All-Fiber Electric Field Sensor With Tapered Two-Mode Fiber Structure on DR1/PMMA Polymer

A novel all-fiber electric field (
${E}$
-field) sensor based on a tapered two-mode fiber (TTMF) structure integrated with disperse red 1/polymethyl methacrylate (DR1/PMMA) polymer film is demonstrated for the first time. Here, a TTMF sandwiched between two single-mode fibers (SMFs) works as the modal interferometer with HE11 and HE12 modes, allowing a high-refractive index (RI) sensitivity of 8154.76 nm/RIU (at RI of 1.55–1.56). The DR1/PMMA polymer film, which is electric-poled successfully to be an electro-optic (EO) polymer film of an EO coefficient of 3.68 pm/V, is integrated with the TTMF to make the all-fiber
${E}$
-field sensor. Experiments show the interferometric spectrum transmitted through the sensor will blue shift when increasing the applied
${E}$
-field, allowing the sensor to have a relatively high sensitivity of 1.26 dB/V for an
${E}$
-field and a high extinction ratio of 6.5 dB. In addition, for ac
${E}$
-field, the sensor exhibits a relatively high 3-dB bandwidth of 1.4 kHz and a high fidelity with a low harmonic distortion of < 2.5%. The EO polymer film is very flexible to be incorporated with high-performance all-fiber devices, opening up a way to endow the fiber devices with the second-order nonlinear optic functions.