Laser Detection And Ranging Research Articles

InP-Based Single-Photon Detectors and Geiger-Mode APD Arrays for Quantum Communications Applications

To meet the increasing demand from quantum communications and other photon starved applications, we have developed various InP-based single-photon detectors, including discrete single-photon avalanche diodes (SPADs), negative feedback avalanche diodes (NFADs), and Geiger-mode avalanche photodiode (GmAPD) arrays. A large quantity of InP SPADs have been fabricated. Out of 1000 devices with a 25-μm active area diameter, operated under gated mode at temperature of 233 K, with a pulse repetition rate of 1 MHz and pulse width of 1 ns, the average dark count rate and afterpulsing probability are 30 kHz and 8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , respectively. Smaller (16-μm active area diameter) and larger (40-μm active area diameter) discrete devices have been fabricated as well, and their performances are presented along with the 25-μm diameter devices. NFAD devices can operate in free running mode and photon detection efficiency of 10-15% can be achieved without applying any hold-off time externally. When the temperature decreases from 240 to 160 K, the noise equivalent power (NEP) decreasesfrom1.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> to 1.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-18</sup> WHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> , with the activation energy being 0.2 eV. The very low NEP at 160 K makes NFAD devices an ideal choice for long distance, entanglement-based quantum key distributions. GmAPD arrays provide an enabling technology for many active optical applications, such as 3-D laser detection and ranging (LADAR) and photon starved optical communications. Both 32 × 32 and 128 × 32 GmAPD arrays have been fabricated with high performance and good uniformity. GmAPD focal plane arrays (FPAs) with framed readout mode have enabled very high-performance flash LADAR systems. GmAPD FPAs with asynchronous readout mode will enable high rate quantum key distributions and other quantum communications applications.

Dual‐mode CMOS feed‐forward transimpedance amplifier for LADARs

A dual-mode transimpedance amplifier (TIA) is realised in a 0.18 μm CMOS technology for the applications of 1 Gbit/s laser detection and ranging (LADAR) systems. The proposed dual-mode CMOS feed-forward TIA consists of a voltage-mode inverter input stage with a feedback resistor, followed by a current-mode common-gate amplifier with a feed-forward technique applied at the gate so as to achieve low noise, low power consumption, high gain and wide bandwidth characteristics simultaneously. The measured results demonstrate 76 dBΩ transimpedance gain, 720 MHz bandwidth for 0.5 pF photodiode capacitance, −26.3 dBm sensitivity for 10−12 bit error rate and 20.7 mW power dissipation from a single 1.8 V supply.

Comb-calibrated laser ranging for three-dimensional surface profiling with micrometer-level precision at a distance.

Non-contact surface mapping at a distance is interesting in diverse applications including industrial metrology, manufacturing, forensics, and artifact documentation and preservation. Frequency modulated continuous wave (FMCW) laser detection and ranging (LADAR) is a promising approach since it offers shot-noise limited precision/accuracy, high resolution and high sensitivity. We demonstrate a scanning imaging system based on a frequency-comb calibrated FMCW LADAR and real-time digital signal processing. This system can obtain three-dimensional images of a diffusely scattering surface at stand-off distances up to 10.5 m with sub-micrometer accuracy and with a precision below 10 µm, limited by fundamental speckle noise. Because of its shot-noise limited sensitivity, this comb-calibrated FMCW LADAR has a large dynamic range, which enables precise mapping of scenes with vastly differing reflectivities such as metal, dirt or vegetation. The current system is implemented with fiber-optic components, but the basic system architecture is compatible with future optically integrated, on-chip systems.

Fully integrated four‐input combining receiver front‐end circuit for laser radar with static unitary detector

A fully integrated four-input combining receiver front-end circuit is designed in a 0.18 μm CMOS technology for laser radar with a static unitary detector (STUD). This circuit consists of four independent transimpedance amplifiers, one signal combiner, a balun and an output buffer in one single integrated chip. The circuit provides 16.2 mW power consumption for a 1.8 V supplied voltage and 59.8 dBΩ transimpedance gain in the implemented experimental prototype for electrical pulse measurement. The fabricated prototype is worked exactly the same as the operation principle of the STUD in the two-dimensional optical pulse scanning measurement. Therefore, the proposed circuit is available for the STUD-based laser detection and ranging (LADAR) system as one integrated chip. This is the first demonstrated IC for the STUD-based laser radar system.

