Optical Subsystems Research Articles

Multiphysics simulation and design framework for developing a vision-based tactile sensor with force estimation and slip detection capabilities

Recent achievements in the field of tactile sensing has enhanced the dexterity of robots interacting with their environments. Superior to other transduction mechanisms, vision-based tactile sensing enables high-resolution sensing of the contact surface. Accordingly, many vision-based tactile sensors have been introduced in recent years, all of which are designed and fabricated based on a trial-and-error approach with limited prior system modeling and simulation. In this study, we introduce a detailed framework for the development of a vision-based tactile sensor with markers motion mechanism. We start with the design and coupled simulation of the mechanical and optical subsystems followed by fabrication, testing, and validation of the proposed sensor. An uncertainty analysis is carried out during the design stage where various errors are propagated to determine the expected sensor accuracy. The simulated sensor showed a maximum error of 0.15 newtons with the error for the camera distance to the rigid membrane having the highest contribution. After fabrication of the sensor, it is observed that there is a very good agreement between simulation and experimental results. The sensor was tested for sensing tangential forces (up to slip) along two directions and normal force (up to 5 newtons) at 30 Hz rate with measurement errors (95 % confidence interval) of 0.39 newton, 0.11 newton, and 0.12 newton, respectively. The sensor detected the slip in 97 % of the tests with an average latency of 10 frames.

Performance evaluation and investigation of diffraction optical elements effect on bit error rate of free space optics and performance investigation of space uplink wireless optical communication under varying atmospheric turbulence conditions

AbstractSeveral other optical antenna topologies have been developed and implemented throughout the years. These topologies include a variety of optical components, including the axicon optical element, dual‐secondary mirror, cone reflecting mirror, prism beam slier, and beam‐splitter/beam combiner. In contrast, the secondary reflecting mirror causes an obscuration loss that must be compensated for by reducing the transmission power in an optical antenna design. In order to address this issue in space optical communication, the present research helps to develop an enhanced two diffractive optical elements (DOEs) technology however the data presented therein only shows that DOEs may boost transmission power efficiency, which is insufficient for system designers. Though On‐Off Keying (OOK) is widely used in optical communication systems at the moment, the proposed research include DOEs into an OOK space uplink optical. The proposed research uses numerical simulation to explore how much a space uplink OOK system's bit error rate (BER) may be improved by using DOEs and adjusting fundamental parameters. The proposed BER model takes environmental factors like wind and detector noise into account. Using this theoretical model, the present work helps to investigate the effect of DOEs on the BER versus fundamental parameter characteristic curves in space uplink optical communication. Based on the findings, the DOEs structure has the potential to significantly enhance the BER performance of space uplink optical communication systems, especially at high obscuration ratios. When the obscuration ratio is 0.25, 0.167, or 0.125 and the transmission power is 1 W, for instance, the DOEs may improve the BER by a factor of two or one order of magnitude or less when the parameters are changed to the typical parameter values as specified. Results increase by a factor of six, three, and two orders of magnitude, respectively, when transmitting at 5 W. The results show that DOEs can significantly enhance the BER performance, especially at high obscuration ratios. The findings suggest that integrating DOEs into the optical subsystem is a straightforward approach to improving the performance of space uplink optical communication systems.

A 3D-Printed Portable UV and Visible Photoreactor for Water Purification and Disinfection Experiments.

Water scarcity and contamination are urgent issues to be addressed. In this context, different materials, techniques, and devices are being developed to mitigate contemporary and forthcoming water constraints. Photocatalysis-based approaches are suitable strategies to address water contamination by degrading contaminants and eliminating microbes. Photoreactors are usually designed to perform photocatalysis in a scalable and standardised way. Few or none have been developed to combine these characteristics with portability, flexibility, and cost effectiveness. This study reports on designing and producing a portable (490 g), low-cost, and multifunctional photoreactor that includes adjustable radiation intensity and two types of wavelengths (UV-A and visible), including combined agitation in a compact mechanism produced through 3D printing technology. The mechanical, electrical, and optical subsystems were designed and assembled into a robust device. It is shown that it is possible to apply radiations that can reach 65 mW/cm2 and 110 mW/cm2 using the installed visible and UV LEDs and apply mechanical agitation up to 200 rpm, all under a ventilated system. Regarding functionality, the photoreactor proof of concept indicated the ability to degrade ~80% and 30% ciprofloxacin under UV and visible irradiation of TiO2 and Ag/TiO2 nanoparticles. The device also showed the ability to eliminate E. coli bacteria, recurring to radiation set-ups and nanoparticles. Therefore, the originally designed and constructed photoreactor concept was characterised and functionally validated as an exciting and flexible device for lab-scaled or outdoor experiments, assuring standardised and comparable results.

