This paper presented a roadmap of optical computing, particularly, for optical implementation of convolution, in comparison with supercomputer. Optical computing power presented in this roadmap is predicted based on a simple mathematic equation of convolution where optics can do matrix convolution in full parallelism with single pass of light, which could be 500 times faster than supercomputer( Fugaku), while energy consumption of optical computing might be 1000 times lower than supercomputer (Fugaku), supposing 8K Spatial Light Modulator with extremely high updating rate <22000 frame per second might be obtained in the future. This roadmap indicates a bright future of optical computing for matrix convolution, which might take up 80% of total computing power required in deep-learning neural network.
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.
An encapsulated metal-dielectric grating is proposed for realization of reflective broadband polarization-independent 1×2 beam splitter under normal incidence. One can quickly choose a grating structure to realize ultrabroad working waveband by using unified designing method for low-dispersion materials based on the diffraction efficiency map versus the normalized period and depth. Moreover, the center wavelength can be flexibly changed. As an example, a reflective ultrabroadband polarization-independent 1×2 beam splitters operating at wavelength of 1550 nm is designed under normal incidence. The simulation results indicated that a bandwidth of 144 nm could be achieved for the total efficiency over 92%. This kind of broadband polarization-independent 1×2 beam splitters could be found in a variety of applications, such as ultrashort pulse splitting, coherent beam combination, complex vector beam shaping, and also high precision displacement measurement.
The optical three-dimension measurement methods have been widely used in face recognition, machine vision, biomedical imaging, virtual reality and aerospace with the advantages of fast speed, high precision and non-contact measurement. Recently, the trend of structured light 3D reconstruction tends to be real-time with improving accuracy and reducing the dependence of time domain. The structured light coding is an active measurement method which could provide abundant feature points. The 2D gold matrix is a spatial coding method and it provides a new type of structured light for optical 3D measurement. This scheme provides the dynamic 2D spatial information based on the fast decoding from the encoded projected light. Here, we proposed a binocular stereo vision system based on the structured light encoded by 2D gold matrix. Only a pair of images, which could be captured in real-time by the two cameras, are needed for 3D reconstruction. The experiment shows that the decoding success rate is up to 99.48% for non-planar object. The system is simple in structure and low in cost. It is expected to be applied to real-time 3D measurement fields such as face recognition and biomedical imaging in the future.
Three-dimensional human face identification card using micro lens array is proposed based on the introduction of integrated imaging technology into three-dimensional human face identification cards. The traditional ID card is a two-dimensional plane photograph. With the development of integrated imaging technology, each unit lens in the integrated imaging technology can record relative parts of information from various directions, combining a lenticular lens array and a concave lens array to realize naked eye in natural light you can see the three-dimensional photos on the ID card. This technology not only achieves visual three-dimensionality and beauty, but also enhances the security of identity cards, and can be widely applied to various situations requiring authentication.
In this paper, we propose a high-density grating interferometry system, which can be applied to measure displacement on the nanometer precision. We make use of the optical subdivision module to improve the measurement resolution which is better than the traditional one. The core part of the whole system is a grating with high-density of 1780 lines/mm and long-range of 100mm*100mm. The apparatus adopts a symmetrical structure to reduce the error resulting from environmental disturbance. The system provides a novel measurement technique to improve the grating interferometry. The experimental results show that the grating interferometer system has good stability, and the in-situ measurement error is within ±5 nm for a long time. The grating interferometer can measure the short distance displacement of 30 nm and can control the error within ±2 nm. The measurement of the distance of 10 mm can control the error within ±20 nm. The results proves the feasibility of our proposed improved.
