High Precision Optical Components Research Articles

Recent Patents for Optical Component Polishing Technology

Background: Fluid jet polishing, Airbag polishing, Magnetorheological polishing, and Ion beam polishing are all emerging polishing technologies commonly used for processing optical components, which can be used to manufacture various high-precision and high-quality optical components. Their processing mechanisms are to remove materials by high-speed jet impacting the surface of the workpiece; using a spherical flexible airbag as a polishing tool to obtain a super-smooth surface by adding polishing fluid containing fine abrasives; controlling the magnetic field to form a flexible polishing belt of Magnetorheological fluid, which undergoes relative motion to achieve material removal; using a neutral ion beam to bombard the surface of the workpiece to remove workpiece surface atoms and obtain a super-smooth surface through energy and momentum transfer between ions and workpiece atoms. The characteristics and removal mechanisms of various polishing methods are briefly described, and the advantages and key issues that need to be addressed for each polishing technology are pointed out, and suggestions and prospects for future research, application, and development are also given. Objective: In order to meet the growing demand for high-precision optical components and mass-manufactured optical components, this paper aims to study the various polishing technologies that are continuously improved and suggestions are made for future research and development directions. Method: This paper reviews the current patents related to various polishing technologies, such as Fluid jet polishing, Airbag polishing, Magnetorheological polishing and Ion beam polishing and other representative polishing technologies. Results: Various types of polishing technologies have been studied, and the main problem at the current stage is the lack of accuracy. The problem of the polishing device, such as fluid jet polishing, only considers the change of fluid velocity and pressure to construct the removal function model for analysis and summary, and suggestions for the latest research progress of various polishing technologies are given. Conclusion: The improvement and optimization of polishing technology are beneficial to improving the polishing accuracy and quality of optical components and have great help for the future development of related patents.

Prediction of the Waviness Error in Ultra-Precision Fly Cutting Using the Direct Integration Method

Abstract Fly cutting is widely used in manufacturing of large-scale, high-precision optical components. However, the discontinuity of fly cutting machining leads to significant relative vibrations between the tool and the workpiece. The cutting process generates periodic waves along the cutting direction, which will deteriorate the wavefront characteristics of optical components. Based on the machining dynamics, this paper proposes a direct integration method to predict the waviness error of the machined surface. The cutting force model of fly cutting is established. The multi-mode characteristics of the spindle-tool system are measured by the experimental method. Then, the influence of uncertainties on the calculation results is analyzed by the variance-based sensitivity analysis method. Finally, the plane cutting experiment verifies that the direct integration method effectively predicts the waviness error and its variation trend, and the waviness prediction research is important for optimization of the machining parameters.

Optical design of a novel near-infrared phase contrast imaging (NI-PCI) diagnostic on the HL-2A tokamak

The optical design of near-infrared phase contrast imaging (NI-PCI) diagnosis on HL-2A is introduced in this paper. This scheme benefits from the great progress of near-infrared laser technology and is a broadening of traditional phase contrast technology. This diagnostic can work as a keen tool to measure plasma wavenumber spectra by inferring string-integrated plasma density fluctuations. Design of both the front optical path which is the path before the laser transmitting into the tokamak plasma and the rear optics which is the path after the laser passing through the plasma is detailed. The 1550 nm laser is chosen as the probe beam and high-precision optical components are designed to fit the laser beam, in which a phase plate with a 194-nm-deep silver groove is the key. Compared with the conventional 10.6 m laser-based PCI system on HL-2A, NI-PCI significantly overcomes the unwanted phase scintillation effect and promotes the measurement capability of high-wavenumber turbulence with an increased maximal measurable wavenumber from 15 cm−1 to 32.6 cm−1.

Research on the influence of the non-stationary effect of the magnetorheological finishing removal function on mid-frequency errors of optical component surfaces.