Structural Design and Simulation of a Multi-Channel and Dual Working Condition Wafer Defect Inspection Prototype.

Detecting and classifying defects on unpatterned wafers is a key part of wafer front-end inspection. Defect inspection schemes vary depending on the type and location of the defects. In this paper, the structure of the prototype is designed to meet the requirements of wafer surface and edge defect inspection. This prototype has four inspection channels: scattering, reflection, phase, and contour, with two working conditions: surface and edge inspection. The key structure of the prototype was simulated using Ansys. The simulation results show that the maximum deformation of the optical detection subsystem is 19.5 μm and the fundamental frequency of the prototype is 96.9 Hz; thus, these results meet the requirements of optical performance stability and structural design. The experimental results show that the prototype meets the requirements of the inspection sensitivity better than 200 nm equivalent PSL spherical defects.

Mid-infrared carbon isotope spectrum logging system combined with a thermostat of optical subsystem for high-precision detection of isotope ratio

In the process of oil and gas exploration and development, carbon isotope ratio can reflect the maturity of oil and gas and predict the recovery factor, and the isotope ratio in the composition of shale gas is particularly important. Thus, a carbon isotope spectrum logging system was designed and exploited based on tunable diode laser absorption spectroscopy (TDLAS) technology under the fundamental frequency absorption band of 12CO2 and 13CO2 molecules, and a quantum cascade laser (QCL) with center wavelength of 4.35 μm was applied. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the modulation of QCL. A multi-pass gas cell (MPGC) with an optical path length of 41 m was utilized for lower limit of detection (LoD). In order to suppress the temperature dependence of the absorption spectrum, the optical subsystem was placed in a high-precision thermostat to maintain a stable temperature, so as to achieve high-precision and high-stability detection. Meanwhile, sparrow search algorithm-back propagation (SSA-BP) was applied for concentration prediction of 12CO2 and 13CO2. Taking advantage of the excellent optimization ability, fast convergence speed and high stability of SSA, the problem that BP neural network algorithm is highly dependent on initial value can be solved to some extent. Sensor performance was validated through calibration and stability experiments. The LoD of 12CO2 reached a minimum of 0.618 parts-per-billion (ppb) with an 88 s averaging time, and the LoD of 13CO2 reached 0.181 ppb when the averaging time was 96 s. Besides, the standard deviation of carbon isotope ratio obtained by this system was ∼ 0.61 ‰. The results illustrate that this self-developed sensor has a bright prospect in the field of shale gas isotope detection.

Design of freeform surface optical component in helmet mounted display

Helmet display (HMD) is the core hardware of virtual display technology. It is a small display device mounted on the helmet to produce visual images for the user. The MHD system mainly consists of an image source, optical, and support system. Still, the traditional optical subsystem cannot achieve the functions of the ideal optical system, such as being light-weight, small in size, and having an extensive field angle. This paper established the proper initial model, and the optimal control conditions and surface upgrade strategy were determined. Herein, the design scheme of the free-form prism with good performance was obtained. We solve the feature of large volume and complicated structure of optical components of helmet display and describe the design idea of free-form prism in detail. In this paper, the system resolution we designed is 800 × 600, the Modulation transfer function (MTF) value of the prism is more significant than 0.1 at the spatial resolution of 30lp/mm, and the distortion is less than 5%. The exit pupil diameter of the system is 8mm, and the field angle is 26°×20°.

