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Multitask measurements with different measuring ranges and resolutions have put forward higher requirements for force sensors. This article presents a novel variable configuration approach to develop an adjustable-resolution force sensor with a compact force-sensitive structure. Unlike the traditional strain gauge-based force measurement, the external force is detected through measuring the displacement of the deformed structure with a precision optical linear encoder. This approach can enable variable measuring range and force resolution through the continuous adjustment of structural stiffness. Specifically, the stiffness adjustment is implemented by changing the second moment of area of the sensor structure through rotating its build-in flexure beam shafts. Analytical models are established to provide the theoretical basis for analysis and design of the sensor. Furthermore, the validity of the design is evaluated with finite element simulations. Finally, a sensor prototype is developed for performance evaluation, and applied for the wire bond pull tests to evaluate the bond strength on the printed circuit board assembly. Experimental results show that it is effective to change the measuring range and force resolution of the developed force sensor through the stiffness adjustment. [ABSTRACT FROM AUTHOR]

The increasing requirement for reliable power demands robust protection with excellent waveform sensors. The presence of nonlinear elements in the modern-day loads brings challenges in sensing the current waveform, which is different from the conventional sinusoids. This research article proposes a novel current waveform sensing philosophy with the help of five numbers of series-connected wire-wound Hall current sensors. Signal conditioning circuits and their mathematical expressions are also discussed here to estimate the current waveform with 9.6% ± 2.4% linearity and 2.1%/A ± 1.3%/A sensitivity. The sensing technology senses the current waveform with a root mean square error (RMSE) value of 0.2. Apart from sensing the typical sinusoidal current waveform, the proposed sensing philosophy also senses the impulse and switching current waveforms with RMSE values 2.7 and 0.65, respectively. These results have a broad scope of improvement by implementing more wire-wound Hall current sensors in series. Digital output features and the optical link between the sensor and receiver offer necessary isolation to the microcontroller against harmful transients and other waveform distortions. The experimental verification and required data analytics confirm the applicability of the sensor with substantial accuracy, sensitivity, and linearity. [ABSTRACT FROM AUTHOR]

This article proposes an absolute-type inductive angle sensor for detecting the position of the YRT turntable bearing. The sensor comprises a multispeed incremental measuring unit and a single-speed absolute measuring unit sharing the same stator, rotor, and excitation circuit. The stator is composed of a ferromagnetic gear groove, two groups of excitation coils, and one group of induction coils arranged according to certain rules. The end cover of the YRT turntable bearing is machined as rotor and it rotated eccentrically relative to the rotation of the stator. A bridge circuit is used to acquire and process the sensor signal from the single-speed measuring unit. Compared with the traditional dual-channel absolute measurement, the proposed measurement method avoids the effects of different magnetic circuit disturbances on signal quality and measurement accuracy, and has more advantages in the volume and weight of the sensor. The structure and working principles of the sensor are presented in detail, the feasibility of sensing scheme is verified via simulation, and a sensor prototype is designed for the final experiment. Experimental results show that the accuracy of the sensor prototype is –0.06758° to 0.1203° before compensation and –0.001139° to 0.0015° after compensation in the range of [0°, 360°], respectively. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is a very sensitive optical metrology technique commonly used in semiconductor manufacturing lines to accurately measure the thickness and refractive index of different layers present on specific dedicated metrology targets on the wafers. In parallel, optical defectivity techniques are widely implemented in production lines to inspect a significant amount of dies representative of the full wafer and detect physical and patterning defects. A new approach can then simply emerge which is to apply ellipsometry metrology techniques at a full or die wafer scale. This strategy, at the frontier between metrology and defectivity field is expected to bring solutions for certain types of process deviation. In our case, ellipsometry’s optical response was collected on large areas of product wafers to capture specific deviations such as film properties, thickness, and patterning variation. This is an innovative strategy that relies on a model-less approach to detect process drifts, using ellipsometry’s sensitivity to material properties and design architecture variations. In this paper, we will present this approach on three industrial cases. [ABSTRACT FROM AUTHOR]

In recent years, nanopore has promisingly emerged as a single molecule sensor and is able to detect biomolecules in a label-free manner. Much progress has been made in biotechnological applications using electrical measurement of temporal changes in ionic current. But it has its own limitation with respect to noise, throughput, spatial and temporal resolutions. By incorporating the optical techniques, we can acquire information about the intrinsic property and heterogeneity of a single molecule. Here we review the recent advancements in electrical and optical sensing in nanopores. [ABSTRACT FROM AUTHOR]

A disambiguation method for dual-comb sampling frequency measurement is proposed and experimentally demonstrated. For dual-comb sampling frequency measurement, multiple solutions may exist if only the frequency information of the output signal is employed for disambiguation. By further exploiting the phase relationship between the intermediate frequencies and the first harmonics of the two sampling rates, most of the ambiguous frequencies can be distinguished in our experiment. The experiment results also indicate that nonideal phase response of the devices will reduce the performance of the method especially in high frequencies. To solve the problem, an improved method, in which the variations of the phases are observed and used to solve the ambiguity, is given so that the method is free from the calibration of the nonideal phase response. [ABSTRACT FROM AUTHOR]

In this letter, we present a novel invisible bilayer ZnSnOy/ZnSnOx memristor for photo sensing. The device exhibits excellent photo sensing features such as a highly stable electrical set and optical reset endurances at least 2200 cycles for blue light and 1800 cycles for green and red light without any deterioration. Moreover, the device shows excellent retention (105 s) at 90 °C without disruption and high transmittance of about 85%. These outstanding device properties would allow us to create either an optical to an electronic memory device or an always-on continuous measurement optoelectronic sensor. [ABSTRACT FROM AUTHOR]

A novel dual-band reflective optical sensing method for simultaneous measurement of hemoglobin (Hb) concentration and temperature by hybrid guide-mode resonance (GMR)-topological photonic state (TPS) sensor was proposed. The dual-band reflection peaks can be explained by two different mechanisms: one is attributed to the excitation of GMR, and the other is due to the generation of TPS. The GMR worked as the sensing channel of Hb concentration because it is in direct contact with the Hb. Moreover, the TPS worked as the sensing channel of temperature. When the Hb concentration and temperature variation, the two reflection peaks would all shift, but with different sensitivities. Excellent biosensor performance can be obtained by systematically adjusting structural parameters such as grating period (P), grating width (W), grating height (h), and spacer layer thickness (d). Notably, by using the dual-wavelength matrix method, the cross-interference caused by temperature variation is eliminated. The results concluded that the Hb concentration sensitivity and the temperature sensitivity of the proposed sensor could reach 264.44 nm/RIU and 0.061 nm/°C, respectively. The proposed sensor provides a promising sensing strategy for multi-parameter sensing. [ABSTRACT FROM AUTHOR]

