Moire Apodization of Fiber Bragg Grating

由于光纤布拉格光栅（FBG）具有非常尖锐的窄带反射光谱，因此它们非常适合于涉及窄带光信号的应用，例如光通信系统中的滤光器、光纤激光器腔和各种类型的光纤传感器。为了抑制旁瓣等频谱整形，需要有效的切趾技术。我们开发了一种新的切趾技术，该技术使用双光束干涉法，在通过紫外激光照射形成FBG的过程中，以非常小的量逐步或连续地控制反射镜的反射角，从而形成光栅周期稍有不同的FBG的叠加，并因此实现切趾。通过两步控制小角的实验已经证明了在抑制旁瓣方面非常清楚的频谱成形。我们的研究成果已发表在日本应用物理杂志上，并在日本应用物理学会会议上作了口头报告，在日本光学杂志上也发表了有关切趾新技术的论文。

Because fiber Bragg gratings (FBGs) have very sharp, narrow-band reflection spectra, they are well suited to applications involving narrow-band optical signals, such as optical filters in optical telecommunication systems, fiber laser cavities, and various types of fiber sensors. There, the effective apodization techniques are ever strongly desired for spectrum shaping such as suppressing side-lobes.We have developed novel technique of the apodization using two-beam interference method that controls the angle of mirror reflection by very small amount in step-wise or continuously during the time of the FBG formation by UV laser irradiation, which consequently forms superposition of FBGs of slightly different grating period and hence achieves the apodization. Experiments by two-step control of the minor angle have demonstrated very clear spectrum shaping in suppressing side-lobes. Thus the new technique appears to provide very powerful apodization technique for the FBG fabrication.We have published the result to Japanese Journal of Applied Physics about our novel technique on two-beam interference method of FBG fabrication, to oral presentation to the conference of Japanese Applied Physics Society, and Japanese Journal of Optics about the new technique of apodization.