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The time-dependent processes, such as bonnet polishing and magnetorheological finishing, utilize the dwell time map to guide material removal distribution. To account for machine dynamic limits and interpolator effects, converting dwell time points to a velocity profile is essential. Current velocity scheduling methods, using trapezoidal velocity planning or cubic splines, do not consider machine dynamic limits and continuous acceleration. Sudden changes in acceleration cause the controller to alter the path to protect the machine, resulting in trajectory deviations from the dwell time requirements. This research proposes a scheduler that uses the position-velocity-acceleration-time (PVAT) mode in the motion controller. First, the velocity scheduling principle of the PVAT-based velocity scheduler is proposed. Second, simulations of the raster, maze, and Hilbert paths demonstrate that this scheduler can ensure accuracy while achieving better continuity compared to the position-velocity-time (PVT) method. Finally, dry-run and magnetorheological figuring experiments were conducted. Using the proposed scheduler, the root mean square (RMS) error of the fused silica sample surface was reduced to 3.115 nm. Additionally, combining the scheduler with the maze path during processing improved the performance in terms of middle spatial frequency (MSF) errors. [ABSTRACT FROM AUTHOR]

Dwell time plays a vital role in determining the accuracy and convergence of the computer-controlled optical surfacing process. However, optimizing dwell time presents a challenge due to its ill-posed nature, resulting in non-unique solutions. To address this issue, several well-known methods have emerged, including the iterative, Bayesian, Fourier transform, and matrix-form methods. Despite their independent development, these methods share common objectives, such as minimizing residual errors, ensuring dwell time's positivity and smoothness, minimizing total processing time, and enabling flexible dwell positions. This paper aims to comprehensively review the existing dwell time optimization methods, explore their interrelationships, provide insights for their effective implementations, evaluate their performances, and ultimately propose a unified dwell time optimization methodology.

In recent years, the atmospheric pressure plasma jet (APPJ) has gained considerable attention in the field of optical fabrication because the chemical etching approach offers the advantage of avoiding mechanical damage to workpieces. This paper presents the development of an atmospheric pressure plasma machining system with a ring-ring typed APPJ, which exhibits several favorable characteristics. It has a relatively low processing temperature, no electrode corrosion, no plasma contamination, and a long discharge plume, etc. Optimization of the dimensional parameters and analysis of reactive gas flow rate are conducted through experimental investigations. Comparative experiments are carried out with the commonly used needle-ring typed APPJ, revealing significant improvements of the ring-ring typed APPJ, i.e., a fourfold increase in machining distance, a tenfold increase in machining efficiency, and a 58% enhancement in the stability of the material volumetric removal rate. Furthermore, on-line temperature monitoring of the footprint has been achieved due to the specific traits of the extended discharge plume. Fabrication experiments are conducted to demonstrate the significant correlation between the temperature and material removal rate, which shows the possibility of improving the accuracy of optical fabrication based on the ring-ring typed APPJ. • A ring-ring typed atmospheric pressure plasma jet (APPJ) is proposed for optical fabrication, which has a relatively low processing temperature, no electrode corrosion, no plasma contamination, and a long discharge plume. • Optimization of the dimensional parameters and analysis of reactive gas flow rate are conducted through simulations and experimental investigations. • Comparative experiments are carried out with the commonly used needle-ring typed APPJ, revealing significant improvements of the ring-ring typed APPJ, i.e., a fourfold increase in machining distance, a tenfold increase in machining efficiency, and a 58 % enhancement in the stability of the material volumetric removal rate. • On-line temperature monitoring of the footprint has been achieved and the significant correlation between the temperature and material removal rate has been demonstrated. • Fabrication of continuous phase plate is conducted to validate the capability of the ring-ring typed APPJ in machining the sophisticated surface. [ABSTRACT FROM AUTHOR]

Abstract The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing.

Abstract The authors report a ductile dicing process for manufacturing optical‐quality facets in a multi‐layered silicon nitride platform without the need for polishing. A surface roughness (Sa) of 1.5 nm was achieved. This technique was extended to fabricate ridge waveguides, and the results and characterization are reported.

