Electro-optical Sensors Research Articles

Uncooperative pose estimation with a LIDAR-based system

This paper aims at investigating the performance of a LIDAR-based system for pose determination of uncooperative targets. This problem is relevant to both debris removal and on-orbit servicing missions, and requires the adoption of suitable electro-optical sensors on board of a chaser platform, as well as model-based techniques for target detection and pose estimation. In this paper, a three dimensional approach is pursued in which the point cloud generated by a LIDAR is exploited for pose estimation. Specifically, the condition of close proximity flight to a large debris is considered, in which the relative motion determines a large variation of debris appearance and coverage in the sensor field of view, thus producing challenging conditions for pose estimation. A customized three dimensional Template Matching approach is proposed for fast and reliable pose initial acquisition, while pose tracking is carried out with an Iterative Closest Point algorithm exploiting different measurement-model matching techniques. Specific solutions are envisaged to speed algorithm convergence and limit the size of the point clouds used for pose initial acquisition and tracking to allow autonomous on-board operation. To investigate proposed approach effectiveness and achievable pose accuracy, a numerical simulation environment is developed implementing realistic debris geometry, debris-chaser close-proximity flight, and sensor operation. Results demonstrate algorithm capability of operating with sparse point clouds and large pose variations, while achieving sub-degree and sub-centimeter accuracy in relative attitude and position, respectively.

Nanosecond transient electric field measurement system using an integrated electro-optic sensor

A lithium niobate optical waveguide-based integrated electro-optic (EO) electric field ( E -field) sensor dedicated to the measurement of intense nanosecond transient electromagnetic pulse (EMP) signals has been developed and calibrated. The time domain calibration system for measurement of intense nanosecond EMP signals has been established. A pure optical bias phase angle control system based on wavelength tuning has been developed and implemented to ensure that the sensor has a linear transfer function. The fluctuations of the sensor static output optical power are with the proposed bias control system while without bias control. The time domain characteristics of the detected pulsed E -fields have been compared with those of the input EMP signals. For the first type nanosecond level (ns-level) EMP signal, the relative errors of the detected E -fields on rise time, fall time, and pulse width are 0.38%, 0.69%, and 0.79%, respectively. Also, for the second type ns-level EMP signal, the relative errors of the measured E -fields on rise time, fall time, and pulse width are 0.40%, 0.31%, and 0.01%, respectively. All these results demonstrate that the developed integrated EO E -field sensing system has the potential to be used to accurately extract the information of transient E -fields.

Electro-optical sensor for measuring amplitude-time characteristics of the electric field strength of ultra-wideband electromagnetic pulses

An electro-optical system is developed for measuring low field strengths (100 V cm−1) of ultra-wideband electromagnetic pulses using the DAST crystal. The electric field strength is measured and the spectral composition is calculated for the radiation of the experimental ultra-wideband electromagnetic pulse oscillator.

Electrooptic sensor module fabrication for near-field intrabody communication

In this paper, we describe how to obtain a low cost electrooptic (EO) sensor module for the mass production of near-field intrabody communication devices. In our previous study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes. In this study, we fabricated EO modulators as a miniaturized chip sensor without a base portion, and clarified the feasibility of assembling optical components by only a passive alignment technique with a compact housing.

파이로테크닉 고섬광 발생장치 조성설계 및 설계검증

The composition of bright flash device is a pyrotechnic mixture consisting of metal powder, oxidizer and additives. A pyrotechnic mixture of bright flash device generates a bright flash through burning after being ignited by initiator. The function of bright flash is to distract or incapacitate electro optical sensor systems and enemy eyes temporally. This study is to develop composition of pyrotechnic mixture of bright flash and to analyze the test results by considering intensity and efficiency of light.

Detection of Energized Structures With an Electro-Optic Electric Field Sensor

An electro-optic, solid-state electric field sensor system for noncontact detection of energized objects at power frequency (60 Hz) was investigated. In laboratory testing, the sensor system was found to have a minimum detectable field amplitude of 4 mV/m/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> , which was further reduced by a factor of 2 through vector averaging over 20 cycles. In an experimental setup emulating the realistic scenario of an energized conducting structure (such as a street light or metal fence post), the detection of a 1-m object energized at 1 VAC at a distance of 2 m was demonstrated.

