Digital Optical Research Articles

Effect of Thermal Pre-treatment on Thermal Gradient Response of Granitic Rocks: Insights from Optical Microscopy and Digital Image Correlation

Effect of Thermal Pre-treatment on Thermal Gradient Response of Granitic Rocks: Insights from Optical Microscopy and Digital Image Correlation

Enabling IP-optical integration in core and metro networks [Invited

IP-optical (Internet protocol and optical) integration, or “IP over DWDM (dense wavelength division multiplexing),” is a concept spanning over two decades since the advent of coherent DSP (digital signal processing). In recent years, coherent DSP technology has progressed to a point where it can be integrated on small pluggable form factors that can be equipped in optical line systems and disaggregated transponders or directly in IP routers to support a range of metro and core applications. The option of equipping pluggable digital coherent optics (DCOs) directly in IP routers has the biggest potential for operational cost savings but hinges on the availability of a unified management environment with a single pane of glass to coordinate and automate IP routing and optical transport functions. This work presents alternative software-defined networking (SDN) architectures and evaluates the challenges associated with the evolution to IP over DWDM network architectures. It demonstrates the first, to our knowledge, implementation of the Transport API supporting colored pluggable interfaces in routers in a real network testbed. This work contributes to the realization of end-to-end network management for IP-optical networks, offering operators comprehensive visibility into multi-layer and multi-domain services and empowering revenue generation.

Deep learning-based optical aberration estimation enables offline digital adaptive optics and super-resolution imaging

Optical aberrations degrade the performance of fluorescence microscopy. Conventional adaptive optics (AO) leverages specific devices, such as the Shack–Hartmann wavefront sensor and deformable mirror, to measure and correct optical aberrations. However, conventional AO requires either additional hardware or a more complicated imaging procedure, resulting in higher cost or a lower acquisition speed. In this study, we proposed a novel space-frequency encoding network (SFE-Net) that can directly estimate the aberrated point spread functions (PSFs) from biological images, enabling fast optical aberration estimation with high accuracy without engaging extra optics and image acquisition. We showed that with the estimated PSFs, the optical aberration can be computationally removed by the deconvolution algorithm. Furthermore, to fully exploit the benefits of SFE-Net, we incorporated the estimated PSF with neural network architecture design to devise an aberration-aware deep-learning super-resolution model, dubbed SFT-DFCAN. We demonstrated that the combination of SFE-Net and SFT-DFCAN enables instant digital AO and optical aberration-aware super-resolution reconstruction for live-cell imaging.

Electro-optic properties of liquid crystal cells with nanowall electrodes

This work fabricates a nanowall electrode for achieving advanced liquid crystal (LC) devices and improving LC displays. The nanowall electrode consists of indium–tin–oxide (ITO) sheets stacked with nanowalls, and the nanowalls have a height and thickness of 4 µm and 500 nm, respectively. The high aspect ratio (8.0) of the nanowalls sets the nanowall electrode apart from previous electrodes. A flat electrode that comprises only ITO sheets is used to evaluate the nanowall electrode. The LC cell with the nanowall electrode exhibits better electro-optic properties than the LC cell with the flat electrode due to the strong transverse electric field and small subelectrode gap of the nanowall electrode. Especially, the operating voltage (3.7 V) of the nanowall cell is 36% smaller than that (5.8 V) of the flat cell. Therefore, nanowall electrodes have potential in LC lenses, LC antennas, metaverse displays, and digital optics.

Development of Computer Vision, Image Processing, and Analysis at the Digital Optics Laboratory of the Institute for Information Transmission Problems of the Russian Academy of Sciences

Development of Computer Vision, Image Processing, and Analysis at the Digital Optics Laboratory of the Institute for Information Transmission Problems of the Russian Academy of Sciences

Panoramic three-dimensional optical digitization system assisted by a bi-mirror.

The digitization of objects' full surfaces finds widespread applications in fields such as virtual reality, art and design, and medical and biological sciences. For the realization of three-dimensional full-surface digitization of objects within complex sceneries, we propose a straightforward, efficient, and robust panoramic three-dimensional optical digitization system. This system contains a laser-based optical three-dimensional measurement system and a bi-mirror. By integrating mirrors into the system, we enable the illumination of the object from all angles using the projected laser beam in a single scanning process. Moreover, the main camera employed in the system can acquire three-dimensional information of the object from several different viewpoints. The rotational scanning method enhances the efficiency and applicability of the three-dimensional scanning process, enabling the acquisition of surface information of large-scale objects. After obtaining the three-dimensional data of the sample from different viewpoints using laser triangulation, mirror reflection transformation was employed to obtain the full-surface three-dimensional data of the object in the global coordinate system. The proposed method has been subjected to precision and validity experiments using samples with different surface characteristics and sizes, resulting in the demonstration of its capability for achieving correct three-dimensional digitization of the entire surface in diverse complex sceneries.

