Design and application of high performance Acousto-Optic Tunable Filters

QC Physics

Valle, Stefano ; Engineering and Physical Sciences Research Council (EPSRC) ; Johnson, Nigel

University:University of Glasgow

Department:School of Engineering

关键词: Acousto-optic, resonant cavity, AOTF, tunable filters, UV, MIR, Tellurium Dioxide, Calomel, Crystal Quartz.;   

Others  :  http://theses.gla.ac.uk/8323/1/20172ValleEngD.pdf

来源: University of Glasgow

【 摘 要 】

The design and application of high performance Acousto-Optic Tunable Filters (AOTFs)is the topic of this thesis. The most common material commercially used to buildAOTFs is Tellurium Dioxide because of its extended wavelength range from 380 nm up4.5 μm, a good acousto-optic figure of merit, and the availability in crystal of large di-mension with good optical quality. The performance of an AOTF can be summarizedby passband versus wavelength, RF power to achieve peak diffraction efficiency andtuning range. One of the most relevant parameters which limits AOTF performanceis the RF power versus diffraction efficiency, which increases with 2. A practical limi-tation has been imposed to 50mW /mm2 , above these level thermal gradient affectsthe performance. This level is easy reached for conventional AOTF for wavelengthabove 2.5 μm. The reduction of RF power requirement is achieved by means of acous-tic resonant cavities. The theoretical development and subsequent design of the firstresonant AOTF developed inside Gooch and Housego is carried out, and the exper-imental results are in good agreement with the predicted performances. The resultsobtained from the experience with resonant AOTFs lead to extending the wavelengthrange from 180 nm up to 10 μm using different acousto-optic materials with limitedperformance with conventional configuration. Crystal quartz is investigated to extendthe wavelength range down to 180 nm, this material is well known in acousto-opticapplications. The resonant configuration is particularly suitable for this crystal sincethe advantage factor is particularly high thanks to the low acoustic attenuation. Theexperimental results show good agreement with the predicted performances, leading toa large aperture AOTF operating between 180 nm and 380 nm with RF power for peakdiffraction efficiency below 8 W. This is the first time that a resonant imaging AOTFmade of crystal quartz is reported in literature, to the best of the authors knowledge.Calomel single crystal is investigated to realise an AOTF operating between 4.5 μmand 10 μm. Due to its physical properties which are incompatible with conventionalmanufacturing processes, different challenges (such as bonding the ultrasonic trans-ducer) are solved by the author in order to build a high performance AOTF. Despite the preliminary results showing promise, the acousto-optic properties of the materialare limiting the achievable performance, at least for acousto-optic tunable filters, afact that does not seem to have been widely appreciated , and which cannot solvedby just optimising the design. From the application point of view an optical spectrumanalyser based on AOTF technology is investigated, where a dual polarization AOTFis developed in order to realize a spectrometer with a competitive price operating in thewavelength range between 2.5 μm and 4.5 μm. The effects of the acoustic attenuationon a large aperture AOTF is investigated theoretically and experimentally since theperformance is affected in the UV range leading to non-ideal operating condition, anda solution is proposed to overcome this issue The results obtained will allow the designof high performance AOTFs in the industrial environment leading to a new types ofdevices with enhanced performance.