Characteristics of a high extinction ratio comb-filter based on LP01–LP11even mode elliptical multilayer-core fibers

• A comb-filter based on homemade fibers can achieve a high extinction ratio.
• The strictly dual-mode EMCF is the first time to produce and apply in MZ comb filer.
• The analysis of the mode coupling is presented theoretically and experimentally.
• For applications, this MZ comb-filter is used as the SRI and temperature sensors.
• A higher sensitivity of 59.875 pm/°C within the range of 0–80 °C is achieved.

We experimentally characterized an all-fiber microstructure Mach–Zehnder comb-filter (MZ comb-filter), which based on homemade elliptical multilayer-core fibers (EMCF) and consisted of an EMCF–SMF–EMCF (ESE) structure. To the best of our knowledge, the dual-mode elliptical multilayer-core fiber was the first time to produce and apply in MZ comb filer. The EMCF, in which only two modes could be propagated, can be easier to fabricate a filter with clean comb spectrum than many fibers, such as multimode fibers, thin-core fibers, PCFs and et al. A comb-filter with extinction ratio (∼25 dB) was successfully achieved with an EMCF–SMF–EMCF structure. The wavelengths of the lead-out light shifted with the changing of surrounding refractive indexes (SRI) and temperature. Thus, this MZ comb-filter had potential for improving the SRI and temperature measurement resolutions. A maximum sensitivity of 53.744 nm per refractive index unit (RIU) within a linear range of 1.333–1.383 and 59.875 pm/°C within temperature range of 0–80 °C were experimentally achieved, respectively.