Trueness and precision of complete arch dentate digital models produced by intraoral and desktop scanners: An ex-vivo study

ObjectivesThe study aimed to compare the trueness and precision of five intraoral scanners (Emerald S, iTero Element 5D, Medit i700, Primescan, and Trios 4) and two indirect digitization techniques for both teeth and soft tissues on fresh mandibular and maxillary cadaver jaws. MethodsThe maxilla and mandible of a fully dentate cadaver were scanned by the ATOS industrial scanner to create a master model. Then, the specimens were scanned eight times by each intraoral scanner (IOS). In addition, 8 polyvinylsiloxane (PVS) impressions were made and digitized with a Medit T710 desktop scanner. Stone models were then poured and again scanned with the desktop scanner. All IOS, PVS, and stone models were compared to the master model to calculate the mean absolute surface deviation for mandibular teeth, maxillary teeth, and palate. ResultsFor mandibular teeth, the PVS trueness was only significantly better than the Medit i700 (p < 0.001) and Primescan (p < 0.05). In maxillary teeth, the PVS trueness was significantly better than all IOSs (p < 0.05–0.001); the stone trueness was significantly better than Emerald S (p < 0.01), Medit i700 (p < 0.001) and Primescan (p < 0.01). In the palate, PVS and stone trueness were significantly lower than the iTero Element 5D (p < 0.01) and Trios 4 (p < p < 0.01). Stone trueness was significantly lower than the Medit i700 (p < 0.05). The precision in the palate was significantly lower for PVS and stone than for Emerald S (p < 0.01, p < 0.05), iTero Element 5D (p < 0.01, p < 0.01), Primescan (p < 0.001, p < 0.001), and Trios 4 (p < 0.001, p < 0.01). Significant differences in trueness between the IOSs were observed only in the mandibular teeth. The Medit i700 performed worse than Emerald S (p < 0.01) and iTero Element 5D (p < 0.01). For mandibular teeth, the Medit i700 was significantly more precise than Primescan (p < 0.01) and the Emerald S (p < 0.05). The Trios 4 was significantly less precise than Emerald S (p < 0.05). The precision of Medit i700 was significantly worse than iTero Element 5D (p < 0.01) for maxillary teeth, as well as the Primescan (p < 0.01) and Trios 4 (p < 0.05) for the palate. ConclusionsIn general, indirectly digitized models from PVS impressions had higher trueness than IOS for maxillary teeth; precision between the two methods was similar. IOS was more accurate for palatal tissues. The differences in trueness and precision for mandibular teeth between the various techniques were negligible. Clinical significanceAll investigated IOSs and indirect digitization could be used for complete arch scanning in mandibular and maxillary dentate arches. However, direct optical digitization is preferable for the palate due to the low accuracy of physical impression techniques for soft tissues.

Logic operation and all-optical switch characteristics of graphene surface plasmons.

Terahertz logic gates play a crucial role in optical signal processing and THz digitization. In this paper, we propose a design strategy for graphene-based metamaterial THz all-optical logic gate devices based on the induced transparency effect of surface isolated. Theoretically, we realize Boolean operations by coupling of a hexagonal graphene resonant cavity with dual embedded rotatable ellipses. Based on the coupled mode theory, the elliptical rotation angle of the resonator is an important factor affecting the PIT phenomenon. We control the logic input by adjusting the rotation angles of the two embedded ellipses. The analysis results show that: under the incidence of y-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 30° represents the input signal '1'. Through numerical simulation, the structure realizes two logical operations of NAND and AND. Under the incidence of x-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 90° represents the input signal '1'. Through numerical simulation, the structure realizes three logical operations of NAND, XNOR and OR. Finally, we analyze the performance of the logic gates by extinction ratio. The extinction ratio of the logic gate is up to 10.38 dB when performing OR Boolean operations. Numerically simulated all-optical logic gates can be key components of optical processing and telecommunication equipment.

