Abstract
Spatial frequency filtering is a fundamental enabler of information processing methods in biological and technical imaging. Most filtering methods, however, require either bulky and expensive optical equipment or some degree of computational processing. Here, we experimentally demonstrate real-time, on-chip, all-optical spatial frequency filtering using a thin-film perfect absorber structure. We experimentally demonstrate edge enhancement of an amplitude image and conversion of phase gradients to intensity modulation in an image. The device is used to demonstrate enhancement of an image of pond algae.
Highlights
Spatial frequency filtering is a fundamental enabler of information processing methods in biological and technical imaging
We experimentally demonstrate edge enhancement of an amplitude image and conversion of phase gradients to intensity modulation in an image
These results demonstrate the potential of the filter to suppress low spatial frequencies in the reflected field enabling edge enhancement and conversion of phase gradients into visible intensity variations as required in many biological imaging applications, visualization of live biological cells
Summary
Spatial frequency filtering underpins many widely used imaging methods ranging from visualizing phase variations in transparent objects, such as live biological cells, to approaches for image enhancements used for object and face recognition. Most common optical methods for spatial frequency filtering, involve relatively bulky optical systems, while other popular image processing techniques rely on computation. While the use of conventional optical components places limits on the potential for miniaturization, the conversion from optical to electrical signals as well as computation time for electronic approaches places limits on applications requiring high throughput, rapid processing, and low energy consumption. Nanophotonic, all-optical image processing methods, on the other hand, offer ultracompact, real time, and low power alternatives for use in emerging integrated analog optical computing and image processing devices. Diffractive object plane filtering using a thick grating was demonstrated decades ago, but with advances in nanofabrication techniques, there is emerging interest in using subwavelength thickness films and structures to perform nondiffractive optical image processing. While nanophotonic devices usually require complex fabrication schemes, thin-film approaches have recently gained attention as solutions for all-optical image processing. Experimental demonstrations of optical image processing using thin films have focused on optical computing spatial differentiation but have been confined to performing operations in one dimension and are still relatively bulky. While directional operations may be desirable in some cases, other applications might require processing in two dimensions. Experimental demonstrations of optical image processing using thin films have focused on optical computing spatial differentiation but have been confined to performing operations in one dimension and are still relatively bulky.. The performance of thin film absorbers is well known to be dependent on the angle of incidence of light, and this spatial frequency filtering capability of suggests an avenue for the development of ultracompact, all-optical information processing devices. Due to their relatively small footprint and simple fabrication process, thin film absorber devices have the potential to be part of generation image processing components in handheld medical diagnostic and other portable sensing systems.. Scitation.org/journal/app image and conversion of phase gradients into intensity modulation using a thin-film absorber
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