Recent Progress in Heterogeneous III-V-on-Silicon Photonic Integration
Di Liang, John E. Bowers
Published Published online: 24 February 2021,  doi: 10.37188/lam.2021.005
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.
[HTML FullText](9328) [PDF 7935KB](1768)
3D-printed miniature spectrometer for the visible range with a 100 × 100 μm2 footprint
Andrea Toulouse, Johannes Drozella, Simon Thiele, Harald Giessen, Alois Herkommer
Published Published online: 04 February 2021,  doi: 10.37188/lam.2021.002
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 × 300 μm3. 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.
[HTML FullText](9266) [PDF 9794KB](1203)
Holography, and the future of 3D display
Pierre-Alexandre Blanche
Published Published online: 20 December 2021,  doi: 10.37188/lam.2021.028
The pioneers of holography, Gabor, Leith, Upatnieks, and Denisyuk, predicted very early that the ultimate 3D display will be based on this technique. This conviction was rooted on the fact that holography is the only approach that can render all optical cues interpreted by the human visual system. Holographic 3D displays have been a dream chased after for many years, facing challenges on all fronts: computation, transmission, and rendering. With numbers such as 6.6 × 1015 flops required for calculations, 3 × 1015 b/s data rates, and 1.6 × 1012 phase pixels, the task has been daunting. This article is reviewing the recent accomplishments made in the field of holographic 3D display. Specifically, the new developments in machine learning and neural network algorithms demonstrating that computer-generated holograms approach real-time processing. A section also discuss the problem of data transmission that can arguably be solved using clever compression algorithms and optical fiber transmission lines. Finally, we introduce the last obstacle to holographic 3D display, which is is the rendering hardware. However, there is no further mystery. With larger and faster spatial light modulators (SLMs), holographic projection systems are constantly improving. The pixel count on liquid crystal on silicon (LCoS) as well as microelectromechanical systems (MEMS) phase displays is increasing by the millions, and new photonic integrated circuit phased arrays are achieving real progress. It is only a matter of time for these systems to leave the laboratory and enter the consumer world. The future of 3D displays is holographic, and it is happening now.
[HTML FullText](8867) [PDF 6406KB](1405)
Multi-material multi-photon 3D laser micro- and nanoprinting
Liang Yang, Frederik Mayer, Uwe H. F. Bunz, Eva Blasco, Martin Wegener
Published Published online: 21 June 2021,  doi: 10.37188/lam.2021.017
Three-dimensional (3D) laser micro- and nanoprinting based upon multi-photon absorption has made its way from early scientific discovery to industrial manufacturing processes, e.g., for advanced microoptical components. However, so far, most realized 3D architectures are composed of only a single polymeric material. Here, we review 3D printing of multi-materials on the nano- and microscale. We start with material properties that have been realized, using multi-photon photoresists. Printed materials include bulk polymers, conductive polymers, metals, nanoporous polymers, silica glass, chalcogenide glasses, inorganic single crystals, natural polymers, stimuli-responsive materials, and polymer composites. Next, we review manual and automated processes achieving dissimilar material properties in a single 3D structure by sequentially photo-exposing multiple photoresists as 3D analogs of 2D multicolor printing. Instructive examples from biology, optics, mechanics, and electronics are discussed. An emerging approach – without counterpart in 2D graphical printing – prints 3D structures combining dissimilar material properties in one 3D structure by using only a single photoresist. A controlled stimulus applied during the 3D printing process defines and determines material properties on the voxel level. Change of laser power and/or wavelength, or application of quasi-static electric fields allow for the seamless manipulation of desired materials properties.
[HTML FullText](9243) [PDF 6851KB](1439)
Crystal plane engineering of MAPbI3 in epoxy-based materials for superior gamma-ray shielding performance
Kai Cui, Yang Li, Wenjing Wei, Qianqian Teng, Tianyu Zhang, Jinzhu Wu, Hongjun Kang, Wei Qin, Xiaohong Wu
Accepted  doi: 10.37188/lam.2022.051