The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing. [ABSTRACT FROM AUTHOR]

Optics with high-precision height and slope are increasingly desired in numerous industrial fields. For instance, Kirkpatrick–Baez (KB) mirrors play an important role in synchrotron X-ray applications. A KB system is composed of two aspherical, grazing-incidence mirrors used to focus an X-ray beam. The fabrication of KB mirrors is challenging due to the aspherical departure of the mirror surfaces from base geometries and the high-quality requirements for slope and height residuals. In this paper, we present the process of manufacturing an elliptical cylinder KB mirror using our in-house-developed ion beam figuring (IBF) and metrology technologies. First, the key aspects of figuring and finishing processes with IBF are illustrated in detail. The effect of positioning error on the convergence of the residual slope error is highlighted and compensated. Finally, inspection and cross-validation using different metrology instruments are performed and used as the final validation of the mirror. Results confirm that relative to the requested off-axis ellipse, the mirror has achieved 0.15-µrad root mean square (RMS) and 0.36-nm RMS residual slope and height errors, respectively, while maintaining the initial 0.3-nm RMS microroughness.Highlights: Demonstrated our in-house developed, high-performance Kirkpatrick–Baez mirror manufacturing solution. Highlighted the key factors and strategies in achieving stringent mirror design specifications. Achieved excellent slope error (0.15 µrad RMS), height error (0.36 nm RMS), and microroughness (0.3 nm RMS). [ABSTRACT FROM AUTHOR]

The authors report a ductile dicing process for manufacturing optical‐quality facets in a multi‐layered silicon nitride platform without the need for polishing. A surface roughness (Sa) of 1.5 nm was achieved. This technique was extended to fabricate ridge waveguides, and the results and characterization are reported. [ABSTRACT FROM AUTHOR]

Magnetorheological finishing (MRF) technology is widely used in the fabrication of high-precision optical elements. The material removal mechanism of MRF has not been fully understood because MRF technology involves the integration of electromagnetics, contact mechanics, and materials science. In this study, the rheological properties of the MR polishing fluid in oscillation model have been investigated. We propose that the shear-thinned MR polishing fluid over the polishing area should be considered a dense granular flow, based on which a new contact model of MRF over the polishing area has been constructed. Removal function and processing force test experiments were conducted under different working gaps. The normal pressure and effective friction equations over the polishing area were built based on the continuous medium and dense granular flow theories. Then, a novel MRF material removal model was established. A comparison of the results of the theoretical model with actual polishing results demonstrated the accuracy of the established model. The novel model proposed herein reveals the generation mechanism of shear force over a polished workpiece and realizes effective decoupling of the main processing parameters that influence the material removal of MRF. The results of this study will provide new and effective theoretical guidance for the process optimization and technology improvement of MRF.

Multimode polymer waveguides were created using epoxy resin materials. The fabrication process used non-contact photolithography, which is a simple and cost-effective method. During the experiments, a reliable and efficient developer was obtained. The samples were analyzed using scanning electron microscopy and the results showed that the ridge waveguides had a smooth surface and vertical sidewalls. The cross-section size was approximately 50 × 55 μm2. The waveguides had a transmission loss was about 0.08 dB/cm at a wavelength of 850 nm, which was measured using the cut-back method. Additionally, the waveguides were found to be stable in thermal and damp heat conditions. • We present a developer for the production of epoxy resin optical waveguides in this paper. • We utilized a non-contact ultraviolet lithography method for the same. • We have also outlined a complete process for preparing the epoxy resin optical waveguide. • The performance of the sample was tested by conducting cut-back and aging tests. [ABSTRACT FROM AUTHOR]

• Laser cleaning can enhance damage threshold by removing defects and impurities. • Chemical structural defects of fused silica are suppressed by laser cleaning. • Intrinsic defects tend to recombine as short rings and densified surface is obtained. • Multi-scale simulation reveals the raising mechanism of damage performance. Ultraviolet (UV) laser-induced damage from defects and impurities in conventional ground and polished fused silica optics significantly hinders their application in high-power laser systems. Laser cleaning, as a non-contact and polishing fluid-free technology, is likely to be a key technology for improving the damage performance of fused silica optics. However, conventional laser cleaning primarily focuses on surface pollution without removing the material. It overlooks the detrimental effects of multiscale defects and impurities inside the fused silica. In this study, microsecond-pulsed CO 2 laser cleaning was proposed to enhance the laser-induced damage threshold (LIDT) by ablating fused silica to nanometer depths. Through multiple-scale simulations, the thermal stress evolution and modulation mechanism of defects and impurities on the damage performance (ranging from the macro- to nanoscale) were revealed. Utilizing multimodal characterization, laser cleaning effectively eliminated and suppressed surface/subsurface defects, absorptive defects, chemical structural defects, and elemental impurities without introducing residual thermal stress and destroying surface roughness. In addition, the evolution of the molecular structures indicated a tendency for intrinsic defects to recombine into shorter-ring structures, which resulted in a densified fused silica surface. The laser-cleaned samples exhibited higher damage thresholds, achieving 47.6 % (0 % probability) and 27.0 % (100 % probability) improvements compared with uncleaned samples. This technology provides a new method for fabricating high damage threshold fused silica optics with superior surface quality for high-power laser applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Three-dimensional printing, also called additive manufacturing (AM), offers a new vision for optical components in terms of weight reduction and strength improvement. A truss, which is a triangulated system of members that are structured and connected in such a way that they mainly bear axial force, is commonly used in steel structures to improve stiffness and reduce weight. Combining these two technologies, an extremely lightweight truss-structured mirror was proposed. First, the finite element analyses (FEA) on surface shape deviation and modal properties were carried out. Results showed that the mirrors had sufficient stiffness and a high weight reduction of up to 85%. In order to verify their performance, the truss-structured mirror blanks were fabricated with AM technology. After that, both the preprocessing and the postprocessing of the mirrors were carried out. The results show that without NiP coating, a surface shape deviation of 0.353λ (PV) and 0.028 λ (RMS) (λ = 632.8 nm) with a roughness of Ra 2.8 nm, could be achieved. Therefore, the truss-structured mirrors in this study have the characteristics of being extremely lightweight and having improved stiffness as well as strong temperature stability. [ABSTRACT FROM AUTHOR]

