All-fiber phase shifter based on hollow fiber interferometer integrated with Au nanorods

We propose and demonstrate a novel all-fiber phase shifter by integrating a microstructured hollow fiber (MHF) and gold nanorods (GNRs) with photothermal effect. There are two cores and a central hole in the MHF. One core is suspended on the inner surface of the central hole, which serves as the sensing arm. The other one located in the cladding is as the reference arm. A Mach-Zehnder interferometer (MZI) can be fabricated simply through splicing multimode fiber-single mode fiber structures at both ends of the MHF. In this device, the center hole of MHF is filled with the solution of GNRs. The GNRs around the sensing arm is excited by near infrared light in the core via the evanescent interaction and the released heat because of the photothermal effect. Then, the refractive index around the sensing arm is modulated and the interference dips can be reversibly shifted. Experimental results show that spectral shift efficiency about -37.5 pm/mW near 1560 nm can be obtained under an excitation laser at the wavelength of 805 nm. This all-optical device based on MHF and GNRs has great potentials in integrated all-fiber signal controlling.