Compact Device Combines Light Sensing and Modulation

A device developed by researchers at CEA-Leti combines the ability to sense light and modulate it accordingly by pairing a liquid crystal cell and a CMOS image sensor into a single device. According to the researchers, this is the first time a single device has had these capabilities simultaneously.

The compact system provides intrinsic optical alignment and compactness and is easy to scale-up, facilitating the use of digital optical phase conjugation (DOPC) techniques in applications such as microscopy and medical imaging.

In a paper presented at the 2024 IEEE International Electron Devices Meeting, the researchers state that this is the first solid-state device integrating a liquid crystal-based spatial light modulator hybridized with a custom lock-in CMOS image sensor. The integrated phase modulator and sensor embeds a 58 × 60 pixel array, where each pixel both senses and modulates light phases.

The device provides significant advantages compared to competing systems requiring separate components, said Arnaud Verdant, CEA-Leti research engineer in mixed-signal integrated circuit design and lead-author of the paper. He expects its benefits to boost deployment in more complex and larger optical systems.

A research team has fabricated a 58 × 60-pixel array in which each 70 μm × 70 μm pixel has its own circuit to measure the incident light phase and modulate it via applying an electric field to the liquid-crystal layer. Courtesy of CEA-Leti.

The device leverages the key advantage of DOPC to dynamically compensate for optical wavefront distortions, which improves performance in a variety of photonic applications and corrects optical aberrations in imaging systems. By precisely controlling laser beams, it improves the resolution and penetration depth of optical imaging techniques for biomedical applications.

Standard DOPC systems rely on separated cameras and light-wavefront modulators, but their bandwidth is limited by the data processing and transfer between these devices. If the system senses and controls the light-phase modulation locally in each pixel, the bandwidth no longer depends on the number of pixels and is only limited by the liquid crystal response time. This feature is a key advantage in fast-decorrelating, scattering media, such as living tissues.

“Scattering in biological tissues and other complex media severely limits the ability to focus light, which is a critical requirement for many photonic applications,” Verdant said. “Wavefront shaping techniques can overcome these scattering effects and achieve focused light delivery. In the future, this will make it possible to envision applications such as photodynamic therapy, where light focusing selectively activates photosensitive drugs within tumors.”

When the technology is more mature, Verdant believes it could have diverse benefits across a range of sectors, in addition to improving biomedical imaging resolution and depth. For example, the technology could enable earlier detection of diseases and support noninvasive therapies. In industry, it could improve laser beam quality and efficiency.

The research was published in Nature Electronics (www.doi.org/10.1038/s41928-024-01321-x).