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- Front Matter Volume: 10840
- Micro- and Nano-Optics, Catenary Optics, and Subwavelength Electromagnetics
Front Matter Volume: 10840
Front Matter: Volume 10840
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This PDF file contains the front matter associated with SPIE Proceedings Volume 10840, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists
Micro- and Nano-Optics, Catenary Optics, and Subwavelength Electromagnetics
Fano resonance based on a subwavelength semi-annular-rectangular cavity resonator
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A semi-annular-rectangular cavity based on metal-insulator-metal (MIM) waveguide is proposed. The results show that there are obvious asymmetric transmission peaks in the transmission spectrum due to Fano resonances. The sharp transmission peak with a transmittance of ~ 0.75 occurs at the wavelength of ~1174.99nm . Then a steep dip arises at its right side, and the transmittance is almost 0 at ~1239.22nm . In addition, high sensitivity and figure of merit are also investigated. The performances of the proposed structure are demonstrated by using FDTD method.
Non-paraxial diffraction of tiny pinhole illuminated by partially coherent light
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The theory of partial coherence has important applications in many fields such as optical system imaging, optical projection lithography, optical communication and speckle metrology. A tiny pinhole is essential to calibrate the wavefront error of the collimating lens when testing the wavefront error of the projection optics by using the method of Shack-Hartmann wavefront sensor. In this paper, a formulation is developed for investigating the intensity distribution in the far field diffracted by a circular tiny pinhole illuminated with partially coherent light. Assuming that aperture complex coherence is Bessel's correlation, the diffraction field far away from the pinhole is numerical calculated. The actual distribution of the field diffracted by the tiny pinhole is influenced by both the pinhole diameter and the coherence of light inside the pinhole aperture.
Design for dynamic wavefront manipulation based on phase change materials
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In the past decades, metasurfaces have shown their extraordinary ability to manipulate the wavefront of electromagnetic wave. However, the most of previously proposed designs based on metasurfaces are fixed once design, which are unsuitable for applications where light manipulation needs to be dynamically. In this paper, we proposed a design for dynamic wavefront manipulation achieved by the combination of metasurfaces and phase change materials (PCM) in the near infrared spectral range. Here, we present a metal-insulator-metal (MIM) configuration with the polarization conversion exceeding 80% for circular polarized (CP) light converted to its opposite handedness when PCM is in the amorphous state, but the efficiency turns to 0 when PCM switch into its crystalline state. By utilizing the Pancharatnam- Berry (PB) phase, we can achieve the dynamic wavefront manipulation between the amorphous and crystalline states. As a proof-of-concept, a deflector and focus lens are designed and characterized, and the results further verify the ability for dynamic wavefront manipulation. It is believed that the design in our work may pave the way towards the dynamic manipulation of light.
An all-dielectric metasurface with asymmetric wavefronts for oppositely propagating circularly polarized light
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Chirality is a key molecular structural concept and a ubiquitous phenomenon in nature that has become an increasingly significant research avenue. Here, we show that an all-dielectric metasurface, an array of spatially varying anisotropic nanofins, exhibits asymmetric wavefronts for forwardly and backwardly propagating circularly polarized lights. Similar to the asymmetric transmission phenomena, two wavefronts generated by one circular polarization from both sides of the proposed metasurface are not limited to the same or mirror symmetric, but also can be arbitrarily and independently manipulated. The observation of this novel effect originates from asymmetric photonic spin-orbit interactions. As an example, a metasurface is designed to produce an optical vortex and holographic image, respectively, when a circular polarization propagates through it in opposite directions. Due to its high efficiency and multifunctionality of the proposed metasurface, this work may have potential applications in many fields, such as optical communications, and provide new ideas for studying chiral and functional materials.
Composite Ag-Ni metal mesh based transparent conductive film for electromagnetic interference shielding application
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With the development of wireless microwave electronic devices, electromagnetic interference (EMI) is a new kind of pollution that is becoming increasingly prevalent and has affected the performance of the electronic devices and the human health. Thus,the transparent EMI shielding film is a key component for many practical applications. Conventional methods for the fabrication of transparent EMI film are time-consuming and costly for their employing expensive vacuum-based process. By combination of the scrape and selective electroplating techniques, a vacuum sputtering/evaporation-free processing is explored for the fabrication of high-performance metal mesh based TCF. The fabricated composite Ag-Ni mesh TCF exhibits ultra-low sheet electrical resistance (Rs=0.07Ω sq−1) at average transmittance of 70% in the visible region. The measured shielding efficiency can be greater than 30dB in X-band. Both experimental and theoretical results are given in the paper. By using the proposed method, TCF based EMI film can be easily fabricated for mass-manufacturing.
Sensing characteristics of the gold-silver alloy waveguided metallic photonic crystals
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The waveguided metallic photonic crystal biosensor based on gold-silver alloy material is expected to achieve better sensing sensitivity than the same structure of pure gold. By using the gold-silver alloy nanoparticles as “building block”, we successfully assemble one-dimensional waveguided metallic photonic crystals through a solution processible method. This is a simple and low cost method to fabricate one or two dimensional metallic crystals in large area. The sensitivity of the biosensor based on the gold-silver alloy waveguided metallic photonic crystal is 2.5 times that of the same structure made by pure gold. The gold-silver alloy nanoparticles assembled waveguided metallic photonic crystals exhibits potential application in biosensing due to its low-cost and simple testing methods.