The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) is a sounding rocket instrument that flew on July 30, 2021 from the White Sands Missile Range, NM. The instrument was designed to address specific science questions that require differential emission measures of the solar soft X-ray spectrum from 6 – 25 Å(0.5 – 2.1 keV). MaGIXS comprises a Wolter-I telescope, a slit-jaw imaging system, an identical pair of grazing incidence paraboloid mirrors, a planar grating and a CCD camera. While implementing this design, some limitations were encountered in the production of the X-ray mirrors, which ended up as a catalyst for the development of a deterministic polishing approach and an improved meteorological technique that utilizes a computer-generated hologram (CGH). The opto-mechanical design approach addressed the need to have adjustable and highly repeatable interfaces to allow for the complex alignment between the optical sub-assemblies. The alignment techniques employed when mounting the mirrors and throughout instrument integration and end-to-end testing are discussed. Also presented are spatial resolution measurements of the end-to-end point-spread-function that were obtained during testing in the X-ray Cryogenic Facility (XRCF) at NASA Marshall Space Flight Center. Lastly, unresolved issues and off-nominal performance are discussed. [ABSTRACT FROM AUTHOR]

When inductively coupled plasma (ICP) is used as a machining tool, its chemical etching-based processing method has the advantage of no contact stress between the tool and the material, thus without any mechanical damage. In recent years, this issue has been widely concerned in optical fabrication. However, there are many differences between low power ICP jet and conventional ICP jet, one of which is that the former does not easily form a rotation-symmetric removal function due to its obvious pinch effect. In this research, the electromagnetism principle of the plasma pinch effect was analyzed firstly, and the jet shape under the pinch effect was classified. Then, experiment was carried out to investigate the plasma jet shape under the pure Ar and mixed gas of CF4-Ar, and the influence law of the reaction gas on the jet propagation shape was analyzed. Finally, the rotational symmetry of the removal function of plasma jet processing was optimized, and the nozzle design criteria were proposed based on pinch effect. [ABSTRACT FROM AUTHOR]

A new and patented polishing tool (ZL2020102387137) called a Self-rotating Wheel Polishing Tool (SWPT) was built, and its tool influence function (TIF) was investigated in this study. The polishing wheel is an innovative two-layer structure: a rigid hub inside and a flexible polishing pad outside. By using finite element analysis, the dynamic contact characteristics between the polishing wheel and the workpiece were studied, and the theoretical TIF was modeled. Due to the influence of friction resistance, the TIF is not circular, but oval. We then ran material removal experiment, and it was found that the experimental TIF and the theoretical TIF are very close and both are close to the Gaussian shape. Finally, optical fabrication was performed. After four times of about 3 h fabrication, the form error converged from PV-1.434λ (λ = 632 nm), RMS-0.308λ to PV-0.144λ, RMS-0.009λ, and PV and RMS converged by 90% and 97%, respectively. The form accuracy achieved the expected target of RMS-0.02λ, which proves that the SWPT has the characteristics of high convergence rate and high fabrication accuracy. The SWPT has a broad application prospect in the field of high-precision optical fabrication. [ABSTRACT FROM AUTHOR]

In the aberration analysis of a wavefront over a certain domain, the polynomials that are orthogonal over and represent balanced aberrations for this domain are used. For example, Zernike circle polynomials are used for analysis of a circular wavefront. When the data available for analysis are the slopes of a wavefront, the polynomials used are those that are orthogonal to the gradient of Zernike polynomials, and are irrotational. Similarly, the annular polynomials are used to analyze the annular wavefronts for systems with annular pupils, as in a rotationally symmetric two-mirror system. In this paper we derive the vector functions that are orthogonal to the gradients of annular polynomials and are irrotational so that they propagate minimum noise from the slope data to the annular aberration coefficients. These vector functions can be used directly to obtain independent annular aberration coefficients as their inner products with the slope data of annular wavefronts. The utility of the functions is demonstrated in a numerical simulation of noisy wavefront slope data to determine the annular coefficients.

