a zigzag wavelength division multiplexer . the zigzag wavelength division multiplexer reduces the wavelength shift in the center of a frequency band caused by temperature changes . the zigzag wavelength division multiplexer includes an intermediate block , an input end and a plurality of output ends . the input end has a first sleeve and an optical collimator disposed in the first sleeve . each of the output ends has a second sleeve , a wave filter and an optical collimator . the optical collimator and the wave filter are disposed in the second sleeve . the zigzag wavelength division multiplexer reduces use of the grin lens and glass ferrule , and thereby manufacturing costs .