A method and apparatus for monitoring MEMS-based optical switches and cross-connects. A plurality of partial reflectors (24) are introduced into optical paths of the switch (10) for reflecting light transmitted along the optical paths through a transparent substrate of the switch (10), without disturbing transmission of the light along the optical paths. The reflected light is transmitted through the substrate (20), which is preferably made of silicon and transparent to wavelengths of light used in DWDM systems. A photodetector array bonded to the underside of the substrate detects the light reflected by the plurality of partial reflectors (24) through the substrate (20). The light detected by the photodetector array (30) indicates the switching states and functionality of the switch (10), and can be processed by circuitry associated with the array.