Lidar Receiver Research Articles

A 256 × 192 -Pixel Direct Time-of-Flight LiDAR Receiver With a Current-Integrating-Based AFE Supporting 240-m-Range Imaging

A 256 × 192 -Pixel Direct Time-of-Flight LiDAR Receiver With a Current-Integrating-Based AFE Supporting 240-m-Range Imaging

A Low-Power Optoelectronic Receiver IC for Short-Range LiDAR Sensors in 180 nm CMOS.

This paper presents a novel power-efficient topology for receivers in short-range LiDAR sensors. Conventionally, LiDAR sensors exploit complex time-to-digital converters (TDCs) for time-of-flight (ToF) distance measurements, thereby frequently leading to intricate circuit designs and persistent walk error issues. However, this work features a fully differential trans-impedance amplifier with on-chip avalanche photodiodes as optical detectors so that the need of the following post-amplifiers and output buffers can be eliminated, thus considerably reducing power consumption. Also, the combination of amplitude-to-voltage (A2V) and time-to-voltage (T2V) converters are exploited to replace the complicated TDC circuit. The A2V converter efficiently processes weak input photocurrents ranging from 1 to 50 μApp which corresponds to a maximum distance of 22.8 m, while the T2V converter handles relatively larger photocurrents from 40 μApp to 5.8 mApp for distances as short as 30 cm. The post-layout simulations confirm that the proposed LiDAR receiver can detect optical pulses over the range of 0.3 to 22.8 m with a low power dissipation of 10 mW from a single 1.8 V supply. This topology offers significant improvements in simplifying the receiver design and reducing the power consumption, providing a more efficient and accurate solution that is highly suitable for short-range LiDAR sensor applications.

Window size dependence of gain and bandwidth in avalanche photodiodes with multiple multiplication layers under near Geiger-mode operation.

We consider avalanche photodiodes (APDs) functioning under near Geiger-mode operation for extremely weak light (single or several photons) detection, such as in LiDAR receivers. To meet such demands, APDs which simultaneously have a large active window size, moderate bandwidth (∼GHz), and high internal gain (responsivity), are highly desired. However, it is difficult to design APDs capable of meeting the afore-mentioned performance requirements due to the intrinsic limitations of the gain-bandwidth product (GBP). In this work, we demonstrate that the GBP bottleneck in the APDs can be overcome by using multiple (3) In0.52Al0.48As based multiplication (M-) layers with a thick In0.53Ga0.47As absorber (2 µm). Moreover, the characteristic invariant 3-dB bandwidth in our APDs, from low to an extremely high operation gain, becomes more pronounced with an increase of its active window diameter (40 to 200 µm). This characteristic makes it very attractive for collecting weak light in free space as is required for LIDAR receiver applications. Comparison shows that the 200 µm APD exhibits a higher 0.9 Vbr responsivity (15 vs. 7 A/W), larger maximum gain (460 vs. 110), and higher GBP (468 vs. 131 GHz) than does the 40 µm reference sample and can sustain a constant 3-dB bandwidth (1.4 GHz) over a wide range of operation gains (10 to 460). The dependence of the APD performance on the window size can be attributed to the influence of the surface states on the edge of the etched mesa. Here, we further demonstrate a backside-illuminated structure with a flip-chip bonding package which minimizes this phenomenon in small APDs ensuring high-speed performance. Compared with the top-illuminated reference samples, the flip-chip bonding packaged device shows a further enhancement of the responsivity (10.7 vs. 7 A/W), 3-dB bandwidth (4.1 vs. 3.9 GHz), and saturation current (4.25 vs. 3.6 mA). The excellent static and dynamic performance of our flip-chip APD in turn leads to an unprecedented high velocity sensitivity (5 µm/sec) and superior quality 4-D FMCW LiDAR images compared to that obtainable with p-i-n-based or top-illuminated reference devices with the same small active window size (40 µm).

