Distributed Liquid Level Sensor Based on Brillouin Optical Frequency-Domain Analysis

Abstract

We propose and demonstrate a distributed liquid level sensor based on high-resolution Brillouin Optical Frequency-Domain Analysis and an actively heated cobalt-doped optical fiber. The liquid level position is determined by localizing the abrupt temperature change occurring along the active fiber at the liquid/air interface, through distributed temperature sensing. Differently from previous works based on the use of optically heated fibers, in the proposed configuration no separate laser source was employed to heat the fiber. In practice, a single laser source was adopted for both optical heating and distributed temperature sensing. The experiments report the measurement of the liquid level position with 5 mm level resolution along a 9-cm long heated fiber. The paper also discusses the limitations of the proposed method. In particular, the negative impact of spontaneous Brillouin scattering, in terms of measurement noise, is revealed by the measurements. We show that the spontaneous Brillouin scattering induces spurious components in the frequency-domain, affecting the accuracy of temperature measurements.