Autonomous Black Hawk in Flight: Obstacle Field Navigation and Landing‐site Selection on the RASCAL JUH‐60A

This paper describes the development and flight test of autonomous obstacle field navigation and safe landing area selection on the U.S. Army Aeroflightdynamics Directorate RASCAL JUH‐60A research helicopter. Using laser detection and ranging (LADAR) as the primary terrain sensor, the autonomous flight system is able to avoid obstacles, including wires, and select safe landing sites. An autonomous integrated landing zone approach profile was developed and validated that integrates cruise flight, low‐level terrain flight, and approach to a safe landing spot determined on the fly. Results are presented for a range of sites and conditions. Approximately 750 km of autonomous flight was performed, 230 km of which was at low altitude in mountainous terrain using the obstacle field navigation system. This is the first time a full‐scale helicopter has been flown fully autonomously a significant distance in low‐level flight over complex terrain, basing its planning solely on sensor data gathered from an onboard sensor. These flights demonstrate tight integration between terrain avoidance, control, and autonomous landing.

Geiger Mode로 동작하는 3차원 LADAR 광수신기 개발

본 논문에서는 3차원 영상 획득을 위한 LADAR(LAser Detection And Ranging)용 광수신기 모듈을 설계-제작하고 측정한 결과를 보고한다. 광수신기 모듈은 1 km 이상의 거리에서도 신호를 측정할 수 있도록 디지털모드(Geiger Mode)에서 동작하는 InGaAs APD(Avalanche Photodiode)로 설계하였으며, <TEX>$16{\pm}16$</TEX> FPA(Focal Plane Array)로 설계-제작하였다. 디지털모드(Geiger Mode)는 항복전압 이상의 영역에서 동작하여 작은 광에 대해 반응 할 수 있게 큰 증폭률을 가지게 된다. 1ns의 FWHM(Full Width at Half Maximum)을 갖는 펄스를 수광할 수 있고, 배열 크기는 <TEX>$16{\pm}16$</TEX>, Geiger Mode 동작 등의 특성을 만족하도록 광수신기를 구성하기 위해 ROIC(Read Out Integrated Circuit)를 자체적으로 설계-제작하였다. 제작된 광수신기 모듈은 원거리 표적정보 획득이 가능하며, PDE(Photon Detection Efficiency)는 28%, DCR(Dark Count Rate)은 140 kHz 이하의 특성을 보였으며, LADAR 시스템에서 3차원 영상을 획득하였다. 이는 <TEX>$16{\pm}16$</TEX> FPA APD를 이용한 광수신기에서 가장 우수한 특성을 나타낸 것이다. In this paper, we report the design, fabrication and characterization of the 3-Dimensional optical receiver for a Laser Detection And Ranging (LADAR) system. The optical receiver is composed of three parts; <TEX>$16{\pm}16$</TEX> Geiger Mode InGaAs Avalanche Photodiode (APD) array device operated at 1560 nm wavelength, Read Out Integrated Circuit (ROIC) measuring the Time-Of-Flight (TOF) of the return signal reflected from target objects, a package and cooler maintaining the proper operational condition of the detector and control electronics. We can confirm that the LADAR system can detect the signal from a target up to 1.2 km away, and it showed low Dark Count Rate (DCR) of less than 140 kHz, and higher than 28%-Photon Detection Efficiency (PDE). This is considered to be the best performance of the <TEX>$16{\pm}16$</TEX> FPA APD optical receiver for a LADAR system.

Improvement of range precision in laser detection and ranging system by using two Geiger mode avalanche photodiodes

In this paper, the improvement of range precision in a laser detection and ranging (LADAR) system by using two Geiger mode avalanche photodiodes (GmAPDs) is described. The LADAR system is implemented by using two GmAPDs with a beam splitter and applying comparative process to their ends. Then, the timing circuit receives the electrical signals only if each GmAPDs generates electrical signals simultaneously. Though this system decreases the energy of a laser-return pulse scattered from the target, it is effective in reducing the range precision. The experimental results showed that the average value of standard deviation of time of flights was improved from 61 mm to 37 mm when the pulse energy is 0.6 μJ. When the time bin width is 0.5 ns, the single-shot precision error of the LADAR system was also improved from 280 mm to 67 mm.