Designing an optical phase element for field of view enhancement by using wavelength multiplexing

Enhancing the image quality of the captured image is one of the prime objectives of modern image acquisition systems. These imaging systems can be broadly divided into two subsystems: an optical subsystem and a digital subsystem. There are various limitations associated with the optical and digital subsystems. One of the crucial parameters that are affected by the limitation of the physical extent of the recording or capturing system is the field of view (FOV). A reduced FOV can lead to loss of information thereby increasing the time for post-processing of images as well as introducing mechanical scanning to achieve a larger FOV. A simple yet efficient technique for FOV enhancement is demonstrated in this paper. An optical element is designed in such a way that it diffracts different wavelengths in the desired manner and the information from different regions of the object is carried by different wavelengths which upon combination at the sensor plane leads to enhancement of FOV.

Design and Fabrication of a Flexible Opto-Electric Biointerface for Multimodal Optical Fluorescence and Electrical Recording

Optical fluorescence and electrical monitoring of cell activity are two powerful approaches to study organ functions. Simultaneous recording of optical and electrical data types will provide complementary information from and take advantage of each approach. However, devices that can concurrently record optical signals from the same cell population underneath the microelectrodes have not been widely explored and remain a grand technical challenge. This work presents an innovative flexible opto-electric device that monolithically integrates transparent gold nanogrid microelectrodes directly above microscale light-emitting diodes, photodetectors, and optical filters to achieve co-localized crosstalk-free optical fluorescence and electrical recording. The optimized gold nanogrid microelectrodes show an excellent optical transparency (>81%) and a low normalized 1 kHz electrochemical impedance (6.3 Ω cm2). The optical recording subsystem offers high wavelength selectivity (>1,300) and linearity (R2 > 0.99) for exciting and capturing green fluorescence from various fluorescent reporters in measurement ranges relevant for in vivo applications with minimal thermal effects. The opto-electric device exhibits remarkable durability under soaking for 40 days and repetitive mechanical bending for 5000 cycles. The work may provide a versatile approach for constructing mechanically compliant biointerfaces containing crosstalk-free optical and electrical modalities with widespread application potentials in basic and clinical research.

Determination of Sessile Drop Wetting Angle Based on μCT without the Direct Angle Measurement.

Wettability is an important factor that controls the position and transport of fluids in the porous structure of a hydrocarbon reservoir. Direct quantitative wettability measurement methods include determination of the contact angle. One of the popular laboratory methods for its measurement is the sessile drop method, where the droplet of liquid is set onto the solid sample surface and the angle between liquid and solid phases in a 2D profile image is measured using a high-resolution optical subsystem. However, this method has disadvantages connected with three complex factors: two-dimensionality of data, image resolution, and the presence of wetting domains on the solid surface. In this work, we propose a method based on 3D μCT scanning of a sessile drop on the surface of a material and determination of the value of the wetting angle using drop height and volume measurements. Since the contact angle is not measured directly, this makes it possible to obtain averaged contact angle values for the entire droplet and leads to more stable values for individual measurements in comparison with the standard optical method. The results demonstrate that contact angles obtained using the μCT method differ from the values obtained by various fitting techniques of the 2D optical method: μCT-values are higher for hydrophilic interaction by 4-6° and lower for hydrophobic interaction by 12-17°. Such differences are associated with the lower susceptibility of the proposed method to the influence of the gravitational effect, which leads to a flattening of the droplet shape and distortion of angle measurements on the 2D projections. However, the described method showed close contact angles for water drops on a polytetrafluoroethylene surface with values obtained in microgravity and can be helpful for its prediction. It also has relatively low sensitivity to the absolute values of the drop volume and drop segmentation errors.

Fourier-Optics Based Opto-Electronic Architectures for Simultaneous Multi-Band, Multi-Beam, and Wideband Transmit and Receive Phased Arrays