Digital adaptive optics with interferometric homodyne encoding for mitigating atmospheric turbulence

Digital adaptive optics (DAO) created using homodyne encoding can mitigate atmospheric turbulence in passive imaging systems. This work demonstrates a self-referencing homodyne interferometry technique that combines the passive imaging utility of multiframe algorithmic procedures with the single-frame correction capability of the Shack–Hartmann adaptive optics technique. This paper presents image reconstruction improvements through the addition of (1) phase diversity modulation techniques within the interferometry reconstruction algorithm and (2) temporal image processing techniques applied after the interferometry reconstruction algorithm. By imaging quick response codes through a turbulent air chamber in the laboratory, it was possible to quantify the machine-readable performance gain provided by DAO when compared with a standard imaging camera. Results from this research verify that DAO from homodyne encoding provides turbulence mitigation for single frames of data, paving the way for environmentally robust, high-speed, self-contained imaging systems.

Real-Time Demonstration of 100 GbE THz-Wireless and Fiber Seamless Integration Networks

We propose and experimentally demonstrate a real-time fiber-THz-fiber 2 × 2 multiple-input multiple-output (MIMO) seamless integration system at 340–510 GHz using commercial digital coherent optics (DCO) modules for baseband signals processing, which realizes a record net rate of 103.125 Gb/s dual polarization quadrature-phase-shift-keying (DP-QPSK) signals delivery over two spans of 20 km wireline single-mode fiber-link and 3 m wireless 2 × 2 MIMO link without using THz power amplifier under 15% soft-decision forward-error-correction threshold (SD-FEC) of 1.56 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> . Two kinds of THz-to-optical conversion schemes based on an integrated dual-polarization Mach-Zehnder modulator (DP-MZM) and two discrete intensity-modulators (IMs) are extensively investigated and compared. To the best of our knowledge, this is the first real-time demonstration of THz-wireless and 100 GbE fiber-optic networks seamless integration transmission, which is compatible with IEEE 802.3 and ITU-T G.798 specifications. It is a promising scheme to meet the demands of future fiber-wireless-integrations communication for low power consumption, low cost and miniaturization.

Multiscale Optical Field Manipulation via Planar Digital Optics

Replacing curved and bulky optical elements with thin and lightweight counterparts is a persistent pursuit of the optical society. Metasurfaces, as two-dimensional artificial metamaterials, have attracted much attention because of their exceptional ability to manipulate electromagnetic waves such as amplitude, phase, polarization, propagation direction, and so on. With the great advances in planar digital optics and vector optical field manipulation via metasurfaces, planar optics with multiscale optical field manipulation from subwavelength meta-atoms (tens of nanometers) to large-scale planar devices (hundreds of millimeters) is highly desired in practical applications, which may replace conventional optical devices with superior performance and decreased weight or even create completely new functionalities. Here, we give a perspective on the multiscale optical field manipulation based on planar optics. Particular emphasis is given to multifunctional optical field manipulation, intelligent design, and mass fabrication, as well as their potential applications in lightweight laser systems, diffractive sails, integrated optics, etc.

ROMI: A Real-Time Optical Digit Recognition Embedded System for Monitoring Patients in Intensive Care Units.

With advances in the Internet of Things, patients in intensive care units are constantly monitored to expedite emergencies. Due to the COVID-19 pandemic, non-face-to-face monitoring has been required for the safety of patients and medical staff. A control center monitors the vital signs of patients in ICUs. However, some medical devices, such as ventilators and infusion pumps, operate in a standalone fashion without communication capabilities, requiring medical staff to check them manually. One promising solution is to use a robotic system with a camera. We propose a real-time optical digit recognition embedded system called ROMI. ROMI is a mobile robot that monitors patients by recognizing digits displayed on LCD screens of medical devices in real time. ROMI consists of three main functions for recognizing digits: digit localization, digit classification, and digit annotation. We developed ROMI by using Matlab Simulink, and the maximum digit recognition performance was 0.989 mAP on alexnet. The developed system was deployed on NVIDIA GPU embedded platforms: Jetson Nano, Jetson Xavier NX, and Jetson AGX Xavier. We also created a benchmark by evaluating the runtime performance by considering ten pre-trained CNN models and three NVIDIA GPU platforms. We expect that ROMI will support medical staff with non-face-to-face monitoring in ICUs, enabling more effective and prompt patient care.