Optical responsivity of mechanical resonators based on suspended membranes of graphene and transition metal dichalcogenides
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Mechanical resonators based on suspended two-dimensional membranes are promising systems for developing sensitive detectors of mass, charge and force. To measure the flexural vibrations of the membrane, it is important to employ a technique capable of resolving tiny fluctuations of vibration amplitude. To this end, researchers have been developing optical detection methods based on Fabry-Perot interferences of light between the membrane and a mirror-like substrate, which relate the intensity of light reflected by the device to the distance between the membrane and the substrate. In this work, we calculate the membrane-to-substrate distances that maximize the optical responsivity of the resonator, which we define as the derivative of the resonator’s reflectivity with respect to membrane’s displacement. In addition, we examine how various substrates with different refractive indices affect this optical responsivity, including bare silicon, silicon coated with silicon oxide, dissipative metal mirrors, and non-dissipative Bragg reflectors. Our calculation method is based on the transfer matrix method for propagating electromagnetic fields. Our results are consistent with earlier theoretical and experimental results, and offer perspectives to enhance the optical responsivity of these mechanical resonators.
realization of moiré imaging by flat micro lens array
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Micro-focusing moiré imaging has found successful application in security and anti-counterfeiting. It comprises of a micro-lens array and a micro-pattern array to visually present impressive dynamic and stereoscopic visual effects. In this paper a moiré imaging device with new features is fabricated using the well-known techniques such as nanoimprinting and photoresist thermal reflow. The features of the moiré imaging device benefit from the novel configuration of the micro lens array. With the same aperture diameter , the Flat Micro Lens Array can realize moiré imaging on thicker substrate, which has better dynamic effect, compared to the moiré image achieved by the traditional microlens array. The working surface of the MLA is buried in the UV layer, and the microlens moiré device is not easily replicated. The Flat Micro Lens Array surface is flat, hard to worn, even if be worn does not affect the imaging quality. Due to the above features, the proposed moiré device has application in the field of anti-counterfeiting.
Practical superoscillation element design for far field non-scanning superresolution imaging
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Superoscillation is a promising method to realize superresolution imaging. Nevertheless, in the point spread function (PSF) of previous superoscillation imaging systems, compared to the several orders of magnitude higher intensity in side-lobes, the extremely small intensity in the focal-spot is a severe constraint for practical applications. In this paper, we creatively segment the conventional superoscillation lens into two simple-fabrication portions to generate the superoscillation optical field and realize superresolution imaging in a local field of view (LFOV). We then analyze the contribution of different portions of the entrance pupil to the system’s resolution and propose a novel superoscillation element (NSOE) design to effectively reduce the intensity of side-lobes. We end by reporting our recent results on the imaging of complex targets, and the validity and potential applications of superresolution imaging is well demonstrated.
Trade-offs between stress control and blister avoidance in MEMS devices
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Thin films such as silicon nitride (SiNx) films, amorphous silicon (α-Si) films are fundamental in most microelectromechanical systems (MEMS). The thin-film stress is, in particular, of great importance for obtaining expected or controlled physical performance in MEMS devices. However, unexpected failures, especially blister defects, often occur when post-processing, for example, rapid thermal processing (RTP), is applied to the device. Through the preliminary experiment, we find that there is a trade-off between stress control and blister avoidance, and the roughness of the as-grown thin film is a good indicator to show the relationship between the thin-film stress and blister defects. Also, the experiment result shows that there is a balance between film stress and blister defects.
Tunable multi-modes resonator based on MIM plasmonic waveguides with circular cavity and rectangular baffle
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In this manuscript, a metal-insulator-metal(MIM) plasmonic waveguide coupled with a circular cavity and a rectangular baffle has been proposed and numerically investigated. Due to the existence of the rectangular baffle and its asymmetry position relative to the feeding ports in the circular cavity, the resonator exhibits multiple sharp Fano-like resonances. The behavior of the proposed structure is analyzed in details with finite element method. The spectral line profile and resonance wavelength can be easily tuned by the parameters of this proposed structure, such as the radius of circular cavity, the height h of baffle and its position, etc. Using the relationship between the height of baffle and resonant wavelength λ, its sensing capabilities are demonstrated through the responses for various refractive indices. The Figure of Merit can be achieved as high as 4.65×104. As an example, a compact 1×2 plasmonic wavelength demultiplexer has been designed with different height of baffles. Moreover, this 1×2 wavelength demultiplexer can also act as a metal detector because different metallic baffle has a different response peak. Our compact plasmonic structure may have widely potential applications in nanosensors, optical communication, optical detection and integration plasmonic devices.
High sensitivity plasmonic sensor using hybrid structure of graphene stripe combined with gold gap-ring
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To reduce the plasmonic line width of the metallic nano-structures and improve its performance when used in sensing, a hybrid structure consisting of a graphene stripe and a gold gap-ring is proposed and studied numerically. The structure works at Middle-IR band(3-6μm). Through strong coupling, some narrow dips caused by absorption of graphene appear on the wide background scattering spectrum of the metallic structure. Due to the high plasmonic confinement of graphene, the line width of these dips is around several tens nano-meters. In addition, the resonance intensity of graphene is enhanced significantly. By index changing, the sensing property of this composite structure is also studied. Simulation results show that its sensitivity exceeds 3000 nm/RIU (refractive index unit) and the figure of merit can reach up to 109 which prove our structure a good sensor.
