85 research outputs found

    Millimeter-Precision Laser Rangefinder Using a Low-Cost Photon Counter

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    In this book we successfully demonstrate a millimeter-precision laser rangefinder using a low-cost photon counter. An application-specific integrated circuit (ASIC) comprises timing circuitry and single-photon avalanche diodes (SPADs) as the photodetectors. For the timing circuitry, a novel binning architecture for sampling the received signal is proposed which mitigates non-idealities that are inherent to a system with SPADs and timing circuitry in one chip

    Millimeter-Precision Laser Rangefinder Using a Low-Cost Photon Counter

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    In this book we successfully demonstrate a millimeter-precision laser rangefinder using a low-cost photon counter. An application-specific integrated circuit (ASIC) comprises timing circuitry and single-photon avalanche diodes (SPADs) as the photodetectors. For the timing circuitry, a novel binning architecture for sampling the received signal is proposed which mitigates non-idealities that are inherent to a system with SPADs and timing circuitry in one chip

    Arrays of Single Photon Avalanche Diodes in CMOS Technology: Picosecond Timing Resolution for Range Imaging (INVITED)

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    A solid-state imager fabricated in CMOS technology is presented for depth information capture of arbitrary 3D objects with millimeter resolution. The system is based on an array of 32x32 pixels that independently measure the time-of-flight of a ray of light as it is reflected back from the objects in a scene. A single cone of pulsed laser light illuminates the scene, thus no complex mechanical scanning is required. Millimetric depth accuracies can be reached thanks to the rangefinder’s optical detectors that enable picosecond time discrimination. The detectors, based on a single photon avalanche diode operating in Geiger mode, utilize avalanche multiplication to enhance light detection. Optical power requirements on the light source can therefore be significantly relaxed. A number of standard performance measurements, conducted on the imager, are discussed in this paper. The 3D imaging system was also tested on real 3D subjects demonstrating the suitability of the approach

    A single photon detector array with 64x64 resolution and millimetric depth accuracy for 3D imaging

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    An avalanche photodiode array uses single-photon counting to perform time-of-flight range-finding on a scene uniformly hit by 100ps 250mW uncollimated laser pulses. The 32x32 pixel sensor, fabricated in a 0.8μm CMOS process uses a microscanner package to enhance the effective resolution in the application to 64x64 pixels. The application achieves a measurement depth resolution of 1.3mm to a depth of 3.75m

    Laser Based Altimetry for Unmanned Aerial Vehicle Hovering Over a Snow Surface

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    A microwave radar for non-invasive snow stratigraphy measurements has been developed. Results were promising, but it failed to detect light powder snow in the air-snowpack interface. The aim of this thesis is to find and verify a system for estimating altitude on centimeter scale over a snow surface, independent of snow conditions. Also, relative pitch and roll angle estimation between the UAV and local surface should be resolved, to help directing the radar beam perpendicularly to the surface. After a variety of technical solutions were examined, we propose a system of three time-of-flight near-infrared altimeters pointing at different directions towards the surface. Experimental results showed RMS error of 1.39 cm for range estimation averaged over the most common snow types, and 2.81 cm for wet snow, which was the least reflective medium. An experiment conducted for an array of two altimeters scanning over a snow surface, showed that the local, relative surface tilt was found to be accurate within ±2° given that it was sufficiently planar. Further, the altitude RMS error was estimated to 1.57 cm. We conclude that the chosen altimeter was within the requirements, and that an array of three altimeters would give acceptable relative tilt estimation in to planes on the snow surface. The system should be subject to flight testing and implemented on UAV platform such that it can aid the microwave radar system during snow scanning

