Digital color imaging relies on spectral filters on top of a pixelated sensor, such as a CMOS image sensor. An important parameter of imaging devices is their resolution, which depends on the size of the pixels. For many applications, a high resolution is desirable, consequently requiring small spectral filters. Dielectric nanostructures, due to their resonant behavior and its tunability, offer the possibility to be assembled into flexible and miniature spectral filters, which could potentially replace conventional pigmented and dye-based color filters. In this paper, we demonstrate the generation of transmissive structural colors based on uniform-height amorphous silicon nanostructures. We optimize the structures for the primary RGB colors and report the construction of sub-micrometer RGB filter arrays for a pixel size down to 0.5 μm.In the past decades we have observed a rapid growth of the spatial resolution of color imaging devices 1-8 . This technological outburst was mainly driven by daily-use hand-held devices, such as mobile phones and compact optical cameras, but a high resolution also serves a role in industrial and environmental imaging 9 . The use of complementary metal-oxide-semiconductor (CMOS) image sensor with pigmented and dye-based color filters allowed to obtain pixels as small
High-index dielectric metasurfaces featuring Mie-type electric and magnetic resonances have been of a great interest in a variety of applications such as imaging, sensing, photovoltaics and others, which led to the necessity of an efficient large-scale fabrication technique. To address this, here we demonstrate the use of single-pulse laser interference for direct patterning of an amorphous silicon film into an array of Mie resonators. The proposed technique is based on laser-interference-induced dewetting. A precise control of the laser pulse energy enables the fabrication of ordered dielectric metasurfaces in areas spanning tens of micrometers and consisting of thousands of hemispherical nanoparticles with a single laser shot. The fabricated nanoparticles exhibit a wavelength-dependent optical response with a strong electric dipole signature. Variation of the pre-deposited silicon film thickness allows tailoring of the resonances in the targeted visible and infrared spectral ranges. Such direct and highthroughput fabrication paves the way towards a simple realization of spatially invariant metasurface-based devices.Keywords dielectric nanostructures, silicon resonators, metasurfaces, laser-matter interaction, direct laser interference patterning, multi-beam interference
The aberrations of reflective optical systems with one plane of symmetry are investigated in the most general case, with freeform surfaces and possibly different locations of the tangential and sagittal object and image. In this first paper in a series of two, we establish generalized ray-tracing equations including transverse aberrations up to the third order in ray coordinates. The ray-tracing treatment allows us to overcome difficulties linked to the non-existence of a suitable astigmatic wavefront reference. The obtained expressions can describe multi-mirror systems and include all induced aberration terms. As an illustration, a simple freeform off-axis mirror is analyzed.
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Hyperbolic Meta-Materials (HMMs) are anisotropic materials with permittivity tensor that has both positive and negative eigenvalues. Here we report that by using a type II HMM as cladding material, a waveguide which only supports higher order modes can be achieved, while the lower order modes become leaky and are absorbed in the HMM cladding. This counter-intuitive property can lead to novel application in optical communication and photonic integrated circuit. The loss in our HMM-Insulator-HMM (HIH) waveguide is smaller than that of similar guided mode in a Metal-Insulator-Metal (MIM) waveguide. c 2018 Optical Society of America Meta-materials are structures engineered at the subwavelength scale to exhibit specific electromagnetic properties. The development of nanofabrication techniques allows to make these structures and to realize new properties that are unobtainable with conventional media. Among the varieties of meta-materials, Hyperbolic Meta-Materials (HMMs) have gained tremendous attention. Their exotic hyperbolic dispersion property is the key to numerous emerging nano-photonics applications, including sub-diffraction-limit imaging [1][2][3][4][5][6][7], Purcell factor enhancement [8][9][10][11][12][13], sensing [14][15][16], and waveguide engineering [17][18][19][20][21][22][23][24]. Here we report a new application of HMM for waveguide spatial mode engineering, which brings up new possibility in Spatial-Division Multiplexing (SDM).SDM utilizes the last unexplored physical dimension, space, to further increase the data carrying capacity in optical communication [25]. The excitation and separation of spatial modes is essential in SDM [26]. In this letter, we propose a mode selective slab waveguide design by using a HMM as a cladding material. With a cladding consisting of HMM, the lower order modes with larger propagation constant become propagating wave in the HMM cladding material, such that they are turned into leaky modes. At the same time, higher order modes with smaller propagation constant are evanescent wave in the HMM cladding and remain guided in the core. Also by choosing the right parameter for the cladding one can design a 'single mode' waveguide only guiding one specific higher order mode, which can be applied as mode launcher or mode receiver in a SDM system. Compared to conventional spatial multiplexing techniques based on interference [27] or holography [28], our approach merely modifies the waveguide property and requires no extra optical component, which is more compact and efficient.We only consider transverse magnetic (TM) wave (E y = 0) because the hyperbolic cladding only has the desired property for this state of polarization. The TM wave is propagating in a slab waveguide core towards the positive z direction (Fig. 1a). The core thickness is 2a. The magnetic field of the mode is independent of the y-coordinate, and has the form H y = H(x) exp(iβ m z), where β m = k z,m is the propagation constant of the m th order mode along the z-direction, which satisfies the equation, where k...
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