Helmet Mounted Displays(HMDs),such as in Virtual Reality(VR),Augmented Reality(AR),Mixed reality(MR),and Smart Glasses have the potential to revolutionize the way we live our private and professional lives,as in commu...Helmet Mounted Displays(HMDs),such as in Virtual Reality(VR),Augmented Reality(AR),Mixed reality(MR),and Smart Glasses have the potential to revolutionize the way we live our private and professional lives,as in communicating,working,teaching and learning,shopping and getting entertained.Such HMD devices have to satisfy draconian requirements in weight,size,form factor,power,compute,wireless communication and of course display,imaging and sensing performances.We review in this paper the various optical technologies and architectures that have been developed in the past 10 years to provide adequate solutions for the drastic requirements of consumer HMDs,a market that has yet to become mature in the next years,unlike the existing enterprise and defense markets that have already adopted VR and AR headsets as practical tools to improve greatly effectiveness and productivity.We focus specifically our attention on the optical combiner element,a crucial element in Optical See-Through(OST)HMDs that combines the see-through scene with a world locked digital image.As for the technological platform,we chose optical waveguide combiners,although there is also a considerable effort today dedicated to free-space combiners.Flat and thin optics as in micro-optics,holographics,diffractives,metasurfaces and other nanostructured optical elements are key building blocks to achieve the target form factor.展开更多
Near-eye displays are the main platform devices for many augmented reality(AR)and virtual reality(VR)applications.As a wearable device,a near-eye display should have a compact form factor and be lightweight.Furthermor...Near-eye displays are the main platform devices for many augmented reality(AR)and virtual reality(VR)applications.As a wearable device,a near-eye display should have a compact form factor and be lightweight.Furthermore,a large field of view and sufficient eyebox are crucial for immersive viewing conditions.Natural three-dimensional(3D)image presentation with proper focus cues is another requirement that enables a comfortable viewing experience and natural user interaction.Finally,in the case of AR,the device should allow for an optical see-through view of the real world.Conventional bulk optics and two-dimensional display panels exhibit clear limitations when implementing these requirements.Holographic techniques have been applied to near-eye displays in various aspects to overcome the limitations of conventional optics.The wavefront reconstruction capability of holographic techniques has been extensively exploited to develop optical see-through 3D holographic near-eye displays of glass-like form factors.In this article,the application of holographic techniques to AR and VR near-eye displays is reviewed.Various applications are introduced,such as static holographic optical components and dynamic holographic display devices.Current issues and recent progress are also reviewed,providing a comprehensive overview of holographic techniques that are applied to AR and VR near-eye displays.展开更多
Structural coloration stemming from microstructure-induced light interference has been recognized as a promising surface colorizing technology,based on its potential in a wide array of applications,including high-defi...Structural coloration stemming from microstructure-induced light interference has been recognized as a promising surface colorizing technology,based on its potential in a wide array of applications,including high-definition displays,anti-counterfeiting,refractive index sensing,and photonic gas and vapor sensing.Vibration-assisted ultraprecision texturing using diamond tools has emerged as a high-efficiency and cost-effective machining method for colorizing metallic and ductile surfaces by creating near-wavelength microstructures.Although theoretically possible,it is extremely challenging to apply the vibration-assisted texturing technique directly to colorize non-metallic and brittle materials(e.g.,silicon and acrylic polymers)with high-quality,crack-free microstructures owing to the intrinsic brittleness of these materials.This study demonstrates the feasibility of direct texturing near-wavelength-scale gratings on brittle surfaces in the ductile regime to fabricate crack-free micro/nanostructures.The effects of tool vibration trajectories on the ductile-to-brittle transition phenomena were investigated to reveal the cutting mechanism of ductile-regime texturing and optimize the processing windows.Structural coloration on silicon and acrylic surfaces was successfully demonstrated by creating programmable and pixelated diffraction gratings with spacing values ranging from 0.75 to 4μm.展开更多
Holography has evolved over its 70+years of history across widespread and diverse communities and locations.This has produced a complex language that is sometimes inconsistent,confusing,and incorrect,resulting in a ge...Holography has evolved over its 70+years of history across widespread and diverse communities and locations.This has produced a complex language that is sometimes inconsistent,confusing,and incorrect,resulting in a general public that often appears widely confused and/or ignorant regarding what holograms actually are and are not.Today’s holographers employ many types of recording media to record all types of waves,such as light,sound,radar,and simulated waves,and for many different applications and purposes.This study examines the language of holography along with its origins,problems,and possible solutions,while recognizing that certain“errors”in the language are so embedded in society that simple and ideal fixes may be beyond reach.This leaves us with certain questions,as follows.First,can the correct language be restored and should we undertake the task,or are we stuck with every three-dimensional image being called a hologram?Is it our duty to better educate the public with a more useful and consistent language,or should we just go with the flow?In this work,beginning with the insights provided by the pioneers of the field,we attempt to set the stage for a more useful holography language and definitions,specialized so as to be understandable and usable by various audiences,including those interested in non-optical holography.Such knowledge can help the general public to take greater interest and enjoyment in holography;this would also be beneficial to those more involved in holography.Accordingly,this article offers advice for achieving this result.展开更多