Dual-band coherent perfect absorption based on graphene patterned metasurface with tunable absorption frequency and absorptivity
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We propose that dual-band coherent perfect absorption in the infrared can be achieved in a metasurface, which contains periodical symmetrically patterned elliptical graphene array on both sides of the silicon dioxide film. The physical mechanism of dual-band absorption is that the major and minor axes of the elliptical graphene disk have different widths and can produce resonances at different frequencies. Based on the independent resonances, the asymmetrically patterned metasurface can separately absorb light of different frequencies for TE and TM polarizations, which is useful to detect the polarization of incident light. In addition, the coherent absorptivity of each peak can be tuned by phase modulation and the dual-band absorption frequencies can be flexibly adjusted by changing the Fermi level of the graphene via chemical or electronic doping. Therefore, our proposed metasurface can achieve the double modulation for both absorption frequency and absorptivity, which make it a good candidate for optical switch and absorption modulator.
Thermal blooming effect of pulse vortex laser beam propagating through the atmosphere
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Thermal blooming is an important nonlinear effect when laser beam propagates through atmosphere. The laser energy will be absorbed by the atmospheric molecular and aerosol particles, and the thermal expansion of the atmosphere will occur. It will lead the local atmospheric refractive index reduced. This effect distorts the laser beam and the transmission characteristic of laser beam is affected. In this paper, the thermal blooming effect of pulse vortex beam is discussed. And a numerical simulation is performed to simulate the light intensity of the pulse laser at different distance. The effect of different topological charge on thermal blooming effect is analyzed.
Theoretical study of strained black phosphorus photodetector integrated with silicon waveguide
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We compare optical characteristics of black phosphorus photodetectors integrated with a stripe waveguide and a ridge waveguide by optical field intensity and absorption spectrum, which proves that the stripe waveguide is better for enhancing the optical absorption of black phosphorus photodetector. The strain effect on the band structure of black phosphorus is investigated using the first-principles method based on density functional theory (DFT). The band structure of 5-layer BP experiences a direct-indirect-direct transition and a semiconductor-metal transition (SMT) when applied different strains. As a result, the cut-off wavelength and the responsivity of this strained BP photodetector can reach 3.76μm and 0.48 A/W respectively. In a word, the waveguide-integrated black phosphorus photodetector under strain for mid-infrared range may promote potential novel optoelectronic device applications based on two-dimensional materials in the future.
A wide-angle and polarization-insensitive tunable metamaterial absorber based on graphene
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In this paper, we propose a frequency tunable metamaterial perfect absorber in the THz region based on graphene. The unit cell consists of a periodically patterned graphene cross-ring resonator and a gold film separated by a dielectric spacer. The simulation results demonstrate that the maximum value of absorption is 99.9% at 4.7 THz. By controlling the graphene conductivity, the frequency tunable characteristics can be achieved in this metamaterial absorber. When varying the diameter of the ring or the length of the cross, we find that resonance absorption frequency will significantly shifts. Moreover, the metamaterial absorber possesses the polarization-insensitive and a wide range of the incident angles up to 70° for both TE and TM polarization. Our absorber can be used in some practical applications due to its excellent absorption and simple structure.
Study on wavelength division multiplexing with chirped volume Bragg gratings
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In order to study the spatial wavelength division diffraction effect, the Chirped Volume Bragg Gratings (CVBG) based on the Photo-thermo-refractive glass on the oblique incident light was analyzed by the fundamental matrix method. When diffracted by grating, the complex beam would be separated into multiple beams in space by wavelength. The diffraction efficiency of the separated optical wave can reach up to 90%. Furthermore, the diffraction efficiency, increases as the refractive index modulation depth increases and decreases as the chirp rate increases. The diffraction spectrum has the characteristics of flat-top band pass. To increase the spatial separation distance, multiple schemes of CVBGs in parallel combination are designed. By combining a self-focusing lens array, the proposed system can realize wavelength division multiplexing with bandwidth less than 0.4nm.
SP resonance angle and Q-factor of metals in ultraviolet band
Lanxi Duan,
Saisai Qin,
Yaru Li,
et al.
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Surface plasmon (SP) properties of more than dozen of metal materials have been comparative analyzed in ultraviolet (UV) band (436nm, 365nm) which are the typical light source used in SP lithography. We excited the SP wave by Otto configuration. The electromagnetic field in the structure were calculated by the full-vector FDTD algorithm. The SP resonance angle and the quality factor of the resonance peak were extracted. The results showed that the calculated SP resonance angle is approximately the same as the angle expected by the SP theory , and the error is no more than 5%. This gave an evidence that the SP theory is still applicable in the UV band although the theoretical model of permittivity, such as Drude, Lorentz and Debye, is ineffective at this time. We choose some metals with smaller errors to research the quality factor of SP resonance peaks. The results showed that even if the excitation angle was similar, the Q-factor was different which mean that the propagation length of the same SP wave was different. It can provide references for material selection when designing SP devices in UV band.
