All-optical bit phase sensing

Details All-optical bit phase sensing All-optical bit phase sensing

2002-05-14

2003-10-21

Pascal, Leslie (Department: 2633)

Optical communications

Receiver

Including optical element

Reexamination Certificate

active

06634813

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the field of optical communications and optical signal processing. In particular, the invention relates to apparatus and methods for all-optical bit phase sensing and clock recovery.
BACKGROUND OF THE INVENTION
High-speed time division multiplexed (TDM) communication systems require high-speed clock recovery or clock synchronization. Multiple-user local area and metropolitan area TDM networks require high-speed clock recovery at each user access node. Typically, this clock recovery will involve locking a local clock to an incoming data or clock stream. Electrooptical and all-optical clock recovery and clock synchronization is advantageous because it has the potential for achieving higher speeds than all-electrical clock recovery and clock synchronization.
Several optical clock recovery and clock synchronization techniques have been demonstrated that utilize injection-locking of diodes, fibers, and lasers. Also, several high-speed optical clock recovery techniques have been demonstrated that utilize electrooptical phase lock loops (PLL) with bit phase sensors. An electrooptical phase lock loop has been demonstrated that utilizes nonlinear cross-correlation of two pulse streams to sense bit phase. Another electrooptical phase lock loop has been demonstrated that utilizes four wave mixing in a semiconductor to sense bit phase. These clock recovery techniques, however, have limited scalability in data and clock rates.
Commercially practical 100-Gb/s TDM communication systems require reliable, inexpensive, clock recovery techniques with sub-picosecond accuracy and a wide range of scalability in data and clock rates. Furthermore, it is desirable for the clock recovery technique to perform optical processing functions, such as multiplexing, demultiplexing, and Boolean logic functions, simultaneously with clock recovery in a single optical switch.
SUMMARY OF THE INVENTION
It is a principal object of this invention to provide an all-optical and an electrooptical bit phase sensor with at least sub-picosecond accuracy. It is another object of this invention to provide an electrooptical and an all-optical phase lock loop that utilizes these bit phase sensors. Other objects are to provide optical processors and optical networks that utilize these bit phase sensors.
A principle discovery is that nonlinear optical switches can be utilized to recover a clock signal with sub-picosecond accuracy. Another principle discovery is that a nonlinear optical switch can be utilized to perform simultaneous optical processing and clock recovery. Another principle discovery is that an all-optical phase lock-loop can be implemented using the optical output from an optical switch and an intensity dependent delay line. Another principle discovery is that nonlinear absorption in optical fibers and semiconductors can be utilized to recover clock signals with sub-picosecond accuracy.
Accordingly, the present invention features an all-optical bit phase sensor having a first optical beam input. A splitter, which is optically coupled to the first optical beam input, separates an input optical beam into a first and a second optical beam that propagates along a first and a second optical path, respectively. A nonlinear material, that forms an intensity dependent phase or transmission change, is positioned in the first optical path. The nonlinear material may also be disposed in the second optical path. The nonlinear material may be an optical fiber or a semiconductor amplifier.
A control optical beam input couples a control optical beam into the first optical path. The control beam causes nonlinear or transmission index changes in the nonlinear material. The input optical beam and the control beam may have substantially the same group velocities and thus may have substantially zero dispersive walk through. A recombiner recombines the first and the second optical beams into an output beam. The intensity of the output beam is proportional to the relative phase between the input optical beam and the control beam. A beam removal element may be positioned in the optical path to remove the control beam from the output beam. The beam removal element may comprise a filter, polarizer, or spatial multiplexer.
The present invention also features an all-optical bit phase sensor having a first optical beam input for accepting a first optical beam into an optical path. An optical differential delay element is disposed in the optical path which forms a second optical beam in the optical path by delaying a portion of the first optical beam in time. A nonlinear material is positioned in the optical path. The nonlinear material forms an intensity dependent phase or transmission change. The nonlinear material may be an optical fiber or a semiconductor amplifier.
A second input introduces a control beam into the optical path. The control beam causes nonlinear index or transmission changes in the nonlinear material. The control beam and the second optical beam may be pulse streams that are timed to overlap in the nonlinear material. The first optical beam and the control beam may have substantially the same group velocities and thus may have substantially zero dispersive walk through. A recombiner recombines the first and the second optical beams into an output beam. The intensity of the output beam is proportional to the relative phase between the first optical beam and the control beam. A beam removal element may be positioned in the optical path to remove the control beam from the output beam. The beam removal element may comprise a filter, polarizer, or spatial multiplexer.
The present invention also features a method of all-optical bit phase sensing. The method includes splitting an input optical beam into a first and a second optical beam that propagates along a first and a second optical path respectively. A nonlinear material is positioned in the first optical path. The control optical beam is coupled into the first optical path causing nonlinear index or transmission changes in the nonlinear material. The first and second optical beams are recombined into an output beam. The intensity of the output beam is proportional to the relative phase between the input optical beam and the control beam.
The present invention also features a second method of all-optical bit phase sensing. The method includes introducing a first optical beam into an optical path. A second optical beam is formed in the optical path by delaying a portion of the first optical beam in time. A nonlinear material is positioned in the optical path which has an intensity dependent phase or transmission change. A control beam is introduced into the optical path which causes nonlinear index or transmission changes in the nonlinear material. The first and the second optical beams are recombined into an output beam. The intensity of the output beam is proportional to the relative phase between the first optical beam and the control beam.
The present invention also features an electrooptic phase lock loop having a nonlinear interferometer. The nonlinear interferometer may comprise a Mach-Zehnder interferometer, a Sagnac interferometer, a Michelson interferometer, or a single arm interferometer. The nonlinear interferometer has a first optical beam input, a control optical beam input, and an optical beam output. An output optical beam of the interferometer has an intensity proportional to a phase difference between an input intensity modulated data stream input to the first optical beam input and a control clock stream input to the control optical beam input.
A feedback control network has an optical input optically coupled to the optical beam output of the interferometer and an electrical output. The electrical output of the feedback control network generates a signal in response to the intensity of the output optical beam of the interferometer. An optical clock stream generator includes an electrical input electrically coupled to the electrical output of the feedback control network and an optical output optica

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