HR-FBG And OC-FBG Used in PM Fiber Laser System

Linearly polarized fiber lasers have many applications, such as sensing, nonlinear frequency conversion, and coherent or polarization beam synthesis. To obtain a linearly polarized fiber laser, a polarizer can be used at the output end or within the fiber laser cavity to select a single polarization. However, this technology has some drawbacks, including high cost, high insertion loss, power limitation, and reliability issues. A more effective technique for achieving a linearly polarized fiber laser is to use polarization-maintaining fiber gratings and the cross-axis fusion splicing technology introduced in this paper.

The central wavelength of an optical fiber Bragg grating (FBG) depends on the refractive index of the fiber, and the stress rod in a polarization-maintaining fiber can apply stress to the core and generate a greater refractive index along an axis, which is called the slow axis because the refractive index is higher and the transmission speed is slower when it is larger.Therefore, the FBG written into the polarization-maintaining fiber has two reflection peaks, with their wavelengths corresponding to the slow axis and the fast axis respectively. The wavelength difference between the fast axis and the slow axis peaks depends on the birefringence of the optical fiber.

To achieve single-polarization operation, the FBG HR and OC grating pairs must be correctly designed to ensure that the central wavelength of the HR-FBG slow axis matches that of the OC-FBG fast axis. For this purpose, a pair of matching HR and OC grating pairs specially designed for this application.

As shown in the figure, HR-FBG and OC-FBG have four fusion points, and for each of them, a 0-degree and 90-degree fusion of polarization-maintaining optical fibers needs to be performed. The quality of the splicing point is very important for the whole laser system. Shinho S-12PM offer accurate alignment for 0 and 90 degrees with side and end-view method.Helps users get high PER and low loss.