Metalenses exhibit significant potential in various fields due to their ability to access comprehensive, complex information. The ability to integrate multiple features into a single device, along with its compact and efficient design, allows for the creation of miniature microscopy systems that showcase remarkable performance. By applying unique design techniques, we have developed and implemented polarization-dependent metalens. This metalens makes smooth transitions between edge enhancement imaging and bright field imaging possible. Employing the principles of geometric phase, we design a dual mode metalens by using hydrogenated amorphous silicon to physically manifest the necessary phase profiles for operation in the visible spectrum. These profiles contain a conventional hyperbolic configuration intended for bright-field imaging, along with spiral metalens with a topological charge of +1, tailored for edge-enhanced imaging functions. When utilizing Left Circular Polarization (LCP), our designed lens enables bright field imaging. Conversely, Right Circular Polarization (RCP) facilitates image edge enhancement. We showcase through numerical demonstration the metalens capability to focus and generate vortices under various states of circular polarization and validate its potential for diverse applications.
The American Society of Cancer reports an annual average of 240,000 breast cancer diagnoses in the USA, resulting in approximately 42,000 women and 500 men succumbing to the disease each year. The conventional diagnosis of critical diseases like breast cancer, lung cancer, and skin cancer frequently necessitates invasive biopsy procedures, which involve the removal of a tissue sample for diagnostic analysis, potentially posing infection risks. However, conventional Optical Coherence Tomography (OCT) has emerged as a non-invasive imaging technique that mitigates these risks by generating cross-sectional biological sample images through the principles of light scattering and reflection. Although conventional OCT excels in its depth of focus, it faces challenges related to limited lateral resolution and diffraction constraints. Consequently, we propose a metalens-based OCT for high-resolution biomedical tissue imaging. Metalens-based OCT achieves optical system miniaturization by replacing traditional bulky lenses. The metalens is designed on a crystalline silicon dioxide (SiO2) substrate with a 490 nm unit cell periodicity. Its dimensions are 380 nm in length, 185 nm in width, and 1100 nm in height. The suggested metalens operates in the 1300–1570 nm wavelength range and has over 65% transmission to provide improved depth of focus and lateral resolution. Simulated results indicate that metalens depth of focus and full-width half maximum approach 260 and 125 μm, respectively. Hence, our metalens proposal, offering high resolution and an increased depth of field, presents a viable choice for surgical and in vivo endoscopy imaging applications.
Metasurfaces offer novel design capability of optical wavefront shaping to realize ultra-compact flat optical components which have remarkable potential to mitigate the constraints of size and design complexities in imaging systems. However, aberration correction and diffraction-limited response over the broad spectrum greatly hindered their applicability because of simultaneous phase engineering at multiple wavelengths on a single metasurface interface. Conventionally reported design methodologies overcome the challenges mentioned earlier by exploiting resonance tuning, layer stacking, and phase mergence strategies. They suppressed the aberration effect with high efficiency but have complex design and meta-atom geometry with limited functionalities. Here in this research script, we have introduced broadband achromatic bifocal metalens based on a single-layer array of nano-rectangular bars in transmission mode. In order to have wavelength-independent focusing, we developed a library of meta-atoms to provide required phase compensations. In addition to this, a novel material zinc selenide (ZnSe) is introduced as a constituent which is a large transparent window in the optical regime. The high efficiency and unprecedented capability of aberration correction along with multi-functionality make the proposed metalens a potential candidate for next-generation advanced imaging technology.
Multi-operational metasurfaces have received a lot of interest because of their significant design improvements for ultra-compact and highly integrated meta-optics. The emergence of near and far-field holography offers an effective solution to enhance the capacity of information encoding in a single metasurface. However, the existing strategies of layer stacking and interleaving, where distinct functionalities are embedded with the help of the combination of multiple meta-atoms, have challenges in terms of design complexity and efficiency. This manuscript proposes a new simplest approach for a tri-channel highly efficient meta-holography based on the photonics spin Hall Effect (PSHE) and Mauls’ Principle of amplitude manipulation. A multi-functional metasurface constituent of a single nano-rectangular pillar over a glass substrate is designed as evidence of conception to highlight the feasibility of parallel manipulation upon near and far-field activities. To achieve control over the entire phase range (0-2π), geometric phase modulation is utilized. Zinc sulphide (ZnS) is used as a constituent material for highly efficient broadband response over the whole visible spectrum due to its characteristics of an extraordinary refractive index and low absorption coefficient. For authentication of the proposed methodology, the designed metasurface is simulated in FDTD, effectively validating the execution of a multi-functional design scheme. For the proof of the broadband operation, optical response over three visible wavelengths (i.e., blue, green, and red) is measured, and it reconstructs all three holograms with high efficiency. Thus, the proposed optical response multiplication approach is a viable contender for various high-end applications in photonics, data storage, and communication.
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