Design Of Wide-band Drive System For Acousto-optic Tunable Filter

Acousto-optic tunable filter is widely used in military, medical, agriculture, aerospace and other fields in spectral imaging, spectral detection, physical object recognition, and remote sensing. It has high diffraction efficiency, fast spectral tuning rate and wide spectral tuning range, and can complete spectral selectionby conveniently by adjusting the external driving signal. It can analyze the location, composition, status and other informations of an object mainly through its spectral response characteristics at different wavelengths. According to the requirement of spectral imaging ellipsometry system, this paper start from the working principle of AOTF, design and make the AOTF wide-band drive system, as a driving source of the spectrum acquisition subsystem.The drive system is divided into two modules, namely the signal source module and power amplifier module. The signal source module using the direct digital frequency synthesis technology, configure the internal registers(frequency, phase, amplitude etc) of DDS through the MCU, and output RF signal whose amplitude and frequency tunable by 200 MHz low pass elliptic filter in the final. Since the power of output signal which AOTF needs to work normally is more than 2W, but the output ability of DDS is limited, we need to amplify the power through power amplifier. The power amplifier module using two stage cascaded structure, building simulation environment and model using ADS2014, and designing appropriate impedance matching circuit using lumped elements, after debugging, adding transmission line transformer at the output matching end, so that the output power of power amplifier reach 2W or more at 60 MHz ~ 200 MHz, with the within gain flatness is 1.54 dB. AOTF diffraction experiment platform is builted eventually, after tested, the diffraction efficiency of the AOTF is above 74.4% and up to 92.7%, and the spectral bandwidth is better than 8nm, with a higher spectral resolution.In the drive system we designed, because of the unconditionally stable of driver stage and the better of internal match, we only need to design the output stage, and the match circuit is designed by lumped elements, structure is simple and easily to debug. The system can not only meet the requirements of the topic, but also can provide help and support for the design of different performance of AOTF driver and application of AOTF spectral imaging.