대면적 APD를 이용한 LADAR용 광대역 광수신기

본 논문에서는 3차원 영상을 위한 LADAR(LAser Detection And Ranging)용 광검출기 모듈을 설계-제작하고 그 특성을 측정한 결과를 보고한다. 광검출기 모듈은 광파이버 어레이와 접속될 수 있도록 200 um 직경을 갖는 InGaAs APD(Avalanche Photodiode)로 설계-제작하였으며, 선형모드 동작 특성을 만족하도록 TIA(Trans-impedance Amplifier)를 설계-제작하였다. 광검출기 모듈을 구성하는 핵심부품들은 12개의 lead pin을 갖는 TO8 상에 집적되었으며, 집적에 필요한 APD 서브마운트 및 TIA 회로 등을 자체적으로 설계-제작하여 사용하였다. 제작한 광검출기 모듈은 450 ps의 rising time과 780 MHz의 대역폭 특성을 보였으며, 0.8 mV 이하의 잡음 특성과, 150 nW의 MDS(Minimum Detectable Signal) 신호 크기에 대해 15 이상의 신호대 잡음비(SNR)를 보임으로써 설계한 모든 특성을 만족하였는데, 이는 저자들이 아는 한 200 um 직경의 대면적 InGaAs APD를 이용한 광수신기에서 가장 우수한 특성을 나타낸 것이다. In this paper, we report design, fabrication and characterization of the WBRM (Wide Band Receiver Module) for LADAR (LAser Detection And Ranging) application. The WBRM has been designed and fabricated using self-made APD (Avalanche Photodiode) and TIA (Trans-impedance Amplifier). The APD and TIA chips have been integrated on 12-pin TO8 header using self-made ceramic submount and circuit. The WBRM module showed 450 ps of rise time, and corresponding 780 MHz bandwidth. Furthermore, it showed very low output noise less than 0.8 mV, and higher SNR than 15 for 150 nW of MDS(Minimum Detectable Signal). To the author's knowledge, this is the best performance of an optical receiver module for LIDAR fabricated by 200 um InGaAs APD.

Phased array on a fingertip

An array of more than 4,000 optical antennas working in unison has been demonstrated on a millimetre-scale silicon chip. The result highlights the remarkable capabilities of optical integration in silicon. See Letter p.195 Nanophotonic approaches allow the construction of chip-scale arrays of optical nanoantennas capable of producing radiation patterns in the far field. This could be useful for a range of applications in communications, LADAR (laser detection and ranging) and three-dimensional holography. Until now this technology has been restricted to one-dimensional or small two-dimensional arrays. This paper reports the construction of a large-scale silicon nanophotonic phased array containing 4,096 optical nanoantennas balanced in power and aligned in phase. The array was used to generate a complex radiation pattern—the MIT logo—in the far field. The authors show that this type of nanophotonic phased array can be actively tuned, and in some cases the beam is steerable.

Parallel Bayesian inference of range and reflectance from LaDAR profiles

Bayesian analysis using reversible jump Markov chain Monte Carlo (RJMCMC) algorithms improves the measurement accuracy, resolution and sensitivity of full waveform laser detection and ranging (LaDAR), but at a significant computational cost. Parallel processing has the potential to significantly reduce the processing time, but although there have been several strategies for Markov chain Monte Carlo (MCMC) parallelization, adaptation of these strategies to RJMCMC may degrade parallel performance.In this paper, we describe an approach to parallel RJMCMC processing that combines data and sampling parallelism in a single framework. This approach, Data Parallel State Space Decomposed RJMCMC (DP SSD-RJMCMC), can be adapted to different parallel cluster size, improve sampling efficiency and maintain parameter estimation accuracy. Formally, it forms a group of parallel chains by decomposing the state space into subsets of parameter space. Each subset has different but restricted dimensionality, and is assigned with an independent chain of variable length. To further improve load balancing, we also employ data decomposition, forming a task queue and conducting dynamic task allocation. The MPI-based implementation on a 32-node Beowulf cluster leads to significant speedup, typically of the order of 15–25 times, while maintaining the estimation accuracy.

