To meet the growing demand for high efficiency stealth dicing (SD), generating dual-focus in silicon to produce double dicing paths has been widely used. However, the challenges in dual-focus SD are the aberration compensation methods based on spatial light modulators (SLM). Until now, the effect of SLM flyback regions that causes focusing intensity reduction has not been considered. Here, an aberration compensation method that considers the effect of SLM flyback regions is proposed to enhance the focusing intensity. This method takes into account not only the total number of flyback regions but also their distribution corresponding to the laser intensity distribution. In addition, the total area of flyback regions is utilized to quantify the impact and determine the optimal compensating phase pattern. Through simulations and experiments, we investigate the generation and control of aberration compensated dual foci. The simulated results demonstrate excellent agreement with theoretical analysis. Moreover, a back crack propagation of 29.9 μm is achieved in the dual-focus SD experiment.
In lithography, the micromirror array (MMA) is utilized in the generation of customized source shapes optimized by source and mask optimization (SMO) technology. With irradiated laser ejecting from the surface of micromirror, the facula is positioned at the designated position. Through the progressive torsion of cantilevers, the electrostatic actuated micromirror realizes high-precision rotation corresponding to different driving voltages. Irradiated by 193nm UV laser, the heat sink accumulated on MMA leads to thermal expansion of structures. Thus, the voltage-angle (V-θ) curve serves deviation from the theoretical value, resulting in the distortion of illumination modes further. In order to estimate and eliminate the unfavorable effects on the rotation of MMA induced by heat sink, a biaxial electrostatic driven micromirror is initially designed and a multi-physical field model is established. Through equating the laser to a 2D surface source, in the thermal equilibrium state, the mirror surface temperature rises to 395.92K, with an introduced angular error of 3.313mrad when the driving voltage is 70V. The additional angle would exceed the design requirements of MMA and result in modes distortion. In order to eliminate the deformation of illumination mode in the pupil, a forced nitrogen cooling system is applied to suppress the accumulation of heat. Ultimately, the MMA without structural deformation could be adopted in the freeform pupil illumination modes generation in lithography.
The most problematic aberrations in 3D DLW are related to mismatched refractive index at surface of the sample. Adaptive optical element placed in a plane conjugate to the objective pupil can be used to apply the correcting phase, providing a promising aberration correction. Currently, the calculation of correcting phase are all based on the assumption of ideal objective lens. In practice, secondary aberration is introduced due to the use of actual objective lens, and has not been researched. In this paper, we compare ideal objective lens and actual objective lens in theory, and simulate the energy distribution inside of sample. The effect of secondary aberration on DLW performance is reported. We make compensation for the secondary aberration, and contract the energy distribution of correcting secondary aberration and without correcting secondary aberration. Correction of secondary aberration caused by actual objective lens provides a more accurate correcting method of 3D DLW.
Diffractive optical elements (DOE) are widely used in modern optical systems due to their advantages of small size, light weight, high design freedom, wide material selectivity and unique dispersion performance[1]1. However, with the development of technology, the optical system has put forward higher requirements on larger diffraction angle, high diffraction efficiency and uniformity of DOEs. According to the grating equation, the diffraction angle can only be increased by reducing the feature size of DOE. When the feature size of the DOE is below the sub-wavelength level, the conventional scalar diffraction theory is no longer applicable. In this paper, an ultra-wide-angle 1×11 beam splitter is designed by using one-dimensional rigorous coupled-wave theory and genetic algorithm. The maximum diffraction angle of the beam splitter can be reach 72°and the diffraction efficiency is 92.98% with the uniformity error is 5.77%. By comparing with the FDTD simulation results, the difference in the diffraction efficiency of the DOE designed based on this method is less than 1%. This method has wide application prospects in the design of large angle beam splitters, structural light generation, holographic projection display and other fields.
Cylindrical vector-polarized vortex pulses from a passively Q-switched laser are demonstrated. Pump radiation reshaped into a size-controlled annular profile via circular Dammann grating produces an efficient excitation of the LG01 mode. The YAG / Nd : YAG / Cr4 + : YAG composite crystal structure is found to reduce the Q-switching threshold and significantly suppress thermal damage, thus allowing ability to obtain a passively Q-switched pulse. The threshold pumping power is found to be 4.35 W, with a slope efficiency of 23.1%. A maximum peak power of 3.24 kW, maximum pulse energy of 53.46 μJ, pulse width of 17.5 ns, and repetition rate of 2.695 kHz are obtained. Furthermore, a radially polarized output with a polarization degree of 88.9% is confirmed. Finally, mode and polarization tuning are also discussed.
We propose and present a high-efficiency circular dichroism device formed by an array of multi-size chiral slits etched in a silicon layer that is on a silicon dioxide substrate. Numerical results show that the all-dielectric chiral metasurface exhibits a high circular dichroism in the range of 1500-1550 nm. At the resonance wavelength of 1540 nm, the highest circular dichroism (CD = TRCP-TLCP) reaches 97%, and the extinction ratio (ER = TRCP/TLCP) is up to 1999:1. It is also found that multiple wavebands operation can be implemented by manipulating the relative positions of multi-size slits in the structure. The proposed 2D all-dielectric chiral metasurface has the advantages of high circular dichroism, easy-fabrication and high compatibility with linear polarized components, which provides a solution for pixelated full-Stokes polarization imaging.
