Graphene and related two-dimensional materials have attracted great research interests due to prominently optical and electrical properties and flexibility in integration with versatile photonic structures. Here, we report an in-fiber photoelectric device by wrapping a few-layer graphene and bonding a pair of electrodes onto a tilted fiber Bragg grating (TFBG) for photoelectric and electric-induced thermo-optic conversions. The transmitted spectrum from this device consists of a dense comb of narrowband resonances that provides an observable window to sense the photocurrent and the electrical injection in the graphene layer. The device has a wavelength-sensitive photoresponse with responsivity up to 11.4 A/W, allowing the spectrum analysis by real-time monitoring of photocurrent evolution. Based on the thermal-optic effect of electrical injection, the graphene layer is energized to produce a global red-shift of the transmission spectrum of the TFBG, with a high sensitivity approaching 2.167×10⁴ nm/A². The in-fiber photoelectric device, therefore as a powerful tool, could be widely available as off-the-shelf product for photodetection, spectrometer and current sensor.

The centrosymmetric nature of silica fibre precludes the realisation of second-order nonlinear processes in optical fibre systems. Recently, the integration of 2D materials with optical fibres has opened up a great opportunity to develop all-fibre active devices. Here, we demonstrate high-efficiency second-order nonlinear frequency conversions in an optical microfibre assisted with few-layer gallium selenide (GaSe) nanoflakes. Attributed to the strong evanescent field of the microfibre and ultrahigh second-order nonlinearity of the GaSe nanoflakes, second harmonic generation (SHG) and sum-frequency generation (SFG) are effectively achieved with only sub-milliwatt continuous-wave (CW) lasers in the wavelength range of 1500–1620 nm, covering the C and L telecom bands. The SHG intensity from the microfibre is enhanced by more than four orders of magnitude with the assistance of the GaSe nanoflakes on fibre nonlinear processes. Moreover, in the SFG process, the intensity transfer between different frequencies can be effectively manipulated by changing the wavelengths and powers of two pump lasers. The realised strong second-order nonlinearity in the GaSe-integrated microfibre might expand the applications of all-fibre devices in all-optical signal processing and new light source generation at awkward wavelengths.

A high-sensitivity curvature sensing configuration is implemented by using a fiber Mach-Zehnder interferometer (MZI) with D-shaped fiber Bragg grating (FBG). A segment of D-shaped fiber is fusion spliced into a single mode fiber at both sides, and then a short FBG is inscribed in the D-shaped fiber. The fiber device yields a significant spectrum sensitivity as high as 87.7 nm/m$^-1$ to the ultra-low curvature range from 0 to 0.3 m$^-1$, and can distinguish the orientation of curvature experienced by the fiber as the attenuation dip producing either a blue or red wavelength shift, by virtue of the asymmetry of D-shaped fiber cladding. In addition, by tracking both resonant wavelengths of the MZI and embedded FBG, the temperature and curvature can be measured simultaneously.

We demonstrate a directional curvature sensor based on tilted few-mode fiber Bragg gratings (FM-FBGs) inscribed by a UV laser. The eigenmodes of ${\mathrm{LP}}_{01}$ and ${\mathrm{LP}}_{11}$ mode groups are simulated along with the fiber bending. The directional curvature sensor is based on the ${\mathrm{LP}}_{11}$ mode resonance in the tilted FM-FBG. For curvature from 4.883 to $7.625{\mathrm{m}}^{-1}$, the curvature sensitivities at direction of 0° and 90° are measured to be $-2.67$ and $0.128\mathrm{dB}/{\mathrm{m}}^{-1}$, respectively. The temperature variation barely affects the resonance depth of ${\mathrm{LP}}_{11}$ mode. The proposed curvature sensor clearly demonstrates the potential to simultaneous directional curvature and temperature measurement with the resolutions of $9.15\times {10}^{-4}{\mathrm{m}}^{-1}$ and 0.952°C, respectively.

We propose and experimentally demonstrate a method to significantly extend the sensitive window of tilted fiber-Bragg grating (TFBG) into low-refractive-index region with the integration of graphene coating. The coupling between cladding modes of TFBG and graphene coating results in an obvious modification of the cladding-mode envelope, which provides a sensitive regime relying on graphene’s complex refractive index. Interacting the graphene-coated TFBG with various aqueous solutions, we observe strongly enhanced sensitivity in the low-refractive-index region of 1–1.428, which is about 10-fold extended from that of the unloaded TFBG. The graphene-coated TFBGs present great potentials in the biochemical sensing window.

We present a refractometer with main- and vernier-scale to measure the refractive index (RI) of liquids with high precision by using the fine spectrum structure of a tilted fiber Bragg grating (TFBG). The absolute RI values are determined by the accurate wavelength of cut-off mode resonances. The main- and vernier-scale are calibrated by measuring large groups of fine spectra at different cut-off mode resonances in a small RI range, and the use of vernier-scale certainly reduces the RI measurement uncertainty resulted from the discrete cladding mode resonances. The performance of the TFBG-based vernier refractometer is experimentally verified by exploring the temperature dependence of RI of anhydrous ethanol in a near infrared region, showing an enhanced accuracy to the order of 10⁻⁴, high repeatability and temperature self-calibration capability.