Extraordinary optical transmission of the double square ring metal nanocomposite structures
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In recent years, metal nanostructure has had rapid development and application in novel optical sensor, filter , optical transparent electrode and other fields, so the study for the design of metal composite nanostructures and the design’s optical characteristics not only has laid the foundation for extraordinary optical transmission (EOT), but also had important significance in the development of optical devices mentioned above all. This paper uses the method of finite difference time domain (FDTD) to calculate the three-dimensional the double square ring metal nanocomposite structure models. We studied a series of factors, such as the parameters of the metal silver film, the groove width and the incident plane wavelength, and so on. As the result of our study, we found that the light transmission intensity of this composite structure is much higher than separated large or small hole array structures. It’s because the resonant excitation of the composite surface plasmon polaritons (SPPs) and the strong coupling are more remarkable in the double square ring structure. Through the study of kinds of composite structures, we discovered that some small holes to be cut in the metal film structure will be more conducive to the light transmission intensity. It is a great potential value in the research and development of optical devices.
Performance improvement in inverted organic solar cells by incorporating core-shell SiO2@Au plasmonic structures
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Organic solar cells (OSCs) are very attractive as a clean and renewable energy technology owing to their advantages of low cost, abundant material sources, good flexibility, etc. Nevertheless, OSCs are faced with the contradictions between the optical and electrical properties. Their low absorption efficiency requires a thick active layer for efficient light harvesting, while the short carrier transport distance implies a thin active layer is necessary for efficient charge extraction. One way to solve this contradiction is to effectively enhance light absorption in the active layer without increasing the thickness. In this work, a core-shell structured plasmonic nanoparticles in the form of Au nanorod core coated with a SiO2 shell (in short of Au NR@SiO2) were introduced at the interface between the active and the cathode buffer layer of an inverted OSC based on PTB7:PC70BM active layer. By adjusting the concentration of the plasmonic nanoparticles of Au NRs@SiO2, we optimized the optoelectronic performances of OSCs. The results indicated when we spin-coated 1 pM Au NRs@SiO2 on top of the buffer layer, the device performances were optimized with the short circuit current increasing significantly while the open circuit voltage bearing negligible change. Overall, the power conversion efficiency of the OSC increases from 6.52% to 7.03%, corresponding to an enhancement of 8% as compared to that of the structurally identical control cell without Au NRs@SiO2. The performance improvement in inverted OSCs is mainly resulted from efficient light trapping effect of the core-shell plasmonic nanoparticles.
Manipulation on thermal radiation spectrum and its polarization with laser manufactured periodic surface patterns
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Manipulation of thermal radiation on metal materials attracted tremendous amount attentions in the past decades. In this study, we successfully designed simulated and manufactured three kinds of periodic micro-patterns on the nickel surface and realized the manipulation of the radiation spectrum and the polarization of nickel. The patterns which were applied to excite the surface plasmons were manufactured by the advanced ultrafast laser micro-machining technique. The experimental results of the thermal radiation showed good agreement with the simulation results. This low cost and designable method could pave the way for the future infrared applications.
The spectroscopic and molecular constants studies of the ground and first excited states of O2 molecule by CCSD(T) and MRCI methods
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The potential energy curves of the ground and first exicted states were calculated by CCSD(T) and MRCI methods. Effects of the core-valence correlation and relativistic corrections on the the potential energy curves are included in present calculation. To obtain reliable results, the Davidson modification (MRCI+Q) which is compensate for the high order truncation is also considered in present calculation. Furthermore, in order to avoid the basis set superposition error, the complete basis set limit extrapolation is also included in present calculation. With these potential energy curves, the spectroscopic parameters are determined and compared with available theoretical and experimental studies. The result indicated that present results are in good agreement with experimental data and the core-valence correlation correction has larger effects on the spectroscopic constants than relativistic correction.
A new long-range single nanotube hybrid plasmonic waveguide
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In this paper, a novel long-range single nanotube hybrid plasmonic waveguide composed of a silicon nanotube and a thin metal layer embedded in it is designed. The geometry of this waveguide is much different from the conventional hybrid plasmonic waveguide such as a tube-wedge or rectangle long-range hybrid plasmonic waveguide. With strong coupling between the silicon nanowire mode and long-range surface plasmon polariton (SPP) mode, both deep subwavelength mode confinement and low propagation loss has been achieved. We evaluate the properties of the ultra-small hybrid plasmonic waveguide including propagation length (L), normalized mode area (Aeff /A0), and figure of merit (FoM). The results show that the designed hybrid plasmonic waveguide enables an ultra-small deep-subwavelength mode in a smaller area than presented long-range hybrid SPP waveguides. What’s more, the propagation length is longer than 1mm and optimization FoM of our waveguide is much larger than 104, which show much better performance that of wedge or rectangle hybrid plasmonic waveguide. Finally, another significant improvement of our structure is that the area of the cross-section is about 0.05um2, which is much smaller than any other presented hybrid plasmonic waveguides.
A terahertz metamaterial analog of electromagnetically induced transparency and its application in loss detection
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Based on metamaterial theory, a terahertz metamaterials with analog of electromagnetically induced transparency (EIT) effect is designed. The cell unit are consisted of three metal wires and polyimide substrates. Through the radiation of the terahertz wave, the bright-dark mode is excited directly and indirectly to form the EIT resonance, and the phase interference is formed through the superposition of the resonant spectrum between the elements to make the metamaterial transparent to the incident terahertz wave. The formation of transparent window has great value in the application of loss detection. In this paper, the influence of the loss of the measured material on the transmission peak is studied based on the change of the peak of transmission peak. The result shows that there is a close nonlinear relationship between the loss tangent angle of the measured material and the penetration rate of the metamaterial, which provided ideas and foundations in the measurement of the loss detection.
