| 摘要 |
PROBLEM TO BE SOLVED: To obtain an optical filter having flat group delay in the effective band by forming two serial Bragg gratings such that each filter has linear chirp opposite to the other filter. SOLUTION: The light signal passes a light guide Gin to enter an optical circulator C3 through a port P1, is reflected by a first filter FBGA in the band of the filter, and returns with group delay added by the linear chirp of the FBGA filter to a port P2 through a guide Ga. Then the signal is sent through a port P3 and a guide Gb to a second Bragg filter FBGB having opposite linear chirp to the first filter FBGA. The light is reflected by the second filter FBGB to the port P3 of the circulator C3 through the guide Gb and supplied to a guide Gout from the circulator C3 through a port P4. Two gradients of the two filters offset each other to produce zero gradient in the output signal, and the group delay is flat in the band of the filters. |
