Linear-mode Avalanche Photodiodes Research Articles

Optical Phased Array-Based Laser Beam Array Subdivide Pixel Method for Improving Three-Dimensional Imaging Resolution

The small number of pixels in the current linear mode avalanche photodiode (LM-APD) array limits its three-dimensional (3D) imaging resolution. We use an optical phased array-based beam array subdivided pixel method to improve the 3D imaging resolution, using an optical phased array to generate a beam array with the same number of pixels as the LM-APD array and matching positions and controlling each sub-beam in the beam array to scan in the field of view of the corresponding pixel. The sub-beam divergence angle in the beam array is smaller than the instantaneous field of view angle of a single pixel in the LM-APD array. The sub-beam scanning in a single pixel’s field of view realizes the multiple acquisition of the target 3D information by the LM-APD array, thus improving the resolution of the LM-APD array. The distribution of the beam array in the far field is simulated, and the main performance parameters of 3D imaging are analyzed. Finally, a liquid crystal phase modulator is used as an optical phased array device to conduct experiments on a target 20 m away, and the results prove that our method can improve the resolution from 4 × 4 to 8 × 8, which can be improved at least four times.

Integrated Encapsulation and Implementation of a Linear-Mode APD Detector for Single-Pixel Imaging Lidar

Single-pixel imaging lidar is a novel technology that leverages single-pixel detectors without spatial resolution and spatial light modulators to capture images by reconstruction. This technique has potential imaging capability in non-visible wavelengths compared with surface array detectors. An avalanche photodiode (APD) is a device in which the internal photoelectric effect and the avalanche multiplication effect are exploited to detect and amplify optical signals. An encapsulated APD detector, with an APD device as the core, is the preferred photodetector for lidar due to its high quantum efficiency in the near-infrared waveband. However, research into APD detectors in China is still in the exploratory period, when most of the work focuses on theoretical analysis and experimental verification. This is a far cry from foreign research levels in key technologies, and the required near-infrared APD detectors with high sensitivity and low noise have to be imported at a high price. In this present study, an encapsulated APD detector was designed in a linear mode by integrating a bare APD tube, a bias power circuit, a temperature control circuit and a signal processing circuit, and the corresponding theoretical analysis, circuit design, circuit simulation and experimental tests were carried out. Then, the APD detector was applied in the single-pixel imaging lidar system. The study showed that the bias power circuit could provide the APD with an operating voltage of DC 1.6 V to 300 V and a ripple voltage of less than 4.2 mV. Not only that, the temperature control circuit quickly changed the operating state of the Thermo Electric Cooler (TEC) to stabilize the ambient temperature of the APD and maintain it at 25 ± 0.3 °C within 5 h. The signal processing circuit was designed with a multi-stage amplification cascade structure, effectively raising the gain of signal amplification. By comparison, the trial also suggested that the encapsulated APD detector and the commercial Licel detector had a good agreement on the scattered signal, such as a repetition rate and pulse width response under the same lidar environment. Therefore, target objects in real atmospheric environments could be imaged by applying the encapsulated APD detector to the near-infrared single-pixel imaging lidar system.

A Near-Infrared Enhanced Field-Line Crowding Based CMOS-Integrated Avalanche Photodiode

This paper presents a CMOS-integrated linear-mode avalanche photodiode based on electric field-line crowding (EFLC-APD) to form an effective multiplication zone and a wide absorption zone. The EFLC-APD possesses a hemispherical avalanching electric field at the n-well/p- epi junction formed due to the curvature of the half-sphere cathode. A lower electric field extends radially across the entire volume of the EFLC-APD towards the substrate and towards the surface anode. Because of such a distribution of the electric field, electrons photogenerated within the whole volume drift towards the cathode. Therefore, the EFLC-APD provides a large sensitive-area to total-area ratio while offering high responsivity and bandwidth for red and near-infrared light due to its thick absorption zone and drift-based carrier transport. It is shown that the electric field distribution can be modified by the design parameters such as cathode radius and diode size in addition to doping profiles. The EFLC-APD achieves a responsivity-bandwidth (R-BW) product of 49.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{\mathrm{A}}{\mathrm{W}}\cdot$</tex-math></inline-formula> GHz, corresponding to the responsivity and bandwidth of 33 A/W and 1.5 GHz, respectively, at the wavelength of 850 nm. In addition, a maximum responsivity of 3.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times\, 10^{\mathrm{3}}$</tex-math></inline-formula> A/W at 2 nW optical power is achieved for the red and near-infrared spectral range. Noise characterization resulted in an excess noise factor F = 6 measured at an avalanche gain of 56.7. Due to the high sensitive-area to total-area ratio, high responsivity, large bandwidth, and CMOS compatibility, this APD is a promising optical detector for many applications.