Current trends in wireless communications require a Base Transceiver Station (BTS) to support an ever-increasing number of antennas, wider bandwidths, multiple frequency bands, and many simultaneous beams. This is a tall order when considering all-electronic implementations, especially when operating at high carrier frequencies. We describe here Fourier-optics based opto-electronic architectures that include analog and fully connected transmit (TX) and receive (RX) implementations that support simultaneous multi-band, multi-beam phased arrays where optical up- and down-conversion are used to generate IF/RF and RF/IF, respectively, signals for simultaneous multi-user and multi-beam transmission and reception over a wide range of frequencies. The proposed lens-based architectures have the ability to transmit and receive multiple distinct beams simultaneously even when only analog beamforming is performed, thus greatly simplifying the tasks of cell search and initial access without having to resort to complex matrix-based beamforming networks. Additionally, lens-based TX and RX beamforming is performed in the analog optical domain with zero power consumption and negligible latency bounded only by the time the light takes to travel through the lens. Photonic signal processing also reduces the number of RF components required at the remote radio unit (RRU) and the number of costly and power-hungry high-performance analog-to-digital/digital-to-analog converters (ADCs/DACs) required. The optical subsystems are ultra-wideband and frequency agnostic as only the front-end components (antennas, amplifiers) are RF frequency/band specific. Therefore, a single photonic system design may be operated at any band and, furthermore, existing installations may be modified/upgraded to operate in different bands with minimal component replacements needed. Finally, the presented architectures provide near unlimited beam-bandwidth product (BBP) with minimal power requirements and no external cooling. Theoretical analysis and experimental confirmation of the proposed architecture will both be reported, including a receiver with a nominal BBP of 36 GHz with a prototype system that consumed less than 300 W, thus yielding a power efficiency of beam formation of 8 W/GHz, which is more than a 6× improvement over the current state of the art.

Dynamic power and chirp measurements of a quantum dash semiconductor optical amplifier amplified picosecond pulses using a linear pulse characterization technique

Quantum Dash (QDash) SOAs are of interest as an alternative to quantum dot SOAs, since they have some dot-like properties and are easier to fabricate such as to operate in the 1550 nm region, albeit with longer gain recovery times in the range of hundreds of picoseconds. QDash-SOAs are promising core component is optical subsystems for applications in next generation coherent communications and optical signal processing, which often involve pulse amplification. It is of interest to measure both the dynamic power, phase and associated chirp and thereby the spectrum of typical QDash-SOA amplified pulses. Non-linear measurement techniques are appropriate for pulsewidths less than 5 ps but have low sensitivity for wider pulsewidths often encountered in practice. This paper describes the use of a modified linear pulse characterization technique to measure the dynamic power and phase of the identical pulses of a QDash-SOA amplified 20 GHz repetition rate 19 ps pulsewidth pulse train. The pulse chirp and power from which the pulse chirp and pulse train power spectrum is calculated. The amplified pulse structure is strongly dependent on the amplifier gain and the input pulse shape and energy.

Pilot-Tone-Assisted Stimulated-Brillouin-Scattering-Based Optical Carrier Recovery for Kramers-Kronig Reception

Optical carrier recovery provides a method to increase the carrier-to-signal power ratio at the receiver side of an optical communications system. Here, we propose to use optical carrier recovery based on stimulated Brillouin scattering to help overcome performance limits of Kramers-Kronig direct detection systems that arise due to the need for a high carrier-to-signal power ratio. By transmitting a low power pilot tone along with the signal, we simplify the stimulated Brillouin scattering based optical carrier recovery subsystem, toward better compatibility with the technology demands of short-reach systems. Experimental results show that after 80 km standard single mode fibre transmission, an 8.8 dB required optical signal-to-noise ratio improvement is achieved by the proposed optical carrier recovery subsystem, when compared with the standard Kramers-Kronig direct detection system. Moreover, we measure a receiver sensitivity enhancement of more than 2.8 dB in an optically pre-amplified receiver. These results indicate the potential of the proposed optical carrier recovery subsystem to improve reach or power requirements for Kramers-Kronig direct detection systems.

Computational optical system design: a global optimization method in a simplified imaging system.

An optical imaging system often has problems of high complexity and low energy transmittance to compensate for aberrations. Here we propose a method to correct aberrations by coupling an optical subsystem with a digital subsystem. Specifically, in the global optimization process, the two subsystems correct their respective, easily handled aberrations so that the final imaging aberration is minimized. We design simple lenses with this method and assess imaging quality. In addition, we conduct a tolerance analysis for the proposed method and verify the effectiveness of deconvolution using a spatially varying point spread function (SVPSF) in the actual imaging process. Simulation results show the superiority of the proposed method compared with the conventional design and the feasibility of simplifying the optical system. Experimental results prove the effectiveness of deconvolution using SVPSF.