Single Shot and Vectorial Characterization of Intense Electric Field in Various Environments With Pigtailed Electrooptic Probe

In this paper we illustrate the ability of electrooptic sensors to perform electric (E)-field vectorial measurements. Thanks to their frequency response spreading over nine decades and to their measurement dynamics reaching 120 dB, these sensors are of high interest for some applications (near field mapping, energy line monitoring, electromagnetic compatibility, and so on). Furthermore, due to their fully dielectric structure and millimetric size, almost no perturbation is induced on the E-field to be measured, even in the near field region. This paper is focused on high-intensity pulsed E-field characterization in different environments such as air, water (bioelectromagnetism applications), or plasmas ( in situ assessment of the E-field associated to an electric discharge and to the induced plasma). The use of such a technology for electrical equipment and energy line monitoring is also investigated.

Evaluation of UAS Class and EO Sensor Payload Type for Applications in Hostage Crisis Missions

Donohue V. (2014). Evaluation of UAS class and EO sensor payload type for applications in hostage crisis missions. International Journal of Unmanned Systems Engineering. 2(1): 1-8. Law Enforcement entities are tasked with ensuring the safety of citizens to the best of their ability. They use every advantage at their disposal to capture and restrain criminals while reducing the risk to civilians. This ability is often limited by the constraints of slim and shrinking budgets. Departments with larger budgets and greater flexibility have historically taken advantage of airborne assets, most often helicopters, which provide a tremendous advantage against criminals due to enhanced surveillance, pursuit, and capture capability. The latest technological advancements in remote electronic sensing, along with major strides in aircraft automation and miniaturization, have allowed a surge in the implementation of Unmanned Aircraft Systems (UAS) in Law Enforcement missions. This paper discusses the use of UAS by Law Enforcement in a hostage crisis situation. A scenario is presented and a Concept of Operations (CONOPS) is developed to thoroughly detail the mission goal, strategy and tactics. The class of UAS appropriate for the mission, including Micro Air Vehicles and small UAS, and a refined selection between fixed wing and rotary wing aircraft are identified. The Draganflyer X6 and the RAPTR rotary wing UAVs are discussed in deciding what system best accomplishes the hostage crisis mission. Electro-optical sensors, including high definition video, low light level TV and infrared sensors, provide superior applicability. © Marques Engineering Ltd.

A Reactive Bearing Angle Only Obstacle Avoidance Technique for Unmanned Ground Vehicles

In this paper, we present a reactive, vision based obstacle avoidance technique for Unmanned Ground Vehicles (UGVs) navigating in an indoor environment without Global Positioning System (GPS) signals. The proposed technique enables UGVs to maneuver using only visual electro-optic sensors. The proposed work is unique in that, to the best of our knowledge, there was no other bearing angle only obstacle avoidance technique for ground vehicles reported in the literature. A Lyapunov-based sliding mode controller is used to maintain the bearing angle of the UGV from obstacles, using a real-time image processing method. The proposed technique is implemented and tested with a Pioneer robot in an indoor environment, and the results demonstrate its effectiveness.

On the Design of Video-Bandwidth Electric Field Sensing Systems Using Dielectric ${\rm LiNbO}_{3}$ Electro-Optic Sensors and Optical Delays as Signal Carriers

As the measurement of wide-band (multi-megahertz) electric fields is often of practical interest in industrial and commercial environments, in this paper, a methodology of design and implementation of a wide-band electric field sensing scheme, using optical delays as information carriers is described. The scheme is based on a lithium niobate (LiNbO3) birefringent optical waveguide that performs simultaneously as an optical retarder and as a dielectric (electrode-less) sensor. In this scheme, the LiNbO3 sensor introduces an optical delay and simultaneously senses an on-air electric field and imprints it around an optical delay. At the receiver, the sensed electric field is detected when the sensor and demodulator are optically matched, i.e., when both introduce identical optical delays. An important aspect, when sensing electric fields using LiNbO3 dielectric sensors, is that the optically sensed field is weaker than the external field by a factor given by the ratio of the permittivity of the surrounding dielectric media over the LiNbO3 permittivity (boundary condition for normal electric fields). When the surrounding media is air, the optically sensed electric field is 35 times weaker than the external field, as described in this paper. Another practical issue is that a birefringent optical waveguide is highly sensitive to optical polarization variations. Such a sensitivity implies that the output dc component of the received light changes with time (dc-drift). The dc-drift performance of the proposed electric field sensing scheme is measured and reported in this paper. The dc-drift can be minimized using polarization-insensitive LiNbO3 unbalanced Mach-Zehnder interferometers.

