Electric phase delays in tunable acousto-optic filters applying extended transducers

The paper examines operation of wide angle tunable acousto-optic filters applying multiple transducers. The analysis was carried out for a tellurium dioxide device with a large transducer consisting of 7 identical sections connected in series. It was found that the sections of the transducer generated acoustic waves with a phase shift. This shift was caused by time delay when a driving electric signal propagated over the sections. The phase shift between adjacent sections was dependent on frequency of a driving electric signal, while a total phase delay between side sections of the transducer depended on a number of connected sections. Experimental investigation of the filter was performed at the driving frequencies 100-240 MHz. The measured total time delay between side sections of the transducer was equal to 1.6 ns, while the delay between adjacent sections was limited to 0.23 ns. It was proved that presence of the phase shifts influenced on spectral transmission characteristics of the tunable acousto-optic filter and also on relative intensity of side lobes.