“Design and building of a high speed Schmidt-Cassegrain objective for space qualified remote sensing camera”

Remote sensing satellites require very accurate pointing to specific locations of interest with high resolution and small latency. Therefore, the space imaging systems attempted to achieve the possible highest ground resolution with minimum cost as possible. In this paper, design process of an electro-optical imaging payload is described considering the limited weight and small volume in addition to minimum power consumptions. The most promising prospects for high resolution imaging are connected with passive optical sub-systems, especially push broom one. For design a multiband Space remote sensing payload with 4°7′ field of view that operates in multi spectral bands and a panchromatic band, it requires the high speed Schmidt–cassegrain objective. The most promising prospects for high resolution imaging are connected with passive optical sub-systems, especially push broom one. The Schmidt-Cassegrain objective is a catadioptric objective that combines a Cassegrain reflector’s optical path with a Schmidt corrector plate to make a compact objective that uses simple spherical surfaces only. Because of the limited weight of the camera (22.2 kg), the multispectral consists of only one single optical system large F-Number (F5) and provided with spectrum splitter.In addition, the key points in design of such types of cameras were listed as well as clarifying the optical design of such objective.

Selectable microwave‐frequency doubling and quadrupling via optical path‐length tuning

A technique to selectively double or quadruple the frequency of a microwave signal is experimentally demonstrated based on a commercial single-output Mach–Zehnder modulator (MZM). Selectability is achieved by only a change in optical path length in a post-MZM optical subsystem, without filtering and without changing the MZM drive voltage. This path length controls the synchronisation of two similarly shaped optical signals that are incoherently combined. Multiplication from 2 GHz (S-band) to 4 GHz (C-band, doubling) and to 8 GHz (X-band, quadrupling) is demonstrated with side-tone suppression greater than 24 dB. At a 10-kHz offset from the quadrupled frequency, the phase-noise degradation is only 7.9 dB, a 4.1-dB improvement over traditional quadrupling techniques.

Design of Meteor and Ionospheric Irregularity Observation System and First Results

AbstractThe Meteor and ionospheric Irregularity Observation System (MIOS), which consists of multi‐station optical subsystem at Ledong (18.4°N, 109°E) and Sanya (18.3°N, 109.6°E), and radar subsystem including a 38.9 MHz all‐sky interferometric radar and a 47.5 MHz coherent phased array radar at Ledong, has been in full operational since December 2021. This paper describes the system design and first results of meteor plasma density irregularities and corresponding meteoroids. The MIOS optical subsystem consists of a few tens of video cameras for observing optical meteor trail and spectrum. The MIOS phased array is composed of 135 Yagi antennas, arranged in sword‐like grid and grouped into 15 identical subarrays, with distances separated by 2–19.5 times the wavelength for unambiguous interferometry measurements. The phased array can form narrow and wide beams, with half power width of 8° and 24° in azimuth, respectively, allowing narrow‐beam pulse‐to‐pulse steering and wide‐beam multi‐baseline imaging observations in the east‐west direction. Observational results show that the MIOS is capable of unambiguously locating various meteor echoes, that is, head, specular and non‐specular echoes, revealing the structural evolution of field‐aligned and non‐field‐aligned irregularity, and of determining the properties of meteoroids producing/not producing irregularities. Cases of bright meteors producing non‐field‐aligned irregularities and not producing field‐aligned irregularities respectively are presented, and possible factors affecting the generation of meteor trail irregularities are discussed based on current understanding. It is expected that the MIOS will provide an important tool to study the generation and evolution of various meteor trail irregularities and the properties of the corresponding meteoroids.

Optical Phase Conjugation Conversion through a Nonlinear Bidirectional Semiconductor Optical Amplifier Configuration

The optical phase conjugation (OPC) process is thoughtfully investigated in a nonlinear bidirectional semiconductor optical amplifier subsystem (SOA), demonstrating the conjugation conversion through the two ports of the SOA, simultaneously. The spectral responses, the nonlinear power curves and the quality optimization of the conjugated are discussed through the simulation in nonlinear bidirectional configuration. The experimental investigation of the polarization-insensitive SOA further confirms the OPC behavior in the bidirectional operation, achieving the error-free conjugation conversion with an output optical signal-to-noise ratio (OSNR) of up to 16 dB. The nonlinear bidirectional SOA configuration tested in the system relaxes the requirement of the conventional four-wave mixing (FWM), enabling the OPC conversion with the signal regeneration in only one unit.