In order to accurately obtain the birefringence dispersion of liquid crystal variable retarder (LCVR) with wavelength ranges from 414nm to 702nm. Here, we propose an improved fitting method of birefringence dispersion by using the theory of polarized light interference. The birefringence of LCVR in 478nm is 0.3863 based on the improved method. The experimental result is 0.3862 and the percentage error is 0.026%, compared to the 1.761% of the original fitting method. This work provides an improved way to character the birefringence dispersion of LCVR.
In this paper, a high sensitivity angle-sensing photodetector at the nanoscale is proposed, which mainly consists of SiO2 substrate and two columns of separate silicon nano-blocks and four gold electrodes. When the light in the incident plane perpendicular to the columns is obliquely incident on the silicon nano-blocks, they will absorb different light energy. Then the concentration of electron hole pairs in nano-blocks is also different, which will affect the photocurrent detected by the detector. Simulation results further show that the detection accuracy of the photodetector in the range of 0-45° can reach 0.152° when irradiated with TM polarized light. This angle sensing photodetector has many advantages, such as high sensitivity, low cost, easy integration. It can be used in the fields of information acquisition of light field, automatic driving scene perception and machine vision.
Axicon is widely used in optical alignment and Bessel–Gauss beam generation. There are rigorous requirements for a highly accurate surface metrology. In this paper, a polarization phase-shifting interferometer measurement method using a concave axicon mirror is proposed to obtain the surface of axicon lens. The measuring beam produced by a polarization phase-shifting interferometer is incident on the flat surface of an axicon lens under test perpendicularly and it is reflected along the original optical path by a concave axicon mirror, which is easy to be manufactured by ultra-precision diamond-turning machine. The reflected beam by the concave axicon mirror interferes with the reflected reference beam by transmission flat (TF) in the interferometer. Consequently, the surface of the axicon lens can be obtained. The measurement method is simple, timesaving and easy to achieve surface metrology of axicon lens of any cone angle. In experiments, the evaluation parameters of the axicon surface profile errors are given by the peak-to-valley(PV) error and Root-Mean-Square(RMS) error. The measurement results verify that the measurement for axicon can be achieved by the proposed method which plays a crucial role in evaluating the manufacturing and image qualities of axicon.
In this paper, we propose a dielectric cavity enhanced high reflective multiband waveplate based on nano-grating structure, which exhibits quarter waveplate at two wavelengths (λ=810nm and λ=1530nm) and half waveplate at another wavelength (λ=1100nm). The simulation results show that at the working wavelengths (i.e., 810nm, 1100nm and 1531nm) of the device, the reflections are larger than 94% and the average value is about 95% with polarization orientation at 45° . As compare with the traditional metal nanograting waveplate, it has large phase difference with the same geometrical parameters (period, aspect ratio and thickness), and it also does not need to rotate the polarization orientation of the incident light when it work at different wavelengths. It provides a great potential for applications in advanced nanophotonic devices and integrated photonic systems.
Iris recognition technology has advantages of high security and high stability and can realize non-contact and living recognition. For iris recognition, iris localization is the first step. The localization precision is assurance of high recognition rate. The existing iris localization method has shortage of slow speed. In this paper, an improved iris region localization method is proposed. Firstly, the images are preprocessed with Gaussian blur algorithm. Then the center of the pupil is coarsely located by Gaussian template convolution operation. Finally, the center and the outer edge of the iris are precisely located based on the Integral-differential operation. In experiments, CASIA iris database is used to test the improved iris region localization method. The results show that the location time can be less than 200 ms and the location precision can reach 98. 82%. This method’s usefulness is verified and can promote the application of the iris recognition
We have proposed and experimentally demonstrated a silicon-based linear polarizer with multilayer nanogratings working in 3 to 5 μm of an infrared region. A dielectric grating is first fabricated in a low-refractive index thin layer on a Si-substrate and then double-layer metallic gratings are formed by evaporating a metallic film onto the dielectric grating. With the designed structure of multilayer nanogratings coupled with a low-refractive-index dielectric layer on the high-refractive index silicon substrate, both high transverse magnetic transmission (TMT) and high extinction ratio (ER) can be effectively achieved across 3- to 5-μm range in the infrared band without the complicated metallic ion etching process that is required in conventional nanowire grids. An ER of 40 dB and TMT of averagely higher than 80% were obtained experimentally from a linear polarizer with a multilayer grating of 280-nm period. The Si-based multilayer grating structure shows possibilities of implementing polarization in a fashion of relatively easy-fabrication, semiconductor process compatible, and high performance.