Robustness of electric field vector sensing of electromagnetic waves by analyzing crystal angle dependence of the electro-optic effect

We theoretically and experimentally investigate the accuracy with which the magnitude and direction of the electric field (E-field) vector of electromagnetic waves can be determined using the crystal angle dependence of the electro-optic (EO) effect. The mathematical treatment in this paper is a large extension of our previous work to determine the E-field direction of terahertz electromagnetic waves by the spinning EO sensor method [Rev. Sci. Instrum.83, 023104 (2012)]. Here we include misadjustments of the wave plate and polarizer in the experimental setup as well as the effect of the residual birefringence of the EO crystal due to uniform and local strains. The main results are as follows: (1) When there is no residual birefringence in the EO crystal, misadjustments of the wave plate and polarizer do not affect the experimentally determined direction of the E-field vector. This is true even when the term proportional to the square of the E-field magnitude of the EO signal becomes important. (2) The error due to residual birefringence can be effectively eliminated by a signal subtraction algorithm and it is roughly the product of the misadjustment angle of the wave plate and the degree of residual birefringence, which is very small. (3) The error does not depend on the magnitude of the E-field; thus, we can apply the technique when the E-field is weak and the polarization rotation of the probe pulse caused by the EO effect is much smaller than that induced by residual birefringence. These results give a mathematical basis for the accuracy and reliability of the spinning EO sensor method, which is robust, and will be useful for ultrabroadband E-field vector sensing at far-infrared to mid-infrared frequencies.

A Nonperturbative Electrooptic Sensor for in Situ Electric Discharge Characterization

Pulsed power and intense electric field now apply to a large variety of domains for which the need of in situ nonperturbative measurements remains a challenge. The main requirements that sensors should fulfill for that purpose are nonmetallic composition, small size, ultrawide bandwidth, compatibility with liquids and gases, possibility for remote measurements at long distances, true vectorial (field direction) time-domain measurements, capability of measuring electric fields up to the electric breakdown of air, and a large dynamic range. Obviously, all these requirements cannot be achieved by a unique sensor. However, most of them are fulfilled by pigtailed electrooptic (EO) sensors. In this paper, after recalling the principle of the EO effect and its use for electric field measurement, we deal with the measurement linearity and selectivity of the EO sensor. Associated with the nonperturbative behavior of the EO sensor, the measurement dynamics of EO sensors exceeds 100 dB. Furthermore, EO sensors present an intrinsic flat response from quasi d.c. (10 Hz) up to a few tens of gigahertz. Thanks to their composition of high dielectric strength materials and their optical pigtail, EO sensors are completely immune to the electromagnetic environment except on a very small volume (≅ 10 mm3) corresponding to the transducer element of the sensor. This leads to a very high spatial resolution. We finally illustrate the capabilities of this technology through in situ measurement of the electric discharge transients and vectors.

Application of Cloud Occurrence Climatology from CALIOP to Evaluate Performances of Airborne and Satellite Electro-Optical Sensors

Abstract A wide variety of optronic sensors, on board a satellite or airborne platform, are used for remote sensing, surveillance applications, and telecommunications. Cloud presence in the field of view is one of the key factors limiting the performances of these sensors. Consequently, cloud presence must be taken into account in order to evaluate their performances. To that end, a Monte Carlo method is used. Geometrical and optical cloud properties necessary to build the model are obtained from Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) measurements that enable one to deal with the optically thinnest clouds. Different viewing geometries are presented, corresponding to surveillance missions by an airborne sensor with close-to-the-horizon viewing and to an optical link between an aircraft and a satellite. Results obtained are compared to a previous study and improvements reached with this new method are discussed.

Electro-optic acquisition system for ECG wearable sensor applications

In the past few years a remarkable progress has been made in the design of sensors for wearable devices. Nevertheless, the existent devices are difficult to integrate, mainly due to the quantity of electrical interconnections and components required at the sensing places. This leads to the need for a new generation of wearable sensors. Photonic sensors have been presented in the medical field as a valuable alternative where power supply, electromagnetic interference and integration constitute a challenge. Therefore, this paper presents an electro-optic (EO) acquisition system designed for wearable Electrocardiogram (ECG) monitoring devices. The system includes a Lithium Niobate Mach-Zehnder Interferometer (MZI) modulator as the sensing element, and an optoelectronic signal conversion and processing stage. Tests were made in order to evaluate system performance in terms of signal amplification and sensitivity, frequency response and linearity. Obtained results have shown a suitable sensor's sensitivity of 20μV and a frequency response of 60dB flat from 0.2 to 40Hz. Clinical sensor's performance was tested considering the requirements for evaluation of ECG. Results were compared with clinical standard electronics. Clear ECGs can be obtained with the EO sensor, showing adequate and reliable clinical performance. This EO sensor can be integrated into wearable materials being a suitable alternative for clinical cardiac monitoring.

Electro-Optical Sensor Fabricated Using a Bulk Cleavage Technique and Its Characteristics for Near-Field Intra-Body Communication

This paper describes how to obtain a low cost electro-optical (EO) sensor module for the mass production of near-field intra-body communication devices. In this study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes, and clarified the feasibility of assembling optical components using only a passive alignment technique with a compact housing.