Analysis and Simulation of Space-Based LM-APD 3D Imaging

The linear mode avalanche photodiode (LM-APD) array has the capability of real-time 3D imaging for moving targets, which is a promising 3D imaging means in space. The main system parameters of the LM-APD array 3D imaging system, the characteristics of the space target itself, and the relative positional relationship between them will affect the 3D imaging results at the same time, and there is a need for an appropriate simulation method to describe the space target point cloud acquired by the LM-APD array 3D imaging system under different conditions. We propose a simulation method for the 3D imaging of space targets with LM-APD arrays, which takes the characteristics of the space targets and the relative position into consideration, and build a link from the laser to the receiving system to simulate the echo waveform of each pixel in the LM-APD array. The experiment results under different conditions show that the proposed simulation method can accurately describe the imaging results of the LM-APD array 3D imaging system for space targets with different shapes, materials, and motion states, which providing theoretical and data support for the design of LM-APD array 3D imaging systems.

High gain, low noise 1550 nm GaAsSb/AlGaAsSb avalanche photodiodes

High sensitivity avalanche photodiodes (APDs) operating at eye-safe infrared wavelengths (1400–1650 nm) are essential components in many communications and sensing systems. We report the demonstration of a room temperature, ultrahigh gain ( M = 278 , λ = 1550 n m , V = 69.5 V , T = 296 K ) linear mode APD on an InP substrate using a G a A s 0.5 S b 0.5 / A l 0.85 G a 0.15 A s 0.56 S b 0.44 separate absorption, charge, and multiplication (SACM) heterostructure. This represents ∼ 10 × gain improvement ( M = 278 ) over commercial, state-of-the-art InGaAs/InP-based APDs ( M ∼ 30 ) operating at 1550 nm. The excess noise factor is extremely low ( F &lt; 3 ) at M = 70 , which is even lower than Si APDs. This design gives a quantum efficiency of 5935.3% at maximum gain. This SACM APD also shows an extremely low temperature breakdown sensitivity ( C b d ) of ∼ 11.83 m V / K , which is ∼ 10 × lower than equivalent InGaAs/InP commercial APDs. These major improvements in APD performance are likely to lead to their wide adoption in many photon-starved applications.

CMOS Integrated 32 A/W and 1.6 GHz Avalanche Photodiode Based on Electric Field-Line Crowding

This letter presents a new Si CMOS linear-mode avalanche photodiode (APD) based on an electric field distribution formed by field-line crowding. In this structure, a spherical avalanching electric field is enforced by field-line crowding due to the curvature of the half-sphere cathode (n-well). The electric field extends radially and, therefore, the entire low-doped epitaxial layer serves as charge collection zone. This APD can provide high responsivity and bandwidth due to its thick absorption zone and drift-based carrier transport. Measurements using a 675 nm laser source at 200 nW optical power show a maximum bandwidth of 1.6 GHz while the responsivity is 32 A/W. In addition, a maximum responsivity of 3.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{3}$ </tex-math></inline-formula> A/W at 5 nW optical power is achieved. Due to the high avalanche gain, large bandwidth, and CMOS compatibility without any process modification, this APD is a promising optical detector for many applications.

