Improving the Sensitivity of Temperature Measurement Based on a Dual-Passband Microwave Photonic Filter

Abstract

In this article, a dual-passband microwave photonic filter (MPF) is proposed and experimentally demonstrated for high-precision temperature sensing. A pair of parallel Mach–Zehnder interferometers (MZIs) sharing the same sensing arm is used to splice the broadband optical light source (BOS). Since the interference spectrum in the optical domain is a combination of two MZIs with different free spectrum ranges (FSRs), an MPF with two passbands is successfully generated in the microwave domain. The kernel of this scheme is precisely controlling the length of the sensing arm between the lengths of the upper arm and lower arm. When the temperature applied to the sensing arm changes, the FSR <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${s}$ </tex-math></inline-formula> of two MZIs vary contrarily, resulting in the two passbands of the MPF shifting in the opposite direction. By tracking the central frequency difference between two passbands, the sensitivity can be enhanced. Experimental results show that with the increased temperature, the first passband moves to the lower frequency range, whereas the second passband shifts to the higher frequency range. The central frequency of an arbitrary passband is proportional to the temperature. The sensitivity is 16.81 ± 4.73 MHz/° by tracking the central frequency of a single passband, while, by recording the central frequency difference between two passbands, the sensitivity can be improved to 33.55 ± 4.17 MHz/°, which is twice over a single passband.