The rapid development of the aerospace and nuclear industries is accompanied by increased exposure to high-energy ionising radiation. Thus, the performance of radiation shielding materials needs to be improved to extend the service life of detectors and ensure the safety of personnel. The development of novel lightweight materials with high electron density has therefore become urgent to alleviate radiation risks. In this work, new MAPbI3/epoxy (CH3NH3PbI3/epoxy) composites were prepared via a crystal plane engineering strategy. These composites delivered excellent radiation shielding performance against 59.5 keV gamma rays. A high linear attenuation coefficient (1.887 cm−1) and mass attenuation coefficient (1.352 cm2 g−1) were achieved for a representative MAPbI3/epoxy composite, which was 10 times higher than that of the epoxy. Theoretical calculations indicate that the electron density of MAPbI3/epoxy composites significantly increases when the content ratio of the (110) plane in MAPbI3 increases. As a result, the chances of collision between the incident gamma rays and electrons in the MAPbI3/epoxy composites were enhanced. The present work provides a novel strategy for designing and developing high-efficiency radiation shielding materials.

Tip-induced bond weakening, tilting, and hopping of a single CO molecule on Cu(100)
Xiaoru Dong, Ben Yang, Rui Zhu, Ruipu Wang, Yang Zhang, et al.
Published Published online: 01 December 2022,  doi: 10.37188/lam.2022.052

The interaction between a probing tip and an adsorbed molecule can significantly impact the molecular chemical structure and even induce its motion on the surface. In this study, the tip-induced bond weakening, tilting, and hopping processes of a single molecule were investigated by sub-nanometre resolved tip-enhanced Raman spectroscopy (TERS). We used single carbon monoxide (CO) molecules adsorbed on the Cu (100) surface as a model system for the investigation. The vibrational frequency of the C−O stretching mode is always redshifted as the tip approaches, revealing the weakening of the C−O bond owing to tip−molecule interactions. Further analyses of both the vibrational Stark effect and TERS imaging patterns suggest a delicate tilting phenomenon of the adsorbed CO molecule on Cu(100), which eventually leads to lateral hopping of the molecule. While a tilting orientation is found toward the hollow site along the [110] direction of the Cu(100) surface, the hopping event is more likely to proceed via the bridge site to the nearest Cu neighbour along the [100] or [010] direction. Our results provide deep insights into the microscopic mechanisms of tip−molecule interactions and tip-induced molecular motions on surfaces at the single-bond level.

[HTML FullText](31) [PDF 4012KB](80)
Mid-infrared all-optical modulators based on an acetylene-filled hollow-core fiber
Kaiyuan Zheng, Shoulin Jiang, Feifan Chen, Yan Zhao, Shoufei Gao, et al.
Published Published online: 17 November 2022,  doi: 10.37188/lam.2022.050

We report all-optical mid-infrared phase and intensity modulators based on the photo-thermal effect in an acetylene-filled anti-resonant hollow-core fiber. Optical absorption of the control beam promotes the gas molecules to a higher energy level, which induces localized heating through non-radiative relaxation and modulates the refractive index of the gas material and hence the accumulated phase of the signal beam propagating through the hollow-core fiber. By modulating the intensity of the control beam, the phase of the signal beam is modulated accordingly. By use of a 1.53 µm near-infrared control beam, all-optical phase modulation up to 2.2π rad is experimentally demonstrated at the signal wavelength of 3.35 µm. With the phase modulator placed in one arm of a Mach-Zehnder interferometer, intensity modulation with on-off ratio of 25 dB is achieved. The gas-filled hollow-core-fiber modulators could operate over an ultra-broad wavelength band from near- to mid-infrared and have promising application in mid-infrared photonic systems.

[HTML FullText](406) [PDF 4242KB](118)
Tilted Wave Fizeau Interferometer for flexible and robust asphere and freeform testing
Christian Schober, Rolf Beisswanger, Antonia Gronle, Christof Pruss, Wolfgang Osten
Published Published online: 28 October 2022,  doi: 10.37188/lam.2022.048

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.