In this article, an $SE(3)$ -constrained extended Kalman filter is proposed in continuous time as well as in a more practical continuous-discrete framework. The filter allows for the state estimation of the 6-DOF rigid body motion while accounting for measurement error statistics and using the rotation matrix instead of quaternions or other attitude parameterizations. The proposed filter differs from the recently proposed $SO(3)$ -constrained attitude filter in that only a subset of the configuration states are constrained in the present filter. Its effectiveness is demonstrated in a numerical example in which its performance is compared with that of an existing $SE(3)$ estimator from the literature and a Monte Carlo simulation is carried out to provide credence to the accuracy of the proposed filter. [ABSTRACT FROM AUTHOR]

The traditional way to detect the vertical structure of seawater optical properties and chlorophyll-a is mainly through shipboard discrete observations or biogeochemical-argo profiling floats, which requires considerable time to cover a limited area. In this study, the vertical distribution of seawater optical properties and chlorophyll-a concentration across two different optically contrasted sea areas from the East China Sea (ESC) to the South China Sea (SCS) were obtained for the first time using a shipboard integrated Mie–Raman–fluorescence Light Detection and Ranging (LiDAR) for large-scale observations, with a total observation distance of over 3700 km. More than 74000 LiDAR profiles were obtained from September 5 to September 15, 2020. In general, the LiDAR-estimated inherent optical properties (IOPs) and chlorophyll-a values decreased from turbid water in the ECS to clear water in the SCS. Subsurface scattering layers were often observed at depths ranging from 10 to 20 m along the SCS coast. Subsequently, the LiDAR-derived results were compared against in situ measurements. In addition, the diurnal hourly variation in IOPs and chlorophyll-a by LiDAR at a fixed coastal station was monitored for the first time, which was relatively lower in the early morning and midday yet was higher in the evening, while the relative tide height showed the reverse change trend, which revealed that the tide possibly impacted the diurnal variation in IOPs and chlorophyll-a on the SCS coast. Overall, our results indicate that the LiDAR remote sensing technique is effective and feasible to monitor large-scale and long-term subsurface phytoplankton structure over different optically contrasted sea regions, and integration of multiple detection mechanisms will enhance the monitoring capacity. [ABSTRACT FROM AUTHOR]

We introduce a detailed theoretical, numerical, and experimental study of the effects of laser’s phase noise on the performance of phase-sensitive optical time-domain reflectometry ($\phi$ -OTDR) sensors that use optical pulse compression (OPC). Pulse compression is a technique that can be used to improve the received signal amplitude by increasing the effective energy of the pulses that are launched into the fiber without degrading the spatial resolution of the measurements. Therefore, it is a valuable tool to extend the range of these sensors and mitigate fiber attenuation constraints. However, it has been observed that the limited coherence of the laser source has a degrading effect on the actual performance enhancement that this method can provide. Here, we derive a theoretical model that can be used to quantify this degradation for any type of OPC such as those based on either linear frequency modulation (LFM) pulses or perfect periodic autocorrelation (PPA) bipolar bit sequences. The model facilitates numerical estimation of the sensitivity of the $\phi$ -OTDR measurements. It also produces theoretical expressions for the mean and the variance of the phase-noise perturbed backscatter response. These results are validated via numerical simulations and experiments in $\phi$ -OTDR setups using LFM as well as PPA OPC. Furthermore, we demonstrate the use of the model to investigate the basic trade-offs involved in the design of OPC $\phi$ -OTDR systems. [ABSTRACT FROM AUTHOR]

A new principle MOEMS accelerometer based on the magneto-optical rotation effect is developed. The design of the magnetic film integrates with the proof mass, using a magneto-optic crystal to detect the magnetic field changes induced by the external acceleration to produce the magneto-optical rotation effect. By detecting the optical rotation angle, the high precision measurement of the acceleration is realized. The structure of the accelerometer was fabricated through structural design, simulation and micro-nano processing technology. The test results show that the noise spectral density of the MOEMS accelerometer is $10.5\mu \text{g}/\surd $ Hz at 1Hz, the bias instability is $37.6\mu \text{g}$ and the output sensitivity is 330.2mV/g. [ABSTRACT FROM AUTHOR]

Objective: Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human eye. Conventional methods of correcting presbyopia divide the field of view, thereby resulting in significant vision impairment. We demonstrate the design, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without dividing the field of view. Methods: The adaptive optics eyeglasses comprise of two variable-focus liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics, housed within an ergonomic frame. Subject-specific accommodation deficiency models were utilized to demonstrate high-fidelity accommodative correction. The abilities of this system to reduce accommodation deficiency, its power consumption, response time, optical performance and MTF were evaluated. Results: Average corrected accommodation deficiencies for 5 subjects ranged from -0.021 D to 0.016 D. Each accommodation correction calculation was performed in ∼67 ms which consumed 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, and featured a restorative accommodative range of 4.3 D. This system was capable of running for up to 19 hours between charge cycles and weighed ∼132 g. Conclusion: The design, assembly and performance of an autofocusing eyeglasses system to restore accommodation in presbyopes has been demonstrated. Significance: The new autofocusing eyeglasses system presented in this article has the potential to restore pre-presbyopic levels of accommodation in subjects diagnosed with presbyopia. [ABSTRACT FROM AUTHOR]