With the continuous development of modern optical systems, the demand for full spatial frequency errors of optical components in the system is increasing. Although computer-controlled sub-aperture polishing technology can quickly correct low-frequency errors, this technology significantly worsens the mid-frequency errors on the surface of the component, which greatly inhibits the improvement of optical system performance. Therefore, we conducted in-depth research on the non-stationary effect of the removal function caused by the fluctuation in magnetorheological polishing and their influence on the mid-frequency errors of the component surface. We established a non-stationary profile model of the removal function and applied this model to simulate the distribution of mid-frequency errors on the surface of the processed component, considering the non-stationary effect. The simulation results showed that the non-stationary effect of the removal function weaken the mid-frequency ripple errors but increase other mid-frequency errors. Therefore, we first proposed the optimal single-material removal thickness corresponding to the non-stationary effect and experimentally verified the effectiveness of the optimal material removal thickness in suppressing mid-frequency errors. The experimental results showed that when the magnetorheological finishing single-material removal thickness is set to the optimal value, both the mid-frequency ripple errors and the mid-frequency RMS on the surface significantly decrease. Therefore, this work provides a basis for improving the existing magnetorheological finishing process and effectively suppressing the mid-frequency errors on the surface of processed components. It also provides theoretical and technical support for the magnetorheological processing and manufacturing of high-precision optical components. At the same time, the non-stationary effect and the corresponding analytical models has the potential to be extended to other polishing tools.

Material removal characteristics in submerged pulsating air jet polishing process

In this paper, the material removal characteristics and mechanism of submerged pulsating air jet polishing (SPAJP) process are investigated by polishing experiment on K9 glass and computational fluid dynamics simulation. The experimental results show SPAJP can etch almost perfect Gaussian footprints with high stability. Under comparable condition, SPAJP achieves nearly 300 times higher material removal rate (3.0 × 10−3 mm3/min) than that of traditional fluid jet polishing (FJP) (9.9 × 10−6 mm3/min) at the cost of a moderate degradation in processed surface roughness from Sa 3.97 nm by FJP to Sa 20.49 nm by SPAJP. Jet evolution, abrasive behavior and material removal mechanism in SPAJP are clarified by numerical modeling and experimental jet observation. It is found that SPAJP relies on jet instability of the submerged airflow beam to entrain and accelerate abrasive particles in the slurry, achieving stable and efficient polishing removal on the workpiece surface. To explore the potential of the process for deterministic polishing, an array structure surface is then designed and polished by SPAJP. The processing results are consistent with numerical prediction results, indicating that the new process has good material removal controllability which makes it applicable to deterministic polishing. This study highlights the possibility of using SPAJP to produce ultra-precise surfaces in terms of form control or fabricate high precision optical components in a more efficient and convenient manner.

Prediction of Process Parameters for Ultra-Precision Optical Processing Based on Dual-Stacked LSTM

High-precision and large-aperture optical components have important applications in modern optics and optoelectronics. However, the traditional continuous polishing technology of optical components relies heavily on the processing experience of the processing personnel. The surface shape of the pitch lap is judged by frequent offline measurement of the surface shape of the processing workpiece, and then the processing personnel judges how to adjust the next process parameters through their own experience, which leads to uncertainty of processing time and low processing efficiency. In this paper, based on the historical processing data, including the surface parameters of workpieces and process parameters before and after each processing, a machine learning-based prediction method of process parameters is proposed. At first, taking the surface shape of the pitch lap as the hidden parameter of the model, a time-series mathematical model of the forward and reverse processing processes is constructed. Theoretical and experimental results show that the prediction method in this paper can effectively reduce the processing time and improve the stability of the workpiece quality.

Spiral scanning nano-profiler using normal vector tracing method.

Unlike interferometers that obtain data from the entire sample, three-dimensional (3D) measuring instruments acquire data from multiple points. A nano-profiler measures slopes at different points on the surface to determine the sample shape, while a coordinate measuring machine (CMM) utilizes contact or non-contact height displacement probes for taking measurements. Therefore, the 3D measurement time increases if the area to be measured is wide. This leads to a reduced measurement accuracy owing to environmental changes. To reduce the 3D measurement time, a nano-profiler that rotates measured objects at a constant velocity and quickly scans each measurement point by following a spiral trajectory was designed. The developed nano-profiler measures angular distribution instead of height distribution. This makes it possible to reduce the drive error during rotation. Compared to an interferometer, the measurement time was reduced from 163 to 17minwith the nano-profiler and a 10nm peak-to-valley difference was achieved. The slope measurement with spiral scanning was confirmed to be a quick and accurate shape measurement technique that can be used while manufacturing high-precision optical components.

