Cryogenic characteristics of in-fiber Mach-Zehnder interferometers based on EDF and MMF

Abstract

In-fiber modal interferometers have been widely used in the applications of biochemical sensing, mine safety and health monitoring of buildings. The temperature feature of sensors is one of the most important characteristics, but the studies are rarely reported under the condition of subzero temperature. In this paper, through core-mismatch fiber splicing method, three in-fiber Mach-Zehnder interferometers (MZIs) are fabricated based on single-mode fiber (SMF), erbium-doped fiber (EDF, with core diameter of 3.6 μm) and multimode fiber (MMF, with core diameter of 50 μm), respectively. Their interference patterns are investigated through beam propagation method and Fast Fourier Transform analysis. The comprehensive tests of temperature are then performed in the range from -40 to 0°C. The experimental results show that, in subzero temperature, the transmission spectrums of MZI sensors based on single mode fiber (SMF) and MMF are worsened in terms of fringe visibility and intensity. And the sensitivity of MMF-based structure is 68.8 pm/°C with a 12.3-dB deduction of fringe visibility. Comparatively, the EDF-based MZI presents ideal sensitivity due to negative gain-temperature feature. By calculation, the 124.7 pm/°C sensitivity is gained with the linearity of 0.9892. Moreover, 10-dB enhancement in intensity and over-20-dB fringe visibility are demonstrated, which indicates that the EDF-based sensor is potential and promising for the applications of cryogenic sensing.