This work presents a 3-D-integrated opto-electrical receiver (RX) analog front end (AFE) operating up to 50 Gb/s. The electronic integrated circuit (EIC) is fabricated in ST SiGe BiCMOS-55-nm technology and flipped and mounted on top of the ST photonic integrated circuits (PICs) die through copper pillars (Cu-Pi). In the RX chain, a low-power fully differential shunt-feedback trans-impedance amplifier (FD SF-TIA) is exploited to reduce the input-referred noise. Following the TIA, a postamplifier (PA) based on a novel active feedback circuit topology extends the bandwidth (BW) and a buffer delivers the output electrical signal to the 100- $\Omega $ differential off-chip load. An automatic offset cancellation loop is included to protect the RX from any offset source at the input. The RX AFE consumes 56 mW from 1.8-V supply voltage and provides a trans-impedance (TI) gain of $78.7~\Omega $ with 27-GHz BW. By exploiting the FD SF-TIA with low parasitic capacitance of the germanium photodiodes (Ge-PD) in the photonic die as well as BW recovery by the PA, the RX achieves the sensitivity of −7.5-dBm OMA at Ge-PD and −2.3-dBm OMA at the single-mode fiber (SMF) optical output with bit error rate (BER) of <10−12 and PRBS-7. To the author’s best knowledge, among published state-of-the-art 50-Gb/s TIAs and RX exploiting SiGe BiCMOS technologies, this work proves the best energy efficiency ((pJ/bit)) and figure of merit (FoM) ($({\text {Gbps}}/{\mu \text {A.mW}})$) in terms of sensitivity and power consumption. [ABSTRACT FROM AUTHOR]

We present an interpretation of conventional figure-of-merit (FOM) and average input-referred noise current density (IRNCD) that characterizes optical receivers to determine how technologies and circuits best address energy efficiency. A design methodology is presented for differential optical receivers based on Cherry-Hooper Emitter Follower (CHEF) front-end designs targeting 56-Gbps applications is realized in a 130-nm SiGe BiCMOS process. The electrical measurements in a 50- $\Omega$ environment demonstrate data rates up to 112 Gbps and 84 Gbps for two design variants. In an open input and maximum gain configuration, the rms input referred noise currents are 3.59 $\mu$ $A_{RMS}$ and 2.41 $\mu$ $A_{RMS}$ and the corresponding average input referred noise current densities are 17.25 $pA/\sqrt{Hz}$ and 12.86 $pA/\sqrt{Hz}$. The packaged electro-optical measurements of the receiver variants is carried out with a single commercial off-the-shelf (COTS) photodetector demonstrate open eyes at data rates up to 64 Gbps. At 60 Gbps, the receiver variants achieve a $BER < 10^{-10}$ and $BER < 10^{-9}$. The total power consumption for the variants are 162 mW and 138 mW for overall energy efficiencies (with respect to electro-optical performance) of 2.53 $pJ/bit$ and 2.3 $pJ/bit$. [ABSTRACT FROM AUTHOR]

We propose herein a novel optical sensing technology using liquid crystal based transducers to measure simultaneously voltage and current from overhead power lines in real time. Doing so, we implemented a proof-of-principle system based on this approach and we demonstrated not only good accuracy, but also small phase shift and adequate bandwidth for power quality and fault monitoring applications. This is supported by experimental results for current, voltage and power monitoring, which include transient measurements and show excellent agreement with commercial reference probes. The system presented in this paper has been developed for single wire earth return (SWER) lines operating at 12.7 kV or 19.1 kV, but can be adapted to work at higher or lower voltages with appropriate modifications. We conclude by discussing the calibration process improvements that would be required for the technology to meet industry standards. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel optical BioNEMS (Biological-Nano-Electro-Mechanical Systems) sensor based on a 1D photonic crystal (PhC) structure in order to develop a label free biosensing platform. The proposed biosensor consists of a BioNEMS cantilever as the tunable defect of the PhC detection part. This optical sensing system is a finite air hole photonic crystal with a nano air gap in the center of the structure so that the NEMS movable part can be freely displaced. Biomolecular interactions induce a surface stress on the functionalized surface of the movable structure. As a consequence, a nanomechanical bending occurs in the NEMS cantilever because of the released energy of binding events. This can change the defect of the proposed PhC which causes shifts in the transmitted wavelength for various concentrations of biomarkers. By analyzing the proposed device using numerical and analytical approaches, the functional characteristics of the present BioNEMS sensor are obtained as follows: optical sensitivity of 13452 nm/RIU, FOM of 7912 RIU−1, mechanical sensitivity of $4.6~\mu \text{m}$ /Nm−1 and resonant frequency of 33.3 kHz. According to the results, this ultra-high sensitive sensor can be a promising choice to realize efficient label-free biosensors for early diagnoses of diseases in Point-of-Care Testing (POCT). [ABSTRACT FROM AUTHOR]

In this work, we report on the fabrication and characterization of a miniature GaN chip with a size of $1.1\times 1.1\times0.21$ mm3 for surface roughness measurement. Unlike conventional optical metrology that requires external components for the optical coupling between light source and detector, a monolithic GaN-on-sapphire chip fabricated through wafer-scale processes provides light emission and photodetection functions and is capable of sensing a range of average surface roughness from 0.025 to $1.6~\mu \text{m}$. The sensing performances are compared with fiber-optic metrology, and the ability to real-time monitor the roughness of the moving surface is demonstrated. The novel chip offers the advantage of non-contact and non-destructive, compact structure, simple operation, and in situ measurement capability, which is highly valuable for various practical and industrial surface metrology applications. [ABSTRACT FROM AUTHOR]

A method to carry out a priori simulations of pulsed-laser-induced single-event effects experiments is reported. Nonlinear optical simulations are conducted to model the 3-D distributions of charge from a laser pulse. These pulsed-laser-induced charge distributions are then incorporated into a charge transport solver to model the movement of charge as the device returns to a steady state. The output of the simulation infrastructure is a current transient from which collected charge and the temporal characteristics of the transient can be determined. This complete approach to modeling, which includes full device structure information, nonlinear optical energy deposition, and the subsequent movement of optically generated charge in a device and measurement circuit, allows for direct comparison between experimental and simulated current transients. A large-area silicon diode was used as the test vehicle, and good agreement was found between simulations and experiments in both total injected charge as well as temporal characteristics. Importantly, the a priori simulation approach does not require knowledge from prior heavy-ion testing, making it a predictive tool with broad versatility and minimal reliance on approximations. [ABSTRACT FROM AUTHOR]

The nondispersive per-sample channel model for the optical fiber channel is considered. Under certain smoothness assumptions, the problem of finding the minimum amount of noise energy that can render two different input points indistinguishable is formulated. This minimum noise energy is then taken as a measure of distance between the points in the input alphabet. Using the machinery of optimal control theory, necessary conditions that describe the minimum-energy noise trajectories are stated as a system of nonlinear differential equations. It is shown how to find the distance between two input points by solving this system of differential equations. The problem of designing signal constellations with the largest minimum distance subject to a peak power constraint is formulated as a clique-finding problem. As an example, a 16-point constellation is designed and compared with conventional quadrature amplitude modulation. A computationally efficient approximation for the proposed distance measure is provided. It is shown how to use this approximation to design large constellations with large minimum distances. Based on the control-theoretic viewpoint of this paper, a new decoding scheme for such nonlinear channels is proposed. [ABSTRACT FROM AUTHOR]