In this paper, superlens imaging with surface plasmon polariton cavities in both object and image space is proposed and investigated. A silver layer is added to an object mask to form a surface plasmon polariton (SPP) cavity in object space, which helps to greatly enhance evanescent waves generated by objects. As a result, better object imaging contrast can be obtained when compared with the single surface plasmon polariton cavity in image space only by amplifying the higher frequency componments while suppressing the long range plasmon mode. This is confirmed by the electric field distributions and optical transfer function of the system. The physical mechanism of the imaging quality improvements based on surface-plasmon polaritons is discussed. Finite-difference time-domain analysis method is used in the simulation.
We propose a continuous tuning SPPs interference photolithography using hybrid Kretschmann and Otto structures. The patterns are formed by the interference of two kinds of SPPs excited by Kretschmann structure and Otto structure respectively, and the tuning capability is implemented by changing the angle between the two kinds of SPPs beams and varying the amplitude and phase of corresponding incident beams. Numerical results show the flexibility and convenience in tuning of interference patterns and resolutions with high contrast, both one and two dimension periodic patterns can be generated and tuned easily. This proposed method is possible to develop a new tunable SPPs photolithography technique for fabrication of periodic nanostructures.
We propose an ultrathin, high-performance quarter waveplate with extreme bandwidth in the near-to-mid infrared wavelength range based on a metasurface consisted of Ag fence-type gratings. The broadband quarter waveplate is realized by optimizing the anisotropic response of the metasurface via changing the geometric dimensions of the fence-type gratings to tailor the interference of light at the subwavelength scale. The near-constant phase difference between two perpendicular electric fields within the broad bandwidth is achieved by manipulating the dimensions of the fence-type gratings along two perpendicular directions in which localized plasmonic resonances along the two directions dominate. Compared to previously reported metasurface-enabled waveplates, the phase retardation of the electric components of the transmitted wave of the proposed structure can be fixed at ~π/2 across a broad wavelength range rather than merely limited within a narrow bandwidth near the resonant wavelength of the metasurface building blocks. Simulation results indicate that a function of quarter waveplates can be realized from 2000nm to 4500nm with the control of polarization orientation of a linearly polarized incident light. Our work gives intriguing possibilities for novel metasurface-enabled optical components with broad bandwidth for photonics devices.
In this paper, we report that normal incidence transmission of different circularly polarized waves through the 2D Archimedes’ nanoscale spirals is asymmetric. The structures consist of raised spiral ridge and two layers metal film covered on the substrate and the ridge. The finite difference time domain method was used to design the structure and perform the simulation. The device can distinguish the different circularly polarized wave across the transmission intensity compare with the common Archimedes’ nanoscale spirals which just exhibit the bright or dark modes in the light field. We confirmed that the device provide about 10% circular dichroism in 3.85um-6.0um broadband region. The circular dichroism in the wavelength 3.95 um can reach 13%. This ultracompact device could prove useful for remote sensing and advanced telecommunication applications.
With the increasing demand for linearly polarized elements with high performance in many fields and applications, design and fabrication of sub-wavelength metallic linear polarizer have made tremendous progress in recent years. In this paper, we proposed a novel structure of a silicon-based linear polarizer working in the infrared (3-5μm) waveband with a double-layered metallic grating structure. A two-layer metallic grating with a transition layer of low refractive index is fabricated on a silicon substrate. In contrast to those conventional single layer metallic polarizing grating, the multilayer polarizing structure has the advantages of easy fabrication and high performance. Numerical simulation results show that an extinction ratio of linear polarization can be up to 58.5dB and the TM-polarized light transmission is greater than 90%. The behaviors and advantages of the proposed multilayer polarizer are compared with that of a traditional single-layer metallic grating. The proposed silicon-based linear polarizer will have great potential applications in real-time polarization imaging with high extinction ratio and high transmission.
KEYWORDS: Polarization, Numerical simulations, Dichroic materials, Silver, Circular polarizers, Linear polarizers, Silicon, Polarizers, Real time imaging, Imaging systems
In this paper, we propose and demonstrate numerically a pixelated component for full Stokes polarization imaging by integrating linear polarizers and circular polarizers on a single silicon chip working in near infrared band (~1.6μm). The micro linear polarizers collect linear polarizing information from different orientations while the circular polarizers collect left-handed or right-handed circular polarization information such that full Stokes polarization imaging can be implemented on a single chip in real time. Numerical results show that the extinction ratio and TM transmission of linearly polarization can reach 45dB and 78%, respectively, with a linear metallic grating of period 300nm, and the dichroism of left-handed and right-handed circular polarization can reach 55% with a plasmonic chiral structure that is compatible with linear gratings in terms of structure and fabrication. The proposed structure is of significance in real-time full Stokes polarization imaging.
We proposed and demonstrated an integrated high linearly polarized InGaN/GaN green LED grown on (0001) oriented sapphire with a structure of combined dielectric/metal wire grids (CDMWG). Both theoretical and experimental results show that the CDMWG can effectively loosen the requirement on the dimension of the grating, and the introduction of a low-refractive dielectric layer can further enhance both TMT and ER significantly for the GaN-type LED. An InGaN/ GaN green LED with an integrated CDMWG of 220 nm period has been fabricated, and a measured extinction ratio(ER) of higher than 20 dB and TMT of 65% within an angle of ±40° is obtained directly from a InGaN/GaN LED.
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