Highlights 1. An optical fiber-based humidity sensor with ultrafast response is proposed by depositing GO onto a tilted fiber grating (TFG) with large tilted angle. 2. The experimental results show sensitivities of 18.5 pm/%RH and 0.02 dB/%RH with highly linear coefficient in the dynamic range of 30%-80%RH. 3. The sensor is successfully applied to monitor human breathing cycles with different breathing frequencies. 4. The sensor also shows the properties of easy fabrication, low hysteresis, ultrafast response, and high repeatability and reliability.

We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating (TFBG) for enhanced refractive index sensing. The TFBG is UV-inscribed in series in ordinary single-mode fiber (SMF) and reduced-diameter SMF with the same tilt angle, and then excites two sets of superposed spectral combs of cladding modes. The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF, enabling an enlarged range and a higher accuracy of refractive index measurement. The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.

We achieve Fano-like resonances in an all-in-fiber structure embedded with an in-line Mach-Zehnder interferometer (MZI). A fiber Bragg grating is inserted into MZI's one arm to form a resonance, which functions as the discrete state of the Fano-like resonance to couple with the continuum propagating mode of MZI in the fiber core. A theoretical model predicts the controllable resonance lineshape by changing the phase difference between the MZI's two interference pathways. Fano-like resonances with an extinction ratio over 20 dB are experimentally observed, which are reliably tuned into Lorentzian and electromagnetically induced transparency-like resonances by versatile methods. The realization of Fano-like resonances with broad tunability in this all-in-fiber structure holds potentials in fiber-based applications of sensing, signal processing and nonlinear optics.