Effective UV Exposure Technique by Holographic Optical Element for the Fabrication of Long Period Fiber Grating

Abstract

We developed a new and effective technique for the fabrication of long period fiber gratings (LPFGs) with UV exposure energy by using a holographic optical element (HOE). Our HOE exposure technique produces a stripe line beam whose period and contrast are variable through a computer generated HOE. The HOE exposure technique is twice as efficient in terms of energy as the conventional contact mask method, because the HOE converts a nonuniform input beam into a stripe line beam, while in the conventional contact mask method, the beam loses energy at two steps: the beam homongenizer and the amplitude mask. In order to clarify which beam intensity profile is efficient for LPFG fabrication, the contrast of the stripe line beam profile was varied from 0.12 to 1.33, which is defined as the ratio of the first harmonics to the DC component of the stripe line beam. The result shows that the increase of the peak loss during the LPFG writing process is strongly dependent on the first harmonics amplitude of the stripe line beam profile, not simply on the total exposure energy, though the peak wavelength shift is linear to the total exposure energy. That is to say, the higher contrast beam effectively reduces the exposure energy to achieve the requisite peak loss.