FIELD: high-efficiency and low-loss channel-division optical devices. SUBSTANCE: filter has plurality of first optical devices and plurality of second optical devices connected in series with the former. Each first optical device has first through third input/output channels and functions to receive input optical signal through first input/output channel, to convey optical signal to second input/output channel, and to pass optical signal returning through second input/output channel to third input/output channel only. Each second optical device has fourth and fifth input/output channels; it is coupled with first input/output channel of respective first optical device and to second input/output channel of other respective first optical device; it functions to reflect only optical signal incorporating component of corresponding wavelength to optical signal received through fourth input/output channel and to pass optical signal incorporating components of other wavelengths to fifth input/output channel. Components of different wavelengths incorporated in optical signal received through fourth input/output channel are reflected in second optical devices. In addition optical signals incorporating components of respective wavelengths and reflected from second optical devices are received by first optical device through its second input/output channel and brought out of first optical device through its third input/output channel. EFFECT: reduced power loss of divided optical signal. 9 cl, 8 dwg
