High sensitivity DC current sensor based on microfiber Mach-Zehnder interferometer combined with copper wire

Abstract

A highly sensitive fiber optic direct current (DC) current sensor based on Mach-Zehnder interferometer (MZI) combined with copper wire was proposed. Firstly, the coatings stripped single-mode fiber (SMF) is directly tapered to form an MZI, named MZI₁. Due to the tapering treatment of SMF, MZI₁ is particularly sensitive to temperature. In addition, due to the excellent heat transfer performance of copper wire, we fixed MZI₁ on a copper wire with a diameter of 1 mm and a length of 3 cm. The DC current generates Joule heat through the copper wire and conducts it to MZI₁. The heat transferred by the copper wire can significantly shift the dip wavelength of MZI₁, and the demodulation wavelength drift can indirectly achieve the measurement of DC current. The current square sensitivity of MZI₁ bonded with copper wire obtained from the experiment reached 209.5 pm/A², with a linearity of 0.9980. To further improve the sensitivity of MZI₁, we manufactured MZI₂ using the same manufacturing method as MZI₁, making the free spectral range of MZI₂ close to that of MZI₁. Then, we connected MZI₁ and MZI₂ in series to form a vernier effect sensor S₁ for DC current measurement. The experimental results show that the current square sensitivity of S₁ is as high as 3.28 nm/A², which amplifies the sensitivity of MZI₁ by 15.6 times. Meanwhile, S₁ also has excellent repeatability and stability, and the wavelength resolution and detection limit of S₁ are 0.65 nm and 0.45 A respectively. Due to the fact that the sensor manufacturing only involves optical fiber cleaving, optical fiber tapering, and materials bonding, this sensor has the advantages of simple structure, easy to manufacture, low cost, sturdy structure, and good structural repeatability, providing a new alternative solution for measuring DC current in practical applications.