A wide-band two-port polarization-independent beam splitter is designed and analyzed at the incident wavelength of 1550nm. Diffraction efficiencies are 49.67%/49.57% and 48.69%/48.88% for TE and TM polarizations in the 0th and the -1st, respectively. Usually, it’s difficult for two-port beam splitter to achieve wide bandwidth for both polarizations. In this paper, the presented grating has advantages of wide incident wavelength range of 110nm and angular bandwidth of 8.8° with good splitting ratio uniformity for both polarizations, particularly TE polarization. Moreover, the aspect ratio of the grating depth to the ridge width is low, which can be etched relatively easily and effectively. This wide-band splitter should be highly interesting for practical applications.
We propose a scheme based on a type of continuous-phase encoding grating for the generation of multiple curved Bessel-like beams simultaneously. It is shown that multiple identical curved Bessel-like beams that diverge from a common center can be generated by overlapping a specially designed phase with a continuous-phase grating, and multiple high-order curved Bessel-like beams can be generated when another spiral phase is embedded. As an example, a 5×5 symmetric continuous-phase grating embedded with the special designed phase and a spiral phase is demonstrated based on a spatial light modulator. The experimental results show that 5×5 square arrays of bright- and dark-center curved Bessel-like beams were well generated. The proposed method provides an interesting method for obtaining simultaneously multiple curved Bessel-like beams, which should be of high interest for its promising applications in parallel optical manipulation, optical guiding, laser machining or laser surgery, particle acceleration, etc.
Displacement laser interferometers and grating interferometers are two main apparatus for the micron-nanometer displacement measurement over a long range. However, the laser interferometers, whose measuring scale is based on the wavelength, are very sensitive to the environment. On the contrast, the grating interferometers change the measuring scale from wavelength to grating period, which is much stable for the measurement results. But the resolution of grating interferometer is usually lower than that of laser interferometer. Therefore, further investigation is needed to improve the performance of grating interferometer. As we known, the optical subdivision is a main factor that affects the measurement resolution. In this paper, a grating interferometer with high optical subdivision is presented based on the Littrow configuration. We mainly use right angle prisms accompanied with plane mirrors to make the measuring lights diffracted by the grating scale for many times. An optical subdivision factor of 1/24 can be obtained by this technique. A main difficulty of this technique is that the grating scale should be with high diffraction efficiency. Fortunately, the measuring light is incident on the grating scale at the Littrow angle, the grating scale can be designed with very high efficiency easily in this condition. Compared with traditional grating interferometers, this kind of grating interferometer can greatly increase the measuring resolution and accuracy, which could be widely used in nanometer-scale fabrications and measurements.
For higher-density integration and acceleration of operating speed in Si ICs, 3D integration of wafers and/or dies is essential. Fabrication of current 3D ICs relies on 3D assembly which electrically connects stacked chips to form a single circuit. A key technology for the 3D assembly is TSVs which are vertical electrical connections passing completely through silicon chips to electrically connect vertically assembled Si ICs. Typical TSVs have wide features, with diameters of a range from several microns to 50 μm and depths up to 500 μm with aspect ratios up to 15 depending on the application and integration scheme. In this work, we present high-throughput, taper-free TSVs fabrication using femtosecond Bessel beams operated at different wavelengths from 400 nm to 2.4 μm. Furthermore, special phase filters are designed to suppress the damages induced by the side-lobes of Bessel beams for high-quality TSVs fabrication. Our technique can be potentially used for 3D assembly in manufacture of 3D silicon integrated circuits.
Optical encoders and laser interferometers are two primary solutions in nanometer metrology. As the precision of encoders depends on the uniformity of grating pitches, it is essential to evaluate pitches accurately. We use a CCD image sensor to acquire grating image for evaluating the pitches with high precision. Digital image correlation technique is applied to filter out the noises. We propose three methods for determining the pitches of grating with peak positions of correlation coefficients. Numerical simulation indicated the average of pitch deviations from the true pitch and the pitch variations are less than 0.02 pixel and 0.1 pixel for these three methods when the ideal grating image is added with salt and pepper noise, speckle noise, and Gaussian noise. Experimental results demonstrated that our method can measure the pitch of the grating accurately, for example, our home-made grating with 20μm period has 475nm peak-to-valley uniformity with 40nm standard deviation during 35mm range. Another measurement illustrated that our home-made grating has 40nm peak-to-valley uniformity with 10nm standard deviation. This work verified that our lab can fabricate high-accuracy gratings which should be interesting for practical application in optical encoders.
