Microfiber Mach-Zehnder interferometer based on long period grating for sensing applications

Abstract

A Mach-Zehnder interferometer (MZI) composed by a pair of long period gratings (LPGs) fabricated in silica microfiber for sensing applications is demonstrated. Each LPG is fabricated with a pulsed CO2 laser by creating six periodical deformations along fiber length with only one scanning cycle. The length of the MZI can reach as short as 8.84 mm when the diameter of the microfiber is 9.5 μm. Compared with the ones fabricated in single-mode fibers, the present MZI is much shorter owing to the large effective-index difference between the fundamental and higher order modes. The microfiber MZI exhibits a sensitivity to surrounding refractive index (RI) of 2225 nm per refractive index unit and the temperature sensitivity of only 11.7 pm/°C. Theoretical analysis suggests that the performances of the MZI sensor can be improved by using thinner microfibers with a diameter down to 3.5 μm: The sensitivity can be greatly enhanced due to the stronger evanescent-field interaction and reduced dispersion factor; the transmission dips become narrower which benefits high-resolution measurement; the thinner fiber also allows further reduction in device length. The present device has great potential in biochemical and medical sensing due to the advantages including easy fabrication, excellent compactness and high sensitivity.

Real‐Time Cellular Cytochrome C Monitoring through an Optical Microfiber: Enabled by a Silver‐Decorated Graphene Nanointerface

“…Its taper structure excites the higher‐order mode (HE 12 ), which interferes with the fundamental mode (HE 11 ), creating an interferometric fringe in the fiber transmission spectrum (Figure S3, Supporting Information) 22, 23. As the HE 12 mode spreads into the surface coating (Figure S4, Supporting Information), it senses the surface RI change and translates it into a wavelength shift in the interferometric fringe 12, 24.…”

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“…Thus, the periodic formation of the locally tapered diameter changed the effective RI, leading to the realization of the LPG structures. Two LPGs were also inscribed in the silica microfiber in order to form a MZI [255]. Owing to the large effective index difference between the fundamental and higher order modes, the LPG-based MZI could be more compact with less than 1cm in length.…”

An Optical Microfiber Taper Magnetic Field Sensor With Temperature Compensation

“…If the waist diameter is larger than 10 m (but smaller than 30 m), multimode interference will appears [-15], which will impact the stabilization of the wavelength shift when the temperature or magnetic field changes. Besides, the sensitivity with smaller diameter can be enhanced due to the stronger evanescent-field interaction [21]. On the other hand, the waist diameter could not be too small.…”