Compact Electro-Optic Sensor Module for Intra-Body Communication Using Optical Pickup Technology

We developed a compact and low-cost electro-optic (EO) sensor module for intra-body communication using optical pickup technology. An EO crystal of zinc telluride (ZnTe) mainly contributes to use of the cost-effective optical pickup technology. ZnTe has the shortest wavelength for optical transmission, about 570 nm; therefore it can use a low-cost 790-nm wavelength laser diode widely used in compact disc players. The measured modulation depth of the new EO sensor module was about 1.56 times deeper than our old one. The measured value agreed with the calculated value; therefore, there is no performance deterioration by downsizing the sensor module. The sensor module was successfully applied to 10-Mbps half-duplex intra-body communication.

Cross-Sectional Study of Macrodefects in MBE Dual-Band HgCdTe on CdZnTe

HgCdTe dual-band mid-wave infrared/long-wave infrared focal-plane arrays on CdZnTe are a key component in advanced electrooptic sensor applications. Molecular beam epitaxy (MBE) has been used successfully for growth of dual-band layers on larger CdZnTe substrates. However, the macrodefect density, which is known to reduce the pixel operability and its run-to-run variation, is larger when compared with layers grown on Si substrate. This paper reports the macrodefect density versus size signature of a well-optimized MBE dual-band growth and a cross-sectional study of a macrodefect that represents the most prevalent class using focused ion beam, scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The results show that the macrodefect originates from a void, which in turn is associated with a pit on the CdZnTe substrate.

A wearable multi-channel fNIRS system for brain imaging in freely moving subjects

Functional near infrared spectroscopy (fNIRS) is a versatile neuroimaging tool with an increasing acceptance in the neuroimaging community. While often lauded for its portability, most of the fNIRS setups employed in neuroscientific research still impose usage in a laboratory environment. We present a wearable, multi-channel fNIRS imaging system for functional brain imaging in unrestrained settings. The system operates without optical fiber bundles, using eight dual wavelength light emitting diodes and eight electro-optical sensors, which can be placed freely on the subject's head for direct illumination and detection. Its performance is tested on N=8 subjects in a motor execution paradigm performed under three different exercising conditions: (i) during outdoor bicycle riding, (ii) while pedaling on a stationary training bicycle, and (iii) sitting still on the training bicycle. Following left hand gripping, we observe a significant decrease in the deoxyhemoglobin concentration over the contralateral motor cortex in all three conditions. A significant task-related ΔHbO2 increase was seen for the non-pedaling condition. Although the gross movements involved in pedaling and steering a bike induced more motion artifacts than carrying out the same task while sitting still, we found no significant differences in the shape or amplitude of the HbR time courses for outdoor or indoor cycling and sitting still. We demonstrate the general feasibility of using wearable multi-channel NIRS during strenuous exercise in natural, unrestrained settings and discuss the origins and effects of data artifacts. We provide quantitative guidelines for taking condition-dependent signal quality into account to allow the comparison of data across various levels of physical exercise. To the best of our knowledge, this is the first demonstration of functional NIRS brain imaging during an outdoor activity in a real life situation in humans.

Electro-optic electric-field sensors utilizing Ti∶LiNbO31×2 directional coupler with dipole antennas

We have demonstrated a Ti∶LiNbO3 electro-optic electric-field sensor based on 1 × 2 directional optical waveguide coupler. The symmet- ric geometry of the 1 × 2 directional coupler provided the sensor with unique characteristics of intrinsic 3-dB operating point and two comple- mentary outputs. A DC switching voltage of ∼12 V and an extinction ratio of ∼8.1 dB were observed with the coupler at a wavelength of 1.3 μm. The minimum detectable electric fields are ∼0.99 and ∼1.67 V∕m corre- sponding to a dynamic range of ∼29.5 and ∼25 dB at frequencies of 20 and 50 MHz, respectively. The sensors exhibit almost linear response for the applied electric-field intensity from 0.29 to 29.8 V∕m. © 2013 Society of

An Optically-Interrogated Rogowski Coil for Passive, Multiplexable Current Measurement

We report on the design and implementation of a novel hybrid electro-optical sensor for the measurement of electric current. A fibre Bragg grating is utilized to passively interrogate an air-cored coil via a low-voltage piezoelectric multilayer stack. Peak Bragg reflections are strain-tuned by the Rogowski coil/piezoelectric transducer combination, allowing primary current reconstruction to be performed remotely and without active electronics at the sensor. The preliminary embodiment demonstrates long-distance, passive measurement of current for metering and protection relaying applications, and retains the fiber transducer's capability for serial multiplexing.