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Valle S.,Ford Motor Company | Valle S.,University of Glasgow | Ward J.D.,Ford Motor Company | Pannell C.,Gooch and Housego Orlando | Johnson N.P.,University of Glasgow
Acta Physica Polonica A | Year: 2015

The λ2 dependence on acoustic field intensity (and hence RF drive power) can render large aperture acousto-optic tunable filters impractical for many applications beyond about 2 μm. One potential technique for reducing the RF drive-power requirement is to configure an acousto-optic tunable filter such that the interaction region is at acoustic resonance. We describe an acousto-optic tunable filter that operates at resonance and present an analysis of the predicted performance. In addition, we address the practical issues in deploying such a scheme. Finally, we present results of a prototype "resonant acousto-optic tunable filter" operating in the 1-2 μm region.


Valle S.,Ford Motor Company | Valle S.,University of Glasgow | Ward J.,Ford Motor Company | Pannell C.,Gooch and Housego Orlando | Johnson N.P.,University of Glasgow
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Acousto-Optic Tunable Filters with large acceptance angle (parallel tangent configuration) are the component of choice for imaging application in visible and NIR region wavelength. AOTF in the wavelength range above 2μm could be impractical due to the λ2 and interaction length dependencies on acoustic field intensity to achieve peak diffraction efficiency. A potential solution to reduce the RF power requirement for full diffraction efficiency is to realize a resonant acoustic cavity, and "recycle" the phonons. This configuration could give a theoretical advantage factor between 4 and 10. A prototype device with an operational wavelength range between 1μm and 2μm has been designed and tested and an optimized design to operate between 2μm-4μm has been prepared and under construction. Due to the presence of standing wave, when the device is not in resonance a feedback signal from the device is affecting the electrical matching and the power delivered to the device is mostly reflected back (VSWR > 25), therefore a special RF driver is required in order to maintain in resonance the device. The resonance frequencies are also affected by the temperature of the device, thus a temperature control mechanism with high accuracy is required. We present the preliminary results of the first prototype, which are in good agreement with the mathematical model and an advantage factor of about 4 has been measured. Further investigation are planned in order to improve the device performance and develop the RF driver for the resonant configuration. © 2015 SPIE.


Ward J.D.,Ford Motor Company | Valle S.,Ford Motor Company | Valle S.,University of Glasgow | Pannell C.,Gooch and Housego Orlando | Johnson N.P.,University of Glasgow
Journal of Physics: Conference Series | Year: 2015

Acousto-Optic Tunable Filters (AOTFs) are electronically-controlled bandpass optical filters. They are often preferred in applications in spectroscopy where their agility and rapid random-access tuning can be deployed to advantage. When used for spectral imaging a large aperture (typically 10mm or more) is desired in order to permit sufficient optical throughput. However, in the mid IR the λ2 dependence on RF drive power combined with the large aperture can prove to be a hurdle, often making them impractical for many applications beyond about 2μm. We describe and compare a series of specialised free-space configurations of AOTF made from single crystal tellurium dioxide, that require relatively low RF drive power. We report on AOTFs specifically optimised for operation with a new generation of Supercontinuum source operating in the 2-4μm window and show how these may be used in a spectral imaging system. Finally, we describe an AOTF with an (acoustic) Fabry-Perot cavity operating at acoustic resonance rather than the conventional travelling-wave mode; the acoustic power requirement therefore being reduced. We present an analysis of the predicted performance. In addition, we address the practical issues in deploying such a scheme and outline the design of a prototype "resonant AOTF" operating in the 1-2μm region. © Published under licence by IOP Publishing Ltd.

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