We present a portable Rydberg-atom-based radio frequency (RF) electric ($E$) field measurement instrument (Rydberg field measurement system or RFMS). The RFMS comprises an atomic RF field probe (RFP) connected by a ruggedized fiber-optic patch cord to a portable mainframe control unit. The unit includes a software interface providing self-calibrated SI-traceable RF measurement and analysis, including real-time field and measurement uncertainty readout and spectral RF waveform visualization. We characterize the RFP and measure polar field and polarization patterns along primary axes of the RFP at 12.6 GHz, obtained by rotations of the RFP in the far-field of a standard gain horn antenna. Field pattern measurements at 2.5 GHz are also presented. The measured field patterns are in good agreement with finite-element simulations of the RFP, establishing that the atom-based RF $E$ -field probe is well-suited for SI-traceable RF measurements over multiple bands. A one-time calibration procedure and an uncertainty analysis are introduced and implemented, as required for practical atomic probe designs to realize absolute-standard SI-traceable measurement capability. This includes uncertainty contributions from the atomic-spectroscopy measurement method and analysis and from the material, geometry, and hardware design. Simultaneous RF field and polarization measurements are demonstrated. RF waveform measurement is demonstrated using example pulsed and modulated RF signals. [ABSTRACT FROM AUTHOR]

This work develops a new optical photodiode array sensor for flow pattern identification of gas-liquid two-phase flow in minichannel. The array sensor is developed by the following steps to acquire comprehensive information of the flow and maintain a simple structure: 1) optical signals of the flow are acquired by a matrix array sensor with 60 sensing elements; 2) the signals are preprocessed and divided into 5 clusters by hierarchical clustering; 3) one typical sensing element from each cluster is selected; 4) the selected elements of four typical flow patterns are combined and the final sensor structure with 7 elements is determined. Experiments of flow pattern identification based on support vector machine (SVM) is carried out to verify the feasibility of the developed sensor in a 4.04 mm diameter channel. In addition, three types of feature vectors are built, including mean value, standard deviation and frequency, and their performance on the identification is investigated. The flowrate of liquid and gas phase range from 55~332 mm/s and 8~41468 mm/s, respectively. The investigated flow patterns include bubble flow, slug flow, stratified flow and annular flow. Results verifies the feasibility of the optical sensor. Among the three types of feature vectors, the standard deviation has the best performance, while the frequency has the worst. Meanwhile, the results also demonstrate that the combination of some specific feature vectors is an effective way to improve the identification performance. [ABSTRACT FROM AUTHOR]

The principle and procedure of coding a convolutional neural network (CNN) in terms of the spectral transmittance of a programmable optical filter are proposed and discussed. They exhibit an intrinsic link between the CNNs and the optical filters, which leads to a methodology by which optical imaging through such spectral transmittance can be seen as equivalent to the results of hyperspectral data numerically postprocessed by the CNN. In such a manner, hyperspectral data acquisition and CNN postprocessing can be implemented simultaneously by the physical process of optical imaging in a snapshot; thus, more intelligent, informative, and real-time optical detection and sensing in the remote sensing applications can be achieved. [ABSTRACT FROM AUTHOR]

For many industrial applications, corrosion is a life-limiting phenomenon and therefore requires careful consideration and rigorous experimental testing before structural materials can be reliably deployed, particularly in harsh chemical environments. The traditional approach to measuring corrosion requires exposing many samples to the intended environment and then extracting them individually at discrete intervals for postexposure characterization. This approach does not provide a high degree of temporal resolution, nor does it provide any real-time information regarding dynamic changes in corrosion rates. Developing an online corrosion monitor capable of surviving harsh chemical environments could provide valuable information regarding the structural health of components and changing process conditions that could accelerate corrosion. To this end, a corrosion sensor was developed based on a pressure-driven Fabry-Pérot cavity (FPC). This sensor uses a pressure control system to internally pressurize the FPC formed between the sensor’s housing and a metal-embedded singlemode optical fiber. Simultaneous measurement of the change in FPC length using low-coherence interferometry and the applied pressure enables the calculation of the relative changes in the sensor’s diaphragm thickness due to corrosion on its outer surface. Measurements were made in situ while actively corroding the sensor and were validated against surveillance specimens that were corroded simultaneously. The uncertainties in the measured corrosion were analyzed using error propagation of the uncertainties in the measured pressures and displacements and were found to be <1% of the initial diaphragm thickness. [ABSTRACT FROM AUTHOR]

Microengineering/nanoengineering is an emerging field that enables engineering and scientific discoveries in the microworld. As an effective and powerful tool for automation and manipulation at small scales, precision motion measurement by computer microvision is now broadly accepted and widely used in microengineering/nanoengineering. Unlike other measurement methods, the vision-based techniques can intuitively visualize the measuring process with high interactivity, expansibility, and flexibility. This article aims to comprehensively present a survey of microvision-based motion measurement from the collective experience. Working principles of microvision systems are first introduced and described, where the hardware configuration, model calibration, and motion measurement algorithms are systematically summarized. The characteristics and performances of different microvision-based methods are then analyzed and discussed in terms of measurement resolution, range, degree of freedom, efficiency, and error sources. Recent advances of applications empowered by the developed computer microvision-based methods are also presented. The review can be helpful to researchers who engage in the development of microvision-based techniques and provide the recent state and tendency for the research community of vision-based measurement, manipulation, and automation at microscale/nanoscale. [ABSTRACT FROM AUTHOR]

In this article, a Shack–Hartmann wavefront sensor is combined with a mechatronic positioning system to overcome the limited dynamic range of the Shack–Hartmann sensor (SHS) by repositioning and reorienting the SHS. Feedback loops to ensure a tangential orientation of the wavefront sensor in every measurement position and a measurement strategy that compensates for tip and tilt between wavefront and sensor are described and implemented. A framework that estimates the admissible measurement trajectories by relating the positioning errors caused by misalignments of the stages to the parameters of the wavefront sensor is developed. It is demonstrated that the setup is capable of directly measuring a highly divergent optical wavefront by combining wavefront data and positioning data acquired along the wavefront generated by a microscope objective with numerical aperture (NA) of 0.45. [ABSTRACT FROM AUTHOR]

