a) Schematic diagram of the strain-sensing system based on the optical microfiber coupler. b) Simulation diagram of strain-CR response under different coupling lengths. c) Simulation analysis of sensitivity under different coupling lengths and radii. d) Experimental results of strain-CR response of the microfiber coupler with radii of 1.0 μm, 1.5 μm and 2.0 μm, respectively. e) Magnified plot of the area outlined in black in (d). f) CR periodic change and loss variation of the microfiber coupler under strains. g) Time-dependent strain-CR response produced from optical microfiber coupler sensor during periodic stretch and release over 10 000 cycles with 0.12% strain. h) Time-dependent strain-CR response produced from a loudspeaker at a frequency of 3 kHz. i) Frequency spectrum of the strain-CR response waveform.