Slow light in a slot photonic crystal waveguide with asymmetric dielectric rods
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A novel air slot photonic crystal slow light waveguide structure is proposed. The symmetry of the waveguide is broken by shifting the dielectric rods asymmetrically along the slot axis. When the photonic crystal lattice vector angle is greater than 60 degrees, it can make the performance of slow light more excellent. A triangular lattice photonic crystal with the lattice vector 90 degrees is obtained by rotating the cubic lattice 45 degrees counterclockwise. Five optimized structures are obtained by optimizing the width of the slot, the radius of the two rows of semicircular dielectric columns in the upper and lower air slots as well as the asymmetric movement of the two rows of dielectric rods near the slot. The dispersion curves of the guided mode, the corresponding group index and group velocity dispersion are analyzed using the plane wave expansion method. Finally, considering a criterion of restricting the group index variation within ±10% range and higher normalized delay bandwidth product, the best group refractive index is 272 with the corresponding normalized delay bandwidth product is 0.3009. The numerical results provide theoretical foundation for potential applications of optical buffer in photonic crystals field.
Enhance the absorption of organic-inorganic perovskite film by nano-surface engineering
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Organic-inorganic perovskite is an emerging material possessing potential applications in solar cell, light-emitting diodes, and photodetectors due to its intrinsic features. High absorption coefficient, as an important parameter, is beneficial to the photo-electrical conversion efficiency and the relevant issues. Therefore, how to further improve the absorption is a meaningful topic. In this work, we turn to the nano-surface engineering to realize great absorption. Concretely, the self-assembled truncated spherical nanovoids are arranged on the surface of the perovskite. In comparison with the planar perovskite film, the absorption coefficient is increased by 18% on average within 300 nm ~ 800 nm wavelength region and a wide incident angle range. The improvement is originated from the special arrangement of effective dielectric constants which can be verified by multilayer effective media theory. This finding paves a way of improving the absorption of perovskite at the scales between the wavelength (perovskite-based gratings) and the quantum (perovskite with quantum dot doping). Moreover, the relevant research has been pointed out that the structured perovskite films have better pressure resistance.
Study of the linewidth measurement with scanning electron microscope based on laser interference principle
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As an imaging tool of nanometer resolution for microstructure analysis, the scanning electron microscope plays an important role in semiconductor and nanometer structure measurement. In this study, a special scanning electron microscopy imaging and line width measuring method is introduced based on principle of laser interference. We design the double stages including micron resolution stage and nanometer resolution stage. A new imaging mode by raster scanning of precision stage is employed in this metrological scanning electron microscope. The line width of standard sample image is measured precisely by calculating the coordination data that come from the laser interferometer system. This nanostructure measuring method is in line with international standard for the dimension measurement of traceability.
Design of a miniature grating displacement sensor with large range
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Compared with laser interferometer, grating displacement sensor has the advantages of small size, low cost, and strong environmental robustness. In this paper, a grating displacement sensor was proposed. The theoretical model of the grating displacement sensor was established using the optical effect of Doppler shift and linearly polarized light interference. Based on this model, the error of the grating constant and the displacement of grating during measurement were analyzed to achieve the measurement accuracy of the grating displacement sensor. The analysis result showed that when the error of grating constant or the displacement of grating increases, the measurement accuracy will decrease. By changing the error of grating constant or the displacement of grating, 42 sets of measurement accuracy were calculated. The analysis result will provide an important reference for the development of nanometer accuracy grating displacement sensors.
Downstream light intensification induced by Gaussian mitigation pits using micro-milling on rear KDP surface
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Micro-machining has been proved the most effective method to mitigate the laser-induced surface damage growth on potassium dihydrogen phosphate (KDP) crystal in high power laser systems. However, the phase contrast of outgoing laser beam, introduced by the mitigated KDP surface, would cause light propagating turbulence and downstream intensification with the potential to damage downstream optics. In this work, a Gaussian mitigation pit with width of 800μm and depth of 10μm is fabricated on KDP rear surface by micro-milling. The effect of the mitigation pit on downstream light intensification is analyzed through propagation calculations based on Fresnel diffraction integral theory. The light intensity modulations reach a peak value at the position of 10mm downstream from the rear surface, decrease sharply subsequently and get stable eventually. The results indicate that the modulations induced by Gaussian mitigation pits would change with various downstream locations. It is essential to notice the unacceptable downstream intensification and reduce the risk of laser damage on other optics by choosing an appropriate installation location.
Design and fabrication of a new tungsten-diamond transmission target for micro-computed tomography
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The Micro-CT uses X-ray to detect the internal structure of a sample on micro&nano scale without destroying it, the main challenges in manufacturing a high power Micro-CT is a target with fast heat dissipation to produce high power intensity of X-ray. In this manuscript, we introduce our progress in manufacturing a target that can withstand higher power of electron beam than previous. Firstly, Monte-Carlo simulation (Genat4) is constructed to determine the optimal thickness of the tungsten film, which optimize the intensity of X-ray. In addition, we examine heat dissipation of tungsten and aluminum by finite element method and find that diamond is the most suitable material for substrate, because it results in the lowest temperature near the impact point according to our simulation. Thirdly, the magnetron sputtering method is used to fabricate a tungsten film on the diamond substrate. We highlight that the Micro-CT based on this target achieve a high resolution of 3μm, and the power of electron beam is 10 watts. Based on these improvements, the experiments show that our tungsten-diamond target provides much better performance with quicker heat dissipation rate (i.e. with lower temperature near the impact point) and the stronger power of X-ray than previous works.
