Disclosed herein is a system comprising: an optical system with a focal plane; an apparatus at the focal plane; a filter; wherein the apparatus comprises an array of vertical-cavity surface-emitting lasers (VCSELs) on a first substrate and an array of detectors on a second substrate, the detectors configured to detect laser beams that are emitted by the VCSELs and backscattered by an object; wherein the first substrate is mounted to the second substrate and is configured to allow the laser beams that are emitted by the VCSELs and backscattered by the object to transmit through the first substrate and reach the detectors; wherein the filter is configured to prevent light other than the laser beams from passing.