Compound eyes(CEs)are advanced optical visual systems with distinct features of large view-fields,infinite depth of field,and dynamic imaging capability,revealing their significant potential in applications including ...Compound eyes(CEs)are advanced optical visual systems with distinct features of large view-fields,infinite depth of field,and dynamic imaging capability,revealing their significant potential in applications including robot vision,unmanned aerial vehicle detection,and medical diagnosis.Compared with macroscopic CEs,which primarily comprise multicamera arrays,compact integrated CEs have garnered significant attention because of their portability and possibility of flexible integration with microrobots and in-vivo medical facilities.To date,considerable effort has been devoted to this field,in which manufacturing technologies are vital to the development of artificial CEs(ACEs)capable of large field-of-view imaging,depth information collection,and threedimensional imaging.Challenges and opportunities exist for the practical application of advanced ACEs.This paper reviews state-of-the-art technologies for manufacturing ACEs,and then briefly summarises their potential applications in different fields.Finally,the current challenges and perspectives of ACEs are discussed.展开更多
In recent years,multi-photon 3D laser printing has become a widely used tool for the fabrication of micro-and nanostructures for a large variety of applications.Typically,thorough sample characterisation is key for an...In recent years,multi-photon 3D laser printing has become a widely used tool for the fabrication of micro-and nanostructures for a large variety of applications.Typically,thorough sample characterisation is key for an efficient optimisation of the printing process.To date,three-dimensional microscopic inspection has usually been carried out on finished 3D printed microstructures,that is,using ex-situ approaches.In contrast,in-situ 3D characterization tools are desirable for quickly assessing the quality and properties of 3D printed microstructures.Along these lines,we present and characterise a Fourier-domain optical coherence tomography(FD-OCT)system that can be readily integrated into an existing 3D laser lithography setup.We demonstrate its capabilities by examining different 3D printed polymer microstructures immersed in a liquid photoresist.In such samples,local reflectivity arises from the(refractive-index)contrasts between the polymerised and non-polymerised regions.Thus,the refractive index of the printed material can be extracted.Furthermore,we demonstrate that the reflectivity of polymer-monomer transitions exhibits time-dependent behaviour after printing.Supported by transfer-matrix calculations,we explain this effect in terms of the time-dependent graded-index transition originating from monomer diffusion into the polymer matrix.Finally,we show exemplary 3D reconstructions of printed structures that can be readily compared with 3D computer designs.展开更多
Tilted Wave Interferometry(TWI)is a measurement technique for fast and flexible interferometric testing of aspheres and freeform surfaces.The first version of the tilted wave principle was implemented in a Twyman-Gree...Tilted Wave Interferometry(TWI)is a measurement technique for fast and flexible interferometric testing of aspheres and freeform surfaces.The first version of the tilted wave principle was implemented in a Twyman-Green type setup with separate reference arm,which is intrinsically susceptible to environmentally induced phase disturbances.In this contribution we present the TWI in a new robust common-path(Fizeau)configuration.The implementation of the Tilted Wave Fizeau Interferometer requires a new approach in illumination,calibration and evaluation.Measurements of two aspheres and a freeform surface show the flexibility and also the increased stability in both phase raw data and surface measurements,which leads to a reduced repeatability up to a factor of three.The novel configuration significantly relaxes the tolerances of the imaging optics used in the interferometer.We demonstrate this using simulations on calibration measurements,where we see an improvement of one order of magnitude compared to the classical Twyman-Green TWI approach and the capability to compensate higher order error contributions on the used optics.展开更多
Three-dimensional(3D)printing,also known as additive manufacturing(AM),has undergone a phase of rapid development in the fabrication of customizable and high-precision parts.Thanks to the advancements in 3D printing t...Three-dimensional(3D)printing,also known as additive manufacturing(AM),has undergone a phase of rapid development in the fabrication of customizable and high-precision parts.Thanks to the advancements in 3D printing technologies,it is now a reality to print cells,growth factors,and various biocompatible materials altogether into arbitrarily complex 3D scaffolds with high degree of structural and functional similarities to the native tissue environment.Additionally,with overpowering advantages in molding efficiency,resolution,and a wide selection of applicable materials,optical 3D printing methods have undoubtedly become the most suitable approach for scaffold fabrication in tissue engineering(TE).In this paper,we first provide a comprehensive and up-to-date review of current optical 3D printing methods for scaffold fabrication,including traditional extrusion-based processes,selective laser sintering,stereolithography,and two-photon polymerization etc.Specifically,we review the optical design,materials,and representative applications,followed by fabrication performance comparison.Important metrics include fabrication precision,rate,materials,and application scenarios.Finally,we summarize and compare the advantages and disadvantages of each technique to guide readers in the optics and TE communities to select the most fitting printing approach under different application scenarios.展开更多
The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to...The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.展开更多
Since its invention,holography has been mostly applied at visible wavelengths in a variety of applications.Specifically,non-destructive testing of manufactured objects was a driver for developing holographic methods a...Since its invention,holography has been mostly applied at visible wavelengths in a variety of applications.Specifically,non-destructive testing of manufactured objects was a driver for developing holographic methods and all related ones based on the speckle pattern recording.One substantial limitation of holographic non-destructive testing is the setup stability requirements directly related to the laser wavelength.This observation has driven some works for 15 years:developing holography at wavelengths much longer than visible ones.In this paper,we will first review researches carried out in the infrared,mostly digital holography at thermal infrared wavelengths around 10 micrometers.We will discuss the advantages of using such wavelengths and show different examples of applications.In nondestructive testing,large wavelengths allow using digital holography in perturbed environments on large objects and measure large deformations,typical of the aerospace domain.Other astonishing applications such as reconstructing scenes through smoke and flames were proposed.When moving further in the spectrum,digital holography with so-called Terahertz waves(up to 3 millimeters wavelength)has also been studied.The main advantage here is that these waves easily penetrate some materials.Therefore,one can envisage Terahertz digital holography to reconstruct the amplitude and phase of visually opaque objects.We review some cases in which Terahertz digital holography has shown potential in biomedical and industrial applications.We will also address some fundamental bottlenecks that prevent fully benefiting from the advantages of digital holography when increasing the wavelength.展开更多