In this study, a portable optical instrument was designed and developed for real-time nondestructive determination of fruit ripeness. A prototype of the instrument using inexpensive parts was developed and calibrated for apple ripeness detection based on moisture content, soluble solids content, pH, and firmness. An array of six optical point sources (light-emitting diodes (LEDs) that emit light at 520-, 670-, 920-, 970-, 1050-, and 1320-nm wavelengths) were selected using visible/near infrarred (Vis/NIR) spectral analysis on apple samples. The instrument was equipped with optical fibers, optical sensors, and an Arduino board for sending and receiving the waves and processing the received signals, as well as controlling the operation of the instrument. The decision tree method was utilized to create a classification model for training the instrument to classify ripe and unripe apples. Test results showed acceptable performance of the developed instrument for apple ripeness estimation and proved useful in classifying fruits into ripe and unripe groups based on their internal quality. [ABSTRACT FROM AUTHOR]

The full body illusion (FBI) is a bodily illusion based on the application of multisensory conflicts that induce changes in bodily self-consciousness (BSC). This has been used to study cognitive brain mechanisms underlying body ownership and related aspects of self-consciousness. Typically, such paradigms employ external passive multisensory stimulation, thus neglecting the possible contributions of self-generated action and haptic cues to body ownership. In this article, the effects of both external and voluntary self-touch on BSC were examined with a robotics-based FBI paradigm. We compared the effects of classical passive visuotactile stimulation and active self-touch (in which experimental participants had a sense of agency over the tactile stimulation) on the FBI. We evaluated these effects using a questionnaire, crossmodal congruency task, and measurements of changes in self-location. The results indicated that both synchronous passive visuotactile stimulation and synchronous active self-touch induced illusory ownership over a virtual body, without significant differences in their magnitudes. However, the FBI induced by active self-touch was associated with a larger drift in self-location towards the virtual body. These results show that movement-related signals arising from self-touch impact the BSC not only for hand ownership but also for torso-centered body ownership and related aspects of BSC. [ABSTRACT FROM AUTHOR]

An electric field measurement system with two optical pulse sources down-converts the high-frequency electric signal to the baseband through a probe exploiting the electro optic-effect. From that process, it is feasible to recover the measured frequency. However, the majority of the current studies focus on the case where the difference between the two repetition frequencies is quite small, while only a few involve larger frequency differences. Nevertheless, in a non-laboratory uncontrolled environment such as a field measurement, it is commonly unfeasible to guarantee a small frequency difference imposing further study on frequency recovery methods under larger frequency difference. Spurred by that, in this paper we propose a universal frequency recovery algorithm relying on the Remainder Matching (RM) technique, which is suitable for both large and small frequency differences. In our method, we employ the RM technique to determine the exact remainder combination in the first repetition frequency intervals and calculate the measured frequency. We also present the theoretical basis of RM, along with a summary of the system design rules, which have a significant impact on the performance of the measurement system. Finally, we challenge our RM-based solution on noise and analyze the corresponding false alarm rate metric. Our results demo nstrate that the proposed RM-based frequency recovery algorithm attains an appealing performance. [ABSTRACT FROM AUTHOR]

We present a CMOS biochip-based photometer for quantitative immunoassay diagnostics. The photometer quantifies the concentration of antigens based on light absorption, which allows for a low-cost implementation without expensive optical components. We propose a light controller to lower the start-up and settling time of the light source to 30 seconds, to facilitate fast measurement starts, and to decrease the overall measurement times. The application-specific integrated circuit (ASIC) contains a 6 x 7-sensor array with 100 μm x 100 μm photodiodes that serve as signal transducers. The ASIC was developed in a normal 0.35- μm CMOS technology, avoiding the need for expensive post-CMOS processes. We present our strategy for the assembly of the ASIC and the immobilization of antibodies. For its first time, we demonstrate the quantification of prostate specific antigen (PSA) with an optoelectronic CMOS biochip using this approach. A PSA immunoassay is performed on the top surface of the CMOS sensor array, enzyme kinetics and PSA concentration are measured within 6 minutes with a limit of detection (LoD) of 0.5 ng/ml, which meets clinical testing requirements. We achieve an overall coefficient of variation (CV) of 7%, which is good compared to other point-of-care (PoC) systems. [ABSTRACT FROM AUTHOR]

We present a concept for networked optical wireless communications, also denoted as LiFi, to meet the requirements of industrial wireless applications. These are primarily mobility support with moderate data rates per device, reliable real-time communication, and integrated positioning. We describe a distributed multiuser multiple-input multiple-output architecture, serving mobile devices via an optical wireless infrastructure. The system consists of a central unit, being connected to a number of distributed optical frontends covering a larger area. Our main contribution is a medium access control protocol based on space division multiple access. Evaluation results demonstrate the advantages of joint transmission from adjacent optical frontends and the dynamic switching between spatial diversity and multiplexing. The relevance of spatial multiplexing becomes obvious through channel measurements in an indoor scenario. Moreover, we highlight a low-power physical layer based on on-off-keying for battery-powered mobile devices. Our architecture can easily integrate positioning by simultaneously measuring the time-of-flight between multiple optical frontends and the mobile device. We highlight the use of plastic optical fiber as an analog fronthaul technology and discuss the integration with other networks. The main functions described in this paper will be supported by the upcoming IEEE Std 802.15.13. [ABSTRACT FROM AUTHOR]

In this study, a method to improve the detection accuracy of a “weak measurement” system of optical rotation was proposed by determining the optimal total phase difference of the system. Analysis of the characteristics of weak measurement regime of the system under different total phase differences provided the total phase difference corresponding to the regime with the smallest ratio of system noise level to sensitivity (that is, the highest system resolution). In this regime, an optical rotation resolution of 5.522 × 10−6° was obtained, which is nearly an order of magnitude higher than the original system. [ABSTRACT FROM AUTHOR]

