TUNABLE OPTICAL ADD/DROP DEVICE AND METHOD

PROBLEM TO BE SOLVED: To realize reduction in data loss and improvement in bandwidth efficiency when tuning by incorporating a hitless tunable optical filter in an optical add/drop device. SOLUTION: The hitless wavelength-tunable optical filter is provided with a broadband reflective region and a tunable filter region, and a reflective surface and a filter surface are positioned adjacent to each other. Hitless tuning of the device is accomplished by changing (moving) a point from which an optical beam is made incident on the filter region along a constant wavelength channel track whenever the optical beam strikes the filter region of the device. Realignment (moving) to a position related to a new wavelength channel track is performed in a state where the optical beam strikes the broadband reflective region. First, the optical beam is moved to a position corresponding to the new wavelength to be added/dropped on the filter region (in the broadband reflective region), subsequently the optical beam is realigned (moved) along the new wavelength channel track within the filter region.