Silicon(Si)photonics is a disruptive technology on the fast track to revolutionise integrated photonics.An indispensable branch thereof,heterogeneous Si integration,has also evolved from a science project 15 years ago...Silicon(Si)photonics is a disruptive technology on the fast track to revolutionise integrated photonics.An indispensable branch thereof,heterogeneous Si integration,has also evolved from a science project 15 years ago to a growing business and compelling research field today.We focus on the scope of Ⅲ-Ⅴ compound semiconductors heterogeneously integrated on Si substrates.The commercial success of massively produced integrated optical transceivers based on first-generation innovation is discussed.Then,we review a number of technological breakthroughs at the component and platform levels.In addition to the numerous new device performance records,our emphasis is on the rationale behind and the design principles underlying specific examples of materials and device integration.Finally,we offer perspectives on development trends catering to the increasing demand in many existing and emerging applications.展开更多
One of the major challenges when fabricating high gamut colour-converted micro-light-emitting diodes(LEDs)displays is severe crosstalk effect among adjacent pixels because of the wide view-angle feature of micro-LED c...One of the major challenges when fabricating high gamut colour-converted micro-light-emitting diodes(LEDs)displays is severe crosstalk effect among adjacent pixels because of the wide view-angle feature of micro-LED chips.In this study,potential factors that contribute to the crosstalk effect were systematically simulated.We observed that precisely filling the space between each micro-LED chip with a light blocking matrix(LBM)can be a promising solution to alleviate this risk.After careful investigations,a press-assisted moulding technique was demonstrated to be an effective approach of fabricating the LBM.Nevertheless,experimental observations further revealed that residual black LBM on the surface of micro-LEDs severely reduces the brightness,thereby compromising the display performance.This problem was successfully addressed by employing a plasma etching technique to efficiently extract the trapped light.Eventually,a top-emitting blue micro-LED-based backlight fine-moulded with a black LBM was developed and combined with red and green quantum dot colour-conversion layers for full-colour display.The colour gamut of our manufactured display prototype can cover as high as 122%that of the National Television Standards Committee.展开更多
Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this techni...Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this technique in industry is the lack of reliability and qualification mainly because of melt pool instabilities during the laser-powder interaction, which degrade the quality of the manufactured components. In this paper, we propose multi- wavelength digital holography as a proof of concept for in situ real-time investigation of the melt pool morphology. A two-wavelength digital holographic setup was co-axially implemented in a laser beam melting facility. The solidified aluminum tracks and melt pools during the manufacturing of 316L were obtained with full- field one-shot acquisitions at short exposure times and various scanning velocities. The evaluation of the complex coherence factor of digital holograms allowed the quality assessment of the phase reconstruction. The motion blur was analyzed by scanning the dynamic melt pool.展开更多
The miniaturisation of spectroscopic measurement devices opens novel information channels for size critical applications such as endoscopy or consumer electronics.Computational spectrometers in the micrometre size ran...The miniaturisation of spectroscopic measurement devices opens novel information channels for size critical applications such as endoscopy or consumer electronics.Computational spectrometers in the micrometre size range have been demonstrated,however,these are calibration sensitive and based on complex reconstruction algorithms.Herein we present an angle-insensitive 3D-printed miniature spectrometer with a direct separated spatial-spectral response.The spectrometer was fabricated via two-photon direct laser writing combined with a super-fine inkjet process.It has a volume of less than 100×100×300μm^(3).Its tailored and chirped high-frequency grating enables strongly dispersive behaviour.The miniature spectrometer features a wavelength range of 200 nm in the visible range from 490 nm to 690 nm.It has a spectral resolution of 9.2±1.1 nm at 532 nm and 17.8±1.7 nm at a wavelength of 633 nm.Printing this spectrometer directly onto camera sensors is feasible and can be replicated for use as a macro-pixel of a snapshot hyperspectral camera.展开更多
Recording and(computational)processing of complex wave fields offer a vast realm of new methods for optical 3D metrology.We discuss fundamental similarities and differences between holographic surface topography measu...Recording and(computational)processing of complex wave fields offer a vast realm of new methods for optical 3D metrology.We discuss fundamental similarities and differences between holographic surface topography measurement and non-holographic principles,such as triangulation,classical interferometry,rough surface interferometry and slope measuring methods.Key features are the physical origin of the ultimate uncertainty limit and how the topographic information is encoded and decoded.Besides the theoretical insight,the discussion will help optical metrologists to determine if their measurement results could be improved or have already hit the ultimate limit of what physics allows.展开更多
Laser powder bed fusion(LPBF)is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution with short lead times...Laser powder bed fusion(LPBF)is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution with short lead times.This technique has been extensively employed in manufacturing Ti-6Al-4V parts for aerospace and biomedical applications.However,many challenges,including poor surface quality,porosity,anisotropy in microstructure and property,and difficulty in tailoring microstructure,still exist.In this paper,we review the recent progress in post-process treatment and its influence on the microstructure evolution and material performance,including tensile,fatigue,fracture toughness,creep,and corrosion properties.The contradictions in simultaneously achieving high strength/ductility and strength/fracture toughness/creep resistance have been identified.Furthermore,research gaps in understanding the effects of the emerging bi-modal microstructure on fatigue properties and fracture toughness require further investigation.展开更多
