CHIRPED BRAGG GRATING REFLECTORS AND ADJUSTABLE DISPERSION APPARATUS INCORPORATING SUCH GRATINGS

摘要

Conventional quadratically chirped fibre Bragg gratings are typically apodised at both their high and low chirp ends. The present specification describes an improved Bragg grating reflector (131, 141) in which a second quadratically chirped region (P2) is arranged in front on the high chirp end of a substantially conventional quadratically chirped portion (P1). The high chirp end of the first portion (P1) is not apodised; instead this apodisation takes place in the second portion (P2), and so enables the first portion to exhibit appreciable reflectivity to signals having wavelengths extending to the Bragg wavelength corresponding to the high chirp end of the first portion. The present invention thus enables the useable bandwidth of a quadratically chirped grating to be increased, and so enables an increased tuning range to be achieved in adjustable dispersion (and adjustable dispersion compensation) apparatus incorporating such gratings.