Linear Mode Avalanche Photodiodes With Antimonide Multipliers on InP Substrates

We provide an overview of our progress on the development of linear mode avalanche photodiodes (LmAPDs) on InP substrates using antimony (Sb)-based multipliers for short-wavelength infrared (SWIR) spectral region. We identify the key figures of merit of LmAPDs to provide higher sensitivity and speed for applications like light detection and ranging (LiDAR) and remote sensing. We discuss the design of separate absorption, charge, and multiplication (SACM) APDs that are used for narrow gap absorption. We summarize our results on the impact ionization, multiplication gain, dark current, and excess noise of AlGaAsSb and AlInAsSb multipliers lattice-matched to InP substrates. Finally, we identify the key technical challenges associated with the development of SACM APDs on InP substrates.

Bit Error Performance of APD and SPAD Receivers in Optical Wireless Communication

This review concentrates on the state-of-the-art hardware-oriented receiver aspects for optical wireless communication (OWC), and points to the importance of BER performance analysis and modeling in presence of non-perpendicular light incidence. Receivers in OWC networks for 6G applications have to work for strongly different light incidence angles, to allow the formation of connections to locally separated transceivers without the need for rotation units and accurate adjustment. In turn, and in combination with fully integrated optical receivers, reduction of cost and increased comfort can be achieved. Fully integrated [bipolar] complementary metal-oxide-semiconductor ([Bi]CMOS) receivers with on-chip avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs) are presented and their performance in optical wireless communication is summarized. Impressive data rates up to 2 Gbit/s and free-space transmission distances up to 27 m at bit error ratios (BER) below 10−9 are reached with linear-mode APD receivers. The importance of optical interference in the isolation and passivation stack on top of the integrated photodiodes is illuminated. To be able to predict the dependence of the BER of single-photon avalanche diode (SPAD) receivers on the light incidence angle, a model, which includes a model for the photon detection probability and a standing-wave model for the isolation and passivation stack, is extended. The dependence of the BER on the light incidence angle onto the photodiodes is investigated by electromagnetic simulation for optical transmission of the layers on top of the photodiode, device simulation for the avalanche triggering probability and BER modeling with MATLAB. It is found that incidence angles up to 30° have moderate influence on the BER and that the BER degrades significantly for incidence angles larger than 50°.

Analytical Evaluation of Signal-to-Noise Ratios for Avalanche- and Single-Photon Avalanche Diodes

Performance of systems for optical detection depends on the choice of the right detector for the right application. Designers of optical systems for ranging applications can choose from a variety of highly sensitive photodetectors, of which the two most prominent ones are linear mode avalanche photodiodes (LM-APDs or APDs) and Geiger-mode APDs or single-photon avalanche diodes (SPADs). Both achieve high responsivity and fast optical response, while maintaining low noise characteristics, which is crucial in low-light applications such as fluorescence lifetime measurements or high intensity measurements, for example, Light Detection and Ranging (LiDAR), in outdoor scenarios. The signal-to-noise ratio (SNR) of detectors is used as an analytical, scenario-dependent tool to simplify detector choice for optical system designers depending on technologically achievable photodiode parameters. In this article, analytical methods are used to obtain a universal SNR comparison of APDs and SPADs for the first time. Different signal and ambient light power levels are evaluated. The low noise characteristic of a typical SPAD leads to high SNR in scenarios with overall low signal power, but high background illumination can saturate the detector. LM-APDs achieve higher SNR in systems with higher signal and noise power but compromise signals with low power because of the noise characteristic of the diode and its readout electronics. Besides pure differentiation of signal levels without time information, ranging performance in LiDAR with time-dependent signals is discussed for a reference distance of 100 m. This evaluation should support LiDAR system designers in choosing a matching photodiode and allows for further discussion regarding future technological development and multi pixel detector designs in a common framework.

Sirius: a prototype astronomical intensity interferometer using avalanche photodiodes in linear mode

