Output noise analysis of optical fiber interferometric sensors using a 3 × 3 coupler

Abstract

The output noise in a digital passive demodulation scheme for optical fiber interferometric sensors using a 3 × 3 coupler is investigated both theoretically and experimentally. In such a scheme, the measured signal is recovered by the linear combination of the three outputs and a digital arctangent approach. The impact of the additive noise (AN), multiplicative noise (MN) and square-root noise (SN) on the output noise is analyzed. Equations to calculate the output noise variance from the inputs AN, MN and SN are derived for both symmetric and asymmetric 3 × 3 couplers. According to our study, the initial phase and the correlation of different input noise also have great impact on the output noise level. Simulations show that the theoretical analysis is of high accuracy. The noise transfer function (NTF) defined as the ratio of output noise and mean input noise variances is proposed to describe the noise performance of a digital passive demodulation scheme using a 3 × 3 coupler. In our experiment, the distribution of the output noise variance as a function of the initial phase is observed. A method was proposed to predict the distribution of the output noise variance by estimating the variances and the correlation coefficients of the input noises using the non-negative least-squares method and polynomial fitting. The distribution of the output noise variance estimated by this method agrees well with the experimental results.

Improvement of Noise Stability of Michelson Optical Fiber Voice Monitoring System

“…In this method, the shot noise of the photodetector and the circuit noise generated by circuits are considered. The shot noise of the photodetector is proportional to the square root of the intensity of the measured light [13], which mainly depends on Δφ d (t) at a certain moment t. Therefore, take the first signal I PD1 as an example, the shot noise in I PD1 is expressed as:…”

“…We just need to adjust the settings of A and D in the algorithm to obtain the best noise stability. The circuit noise generated by photoelectric detection and data acquisition does not change with measured light [13]. The photodetectors used in our system are integrated on the same circuit board, thus the circuit noise is same for three signals, expressed as ne(t).…”

“…The power of background noise of the sensor changes up and down with the change of the working point of the interferometer. In MI with lengths of the two arms precisely matched, the background noise mainly comes from the circuit noise of electrical devices such as photodetectors and data acquisition card, and the shot noise of photodetectors [13]. The power of circuit noise is relatively constant and small, but the power of the shot noise change with the optical power entering the photodetector, which is the main cause of unstable noise.…”

Equivalent phase noise analysis in broadband source sensing system using a 3×3 coupler

“…The shot noise is additive noise. For multiplicative noise and additive noise, Zhang et al analyzed that the expected value of equivalent phase noise contributed by them through the arctangent algorithm is [5] ( )(…”

“…Todd analyzed the output noise statistical characteristics of the 3×3 coupler demodulation scheme and derived a generalized transfer function for intensity noise to convert into phase noise [4]. Zhang et al analyzed the impact of the input noise intensity, correlation, and initial phase on output noise [5]. These studies reveal the noise conversion relationship of the demodulation scheme using a 3×3 coupler.…”