Abstract: A display may include an optical emitter that emits infrared light, a first coupler that couples the infrared light into a waveguide, and a second optical coupler that couples the infrared light out of the waveguide and towards the eye box. The infrared light may reflect off an eye as reflected light. The second optical coupler may couple the reflected light into the waveguide and the first optical coupler may couple the reflected light out of the waveguide and towards a camera for performing gaze tracking operations based on the sensor data. The display may sequentially illuminate different regions of the eye with the infrared light at different times using a scanning mirror, an array of light sources, or a wavelength-adjustable light source and gratings. This may minimize infrared light scattering, which minimizes background generation and maximizes signal-to-noise ratio for gaze tracking operations.