Optical Rangefinders Research Articles

Amorphous silicon intrinsic photomixing detector for optical ranging

Today’s optical range finders or 3D imagers suffer from significant drawbacks and do not allow to combine performance (sensitivity, precision) with simplicity, and scalability enabling very-large scale integration with minimum footprint. Here, we present the amorphous silicon Intrinsic Photomixing Detector (IPD) for direct and highly sensitive optical envelope mixing. The ability to generate a photocurrent that is proportional to the nonlinear mixing of two optical modulation envelope functions enables high performance Time-of-Flight optical ranging at low light levels down to ~0.1mWcm−2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim \\!0.1\\,{{{{{\\rm{mW}}}}}}{{{{{\\rm{cm}}}}}}^{-2}$$\\end{document} at 444nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$444\\,{{{{{\\rm{nm}}}}}}$$\\end{document}. The IPD exceeds MHz bandwidth, covers a broad distance detection range from 10cm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10\\,{{{{{\\rm{cm}}}}}}$$\\end{document} to 101m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$101\\,{{{{{\\rm{m}}}}}}$$\\end{document}, and achieves a mean depth resolution below 44mm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$44\\,{{{{{\\rm{mm}}}}}}$$\\end{document} for distances up to 25m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$25\\,{{{{{\\rm{m}}}}}}$$\\end{document}. The IPD paves the way towards simple but high-performance photodetectors that allow for very-large scale integration on top of silicon or flexible electronics at low costs with pixel fill factors up to 100%.

Synchronous micromechanically resonant programmable photonic circuits

Programmable photonic integrated circuits (PICs) are emerging as powerful tools for control of light, with applications in quantum information processing, optical range finding, and artificial intelligence. Low-power implementations of these PICs involve micromechanical structures driven capacitively or piezoelectrically but are often limited in modulation bandwidth by mechanical resonances and high operating voltages. Here we introduce a synchronous, micromechanically resonant design architecture for programmable PICs and a proof-of-principle 1×8 photonic switch using piezoelectric optical phase shifters. Our design purposefully exploits high-frequency mechanical resonances and optically broadband components for larger modulation responses on the order of the mechanical quality factor Qm while maintaining fast switching speeds. We experimentally show switching cycles of all 8 channels spaced by approximately 11 ns and operating at 4.6 dB average modulation enhancement. Future advances in micromechanical devices with high Qm, which can exceed 10000, should enable an improved series of low-voltage and high-speed programmable PICs.

Self-Mixing Laser Distance-Sensor Enhanced by Multiple Modulation Waveforms.

Optical rangefinders based on Self-Mixing Interferometry are widely described in literature, but not yet on the market as commercial instruments. The main reason is that it is relatively easy to propose new elaboration techniques and get results in controlled conditions, while it is very difficult to develop a reliable instrument. In this paper, we propose a laser distance sensor with improved reliability, realized through a wavelength modulation at a different frequency, able to decorrelate single measurement errors and obtain improvement by averages. A dedicated software is implemented to automatically calculate the modulation pre-emphasis, needed to linearize the wavelength modulation. Finally, data selection algorithms allow to overcome signal fading problems due to the speckle effect. A prototype demonstrates the approach with about 0.1 mm accuracy up to 2 m of distance at 200 measurements per second.

Segmentation-Based Color Channel Registration for Disparity Estimation of Dual Color-Filtered Aperture Camera.

Single-lens-based optical range finding systems were developed as an efficient, compact alternative for conventional stereo camera systems. Among various single-lens-based approaches, a multiple color-filtered aperture (MCA) system can generate disparity information among color channels, as well as normal color information. In this paper, we consider a dual color-filtered aperture (DCA) system as the most minimal version of the MCA system and present a novel inter-color image registration algorithm for disparity estimation. This proposed registration algorithm consists of three steps: (i) color channel independent feature extraction; (ii) feature-based adaptive weight disparity estimation; and (iii) color mapping matrix (CMM)-based cross-channel image registration. Experimental results show that the proposed method can not only generate an accurate disparity map, but also realize high quality cross-channel registration with a disparity prior for DCA-based range finding and color image enhancement.

Regression-based technique for improved optical rangefinding using tunable focus lenses.

In this paper, we present a novel method of target range estimation by tuning the spot size of a Gaussian beam at the plane of a reflective target. The beam spot size tuning is achieved through the use of a tunable focus lens (TFL). Using a carefully aligned sensor assembly, the diameter of the reflected beam is recorded at the plane of an imaging detector for different TFL focal length settings. This dataset is then used to estimate the distance of the target from the TFL. The proposed rangefinder is compact and requires minimal post-data-acquisition signal processing resulting in a fast response time compared to other spatial signal processing-based sensor designs. The estimation of target distance through a multiple data-point measurement dataset also ensures that the proposed method is robust to errors associated with obtaining range estimates from a single measurement data point. Experimental results demonstrate an excellent agreement with theory. With our proposed estimation method, we show a significant improvement in the measurement dynamic range of the sensor as well as its resolution compared to similar sensing schemes in prior art. We also experimentally demonstrate the possibility to extend the measurement dynamic range by incorporating a bias lens of a fixed focal length with the sensor module. The proposed sensor module is electronically controlled and consequently can be fully automated and compactly packaged with the use of commercially available miniature optical components.

