Thermally tunable optical fiber loss filter with wide tuning range

Summary form only given. Loss filters based on long-period fiber gratings (LPGs) have generated great interest for applications in optical fiber systems. Tuning such filters is also very attractive, since tunable filters can offer some form of active control in optical networks. However, the resonance of a typical LPG written in standard communication fiber can only shift by 3-10 nm with 100/spl deg/C temperature change, which is insufficient for many applications. It has been reported that the temperature sensitivity of LPGs can be dramatically enhanced by recoating the fiber or incorporating into the fiber with special polymers (Abramov et al, Electron. Lett., vol. 35, pp. 81-82, 1999). In this paper, we show that widely tunable LPGs can be realized simply by using B/Ge codoped fiber combed with selection of an appropriate resonant mode. The achieved filter exhibits extremely high temperature sensitivity and has been tuned by -115.9 nm when temperature increases from 0/spl deg/C to 80/spl deg/C, corresponding to an average thermal tuning efficiency of 144.9 nm/100/spl deg/C, which is almost twice that of LPG with sensitivity enhanced by polymer.