Efficient and Accurate Optical Signal Processing and Digitization System for High Speed Data Acquisition and Analysis

The evolution of optical fiber technology has expanded its utility beyond communication to encompass measurement. Key components include the light source, detection elements, and processing circuits. This paper describes a system for optical signal processing and digitization of light pulses, employing advanced components to enhance data acquisition and analysis performance. The optical signal processing phase employed the LF356N operational amplifier, offering attributes like low bias current, high bandwidth, and rapid settling time. Configured as a transimpedance amplifier, the opamp transformed light signals into corresponding analog voltage signals. Subsequently, the voltage signal underwent digitization using the AD976AN, a 16-bit ADC with advanced features such as high-speed data acquisition and an integrated clock. This ADC was controlled by a Teesny 3.6 board with a fast CPU clock speed of up to 256 MHz, greatly facilitating rapid data analysis and algorithm execution. The hardware circuit underwent meticulous design, simulation, and fabrication, followed by rigorous testing involving various distinct light sources with differing parameters. The digitized and computed parameter values (obtained after subjecting the ADC outputs to the suggested algorithm) exhibited a high degree of similarity in comparison to the observed values on the oscillo-scope.

Special issue on digital and intelligent optics

Special issue on digital and intelligent optics

Model based view planning for the robot-guided automation of optical 3D digitization based on a variable mesh resolution processing approach

The digital 3D representation of manufactured parts plays a crucial role in the quality assurance of small, individualized lot sizes. Machine vision systems, such as optical 3D scanners, guided by an industrial robotic arm, allow for a contactless full digital reconstruction of surface geometries. In order to digitize the whole geometry, it is necessary to acquire 3D scans from multiple viewpoints with respect to the part, which in combination cover the entire surface. With efficiency in mind, this results in an optimization problem between a high surface area coverage and low measurement effort, referred to as the view planning problem. In the presented work, two popular viewpoint candidate generation methods are implemented: Firstly, a surface-based random sampling method, which generates viewpoints within a solution space, in which visibility of a given model surface can be expected. Secondly, a view sphere viewpoint generation approach, which is independent of the object geometry but avoids clustering by generating evenly spaced viewpoints on a sphere around the centre of the object. Using an adjustable remeshing procedure, a multi-stage approach is implemented by generating multiple meshes with different resolutions. Through this, the benefits of working on a coarse mesh, such as fast viewpoint candidate evaluation and selection, are combined with the level of detail of a fine mesh. It is found that it is possible to considerably reduce the mesh resolution while maintaining a reasonably high surface area coverage on a reference model. Applying the proposed procedure to the view planning for a state-of-the-art 3D fringe light projection scanner with highly sophisticated scanning capabilities, it is demonstrated that the view sphere approach is more suitable for this use-case due to the large measurement volumes of the 3D scanner. The frequently used random sampling approach requires an excessively higher computational effort to achieve similar results in comparison.

Design of an all-optical multi-logic operation-integrated metamaterial-based terahertz logic gate.

Terahertz logic gates play a vital role in optical signal processing and terahertz digitization. Herein, a strategy to design an all-optical terahertz logic gate device composed of metamaterials with a semiconductor-metal hybrid is proposed; accordingly, a concrete logic gate composed of Ge embedded-in Au stripe supported by a Si board is presented theoretically. Simulation results reveal the dependence of the terahertz transmission spectra on the different illuminations in the device. Based on the illumination-transmission response, the designed device can realize the NOR or OR Boolean operation. The effects of the width of the Ge-Au stripe as well as the Si board on the transmission spectra and logic performance were also investigated.

Fetal intervention: Less developed field of interventional radiology

Interventional radiology (IR) has played an essential role in diagnosing and treating various intra natal entities with minimally invasive surgical procedures. IR treatment is the substitute to the many procedures in which once open surgery was needed. IR procedure can be performed under Digital Radiography (x-ray), Ultrasound, Magnetic Resonance Imaging (MRI) or Computed Tomography (CT). IR has proved to increase effectiveness as medical imaging technology gives radiologists high visibility, reduces risk as surgery performed are minimally invasive, saves time as there is a short hospital stay, and reduces the pain as procedures are performed with a small incision. Because of quicker recovery time, patients can get back to their daily routine early. Progressive development of prenatal intervention and surgeries was possible due to rapid advances in imaging techniques and prenatal diagnosis over the last few decades. Rapid advanced techniques have become an integral part of managing high-risk pregnancies. In addition to this, the rapidly growing capability of digital optics and miniaturized instrumentation has now allowed fetoscopic procedures to become a reality. With improved imaging techniques, the identification of congenital defects and fetal malformations increases during the antenatal period. Understanding how to treat specific fetal conditions improves outcomes from these treatment modalities. We provide an assessment that begins with a crisp background of fetal surgery, including the history, ethics surrounding fetal surgery, and considerations of dealing with the problems during the fetal intervention.