Abstract In order to remove mid-spatial frequency errors on aspheric and freeform surfaces, we have developed an aspheric smoothing tool which, unusually, is rigid. This has been proved feasible in the special case where the abrasive grit size exceeds the aspheric misfit, providing a cushion. Firstly, experimental parameters were derived from simulation of Influence Functions regarding misfit between the tool and the surface, which leads to dynamic Influence functions. Then the experimental part was polished into an aspheric surface from generated spherical surface. Thirdly, the choice of tool’s shape parameters was completed with optimisation of conic constant and tilt angle. The tool was machined into aspheric shape with a single-point cutter. Finally, experiments were carried out to compare this tool with a standard spherical smoothing tool. The results showed that this aspheric smoothing tool can removal mid-spatial errors effectively on aspheric surfaces.

A new and patented polishing tool (ZL2020102387137) called a Self-rotating Wheel Polishing Tool (SWPT) was built, and its tool influence function (TIF) was investigated in this study. The polishing wheel is an innovative two-layer structure: a rigid hub inside and a flexible polishing pad outside. By using finite element analysis, the dynamic contact characteristics between the polishing wheel and the workpiece were studied, and the theoretical TIF was modeled. Due to the influence of friction resistance, the TIF is not circular, but oval. We then ran material removal experiment, and it was found that the experimental TIF and the theoretical TIF are very close and both are close to the Gaussian shape. Finally, optical fabrication was performed. After four times of about 3 h fabrication, the form error converged from PV-1.434λ (λ = 632 nm), RMS-0.308λ to PV-0.144λ, RMS-0.009λ, and PV and RMS converged by 90% and 97%, respectively. The form accuracy achieved the expected target of RMS-0.02λ, which proves that the SWPT has the characteristics of high convergence rate and high fabrication accuracy. The SWPT has a broad application prospect in the field of high-precision optical fabrication.

The authors proposed a flexible microresonator based on nanowires composed of Ⅱ–Ⅵ compounds to detect the small strain caused by external motion. The nanowire ring resonator is embedded in polydimethylsiloxane (PDMS) flexibility to improve the coupling efficiency. In this work, CdS nanowire is fabricated onto a PDMS flexible substrate. With the help of a fibre tip, the single nanowire is manipulated under a microscope, allowing the curved line to be a ring and making the litter overlapping. This overlap increases coupling efficiency and sensor performance. The ring cavity has the parameters of diameter 1 µm, length 75 µm and radius ∼10 µm. Experiments demonstrated the process of fabricating a strain sensor and detected peak shifts. This resonant wavelength appeared red‐shift and linear tuned when stretching the flexible substrate. The quality factor was about 2000 and the gauge factor was about 80 nm per stretching unit. Being a small structure and high sensitivity, the sensor can be integrated into the chip. This promotes the development of miniaturisation to some extent. As a result, this work is beneficial to optical manipulation, further being extended to the tunable light source. [ABSTRACT FROM AUTHOR]

Off-axis reflective optical systems find wide applications in various industries, but the related manufacturing issues have not been well considered in the design process. This paper proposed a design method for cylindrical reflective systems considering manufacturing constraints to facilitate ultra-precision raster milling. An appropriate index to evaluate manufacturing constraints is established. The optimization solution is implemented for the objective function composed of primary aberration coefficients with weights and constraint conditions of the structural configuration by introducing the genetic algorithm. The four-mirror initial structure with a good imaging quality and a special structural configuration is then obtained. The method's feasibility is validated by designing an off-axis four-mirror afocal system with an entrance pupil diameter of 170 mm, a field of view of 3° × 3° and a compression ratio of five times. All mirrors in the system are designed to be distributed along a cylinder. [ABSTRACT FROM AUTHOR]

In this work, the authors demonstrate the control of quality factor (Q‐factor) is laterally coupled vertical cavities. A 3 μm‐side‐length square cavity directly connected to a 1.5 μm‐width, 10 μm‐length Fabry–Perot (FP) cavity has been fabricated and measured. Dynamic tuning of the Q‐factor has been successfully observed by bringing the square cavity and FP cavity into resonance. The vertical‐cavity‐based Q‐factor control scheme provides a new choice for the modulation of light and holds potentials for applications associated with optical information processing. [ABSTRACT FROM AUTHOR]