Quantitative phase microscopy by digital holography is a good candidate for high-speed,high precision profilometry.Multi-wavelength optical phase unwrapping avoids difficulties of numerical unwrapping methods,and can ...Quantitative phase microscopy by digital holography is a good candidate for high-speed,high precision profilometry.Multi-wavelength optical phase unwrapping avoids difficulties of numerical unwrapping methods,and can generate surface topographic images with large axial range and high axial resolution.But the large axial range is accompanied by proportionately large noise.An iterative process utilizing holograms acquired with a series of wavelengths is shown to be effective in reducing the noise to a few micrometers even over the axial range of several millimeters.An alternate approach with shifting of illumination angle,instead of using multiple laser sources,provides multiple effective wavelengths from a single laser,greatly simplifying the system complexity and providing great flexibility in the wavelength selection.Experiments are performed demonstrating the basic processes of multi-wavelength digital holography(MWDH)and multi-angle digital holography(MADH).Example images are presented for surface profiles of various types of surface structures.The methods have potential for versatile,high performance surface profilometry,with compact optical system and straightforward processing algorithms.展开更多
The thin-film optical inverse problem has attracted a great deal of attention in science and industry,and is widely applied to optical coatings.However,as the number of layers increases,the time it takes to extract th...The thin-film optical inverse problem has attracted a great deal of attention in science and industry,and is widely applied to optical coatings.However,as the number of layers increases,the time it takes to extract the parameters of thin films drastically increases.Here,we introduce the idea of exploiting the structural similarity of all-optical neural networks and applied it to the optical inverse problem.We propose thin-film neural networks(TFNNs)to efficiently adjust all the parameters of multilayer thin films.To test the performance of TFNNs,we implemented a TFNN algorithm,and a reflectometer at normal incidence was built.Operating on multilayer thin films with 232 layers,it is shown that TFNNs can reduce the time consumed by parameter extraction,which barely increased with the number of layers compared with the conventional method.TFNNs were also used to design multilayer thin films to mimic the optical response of three types of cone cells in the human retina.The light passing through these multilayer thin films was then recorded as a colored photo.展开更多
We report variable shear interferometers employing liquid-crystal-based geometric-phase(GP)gratings.Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting ...We report variable shear interferometers employing liquid-crystal-based geometric-phase(GP)gratings.Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting capabilities in x-and y-direction and two axial shifts of the gratings to adjust the shear amount in x-and ydirection,i.e.,these systems need control of four axes mechanically.Here we show that the GP gratings combined with a pixelated polarization camera give instantaneous-phase shifting so that no mechanical movement is necessary to obtain phase shifts.Furthermore,we show that a single fixed shear with a rotational shear axis provides a more robust selection of shears while requiring the control of only one mechanical axis.We verify this statement using spatial domain and frequency domain criteria.We further show that the resolution of the reconstructed wavefield depends not only on the numerical aperture of the imaging system,the pixel size of the detector,or the spatial coherence of the source but also on the ability to determine the shear amount accurately.To improve this,we report a methodology to accurately detect the shear amounts using the second derivative of the autocorrelation function of the measured holograms,which further relaxes the requirements on mechanical stability.展开更多
Three-dimensional(3D)semiconductor devices can address the limitations of traditional two-dimensional(2D)devices by expanding the integration space in the vertical direction.A 3D NOT-AND(NAND)flash memory device is pr...Three-dimensional(3D)semiconductor devices can address the limitations of traditional two-dimensional(2D)devices by expanding the integration space in the vertical direction.A 3D NOT-AND(NAND)flash memory device is presently the most commercially successful 3D semiconductor device.It vertically stacks more than 100 semiconductor material layers to provide more storage capacity and better energy efficiency than 2D NAND flash memory devices.In the manufacturing of 3D NAND,accurate characterisation of layer-by-layer thickness is critical to prevent the production of defective devices due to non-uniformly deposited layers.To date,electron microscopes have been used in production facilities to characterise multilayer semiconductor devices by imaging cross-sections of samples.However,this approach is not suitable for total inspection because of the wafer-cutting procedure.Here,we propose a non-destructive method for thickness characterisation of multilayer semiconductor devices using optical spectral measurements and machine learning.For>200-layer oxide/nitride multilayer stacks,we show that each layer thickness can be non-destructively determined with an average of approximately 1.6Åroot-mean-square error.We also develop outlier detection models that can correctly classify normal and outlier devices.This is an important step towards the total inspection of ultra-high-density 3D NAND flash memory devices.It is expected to have a significant impact on the manufacturing of various multilayer and 3D devices.展开更多
文摘Helmet Mounted Displays(HMDs),such as in Virtual Reality(VR),Augmented Reality(AR),Mixed reality(MR),and Smart Glasses have the potential to revolutionize the way we live our private and professional lives,as in communicating,working,teaching and learning,shopping and getting entertained.Such HMD devices have to satisfy draconian requirements in weight,size,form factor,power,compute,wireless communication and of course display,imaging and sensing performances.We review in this paper the various optical technologies and architectures that have been developed in the past 10 years to provide adequate solutions for the drastic requirements of consumer HMDs,a market that has yet to become mature in the next years,unlike the existing enterprise and defense markets that have already adopted VR and AR headsets as practical tools to improve greatly effectiveness and productivity.We focus specifically our attention on the optical combiner element,a crucial element in Optical See-Through(OST)HMDs that combines the see-through scene with a world locked digital image.As for the technological platform,we chose optical waveguide combiners,although there is also a considerable effort today dedicated to free-space combiners.Flat and thin optics as in micro-optics,holographics,diffractives,metasurfaces and other nanostructured optical elements are key building blocks to achieve the target form factor.