Design of automatic out-of-focus correction system for near-space lidar receivers

Design of automatic out-of-focus correction system for near-space lidar receivers

Compact all-fiber quantum-inspired LiDAR with over 100 dB noise rejection and single photon sensitivity

Entanglement and correlation of quantum light can enhance LiDAR sensitivity in the presence of strong background noise. However, the power of such quantum sources is fundamentally limited to a stream of single photons and cannot compete with the detection range of high-power classical LiDAR transmitters. To circumvent this, we develop and demonstrate a quantum-inspired LiDAR prototype based on coherent measurement of classical time-frequency correlation. This system uses a high-power classical source and maintains the high noise rejection advantage of quantum LiDARs. In particular, we show that it can achieve over 100dB rejection (with 100ms integration time) of indistinguishable (with statistically identical properties in every degree of freedom) in-band noise while still being sensitive to single photon signals. In addition to the LiDAR demonstration, we also discuss the potential of the proposed LiDAR receiver for quantum information applications. In particular, we propose the chaotic quantum frequency conversion technique for coherent manipulation of high dimensional quantum states of light. It is shown that this technique can provide improved performance in terms of selectivity and efficiency as compared to pulse-based quantum frequency conversion.

Study of 256 fiber array biaxial LiDAR optical assembly measurements.

This paper presents a method for measuring the optical assembly results based on multi-beam biaxial LiDAR. This method analyzes the optical assembly parameters of a LiDAR system affecting the LiDAR operation, and an experimental measurement system is built using a collimator to simulate the infinity imaging field. An InGaAs infrared camera is used to take pictures of the laser spot from the LiDAR transmitter and receiver, and then fit the laser spot images with Gaussian equations to calculate the biaxial LiDAR optical assembly results. Finally, the possible effecting factors of LiDAR alignment results are analyzed. This method is experimentally proven to achieve the measurement of the optical assembly results of a large scale multi-beam LiDAR. The possibility of further optimizing the measurement method by shaping the transmit laser is also reported.

A Low-Cost Measurement Methodology for LiDAR Receiver Integrated Circuits

This paper presents a test methodology to facilitate the measuring processes of LiDAR receiver ICs by avoiding the inherent walk error issue. In a typical LiDAR system, a costly laser diode driver emits narrow light pulses with fast rising edges, and the reflected pulses from targets enter an optical detector followed by an analog front-end (AFE) circuit. Then, the received signals pass through the cascaded amplifiers down to the time-to-digital converter (TDC) that can estimate the detection range. However, this relatively long signal journey leads to the significant decline of rising-edge slopes and the output pulse spreading, thus producing inherent walk errors in LiDAR receiver ICs. Compensation methods requiring complex algorithms and extra chip area have frequently been exploited to lessen the walk errors. In this paper, however, a simpler and lower-cost methodology is proposed to test LiDAR receiver ICs by employing a high-speed buffer and variable delay cells right before the TDC. With these circuits, both START and STOP pulses show very similar pulse shapes, thus effectively avoiding the walk error issue. Additionally, the time interval between two pulses is easily determined by varying the number of the delay cells. Test chips of the proposed receiver IC implemented in a 180-nm CMOS process successfully demonstrate easier and more accurate measurement results.

Bathymetry of a macro-pulsed chaotic laser based on a 520 nm laser diode subject to free space optical feedback.

We generate a macro-pulsed chaotic laser based on pulse-modulated laser diode subject to free space optical feedback, and demonstrate the performance of suppressing backscattering interference and jamming in turbid water. The macro-pulsed chaotic laser with a wavelength of 520 nm as a transmitter is used with a correlation-based lidar receiver to perform an underwater ranging. At the same power consumption, macro-pulsed lasers have higher peak power than in the continuous-wave form, enabling the former to detect longer ranging. The experimental results show that a chaotic macro-pulsed laser has excellent performance of suppressing the backscattering of water column and anti-noise interference compared with traditional pulse laser, especially by multiple accumulations about 10∼30 times, and target position can still be determined when SNR is -20 dB.