• A method of promoting the axial feature size of PPI-DLW is proposed. • A 3D hollow focus was generated using one beam without light field superposition. • Two-focus parallel scanning using 3D hollow focus was realized without hardware updating based on a classic method. • The isotropic 30 nm feature size was realized. • This work will improve the ability of PPI-DLW to fabricate arbitrary 3D structures. Peripheral-photoinhibition (PPI)-based direct laser writing (DLW) inspired by simulated emission depletion (STED) microscopy has improved the fabrication resolution of three-dimensional (3D) structures on the nano-scale. However, most previous studies have focused on the lateral feature size, neglecting axial-feature-size enhancement. This article proposes a novel method to simultaneously reduce the axial and lateral feature sizes of PPI-DLW. By employing a pseudo 3D hollow focus, a suspended nanowire with an isotropic 30-nm feature size was realized. Such an isotropic 3D hollow focus for photoinhibition is generated using a single beam instead of two-beam superposition, thus it does not increase the system complexity of a PPI-DIW system. Owing to the reduced feature size in all three dimensions and the low systematic complexity, the proposed method improves the capabilities of PPI-DLW for fabricating arbitrary 3D structures. [ABSTRACT FROM AUTHOR]

Angular precision of 0.1° for the blaze angle of echelle gratings is an important technical requirement for spectral instruments with echelle gratings. This paper proposes a precise adjustment method for the blaze angle of echelle gratings that are etched or deposited by self-shadowing rotating mask. The blaze angle will decrease or increase when the grating is rotated in beams for etching or deposition, respectively. The blaze angle can be controlled by adjusting the etching or deposition conditions. For the echelle grating with nominal blaze angle of 63.0° and groove density of 52.7 g/mm, the blaze angle was decreased by 0.12° with a maximum etching depth of 19 nm on the blaze facet. Additionally, the blaze angle adjustment precision will be better than 0.02° if the maximum etch depth on the blaze facet is less than 3 nm.

Abstract Background We have developed edge-control for the Precessions TM process suitable for fast fabrication of large mirror segments, and other applications sensitive to edge mis-figure. This has been applied to processing of European extremely large telescope (E-ELT) prototype mirror-segments, meeting the specification on maximum edge mis-figure. However we have observed residuals that have proved impossible to correct with this approach, being in part the legacy of asymmetries in the input edge-profiles. Methods We have therefore compared different proposed methods experimentally and theoretically and report here on a new edge-rectification step, which operates locally on edges, does not disturb the completed bulk area. Results A new toolpath has been developed and experiments have been carried out to demonstrate that local edge rectification can be carried out. Conclusions With this method, the residue error on edges can be removed separately and has potential to reduce total process time.

The scratches on an optical surface can worsen the performance of elements. The normal process method is removing scratches entirely. However, it is a tough and high-cost requirement of removing extremely deep scratches and maintaining all the other excellent indicators at the same time. As the alternative of removing, we propose the method of scratch morphology transformation to diminish the drawbacks induced by scratches. We measure the morphology of scratches, establish the transformation models and transform them to the needed shape. In engineering applications, transformation can solve scratch drawbacks or limitations in an efficient and effective way. Then, residual scratches become acceptable. The transformation can also be amalgamated into the error figuring processes. Typical scratch transforming examples are experimented and AFM measurement is conducted. We explore the rule of scratch morphology transformation by two typical fabrication means: magnetorheological finishing (MRF) and HF etching. This morphology transforming method is an economical alternative for current defect-free fabrication. That will significantly decrease fabrication time, cost and risk, while the optical quality maintain.

Two‐dimensional (2D) metasurface integrated with strip waveguide in silicon‐on‐insulator (SOI) has been designed to achieve high coupling efficiency for 3.8 μm wavelength. The optimisation in period and radius has been achieved using 3D finite‐difference time‐domain (FDTD). The calculated coupling efficiency in the in‐plane waveguide for the out‐of‐plane surface illumination is over 90% with a bandwidth of 1 μm. The design is consistent with the available lithography using 400 nm thick SOI for mid‐IR applications. Finally, monolithic integration can be achieved using standard multi‐project wafer run. [ABSTRACT FROM AUTHOR]

Loose abrasive grinding was performed on a wide range of optical workpiece materials [single crystals of Al2O3 (sapphire), SiC, Y3Al5O12 (YAG), CaF2, and LiB3O5 (LBO); a SiO2-Al2O3-P2O5-Li2O glass-ceramic (Zerodur); and glasses of SiO2  :  TiO2 (ULE), SiO2 (fused silica), and P2O5-Al2O3-K2O-BaO (phosphate)]. Using the magneto rheological finishing (MRF) taper wedge technique (where a wedge was polished on each of the ground workpieces and the resulting samples were appropriately chemically etched), the subsurface mechanical damage (SSD) characteristics were measured. The SSD depth for most of the workpiece materials was found to scale as E11/2  /  H1, where E1 is the elastic modulus and H1 is the hardness of the workpiece. This material scaling is the same as that for the growth of lateral cracks, suggesting that lateral cracks are a dominant source for SSD rather than radial/median cracks, as previously proposed. Utilizing the SSD depth data from both this study and others, semiempirical relationships have been formulated, which allows for estimating the SSD depth as a function of workpiece material and important grinding parameters (such as abrasive size and applied pressure). [ABSTRACT FROM AUTHOR]