[HTML FullText](877) [PDF 5708KB](375)
FEM-based modeling of microsphere-enhanced interferometry
Tobias Pahl, Lucie Hüser, Sebastian Hagemeier, Peter Lehmann
Published Published online: 28 October 2022,  doi: 10.37188/lam.2022.049

To improve the lateral resolution in microscopic imaging, microspheres are placed close to the object’ s surface in order to support the imaging process by optical near-field information. Although microsphere-assisted measurements are part of various recent studies, no generally accepted explanation for the effect of microspheres exists. Photonic nanojets, enhancement of the numerical aperture, whispering-gallery modes and evanescent waves are usually named reasons in context with microspheres, though none of these effects is proven to be decisive for the resolution enhancement. We present a simulation model of the complete microscopic imaging process of microsphere-enhanced interference microscopy including a rigorous treatment of the light scattering process at the surface of the specimen. The model consideres objective lenses of high numerical aperture providing 3D conical illumination and imaging. The enhanced resolution and magnification by the microsphere is analyzed with respect to the numerical aperture of the objective lenses. Further, we give a criterion for the achievable resolution and demonstrate that a local enhancement of the numerical aperture is the most likely reason for the resolution enhancement.

[HTML FullText](591) [PDF 4249KB](186)
High-speed, large-area and high-precision fabrication of aspheric micro-lens array based on 12-bit direct laser writing lithography
Shiyi Luan, Fei Peng, Guoxing Zheng, Chengqun Gui, Yi Song, et al.
Published Published online: 19 September 2022,  doi: 10.37188/lam.2022.047

Aspheric micro-lens array (AMLA), featured with low dispersion and diffraction-limited imaging quality, plays an important role in advanced optical imaging. Ideally, the fabrication of commercially applicable AMLAs should feature low cost, high precision, large area and high speed. However, these criteria have been achieved only partially with conventional fabrication process. Herein, we demonstrate the fabrication and characterization of AMLAs based on 12-bit direct laser writing lithography, which exhibits a high fabrication speed, large area, perfect lens shape control via a three-dimensional optical proximity correction and average surface roughness lower than 6 nm. In particular, the AMLAs can be flexibly designed with customized filling factor and arbitrary off-axis operation for each single micro-lens, and the proposed pattern transfer approach with polydimethylsiloxane (PDMS) suggests a low-cost way for mass manufacturing. An auto-stereoscopic-display flexible thin film with excellent display effect has been prepared by using above technology, which exhibits a new way to provide flexible auto-stereoscopic-display at low cost. In brief, the demonstrated fabrication of AMLAs based on direct laser writing lithography reduce the complexity of AMLA fabrication while significantly increasing their performance, suggesting a new route for high-quality three-dimentional optical manufacturing towards simplified fabrication process, high precision and large scale.

[HTML FullText](2091) [PDF 5335KB](566)
A quasi-3D Fano resonance cavity on optical fiber end-facet for high signal-to-noise ratio dip-and-read surface plasmon sensing
Xiaqing Sun, Zeyu Lei, Hao Zhong, Chenjia He, Sihang Liu, et al.
Published Published online: 18 September 2022,  doi: 10.37188/lam.2022.046

Surface plasmon devices mounted at the end-facets of optical fibers are appealing candidates for rapid and point-of-care sensing applications, by offering a special dip-and-read operation mode. At present, these devices’ noise-equivalent limits-of-detection lag far behind the free-space counterparts, leaving them incapable of most biosensing applications. Here we report a quasi-3D Fano resonance cavity and its fabrication method to fundamentally improve the quality factor and coupling efficiency for fiber-coupled surface plasmon resonance. In this device, the Fano resonance combines the high coupling efficiency of a Fabry-Pérot etalon and the high quality factor resonance of a plasmonic crystal cavity. The quasi-3D device was fabricated on a planar substrate and transferred to a single-mode fiber end-facet, which requires a low-adhesion yet surface-plasmon-tunneling interface between the device and the planar substrate. Such an interface was realized with a nanocap-slit unit structure, of which the plasmonic crystal was consisted. A noise-equivalent limit of detection of ~ 10-7 RIU was experimentally obtained, allowing bovine serum albumin physical adsorption to be distinguished at ng mL-1 level concentrations. Therefore, breaking through the long-standing signal-to-noise ratio bottleneck, this work makes fiber end-facet surface plasmon devices into one of high sensitivity label-free sensing technologies. At the same time, it provides an enabling top-down fabrication technology for making 3D plasmonic structures on fiber end-facets at the nanometer scale.

