. . . "When a multiplexed optical signal 204 including wavelengths ??1??2??3 . . . ??x . . . ??K is coupled into the tunable device 200, a channel 206 (i.e. wavelength ??x) will be reflected from the tunable FBG 200 and the rest of the channels 208 at ??1??2??3 . . . ??K (not including ??x) will transmit through the tunable FBG 200, wherein K is a finite positive integer and X is between 1 and K. As used" .