Synthesis of indium (III) oxide (In2O3) and chromium (Cr)‐doped In2O3 thin film (TF) by spin‐on technique was reported. The device showed the Schottky nature under dark and light illumination condition. The ideality factor of the diode showed an exponential increase with the decrease in temperature. The low ideality factor of ∼4 was calculated at 300 K. The barrier height of the device increased with temperature. The Cr‐doped In2O3 TF device possessed high sensitivity compared with undoped In2O3 TF at −2 V all over the temperature range from 10 to 300 K. The Cr‐doped In2O3 TF‐based device showed extremely high sensitivity toward ultraviolet (320 nm) light as compared with visible light. [ABSTRACT FROM AUTHOR]

Highlights • An interferogram simulation algorithm for off-axis conic surfaces is proposed. • The algorithm is used in stressed mirror polishing technique. • The described procedure gives information in real time in a quantitate way. • The procedure helps to control the fabrication process for off-axis optical surfaces. • Irregularity data and aberration coefficients of the surface is obtained. Abstract Off-axis conic sections optimizes the design of optical instruments, allowing unrestricted access to the focal point, and making possible to analyze the deflected light without disturbing the incident beam. In this paper are derived, as a first aim, a set of equations representing all kind of conical surfaces and their off-axis sections. With these analytical expressions, we found the associated wavefront coming from the off-axis sections. To complete this analysis, an algorithm was developed to obtain simulated interferograms for off-axis optical surfaces and was used in combination with interferometry to optical test this kind of surfaces in a quantitative way, an important aspect in optical fabrication, specifically the stressed mirror polishing technique. To test the algorithm and the derived equations, we compared experimental interferograms against interferograms calculated with our algorithm. Finally, we found that our method can calculate the aberration coefficients for any off-axis conical surface in a satisfactory manner, giving us the necessary data to control the fabrication process. [ABSTRACT FROM AUTHOR]

In this work, the authors present their recent progress in the development of a platform for the mid‐infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch‐step and can be designed for strong light–matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides. [ABSTRACT FROM AUTHOR]

An inverted lateral taper with one vertical discrete step was designed for a medium confinement silicon nitride waveguide platform in the C‐band, as a chip edge coupler, with a predicted insertion loss of 0.58 dB. The design is supported by an extensive study to evaluate the impact of fabrication process variations on the performance of such a coupler. The device was manufactured and measured, showing an insertion loss of 1.47 dB, which was traced back to fabrication process variations as cross‐checked with simulations. To the authors' knowledge, the reported edge coupler is the shortest and among the best performing found for silicon nitride platforms. [ABSTRACT FROM AUTHOR]

In recent years, the precision of the manufacturing process for optical surfaces has improved tremendously. As a result, freefrom surfaces have become more attractive options for imaging applications with increased accuracy requirements. However, with regards the integration into an optical system, performance is often limited due to surface imperfections, such as mid-spatial frequency errors and alignment errors. This demonstrates the need for a more holistic description of systems, including multiple freeform components, which enable performance predictions based on the system as a whole. In this work, a solution for such a simulation is presented and verified by a comparison with the experimental data. This procedure not only predicts system performance but also supports tolerancing and easier alignment. [ABSTRACT FROM AUTHOR]

Abstract Recent research has shown that the computer-controlled fluid jet polishing (FJP) process can generate nanometer-level form accuracy on free surface optical components. The key issues affecting the machining accuracy of the FJP process, including the deviation of the removal function, dynamic response of the moving tables and the change of material removal rates at a small-scale dwell time, have been investigated. Approaches using signal filtering and alignment methods to reduce the measurement errors of the removal functions in FJP are presented. An enhancing algorithm is proposed to improve the rotational symmetry of the removal function, with correction factors being included in the quality assessment to adjust the change in the quality of the removal function with different dwell times. The dynamic responses and moving accuracy of the worktable were measured, and their effects on the FJP polishing process were analyzed. Fluid jet polishing experiments using small-scale dwell time (less than 5 s) under intermittent motion and continuous motion modes were also performed. The experimental results show that the fluctuation of enhanced removal functions is less than that of the original functions. The residual information on the surface, related to the path distance, is barely noticeable when the distance is less than 0.4 mm, when a nozzle with a diameter of 1 mm diameter is used. The material removal experiments with small-scale dwell times indicate that the removal rate is stable when the worktable is in continuous motion. Highlights • Key issues affecting the machining accuracy of the FJP process, including the deviation of the removal function, dynamic response of the moving tables and the change of material removal rates at small-scale dwell time, have been investigated. • Approaches using signal filtering and alignment methods to reduce the measurement errors are presented. • An enhancing algorithm is proposed to improve the rotational symmetry of the removal function, with adjusting the change of removal function quality with different dwell time. • It has been found that the depth of the removal function at the small scale dwell time has a nonlinear relationship with that obtained at the large scale dwell time, whilst the depth over width ratios under these two conditions are also different. [ABSTRACT FROM AUTHOR]