    High Precision Hybrid Pulse and Phase-Shift Laser Ranging System

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    With the rapid development of military, aerospace, and precision manufacturing technology, a multitude of situations need to carry out a large-range and high-precision distance measurement. The growth of measurement applications has led to a higher requirement for the laser ranging technology which can be accomplished by using different patterns. At present, the pulse laser ranging method is widely used for medium-range and long-range measurement because of the fast measurement speed and considerable measurement range. However, the ranging precision is low. The short-distance measurement mostly adopts the phase-shift laser ranging method which has high ranging accuracy but limited measurement range. Therefore, the research on lifting the accuracy of pulse laser ranging method and extending the measurement range of the phase-shift laser ranging method will be carried out. In this thesis, combining the existing pulse laser ranging system and phase-shift laser ranging system, dual-frequency and single-frequency hybrid pulse and phase-shift laser ranging systems are proposed. The basis for solving the current problems of poor measurement precision in pulse laser ranging method and short measurement distance in phase-shift laser ranging method are provided. Also, the designed structures have a broad application prospect in the fields of industrial production, military, and aviation. At the beginning of the thesis, the principle and characteristics of the current typical laser ranging methods are introduced and analyzed. According to the Fourier Series theory, the spectrum analysis of the pulse signal and the relationship between the pulse signal and the same-frequency sinusoidal signal, the idea of phase-shift laser ranging based on pulse modulation signal is generated. Instead of a continuous sinusoidal signal, the laser is modulated with a periodic pulse signal. Distance measurement by calculating the phase difference on the sinusoidal signal extracted from the pulse signal with the same frequency at the receiving end. Based on the principle of conventional dual-frequency phase-shift laser ranging method, a dual-frequency pulse laser ranging method is proposed. The distance to be measured is obtained by transmitting two periodic pulse signals with different frequency and then combining the implementation of rough and accurate measurement outcomes. Afterward, a single-frequency pulse laser ranging method is introduced. After receiving the pulse signal, the direct counter method is used to realize rough measurement and phase-shift of the co-frequency sinusoidal signal is utilized to improve the ranging accuracy. This proposed model has the advantages of high ranging precision and long-distance measurement without any other auxiliary frequency. The accuracy of the phase difference calculation is the most critical element in both the dual-frequency and single-frequency laser ranging systems. Currently, the commonly used phase difference calculation methods operated in phase-shift laser ranging system are digital synchronous detection, fast Fourier transform method, and all phase fast Fourier transform method. Published works have discussed the performance of frequency estimation and initial phase calculation using these approaches. In this thesis, the precision of phase difference measurement based on these methods above is compared. The effects of normalized frequency deviation, white Gaussian noise, harmonics are simulated in MATLAB. Simulation results show that all phase fast Fourier transform method has a superior anti-noise ability so that exceptional accuracy of phase difference measurement can be achieved. Furthermore, as the number of sampling points increases, all phase fast Fourier transform method will obtain a more accurate calculation consequence. Finally, this thesis carries on the co-simulation test of the designed dual-frequency and single-frequency hybrid pulse and phase-shift laser ranging systems in Optisystem and MATLAB. The transmitting frequencies of pulse signals operated in the dual-frequency method are 15 MHz and 150 KHz. The pulse used in the single-frequency method is set to 15 MHz. In the simulation, the performance of proposed methods is tested by setting various measuring distance. When the number of sampling points is 1024, the standard deviation and ranging error of the dual-frequency method are 3.72 cm and 13.6 cm within 963.15 meters. For the single-frequency method, the results show a 3.78 cm standard deviation and 14.6 cm ranging error. Simulation results illustrate that the proposed ranging methods have lower ranging error compared with recently published works. It means that the combination of the pulse method and the phase-shift method can achieve high-accuracy and long-range measurement

    Nd:YAG development for spaceborne laser ranging system

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    The results of the development of a unique modelocked laser device to be utilized in future NASA space-based, ultraprecision laser ranger systems are summarized. The engineering breadboard constructed proved the feasibility of the pump-pulsed, actively modelocked, PTM Q-switched Nd:YAG laser concept for the generation of subnanosecond pulses suitable for ultra-precision ranging. The laser breadboard also included a double-pass Nd:YAG amplifier and provision for a Type II KD*P frequency doubler. The specific technical accomplishment was the generation of single 150 psec, 20-mJ pulses at 10 pps at a wavelength of 1.064 micrometers with 25 dB suppression of pre-and post-pulses

    LinoSPAD maatrikstajuril põhineva kolmemõõtmelise arvutusliku kummituskuva teaduskatse kavand

