Advances towards the automated alignment of freeform optical systems

Freeform optics can enable cutting edge optical systems through increased aberration correction to enable wider fields of view, higher resolution, and lower size, weight, and power (SWaP) designs. However, freeform optics come with challenges in design, manufacturing, and alignment due to their nontraditional shapes. To address challenges in the alignment process of freeform optics, we have created a system that will self-align using a motorized mount and optical feedback fed into an optimization software package. The system thus aligned consisted of an off-axis parabolic mirror (3- inch diameter) mounted onto a low SWaP, custom hexapod, with a return sphere at its focal point. Collimated light was sent into the system using a 633nm laser, and a Shack-Hartman wavefront sensor was used to collect the output. Aberrations from the mirror’s misalignment measured by the wavefront sensor were then translated by the optimizing software to a corresponding movement of the hexapod mount. This created a feedback loop that was able to actively align the system in less than one minute, thus reducing the RMS wavefront. Potential limiting factors of the minimization were the resolution of the piezo actuators, noise of the sensor, or local minima the optimizer may be stuck in. This system is an important first step towards active alignment of a freeform optical system. Actively aligning systems will enable complex freeform elements to be aligned in a fraction of the time and effort, as well as allowing for the realignment of systems remotely or in dynamic environments.