Wideband Vector Network Analyzer Based on Direct Microwave Photonic Digitization

Vector network analyzers (VNAs) are established as one of the indispensable tools for measuring and analyzing the characteristics of objects under test in various fields, ranging from medicine and material to geology and communication. Conventional VNAs are commonly based on microwave mixing architectures that inevitably compromise accuracy, dynamic range, and bandwidth. Spurred by the deficiencies of conventional VNAs, this paper proposes a wideband photonic vector network analyzer (PVNA) that exploits the concept of direct microwave photonic digitization. In our method, ultra-stable optical trains directly sample the response signals from the objects under test, followed by opto-electronic conversion and quantization, to ultimately obviate the intricate down-conversion procedures in traditional VNAs. The contribution of our method relies on the direct microwave photonic digitization process enabling a novel and compact PVNA architecture that extends the measurable frequency range to 110 GHz with existing commercial devices or even higher by employing a high bandwidth modulator. In any case, our technique reduces the bandwidth requirements of the optical intensity digitizers. To validate our architecture’s theoretical principle, we establish an experimental PVNA with a measurable frequency range of up to 40 GHz and a dynamic range exceeding 90 dB. The developed methodology based on direct microwave photonic digitization paves a new path to the study of broadband, low-cost, and compact VNAs.

Peer-to-peer disaggregated telemetry for autonomic machine-learning-driven transceiver operation

Autonomic networking and monitoring will drive the evolution of next generation software defined networking (SDN) optical networks towards the zero touch networking paradigm. Optical telemetry services will play a key role to enable advanced network awareness at device and component granularity. Optical disaggregation is pushing the adoption of open models, enabling multi-vendor interoperability, including telemetry. Moreover, due to whitebox programmability and the adoption of open source micro services, it is becoming feasible to monitor data streams from optical devices related to quality of transmission key performance indicators. Finally, due to mature big data analytics platforms, including machine learning and artificial intelligence, the telemetry data lake is processed to effectively detect network anomalies. However, current centralized telemetry architectures are prone to scalability issues, suboptimal soft failure recovery due to operational mode limitations, and/or the inability of the SDN controller of tuning finer or proprietary transmission parameters. Conversely, a number of soft failures might be detected and recovered directly at the optical card transmitter, often in a hitless fashion, also relying on optimized vendor-proprietary configurations. The paper proposes what we believe to be a novel peer-to-peer telemetry (P2PT) service ready for next generation digital coherent optics cards, for local processing and soft failure recovery at the transceiver agent level. The P2PT architecture, workflow, and subscription extensions are conceived to enable direct and fast recovery at the transceiver level, resorting to optical signal retuning and adaptations. Experimental evaluations, including lightweight machine learning detection at the card agent, are provided in a multi-vendor disaggregated optical network testbed to assess different soft failure use cases and P2PT service scalability.

A practical guide to scanning light-field microscopy with digital adaptive optics.

With the development of a wide variety of animal models in recent years, there is a rapidly growing demand for long-term, high-speed intravital fluorescence imaging to observe intercellular and intracellular interactions in their native states. Scanning light-field microscopy (sLFM) with digital adaptive optics provides a compact computational solution by imaging the entire volume in a tomographic way with orders-of-magnitude improvement in spatiotemporal resolution and reduction in phototoxicity, as compared to traditional intravital microscopy. Here, we present a step-by-step protocol for both hardware and software implementation of multicolor sLFM as an add-on to a normal wide-field fluorescence microscope by using off-the-shelf lenses and devices at low cost. The procedure can be easily applied to other LFM variants, which can be advantageous in certain experimental contexts. Owing to the strong reliance of sLFM on algorithmic post-processing for high-quality data, the protocol describes various kinds of artefacts and corresponding parameters used for correcting and performance optimization. To increase the tolerance to system misalignment and differences in device fabrication, we describe a one-step calibration method for robust imaging performance up to the diffraction limit. An open-source graphical user interface is presented for hardware synchronization and real-time rendering of multiview images. The whole procedure including optical setup, software installation, system calibration and 3D reconstruction can be executed in 3-4 d with basic knowledge in optics and electronics.