At&t Bell Laboratories

M Christina Gabriel

Norman A Whitaker, Jr

Hercules Avramopoulos

Alan Huang

Paul M William French

Henry H Houh

An all-optical circulating shift register encodes a received optical clock signal with a value derived from an encoded optical signal received at a control port thereof. A data input to the shift register is used to modify an encoded optical signal. The resulting encoded clock signal, appearing at an output port, is coupled back to the control port. The shift register uses the encoded clock signal at the control port to encode a subsequently-received clock signal. In one embodiment, the optical shift register is implemented using a Sagnac switch having a feedback path coupled between an output port and a control port of the Sagnac switch.

Optical circulating shift register

Transmission capabilities of optical fibers are enhanced with all-optical means for removing noise from signal pulses and for creating clean output pulses with specified characteristics. This is accomplished with a nonlinear interferometer that is designed to operate on an amplified optical signal in the manner of a threshold device. More specifically, the nonlinear interferometer is designed to have a relatively level region in its input/output transfer function in the neighborhood of the low input signal and in the neighborhood of the high input signal. Depending on the input signal characteristics, it is sometimes beneficial to design the interfereometer so that the nominal high level of the input signal falls approximately in the middle of its corresponding flat region. In another embodiment, a bandpass filter is included at the output of the interferometer to remove the excess bandwidth that is created by the preceding amplifiers and the interferometer itself. The filter also removes the out-of-band noise in the input signal.

Low distortion all-optical threshold device

An optical switch employs a modified sagnac arrangement that includes a sagnac loop and a coupler for injecting a signal into the loop and developing thereby two signals that travel along the loop in opposite directions. The coupler has at least one signal port that is accessible from outside the switch. In addition, a coupler is included to inject a pump signal into the loop to travel through the loop only in one direction. The loop is made of, or comprises, a material that has a controllable propagation speed. More particularly, the propagation speed in the material is a function of, for example, the intensity of the pump signal. The switch action is attained when the applied signals are in the form of pulses with pulse widths and relative positions are controlled to achieve a particular interaction. The switch action is observed by sending a pulse down a sagnac loop and observing its return. Switching is activated by either sending or not sending a pump pulse concurrently with the signal pulse that is sent down the sagnac loop. When a pump pulse is sent, it is timed to orient itself so that the pulse that propagates faster through the loop precedes the pulse that propagates slower. While propagating through the loop, the faster pulse overtakes and surpasses the slower pulse, causing the two pulses to transverse each other. In this manner the pump pulse affects the propagation speed of the pulse sent through the sagnac loop and modifies the phase of the affected pulse as it re-enters the sagnac coupler. When the intensity of the pump pulse is properly controlled, the phase shift caused by the pump pulse is such that no output appears at the port of the sagnac arrangement.

Growing community of inventors

Washington, DC, United States of America

M Christina Gabriel