a substrate having a rectangular shape defined by a top surface and a bottom surface separated by two oppositely arranged pairs of side surfaces, wherein a first pair of the side surfaces consists of

a planar front surface that defines a near end of the substrate; and

a planar back surface that defines a far end of the substrate,

a laser, the laser having a front-facet that provides a main light output of the laser and a back-facet that provides back-facet illumination, the front-facet and the back-facet arranged at opposite sides of the laser, the laser back-facet physically and optically coupled to the planar front surface;

an application specific integrated circuit (ASIC) fabricated on the top surface of the substrate; and

a monitor physically and optically coupled to the planar front surface and arranged near to, and at an offset from, the laser;

wherein the substrate comprises a solid semiconductor material that is transparent to a wavelength of light from the laser, and

wherein the back-facet illumination enters the solid semiconductor material of the substrate through the planar front surface,

travels through the solid semiconductor material of the substrate to reflect off the planar back surface, and

travels through the solid semiconductor material of the substrate to exit the solid semiconductor material of the substrate through the planar front surface for detection by the monitor.