[HTML FullText](1794) [PDF 4330KB](552)
‘Plug-and-play’ plasmonic metafibers for ultrafast fibre lasers
Lei Zhang, Huiru Zhang, Ni Tang, Xiren Chen, Fengjiang Liu, et al.
Published Published online: 02 September 2022,  doi: 10.37188/lam.2022.045
Metafibers expand the functionalities of conventional optical fibres to unprecedented nanoscale light manipulations by integrating metasurfaces on the fibre tips, becoming an emerging light-coupling platform for both the nanoscience and fibre optics communities. Current metafibers remain proof-of-concept demonstrations that mostly explore isolated bare fibres owing to the lack of standard interfaces with universal fibre networks. Here, we develop methodologies for fabricating well-defined plasmonic metasurfaces directly on the end facets of commercial single -mode fibre jumpers using standard planar technologies and provide the first demonstration of their practical applications in the nonlinear plasmonic regime. Featuring plug-and-play connections with fibre circuitry and arbitrary metasurface landscapes, the metafibers with tunable plasmonic resonances are implemented into fibre laser cavities, yielding all-fibre sub-picosecond (minimum 513 fs) soliton mode locked lasers at optical wavelengths of 1.5 μm and 2 μm, demonstrating their unusual polarimetric nonlinear transfer functions and superior saturation absorption responses. The nanofabrication process flow is compatible with existing cleanroom technologies, offering metafibers an avenue to become a regular member of functionalised fibre components. This work paves the way toward the next generation of ultrafast lasers, optical frequency combs, and ultracompact ‘all-in-fibre’ optical systems.
[HTML FullText](1464) [PDF 5761KB](672)
Integrated self-referencing single shot digital holographic microscope and optical tweezer
Subhash Utadiya, Sachin Joshi, Nimit Patel, Chetna Patel, Mugdha Joglekar, et al.
Published Published online: 04 August 2022,  doi: 10.37188/lam.2022.037
Digital holographic microscopy is a single-shot technique for quantitative phase imaging of samples, yielding thickness profiles of phase objects. It provides sample features based on their morphology, leading to their classification and identification. However, observing samples, especially cells, in fluids using holographic microscopes is difficult without immobilizing the object. Optical tweezers can be used for sample immobilization in fluids. The present manuscript provides an overview of our ongoing work on the development of a compact, low-cost microscopy system for digital holographic imaging of optically trapped samples. Integration of digital holographic microscopy system with tweezers is realized by using the optical pickup unit extracted from DVD burners to trap microsamples, which are then holographically imaged using a highly compact self-referencing interferometer along with a low-cost, in-house developed quadrant photodiode, providing morphological and spectral information of trapped particles. The developed integrated module was tested using polystyrene microspheres as well as human erythrocytes. The investigated system offers a multitude of sample features, including physical and mechanical parameters and corner frequency information of the sample. These features were used for sample classification. The proposed technique has vast potential in opening up new avenues for low-cost, digital holographic imaging and analysis of immobilized samples in fluids and their classification.
[HTML FullText](1461) [PDF 4502KB](495)
Towards in-situ diagnostics of multi-photon 3D laser printing using optical coherence tomography
Roman Zvagelsky, Frederik Mayer, Dominik Beutel, Carsten Rockstuhl, Guillaume Gomard, et al.
Published Published online: 03 August 2022,  doi: 10.37188/lam.2022.039
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.
[HTML FullText](2243) [PDF 8136KB](466)
Design of broadband terahertz vector and vortex beams: II. Holographic assessment
Nikolay V. Petrov, Bogdan Sokolenko, Maksim S. Kulya, Andrei Gorodetsky, Aleksey V. Chernykh
Published Published online: 02 August 2022,  doi: 10.37188/lam.2022.044
In this paper, we demonstrate the capabilities of the terahertz pulse time-domain holography in visualisation, simulation, and assessment of broadband THz vortex beam formation dynamics upon its shaping by elements of beam converter, and further propagation and manipulation. By adding Jones matrix formalism to describe broadband optical elements, we highlight the differences in the spatio-spectral and spatio-temporal structure of the formed vortex and vector beams dependence on the modulator used and visualise their modal features. The influence of diffraction field structure from each element in the broadband vortex modulator is revealed in numerical simulation and the formed beams are analysed against the simplified Laguerre-Gaussian beam model.
