Fig. 1. (a) Schematic diagram of the cl-RSE structure preparation (inset shows the position of the cl-RSE structure in the electric mode field of the fiber). (b) Rayleigh backscattering profile of a 100 mm long cl-RSE structure. (c) Optical micrograph of the side of the cl-RSE structure. (d) SEM image of the fiber cross section with a modulation point.

Fig. 2. (a) 2D model setup of the cladding refractive-index modulation point in SMF. (b) Periodic refractive-index distribution in the cladding. (c) Electric field mode distribution with 100 cladding scatterers in the SMF; fiber length set to 3 mm. (d) Electric field mode intensity distribution of z axis at x=15  μm in (c). Electric field mode distributions localized without (e) and with (f) cl-RSE structures. (g) Electric field mode intensity distribution along the radius.

Fig. 3. Effect of different cl-RSE structures on the enhancement of backscattered signals. (a) Micrographs of representative samples at different parameters. (b) Statistics of Rayleigh scattering enhancement at different offsets and pulse energies. (c) Statistics of Rayleigh scattering enhancement at different intervals. (d) The backscattering profile of 11 scatterers spaced at 2000 μm intervals allows the backscattering enhancement of each point to be clearly distinguished.

Fig. 4. (a) IL for different numbers of scatterers; inset shows the trend of average IL. (b) Transmission spectra of the cl-RSE structure in the 1000 nm range, which did not exhibit wavelength-dependent absorption.

Fig. 5. High-temperature testing of cl-RSE fiber. (a) Schematic of cl-RSE fiber placed in a tube furnace. (b) Temperature response of 100 mm long cl-RSE fiber at 0°C–800°C for three temperature cycles. (c) Long-term stability of 100 mm long cl-RSE fiber at different temperatures: (c1) 800°C, (c2) 900°C, and (c3) 1000°C. Temperature measurement fluctuations of cl-RSE fiber (d) before and (e) after annealing at 800°C.

Table 1. Performance Comparison of Scattering Enhanced Structures Fabricated Based on Femtosecond Laser