Movement Modeling and Control for Robotic Bonnet Polishing

With the increasing demand for high-precision optical components, bonnet polishing technology is increasingly being used in the polishing process of optical components owing to its high removal efficiency and high surface accuracy. However, it is expensive and difficult to implement dedicated bonnet polishing machine tools, and their processing range is limited. This research combines bonnet polishing technology with industrial robot-assisted processing technology to propose a robotic bonnet polishing control model for large-diameter axisymmetric aspherical optical components. Using the transformation relations of the spatial coordinate system, the transformation relations of the workpiece coordinate system, local coordinate system of the polishing point, and tool coordinate system of the bonnet sphere center are established to obtain the bonnet precession polishing motion model. The polishing trajectory of large-diameter axisymmetric aspherical components and the variation in the linkage angle difference were simulated by adding an efficiency-optimal control strategy to the motion model. The robot motion was simulated in Robostudio to verify the correctness of the precession motion model and control algorithm. Lastly, the robotic bonnet polishing system was successfully applied to the polishing process of the optical components.

High-resolution dark-field confocal microscopy based on radially polarized illumination.

Dark-field confocal microscopy (DFCM) facilitates the 3D detection and localization of surface and subsurface defects in high-precision optical components. The spatial resolution of conventional DFCM is commonly undermined owing to complementary aperture detection. We employed a radially polarized (RP) beam for illumination in DFCM. The RP beam creates a sub-diffraction-sized longitudinal optical component after being focused and effectively enhances the lateral resolution by 30.33% from 610 nm to 425 nm. The resolution improvement was verified by imaging a 2D sample containing sparsely distributed gold nanorods along with a 3D neodymium glass containing surface and subsurface defects.

Wafer scale manufacturing of high precision micro-optical components through X-ray lithography yielding 1800\xa0Gray Levels in a fingertip sized chip

We present a novel x-ray lithography based micromanufacturing methodology that offers scalable manufacturing of high precision optical components. It is accomplished through simultaneous usage of multiple stencil masks made moveable with respect to one another through custom made micromotion stages. The range of spectral flux reaching the sample surface at the LiMiNT micro/nanomanufacturing facility of Singapore Synchrotron Light Source (SSLS) is about 2 keV to 10 keV, offering substantial photon energy to carry out deep x-ray lithography. In this energy range, x-rays penetrate through resist materials with only little scattering. The highly collimated rectangular beam architecture of the x-ray source enables a full 4″ wafer scale fabrication. Precise control of dose deposited offers determined chain scission in the polymer to required depth enabling 1800 discrete gray levels in a chip of area 20 mm2 and with more than 2000 within our reach. Due to its parallel processing capability, our methodology serves as a promising candidate to fabricate micro/nano components of optical quality on a large scale to cater for industrial requirements. Usage of these fine components in analytical devices such as spectrometers and multispectral imagers transforms their architecture and shrinks their size to pocket dimension. It also reduces their complexity and increases affordability while also expanding their application areas. Consequently, equipment based on these devices is made available and affordable for consumers and businesses expanding the horizon of analytical applications. Mass manufacturing is especially vital when these devices are to be sold in large quantities especially as components for original equipment manufacturers (OEM), which has also been demonstrated through our work. Furthermore, we also substantially improve the quality of the micro-components fabricated, 3D architecture generated, throughput, capability and availability for industrial application. Manufacturing 1800 Gray levels or more through other competing techniques is either limited due to multiple process steps involved or due to unacceptably long time required owing to their pencil beam architecture. Our manufacturing technique presented here overcomes both these shortcomings in terms of the maximum number of gray levels that can be generated, and the time required to generate the same.

Amorphous Carbon Coated Silicon Wafer as Mold Insert for Precision Glass Molding

Press molding of glass is an emerging research area for micro-optics manufacturing. Despite advancements on coating layers of precision molds for glass molding, challenges still exist towards tailoring non-stick coating to provide consistent replication accuracy in thousands of repetitive molding cycles. In this study, atmospheric pressure chemical vapor deposition (APCVD) is introduced to synthesize nanoscale-thickness amorphous carbon layer on the surface of silicon wafer with liquid benzene as the carbon source and silicone rubber as the silicon oxycarbide (SiOC) source. The micro-morphologies of the coating layers under different conditions are obtained and analyzed. In the press molding, the coating exhibits extraordinary physical properties and can remarkably prevent silicon-glass adhesion under elevated temperature. Typical micro-structures, such as micro-pillar and micro-lens arrays on the amorphous carbon coated silicon wafers, are used as mold inserts in precision glass molding to replicate high-precision optical components. The results indicate that this amorphous carbon coated silicon wafer can replicate intricate micro-structures to glass substrates with high-precision dimensions without macroscopic adhesion. This coating technology will protect the mold materials with low adhesion and improve precision glass molding process.