Современные подходы к созданию пассивных дальномеров

Современные подходы к созданию пассивных дальномеров

The thirty-meter laser interference comparator which forms part of the state primary standard of the unit of length – the meter

A brief review of the measurement capabilities of the leading national metrological institutes of the world in the field of measurements of ruled length gauges (tape measures) is given. A comparative analysis of the construction of comparators is carried out. The thirty-meter laser interference comparator, which forms part of the State Primary Standard of the unit of length (the GET 2-2010 meter), is described. Ways of further improvement and new areas of application, e.g. checking scanners, trackers, level meters, optical range finders and other measuring instruments, are indicated.

A 128 $\times$ 128 Single-Photon Image Sensor With Column-Level 10-Bit Time-to-Digital Converter Array

An imager for time-resolved optical sensing was fabricated in CMOS technology. The sensor comprises an array of 128times128 single-photon pixels, a bank of 32 time-to-digital-converters, and a 7.68 Gbps readout system. Thanks to the outstanding timing precision of single-photon avalanche diodes and the optimized measurement circuitry, a typical resolution of 97 ps was achieved within a range of 100 ns. To the best of our knowledge, this imager is the first fully integrated system for photon time-of-arrival evaluation. Applications include 3-D imaging, optical rangefinding, fast fluorescence lifetime imaging, imaging of extremely fast phenomena, and, more generally, imaging based on time-correlated single photon counting. When operated as an optical rangefinder, this design has enabled us to reconstruct 3-D scenes with milimetric precisions in extremely low signal exposure. A laser source was used to illuminate the scene up to 3.75 m with an average power of 1 mW, a field-of-view of 5deg and under 150 lux of constant background light. Accurate distance measurements were repeatedly achieved based on a short integration time of 50 ms even when signal photon count rates as low as a few hundred photons per second were available.

High-frequency phase measurement for optical rangefinding system

A phase measuring circuit has been designed and tested that is capable of accurately measuring phase differences (±0.5°) between transmitted and received signals having frequencies up to 75 MHz. The measurement output rate was 100 phases per second and this allowed for a signal averaging of 50 consecutive measurements per output. The received signal level could be reduced by 30 dB without creating any additional phase delays. The system has been extensively tested with a time-of-flight optical rangefinding system using continuously modulated laser light transmitted to and received from a variety of targets.

Single-beam diode-laser technique for optical path-length measurements

A simple single-beam technique employing radio-frequency modulation of a tunable diode laser with homodyne demodulation is demonstrated as a means of measuring optical path lengths. This technique offers a straightforward method for determining path lengths traversed through optical multipass cells or performing optical range-finding over short (i.e., tens of meters) standoff distances. The radio-frequency phase-sensitive nature of the technique permits narrow-band detection and high signal-to-noise ratios, even when range-finding measurements are made with range resolutions of «1 m. This compares favorably with traditional short-pulse, wide-bandwidth optical range finders.

Single-photon detection beyond 1 μm: performance of commercially available InGaAs/InP detectors

Commercially available InGaAs/lnP avalanche photodiodes, designed for optical receivers and range finders, can be operated biased above the breakdown voltage, achieving single-photon sensitivity. We describe in detail how to select the device for photon-counting applications among commercial samples. Because of the high dark-counting rate the detector must be cooled to below 100 K and operated in a gated mode. We achieved a noise equivalent power of 3 × 10(-16) W/Hz(1/2) to a 1.55-µm wavelength and a time resolution well below 1 ns with a best value of 200-ps FWHM. Finally we compare these figures with the performance of state-of-the-art detectors in the near IR, and we highlight the potentials of properly designed InGaAs/lnP avalanche photodiodes in single-photon detection.

Three-color optical range finding

In the known three-wavelength distance-measuring systems two optical wavelengths are used and a microwave is added for air-humidity influence consideration. In our research, which proceeds from results obtained at the National Research Laboratory of Metrology (Japan), the possibility of constructing a three-optical-wavelength ranging system is discussed. We investigate different versions by using a CO(2) laser as the source of the third wavelength. Analysis shows that the three-wavelength system with two lasers (YAG:Nd(3+) laser, which yields first- and second-harmonic radiation, and a CO(2) laser) seems to be optimum. A possible schematic structure of the three-wavelength YAG-CO(2) laser system is given.

An autonomous robot navigation system - integrating environmental mapping, path planning, localisation and motion control

SUMMARYThis paper describes an autonomous robot vehicle which can navigate through an initially unknown obstacle field to a nominated goal or systematically map its working environment. The navigation system uses combined ultrasonic beacon/odometry based localisation, optical range finders for environmental mapping, an A path planning procedure and continuous motion control. The computational support is divided between a graphics workstation 'home base' and a PC hosted transputer array on-board. The integration of all the subsystems cited above has been achieved and many successful navigation experiments completed. Possible further developments which would enhance the capabilities of the system are also discussed.