[HTML FullText](1314) [PDF 5642KB](369)
Miniaturization of a coherent monocular structured illumination system for future combination with digital holography
Andreas Walter Stark, Eugene Wong, Holger Babovsky, Christian Franke, Richard Kowarschik
Published Published online: 15 July 2022,  doi: 10.37188/lam.2022.034
Holographic and 3D-measurement processes are an often-used tool in industry, medicine, and scientific applications. While small deviations of objects can be visualized by holographic means with high accuracy, optical systems with active structured illumination are a reliable source of absolute 3D-information in these fields. The combination of digital holography with structured illumination allows to simultaneously measure deformations and absolute 3D coordinates but also requires coherent light and has already been demonstrated in principle with a stereo camera setup. Multi-camera systems are limited to certain setup sizes given by the volume and distance of the detectors. Reducing the system to a one-camera (monocular) setup reduces space and acquisition costs. By using a multi-aperture illumination source an extremely high projection rate could be realized and reduced to a monocular approach with a novel voxel-calibration technique, while the projection system itself still requires a large amount of space. In this paper we present a miniaturized, monocular 3D-measurement system that works with repeatable, coherent speckles, generated by a fiber-coupled laser whose light was distributed by a fiber-switch to a diffuser plate connected with a measurement-head, also including a camera. By addressing different fibers through the switch, varying but repeatable patterns are generated. The size of the device (diameter < 3 cm) is now mainly limited by the volume of the camera. A first 3D-reconstruction of an object and an outlook for a combination of this system with digital holography is given, allowing absolute 3D-coordinates and relative deviations of object points to be measured simultaneously.
[HTML FullText](1112) [PDF 6224KB](300)
Material removal model of magnetorheological finishing based on dense granular flow theory
Yang Bai, Xuejun Zhang, Chao Yang, Longxiang Li, Xiao Luo
Published Published online: 06 July 2022,  doi: 10.37188/lam.2022.041
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.
[HTML FullText](1723) [PDF 3254KB](236)
Hybrid multimode - multicore fibre based holographic endoscope for deep-tissue neurophotonics
Yang Du, Sergey Turtaev, Ivo T Leite, Adrian Lorenz, Jens Kobelke, et al.
Published Published online: 21 June 2022,  doi: 10.37188/lam.2022.029
In-vivo microendoscopy in animal models became a groundbreaking technique in neuroscience that rapidly expands our understanding of the brain. Emerging hair-thin endoscopes based on multimode fibres are now opening up the prospect of ultra-minimally invasive neuroimaging of deeply located brain structures. Complementing these advancements with methods of functional imaging and optogenetics, as well as extending its applicability to awake and motile animals constitute the most pressing challenges for this technology. Here we demonstrate a novel fibre design capable of both, high-resolution imaging in immobilised animals and bending-resilient optical addressing of neurons in motile animals. The optimised refractive index profile and the probe structure allowed reaching a spatial resolution of 2 μm across a 230 μm field of view for the initial layout of the fibre. Simultaneously, the fibre exhibits negligible cross-talk between individual inner-cores during fibre deformation. This work provides a technological solution for imaging-assisted spatially selective photo-activation and activity monitoring in awake and freely moving animal models.
[HTML FullText](1802) [PDF 4744KB](414)
Simulation-based design optimization of the holographic wavefront sensor in closed-loop adaptive optics
Andreas Zepp, Szymon Gladysz, Karin Stein, Wolfgang Osten
Published Published online: 21 June 2022,  doi: 10.37188/lam.2022.027
Adaptive optics systems are used to compensate for wavefront distortions introduced by atmospheric turbulence. The distortions are corrected by an adaptable device, normally a deformable mirror. The control signal of the mirror is based on the measurement delivered by a wavefront sensor. Relevant characteristics of the wavefront sensor are the measurement accuracy, the achievable measurement speed and the robustness against scintillation. The modal holographic wavefront sensor can theoretically provide the highest bandwidth compared to other state of the art wavefront sensors and it is robust against scintillation effects. However, the measurement accuracy suffers from crosstalk effects between different aberration modes that are present in the wavefront. In this