Search

High-resolution endoscopic optical imaging is a crucial technique in biological imaging to examine the inside organs. There is a trade-off between lateral resolution and depth of focus in such applications. Traditional Optical Coherence Tomography provides an increased depth range but falls short of desired resolution. The combination of both higher resolution and larger imaging depth of focus of metalens can improve the clinical utility of endoscopic optical imaging. In this work, we designed, analyzed, and fabricated a 500 µm diameter metalens operating at 1300 nm to achieve high resolution and large imaging depth of focus, therefore, addressing this need. The full width at half maximum and depth of focus for the proposed metalens are 3.10 and 286 µm, respectively. [ABSTRACT FROM AUTHOR]

Filtering light by coherence by metasurfaces would enable compact, integrable coherence filters. A recent such proposal centered on a metasurface of zigzags. Here, we show that spatial coherence filtering can be achieved at normal incidence with a similar zigzag metasurface and can be traced to the band structure of the leaky modes of the thin film structure. We fabricate a metasurface of zigzags etched through a gold film deposited on a GaAs substrate and measure the transmittance of long wave infrared radiation. Selectivity matches predictions based on the band structure of fully coherent radiation. Furthermore, the degree of coherence filtering is shown to be controlled by the Q-factor of leaky modes. [ABSTRACT FROM AUTHOR]

In this paper, we present an achievable gradient refractive index in bi-continuous holographic structures that are formed through five-beam interference. We further present a theoretic approach for the realization of gradient index devices by engineering the phases of the interfering beams with a pixelated spatial light modulator. As an example, the design concept of a gradient index Luneburg lens is verified through full-wave electromagnetic simulations. These five beams with desired phases can be generated through programming gray level super-cells in a diffractive spatial light modulator. As a proof-of-concept, gradient index structures are demonstrated using synthesized and gradient phase patterns displayed in the spatial light modulator. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel design of broadband monopole optical nano-antennas. It is consisted of a corrugated half elliptical patch inside an elliptical aperture. By adjusting the dimensions of the elliptical patch and the elliptical aperture, the overall performance of the proposed monopole nano-antenna can be made remarkable broadband. Full wave electromagnetic simulations have been used to investigate the effects of different parameters on the nano-antenna performance. Moreover, the proposed broadband nano-antenna can support light waves with different polarizations. It is expected that the new optical antenna will pave the way towards the development of high performance optical antennas and optical systems. [ABSTRACT FROM AUTHOR]

Gradient index (GRIN) structures have attracted great interests since their invention. Especially, the recent advance in the fields of transformation optics, plasmonics, and nanofabrication techniques has opened new directions for the applications of GRIN structures in nano-photonic devices. In this paper, we apply Luneburg lens and its transformed counterpart to realize efficient coupling to plasmonic nano-waveguides. We first briefly present the general structures of Luneburg lens and generalized Luneburg lens, as well as the design process of flattened Luneburg lens applying quasi-conformal mapping techniques. After that, we study the performance of these lenses for coupling electromagnetic signals to nano-waveguides (the metal-insulator-metal nano-waveguide). Different coupling schemes are investigated. It is found that the proposed Luneburg lens based optical couplers can be used to provide broadband light couplings to plasmonic nano-waveguides under wide incident angles. [ABSTRACT FROM AUTHOR]

In this paper, a single-layer transmissive metasurface (TMS) is designed to generate orbital angular momentum (OAM) vortex waves with homogeneous radiation at microwave frequencies (e.g., 10 GHz). A single-layer TMS with the thickness of 3 mm (0.1λ0) is designed by well connecting the phase shift range of two elemental TMS structures. Specifically, two TMS structures—meandering patch-double meandering rings and meandering patch-single meandering ring with the unit-cell size of 7.5 mm (0.25λ0)—are used together to achieve high transmission efficiency (>0.8) and a large phase coverage range (>360°). In order to address issues such as uneven circumferential radiation and posterior lobe radiation and further enhance the efficiency of the TMS, the modified principle of Fabry-Perot cavity (FPc) suited for realizing the TMS to generate OAM vortex waves is proposed, analyzed closely, and applied. Specifically, an improved rectangular microstrip antenna is employed as a feeding source and a double square ring array is used to construct the backplane. A prototype of the proposed TMS with a FPc is designed, simulated, manufactured, and measured. The simulated and experimental results agree well, which demonstrate the feasibility of the presented design methodology. [ABSTRACT FROM AUTHOR]

This paper presents a holographic formation of compound photonic crystal and nano-antenna templates through a reflective optical element based laser interference. The reflective optical element consists of four Si facets where a circularly polarized single beam impinges at the Brewster angle and is reflected into four linearly s-polarized beams for the inference lithography. By tuning the phase delay in one of the interfering beams, dual-lattice photonic crystal, and nano-antenna templates are fabricated and compared with theoretic simulation. The design conditions for the nano-antenna formation are discussed. [ABSTRACT FROM AUTHOR]