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    Automatiseerimise ja robootika suurenevad nõudmised seireseadmetele on tinginud kõrglahutusega kolmemõõtmelise kuva kiire arengu. Arvutuslikul kummituskuval põhinev kolmemõõtmeline (3D) kuva on arenev tehnoloogia, millel on harjumuspärase maatrikssensoritepõhise 3D välkkuvaga (ash imaging) võrreldes suurem lahutusvõime. Paraku iseloomustab arvutusliku kummituskuva seadmeid tavaliselt kompromiss kujutise saamiseks kuluva aja ning saadava kujutise lahutusvõime vahel. Magistritöös esitatakse LinoSPAD maatrikstajuril põhineva teaduseksperimendi kavand uudse valguse lennuaja mõõtmisel põhineva 3D arvutusliku kummituskuva meetodi katsetamiseks. Vastupidiselt ühepikslilist valgusdetektorit rakendavale arvutuslikule kummituskuvale, kus üht pikslit kasutatakse terve stseeni pildistamiseks, jaotatakse esitatud meetodis tipptehnoloogilist prototüüp-maatrikstajuritit kasutades pildistatav stseen osadeks nii, et iga maatrikstajuri üksiku piksli vaateväli jälgib vaid osa stseenist. See lahendus lühendab märkimisväärselt kujutise saamiseks kuluvat mõõteaega, kuid ei vähenda saadava kujutise lahutusvõimet. Teaduskatse kavandi koostamisel analüüsiti nõudeid süsteemi valgusallikale ning ruumilisele valgusväljamodulaatorile ja uuriti LinoSPAD maatrikstajuri tööpõhimõtet. Lisaks täiendati kavandit footonihulgaarvutuste, haavelmüra ning üksikfootondetektori surnud aja simulatsioonidega ja esitatava süsteemikavandi ajastusahela katsetamisega. Esitatud süsteemi ranged piirangud ajastamissignaalidele nõuavad piisava sügavuslahutuse saavutamiseks katse elluviimisel optimeerida ajastamissignaale vahendava elektroonika parameetreid. Sellegipoolest kinnitavad tehtud katsed ning simulatsioonid teaduseksperimendi kavandi rakendatavust uudse 3D arvutusliku kummituskuva meetodi katsetamiseks.High-resolution 3D-imaging is a rapidly developing field driven by the increasing sensing requirements of automation and robotics. Computational ghost imaging based 3Dimaging is an emerging technology, offering increased spatial resolution when compared to conventional 3D ash imaging systems. Usually, however, computational ghost imaging systems are characterized by their compromise between image acquisition times and image spatial resolution. This thesis presents a LinoSPAD line sensor based experiment design for a novel time of flight based 3D computational ghost imaging method. Contrary to single-pixel computational ghost imaging, where a single-pixel detector is used for imaging the entire scene, the proposed method utilizes a state-of-the-art prototype sensor array to divide the scene to be imaged between the detector's individual pixels' fields of view. This approach significantly reduces the system's image acquisition times while avoiding a reduction in its spatial resolution. Prior to developing a final design, the requirements for the light source and the spatial light modulator and the capabilities of the LinoSPAD sensor were analyzed. Furthermore, the design was complemented with photon budget calculations, shot noise and detector dead time simulations, and preliminary setup tests focusing on the triggering scheme of the design. The system's stringent timing requirements require the optimizing the parameters of triggering electronics in the experiment's implementation. Regardless, conducted tests and simulations confirm the feasibility of the experiment design for the novel 3D computational ghost imaging approach

    Multi-wavelength, multi-beam, photonic based sensor for object discrimination and positioning

