An optical device enabling reducing device scale is constituted by M circulators (11a, 11b), (M being a natural number), a waveguide-type diffraction grating (12) including M first input/output waveguides (121a, 121b) formed at its one end and M×N second input/output waveguides (125a-1 to 125a-N and...http://www.google.com/patents/US7428355?utm_source=gb-gplus-sharePatent US7428355 - Wavelength selective and level adjusting optical device