Target extraction and classification base on imaging LADAR range image

Active imaging LADAR(Laser Detection And Ranging) stands out from other passive imaging systems for its function of acquiring range image of targets.Compared with traditional optical image,range image has more particular statistical characteristics,it can obviously show multi-peak structures when multiple targets exist in the range image.Target Extraction of range image could be realized by extracting peaks of its stat-histogram;and targets could be classified by the size and rectangle degree obtained by the use of minimum enclosing rectangle.Processing a real range image by using this method has obtained the anticipated result.

Range separation performance and optimal pulse-width prediction of a three-dimensional flash laser detection and ranging using the Cramer–Rao bound

This paper derives the Cramer-Rao bound (CRB) on range separation estimation of two point sources interrogated by a three-dimensional flash laser detection and ranging (LADAR) system. An unbiased range separation estimator is also derived to compare against the bound. Additionally, the CRB can be expressed as a function of two LADAR design parameters (range sampling and transmitted pulse width), which can be selected in order to optimize the expected range resolution between two point sources. Given several range sampling capabilities, the CRB and simulation show agreement that there is an optimal pulse width where a shorter pulse width would increase estimation variance due to undersampling of the pulse and a longer pulse width would degrade the resolving capability. Finally, the optimal pulse-width concept is extended to more complex targets and a normalized pulse definition.

Development and analysis of a photon-counting three-dimensional imaging laser detection and ranging (LADAR) system

In this paper, a photon-counting three-dimensional imaging laser detection and ranging (LADAR) system that uses a Geiger-mode avalanche photodiode (GAPD) of relatively short dead time (45 ns) is described. A passively Q-switched microchip laser is used as a laser source and a compact peripheral component interconnect system, which includes a time-to-digital converter (TDC), is set up for fast signal processing. The combination of a GAPD with short dead time and a TDC with a multistop function enables the system to operate in a single-hit or a multihit mode during the acquisition of time-of-flight data. The software for the three-dimensional visualization and an algorithm for the removal of noise are developed. For the photon-counting LADAR system, we establish a theoretical model of target-detection and false-alarm probabilities in both the single-hit and multihit modes with a Poisson statistic; this model provides the prediction of the performance of the system and a technique for the acquisition of a noise image with a GAPD. Both the noise image and the three-dimensional image of a scene acquired by the photon-counting LADAR system during the day are presented.

Three-dimensional LADAR range estimation using expectation maximization

Laser detection and ranging (LADAR) systems can be used to provide 2-D and 3-D images of scenes. Generally, 2-D images possess superior spatial resolution but without range data due to the density of their focal plane arrays. A 3-D LADAR system can produce range-to-target data at each pixel but lacks the 2-D system's superior spatial resolution. We develop an algorithm using an expectation maximization approach to estimate both 3-D LADAR range and the bias associated with a 3-D LADAR system. The algorithm we develop demonstrates both spatial and range resolution improvement over standard interpolation techniques using both real and simulated 3-D and 2-D LADAR data.

Cramer–Rao lower bound on range error for LADARs with Geiger-mode avalanche photodiodes

The Cramer-Rao lower bound (CRLB) on range error is calculated for laser detection and ranging (LADAR) systems using Geiger-mode avalanche photodiodes (GMAPDs) to detect reflected laser pulses. For the cases considered, the GMAPD range error CRLB is greater than the CRLB for a photon-counting device. It is also shown that the GMAPD range error CRLB is minimized when the mean energy in the received laser pulse is finite. Given typical LADAR system parameters, a Gaussian-envelope received pulse, and a noise detection rate of less than 4 MHz, the GMAPD range error CRLB is minimized when the quantum efficiency times the mean number of received laser pulse photons is between 2.2 and 2.3.