paper we evaluate whether the sensor can be used effectively in a closed-loop AO system under realistic turbulence conditions. We simulate realistic optical turbulence represented by more than 2500 aberration modes and take different signal-to-noise ratios into account. We determine the performance of a closed-loop AO system based on the holographic sensor. To counter the crosstalk effects, careful choice of the key design parameters of the sensor is necessary. Therefore, we apply an optimization method to find the best sensor design for maximizing the measurement accuracy. By modifying this method to take the changing effective turbulence conditions during closed-loop operation into account, we can improve the performance of the system, especially for demanding signal-to-noise-ratios, even more. Finally, we propose to implement multiple holographic wavefront sensors without the use of additional hardware, to perform multiple measurement at the same time. We show that the measurement accuracy of the sensor and with this the wavefront flatness can be increased significantly without reducing the bandwidth of the adaptive optics system.
[HTML FullText](1120) [PDF 7784KB](440)
Parallax limitations in digital holography: a phase space approach
Ulf Schnars, Claas Falldorf
Published Published online: 20 June 2022,  doi: 10.37188/lam.2022.028
The viewing direction in Digital Holography can be varied if different parts of a hologram are reconstructed. In this article parallax limitations are discussed using the phase space formalism. An equation for the parallax angle is derived with this formalism from simple geometric quantities. The result is discussed in terms of pixel size and pixel number of the image sensor. Change of perspective is demonstrated experimentally by two numerical hologram reconstructions from different parts of one single digital hologram.
[HTML FullText](1039) [PDF 4676KB](255)
The application of digital holography for accurate three-dimensional localisation of mosquito-bednet interaction
Matthew L Hall, Katherine Gleave, Angela Hughes, Philip J McCall, Catherine E Towers, et al.
Published Published online: 09 June 2022,  doi: 10.37188/lam.2022.020
Understanding mosquito interaction with long-lasting insecticidal bednets is crucial in the development of more effective intervention methods to protect humans from malaria transmission. As such, a 240 × 240 × 1000 mm laboratory setup for the in-line recording of digital holograms and subsequent in-focus reconstruction and 3D localisation of mosquitoes is presented. Simple bednet background removal methods are used to accurately localise a mosquito obscured by a bednet in 3D coordinates. Simulations and physical data demonstrate that this method is suitable for mosquitoes positioned 3−1000 mm behind a bednet. A novel post-processing technique, involving a cascade-correlation of a Tamura of Intensity focus metric extracted from digitally reconstructed scenes, accurately localises mosquitoes positioned 35−100 mm behind a bednet from a single digital hologram. The result of this study is a scalable digital holographic methodology to examine mosquito-bednet interaction in 3D at a level of accuracy previously only seen in 2D imaging of mosquitoes in a much smaller volume.
[HTML FullText](1361) [PDF 4220KB](403)
Alleviating the crosstalk effect via a fine-moulded light-blocking matrix for colour-converted micro-LED display with a 122% NTSC gamut
Yongming Yin, Zhiping Hu, Muhammad Umair Ali, Miao Duan, Yongwei Wu, et al.
Published Published online: 06 June 2022,  doi: 10.37188/lam.2022.036
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.
[HTML FullText](2030) [PDF 3339KB](476)
Integrated binary hologram to monitor cargo release from a drug-eluting film
Arkady S. Abdurashitov, Pavel I. Proshin, Valery V. Tuchin, Gleb B. Sukhorukov
Published Published online: 19 May 2022,  doi: 10.37188/lam.2022.030
Nowadays, holography translates from a pure technical tool for recording the phase and amplitude of the light wave to a widely applicable research-based method. Holographic devices are used for security enhancement, entertainment, 3D display technologies and augmented reality. Binary computer-generated holograms (amplitude or phase-based) are of specific interest. They are easy to compute and their manufacturing methods are fast and robust. In this work, a method of manufacturing amplitude-only binary holograms out of biopolymers films is proposed. Opaque cargo bits made out of different bioactive substances (antibiotics, dyes, etc.) absorb or scatter specific parts of the incoming light wave. Cargo release was conducted by submerging the produced holograms into the aqueous solution at specific pH and temperature levels. Drug elution from the film was traced out by the numerical analysis of the far-field diffraction pattern, which otherwise could only be measured post-factum using sophisticated spectroscopic or chromatography devices. This approach broadens the application of general holography over to the field of biomedical research relevant to quantitative monitoring of the drug elution.