Amplitude modulated external cavity high power laser diode with electric phase stabilization in the far field

The emission properties of an Amplitude Modulated diffraction limited external cavity multi-stripe high power laser diode are here reported. When resolving the resulting electric phase in the far field, a stabilization of a factor of 10 is obtained compared to the free running laser diode. Such a device is of interest for free space optical communication and range-finding. An original method based on white-light interferometry is also reported for measuring the reflection coefficient of the anti-reflection coated facet of the laser diode

Computer simulation of the photodetection process in optical range finding

Computer simulation of the photodetection process in optical range finding

Theory Of Tracking Accuracy Of Laser Systems

Optical rangefinders, lidars, and laser tracking systems offer new options for a variety of applications. When a laser system operates in a tracking regime, it must continuously estimate target angle coordinates. This purpose may be achieved by means of a quadrant detector (QD) incorporated in the optical receiver. In this paper, performance of the QD-based laser tracker is evaluated theoretically. Angle measurement span, angle estimation bias, and angle estimation variance are analyzed with the emphasis on the quantitative evaluation of the estimation bias and variance. It is shown that the estimation error contains both systematic error (signal-independent bias) and signal-dependent bias. The systematic error is caused by the signal processing circuitry of the receiver; this error is rather large (up to 1 1.5% of the measurement span), but may be easily cancelled by means of a permanent look-up correction table stored in a ROM (read-only memory). Signal-dependent bias cannot be cancelled with the same technique since it depends on the a priori unknown signal intensity. Fortunately, signal-dependent bias decreases when the SNR (signal-to-noise ratio) increases, at a rate proportional to s/SNR; however, it increases rapidly when the light spot approaches the end of the measurement span. Estimation variance is also evaluated. It is found to decrease when the SNR increases, at a rate roughly proportional to SNR. Estimation variance remains approximately constant as the light spot moves over the measurement span. Thus, the main consequence of the deviation of the light spot from the QD center is the increase of the estimation bias, rather than a change of the estimation variance.

AUTOMATIC PASSIVE LOW LIGHT LEVEL TELEVISION GUN‐DIRECTOR RANGEFINDER

ABSTRACTOn many Navy ships, gunnery is directed and controlled using radar and stereoscopic optical rangefinders. Radar is rapid, automatic, functional day and night, but is subject to limitations, especially at low angles of elevation. The stereoscopic optical rangefinder, because of its superior resolution, supplements radar with information on imagery and identification of target and gunnery accuracy through observation of the shell bursts relative to the target. Also, under Emission Control conditions, the passive rangefinder substitutes for radar. However, rangefinder usefulness is limited because 1) it requires sufficient daylight illumination and weather clarity, 2) there is a shortage of Fleet personnel with good stereoscopic perception, and 3) operator mechanical manipulation of the rangefinder optics makes it too slow for ranging on high‐speed aircraft.To improve the rangefinder utility, a passive day/night Low Light Level Television Rangefinder System has been proposed that will provide an image of the target and automatically display range in digital format on cathode ray tubes. Without modifying the stereoscopic range‐finder and with appropriate external optics, the range‐finder can be adapted to operate with the low light level television camera. Automatic ranging, which eliminates the operator, is obtained with new electronic TV time‐scanning circuitry which will provide rapid, continuous digital range. Ranging on high‐speed aircraft will be possible.The gun‐director rangefinder is, at times, used for general navigation, collision avoidance, stationkeeping, surveillance, etc. The Low Light Level Television Range‐finder System will provide night and automatic ranging capabilities for these applications.

Empfangsleistung in Abhängigkeit von der Zielentfernung bei optischen Kurzstrecken–Radargeräten

The dependence of the received optical power on the range in optical short-distance radar range finders is calculated by means of the methods of geometrical optics. The calculations are based on a constant intensity of the transmitter-beam cross section and on an ideal thin lens for the receiver optics. The results are confirmed by measurements. Even measurements using a nonideal thick lens system for the receiver optics are in reasonable agreement with the calculations.

Calibration, Precision, and Efficiency of Optical Range Finders

Properties of pulsed optical range finders which are affected by the transmitter pulse waveshape have been analyzed. This was done by deriving the probability density functions of the random variable representing range delay time with respect to the start of the transmitter pulse. These functions were used to predict the calibration or bias time, random range errors, the probability that a range measurement is made, and its entropy, all vs signal energy. Noise and other important system properties are treated as parameters, and it is assumed that photoemission is Poisson-distributed. A number of experiments were performed, including a simulation of geodetic satellite conditions. Although more experimental work remains to be done, the agreement between these measurements and theoretical predictions tends to verify the theory, including the basic assumption that photoemission is accurately described by Poisson statistics under almost all likely conditions.

Radiation beam alignment device for use with a hyperbaric oxygen chamber.

This mechanico-optical device was designed to facilitate field alignment when using a hyperbaric chamber. Optical range-finders using convergent beams are subject to error when used with such chambers because of refraction in the Perspex chamber walls. The light beams from this device normally strike the Perspex at right angles, thus giving minimal deviation. Three sets of cross-hairs are used for alignment. One set of cross-hairs (A) is built into the 60Co treatment head to centre the entrance beam.