Control of the characteristics of a long-period grating by cladding etching

We have analyzed the effects of the fiber cladding radius on the characteri stics of long-period fiber gratings. By etching the cladding of a common si ngle-made fiber, we verified the characteristics experimentally. When by et ching we reduce the cladding radius of a common single-mode fiber on which a long-period refractive-index modulation has been imposed, the coupling st rength of the core and the cladding modes increases. In addition, the diffe rence in the propagation constants (for a fixed wavelength) between the cor e mode and the cladding modes increases; hence the resonant transmission di p wavelengths shift to longer wavelengths. The proposed method can be usefu l in making and detuning long-period tiber grating filters. (C) 2000 Optica l Society of America.