[HTML FullText](1103) [PDF 4592KB](285)
In-process monitoring in laser grooving with line-shaped femtosecond pulses using optical coherence tomography
Satoshi Hasegawa, Masatoshi Fujimoto, Toshihisa Atsumi, Yoshio Hayasaki
Published Published online: 17 May 2022,  doi: 10.37188/lam.2022.033
A line-shaped beam is useful for increasing the processing speed in laser grooving and scribing. In laser grooving, depth control of the processed structure is important for performing precise processing. In this paper, in-process monitoring of the depth of a structure formed by femtosecond laser processing with a line-shaped beam using swept-source optical coherence tomography (SS-OCT) was demonstrated. In the evaluation of the SS-OCT system, the depth resolution, measurement accuracy, and axial measurable range were 15.8 μm, ±2.5 μm and 5.3 mm, respectively. In laser grooving, the structural shape and the distribution of deposited debris were successfully monitored. The measured depth agreed well with the depth obtained using a laser confocal microscope. The proposed method will be effective for precise laser processing with feedback control of the laser parameters based on in-process monitoring of the processed structure.
[HTML FullText](1826) [PDF 4725KB](396)
Additive manufacturing of high aspect-ratio structures with self-focusing photopolymerization
Mingyu Yang, Kavin Kowsari, Nia O. Myrie, Daniela Espinosa-Hoyos, Anna Jagielska, et al.
Published Published online: 25 August 2022,  doi: 10.37188/lam.2022.032
Photocrosslinkable polymers have been exploited to attain impressive advantages in printing freestanding, micrometer-scale, mechanically compliant features. However, a more integrated understanding of both the polymer photochemistry and the microfabrication processes could enable new strategic design avenues, unlocking far-reaching applications of the light-based modality of additive manufacturing. One promising approach for achieving high-aspect-ratio structures is to leverage the phenomenon of light self-trapping during the photopolymerization process. In this review, we discuss the design of materials that facilitate this optical behavior, the computational modeling and practical processing considerations to achieve high aspect-ratio structures, and the range of applications that can benefit from architectures fabricated using light self-trapping—especially those demanding free-standing structures and materials of stiffnesses relevant in biological applications. Coupled interactions exist among material attributes, including polymer composition, and processing parameters such as light intensity. We identify strong opportunities for predictive design of both the material and the process. Overall, this perspective describes the wide range of existing polymers and additive manufacturing approaches, and highlights various future directions to enable constructs with new complexities and functionalities through the development of next-generation photocrosslinkable materials and micromanufacturing methods.
[HTML FullText](904) [PDF 9278KB](842)
Design of broadband terahertz vector and vortex beams: I. Review of materials and components
Nikolay V. Petrov, Bogdan Sokolenko, Maksim S. Kulya, Andrei Gorodetsky, Aleksey V. Chernykh
Published Published online: 02 August 2022,  doi: 10.37188/lam.2022.043
In this paper, we review the existing approaches for vortex and vector beam shaping and generation in the terahertz frequency range. The particular focus of this review is on the possibility of homogeneous topological charge formation in the ultra-wide spectral interval inherent to ultrashort terahertz pulses. We review the available materials and components, analyse proposed and potentially possible solutions for broadband terahertz vortex and vector beam shaping, compare all developed approaches, and put forward a unified concept for constructing passive shapers of such beams from the existing component base.
[HTML FullText](1148) [PDF 5305KB](420)
Holographic optics in planar optical systems for next generation small form factor mixed reality headsets
Bernard C. Kress, Maria Pace
Published Published online: 02 August 2022,  doi: 10.37188/lam.2022.042
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.
[HTML FullText](3109) [PDF 6855KB](846)
Compression strategies for digital holograms in biomedical and multimedia applications
Peter Schelkens, Ayyoub Ahar, Antonin Gilles, Raees Kizhakkumkara Muhamad, Thomas J. Naughton, et al.
Published Published online: 20 July 2022,  doi: 10.37188/lam.2022.040
