Introduction. Among acousto-optic spectrum analyzers with spatial integration, schemes based on optical interferometers provide the largest dynamic range. Nevertheless, they form the signal amplitude spectrum on a certain spatial carrier. Formation of quadrature components can eliminate this spatial carrier. The two-dimensionality of the transformations performed in optical processors provides this elimination by reading of the additional charge of matrix photosensor lines. A renowned method implements this approach using four lines, which in turn determines the estimation time of the signal spectrum.Objective. The objective of the work is to study the possibility of time reduction of the spectrum estimation.Materials and methods. The paper presents the description of two methods of forming the necessary components.The first method uses three photosensor lines, the charge distribution in which has the spatial carrier phaseshifted by 90 ° from line to line. The second method forms the necessary distributions sequentially in three accumulation cycles by means of variation of the initial phase of the reference signal. By the mathematical proof, three distributions with a 90 ° relative phase shift are sufficient to eliminate the spatial carrier.Results. In the first method, reduction of the spectrum estimation time is insignificant, but the parallel distributions formation affords not to impose additional requirements on the signal spectrum. The second method, due to the possibility of using any three sequentially formed distributions for estimation, is potentially three times faster than the first method, but requires the stationary signal spectrum within three accumulation cycles. Researchers can implement this meth-od using a linear photosensor or TDI photosenor. In addition, the method is less demanding to optical scheme parameters.Conclusion. The proposed quadrature components formation methods provide time reduction of the spectrum estimation in interference acousto-optic spectrum analyzers and simplify their design.

Introduction. For a homodyne acousto-optic spectrum analyzer functioning a reference optical channel must be organized. The signal in this channel should provide uniform reference illumination throughout the spatial frequency range. In the general case, the spectrum analyzer functioning can be considered with a continuous photosensor and photosensor with charge accumulation. With the last one, the signal in the reference channel is proposed to be a wideband pulses periodic sequence. Objective. Analyze the spectrum analyzer functioning with a periodic reference signal. Materials and methods. We derive the mathematical expression to describe the influence of the reference signal structure on the analyzer’s output signal for the cases of continuous photosensor and photosensor with charge accumulation. Results. It is shown that in the case of continuous photosensor, the reference signal periodicity does not lead to characteristics degradation. However, in the case of many frequency resolution points it is impractical, since each photodetector signal is parallel, processing is required: filtering, amplification and digitization. In the case of using of the charge accumulation sensor, the discrete frequency grid appears, which means signals omissions in frequency. This can be avoided by choosing the accumulation time equal to the minimum among the values of the acousto-optic modulator time aperture and the reference signal period, which is hard to implement, or still leads to the signal omissions in frequency or time. Conclusion. To perform a real-time mode in the homodyne acousto-optic spectrum analyzer, the reference signal must be either non-periodic, which raises the question of its synthesis, or a continuous photodiode array should be used.

Introduction. Acousto-optic spectrum analyzers interferometric schemes have been developed to increase dynamic range. It was assumed that dynamic range, expressed in dB, would double. An expected increase was not achieved yet.Aim. To analyze the homodyne acousto-optic spectrum analyzer noise characteristics, to estimate the signal-tonoise ratio and the dynamic range.Materials and methods. A mathematical model was compiled which took into account the need to form quadrature components to obtain an amplitude spectrum of an input signal, shot noise and readout noise.Results. An interferometric scheme did not allow to achieve dynamic range doubling compared to an acoustooptical power spectrum analyzer. The dynamic range increase was less than 1.35 dB. Constant illumination led to a significant increase of the spectrum analyzer self-noise due to shot noise, compared to which thermal noise and readout noise became insignificant. The spurious-free dynamic range estimation expression was obtained. It was prior determined by acousto-optic interaction nonlinearity. With typical analyzer blocks parameters the spurious-free dynamic range covered a single-signal dynamic range. Signal-to-noise ratio estimation expression was presented.Conclusion. The homodyne acousto-optic spectrum analyzer single-signal dynamic range is determined primarily by the photosensor saturation charge. One needs to optimize their relation by taking into account light source power, acousto-optical modulator diffraction efficiency and photosensor saturation charge. Presented noise model gives more accurate estimation of the dynamic range with an error of 1 dB.