We propose a method for generating axial multifocal spots (AMS) with a high numerical aperture (NA) objective. The AMS is generated by using phase-only modulation at the back aperture of the objective. Without using any iteration algorithm, the modulated phase distribution is directly calculated by an additional phase analytical formula with different focal distances. By dividing the back aperture of the objective into multi sectorial zones and applying the corresponding additional phase with different focal distances, the AMS can be created. Numerical simulation shows that the numbers of the axial focus depends solely on the different phase distribution calculated by different focal distances. By engineering the phase pattern with different focal distances, axial multifocal spots with different spacing can be realized. Furthermore, combined with vortex phase, the AMS with specific shape spots also can be created. In addition, the AMS focused by incident beams of circular polarization, radial polarization and angular polarization are also studied. This kind of AMS may be found applications in optical imaging, especially in three-dimensional (3D) biological imaging, and also be attractive in mult-plane optical trapping.
This paper will report our recent works on fabrication, evaluation, and applications of gratings. We are using the Dammann parallel laser writing facility for fabrication of gratings. High-efficiency reflective gratings and large-sized grating are fabricated. We have fabricated high-power reflective laser vortex grating with expectation of a new laser drilling effect for laser fusion in the future, which is just evaluated by our developed method. These gratings are essential elements for high-power laser systems and other high-demanding metrology applications.
KEYWORDS: Zone plates, 3D metrology, 3D image processing, Computer generated holography, Cameras, Optical components, Femtosecond phenomena, 3D optical data storage, Eye, 3D scanning
This paper summarized our work on three-dimensional optical technologies using Dammann gratings, e.g., threedimnensional Dammann gratings, three dimensional imaging using a Dammann grating, etc.. We developed threedimensional Dammann grating which can produce three-dimensional array with equal distance and equal intensity with a high-numerical-aperture lens. As we know, a lens usually has a single focal point. Fresnel zone plate can generate several axial focal points, but the intensity between them is unequal. By introducing the concept of Dammann grating into the circular phase plate, we invented Dammann zone plate(DZP) which can produce a series of axial focal points with equal intensity. Combining DZP with a Dammann grating, three-dimensional Dammann array will be generated, which is highly interesting for various applications. We also built a three–dimensional measuring system using a Dammann grating, with two cameras as the right eye and right eye, respectively. We used a 64×64 Dammann grating for generation of a square array of light spots for parallel capturing the three-dimensional profile of an object. The two cameras and the illuminating part are packaged together. After scanning the object, its three-dimensional profile will be obtained. Experimental results demonstrated the effectiveness of this technique.
The focal shift effect and axial dispersion property of binary pure-phase filters (BPFs) in focusing systems are described
in the regime of the scalar Debye theory. By expanding the formula of the electric field in focal region into a summation
of a polynomial series, the axial behavior and the general rule of the focal shift effect of BPFs are analytically studied.
The small focal shift formula of BPFs is derived based on the second-order approximation, and its scope of validity is
also discussed. Based on this small focal shift formula, the property of axial dispersion for a given BPF is also
analytically discussed. Furthermore, numerical results of 2-zone and 3-zone BPFs with various normalized radii and
phase shift values are also given for verifying these analytical results. At last, as an example, the application of BPFs
with negative axial dispersion in compensation of chromatic aberration of a single lens in an ultrashort laser focusing
system is presented. The numerical results show that the chromatic aberration induced by the single lens is compensated
well nearly for the whole spectral bandwidth of the ultrashort laser. Therefore, this focal shift effect induced by BPFs
should be of great interest for its potential applications in compensation of chromatic aberration and compact tunable
focal modulation in some special cases.
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