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A novel broadband LP01↔LP02 mode converter for dispersion compensation based on special dual-core fiber is theoretically investigated by using the coupled-mode theory. The simulated mode converter has ∼22  nm bandwidth with a conversion efficiency of over 80%. Furthermore, this noncomplete conversion only introduces the insertion loss rather than multipath interference resulting from the residual LP01 mode. Finally, one optimal scheme for broadening the bandwidth of high-efficiency conversion has been proposed by longitudinally tapering the dual-core fiber. The simulation results show that the conversion bandwidth can be improved to ∼31  nm by tapering with a scaling range of only 2%.

An approach to achieve refractive index sensing at an air and aqueous glycerol solution interface is proposed using a tapered-fiber-based microfiber Mach-Zehnder interferometer (MFMZI). Compared to a surrounding uniform medium of air or solutions, the spectral interference visibility of the MFMZI at the air/solution interface is significantly reduced due to a weak coupling between the fundamental cladding mode and high-order asymmetric cladding modes, which are extremely sensitive to the external refractive index. The MFMZI is experimentally demonstrated as an evanescent wave refractive index sensor to measure concentrations of glycerol solutions by monitoring average power attenuation of the tapered fiber.

This paper presents an all-fiber tunable comb filter based on high-order mode fiber (HOMF). The filter is constructed by splicing a segment of HOMF between two sections of conventional single-mode fibers (SMFs), with an intentionally introduced offset at the first joint between the SMF and HOMF, and without an offset at the second joint between the HOMF and SMF, to optimize the visibility of the transmission spectrum. The optimal transverse offset of the fibers at the first joint and the tunable polarization-independent properties of the filter were studied theoretically and experimentally. An example of using this tunable comb filter in the application of a sensor, based on demodulating the wavelength shift of a fiber Bragg grating, has also been demonstrated. The particular advantages of this all-fiber tunable filter make it valuable in various applications.

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