Investigation of a flexibly tunable dispersion compensator based on uniform fiber Bragg grating without central wavelength shift and its application to tunable repetition-rate multiplication

摘要

We propose and experimentally demonstrate a new and simple chromatic dispersion controller based on the uniform FBG with the symmetrical bending technique. Dispersion compensation has been one of the most significant issues for the high-speed optical communication systems. Chirped fiber Bragg gratings (CFBGs) have been of interest in the applications to dispersion compensating devices due to their versatile advantages like fiber compatibility, polarization insensitivity, low nonlinearity, low loss and so on. To provide the dispersion tunability of CFBGs, the great efforts based on thermal heater, tapered fiber by etching, stacks of piezoelectric actuators, and adhesive package with gradient thickness. The previous methods, however, have the drawback of the center wavelength shift into the longer wavelength. To solve the limitation of previous methods, a range of methods to induce the wide tuning range of dispersion without the center wavelength shift have been intensively investigated. Using a divided thin-film heater with a peltier element, the tunable dispersion compensator based on a fiber grating was reported. To prevent the center wavelength shift, two heating elements like a thin-film heater and a peltier element were used. However, it has the complex structure and the small tuning range of dispersion. Most of methods to improve the dispersion controllability of a fiber grating without the center wavelength shift are based on the symmetrical bending method. To induce the symmetrical bending along a fiber grating, versatile schemes based on moving block, curved fiber gratings attached on a plate, and a rotational stage with pivots were proposed. In this letter, a new method to control the chromatic dispersion of uniform FBG is proposed and experimentally demonstrated. We precisely controlled the dispersion value of uniform FBG by inducing the linear strain gradient based on the proposed tuning device. Since the symmetric bending of the flexible cantilever beam with the uniform FBG is induced by the interaction between two translation stages and a sawtooth wheel, the tension and compression caused by the symmetrical bending can effectively control the properties of the fiber grating like bandwidth and group delay. We successfully obtain the wide tuning range of chromatic dispersion of the uniform FBG (from 312.6 ps/nm to 35.9 ps/nm) without the center wavelength shift, which is less than 0.02 nm. We also suppress the group delay ripple as low as ～ ±5 ps. And we also demonstrate the application of the proposed tunable dispersion compensation technique to the tunable repetition-rate multiplication and obtain high quality pulses at repetition-rates in the range of 20 ～ 40 GHz from an original 1.8 ps, 10 GHz soliton pulse train.