A tapered hollow waveguide multiplexer is proposed to combine the output of a multi-wavelength VCSEL array. The
design of the proposed hollow waveguide is presented based on ray optics. We demonstrated the multiplexing of 4-
channel output of a VCSEL array for coupling into a multi-mode fiber with the tapered hollow waveguide. The
wavelength of each channel was allocated with adjusting driving current. The proposed hollow waveguide multiplexer is
useful for realizing compact and low-cost WDM transceivers with a multi-wavelength VCSEL array for high capacity
short reach optical networks.