On October 31, Nature Communications published a paper titled “Exploiting the speckle correlation scattering matrix for a compact reference-free holographic image sensor”, written by Professor YongKeun Park and graduate student KyeoReh Lee, both from the Biomedical Optics Laboratory at KAIST.
In the paper, the authors describe a novel method to build holographic image sensors with the use of commercially available diffusers as holographic lens. The said method has gathered attention for overcoming the impracticality of previously studied methods, such as reference-assisted holography. The authors define holography as “a drawing that contains all of the information for light, both amplitude and wavefront”. A conventional camera, as shown in figure a), fails to capture the depth perception of the target and instead presents a flattened still frame of the target. To overcome such an issue, the earliest holographic methods dating back to the 40s “exploited the interferometric nature of waves”, as shown in figure b). By analyzing how the incident light interferes with a known reference field, the image projected onto the image sensor is processed to reconstruct the depth perception of the original target. This reference-assisted holographic method has been utilized for so long, until its applicability was eventually found to be limited when it comes to X-ray optics. The research team led by Professor Park proposed a reference-free holographic method, which consists mainly of a regular image sensor and a disordered layer (called a diffuser) utilized as the holographic in figure d). The researchers removed the need for the choice of a reference field, which often made the holographic imaging system “complex, incompatible, and vulnerabletoambientnoise”.The use of a regular image sensor would mean that the reference-free holographic image sensors could function just like a conventional point-and-shoot camera, only better in that they would also capture the depth information, thereby producing a fully holographic image. An immediate application of the technology would be in mobile phones, which, with the new holographic method, are expected to popularize holographic images in no time.