An example demultiplexer may include at least one dispersive element that is common to multiple wavelength channels. The demultiplexer may additionally include multiple field lenses positioned optically downstream from the at least one dispersive element, where a number of the field lenses is equal to a number of the wavelength channels. An example multiplexer may include a single piece power monitor assembly that includes a collimator lens array, a focusing lens array, and a slot integrally formed therein. The collimator lens array may be positioned to receive multiple wavelength channels from a laser array. The focusing lens array may be positioned to focus multiple portions of the wavelength channels onto an array of photodetectors. The slot may be configured to tap the portions from the wavelength channels collimated into the single piece power monitor assembly by the collimator lens array and to direct the portions toward the focusing lens array.