Design of a radio frequency compensation system, using the electrical characterisation of a multi-transducer acousto-optical tunable filter

Abstract

Acousto-Optical Tunable Filters (AOTFs) make use of the interaction between sound and light. To generate an ultrasound diffraction grating, a Radio-Frequency (RF) signal is applied to a piezoelectric transducer. The optical pass band can be controlled by adapting the properties of this transducer and the RF-signal. To achieve more precise control of the optical spectral bandwidth, we propose to use a multi-electrode array, consisting of five consecutive transducers. The Voltage Standing Wave Ratio (VSWR) is then used to evaluate the efficiency of the coupling between the RF-signal applied to the transducer and the acousto-optical crystal. A higher VSWR indicates that more power is being reflected back and less is being absorbed by the transducer, which in turn results in a decrease in optical performance. The aim of this paper is to develop an RF driving system capable of compensating for the VSWR behavior, linked to the individual impedance matching network of each transducer. For this, the five transducer setups were
electrically characterized. These measurements allow the development of an RF power compensation system, leading to an increase of applied power at the level of each transducer. Hence, the absorbed power at transducer level increases, resulting in improved optical diffraction efficiency.