Fresnel zone plate method for measuring lens transmission wavefront power spectral density
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The optical components employed in high power density solid-state laser for inertial confinement fusion (ICF) must be measured accurately to provide the high resolution measurement neccessary to detect mid-spatial-frequency errors in the wavefront. The use of a Fresnel zone plate (FZP) technique to measure lens transmission wavefront power spectral density (PSD) in mid-frequency domain is disscussed. FZP can provide reference sphere with high-precision, in the meantime greatly shorten air space, thus reduce the effect of vibration and air turbulence, therefore is of great importance for lens transmission wavefront PSD measurement, especially for lens with long focal length used in the ICF facility. To verify the accuracy of the measurement, a comparison experiment of the FZP measurement with results from a Fizeau sphere interferometry method is carried out. Measurement results show excellent agreement, which proves the validity of this method. Finally, measurement uncertainty due to FZP fabrication process is analyed. Analysis of the FZP test showed the overall accuracy of 4.5nm RMS for a sphere lens with 1.5 m focal length and Φ70mm clear aperture. Thus, the measurement accuracy using the proposed FZP method is proved to be very high, FZP can therefore be used to measure lens transmission wavefront PSD accurately.
Measurement of optical intercept of micro lens arrays
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At present, micro lens arrays have been widely used in the fields of infrared detection, light gathering, portable solar battery and so on. The focusing and imaging properties of micro lens arrays are closely related to the performance parameters such as point diffusion function, diffraction efficiency and optical intercept. In order to better evaluate the quality of micro lens, this paper introduces a method for accurately measuring the optical intercept of micro lens arrays, which is more precise and has less deviation than interferometry, CCD direct imaging and so on. This experiment is based on the principle of CCD imaging and image processing, and a set of testing system is established. The system is mainly composed of a laser light source, a collimation system, samples and a camera. After many experiments, The optical post intercept detection device can obtain test accuracy below 5μm
The research of single point diamond turning Fresnel lens technology
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In order to obtain high precision Fresnel lens, the processing technology of the single point diamond turning (SPDT) is investigated. Through the cutting experiments, compared the performance of Fresnel lens manufactured on different metal materials and by different diamond tools, respectively. The results show that material characteristics and tool nose radius affect the shape precision of the Fresnel lens, and the machining parameters affect the surface roughness. Therefore, choosing appropriate tool parameters and material is extremely important for improving the precision of Fresnel lens.
Analysis error of machining radial Fresnel lens on roller mold
Yawen Guo,
Ziqiang Yin,
Sujuan Wang
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Roll-to-Roll imprint process is considered to be the most promising technology for manufacturing large-area micro-structured surface. However, the traditional turning technique was considered to be incapable of machining radial Fresnel lenses on roller mold. This study deals with the problem of machining the radial Fresnel lens on a roller mold, which is achieved by using the diamond cutting tools mounted on a multiple axis control ultra-precision machining center. In addition, this study simulates the effect of the deviation of the tool tip position from the rotation center of the platform and the deviation from the vertical plane of the roller axis on the machining results.
Dynamic fractal digital lithography for the fabrication of microlens array
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To improve the transverse resolution of digital mask lithography pattern, we present a novel dynamic fractal digital lithography to fabricate microlens array. The basic idea of this technique is to divide a high-frequency digital mask into a group of low-frequency masks by using equal-height-rounding quantization. Consequently, dynamic fractal digital lithography has the advantage in decrease of mask quantity and mask quantization error. Then these low-frequency masks are exposed in sequence and the superimposed exposure of multiple masks takes the place of single exposure of original high-frequency mask. We demonstrate the feasibility of dynamic fractal digital lithography by experimental fabrication. The uniform microlens array with smooth surface and clear edge profile are achieved.
Fabrication of micro-pyramid structured optical element based on SPDT
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As the need of micro-pyramid structured molds and optical element getting bigger, the requirement of its accuracy and effective and economical fabrication method is increasing faster. Single point diamond turning (SPDT) is a good technology for fabricating micro-pyramid structured, and it has be used very widely. Different processing mode can get different feature size of pyramid structured. In this paper, for different feature size of pyramid structures, the processing modes including Fast Tool Serve (FTS) and fly-cutting are discussed, meanwhile the limits of them are also analyzed. After that, a mass of experiments with different materials and different feature sizes have been done. Through measuring the surface structure with Scanning Electron Microscope (SEM) and White Light Interferometer (WLI), we find that FTS is suitable to fabricate pyramid structure with millimeter dimension or large, meanwhile the radius of diamond tool should be smaller to avoid the interference. When the size of pyramid structure reduces to micron dimension, fly-cutting with sharp angle tool is a good choice. All of them is very useful for engineering application.
