There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Statistics for Spatial Data.

Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.

Flat Optics With Designer Metasurfaces

Using a metasurface comprising an array of nanorods with different orientations and a backreflector, a hologram image can be obtained in the visible and near-infrared with limited loss of light intensity.

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Metasurface holograms reaching 80% efficiency

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Photochromism of Diarylethene Molecules and Crystals: Memories, Switches, and Actuators

A spectral device based on multiple holographic gratings is proposed. Several volume holograms are superimposed into a common volume of photorefractive crystal Fe:LiNbO 3 using the wavelength and angular multiplexing method. This device is implemented by only one single wavelength laser using a two-lambda method. The imaging function of the device is realized with convergent recording beams. It can reduce the spectral system because the focusing lens is removed. Because the diffraction efficiency and the spectral resolution of the superimposed volume holographic gratings could be very high, the spectral device could achieve attracting characteristics of the diffraction efficiency and spectral resolution. Theoretical analysis and model design are presented and a discrete spectral device working at four wavelengths is demonstrated. The device has a uniform diffraction efficiency of 10% and the resolution of 1 to 2 nm. In addition, it has the advantages of wide spectral coverage, simple structure, and flexible design.

Imaging spectral device based on multiple volume holographic gratings

In this paper, mixed-surface-type optical system is defined as the optical system comprised of various types of surfaces, including spherical, aspheric, and freeform surfaces. A general point-by-point design method for mixed-surface-type systems is proposed. In detail, methods for spherical system design and optical power assignment are proposed during the point-by-point design process. Additionally, three surface evolutions are proposed: from spherical to aspheric surfaces and freeform surfaces, and from aspheric surfaces to freeform surfaces. A mixed-surface-type off-axis three-mirror system is designed as an example and as a starting point for further optimization. The sphere receives most of the system optical power while the freeform surface has little power, which can reduce system fabrication difficulty.

Point-by-point design method for mixed-surface-type off-axis reflective imaging systems with spherical, aspheric, and freeform surfaces

By use of speckle modulation on the object beam of a volume holographic optical correlation system, we show that the sidelobes of the correlation patterns along the vertical direction, as well as those along the horizontal direction, are well suppressed. A theoretical explanation and experimental results are presented and discussed.

Sidelobe suppression in volume holographic optical correlators by use of speckle modulation.

In this paper, the diffractive optical element (DOE) is used to realize beam smoothing with the smoothing by spectral dispersion (SSD) technique. The influences of the high and low frequency phase distortions on the DOE for beam smoothing are statistically analyzed based on the spatial frequency spectrum method. The amplitude and initial phase spectra of the far field intensity distribution are modulated by the characteristic of the phase distortion. The relationship between the performance parameters of the beam smoothing and the characteristic of the phase distortion is obtained. This can afford a theoretical tool to determine whether the characteristic of the phase distortion and the performance of the designed DOE for beam smoothing are able to satisfy the requirement of the light efficiency and the non-uniformity simultaneously or not.

Statistic analysis of influence of phase distortion on diffractive optical element for beam smoothing.

In this paper, a design method based on a construction and iteration process is proposed for designing freeform imaging systems with linear field-of-view (FOV). The surface contours of the desired freeform surfaces in the tangential plane are firstly designed to control the tangential rays of multiple field angles and different pupil coordinates. Then, the image quality is improved with an iterative process. The design result can be taken as a good starting point for further optimization. A freeform off-axis scanning system is designed as an example of the proposed method. The convergence ability of the construction and iteration process to design a freeform system from initial planes is validated. The MTF of the design result is close to the diffraction limit and the scanning error is less than 1 μm. This result proves that good image quality and scanning linearity were achieved.

Guofan Jin

Papers

Imaging spectral device based on multiple volume holographic gratings

Point-by-point design method for mixed-surface-type off-axis reflective imaging systems with spherical, aspheric, and freeform surfaces

Sidelobe suppression in volume holographic optical correlators by use of speckle modulation.

Statistic analysis of influence of phase distortion on diffractive optical element for beam smoothing.

Design of freeform imaging systems with linear field-of-view using a construction and iteration process.