While 60 years of successful application of holography is celebrated in this special issue, efficient representation and compression of holographic data has received relatively little attention in research. Notwithstanding this observation, and particularly due to the digitization that is also penetrating the holographic domain, interest is growing on how to efficiently compress holographic data such that interactive exchange of content, as well as digital storage can be facilitated proficiently. This is a particular challenge, not only because of its interferometric nature and the various representation formats, but also the often extremely large data volumes involved in pathological, tomographic, or high-end visualization applications. In this paper, we provide an overview of the state of the art in compression techniques and corresponding quality metrics for various practical applications in digital holography. We also consider the future by analyzing the emerging trends for addressing the key challenges in this domain.
[HTML FullText](1081) [PDF 3135KB](191)
The state-of-the-art in computer generated holography for 3D display
David Blinder, Tobias Birnbaum, Tomoyoshi Ito, Tomoyoshi Shimobaba
Published Published online: 10 June 2022,  doi: 10.37188/lam.2022.035
Holographic displays have the promise to be the ultimate 3D display technology, able to account for all visual cues. Recent advances in photonics and electronics gave rise to high-resolution holographic display prototypes, indicating that they may become widely available in the near future. One major challenge in driving those display systems is computational: computer generated holography (CGH) consists of numerically simulating diffraction, which is very computationally intensive. Our goal in this paper is to give a broad overview of the state-of-the-art in CGH. We make a classification of modern CGH algorithms, we describe different algorithmic CGH acceleration techniques, discuss the latest dedicated hardware solutions and indicate how to evaluate the perceptual quality of CGH. We summarize our findings, discuss remaining challenges and make projections on the future of CGH.
[HTML FullText](2933) [PDF 12495KB](633)
Holography with high-power CW coherent terahertz source: optical components, imaging, and applications
Yulia Choporova, Boris Knyazev, Vladimir Pavelyev
Published Published online: 09 June 2022,  doi: 10.37188/lam.2022.031
This paper presents the results of 15 years of studies in the field of terahertz holography at the Novosibirsk free electron laser. They cover two areas: research on obtaining holographic images in the terahertz range and the use of diffractive optical elements to form high-power terahertz radiation fields with specified characteristics (intensity, phase, and polarization), using well-studied and widely applied in the optical range methods of optical (analog), digital, and computer-generated holography. All experiments were performed with the application of high-power coherent monochromatic frequency-tunable radiation from the Novosibirsk free electron laser. The features of hologram registration in the terahertz range are described. Methods, technologies, and optical materials for terahertz holographic elements are discussed. A wide range of promising applications of high-power terahertz fields with a given spatial structure is considered. The results of the study of terahertz holograms recorded as digital holograms, as well as radiation-resistive optical elements realized as computer-synthesized holograms, are presented.
[HTML FullText](1033) [PDF 10899KB](473)
Phase microscopy and surface profilometry by digital holography
Myung K. Kim
Published Published online: 06 May 2022,  doi: 10.37188/lam.2022.019
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.
[HTML FullText](1714) [PDF 6879KB](413)
Advanced optical methods and materials for fabricating 3D tissue scaffolds
Xiaobo Li, Wanping Lu, Xiayi Xu, Yintao Wang, Shih-Chi Chen
Published Published online: 06 May 2022,  doi: 10.37188/lam.2022.026
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.
[HTML FullText](3655) [PDF 10335KB](636)
Review of engineering techniques in chaotic coded aperture imagers
Vijayakumar Anand, Joseph Rosen, Saulius Juodkazis
Published Published online: 01 May 2022,  doi: 10.37188/lam.2022.024
Coded aperture imaging (CAI) is a technique to image three-dimensional scenes with special controlled abilities. In this review, we survey several recently proposed techniques to control the parameters of CAI by engineering the aperture of the system. The prime architectures of these indirect methods of imaging are reviewed. For each design, we mention the relevant application of the CAI recorders and summarize this overview with a general perspective on this research topic.
[HTML FullText](1094) [PDF 13086KB](464)

ISSN 2689-9620

EISSN 2831-4093

Diamond Open Access