Coronagraph design with the electric field conjugation algorithm

The requirements for a coronagraph instrument to image and obtain spectra of rocky planets around bright stars from space are tight. Indeed, the goal of imaging an Earth-like planet requires a starlight suppression system that cancels light to a level of 10 − 10 with sufficient stability and robustness to errors. Furthermore, the key science questions necessitate an adequate sample size; consequently, the throughput of the coronagraph drives the achievable yield of a given mission. The trade among achievable raw contrast, sensitivity to wavefront errors, and throughput poses a challenging problem in coronagraph design. The complexity of this problem drives us toward the simultaneous solving of all optical elements. We present a set of methods to optimize the design of a coronagraph. We implement these for the case of the hybrid Lyot coronagraph in the context of the Nancy Grace Roman Space Telescope Coronagraph Instrument. We discuss our findings in terms of coronagraph instrument design, and optical subsystems, and performance interplay.

Optical and thermal integration analysis of supercritical CO2 Brayton cycles with a particle-based solar thermal plant based on annual performance

Central receiver concentrating solar power (CSP) plants based on particles as heat transfer fluid in solar circuits and supercritical CO2 (S–CO2) Brayton cycles can fulfil the requirements for next generation CSP to improve solar-to-electric efficiency and reduce energy storage costs. However, effective incorporation of these two concepts requires an in-depth understanding of their characteristics and an appropriate approach to match them. This paper addresses the importance of the design features and annualized performances of the optical subsystem (heliostat-receiver) and the thermal-to-electricity subsystem (solar receiver-energy storage-power block) on the global optimization of any integrated CSP plant. The analysis lies in a complete model of a particle-based CSP plant, which includes detailed modeling for the solar field, a cavity solar receiver with an up bubbling fluidized bed (UBFB) tubular panel, particles storage tanks and a recompression S–CO2 Brayton cycle. The design incident irradiance on the receiver aperture (IR) and the particles temperature at the receiver outlet (Tp) are identified as key parameters determining the solar-to-electric integration procedure and affecting the overall plant design and annual performance. Regarding subsystems located upstream and downstream of the receiver, the effects of heliostat and power block characteristics on the optimal IR and Tp are also evaluated, represented by the heliostat beam quality and main compressor inlet temperature. Results show that IR around 1,200–1,500 W/m2 provides the maximum system design efficiency and annual efficiency. Improvements on heliostat beam quality and power block efficiency help to increase the optimal IR and overall system efficiency. In the optimal range of IR, increasing Tp leads to higher system design efficiency, but lower system annual efficiency and annual electricity output. The optimal combination of IR and Tp contributes to a minimum heliostat design area, representing the integration trade-off between the system optical and thermal characteristics.

Power Generation Analysis of Terrestrial Ultraviolet-Assisted Solid Oxide Electrolyzer Cell

This paper presents a novel system design that considerably improves the entrapment of terrestrial ultraviolet (UV) irradiance in a customized honeycomb structure to produce hydrogen at a standard rate of 7.57 slpm for places with a UV index > 11. Thermolysis of high salinity water is done by employing a solid oxide electrolyzer cell (SOEC), which comprises three customized, novel active optical subsystems to filter, track, and concentrate terrestrial UV solar irradiance by Fresnel lenses. The output of systems is fed to a desalinator, a photovoltaic system to produce electrical energy, and a steam generator with modified surface morphology to generate the required superheated steam for the SOEC. A simulation in COMSOL Multiphysics ver. 5.6 has shown that a customized honeycomb structure, when incorporated on the copper–nickel surface of a steam generator, improves its absorptance coefficient up to 93.43% (48.98%—flat case). This results in generating the required superheated steam of 650 °C with a designed active optical system comprising nine Fresnel lenses (7 m2) that offer the concentration of 36 suns on the honeycomb structure of the steam generator as input. The required 1.27 kW of electrical power is obtained by concentrating the photovoltaic system using In0.33Ga0.67N/Si/InN solar cells. This production of hydrogen is sustainable and cost effective, as the estimated cost over 5 years by the proposed system is 0.51 USD/kg, compared to the commercially available system, which costs 3.18 USD/kg.