Diffraction of optical waves by an acoustic grating is a well-known phenomenon that enables the design of very versatile devices useful in photonic systems. For example, Acousto-Optic Tuneable Filters (AOTFs) can be dynamically tuned by radio-frequency signals. Among possible material choice, tellurium dioxide crystal is often used for practical applications due to its high efficiency. In such a birefringent material, the anisotropic configuration is often used. A feature of this configuration is the sensitivity to optical input polarisation: a selective coupling between polarized modes occurs. The incident must be polarised and the diffracted mode polarisation is orthogonal to the incident one. However, during the design process a very specific operation point can be found that ensures the simultaneous diffraction of both the ordinary and the extraordinary optical modes. In this presentation, we introduce the design of AOTF in birefringent crystals and present the main parameters that are subject to trade-off. Acousto-optic diffraction efficiency is sensitive to the so-called phase matching condition between optical wave and the ultrasonic wave. The offset from synchronicity is considered introducing a phase mismatch parameter. Diffraction efficiency evolution with respect to Bragg condition offset are illustrated. A custom device is finally presented that ensures simultaneous diffraction of both polarisation modes and compared to experimental results.@en

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.@en

We present an original acousto-optic tunable filter that is able to filter visible light from 400 to 650 nm and is designed to interact simultaneously with two polarizations. The filter shows an adjustable optical bandwidth and apodization capabilities. These features make it suitable for practical spectroscopic applications. Experimental validation is also presented.@en