In this device, wavelength selective true-time-delay is obtained by a phased-array waveguide grating in a symmetric feedback configuration. In the transmit mode the r.f. modulated optical carrier is steered by the waveguide grating to the appropriate integrated delay line dependent on the carrier wavelength. The signal is delayed and is fed back into the symmetric input port. Thereafter the grating diffracts the delayed beam into the common output port of the grating. In the receive mode, the time-reversed signals arriving from the antenna element are synchronized according to their wavelength. Hence the device functions as its own matched filter.

The device has several advantages over other wavelength-selective techniques. For example, since this device has only two ports, it eliminates the need for optical circulators required in the Bragg fiber grating approach. Additionally, there is no trade-off between bandwidth and loss, therefore it is inherently broadband. The device can be integrated on a single substrate, therefore it is compact, easily temperature controlled, and can be mass produced at low cost. It has not splitting loss and as a result all the power in a given wavelength is diffracted back into the output port. Finally, besides its main application for time-delay beam steering, this invention can also be used as a matched-filter pair for spread-spectrum optical communications.

Reference: UCLA Case No. 1996-513

US Patent Number: 5,793,907