Acousto-Optic Filters are versatile devices with a range of applications in modern optics. Their technology has reached a mature industrialability. They are particularly valuable in fields requiring precise wavelength selection and fast switching capabilities, making them essential tools in various applications. The generalisation of their use has led to new applications still requiring specific developments.We present the design and validation of an AOTF for spectro-polarimetry analysis which provides a constant spectral resolution over a wide spectral band. The variation of the spectral resolution is made possible by the manufacture of a transducer divided into multiple electrodes allowing to play on the interaction length easily by activating and deactivating the electrodes. In addition, the power distribution supplying the electrodes can be modulated, which offers the possibility of finely controlling the spectral template.The device developed has an acoustic cut of 5°, operating from 450 to 800 nm. We opted for a transducer equipped with 5 electrodes. This strategy makes it possible, depending on the power supply conditions, to modulate the selectivity of the filter by a factor of 4 for a given wavelength and to maintain a constant selectivity of the order of 10 nm over the entire operating range.

One of the main challenges for users applying an AOTF as a commercial off-the-shelf component for optical wavelength filtering, is the lack of detailed manufacturing information on critical parameters. Information such as diffraction angles, the precise RF driving frequencies required for momentum-matching conditions, as well as the data for each wavelength across a certain optical spectrum is not always easily available. To obtain this information, users must perform physical tests to configure the optimal frequencies, diffraction angles, and incidence angles for each wavelength of interest which is labor-intensive and costly.This research uses an optimization algorithm applied to an analytical model which can characterize key angles related to the AOTF’s crystallographic axis, such as the crystallographic axis angle θc, the tilt-angle α, as well as facet inclination angles β and γ. First, diffraction testing on an AOTF is done, by recording both output ray angles and the momentum-matching frequency. Then the optimization algorithm is chosen and applied to the analytical model to determine the optimal parameters for θc, α, γ, and β. With these parameters, the AOTF’s behavior can be extrapolated to multiple wavelengths, which not only saves time, but also enables more versatile planning of optical setups.

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.

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.

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.