Off-axis reflective optical systems find wide applications in various industries, but the related manufacturing issues have not been well considered in the design process. This paper proposed a design method for cylindrical reflective systems considering manufacturing constraints to facilitate ultra-precision raster milling. An appropriate index to evaluate manufacturing constraints is established. The optimization solution is implemented for the objective function composed of primary aberration coefficients with weights and constraint conditions of the structural configuration by introducing the genetic algorithm. The four-mirror initial structure with a good imaging quality and a special structural configuration is then obtained. The method’s feasibility is validated by designing an off-axis four-mirror afocal system with an entrance pupil diameter of 170 mm, a field of view of 3° × 3° and a compression ratio of five times. All mirrors in the system are designed to be distributed along a cylinder.

An eight‐channel hybrid‐integrated light source with 100 GHz channel spacing fabricated by a passive alignment technology is demonstrated. Side mode suppression ratios of better than 40 dB were obtained via grating couplers under eight‐channel simultaneous operation at a continuous wave current of 600 mA and 25°C. The surface slotted laser array fabricated by standard lithography butt‐joint with silicon photonic devices was demonstrated for the first time, to the best of the authors' knowledge. [ABSTRACT FROM AUTHOR]

In this Letter, high-uniformity 1 × 64 linear arrays of 4H-SiC avalanche photodiode (APD) are reported for ultraviolet detection. Multi-cycle inductively coupled plasma dry etching was adopted for the bevelled mesa formation, during which the wafers were rotated with a small angle for each cycle to suppress the process variation. As a result, a high pixel yield of 100% and a high-uniformity breakdown voltage with a fluctuation of smaller than 0.5 V are achieved for the fabricated 1 × 64 4H-SiC APD linear arrays, which is a great improvement for 4H-SiC APD arrays. Moreover, the dark currents at 95% of breakdown voltage are below 1 nA for all the 64 pixels. Besides, the pixels in the array show a multiplication gain of larger than 106 and a peak responsivity of 0.12 A/W at 285 nm (corresponding to a maximum quantum efficiency of 52%) at room temperature. [ABSTRACT FROM AUTHOR]

Abstract The aperture of space remote sensing camera is increasing, and the demand for lighter weight is getting higher and higher. With the advancement of active optics, the thickness of optical components has gradually grown to light and thin. It is extremely difficult to develop ultrathin mirrors using brittle materials such as traditional optical glass and silicon carbide. Due to advantages such as low density, high specific stiffness, low thermal expansion coefficient, toughness, and additive rapid manufacturing properties, carbon fiber reinforced plastic (CFRP) is one of potential applications for large-diameter ultra-thin mirrors. However, the carbon fiber composite material is a two-phase material that cannot be used as optical surface and must be surface-modified. In this paper, the surface modification of CFRP substrate was carried out by chemical nickel plating and nickel electroplating. The modified nickel layer covers all surfaces of CFRP substrate, and nickel layers satisfying the thickness, bonding force, and internal stress requirements. A Φ100 mm aperture ultra-thin carbon fiber mirror developed, after optical fabricating, its surface accuracy RMS is better than λ/15. Thermal deformation analysis and test show that the thermal deformation of ultra-thin carbon fiber mirrors is mainly manifested by the change of radius of curvature, which is caused by the thickness error of the nickel layer on the front and rear faces. In addition, although thermal deformation caused by the lamination angle error of CFRP substrate is relatively small in value, it should still be given enough attention, because the astigmatic error produced is hard to eliminate. [ABSTRACT FROM AUTHOR]

A highly selective and sensitive optical sensor based on localised surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) for the determination of a sulphide ion in aqueous solution is presented. The existence of sulphide is change the intensity of the LSPR band around 520 nm. In this sensor, sulphide ions were recognised and measured by UV–vis spectrophotometry. Three factors such as pH, time and concentration of AuNPs have been studied. The optimisation of effective parameters is done by one at a time method. This method was simple, rapid and cost efficient for the detection of sulphide. The linear range is 1.00–10.00 (4.16–41.63 µM) ppm with the correlation coefficient of 0.9874 and the detection limit of 0.54 ppm. The relative standard deviation of the reported method is 1.01%. [ABSTRACT FROM AUTHOR]

This letter reports a simple technique of fabricating complex micro-optical elements integrated with silicon-based microelectromechanical systems. The proposed method utilizes a replication technique using soft-mold to fabricate optical components on top of a machined wafer, followed by patterning of produced replica by photolithography. Combination of replication and patterning on wafer-level allows simultaneous fabrication and integration of complex micro-opto-mechanical systems. The optical components are fabricated with negative photoresist SU-8, allowing the production of transmissive or reflective optical structures. In this letter, fabrication of diffraction grating and spherical and cylindrical microlenses is demonstrated. [ABSTRACT FROM AUTHOR]

