Improved far-field holograms using spatial light modulators and camera-in-the-loop optimization

Spatial light modulators allow for precise beam shaping in a lot of applications, ranging from microscopy to manufacturing. Therefore, the calibration of spatial light modulators (SLMs) is essential for achieving optimal beam quality. Camera-in-the-loop calibration schemes provide an easily deployable method for characterizing the entire optical system, mitigating the need for separate measurements of specific aberrations. In this work, we apply a camera-in-the-loop calibration to a far-field holographic projection system utilizing a phase-only SLM. Our approach achieves high fidelity between the digital twin’s prediction and the sensor image, including a precise match of speckle positions. We validate the calibration by comparing extracted system parameters (e.g., defocus, SLM-illumination, and sensor tilt) with reference measurements. We further use the calibrated system and extend the hologram calculation with a speckle suppression operation to experimentally demonstrate speckle-reduced intensity distributions in the far field. The calibration is extended for tilted far fields using a nonuniform fast Fourier transform. We demonstrate successful calibration for a target plane tilted by more than 12 deg and achieve effective speckle suppression within the tilted target window.