Research on the Performance of an Active Rotating Tropospheric and Stratospheric Doppler Wind Lidar Transmitter and Receiver

This paper investigates the transmitter and receiver performance of an active rotating tropospheric stratospheric Doppler wind Lidar. A 532 nm laser was determined as the detection wavelength based on transmission and scattering aspects. A ten-fold Galileo beam expander consisting of spherical and aspherical mirrors was designed and produced to compress the outgoing laser’s divergence angle using ZEMAX simulation optimization and optical-mechanical mounting means. The structure and support of the 800 mm Cassegrain telescope was redesigned. Additionally, the structure of the receiver was optimized, and the size was reduced. Meanwhile, the detectors and fiber mountings were changed to improve the stability of the received optical path. A single-channel atmospheric echo signal test was used to select the best-performing photomultiplier tube (PMT). Finally, the atmospheric wind field detection results of the original and upgraded systems were compared. The results show that after optimizing the transmitter and receiver, the detection altitude of the system is increased to about 47 km, and the wind speed and wind direction profiles match better with radiosonde measurements.

Effect of Lidar Receiver Field of View on UAV Detection

Researchers have shown that single-photon light detection and ranging (lidar) is highly sensitive and has a high temporal resolution. Due to the excellent beam directivity of lidar, most applications focus on ranging and imaging. Here, we present a lidar detection system for night environments. Different from MEMS, we choose a large divergence rather than scanning to detect unmanned aerial vehicles (UAVs). Collection and detection are achieved through the use of high-efficiency optical devices. With time-correlated single photon counting (TCSPC), we performed subsequent drone search work at centimeter resolution. We believe that we have developed a new technique for detecting UAVs. We show how the field of view influences the detection process. For some key areas of air defense, it is extremely necessary to find UAVs quickly and in a timely manner. In short, the results represent an important step toward practical, low-power drone detection using lidar.

All-MEMS Lidar Using Hybrid Optical Architecture with Digital Micromirror Devices and a 2D-MEMS Mirror.

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the lidar transmitter and receiver. A new quasi-solid-state lidar optical architecture employs a transmitter with a two-dimensional MEMS mirror for fine beam steering at a fraction of the degree of the angular resolution and is combined with a digital micromirror device for wide FOV scanning over 37 degree while sustaining a large aperture area of 140 mm squared. In the receiver, a second digital micromirror device is synchronized to the transmitter DMD, which enables a large FOV receiver. An angular resolution of by was achieved with 0.588 fps for scanning 1344 points within the field of view.

A CMOS AFE With 37-nA rms Input-Referred Noise and Marked 96-dB Timing DR for Pulsed LiDAR

This paper presents an analog front-end (AFE) circuit with marked timing point for pulsed time-of-flight LiDAR that employs either sampling- or event-based timing approach. The proposed AFE adopts a dual-mode structure for its pre-amplifier which can be configured as a charge-sensitive amplifier (CSA) or a gated active load-assisted TIA (GALA-TIA), depending on the intensity of input current. As a result, both the sensitivity and dynamic range (DR) of the AFE have been effectively improved. In addition, the zero-crossing point of the output signal has been marked as the timing point with a built-in pulse shaper, which allows the back-end circuits of LiDAR receiver discriminate the timing conveniently and accurately. The measured input-referred RMS noise current of the proposed AFE is 37 nA. With dual-mode control, a linear output DR of 80 dB and a wide timing DR of 96 dB with walk error no more than ±160 ps have been achieved. For single-shot measurement application, only CSA mode was enabled and the pulse widths of saturated output signals have been measured to compensate the walk errors, which realized a timing DR of 78 dB with accuracy of ±150 ps. The averaged power consumption is 66 mW and the total silicon area is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.79\times 0.42\,\,mm^{2}$ </tex-math></inline-formula> in 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process.

Simulation and misalignment analysis of the gain ratio of a polarization Mie Raman lidar.

The gain ratio is a critical parameter in a polarization Mie lidar. Calibrating the gain ratio is essential in aerosol classification studies. We developed a ray-tracing-based simulation method to investigate the impact of mounting errors on the gain ratio. In this method, a computational model for each element of the lidar was built, and Zemax was used to simulate the lidar receiver to obtain the optical gain ratio by theoretical calculations. This method can analyze the influence of each element's mounting errors and offer a theoretical foundation for the machining and mounting accuracy of the lidar design. The correctness of the model was verified by applying it to a single-wavelength polarization Mie Raman lidar.