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    Over the last decade, substantial research efforts have been dedicated towards the development of advanced laser scanning systems for discrimination in perimeter security, defence, agriculture, transportation, surveying and geosciences. Military forces, in particular, have already started employing laser scanning technologies for projectile guidance, surveillance, satellite and missile tracking; and target discrimination and recognition. However, laser scanning is relatively a new security technology. It has previously been utilized for a wide variety of civil and military applications. Terrestrial laser scanning has found new use as an active optical sensor for indoors and outdoors perimeter security. A laser scanning technique with moving parts was tested in the British Home Office - Police Scientific Development Branch (PSDB) in 2004. It was found that laser scanning has the capability to detect humans in 30m range and vehicles in 80m range with low false alarm rates. However, laser scanning with moving parts is much more sensitive to vibrations than a multi-beam stationary optic approach. Mirror device scanners are slow, bulky and expensive and being inherently mechanical they wear out as a result of acceleration, cause deflection errors and require regular calibration. Multi-wavelength laser scanning represent a potential evolution from object detection to object identification and classification, where detailed features of objects and materials are discriminated by measuring their reflectance characteristics at specific wavelengths and matching them with their spectral reflectance curves. With the recent advances in the development of high-speed sensors and high-speed data processors, the implementation of multi-wavelength laser scanners for object identification has now become feasible. A two-wavelength photonic-based sensor for object discrimination has recently been reported, based on the use of an optical cavity for generating a laser spot array and maintaining adequate overlapping between tapped collimated laser beams of different wavelengths over a long optical path. While this approach is capable of discriminating between objects of different colours, its main drawback is the limited number of security-related objects that can be discriminated. This thesis proposes and demonstrates the concept of a novel photonic based multi-wavelength sensor for object identification and position finding. The sensor employs a laser combination module for input wavelength signal multiplexing and beam overlapping, a custom-made curved optical cavity for multi-beam spot generation through internal beam reflection and transmission and a high-speed imager for scattered reflectance spectral measurements. Experimental results show that five different laser wavelengths, namely 473nm, 532nm, 635nm, 670nm and 785nm, are necessary for discriminating various intruding objects of interest through spectral reflectance and slope measurements. Various objects were selected to demonstrate the proof of concept. We also demonstrate that the object position (coordinates) is determined using the triangulation method, which is based on the projection of laser spots along determined angles onto intruding objects and the measurement of their reflectance spectra using an image sensor. Experimental results demonstrate the ability of the multi-wavelength spectral reflectance sensor to simultaneously discriminate between different objects and predict their positions over a 6m range with an accuracy exceeding 92%. A novel optical design is used to provide additional transverse laser beam scanning for the identification of camouflage materials. A camouflage material is chosen to illustrate the discrimination capability of the sensor, which has complex patterns within a single sample, and is successfully detected and discriminated from other objects over a 6m range by scanning the laser beam spots along the transverse direction. By using more wavelengths at optimised points in the spectrum where different objects show different optical characteristics, better discrimination can be accomplished

    An Application of Optical Interference to Dynamic Position Measurement in Three Dimensions

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    This thesis is concerned with the measurement of the positions of points and bodies moving in trajectories in three dimensions, and the use of a new technique of optical interference which allows such measurements to be made dynamically. A variety of existing techniques for both static and dynamic three-dimensional position measurement are discussed, and the design of the new interferometer is introduced. The geometry of points, curves and surfaces in three dimensions is examined, with emphasis on the intersection of the point loci represented by the coordinate output of measuring instruments. The coordinates output by the interferometer represent surface loci which are quadric surfaces. A method of calculating the position and orientation of a body using three quadric surface intersection curves is presented. Diffraction of monochromatic light at an aperture is considered and it is shown that an interferometer working by division of wavefront can be used to obtain continuous information about the movement of the source of radiation, with that source free to move in up to three dimensions. A lens may be used to produce a compact instrument based on these principles. The diffraction integral equations are modified to incorporate the effect of a lens in the diffraction field. It is shown that even complex lenses can be represented by a few parameters in the diffraction equations. From the evaluation of these diffraction integrals, it is shown how the movement of interference fringes provides a coordinate output and how this is related to the locus of the radiation source. A method of obtaining very high resolution measurements of interference fringe pattern movement is presented. The interferometer was built and tested and the above theory verified in practice in a series of optical bench tests. The implementation of a system which uses this interferometer to measure the dynamic performance of industrial robots is considered. The optimum positions for the instruments are derived, and the method of designing the interferometer to give the required resolution is presented
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