We have solved the wavelength-depende nt rate equation applicable to the FRSLs.An analytical expression for position- dependent photon flux in FRSLs is deduced.Dependence between the tunable output power and device parameters (including on splitting ratio,coupling coefficients and residual reflectivity et al.) was investigated using the rate equations.The experimental results are compared with theoretical simulations in order to deter mine the factors that influence the tunable output characteristics of FRSLs.Dyna mic sing-mode tuning of a FRSLs is realized and tuned over a wavelength range o f 36 nm using band-pass filter as a selected wavelength element.