A Hadamard-multiplexed spectrometer based on an acousto-optic tunable filter

This paper presents a Hadamard-multiplexed spectrometer based on an acousto-optic tunable filter (AOTF). The multifrequency capability of the AOTF enables it to be operated in a multiplexed mode. The AOTF can then be operated at lower power to obtain improved passband characteristics without a reduction in the signal-to-noise ratio as compared to a higher-power, nonmultiplexing instrument. An expandable, PC-based spectrometer has been developed to illustrate this technique. The current implementation provides seven-frequency Hadamard multiplexing and collects the spectra in multiplexed blocks. The AOTF is controlled via IEEE-485 bussed VHF synthesizer modules based on a hybrid DDS/PLL technique. The modular design allows convenient system expansion. The design of and specifications for this instrument are discussed.