Aberration Theory of a Flat, Aplanatic Metalens Doublet and the Design of a Meta-Microscope Objective Lens.

A theoretical approach for reducing multiple monochromatic aberrations using a flat metalens doublet is proposed and verified through ray tracing simulations. The theoretical relation between the Abbe sine condition and the generalized Snell's law is revealed in the doublet system. Starting from the Abbe aplanat design, minimization conditions of astigmatism and field curvature are derived. Based on the theory, a metalens doublet is semi-analytically optimized as a compact, practical-level meta-microscope objective lens working for a target wavelength. The proposed approach also reveals how to reduce lateral chromatism for an additional wavelength. The design degree of freedom and fundamental limits of the system are both rigorously analyzed in theory and verified through ray tracing simulations. It is expected that the proposed method will provide unprecedented practical opportunities for the design of advanced compact microscopic imaging or sensing systems.

Dielectric Metalens: Properties and Three-Dimensional Imaging Applications.

Recently, optical dielectric metasurfaces, ultrathin optical skins with densely arranged dielectric nanoantennas, have arisen as next-generation technologies with merits for miniaturization and functional improvement of conventional optical components. In particular, dielectric metalenses capable of optical focusing and imaging have attracted enormous attention from academic and industrial communities of optics. They can offer cutting-edge lensing functions owing to arbitrary wavefront encoding, polarization tunability, high efficiency, large diffraction angle, strong dispersion, and novel ultracompact integration methods. Based on the properties, dielectric metalenses have been applied to numerous three-dimensional imaging applications including wearable augmented or virtual reality displays with depth information, and optical sensing of three-dimensional position of object and various light properties. In this paper, we introduce the properties of optical dielectric metalenses, and review the working principles and recent advances in three-dimensional imaging applications based on them. The authors envision that the dielectric metalens and metasurface technologies could make breakthroughs for a wide range of compact optical systems for three-dimensional display and sensing.

Static moiré patterns in moving grids.

We describe an optical phenomenon of unmovable moiré patterns in sliding (moving) grids and gratings. The phenomenon was observed visually in the planar straight movement of the black-and-white gratings with a period of several mm. This is a velocity-independent effect confirmed analytically and in a computer simulation based on the spatial averaging. We found the static directions of the moiré patterns in the regular grids, but our technique can be also applied to other objects. The orientation and period of the static moiré patterns are not obvious, especially in the presence of the distance effect. The phenomenon can be practically used in security applications.

Toward a miniature endomicroscope: pixelation-free and diffraction-limited imaging through a fiber bundle.

A fiber bundle is widely used for endoscopic imaging due to its direct image delivery capability. However, there exists an inevitable pixelation artifact, which limits spatial resolution to the diameter of individual fibers. In this Letter, we present a method that can eliminate this artifact and achieve diffraction-limited spatial resolution. We exploited the binary control of a digital micromirror device to measure a transmission matrix of a fiber bundle and to subsequently control mode mixing among individual fibers. In doing so, we achieved a 22 kHz scanning rate of a diffraction-limited focused spot and obtained fluorescence endoscope imaging (58 µm × 58 µm) with near video-rate (10.3 Hz) acquisition. Our study lays a foundation for developing an ultrathin and high-resolution microendoscope.

Approach to investigating the spherical aberration variation with the object position in an aplanatic system.

In a general optical system, spherical aberration will arise when the on-axis position of an object is changed from its optimum position to another point. Induced spherical aberration can be used to compensate the aberration caused by inserting or removing a medium plate with any thickness that has a refractive index that differs from that of the original. To generate a degree of adequate aberration to balance the aberration from a thin layer, it is necessary to estimate the amount of arising aberration correctly when a point object deviates from its aberration-free position. We analytically induce the exact form of an arising spherical aberration with an on-axis object position for general optical systems that satisfy the Abbe sine condition and express a fourth-order approximation of that form using simple parameters that are conventionally used for the aberration of a thin lens. To verify the correctness of the proposed formula, a comparison between this analysis and simulation results is applied to several sample optical systems using commercial lens-design software.

Observation of coiled blood plexus in rat skin with diffusive light illumination.

Blood plexuses are characteristic anatomical features of acupuncture points (APs). We developed an optical technique using diffusive light illumination to increase the brightened area of skin for observation of the blood plexuses in skin. We found that the blood plexuses were coiled blood vessels which came out of the perforations in the fascia of muscle. The coiled vessels could be straightened by stretching the skin. We observed a series of blood plexuses at the putative APs along the left and right kidney meridian lines in the abdominal skin of rats. In addition, the locations of the plexuses on the muscle fascia were just above the putative acupuncture muscle channels along the kidney meridians. Furthermore, immunohistochemical analysis of the skin specimens of the plexuses revealed its neurovascular bundle nature as expected from known anatomical features of the APs.

Dependence of transverse and longitudinal resolutions on incident Gaussian beam widths in the illumination part of optical scanning microscopy.

We studied both theoretically and experimentally the intensity distribution of a Gaussian laser beam when it was focused by an objective lens with its numerical aperture up to 0.95. Approximate formulas for full width at half-maximum (FWHM) of the intensity distribution at focus were derived for very large and very small initial beam waists with respect to the entrance pupil radius of the objective lens. In experiments, the energy flux through a 0.5 microm pinhole was measured for various pinhole positions. It was found in theoretical analysis and confirmed in experiments that the FWHMs at focus in the transverse and longitudinal directions do not increase much from the ultimate FWHMs until the input beam waist is reduced below half of the entrance pupil radius.