基金National Research Foundation of Korea(NRF-2017R1A2B2011084).
文摘Near-eye displays are the main platform devices for many augmented reality(AR)and virtual reality(VR)applications.As a wearable device,a near-eye display should have a compact form factor and be lightweight.Furthermore,a large field of view and sufficient eyebox are crucial for immersive viewing conditions.Natural three-dimensional(3D)image presentation with proper focus cues is another requirement that enables a comfortable viewing experience and natural user interaction.Finally,in the case of AR,the device should allow for an optical see-through view of the real world.Conventional bulk optics and two-dimensional display panels exhibit clear limitations when implementing these requirements.Holographic techniques have been applied to near-eye displays in various aspects to overcome the limitations of conventional optics.The wavefront reconstruction capability of holographic techniques has been extensively exploited to develop optical see-through 3D holographic near-eye displays of glass-like form factors.In this article,the application of holographic techniques to AR and VR near-eye displays is reviewed.Various applications are introduced,such as static holographic optical components and dynamic holographic display devices.Current issues and recent progress are also reviewed,providing a comprehensive overview of holographic techniques that are applied to AR and VR near-eye displays.
基金Jianjian Wang would like to acknowledge the fellowship support received from the Alexander von Humboldt FoundationJianfu Zhang gratefully acknowledges the financial support for this research received from the National Natural Science Foundation of China(Grant No.51761145103)Yang Yang would like to acknowledge the financial support received from the Open Research Foundation of the State Key Laboratory of Digital Manufacturing Equipment and Technology,China(Grant No.DMETKF2020011).
文摘Structural coloration stemming from microstructure-induced light interference has been recognized as a promising surface colorizing technology,based on its potential in a wide array of applications,including high-definition displays,anti-counterfeiting,refractive index sensing,and photonic gas and vapor sensing.Vibration-assisted ultraprecision texturing using diamond tools has emerged as a high-efficiency and cost-effective machining method for colorizing metallic and ductile surfaces by creating near-wavelength microstructures.Although theoretically possible,it is extremely challenging to apply the vibration-assisted texturing technique directly to colorize non-metallic and brittle materials(e.g.,silicon and acrylic polymers)with high-quality,crack-free microstructures owing to the intrinsic brittleness of these materials.This study demonstrates the feasibility of direct texturing near-wavelength-scale gratings on brittle surfaces in the ductile regime to fabricate crack-free micro/nanostructures.The effects of tool vibration trajectories on the ductile-to-brittle transition phenomena were investigated to reveal the cutting mechanism of ductile-regime texturing and optimize the processing windows.Structural coloration on silicon and acrylic surfaces was successfully demonstrated by creating programmable and pixelated diffraction gratings with spacing values ranging from 0.75 to 4μm.
文摘Holography has evolved over its 70+years of history across widespread and diverse communities and locations.This has produced a complex language that is sometimes inconsistent,confusing,and incorrect,resulting in a general public that often appears widely confused and/or ignorant regarding what holograms actually are and are not.Today’s holographers employ many types of recording media to record all types of waves,such as light,sound,radar,and simulated waves,and for many different applications and purposes.This study examines the language of holography along with its origins,problems,and possible solutions,while recognizing that certain“errors”in the language are so embedded in society that simple and ideal fixes may be beyond reach.This leaves us with certain questions,as follows.First,can the correct language be restored and should we undertake the task,or are we stuck with every three-dimensional image being called a hologram?Is it our duty to better educate the public with a more useful and consistent language,or should we just go with the flow?In this work,beginning with the insights provided by the pioneers of the field,we attempt to set the stage for a more useful holography language and definitions,specialized so as to be understandable and usable by various audiences,including those interested in non-optical holography.Such knowledge can help the general public to take greater interest and enjoyment in holography;this would also be beneficial to those more involved in holography.Accordingly,this article offers advice for achieving this result.
基金the National Natural Science Foundation of China under Grants and National Key Research and Development Program of China#61935008,#61775078,#61905087,#61590930,and#2017YFB1104600 for support.
文摘Compound eyes(CEs)are advanced optical visual systems with distinct features of large view-fields,infinite depth of field,and dynamic imaging capability,revealing their significant potential in applications including robot vision,unmanned aerial vehicle detection,and medical diagnosis.Compared with macroscopic CEs,which primarily comprise multicamera arrays,compact integrated CEs have garnered significant attention because of their portability and possibility of flexible integration with microrobots and in-vivo medical facilities.To date,considerable effort has been devoted to this field,in which manufacturing technologies are vital to the development of artificial CEs(ACEs)capable of large field-of-view imaging,depth information collection,and threedimensional imaging.Challenges and opportunities exist for the practical application of advanced ACEs.This paper reviews state-of-the-art technologies for manufacturing ACEs,and then briefly summarises their potential applications in different fields.Finally,the current challenges and perspectives of ACEs are discussed.
基金This work was funded by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)under Germany’s Excellence Strategy 2082/1-390761711(Excellence Cluster“3D Matter Made to Order”).
