Wavelength division multiplexer with multiple inputs and outputs

The invention relates to a wavelength division multiplexer with multiple inputs and outputs. A wavelength division multiplexer (WDM) includes one or more lenses, a WDM filter, and a plurality of common optical fibers, a plurality of reflective optical fibers, and a plurality of transmissive optical fibers optically coupled to the one or more lenses. Light at the first wavelength propagates in either direction between a common optical fiber and a reflective optical fiber via the one or more lenses and a WDM filter, wherein the WDM filter reflects the light at the first wavelength during propagation in either direction between the common optical fiber and the reflective optical fiber. Light at the second wavelength propagates in either direction between the common optical fiber and one transmissive optical fiber via the one or more lenses and a WDM filter, wherein the WDM filter passes light at the second wavelength during propagation in either direction between the common optical fiber and the transmissive opt