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Integrated Optical Technologies for Real-Time Wideband Optical Signal Processing

Objective

The objective of COUSTO was to develop an integrated acousto-optical device including processing in the 0.1-1GHz range. This was to include various optical elements as well as the radiation source and suitable detectors for a 1-D signal. Applications for such a device range from super-fast LAN connections to 1-D correlation in radar processing systems (for dynamic clutter rejection).
The key to acoustooptics is the interaction between sound and light in a crystal (the Bragg cell). The interaction modifies not only the amplitude, frequency and phase of the light beam but also its direction. In this way, the information carried by both the sound and light is processed and revealed. By the use of integrated optics, the information brought by the device under development measures the degree of similarity between an input signal and a reference signal by computing their correlation. The Bragg cell used in the integrated device was a surface acoustic wave (SAW) cell. Various alternatives for the different components were studied and compared with respect to the required performances: The lithium niobate (LiNbO3) substrate on which the waveguides were fabricated was found to be the best option for the acoustooptic interaction zone. The most significant alternative material, silicon, was rejected because of its poor acoustic properties in spite of the possibility of integrating the optical detectors directly on the silicon substrate. The protonic exchange technique was selected to build the wavegudies on the Y-cut of the lithium niobate. The 2 signals, received and reference, are launched in opposite directions, and their correlation, taking place in the interaction zone, results in the deviation of the incoming laser produced light. The niobate (Nb205) Fresnel option was selected to build the collimating lens (between) the laser source and the acoustooptic interaction region) and the detector lenses (between the acoustooptic interaction region and the detector). The project pioneered a lithium niobate waveguide with the proton exchange process. A well engineered working device with integrated optics was delivered, demonstrated and evaluated, operating at a central frequency of 850 MHz with a bandwidth of 300 MHz.
The key to acousto-optics is the interaction between sound and light in a crystal (the Bragg cell). The interaction modifies not only the amplitude, frequency and phase of the light beam but also its direction. In this way, the information carried by boththe sound and light is processed and revealed.
By the use of integrated optics, the information brought by the device under development measures the degree of similarity between an input signal and a reference signal through computing their correlation. The Bragg cell used in the integrated device in this project was a surface acoustic wave (SAW) cell.
Various alternatives for the different components were studied and compared with respect to the required performances:
-The lithium niobate (LiNbO3) substrate on which the waveguides were fabricated was found to be the best option for the acousto-optic interaction zone. The most significant alternative material, silicon, was put aside because of its poor acoustic propert ies in spite of the possibility of integrating the optical detectors directly on the silicon substrate. The protonic exchange technique was selected to build the waveguides on the Y-cut of LiNbO3. The two signals, received and reference, are launched in opposite directions, and their correlation, taking place in the interaction zone, results in the deviation of the incoming laser-produced light.
-The Nb2O5 Fresnel option was selected to build the collimating lens (between the laser source and the acousto-optic interaction region) and the detector lenses (between the acousto-optic interaction region and the detector).
The project pioneered a LiNbO3 waveguide with the proton exchange process. A well-engineered working device in integrated optics was delivered, demonstrated and evaluated, operating at a central frequency of 850 MHz with a bandwidth of 300 MHz.
Exploitation
The partner companies will endeavour to capitalise on the results achieved so far by developing system components in integrated optics: an interferometric spectrum analyser and a wide bandwidth correlator are some of the envisaged short-term exploitation of the results. Longer-term exploitation requires improvement of performance of the device.

Coordinator

Selenia SpA - Industrie Electroniche Associate
Address
Via Tiburtina Km 12.400
00013 Roma
Italy

Participants (2)

GEC Marconi Research Centre
United Kingdom
Address
West Hanningfield Road Great Baddow
CM2 8HN Chelmsford
Birkbeck College, University of London
United Kingdom
Address
Malet Street, Bloomsbury
WC1E 7HX London