文摘In recent years,multi-photon 3D laser printing has become a widely used tool for the fabrication of micro-and nanostructures for a large variety of applications.Typically,thorough sample characterisation is key for an efficient optimisation of the printing process.To date,three-dimensional microscopic inspection has usually been carried out on finished 3D printed microstructures,that is,using ex-situ approaches.In contrast,in-situ 3D characterization tools are desirable for quickly assessing the quality and properties of 3D printed microstructures.Along these lines,we present and characterise a Fourier-domain optical coherence tomography(FD-OCT)system that can be readily integrated into an existing 3D laser lithography setup.We demonstrate its capabilities by examining different 3D printed polymer microstructures immersed in a liquid photoresist.In such samples,local reflectivity arises from the(refractive-index)contrasts between the polymerised and non-polymerised regions.Thus,the refractive index of the printed material can be extracted.Furthermore,we demonstrate that the reflectivity of polymer-monomer transitions exhibits time-dependent behaviour after printing.Supported by transfer-matrix calculations,we explain this effect in terms of the time-dependent graded-index transition originating from monomer diffusion into the polymer matrix.Finally,we show exemplary 3D reconstructions of printed structures that can be readily compared with 3D computer designs.
文摘Tilted Wave Interferometry(TWI)is a measurement technique for fast and flexible interferometric testing of aspheres and freeform surfaces.The first version of the tilted wave principle was implemented in a Twyman-Green type setup with separate reference arm,which is intrinsically susceptible to environmentally induced phase disturbances.In this contribution we present the TWI in a new robust common-path(Fizeau)configuration.The implementation of the Tilted Wave Fizeau Interferometer requires a new approach in illumination,calibration and evaluation.Measurements of two aspheres and a freeform surface show the flexibility and also the increased stability in both phase raw data and surface measurements,which leads to a reduced repeatability up to a factor of three.The novel configuration significantly relaxes the tolerances of the imaging optics used in the interferometer.We demonstrate this using simulations on calibration measurements,where we see an improvement of one order of magnitude compared to the classical Twyman-Green TWI approach and the capability to compensate higher order error contributions on the used optics.
基金This work was supported by the Innovation and Technology Commission(ITC)(ITS/178/20FP)Centre for Perceptual and Interactive Intelligence(CPII)Ltd under the Innovation and Technology Fund.
文摘Three-dimensional(3D)printing,also known as additive manufacturing(AM),has undergone a phase of rapid development in the fabrication of customizable and high-precision parts.Thanks to the advancements in 3D printing technologies,it is now a reality to print cells,growth factors,and various biocompatible materials altogether into arbitrarily complex 3D scaffolds with high degree of structural and functional similarities to the native tissue environment.Additionally,with overpowering advantages in molding efficiency,resolution,and a wide selection of applicable materials,optical 3D printing methods have undoubtedly become the most suitable approach for scaffold fabrication in tissue engineering(TE).In this paper,we first provide a comprehensive and up-to-date review of current optical 3D printing methods for scaffold fabrication,including traditional extrusion-based processes,selective laser sintering,stereolithography,and two-photon polymerization etc.Specifically,we review the optical design,materials,and representative applications,followed by fabrication performance comparison.Important metrics include fabrication precision,rate,materials,and application scenarios.Finally,we summarize and compare the advantages and disadvantages of each technique to guide readers in the optics and TE communities to select the most fitting printing approach under different application scenarios.
基金support from the US National Institute on Deafness and Other Communication Disorders(NIDCD R01 DC016079)is gratefully acknowledgedsupport by the Center for Holographic Studies and Laser micro-mechaTronics(CHSLT)at WPI.
文摘The auditory system of mammals enables the perception of sound from our surrounding world.Containing some of the smallest bones in the body,the ear transduces complex acoustic signals with high-temporal sensitivity to complex mechanical vibrations with magnitudes as small as tens of picometers.Measurements of the shape and acoustically induced motions of different components of the ear are essential if we are to expand our understanding of hearing mechanisms,and also provide quantitative information for the development of numerical ear models that can be used to improve hearing protection,clinical diagnosis,and repair of damaged or diseased ears.We are developing digital holographic methods and instrumentation using an ultra-high speed camera to measure shape and acoustically-induced motions in the middle ear.Specifically we study the eardrum,the first structure of the middle ear which initializes the acoustic-mechanical transduction of sound for hearing.Our measurement system is capable of performing holographic measurement at rates up to 2.1 M frames per second.Two shape measurement modalities had previously been implemented into our holographic systems:(1)a multi-wavelength method with a wavelength tunable laser;and(2)a multi-angle illumination method with a single wavelength laser.In this paper,we present a third method using a miniaturized fringe projection system with a microelectromechanical system(MEMS)mirror.Further,we optimize the processing of large data sets of holographic displacement measurements using a vectorized Pearson's correlation algorithm.We validate and compare the shape and displacement measurements of our methodologies using a National Institute of Standards and Technology(NIST)traceable gauge and sound-activated latex membranes and human eardrums.
基金M.G.and Y.Z.acknowledge European Regional Development Fund/Wallonia region project(TERA4ALL)MG.and JF.V.acknowledge the support of ESA(GSTP project Contract No.22540/09/NL/SFe)EU(FP7 European project FANTOM ACP7-GA-2008-213457).
