Incoherent Optoelectronic Differentiation Based on Optimized Multilayer Films

Abstract

Fourier‐based optical computing operations, such as spatial differentiation, have recently been realized in compact form factors using flat optics. Experimental demonstrations, however, have been limited to coherent light requiring laser illumination and leading to speckle noise and unwanted interference fringes. Here, the use of an optimized multilayer film, combined with dual color image subtraction, is demonstrated to realize differentiation with unpolarized incoherent light. Global optimization is achieved by employing neural networks combined with the reconciled level set method to optimize the optical transfer function of a multilayer film at wavelengths of 532 and 633 nm. Spatial differentiation is then achieved by subtracting the normalized incoherent images at these two wavelengths. The optimized multilayer film is experimentally demonstrated to achieve incoherent differentiation with a resolution of 6.2 μ$\umu$m. The use of a multilayer film allows for scalable lithography‐free fabrication and results in a system that could open the door to high‐speed processing for a wide variety of incoherent, and coherent, imaging systems.

Compact Incoherent Spatial Frequency Filtering Enabled by Metasurface Engineering

“…Opto-electronic filtering with incoherent light has recently been revisited in [43], [44], where a photonic crystal slab or a multi-layer film is coupled with a refractive lens. In both cases, the optical responses at two narrow wavelength bands are engineered to create two coded measurements that are captured at the photosensor using an array of spectral filters.…”

Broadband and large-aperture metasurface edge encoders for incoherent infrared radiation

“…However, a bipolar PSF can be synthesized with a hybrid optoelectronic system, which collects two images using two different PSFs and then performs pixel-by-pixel digital subtraction ( 6 ). This can be achieved with two separate apertures, a single aperture with wavelength ( 23 , 24 ), or polarization ( 25 ) multiplexing.…”

Metalens for Accelerated Optoelectronic Edge Detection under Ambient Illumination

“…However, the proposed wavelength multiplexing schemes still require two narrow-band incoherent light sources for illumination, typically generated by passing a narrow-band laser beam through a rotating diffuser. 41 Besides, the system requires the reflectance of the target object to be wavelength-independent.…”

“…However, using multiple optical elements results in a complex and bulky system. Recently, metasurface, a new class of planar diffractive elements composed of an array of sub-wavelength meta-atoms, has been proposed to greatly shrink the size and complexity of an optical system. − Compact optical systems for image differentiation have been realized using a nonlocal metasurface with an angle-dependent response to mimic first- or second-order spatial differentiation. − Alternatively, one can leverage the spin–orbital interaction or spiral phase generated by a metasurface for edge detection. − Furthermore, recently multilayer thin films have been demonstrated to be an even more straightforward platform for ATF manipulation toward applications including but not limited to image differentiation, − space compression, and wavefront sensing . Those compact nanophotonic devices can be conveniently integrated with a camera sensor, forming a miniature and lightweight edge detection system.…”

“…This contradicts the requirement of a vanishing transfer function at the center of the spatial frequency for image differentiation . Recently, a couple of studies have attempted to address this issue via wavelength multiplexing. , It was found that using either photonic crystals or multilayer thin films with an optimized wavelength-dependent OTF, one can construct an effective OTF with a high-pass frequency response through digital substruction between two OTFs at two separate wavelengths. However, the proposed wavelength multiplexing schemes still require two narrow-band incoherent light sources for illumination, typically generated by passing a narrow-band laser beam through a rotating diffuser .…”