Properties of off-axis helical long-period fiber gratings

In this paper, a new four-electrode arc discharge machining device with large constant temperature region is designed for fabricating high quality off-axis helical long-period fiber Bragg grating. The larger constant temperature heating area is more conducive to releasing the stress of optical fiber, so that the prepared device is less off-axis. In order to show that low off-axis is the key parameter of high quality off-axis helical long-period fiber Bragg grating, the effects of single mode fiber on transmission spectrum of off-axis helical long-period fiber Bragg grating under different coupling length, pitch, core refractive index, cladding refractive index, core diameter, cladding diameter and off-axis quantity are simulated by using beam propagation method. Since traditional methods are difficult to measure the off-axis helical long-period fiber Bragg grating with small off-axis quantity, this paper estimates the off-axis quantity of the prepared device by using the method of spectral comparison and back-thrust off-axis quantity. The off-axis helical long-period fiber grating was prepared by the established processing device. The off-axis quantities of the prepared devices were about 0.12µm, 0.13µm and 0.16µm, respectively, according to the comparison between the simulated transmission spectrum and the actual spectrum.Finally, experiments on the torsional resistance and repeatability of the off-axis helical long-period fiber Bragg grating prepared by the device are carried out. The experiments show that the prepared Bragg grating has certain torsional resistance and good spectral repeatability.