Silicon nonlinear switch as a conditional circulator for monostatic LiDAR systems

All-optical silicon-photonics-based LiDAR systems allow for desirable features in scanning resolution and speed, as well as leverage other advantages such as size, weight, and cost. Implementing optical circulators in silicon photonics enables bidirectional use of the light path for both transmitters and receivers, which simplifies the system configuration and thereby promises low system cost. In this work, to the best of our knowledge, we present the first experimental verification of all-passive silicon photonics conditional circulators for monostatic LiDAR systems using a nonlinear switch. The proposed silicon nonlinear interferometer is realized by controlling signal power distribution with power-splitting circuits, allowing the LiDAR transmitter and receiver to share the same optical path. Unlike the traditional concept requiring a permanent magnet, the present device is implemented by using common silicon photonic waveguides and a standard foundry-compatible fabrication process. With several additional phase shifters, the demonstrated device exhibits considerable flexibility using a single chip, which can be more attractive for integration with photodetector arrays in LiDAR systems.

A Transimpedance-to-Noise Optimized Analog Front-End With High PSRR for Pulsed ToF Lidar Receivers

This paper presents a transimpedance-to-noise optimization approach for design of a resistive shunt-feedback TIA. This optimization offers an enhancement in the transimpedance and a noise performance very close to the theoretical minimum noise of the TIA. In addition, the transimpedance-to-noise optimization approach results in a small front-end FET size which enables a further reduction in power and area. Moreover, this approach enables using a fewer number of stages in the receiver chain which makes a high PSRR feasible and obviates the necessity for using an offset cancellation circuitry. Building on this approach, a fully differential analog front-end including a resistive shunt-feedback TIA and a post amplifier (PA) for time-of-flight (ToF) Lidar receivers is designed and implemented, achieving 94dB Ω transimpedance gain, 71nA input-referred rms noise current, -3dB bandwidth of 340MHz, and power supply rejection ratio (PSRR) of more than 87dB in a 0.11 μm CMOS process. The associated DC power consumption is 19.4mW with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> of 1.8V. Moreover, a push-pull buffer with 1V output swing is integrated for driving 50 Ω loads, such as off-chip time discriminators, which also additionally amplifies the signal with a gain of 5dB while consuming an extra 20.9mW of DC power. The whole chip (excluding pads) occupies 210 μm × 110 μm in area.

High-spectral-resolution lidar for measuring tropospheric temperature profiles by means of Rayleigh-Brillouin scattering.

A novel high-spectral-resolution lidar receiver based on a Fizeau interferometer and a photomultiplier tube array for tropospheric temperature profiling is introduced. Compared to other temperature lidars, an imaging approach is used to resolve the entire Rayleigh-Brillouin (RB) spectrum without applying frequency scanning techniques. The functionality of the system is demonstrated by means of a nighttime measurement. Atmospheric temperature is retrieved from 4.0 km to 9.2 km by analyzing the measured RB spectra with the Tenti S6 line shape model. The systematic error of the retrieved temperatures is determined to be smaller than 3 K, and the corresponding random error varies between 1.7 K (4.0 km) and 2.3 K (9.2 km) for an observation time of 5 min and a vertical resolution of 0.3 km. Considering the short averaging time and the stable arrangement of the system, the suggested approach is also attractive for future airborne applications.

Impacts of laser beam divergence on lidar multiple scattering polarization returns from water clouds

Theoretically, laser beam divergence can redistribute multiple scattering lights by spreading laser illumination and thus alter lidar polarization measurements. To study multiple scattering effects of laser divergence on lidar polarization signals, we apply the Monte Carlo polarized radiative transfer model MSCART to simulate lidar Stokes vector signals from a uniform water cloud with and without taking account of laser divergences. The comparison analysis shows that for lidar receiver footprints with roughly the same sizes of the multiple scattering regimes, laser divergence has almost no effect on ground-based lidar signals, but can have significantly large and much complex polarization effects on spaceborne lidar signals. An increase in laser divergence on one hand can greatly enhance spaceborne lidar multiple scattering depolarization when the divergence is larger than the FOV, and on the other hand can also weaken it slightly when the divergence less than the FOV. The weakest multiple scattering depolarization occurs at the divergence equal to the FOV. Furthermore, laser divergence can significantly reduce the sensitivity of FOV-resolved polarization measurement of spaceborne lidar to non-diagonal elements of phase matrix and make the measurement at different receiving polar angles only sensitive to diagonal elements of phase matrix at almost the same scattering angles. The spaceborne MFOV and CCD polarized lidar thus might not provide more information about phase matrix than the single FOV lidar does.

