A novel acousto-optic tunable filter for use in hyperspectral imaging systems

C. Stedham, M. Draper, J. Ward, E. Wachman, C. Pannell

Research output: Chapter in Book/Report/Conference proceedingConference contribution

9 Citations (Scopus)


The design and performance characteristics of a novel Acousto Optic Tunable Filter (AOTF) are presented. Particular attention has been paid to the reduction of optical side lobes, maximising the light throughput and achieving efficient wideband RF matching of a device for use in hyperspectral imaging systems. Conventional AOTFs are known to yield an optical pass band with side lobes at unacceptable levels of ~-10dB relative to the transmission peak. It is known that shaping the acoustic beam ("apodisation") can suppress the side lobe transmission of the AOTF and improve its imaging capabilities. Results of a novel electrode apodisation pattern are presented, reducing sidelobes to ~-25dB. This produces an AOTF which is capable of being placed in a diffraction limited optical system and introduces negligible amounts of image degradation. The large transducer area (associated with the large optical aperture) and acoustic impedance mismatch between the AO substrate (TeO 2) and transducer (LiNbO3´) pose a challenge in achieving wideband RF performance. Acoustic mismatch between substrate and transducer has been addressed by the introduction of a special acoustic matching layer in the bond. The layer reduces dispersion in the transducer impedance easing broadband matching. The transducer has a low (<1 Ohm) radiation resistance which must be matched to the RF driver (typically 50 ohms). This very low impedance may be swamped by the parasitic impedances of the electrode, bond layers and wire bonds used for electrical connection. Thus, the transducer is split into series-connected sections to increase the "bare" impedance. We present results to show the performance increase that can be obtained this way.

Original languageEnglish
Title of host publicationPhysics and Simulation of Optoelectronic Devices XVI
Publication statusPublished - 2008
EventPhysics and Simulation of Optoelectronic Devices XVI - San Jose, CA, United States
Duration: 21 Jan 200824 Jan 2008


ConferencePhysics and Simulation of Optoelectronic Devices XVI
Country/TerritoryUnited States
CitySan Jose, CA


  • Acousto-optics
  • Hyperspectral imaging
  • Impedance matching
  • Spectral imaging
  • Tunable filters


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