A multi-channel high-throughput chiral molecule determination method based on weak value amplification (WVA) is proposed for the first time. This method can be used for high-throughput and high-precision determination of chiral molecule. Through the design of multi-channel weak measurement system, we realized the real-time, high-throughput, high-sensitivity and high-resolution detection of chiral molecules by selecting proper measurement states. In this work, we have realized a sensitivity of 11.8 nm/° and a resolution of 3.13 × 10-4° for measuring optical rotation. Moreover, the proposed method is successfully applied for detection of lactose content in milk samples. Furthermore, the system has the advantages of simple and robust real-time detection settings, strong stability, high measurement efficiency and good scalability. This method has important significance in clinical diagnosis, food safety and biological system. [ABSTRACT FROM AUTHOR]

A centimeter-level spatial resolution distributed temperature sensor (DTS) based on polarization-sensitive optical frequency domain reflectometry (OFDR) is proposed. Polarization-maintaining fiber (PMF) is employed as the sensing fiber. The birefringence along the PMF is detected from the Rayleigh backscattering (RBS) spectral difference between the two orthogonal polarization axes, which is retrieved by short-time Fourier transform and distributed cross-correlation algorithm, and thus the large error induced by the auto-correlation is eliminated. Since the birefringence is roughly uniform for the same type of PMF, relationship between the absolute temperature and the birefringence calibrated on a small fiber section can be applied to the whole fiber, or even the same batch of fiber, which brings convenience in practice. The linear relationship between the absolute temperature and the RBS spectral difference is experimentally verified, and distributed temperature measurements are implemented with a high spatial resolution of 1.3 cm along the 94 m sensing fiber. The absolute temperature measurement uncertainty is ± 4.5°C in the experiment, which is mainly limited by the birefringence non-uniformity. In some cases the impact of birefringence non-uniformity can be eliminated, and thus the temperature measurement uncertainty can be improved up to ± 0.8°C, which is limited by the random noise in the proposed system. [ABSTRACT FROM AUTHOR]

In this paper, an absolute time-grating displacement sensor with high accuracy and high resolution is proposed, where primary, secondary, and tertiary stage capacitor arrays with ${M}$ , ${N}$ , and ${N}$ –1 measurement periods, respectively, are combined by a multi-stage composite method that applies the four orthogonal traveling wave signals output by the primary-stage as the excitation signals of the secondary and tertiary stages. Combining the primary and secondary stages yields sensor A, with ${M}\,\,+\,\,{N}$ measurement periods. Similarly, sensor B, composed of the primary and tertiary stages, has ${M}\,\,+\,\,{N}$ –1 measurement periods. Sensor A is used as the fine measurement component, and the phase difference between sensors A and B is used as the coarse measurement component. Absolute positioning is realized in a similar manner to a Vernier caliper measurement. The output signal of each stage includes odd harmonics, such that the measurement error of each stage contains the fourth harmonic. This is retained in the synthesis stage by the multi-stage composite method. Experimental results for a prototype sensor yield an absolute positioning error of ±200 nm over a measurement range of 200 mm. Depending on the multi-stage composite method, the measurement accuracy and resolution of the same size time-grating are improved, and the connection of the input and output are focused on a stationary component. This compact and convenient sensor has wider application prospects for machine tools and automatic machine systems. [ABSTRACT FROM AUTHOR]

We report on hybrid BiCMOS-Silicon photonics receivers with waveguide coupled Ge/Si avalanche photodiodes, designed in a lateral separate charge absorption multiplication configuration. We demonstrate optical modulation amplitude sensitivities of −14.4 dBm for error-free operation at 50 Gb/s and −18.6 dBm under the KP4-FEC limit at 56 Gb/s using NRZ-OOK modulation. An in-depth analysis of the receiver sensitivity is carried out to understand the impact of dark current, and to identify pathways for further improvements. The demonstration of such highly sensitive receivers, supported with a receiver model, paves the way to improve optical link margins at 50 Gb/s and beyond. [ABSTRACT FROM AUTHOR]

The conventional method of detecting inhibitor content in transformer oil is by using fourier-transform infrared spectroscopy at the mid-infrared region. This wavelength of detection brings several technical challenges in fabricating the photodetector and light source. Therefore, as a fundamental research that can potentially lead to the development of an on-site measuring device, this study reports on the discovery of a new optical detection wavelength (959 nm) that can be used to measure the concentration of inhibitor in transformer oil. A total of 35 samples were manually prepared and measured using the Agilent Cary5000 Spectrophotometer from 950 nm – 970 nm with cuvettes of three different path lengths. The peak at 959 nm shows the second overtone of O-H stretch in inhibitor and has a strong correlation with Morse oscillation model. Two mathematical models were established for fixed and variable optical path lengths based on the correlation between the concentrations of inhibitor and the optical absorbance spectra of the samples. The mathematical models were verified with average errors of 4.00% and 5.49% for single and variable path length models, respectively. Finally, the importance of a variable path length measurement and the application of the newly discovered wavelength are critically analyzed and presented. The combination of the variable path length model and the detection of inhibitor at Silicon-detectable wavelengths (< 1100 nm) enables the utilization of Silicon technology in the development of an inhibitor monitoring device which can be used in various industries. [ABSTRACT FROM AUTHOR]

Since the late 1950s, blood pCO2 can be measured by using electrodes and, more recently, also by using point-of-care instruments such as blood gas and chemistry analyzers. Nevertheless, nowadays no measurement method has succeeded in providing an economic, reliable, and accurate estimate of the blood- pCO2 to be routinely used for the monitoring of extracorporeal (blood) circulation (ECC) treatments. Indeed, blood is a very complex biological matrix composed of several different constituents, thus apart from a limited maximum-admitted measurement error (about some mmHg) and a quite wide measuring interval (about [20, 100] mmHg), the measuring systems have to provide significant selectivity taking hemocompatibility and safety for the patient as a primary concern. In this article, we propose and demonstrate a measuring instrument consisting of a low-cost and disposable fluorescent pco-sensor that can be inserted in series with the bloodline, and a nondisposable optical head that contactless reads the sensor. The proposed measuring system is intrinsically safe for the patient, has adequate metrological performance, avoids blood sampling and the related issues, and may allow to comply with cost requirements. Preliminary tests, conducted simulating a 6-h ECC treatment by using bovine blood, revealed deviations from the reference measuring instrument of less than ±4 mmHg, while the blood- pCO2 was varied in the range [20, 100] mmHg. [ABSTRACT FROM AUTHOR]