Initial results of Rayleigh scattering lidar observations at Zhongshan station, Antarctica

A Rayleigh scattering lidar for measuring the atmospheric density and temperature has been deployed at Zhongshan Station (69.4° S, 76.4° E), Antarctica. Lidar transmitter was a frequency doubled Nd:YAG laser with ~400 mJ pulse energy and 30 Hz repetition rate. A telescope with 0.8 m diameter pointing to the zenith direction served as the lidar receiver. This lidar was capable of profiling the density and temperature in the Upper Stratosphere and Lower Mesosphere (USLM) region. At the vertical resolution of 300 m and the temporal resolution of 30 min, the lidar measurement uncertainties, mainly due to the photon noise, were calculated to be within 1.5% and 1 K for density and temperature, respectively. Since March 2020, this lidar has been routinely operated at Zhongshan station for exploring the atmospheric density and temperature variations and wave propagation characteristics in the polar USLM region.

OLE: A Novel Oceanic Lidar Emulator

Oceanic lidar is an effective tool for detecting water’s vertical structure. Cost-effective design of an oceanic lidar system and processing algorithms requires an effective lidar simulator. In this study, an oceanic lidar simulation tool was developed, which is available to the public ( <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/soedchen/OLE</uri> ), and named the Oceanic Lidar Emulator (OLE). OLE is an improved semianalytic Monte Carlo-based lidar simulator, which has the capability of dealing with the physics of light propagating through wind-driven rough air–water interface into the ocean, being scattered by subsurface phytoplankton and reflected from the sea bottom, and returning to the lidar receiver. OLE has three main features: 1) it can deal with stratified water, while most existing lidar models can only be used for homogeneous water; 2) it can be applied to arbitrary scattering phase function (SPF) (e.g., Fournier–Forand or Petzold), while most existing lidar models can only use the Henyey–Greenstein SPF due to the difficulty of solving the inverse equation for the cumulative distribution function; and 3) it takes general consideration of lidar system observation geometry (e.g., receiver field of view, receiving aperture, altitude, incident angle, and so on) and environmental parameters (e.g., wind-driven rough water surface, vertical structure of water optical properties, and sea bottom albedo). We studied lidar extinction caused by multiple scattering and the effects of the SPF, rough sea surface, and stratified water, by comparing simulation results with measurements. These results demonstrated that our model is effective for oceanic lidar simulation.

Diurnal variation of atmospheric metal Na layer and nighttime top extension detected by a Na lidar with narrowband spectral filters at Beijing, China

Diurnal observations of metal Na layer can be implemented by making use of narrowband Faraday filters. On one hand, the narrowband spectral filters help to effectively suppress the background noise; on the other hand, the narrow bandwidth leads to different transmissions of Na layer resonance fluorescence signal and stratosphere Rayleigh scattering signal. The influence of the narrow spectral transmission on Na density retrieval cannot be canceled out by Rayleigh normalization and would result in a systematic error. In this paper, the Na density retrieval method when narrowband Faraday filters are used in the lidar receiver is discussed based on the transmission spectrum of Faraday filters and echo spectra of Rayleigh scattering and Na fluorescence. The results of Na layer diurnal variations that have been obtained from Na lidar observations at Beijing, China are presented. Considerable diurnal variation in Na density on the layer top and bottom are clearly revealed on a logarithmic scale. Intriguingly, larger height-scale nighttime extensions on the Na layer topside have been frequently observed from early summer to autumn. These observational results can provide valuable evidence for studying solar effect on the metal layer variation, atmospheric dynamical and chemical processes in the mesosphere and lower thermosphere region.