This paper presents a Hadamard-multiplexed spectrometer based onan acousto-optic tunable filter (AOTF). In a multiplexed instrumentmultiple signals are measured simultaneously. The signals are combinedin such a way that subsequent processing can recover the individualsignal values. The multiplexing technique used in this instrument isbased on the Hadamard matrix. The Hadamard encoding process can beperformed by an AOTF. The AOTF transmits an optical wavelength inresponse to an applied acoustic signal in the filter. The transmissionefficiency is a nonlinear function of power and varies with frequency.Dynamic range and constraints on maximum power place a limit on thenumber of signals that can be simultaneously applied. Under amaximum-total-power constraint, the power per frequency can be tradedoff for maximum multiplex advantage, due to the nonlinearity of thepower transmission relationship. Determination of the optimal powerallocations and the number of frequencies to multiplex are considered.An expandable, PC-based spectrometer has been developed to illustratethis technique. The current implementation provides four-frequencymultiplexing and collects the spectra as multiplexed blocks. The AOTF iscontrolled via VHF synthesizers. The synthesizers are IEEE-485 bussedmodules based on a hybrid DDS/PLL technique. The modular design allowsconvenient system expansion
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