Over the past decade, major progress in emerging mid-infrared (IR) sources and detectors leads to increased interests for various IR-based applications, such as trace-gas detection, biological and medical sensing, and environmental monitoring. However, a limiting factor in the middle and long wave IR range is the lack of suitable materials that are transparent, low cost, lightweight and easy to fabricate. Here, we numerically demonstrate the artificially constructed Huygens meta-surface with versatile mid-IR wavefront control, by hybridizing the dielectric meta-atoms of high-permittivity chalcogenide on fluoride substrates. Based on the double-elements Huygens meta-atom design for linear phase tuning, transmission is enhanced substantially with high-efficiency (85%) by concentrating beam propagation into the first diffraction order similar as traditional blazed grating but with ultra-thin thickness (λ/8). Further, based on centrosymmetric deflection to produce a local and highly focused propagation mode, a Bessel beam generator is demonstrated (λ=5.22 μm, NA = 0.5) by coding a well-defined phase map into dielectric meta-atoms. As a result, the proposed dielectric metasurface with nanometer level thickness shows great prospects in the field of integrated photonics.
Photonic integrated circuits (PICs) as potential candidate to overcome the “von Neumann bottleneck” of current electronic technologies beyond Moore’s law gain increasing applications in fields of optical communication, data exchange and highperformance interconnect networks etc. Currently, elementary active devices such as photonic switches and modulators play essential roles in light-flow control of optical interconnection network, but suffer from high static power consumption because of volatile control and large footprint that is hard to integrate. In this trend, optical phase change materials (OPCMs) based active devices emerge as promising solutions due to advantages of large optical contrast between the amorphous and crystalline states, optically or electrically switchable and non-volatile control, easy to integration etc. In this paper, we propose a non-volatile O-PCMs photonic switch by integrating a thin film of germanium antimony telluride (GST) alloy on top of a micro-ring resonator. As confirmed by our analytical and computational results, upon an amorphous-to-crystalline phase change, two output ports of the O-PCM microring switch exhibit gigantic transmission contrast with a ratio up to highest 47:1. Further, the O-PCM based photonic switch also demonstrates extremely low extinction ration to 13.58 dB and 14.40 dB for both output ports from 1.5 μm to 1.6 μm.
The combination of phase change materials and metasurfaces has enabled myriads of versatile platforms for dynamic wave control, especially for various applications in integrated photonics and optoelectronics. In this paper, an electrically reconfigurable metasurface is demonstrated to work as a terahertz (THz) broadband digital switch by integration of vanadium dioxide (VO2). In such integrated optoelectronic frameworks, active and bistable digital control of optical responses is enabled by applying electrical stimuli to vertically cascaded metasurfaces with broadband behaviors for Joule heating that causes phase change and state switching. Before and after phase change, a high contrast ratio of transmittance is demonstrated within a broad THz range up to 400 GHz. Essentially, fast switching can be guaranteed compared with current devices based on thin film phase change materials, due to the local electrical heating that proves inherently efficient and faster to trigger the phase transition process. As a result, such active optoelectronic framework based on phase change materials may pave a new way for emerging integrated devices such as photoelectric switch, photonic memory, signal processing and so on
The spectrum-integral Talbot lithography (STIL) was introduced into the fabrication of one-dimensional micro gratings using the broad-band UV illumination in this paper. In the process of spectrum-integral Talbot lithography, the self-images and π-phase-shifted images generated by different wave lengths overlap and integrate collectively to enormously extend the continuous depth-of-focus area since a certain distance away from the mask. As a result, the route of STIL proves to be of great potential for periodic frequency-doubling in good contrast without any complex improvement and operation to the traditional proximity lithographic system of UV mask aligner.
A simple but effective phase analysis method for the fringe pattern that occurs in two superposed grating marks applied in the previously designed dual-grating-based alignment scheme for lithography is proposed. First, the fringe pattern is processed and analyzed using a frequency domain method based on two-dimensional (2D) Fourier transform, and the 2D notch filter is appropriately designed to select the useful spectrum to obtain the target phase information. Further, phase difference of two sets of fringes is computed to acquire the alignment offset. Numerical simulation and experiment are both performed to verify this method. Finally, certain analysis about the error of phase difference extraction in the fringe pattern and precision of alignment are also presented. The results indicate that the background and noise of the fringe pattern can be efficiently filtered and target phase information can be extracted with high accuracy through this method.
As the critical techniques of lithographic system, the nano-positioning techniques, including the wafer-mask alignment,
gapping between wafer and mask and wafer focusing, are of great significance to the improvement of resolution of the
projection lithography and the proximity nanolithography, such as X-ray lithography, nanoimprint, and zone-plate-array
lithography etc. This paper presents a scheme based on grating modulation and spatial phase imaging. The relative move
and gap variation between mask and wafer can be associated with the shift or phase variation of fringe pattern and
obtained simultaneously. Two gratings with slightly different periods are adopted as alignment marks and gapping marks
on wafer and mask. Fringes with period that is inversely proportional to the difference of periods of two gratings occur in
the superposition of two grating marks. First, the theoretical background is introduced and the mechanism of alignment
gapping is detailed. Next, the scheme and framework of alignment and gapping method is constructed. Finally, numeric
computational and experimental results indicate that the displacement detectivity at nanometer or even sub-nanometer
level can be realized in this scheme.
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