Digitized, networked optics production

The increasing demands on the quality of high-precision optical components mean that established manufacturing processes are reaching their technical limits. While individual processes can therefore hardly be improved any more, networking production machines digitally throughout the entire process chain offers high potential for meeting the tight tolerances in the optics industry and increasing the production output.To gain these benefits, first, an infrastructure is needed, containing a flexible and module data structure to satisfy different requirements from the processes. Second, the idea of offering services such as initial data analytics, artificial intelligence (AI) and machine learning (ML) must be integrated. In this paper, we present a digital infrastructure, that contains data from the entire process chain of glass and polymer optics production including simulation, process and measurement data. Services to optimize the production process are integrated and provide an outlook on how AI/ML can be added.

Absolute characterization of high numerical aperture microscope objectives utilizing a dipole scatterer

Measuring the aberrations of optical systems is an essential step in the fabrication of high precision optical components. Such a characterization is usually based on comparing the device under investigation with a calibrated reference object. However, when working at the cutting-edge of technology, it is increasingly difficult to provide an even better or well-known reference device. In this manuscript we present a method for the characterization of high numerical aperture microscope objectives, functioning without the need of calibrated reference optics. The technique constitutes a nanoparticle, acting as a dipole-like scatterer, that is placed in the focal volume of the microscope objective. The light that is scattered by the particle can be measured individually and serves as the reference wave in our system. Utilizing the well-characterized scattered light as nearly perfect reference wave is the main idea behind this manuscript.

An experimental study of PMMA precision cryogenic micro-milling

Polymethyl methacrylate (PMMA) has been used more and more widely in the fields of microfluidic devices and high-precision optical components due to its excellent mechanical and optical properties. Micro-milling is one of the methods that has been used in the machining of polymer materials. The machinability of PMMA is highly dependent on temperature, and the cryogenic method is also applied to control the processing temperature. In this work, the PMMA was milled with different processing parameters at the temperature of -55℃ and 25℃. The influence of each milling parameter on the surface quality under different temperature conditions were investigated. According to the results, the cutting depth is the dominant factor that influenced the surface roughness. The shape accuracy of the rectangular microgroove processed under low-temperature conditions is better. The material removal mechanism under different temperatures was also discussed, and the material is cut in a brittle way under low temperatures.

Development of solar cell for large area position detection: proof of concept

Detecting and analyzing a moving body position are helpful in many fields, such as medicine, sports performance, virtual reality and many more. Therefore, researchers try to develop a tool or a system that helps to detect the motion and tracking its position. This paper shows how a Si solar cell can be modified to function as a Position Sensitive Detector (PSD), which could be used as a large area detector in a position detection system. To develop the new detector, we modeled and simulated the modified solar cell by TCAD simulation tools to calculate the detected photocurrent as a function of the position of an incident laser beam sourced by the moving object. Further, an optical position detection system is implemented containing the modified solar cell, a signal amplifier and a microcontroller. The output is then displayed on a Laptop. By measuring the same simulated output photocurrents, it is found that the measured system output matches the simulation results. This proposed position detection system is relatively cheap because it does not contain high precision optical image building components such as lenses and mirrors. Besides, the proposed system could substitute the optical system by using a large area PSD made from a broad array of solar cells. The electronics are also much more straightforward than those in systems based on image processing. So, it has a high-speed response. The error assessment of the proposed system showed a low position detection error of less than 10%.