文摘Since its invention,holography has been mostly applied at visible wavelengths in a variety of applications.Specifically,non-destructive testing of manufactured objects was a driver for developing holographic methods and all related ones based on the speckle pattern recording.One substantial limitation of holographic non-destructive testing is the setup stability requirements directly related to the laser wavelength.This observation has driven some works for 15 years:developing holography at wavelengths much longer than visible ones.In this paper,we will first review researches carried out in the infrared,mostly digital holography at thermal infrared wavelengths around 10 micrometers.We will discuss the advantages of using such wavelengths and show different examples of applications.In nondestructive testing,large wavelengths allow using digital holography in perturbed environments on large objects and measure large deformations,typical of the aerospace domain.Other astonishing applications such as reconstructing scenes through smoke and flames were proposed.When moving further in the spectrum,digital holography with so-called Terahertz waves(up to 3 millimeters wavelength)has also been studied.The main advantage here is that these waves easily penetrate some materials.Therefore,one can envisage Terahertz digital holography to reconstruct the amplitude and phase of visually opaque objects.We review some cases in which Terahertz digital holography has shown potential in biomedical and industrial applications.We will also address some fundamental bottlenecks that prevent fully benefiting from the advantages of digital holography when increasing the wavelength.
文摘Silicon(Si)photonics is a disruptive technology on the fast track to revolutionise integrated photonics.An indispensable branch thereof,heterogeneous Si integration,has also evolved from a science project 15 years ago to a growing business and compelling research field today.We focus on the scope of Ⅲ-Ⅴ compound semiconductors heterogeneously integrated on Si substrates.The commercial success of massively produced integrated optical transceivers based on first-generation innovation is discussed.Then,we review a number of technological breakthroughs at the component and platform levels.In addition to the numerous new device performance records,our emphasis is on the rationale behind and the design principles underlying specific examples of materials and device integration.Finally,we offer perspectives on development trends catering to the increasing demand in many existing and emerging applications.
基金This work was financially supported by the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515110085)Key-Area Research and Development Program of Guangdong Province(No.2019B010924003)+2 种基金Shenzhen Hong Kong Innovation Circle Joint R&D Project(SGDX20190918105201704)Shenzhen Fundamental Research Program(No.GXWD20201231165807007-20200810113811001)Shenzhen Science and Technology Research Grant(JCYJ20170818085627903).
文摘One of the major challenges when fabricating high gamut colour-converted micro-light-emitting diodes(LEDs)displays is severe crosstalk effect among adjacent pixels because of the wide view-angle feature of micro-LED chips.In this study,potential factors that contribute to the crosstalk effect were systematically simulated.We observed that precisely filling the space between each micro-LED chip with a light blocking matrix(LBM)can be a promising solution to alleviate this risk.After careful investigations,a press-assisted moulding technique was demonstrated to be an effective approach of fabricating the LBM.Nevertheless,experimental observations further revealed that residual black LBM on the surface of micro-LEDs severely reduces the brightness,thereby compromising the display performance.This problem was successfully addressed by employing a plasma etching technique to efficiently extract the trapped light.Eventually,a top-emitting blue micro-LED-based backlight fine-moulded with a black LBM was developed and combined with red and green quantum dot colour-conversion layers for full-colour display.The colour gamut of our manufactured display prototype can cover as high as 122%that of the National Television Standards Committee.
文摘Over the past two decades, laser beam melting has emerged as the leading metal additive manufacturing process for producing small- and medium-size structures. However, a key obstacle for the application of this technique in industry is the lack of reliability and qualification mainly because of melt pool instabilities during the laser-powder interaction, which degrade the quality of the manufactured components. In this paper, we propose multi- wavelength digital holography as a proof of concept for in situ real-time investigation of the melt pool morphology. A two-wavelength digital holographic setup was co-axially implemented in a laser beam melting facility. The solidified aluminum tracks and melt pools during the manufacturing of 316L were obtained with full- field one-shot acquisitions at short exposure times and various scanning velocities. The evaluation of the complex coherence factor of digital holograms allowed the quality assessment of the phase reconstruction. The motion blur was analyzed by scanning the dynamic melt pool.
基金funded by Bundesministerium für Bildung und Forschung(Printoptics,Printfunction)Baden-Württemberg Stiftung gGmbH(Opterial)+2 种基金Ministerium für Wissenschaft,Forschung und Kunst Baden-Württemberg(funding line"RiSC")Vector-Stiftung(funding line"MINT Innovationen")the European Research Council(ComplexPlas,3DPrintedOptics)。
文摘The miniaturisation of spectroscopic measurement devices opens novel information channels for size critical applications such as endoscopy or consumer electronics.Computational spectrometers in the micrometre size range have been demonstrated,however,these are calibration sensitive and based on complex reconstruction algorithms.Herein we present an angle-insensitive 3D-printed miniature spectrometer with a direct separated spatial-spectral response.The spectrometer was fabricated via two-photon direct laser writing combined with a super-fine inkjet process.It has a volume of less than 100×100×300μm^(3).Its tailored and chirped high-frequency grating enables strongly dispersive behaviour.The miniature spectrometer features a wavelength range of 200 nm in the visible range from 490 nm to 690 nm.It has a spectral resolution of 9.2±1.1 nm at 532 nm and 17.8±1.7 nm at a wavelength of 633 nm.Printing this spectrometer directly onto camera sensors is feasible and can be replicated for use as a macro-pixel of a snapshot hyperspectral camera.
文摘Recording and(computational)processing of complex wave fields offer a vast realm of new methods for optical 3D metrology.We discuss fundamental similarities and differences between holographic surface topography measurement and non-holographic principles,such as triangulation,classical interferometry,rough surface interferometry and slope measuring methods.Key features are the physical origin of the ultimate uncertainty limit and how the topographic information is encoded and decoded.Besides the theoretical insight,the discussion will help optical metrologists to determine if their measurement results could be improved or have already hit the ultimate limit of what physics allows.
