Four-port wavelength division multiplexing device

The invention discloses a four-port wavelength division multiplexing device. The four-port wavelength division multiplexing device comprises a first collimator, a second collimator and a diaphragm filter, wherein the first collimator and the second collimator are provided with two fibers respectively; the diaphragm filter allows light of a part of wavelengths to pass through, and the other part oflight is reflected; a light signal containing multiple wavelengths is transmitted to a first fiber of the first collimator, and emitted to the diaphragm filter through the first collimator; a light signal containing a part of wavelengths is transmitted to the second collimator through the diaphragm filter, and output by the first optical fiber of the second collimator; a light signal containing another part of wavelengths is reflected by the diaphragm filter to the first collimator, and then output by the second fiber of the first collimator; a light signal containing multiple wavelengths istransmitted to the second