Simulation and experimental study on the precision glass molding for microstructures on optical glass based on relaxation effect
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To manufacture high precision optical glass microstructures, finite element simulation and experiments of precision glass molding (PGM) are carried out to study the influence of relaxation effect on internal stress and deformation of the glass material. Two kinds of microstructures including microgrooves and micropyramids are fabricated by PGM. First, a two-dimensional axisymmetric finite element model of the PGM is established, and three kinds of molding schemes are put forward and analyzed, including quick molding and holding for a period of time, molding with low speed, molding by gravity. The advantages and disadvantages of the three schemes are also analyzed. Second, the microgrooves are fabricated using the scheme of molding by gravity, and then the existing problems are discussed. Finally, the micropyramids are fabricated by the low speed molding method, and the forming profiles are compared.
Research and design of functional microstructures with directional transport for bionic microfluidics
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Optical microscopy is an important means and tool for the research of microcosmic life science. As an important technology to study the life process with optical methods, microfluidics is widely used in the field of biology and medicine. Inspired by bionics, biomimetic microfluidic control has become a promising branch of microfluidic field. In the microfluidic channel, it imitates biological functions such as collecting water droplets and cilia driven fluid motion, which provides an alternate approach for the design and development of new microfluidic devices. This paper presents a study of functional microstructures with directional transport for the application of bionic microfluidics. Biological microstructured surface with directional transport function was first studied and designed, to imitate the rose petals, the outer skin of the Texas horned lizard and the peristome surface of Nepenthes alata. The model of bionic microstructure with directional transportation was then established to reveal the characteristic mechanism of typical directional transport microstructures. Microstructures with function of directional transport were designed regarding to the criteria of distance and speed of directional transportation of water droplets. Simulation studies show that the designed functional microstructured surface is capable to achieve the expected function of directional transport. Such microstructures can be applied to the design and processing of microfluidic chips, therefore the research is helpful to promote the application and development of bionic microfluidics in optical microscopy.
Research and development of light field microscope for measuring 3D microstructures
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Precision measurement of three-dimensional (3D) microstructures has drawn great interests from researchers and industries. Currently there are a bunch of high precision measurement methods such as contour-graphs, interferometers and optical computed tomography used in industrial applications. Nonetheless, the loss of information, low efficiency and possible surface damaging of traditional ways still exist. This paper presents a new way to measure micro/nano structures based on light field microscope. The light field information of the microstructures is acquired by using a microlens array which is inserted between the camera sensor and the objective lens. Then a series of regular sub-images are recorded by the photosensor, which is used to reconstruct a 3D image by the developed algorithms. The non-contact shooting process is realized through only one exposure which is much more efficient than the traditional ways. Microlens array with aspheric surface is also designed and used in the developed system, to eliminate aberrations and compensate the loss of spatial resolution. A series of simulation and experimental studies have been undertaken to measure microstructures, and the feasibility of the developed system is validated.
Optimization design and performance test of optical antenna for laser communication
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Laser communication has many outstanding advantages, such as high optical gain, high anti-interception, high anti-interference ability and high communication rate, it is an important technical method to solve the problem of high speed communication. The optical antenna is responsible for the reception and transmission of the signal, which is an important part of the laser communication terminal. Based on the general research situation at home and abroad, from the aspect of system SNR and efficiency, this article has determined some targets such as receiving / emission efficiency, wave aberration and ability of off-axis stray light suppression; combined with specific application requirements, we have determined the basic parameters such as communication wavelength: 1545nm, aperture: 100mm, FOV: 0.1 degrees, optical magnification: 15 times. According to the above parameters, a set of reasonable optical antenna system has been designed and the test equipment is set up to measure, the test results are all satisfied. This paper has some reference value for the design and test of laser communication optical antenna.
Athermal design of refractive/diffractive hybrid infrared optical system with large relative aperture
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Infrared detection system, due to its high stability and all-weather adaptability, has been widely applied in civil and military areas. In this paper, based on the refractive/diffractive hybrid structure and the passive athermalization, a dualband infrared optical system with large relative aperture (F=1) is designed, which has excellent performance in the correction of thermal aberration, chromatic aberration and second spectrum between -40°C to 60°C. By precisely arranging the double-layer diffraction element, the system designed is simplified effectively, which contains only four lenses. Meanwhile, the optical layout has the advantages of lower weight and smaller volume. The MTF in mid-wave infrared is larger than 0.6, which demonstrates good capacity of target recognition and anti-inference, and thus it is suitable for practical usage in the field of aviation remote sensing.
Design and fabrication of CGH for 820mm diameter tertiary mirror surface figure testing without center hole
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Computer-generated hologram (CGH) is an effective way to compensate wavefront aberration in null test of aspheric surfaces and freeform surfaces. Our strategies of CGH design for 820mm diameter tertiary mirror surface figure testing are presented, and an experiment demonstrating the compensation test results of CGH is reported. We design a CGH including two sections on the same substrate in order to align the CGH to the incident wavefront: main section for compensating wavefront in null test, alignment section for adjusting the relative position between CGH and interferometer. Because there is no center hole in the mirror, in order to isolate different orders of diffraction, we used tilt carrier to make different orders of diffraction come to focus at different position perpendicular the axis to avoid ghost reflections.
