Yoji Makiuchi and Hiroshi Matsuura
The optical circulator is one of the key devices in the optical add-drop modules (OADMs) used in wavelength-division multiplexing (WDM) technology, which finds applications in large-capacity long-haul telecommunications systems. A low-loss optical circulator has been developed to significantly improve OADM performance. Insertion loss for these modules is extremely low--less than 0.44dB at the operating temperature and wavelength range. High reliability and high power resistance are assured by fabrication techniques that use YAG welding for mechanical components, eliminating the use of adhesives in the optical path.