Wavelength division multiplexing device

A wavelength division multiplexing device comprising:

• a pair of 1×N optical couplers (2≦N≦16), N light emission devices in which one of peak wavelengths thereof differs from every other one by at least 30 nm and N light receivers having optical filters having light-transmission wavelength bands adjusted to correspond to said peak wavelengths,
• wherein the light emission devices and the light receivers having optical filters corresponding to peak wavelengths of the light emission devices form pairs, said light emission devices or said light receivers are optically connected to N-port-side ports of one of the 1×N optical couplers, and each optical filter is defined by the following expression (1),
• |λ−λn|≧0.01λ+2(nm) (1)
• wherein λ (nm) is a light wavelength of a light emission device, which is to form a pair with an optical filter, at a room temperature, and λn (nm) is a wavelength corresponding to 50% of transmittance of the optical filter in an optical absorption curve near λ.