multiwavelength laser sources that are precisely aligned relative to each other and suitable , for instance , for multistation , multicolor ros . the device is made by growing on a semiconductor substrate a set of epitaxial layers in a laterally injecting laser configuration with progressively narrower bandgap quantum well active regions towards the surface of the crystal . selective etching can then be used to remove all quantum wells with emissions shorter than the ultimately desired wavelength in a given cavity . this approach can be applied to three different types of laser structures ; conventional edge emitting lasers , grating surface emitting lasers , and vertical surface emitting lasers . also described is a vertical cavity , surface - emitting laser with lateral injection employing a reflector structure comprised of a iii - v semiconductor layer beneath the active region , and a reflecting mirror above the active region .