基金funded by Australian Research Council IH130100008“Industrial Transformation Research Hub for Transforming Australia's Manufacturing Industry through High Value Additive Manufacturing”.
文摘Laser powder bed fusion(LPBF)is a timely important additive manufacturing technique that offers many opportunities for fabricating three-dimensional complex shaped components at a high resolution with short lead times.This technique has been extensively employed in manufacturing Ti-6Al-4V parts for aerospace and biomedical applications.However,many challenges,including poor surface quality,porosity,anisotropy in microstructure and property,and difficulty in tailoring microstructure,still exist.In this paper,we review the recent progress in post-process treatment and its influence on the microstructure evolution and material performance,including tensile,fatigue,fracture toughness,creep,and corrosion properties.The contradictions in simultaneously achieving high strength/ductility and strength/fracture toughness/creep resistance have been identified.Furthermore,research gaps in understanding the effects of the emerging bi-modal microstructure on fatigue properties and fracture toughness require further investigation.
文摘Quantitative phase microscopy by digital holography is a good candidate for high-speed,high precision profilometry.Multi-wavelength optical phase unwrapping avoids difficulties of numerical unwrapping methods,and can generate surface topographic images with large axial range and high axial resolution.But the large axial range is accompanied by proportionately large noise.An iterative process utilizing holograms acquired with a series of wavelengths is shown to be effective in reducing the noise to a few micrometers even over the axial range of several millimeters.An alternate approach with shifting of illumination angle,instead of using multiple laser sources,provides multiple effective wavelengths from a single laser,greatly simplifying the system complexity and providing great flexibility in the wavelength selection.Experiments are performed demonstrating the basic processes of multi-wavelength digital holography(MWDH)and multi-angle digital holography(MADH).Example images are presented for surface profiles of various types of surface structures.The methods have potential for versatile,high performance surface profilometry,with compact optical system and straightforward processing algorithms.
基金This work was supported by the China National Key Basic Research Program(2018YFA0306201)the National Science Foundation of China(11774063,11727811,and 91963212)+1 种基金A.C.was supported by the Shanghai Rising-Star Program(20QR1402200)L.S.was further supported by the Science and Technology Commission of Shanghai Municipality(19XD143600,2019SHZDZX01,19DZ2253000,20501110500).
文摘The thin-film optical inverse problem has attracted a great deal of attention in science and industry,and is widely applied to optical coatings.However,as the number of layers increases,the time it takes to extract the parameters of thin films drastically increases.Here,we introduce the idea of exploiting the structural similarity of all-optical neural networks and applied it to the optical inverse problem.We propose thin-film neural networks(TFNNs)to efficiently adjust all the parameters of multilayer thin films.To test the performance of TFNNs,we implemented a TFNN algorithm,and a reflectometer at normal incidence was built.Operating on multilayer thin films with 232 layers,it is shown that TFNNs can reduce the time consumed by parameter extraction,which barely increased with the number of layers compared with the conventional method.TFNNs were also used to design multilayer thin films to mimic the optical response of three types of cone cells in the human retina.The light passing through these multilayer thin films was then recorded as a colored photo.
基金support and funding from the Center for Precision Metrology(CPM)。
文摘We report variable shear interferometers employing liquid-crystal-based geometric-phase(GP)gratings.Conventional grating-based shear interferometers require two lateral shifts of the gratings to enable phase-shifting capabilities in x-and y-direction and two axial shifts of the gratings to adjust the shear amount in x-and ydirection,i.e.,these systems need control of four axes mechanically.Here we show that the GP gratings combined with a pixelated polarization camera give instantaneous-phase shifting so that no mechanical movement is necessary to obtain phase shifts.Furthermore,we show that a single fixed shear with a rotational shear axis provides a more robust selection of shears while requiring the control of only one mechanical axis.We verify this statement using spatial domain and frequency domain criteria.We further show that the resolution of the reconstructed wavefield depends not only on the numerical aperture of the imaging system,the pixel size of the detector,or the spatial coherence of the source but also on the ability to determine the shear amount accurately.To improve this,we report a methodology to accurately detect the shear amounts using the second derivative of the autocorrelation function of the measured holograms,which further relaxes the requirements on mechanical stability.
基金supported by the Industry–Academia Cooperation Program of Samsung Electronics Co.,Ltd.
文摘Three-dimensional(3D)semiconductor devices can address the limitations of traditional two-dimensional(2D)devices by expanding the integration space in the vertical direction.A 3D NOT-AND(NAND)flash memory device is presently the most commercially successful 3D semiconductor device.It vertically stacks more than 100 semiconductor material layers to provide more storage capacity and better energy efficiency than 2D NAND flash memory devices.In the manufacturing of 3D NAND,accurate characterisation of layer-by-layer thickness is critical to prevent the production of defective devices due to non-uniformly deposited layers.To date,electron microscopes have been used in production facilities to characterise multilayer semiconductor devices by imaging cross-sections of samples.However,this approach is not suitable for total inspection because of the wafer-cutting procedure.Here,we propose a non-destructive method for thickness characterisation of multilayer semiconductor devices using optical spectral measurements and machine learning.For>200-layer oxide/nitride multilayer stacks,we show that each layer thickness can be non-destructively determined with an average of approximately 1.6Åroot-mean-square error.We also develop outlier detection models that can correctly classify normal and outlier devices.This is an important step towards the total inspection of ultra-high-density 3D NAND flash memory devices.It is expected to have a significant impact on the manufacturing of various multilayer and 3D devices.