We present an intraocular lens (IOL) design that renders it more compliant to actual conditions where tilt may be present in the fabricated lens or the implanted locus. When an IOL is implanted in the eye some degree of tilt is commonly observed, negatively affecting the retinal image (Eppig et al., 2009). The distinguishing feature of the proposed design method is the use of a tilted lens as reference, with a genetic algorithm (NSGA-II) applied and followed by a Damped Least Square (DLS) optimization. It is compared to the classical IOL optimization based on the DLS applied to a perfectly aligned lens. The optimized IOL was evaluated considering the specifications of ISO and Liou and Brennan eye models. The image resolution (MTF curves) of the resulting IOL is analyzed for both to compare performance. It is demonstrated that in the Liou and Brennan eye model the visual acuity is comparable for both design methods when the lens is aligned to the optical axis, however, when tilt is present the proposed method presents a significant benefit in relation to the classical method. This approach can be used for a more robust design of any lens system at no additional cost. [ABSTRACT FROM AUTHOR]

In this study, we present the fabrication route of quasicrystal surface relief grating (SRG) of azopolymer. Based on photo-reconfigurable azobenzene property, various morphologies of grating patterns were inscribed on azopolymer thin-films by two-beam coupling light interference lithography (LIL) process. Multiplexing the LIL with different rotation sequence on azopolymers resulted in unusual surface structures including quasicrystal-like SRGs with Fibonacci sequences in rotational LIL. We investigated the effect of rotation sequence on the grating patterns by atomic force microscope, revealing that rotation sequence is a critical parameter determining surface structures of azopolymer films. [ABSTRACT FROM AUTHOR]

Two principal two‐stage switch architectures (cascaded and parallel), both of which are composed of two identical optical crossbar switches with an extra set of inputs and outputs, are compared in terms of their number of crosspoints, switch control complexities, and key optical performances, such as insertion loss and crosstalk power, through theoretical analysis. The authors begin by briefly introducing a known N × N cascaded optical crossbar switch with N2 /2 crosspoints, where N is the switch size, and present a new functional perspective based on quasi‐bitonic sorting. Subsequently, the authors derive two types of two‐stage parallel optical crossbar switches with reduced crosspoints from a conventional single‐stage parallel crossbar switch with N2 + 2N crosspoints. The first type uses two N /2 × N asymmetric switches in parallel, both of which are embedded in a single N /2 × N /2 crossbar switch. It has (N2 + 2N)/2 crosspoints and suffers from a complex switch control of O (N2). The second type is equivalent to a three‐stage Benes network and exploits bidirectional transmission to reduce the number of switching stages. It requires (N2 + 3N)/2 crosspoints, but has a dramatically reduced switch control complexity of O (N), and significantly improved optical performance. [ABSTRACT FROM AUTHOR]

Controlled translational displacement between a large-surface photosensitive planar substrate and a wide and short 1D grating phase-mask enables the printing of large-width, spatially highly coherent gratings of principally unlimited length, using a limited number of opto-mechanical control parameters. The phase-mask is illuminated by a temporally modulated exposure light sheet controlled by a displacement sensor. The proposed method is compared with existing techniques, and its functional elements and their combination are analyzed. [ABSTRACT FROM AUTHOR]

We report pulsed laser deposition of high-quality crystalline yttrium aluminium oxide and yttrium gallium oxide with a growth rate approaching 20 μm per hour by using an excimer laser operating at a repetition rate of 100 Hz. This result demonstrates the capability of PLD at 100 Hz for upscaling deposition speeds to a rate that is industrially relevant. In addition, we show that use of this high repetition rate can cause additional heating of the substrate, which in turn affects the film composition. This effect is used as an additional control parameter on the composition, and thus refractive index, of the grown material. [ABSTRACT FROM AUTHOR]

We present a disposable miniaturized confocal imager, consisting mostly of three-dimensional (3-D)- printed components. A 3-D printed laser scanner with 10 × 10 mm2 frame size is employed for Lissajous scan, with 180 and 315 Hz frequencies in orthogonal directions corresponding to ± 8 deg and ± 4 deg optical scan angles, respectively. The actuation is done electromagnetically via a magnet attached to the scanner and an external coil. A miniaturized lens with 6-mm clear aperture and 10-mm focal length is 3-D printed and postprocessed to obtain desired (≤λ/5 surface roughness) performance. All components are press-fitted into a 3-D-printed housing having 17 mm width, which is comparable to many of the MEMS-based scanning imagers. Finally, line-scan from a resolution target and two-dimensional scanning in the sample location were demonstrated with the integrated device. [ABSTRACT FROM AUTHOR]