408 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 17, NO. 2, FEBRUARY 2005 Dispersion Tuning of a Chirped Fiber Bragg Grating Using a Multisectional Bending Structure Jaejoong Kwon and Byoungho Lee, Senior Member, IEEE Abstract—A new method to adjust the dispersion of a fiber grating with enhanced flexibility and accuracy is described. The proposed method involves bending a fiber grating attached on a metal beam with multisectional bending scheme. The device is composed of several pairs of bolts which hold the metal beam at designated deflection positions. Because the curvature induced by bending defines the local strain, the strain distribution along the fiber can be tailored by positioning the pairs of bolts according to designated deflection curve. We demonstrated linear and quadratic dispersion tuning by using the proposed method. Index Terms—Gratings, optical fiber communication, optical fiber devices, optical fiber dispersion, optical fiber filters. I. INTRODUCTION C HIRPED fiber Bragg gratings (CFBGs) have been ac- tively researched for chromatic dispersion compensation in optical fiber communication systems. CFBGs have attractive advantages such as low loss, small footprint, low optical nonlin- earity, and the simple tuning mechanism involved. The tuning of a CFBG is done by inducing temperature or strain gradient along the CFBG after grating fabrication [1]–[9]. Between these two methods, due to difficulties in precise control and contin- uous power consumption in temperature distribution control, a CFBG tuning based on a strain is more widely researched. The strain control has been done by stretching or bending a fiber attached on a properly designed supporting structure [3]–[9]. In the case of the strain gradient-based method, the shape of the supporting structure defines the strain distribution. Therefore, once the structure shape is selected, although the dispersion value can be varied, the order of the dispersion slope is fixed. We previously introduced tuning methods using a tapered elastic plate that induces linear–nonlinear chirp on a fiber grating and switching the dispersion order by using strain modification blocks [7], [8]. However, even with this method, the dispersion tuning is limited to the shape of elastic plates. In this letter, we propose a method to tune the dispersion of a CFBG with enhanced flexibility by using multisectional bending scheme. Compared with previous research which are limited by the shape of supporting structure, the proposed method is not limited in strain distribution controlling because the local strain does not depend on the shape of the supporting structure. Manuscript received August 10, 2004; revised September 15, 2004. This work was supported in part by Novera Optics, Palo Alto, CA, USA. The authors are with the School of Electrical Engineering, Seoul National University, Seoul 151-744, Korea (e-mail: byoungho@snu.ac.kr). Digital Object Identifier 10.1109/LPT.2004.839379 Fig. 1. Schematic diagram of the multisectional bending structure. II. DEVICE DESIGN AND EXPERIMENTAL RESULTS When a straight uniform metal beam is bent and the action is elastic, the bending curve is an arc of a circle of radius . The strain distribution along the surface of the beam is given by (1) where , , , , and are local strain, bending angle, length change, local radius, and distance between the surface and neutral surface. Therefore, if a fiber is attached on the sur- face of the beam, the strain along the fiber axis is inversely proportional to the local radius . The curvature of the beam with deflection can be expressed as [10] (2) In the case of bending with small angle ( ), (2) can be approximated as (3) From (1) and (3), we can notice that the strain distribution along a fiber attached on a bent beam is defined by the second derivative of the beam deflection. Therefore, we can obtain the desired strain distribution by properly deflecting the beam. Fig. 1 shows the schematic diagram of the proposed method to deflect the supporting metal beam more precisely and flexibly. The device is composed of a CFBG attached on a metal beam and several pairs of bolts to bend the beam. Each pair of bolts can be moved separately, as shown in Fig. 1. The two pairs of bolts at the sides have flat tips so they can hold the beam tightly without beam bending. The bolts within mid-section have sharp tips so that they can hold the beam at specific position and allow the beam bending. Therefore, by positioning the joint points of 1041-1135/$20.00 © 2005 IEEE