MINIMIZATION OF NOISE FLOOR LEVEL OF FIBER-OPTIC INTERFEROMETRIC SENSOR ARRAY BY ADJUSTMENT OF OPERATIONAL AMPLIFIER CASCADE PARAMETERS

Subject of Research. The paper presents results of the experimental study on the dependence of the noise floor level of a fiber-optic interferometric sensor array on the gain factor of operational amplifiers located on the signal processing board and connected in series into a single cascade. Method. The fiber-optic interferometric sensor array is based on Michelson interferometers, arrayed with time division multiplexing. Operational amplifier cascade consists of a variable operational amplifier and a current feedback operational amplifier (transimpedance amplifier), which converts the photocurrent from the photodiode to voltage. A signal from the photodetector is transmitted to transimpedance amplifier, which has two operating modes with gain factors equal to 0 and 6 dB, and then to programmed operational amplifier, which additionally amplifies the incoming electric signal in the range from 0 to 40 dB. Further, enhanced signals from the amplifier cascade are fed to analog-todigital converter and then they are demodulated. During the experiment the fiber-optic sensor array under research was closed off from external vibroacoustic impacts on the sensor. Noise signals from four sensors were recorded after demodulation into data files at the various values of gain factors of operational amplifiers. Spectral estimations of noise floor levels of the fiberoptic interferometric sensors were performed by the averaged modified periodogram method depending on the gain factors of operational amplifiers. Main Results. The following minimal average noise floor levels were obtained: 65 urad/Hz0.5 at 1000 Hz with the gain factor of the current feedback operational amplifier equal to 6 dB and the gain factor of the variable operational amplifier equal to 12 dB, and 80 urad/Hz0.5 at 1000 Hz with the gain factor of the current feedback operational amplifier equal to 0 dB and the gain factor of the variable operational amplifier equal to 20 dB. Practical Relevance. The study has shown that optimal operating conditions are achieved with the gain factor of the current feedback operational amplifier equal to 6 dB and in the range of the gain factor of the variable operational amplifier from 5 dB to 20 dB, which provided the minimal average noise floor level of the fiber-optic interferometric sensors at the level of 65–70 urad/Hz0.5. The proposed method of applying operational amplifiers is usable for the amplification of optical signals from the fiber-optic multiplexed sensor array without significant deterioration of their noise performance in case of the optimal operating domain selection.