An in-line optical fiber Mach–Zehnder interferometric (MZI) sensor is proposed and experimentally demonstrated for magnetic field measurement. The fabrication mechanism of the optical fiber microstructures by CO₂ laser is described in detail. The sensor with symmetrical structure is fabricated by splicing a 7-mm length of seven-core fiber and two fiber peanuts, which is encapsulated with magnetic fluid in the capillary. The transmission spectrum of the MZI is modulated by the refractive index of the magnetic fluid, which is affected by the magnetic field. The experimental results indicate that the mode interference is sensitive to the magnetic field and different dips of the interference spectrum have different sensitivities. Hence, simultaneous measurement of the temperature and magnetic field can be achieved by simultaneously monitoring two different dips. The sensitivities of the magnetic field and temperature can reach up to 0.062 nm / Gs and 0.081 nm / ° C, respectively. The proposed Mach–Zehnder interference sensor has a more compact structure, simple manufacturing process, and high reliability, which would find potential applications in weak magnetic sensing fields.

The predecessor of China Optics was China Optics and Applied Optics Digest, which was founded in 1985. At that time, it was the only retrieval journal in the field of optics in China. At the end of 2008, China Optics and Applied Optics Digest was renamed 《中国光学》的前身是1985年创办的《中国光学与应用光学文摘》，当时是国内光学领域唯一的检索刊物。2008年底《中国光学与应用光学文摘》转型更名为《中国光学与应用光学》期刊，刊载内容突破了文摘的限制，正式成为学术刊物。

A tapered-optical fiber tip coupler for the excitation of capillary whispering gallery modes (WGMs) is proposed. The phase matching theory and spectral features are analyzed. The light transmission characteristics and cross-sectional mode fields of the coupler are simulated. The impact of fabrication tolerance on excited WGM is studied, and the structure is fabricated based on the simulation results. It has been experimentally verified that this structure can excite the WGM resonance of capillaries of various sizes, with the highest quality factor (Q factor) of 3.6×103 and refractive index sensitivity of 22.28 nm/RIU. The resonant coupler is not fragile, large fabrication tolerance, and can excite WGM in capillaries of different sizes, which can provide a new means of detection in the field of capillary biochemical sensing.