Design and analysis of In 0.53Ga 0.47As/InP symmetric gain optoelectronic mixers

A symmetric gain optoelectronic mixer based on an indium gallium arsenide (In 0.53Ga 0.47As)/indium phosphide (InP) symmetric heterojunction phototransistor structure is being investigated for chirped-AM laser detection and ranging (LADAR) systems operating in the “eye-safe” 1.55 μm wavelength range. Signal processing of a chirped-AM LADAR system is simplified if the photodetector in the receiver is used as an optoelectronic mixer (OEM). Adding gain to the OEM allows the following transimpedance amplifier’s gain to be reduced, increasing bandwidth and improving the system’s noise performance. A symmetric gain optoelectronic mixer based on a symmetric phototransistor structure using an indium gallium arsenide narrow bandgap base and indium phosphide emitter/collector layers is proposed. The devices are simulated with the Synopsis TCAD Sentaurus tools. The effects of base–emitter interface layers, base thickness and the doping densities of the base and emitters on the device performance are investigated. AC and DC simulation results are compared with a device model. Improved responsivity and lower dark current are predicted for the optimized InGaAs/InP device over previously reported devices with indium aluminum arsenide emitter/collector layers.

LADAR resolution improvement using receivers enhanced with squeezed-vacuum injection and phase-sensitive amplification

The use of quantum resources—squeezed-vacuum injection (SVI) and noise-free phase-sensitive amplification (PSA)—at the receiver of a soft-aperture homodyne-detection LAser Detection And Ranging (LADAR) system is shown to afford significant improvement in the receiver's spatial resolution. This improvement originates from the potential for SVI to ameliorate the loss of high-spatial-frequency information about a target or target complex that is due to soft-aperture attenuation in the LADAR's entrance pupil, and the value of PSA in realizing that potential despite inefficiency in the LADAR's homodyne detection system. We show this improvement quantitatively by calculating lower error rates—in comparison with those of a standard homodyne detection system—for a one-target versus two-target hypothesis test. We also exhibit the effective signal-to-noise ratio (SNR) improvement provided by SVI and PSA in simulated imagery.

Verification of a 3-D terrain mapping LADAR on various materials in different environments

A field validation of a laser detection and ranging (LADAR) system was conducted by the U.S. Army Engineer Research and Development Center (ERDC), Vicksburg, Mississippi. The LADAR system, a commercial-off-the-shelf (COTS) LADAR system custom-modified by Autonomous Solutions, Inc. (ASI), was tested for accuracy in measuring terrain geometry. A verification method was developed to compare the LADAR dataset to a ground-truth dataset that consisted of total station measurements. Three control points were measured and used to align the two datasets. The influence of slopes, surface materials, light, fog, and dust were investigated. The study revealed that slopes only affected measurements when the terrain was obscured from the LADAR system, and ambient light conditions did not significantly affect the LADAR measurements. The accuracy of the LADAR system, which was equipped with fog correction, was adversely affected by particles suspended in air, such as fog or dust. Also, in some cases the material type had an effect on the accuracy of the LADAR measurements.

Effect of target surface orientation on the range precision of laser detection and ranging systems

Airborne laser detection and ranging (LADAR) systems are used for applications such as three-dimensional imaging, topographic mapping, and target recognition. Typical systems transmit laser beams through apertures that are a few inches wide and use pulses that are roughly a nanosecond in duration. If the pulse reflects off a target that is tilted with respect to the LADAR's line-of-sight, then the reflection process will elongate the received signal as compared to the transmitted pulse. If the range is more than a few kilometers and the target is tilted more than about forty-five degrees, the increase in the width of the received pulse produces a signifcant drop in range precision as compared to when the target is perpendicular to the line-of-sight.

Using LADAR to characterize the 3-D shape of aggregates: Preliminary results

Previous publications have shown how a combination of X-ray computed tomography and spherical harmonic series could be used to characterize the 3-D shape of rocks used for aggregates in concrete. The X-ray computed tomography was used to obtain the raw 3-D numerical data for the coordinates of the aggregate surface. In this paper, we demonstrate how laser detection and ranging (LADAR) numerical data can replace X-ray computed tomography data and be used in conjunction with spherical harmonic series analysis to analyze the 3-D shape of aggregates.