Electric field is one of the key parameters to study the charge dynamics for corona discharge. To study the motion characteristics of space charge in different corona modes of ac corona, electrooptic (EO) modulation technique was used to obtain the electric field in corona space. This article focuses on the time-varying characteristics of electric field for ac corona discharge modes. The step phenomenon is observed and the evolution characteristics of electric field for corona modes, from the Trichel pulses to the stable glow, are obtained. It was found that the background field could not remove the space charge generated by the discharge completely within half a cycle, which directly proved the existence of retained charge. And it is proposed that the continuous and fast rising electric field is the characteristic of positive glow in ac corona, which may be an effective method to judge the positive glow. Additionally, electric fields at different spatial locations were studied. The electric field step at the migration zone is suppressed, and as the space charge density increases, the suppression phenomenon becomes more obvious. This article provides more information on the physical mechanisms of the ac corona modes and gives support for the research of corona plasma. [ABSTRACT FROM AUTHOR]

Optical frequency domain reflectometry (OFDR) measurements are performed by recording the interference pattern of light backscattered by density fluctuations or Bragg gratings along the length of an optical fiber. Changes in local temperature or strain in the fiber cause shifts in the backscattered light spectrum, which can be calibrated to the applied temperature or strain. Comparing the backscattered optical spectra from each reflection site with a reference (unstrained) spectrum allows for quantification of local spectral shifts. While mature OFDR-based technologies can provide high-precision spatially distributed measurements over kilometer lengths, the post-processing approaches used to recover spectral shifts from raw optical intensity data can limit the use of OFDR in harsh environments. This paper presents a novel approach to post-processing OFDR data which extends the usability of optical fibers exposed to harsh environments. This approach is the first to use the spectral shift quality, calculated for two OFDR measurements, to identify an appropriate reference scan from which the spectral shift can be determined. Three experimental data sets are used to test the algorithm: (1) an optical fiber heated to >950°C, (2) an aluminum-embedded optical fiber under strain from differential thermal expansion, and (3) an optical fiber exposed to a total neutron flux of $2\times 10^{13}$ n/cm2/s over 40 hours in a nuclear test reactor. Results show that using a metric of quality to select an appropriate reference measurement extends the functional range of OFDR strain and temperature sensors. Furthermore, this algorithm can be applied to existing OFDR data. [ABSTRACT FROM AUTHOR]

Nowadays, the most successful optical technique developed for measuring high voltages in 50-/60-Hz electric power lines utilizes the bulk lithium niobate Pockels cell, constituting the so-called optical voltage sensor (OVS). However, unlike the area of vibrometry, where there are ISO standards based on reliable and simple interferometric methods for calibrating the sensors, there is still no standardized procedure for measuring $V_{\pi }$ (half-wave voltage) of Pockels cells or for calibrating OVSs. As the Pockels cell-based OVSs can be considered as a polarimetric interferometer, and inspired by the ISO 16063–41 standard (for the calibration of vibration and shock transducers), specifically the technique called signal coincidence method (SCM), this work presents a new digital and real-time method for optical phase detection tailored for the measurement of $V_{\pi }$ in OVSs. Measurements were made in order to demonstrate the effectiveness of the new technique by applying a voltage signal to the OVS, composed by the superposition of a 60-Hz sinusoidal voltage, with amplitude equal to the reference value of $V_{\pi }$ (4.068 kV in this case) and a dc voltage high enough to provide a 90° bias static phase shift, as specified by SCM, proving that the method can recover the value of $V_{\pi }$ in accordance with the estimated value. However, it is well known that the adjustment of the bias phase in a polarimetric interferometer can undergo undesired variations from time to time, due to drifts in ambient temperature and other external disturbances, taking the OVS out of its optimal operating point and thus not attending the ISO standard. As an advantage, experiments have shown that the new method is tolerant to variations in the 90° bias static phase (ranging from 60° to 120°), as well as to variations in the amplitude of the voltage applied to the OVS, varying ±25% in relation to the 4.068-kV reference voltage. The $V_{\pi }$ values were accurately detected, with a maximum percentage error of 0.2% and, therefore, satisfying the specification of the ISO 16063 standard. [ABSTRACT FROM AUTHOR]

Attenuated backscatter measurements from a Vaisala CL31 ceilometer and a modified form of the well-known slope method are used to derive the ceilometer extinction profiles during rain events, restricted to rainfall rates (RRs) below approximately 10 mm/h. RR estimates from collocated S-band radar and portable disdrometer are used to derive the RR-to-extinction correlation models for the ceilometer–radar and ceilometer–disdrometer combinations. Data were collected during an intensive observation period of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) conducted in northern Alabama. These models are used to estimate the RR from the ceilometer observations in similar situations that do not have collocated radar or the disdrometer. Such correlation models are, however, limited by the different temporal and spatial resolutions of the measured variables, measurement capabilities of the instruments, and the inherent assumption of a homogeneous atmosphere. An empirical method based on extinction and RR uncertainty scoring and covariance fitting are proposed to solve, in part, these limitations. [ABSTRACT FROM AUTHOR]

For the first time, a CAOS (i.e., Coded Access Optical Sensor) spectrometer is demonstrated. The design implemented uses a reflective diffraction grating and a time-frequency CAOS mode operations Digital Micromirror Device (DMD) in combination with a large area point photo-detector to enable highly programmable linear High Dynamic Range (HDR) spectrometry. Experiments are conducted with a 2850 K color temperature light bulb source and visible band color bandpass and high-pass filters as well as neutral density (ND) attenuation filters. A ~369 nm to ~715 nm input light source spectrum is measured with a designed ~1 nm spectral resolution. Using the optical filters and different CAOS modes, namely, Code Division Multiple Access (CDMA), Frequency Modulation (FM)-CDMA and FM-Time Division Multiple Access (TDMA) modes, measured are improving spectrometer linear dynamic ranges of 28 dB, 50 dB, and 96.2 dB, respectively. Applications for the linear HDR CAOS spectrometer includes materials inspection in biomedicine, foods, forensics, and pharmaceuticals. [ABSTRACT FROM AUTHOR]

The paper presents an approach to noninvasively measure pulse wave delay and velocity by means of two multiplexed fiber-optic Fabry-Perot interferometric sensors interrogated by means of spectral interferometry. The pulse wave signals were measured with 1 kHz sampling rate. The obtained optical path difference resolutions are on the order of tens picometers, which allowed the pulse wave signal features as small as 100 pm to be clearly observed in the demodulated waveforms. The pulse wave velocity between different arteries was measured, demonstrating good agreement with the known data, where applicable. The paper also presents a mathematical model based on Cramer-Rao approach, describing the fundamental resolution limits of the pulse wave delay measurement. The derived mathematical model is not limited to fiber-optic pulse wave sensors and can be used for estimating the performance of other systems, such as photoplethysmographic and ultrasound. The reported work paves the way to development of novel all-optical non-invasive systems for medical diagnostics and vital signs monitoring, including portable devices. [ABSTRACT FROM AUTHOR]

