the first optical data signal to generate a modulated-amplified first optical data signal. The clock recovery system then recovers the optical clock signal after the modulated-amplified first optical data signal and the second optical data signal interact in the fiber loop.
In some embodiments of the invention, the clock recovery system aligns the polarization of the modulated-amplified first optical data signal and the second optical data signal. Also, in one embodiment of the invention, the optical clock signal is above the Brillouin power threshold. In some embodiments of the invention, the optical data signal is an optical WDM data signal.
One advantage of the invention is that the clock recovery system is data rate independent. Thus, the clock recovery system can recover clock signals at different data rates. Another advantage is the clock recovery system is wavelength independent. The clock recovery system recovers clock signals from different wavelengths. Therefore, the invention can recover clock signals from WDM signals, which have different clock signals at different wavelengths with different data rates.


REFERENCES:
patent: 5911015 (1999-06-01), Bigo
patent: 6081631 (2000-06-01), Brindel et al.
Ellis, A. D., Smith K., and Patrick, D.M., “All Optical Clock Recovery at Bit Rates Up to 40 Gbit/s,” Electronics Letters, vol. 29 (No. 15), p. 1323-1324, (Jul. 22, 1993).
Ludwig, R, Ehrhardt A., Pieper W., Jahn E., Agrawal N., et al., “40 Gbit/s demultiplexing experiment with 10 GHz all-optical clock recovery using a medelocked semiconductor laser,” Electronics Letters, vol. 32 (No. 4), p. 327-329, (Feb. 15, 1996).
Barnsley, P.E., Wickes H.J., Wickens G.E., Spirit D. M., “All-Optical Clock Recovery from 5 Gb/s RZ Data Using a Self-Pulsating 1.56 um Laser Diode,” IEEE, vol. 3 (No. 10), p. 942-945, (Oct., 1991).
Jinno, Masahiko, Matsumoto, Takao, “Optical Tank Circuits Used for All-Optical Timing Recovery,” IEEE, vol. 28 (No. 4), p. 895-900, (Apr., 1992).
Butler

Affiliated with

Also associated with

Rating

Method and apparatus for recovering an optical clock signal does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and apparatus for recovering an optical clock signal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for recovering an optical clock signal will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3051324