It is suggested that multimode slab waveguide spectrographs currently under development for wavelength division multiplexing in optical communications might have an application in astronomy. The nature of these devices is described, and a survey of their development in the communications industry presented. The applicability of existing devices is investigated and found to be limited. However, it is shown that only a modest improvement in resolution (factor of 2-4), together with a realization of the potentially very high optical efficiency, could yield an astronomically useful device. The anticipated problems in developing such as instrument are outlined.