A liquid-level sensor using a gallium nitride (GaN) ultraviolet (UV) photodetector was successfully demonstrated. As the liquid level was changed, the intensity of UV light on the GaN surface was varied owing to the refraction of light on the liquid surface. For the fabrication of the liquid-level sensor, facile and rapid manufacturing was employed, involving metal wire bonding on the semiconductor surface. To characterize the fabricated sensor, the water level in the cylinder was measured according to the photocurrent change of the GaN UV photodetector. The responsivity of the liquid-level sensor depended on the diameter of the cylinder, applied voltage, and emission angle of the UV source. In particular, a cylinder diameter of 16 cm and an emission angle of 45° yielded a resolution of 0.05 cm up to the water level of 10 cm. The results of this study confirm the feasibility of liquid-level sensors for continuous and simultaneous liquid-level monitoring in harsh environments, including high-temperature plants, nuclear reactors, and chemical tanks. [ABSTRACT FROM AUTHOR]

Electromagnetic coil launcher (ECL) is a specific application of electromagnetic launching technology and has broad prospects in the fields of new weapon systems and launching microsatellites. The acceleration force of the projectile in the ECL depends on the current of the driving coil and the projectile together with the mutual inductance between them, and to maximize the launch coefficient, each drive coil should be energized according to the projectile’s movement position. In order to realize the closed-loop control of the ECL and improve the energy utilization, a new position detection system (PDS) based on fiber optic sensor (FOS) is designed in this article, which can obtain the armature displacement and velocity in real time during the launch process. Then, the main factors influencing the detection results are analyzed and studied. Finally, after experimental verification, the PDS designed in this article has an error of 4.2% and 1.41% in the measurement of the armature position and velocity, respectively. The results are of great significance to the realization of ECL engineering. [ABSTRACT FROM AUTHOR]

The possibility of real-time monitor critical care analytes, such as pH, is recognized to provide relevant information for the diagnosis and treatment of a variety of disorders and would be of considerable support for the management of extracorporeal circulation (ECC). However, despite that blood pH can be measured from a long time by using electrodes or point-of-care instruments, such as blood-gas analyzers, costs, and complications associated with such measurement methods limit their use, thus, blood pH is generally not monitored during routinary ECC. In this article, we propose to exploit the tubing composing the ECC line to realize a low-cost and disposable pH-sensor and to interrogate such fluorescent sensors by using optical radiations. The proposed measuring system avoids complications related to blood sampling and may allow achieving single-patient cost requirements. Preliminary tests performed on a real ECC bloodline demonstrate that the system can operate with blood in ECC. Indeed, a 6-h ECC treatment simulated using bovine blood revealed a deviation with respect to the reference pH-meter typically of about a few thousandths pH and with a maximum of about 0.01 pH. [ABSTRACT FROM AUTHOR]

Accurate measurement of oxygen concentration for pharmaceutical glass bottles is of great significance to ensure the asepsis of medicine and stability of ingredients. With merits of high sensitivity, low cost, noncontact, and real-time response, the wavelength-modulation-based tunable diode laser absorption spectroscopy (TDLAS/WMS) technology shows great potential to achieve in-site oxygen concentration detection by the single-line spectrum measurement. This article focuses on headspace oxygen concentration measurement in the open-path optical environment, which is extremely challenging due to the short light path length and random ambient noises. First, a signal reconstruction method is established based on the discrete wavelet packet transform (DWPT), where random noise suppression is implicitly achieved. Then, oxygen concentration is inversed among the data between two adjacent valley values of the demodulated second-harmonic signal by multiple linear regression (MLR), and the linear discriminant analysis (LDA) is imported to enhance the information sparsity of second-harmonic signal matrix and to address the multicollinearity problem. Simulation results prove that our proposed method achieved considerable detection accuracy with the average absolute error of 0.05%. This article also designed a TDLAS/WMS prototype, and the experimental results aiming at glass bottles with different oxygen concentration of 0%, 5%, 10%, and 21% in open-path optical environment indicate our method has achieved an encouraging average absolute error of 0.54% and can survive well when the normalized signal-to-noise ratio (SNR) is within 0.85–1. These results promise that the proposed methodology can be widely applied in in-site automatic optic inspection (AOI) instrumentation of headspace oxygen concentration measurement for glass vials. [ABSTRACT FROM AUTHOR]

In this article, to improve navigation performance, observability-based navigation using optical and radiometric measurements for asteroid approach phase is proposed in tandem with the optimization of the configuration of spacecraft formation. By introducing the relative range and range-rate between spacecraft measured by radiometric sensors, the position and velocity of the two spacecraft are estimated, and the estimation performance degradation at the end of asteroid approach phase is reduced. A better observability of the integrated navigation system has been proven based on a novel geometry measurement model. Furthermore, a configuration optimization method is developed based on the lower bound of the Cramer–Rao inequality and the observability degree of the navigation system. By optimizing the configuration of spacecraft formation, the observability and estimation accuracy of the navigation system have been improved. Three cases of different configurations of spacecraft formation are established for numerical simulation, demonstrating the improvement in the accuracy of the navigation method. [ABSTRACT FROM AUTHOR]

Single-pixel camera (SPC) is an alternative architecture for imaging systems that emerged as an application of the compressive sensing theory. The SPC’s distinctive feature is the single detector that measures the linear combinations of pixels instead of pixels as in imaging array cameras. The measurements are obtained by projecting the scene on a spatial light modulator (SLM), the other distinctive component of the SPC architecture. This paper discusses the problem of resolution in SPC. We show that in terms of point spread function (PSF), the resolution model is similar to that of an imaging array camera except the fact that the role of the imaging array is taken over by the SLM. This reduces the contribution of the optics to the SPC resolution comparing with the CCD cameras. Relying on an existing method, we develop a procedure that uses a circular chart to measure the camera PSF. Our procedure has additional facilities: the correction of chart tilt and the capability to work with non-circular apertures. At low noise, tilts up to 15° are practically removed. [ABSTRACT FROM AUTHOR]