EE Seminar
Abstract: Spatial light modulators (SLMs) are devices that modulate the amplitude, phase, or polarization of light beams in a spatially varying manner. They are integral components in various optical systems, enabling applications such as holography, beam shaping, and adaptive optics. The current state-of-the-art SLMs are predominantly based on liquid crystal technology, which, while versatile, is limited in speed due to the intrinsic properties of liquid crystals. Typical liquid crystal SLMs operate at frame rates below 1 kHz. Digital micromirror device (DMD)-based SLMs, on the other hand, are limited to frame rates below 10 kHz.
Our group is developing high-speed SLMs with frame rates exceeding 100 kHz. High-speed SLMS would arguably be the most powerful optoelectronic devices as they would enable the control over billions spatial and temporal degrees of freedom. These devices have the potential to significantly impact many fields, such as imaging through scattering media for optical in vivo imaging, cancer photothermal therapy, and imaging in foggy environments. Moreover, these devices are crucial for advancements in optical communication, quantum control, photonic computing, and optical neural networks.
In this talk, I will present our recent efforts to overcome these speed limitations. In the first part of the talk, I will discuss our work in developing CMOS Nanophotonics and its application in high-speed optical modulators. We repurposed the wires in a CMOS chip's back-end-of-the-line to act as an alignment layer for liquid crystal molecules, as interdigitated electrodes, and as a metal-optic resonator with a photonic resonance sensitive to the orientation of the liquid crystal molecules. We have shown that speeds up to 40 kHz are readily achievable.
We have also investigated the integration of electro-optic thin films, such as lithium niobate, onto CMOS backplanes. By bonding EO films patterned with a photonic crystal onto these substrates and exciting optical resonances within the film, we can modulate the optical response via an applied bias. Our results indicate that such EO-modulated SLMs could achieve modulation rates greater than 1 GHz, offering a drastic improvement over the speed of traditional LC-based SLMs. I will discuss the challenges associated with that approach to develop a mature and usable high-speed SLM.
Finally, I will discuss ongoing research aimed at enhancing SLM speeds without completely overhauling existing infrastructure. We are proposing a new technique that uses the same design as existing liquid-crystal on silicon SLMs with a thin liquid crystal cell that imparts a small phase shift. Through accumulating partial phase shifts through a multiplane light conversion process, we show that speeds > 100 kHz are feasible. We are also exploring methods to enhance the speed of DMD-based SLMs through the post-CMOS integration of photonic crystals onto micro-mirror surfaces, potentially improving their switching speed.