Discrete optical unit on a substrate of an integrated photonics chip

An integrated photonics device that emits light out towards a measured sample value is disclosed. The device can include a discrete optical unit that attaches to a supporting layer. The discrete optical unit can include mirror(s), optics, detector array(s), and traces. The supporting layer can include one or more cavities having facet walls. Light emitter(s) can emit light that propagate through waveguide(s). The emitted light can exit the waveguide(s) (via termination point(s)), enter the one or more cavities at the facet walls, and be received by receiving facets of the discrete optical unit. The mirror(s) of the discrete optical unit can redirect the received light towards collimating optics, which can direct the light out of the device through the system interface. The discrete optical unit can be formed separately from the supporting layer or bonded to the supporting layer after the mirror, optics, detector arrays, and traces are formed.