An apparatus comprising a diffractive combiner having a front side, a rear surface, and an optical axis running substantially through the center of the diffractive combiner and normal to the back side. A display unit directs display light toward the back side of the diffractive combiner; the display unit positioned at a first angle relative to the optical axis, and the display light having a first range of wavelengths. An eye-tracking sensor receives eye-tracking radiation reflected by the back side of the diffractive combiner, the eye-tracking sensor positioned next to the display unit at a second angle relative to the optical axis, the second angle being different than the first angle and the eye-tracking radiation having a wavelength outside the first range of wavelengths. Other embodiments are disclosed and claimed.