Diffractive optical characteristics of nanometric surface topography generated by diamond turning

Abstract High-precision optical components with nanometric surface finish can be obtained directly through single point diamond turning. However, residual cutting marks on the machined surfaces are likely to cause serious diffraction and deteriorate the optical performance of a machined component. This paper proposes a novel method for diffractive optical characterization of diamond-turned surfaces based on the vector diffraction theory. The distribution characteristics of the diffraction spots are revealed by using the finite-difference time-domain method. Simulation results supported by experimental verification demonstrate that the height and spacing of nanometric surface topography exert different influences on the intensity and angle of the diffraction spots. The intensity of high-order diffraction spots would be more prominent if a laser beam with a smaller wavelength and incident angle is used to illuminate the machined surface. Even if the areal surface roughness Sa changes less than 2 nm, the gray values of high-order diffraction spots may increase by nearly 5 times under certain conditions.

Curvature effect on surface topography and uniform scallop height control in normal grinding of optical curved surface considering wheel vibration.

High-precision optical components with complex shapes or microstructures have been extensively used in numerous fields such as biomedicine, energy and aerospace. In order to accurately achieve the specific functions of the components, the form accuracy and uniform surface quality need to reach an ever-high level. To achieve this, ultra-precision normal grinding is used for machining various types of complex optical surfaces. However, the intricate variation of the workpiece curvature and grinding wheel vibration gives rise to great challenges to obtain higher precision and uniform surface conditions. In this study, the influence of curvature on surface topography generation has been investigated and a novel model of scallop height has been developed for surface topography generation in the normal grinding of the curved surface. In addition, the relative influence of the curvature is analyzed experimentally, in which the micro-waviness generation as a consequence of the unbalanced vibration of the grinding wheel is modeled and validated by experiments. Finally, the micro sinusoidal array with the setting value for scallop height is achieved by controlling the feed speed, which is determined by the local curvature of surface profile. The results indicated that the curvature variation posed a significant effect on surface uniformity and the model is valid to achieve surface scallop height control in the normal grinding effectively.

A process for shaping high-precision optical components for ground- and space-based electrooptic systems

The paper reviews advanced process for manufacturing high-precision optical components used in space-based electrooptic systems for scientific research and Earth remote sensing. It presents an integrated process for automatic shaping (TESAF) of aspheric surfaces, including off-axis surfaces, of optical elements for electrooptic systems. This paper discusses various methods for shaping optical parts with virtually any degree of asphericity and various values of the off-axis parameter (off-axis aspherics) achieving surface shape precision to within λ/60…λ/80 (λ = 0.6328 micron) by the standard deviation criteria. The paper also presents the newly developed off-axis collimators, designed to shape a reference wavefront within a broad spectral range from ultraviolet to infrared radiation. In particular, a mirror collimator with an adaptive off-axis mirror that is capable of changing the wavefront that is being formed in order to obtain the response function of the electrooptical system under study. Optical systems built using the TESAF process are already successfully used. Key words: surface shaping, aspheric surface, surface interferogram, standard deviation.

The PANDA DIRC detectors

Abstract The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) will address fundamental questions of hadron physics with unprecedented precision. To reach this goal excellent Particle Identification (PID) is essential over a large range of particle momenta and solid angles. Most of the phase space will be covered by two innovative DIRC (Detection of Internally Reflected Cherenkov light) detectors. The Endcap Disc DIRC and Barrel DIRC will cover the polar angle range from 5 to 22°and 22 to 140°, respectively. Both detectors rely on high precision optical components, lifetime-enhanced Microchannel Plate PMTs (MCP-PMTs), and fast readout electronics.

Effects of oxygen flows on optical properties, micro-structure and residual stress of Ta2O5 films deposited by DIBS

High precision optical components, such as ultra-high reflectors, severely suffer from absorption losses. In order to get optical films with low absorption losses, many techniques, such as annealing and laser conditioning, have been widely employed as a post-deposition treatment process to deal with as-deposited films. However, the success of these processes starts with the correct choice of the deposition parameters. In this paper, Ta2O5 films are deposited by dual ion beam sputtering (DIBS) method and the effects of target oxygen flows on optical properties, microstructure and residual stress are systematically investigated. The results show that target oxygen flows can significantly affect the absorption losses and residual stress of Ta2O5 film. The XRD patterns reveal that Ta2O5 films deposited at different parameters are all amorphous. Finally, based on the results of Ta2O5 films, broadband dielectric mirror with high reflection and low absorption losses in the range from 380 nm to 750 nm is successfully fabricated.