Fig. 1. (a) Schematic diagram of the micro-helix taper-CLPG. (b) Schematic diagram of the grating fabrication process. (c) Microscopic image of the off-axis micro-helix taper.

Fig. 2. Intensity distributions along the propagation direction. The chirped structure with different off-axis twisted radii. (a) 1 µm, (b) 3 µm, and (c) 5 µm. (d) The non-chirped structure (R = 3 µm).

Fig. 3. (a) The cross section of a helical core fiber. (b) The equivalent cross section of the fiber bent in the radius direction axis.

Fig. 4. Diagram of a curved coordinate system. The section diagram of the bending direction with (a) minimum and (b) maximum refractive index variation.

Fig. 5. (a) Measured transmission spectra of the CLPG with different torsional radian values. The mode field patterns at (b) 1441.2 nm and (c)1580.4 nm.

Fig. 6. Spectral evolution of dip A for different bending directions. (a) 0°, (b) 90°, (c) 180°, and (d) 270°. (e) The wavelength of dip A as a function of the curvature for different bending directions.

Fig. 7. Spectral evolution of dip B for different bending directions. (a) 0°, (b) 90°, (c) 180°, and (d) 270°. (e) The wavelength of dip B as a function of the curvature for different bending directions.

Fig. 8. Bending sensitivity of grating as a function of the rotational angle for (a) dip A and (b) dip B. Insets: diagram of the bending angle.

Fig. 9. The wavelength of the dip as a function of the curvature for bending directions 0°, 90°, 180°, and 270°.

Fig. 10. The temperature responses of dips A and B.