Design of wide-spectrum directed multispectral imaging system with visible light
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In this paper, a visible spectral multi-spectral imaging system with spectral resolution better than 14nm is designed. The system uses dual Amici dispersive prisms as the optical splitters to provide the parallel beam dispersion with the widen spectral range. When designed, the fore-telescope、collimating lens and imaging objective lens adopt telecentric structure to facilitate pupil matching, and the directed characters of dual Amici prisms make the coaxial design realized. The spectral range is 400nm-900nm, the relative aperture is 1/2.4, the optical design software CodeV is used for ray tracing and optimization of the spectral imaging system, and the design results are analyzed. The analysis result show that the optical modulate transfer function has reached 0.75 or more in each spectral segment of the optical system, the spectral resolution is better than 14nm, the smile and keystone are better than 5um, meeting the design requirements. The system has the features of widen spectral range, the smaller of the smile and keystone.
Research on two test methods of polarizer extinction ratio
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According to the definition of extinction ratio, the paper analyzed two test methods of polarizer extinction ratio, and proved that these two kinds of systematic errors caused by the approximate formula are equal under the same condition. Generally, the extinction ratio of the polarizers to be measured is 2 orders of magnitude lower than the known polarizers, and the system error can be controlled within 1%.
Nano-grating structure optimal design of bio-inspired polarized light compass
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The directional accuracy of bio-inspired polarized light compass mainly depends on the extinction ratio and transmittance of the polarized light sensor. This paper first analyzes the influence of structure parameters, such as grating period, duty cycle and depth of grating, on the extinction ratio and transmittance of the grating. Then, this paper proposes the design scheme of the grating array structure, and conducts a preliminary experimental verification of the strategy to demonstrate its effectiveness.
Study on long period fiber grating sensor based on deep-grooved process
Yang Cao,
Min Zhou,
Yu Liu,
et al.
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A high-sensitivity strain sensor of LPFG based on deep-grooved process was investigated. The LPFG was fabricated by a high frequency focused CO2 laser irradiation system in ways of periodic spaced heating on the ordinary single-mode fiber. Combined with a high precision position controller and optical measurement platform, an optical fiber strain sensor measurement platform was established. A theoretical analysis based on coupled mode theory and transmission matrix method for parameter design and optimization of LPFGs was adopted. Experimental results demonstrated that the axial strain sensitivity of a LPFG strain sensor would be increased with the increase of groove depth of the grating, and such a deep-grooved LPFG strain sensor would have an axial strain sensitivity up to -10.28pm/με which should be much larger than the strain sensor without grooves on one side of fiber grating. Therefore, this novel sensor should be able to find a potential value in the field of sensor applications.
A multilayer structure with high Vis-absorption based on ultrathin NiCr film
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High vis-absorption materials were widely used in solar cells and light detectors. Here, we achieved an Al/SiO2/NiCr/Si3N4/NiCr multilayer structure with high vis-absorption based on ultrathin NiCr film. The Al and NiCr layers were deposited through DC magnetron sputtering, and the SiO2 and Si3N4 layers were prepared through Plasma Enhanced Chemical Vapor Deposition (PECVD). The average absorption of the multilayer structure was beyond 83% in the range of 400-1100 nm and the maximum absorption was 99.34% at 530nm when the thicknesses of Al, SiO2, middle NiCr, Si3N4 and top NiCr layers were 80 nm, 40 nm, 4.6 nm, 30 nm and 4.6nm, respectively. Moreover, the absorption peak, along with color change of the multilayer structure from deep blue to light blue, could be adjusted by changing the thickness of Si3N4 layer from 30 nm to 50 nm. X-ray photoelectron spectroscopy (XPS) analyses revealed that the concentration ratio of Ni and Cr in the ultrathin NiCr films was very close to that of NiCr alloy target, and that the dielectric layers (SiO2 and Si3N4) have completely covered the metal layers. Atomic force microscopy (AFM) patterns have indicated the ultrathin NiCr film has a smooth surface with the root-mean-square (RMS) roughness of 0.883 nm. The multilayer structure based on ultrathin NiCr film could be promising for building highly-efficient solar collectors.
A multi-band terahertz metamaterial absorber with novel structure
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A multi-band terahertz metamaterial absorber (MA) is proposed. The unit cell is formed by windmill-shaped elements in a square ring, a dielectric substrate and a metallic ground plane. The MA unit cell is investigated at normal and oblique incidence for both transverse electric (TE) and transverse magnetic (TM) polarizations. The simulated results show that the MA has three high absorption (greater than 99%) resonance narrow bands. The LC equivalent circuit is employed to analyze the origin of multi-band. The proposed MA is easy to fabricate, what’s more, the proposed MA has high absorption rate and insensitive to polarization, which is favorable for various applications, such as terahertz detecting, imaging, and so on.
Research on micro displacement measurement technology based on chromatic confocal method
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Compared with other non-contact displacement sensors, the chromatic confocal sensor, which based on wavelengthdisplacement modulation technique, has no special requirements on the material and texture of the measured surface, and suitable for measuring the displacement of objects whose size range from micro to macro with high precision. In this paper, the chromatic confocal method is applied to measure the micro displacement. A hyperchromats with a measurement range of 1.27mm and linear regression coefficient R2 of 0.996 has been designed by using ZEMAX optical design software. The experimental system of chromatic confocal displacement measurement is set up. Through two miniature fiber optic spectrometers, the large measurement range and high precision spectrum detection are realized. The system error is calibrated synthetically. The measurement range of 1.2mm and linear regression coefficient R2 of 0.997 is realized. The research results are of great significance for the development of micro-nanometer displacement measurement technology.