The mechanical-induced long-period fiber grating(LPFG) is obtained by pressing the fiber in single side,whose cladding is etched by HF solution,and the pitch of the grooved plate is 600 μm.The influence of the cladding diameter on the coupling characteristics between the core fundamental mode and the cladding LP12 and LP13modes is analyzed by measuring the transmission spectra of LPFGs with different cladding diameters under different pressurs.Experimental results show that the red-shift of the ...