ABSTRACT Optical intensity interferometry, developed in the 1950s, is a simple and inexpensive method for achieving angular resolutions on microarcsecond scales. Its low sensitivity has limited intensity interferometric observations to bright stars so far. Substantial improvements are possible by using avalanche photodiodes (APDs) as light detectors. Several recent experiments used APDs in single-photon detection mode; however, these either provide low electronic bandwidths (few MHz) or require very narrow optical bandpasses. We present here the results of laboratory measurements with a prototype astronomical intensity interferometer using two APDs observing an artificial star in continuous (‘linear’) detection mode with an electronic bandwidth of 100 MHz. We find a photon–photon correlation of about 10−6, as expected from the ratio of the coherence times of the light source and the detectors. In a configuration where both detectors are on the optical axis (zero baseline), we achieve a signal-to-noise ratio of ∼2700 after 10 min of integration. When measuring the correlation as a function of baseline, we find a Gaussian correlation profile with a standard deviation corresponding to an angular half-width of the artificial star of 0.55 arcsec, in agreement with the estimate by the manufacturer. Our results demonstrate the possibility to construct large astronomical intensity interferometers using linear-mode APDs.

Adjustable higher SNR and long-range 3D-imaging cluster lidar based on a coded full-waveform technique.

Three-dimensional (3D) lidar imaging technology is developing rapidly in civil, commercial, and military fields. Especially in the military field, lidar with a high signal-to-noise ratio (SNR) and long range is essential. However, high SNR is contradictory to long-range detection, which is a difficult problem to be resolved. In this paper, we propose an adjustable higher SNR and long-range 3D-imaging cluster lidar (C-Lidar) based on a coded full-waveform technique. C-Lidar makes full use of linear mode avalanche photodiode (Lm-APD) multiplexing and space-time domain laser codec technology. The system uses only an 8×8 Lm-APD array to acquire 64×64×64 pixels in a single imaging process within 6.4×10-3 s. Based on the C-Lidar system, we establish a mathematical model to analyze the increased SNR by 18dB. It is noteworthy that the SNR can be increased much higher when the product of the number of Lm-APDs and the length of the encoding sequence increase. The SNR is adjusted with the product, and C-Lidar changes the SNR by controlling the product. To verify the feasibility of the above theory, we conduct a principle prototype imaging experiment, and the result shows that C-Lidar achieves a clear image at 2km.

A new three-dimensional nonscanning laser imaging system based on the illumination pattern of a point-light-source array.

One of the most important goals of research on three-dimensional nonscanning laser imaging systems is the improvement of the illumination system. In this paper, a new three-dimensional nonscanning laser imaging system based on the illumination pattern of a point-light-source array is proposed. This array is obtained using a fiber array connected to a laser array with each unit laser having independent control circuits. This system uses a point-to-point imaging process, which is realized using the exact corresponding optical relationship between the point-light-source array and a linear-mode avalanche photodiode array detector. The complete working process of this system is explained in detail, and the mathematical model of this system containing four equations is established. A simulated contrast experiment and two real contrast experiments which use the simplified setup without a laser array are performed. The final results demonstrate that unlike a conventional three-dimensional nonscanning laser imaging system, the proposed system meets all the requirements of an eligible illumination system. Finally, the imaging performance of this system is analyzed under defocusing situations, and analytical results show that the system has good defocusing robustness and can be easily adjusted in real applications.

Guest Editorial: Introduction to the Special Issue on Optical Detectors

The objective of this special issue is to document the current state-of-the-art in the area of Optical Detectors and highlight recent progress and trends in innovative optical detector technology and its applications. This issue combines 11 invited and 21 contributed papers, authored byworld-renowned research groups and promising scientists from around the world. The invited papers present extended reviews on recent progress and significant perspectives on future research directions. They cover lownoise linear-mode avalanche photodiodes (APDs) for fiber optic communications, single photon APDs (SPADs) and Si SPAD arrays for photon counting imagers, hybrid integration technologies, waveguide APDs, lowcapacitance nano-photodetector, integrated photodetectors for coherent receivers, and high-speed uni-traveling carrier (UTC) photodiodes (PDs) for THz applications. The contributed papers cover a broad variety of key research areas and emerging technologies in optical detectors including graphene-based detectors, plasmonic structures for current enhancement, phototransistors, and UTC-type PDs on silicon-on-insulator waveguide as well as a UTC PD with type II hybrid absorber. Several papers describe advances in SPADs and CMOS SPAD arrays for UV and visible detection and four papers cover quantum well and quantum dot devices. This special issue also illustrates a wide range of optical detector technology applications including UV, visible, and IR imaging, fiber optic communications, microwave and THz analog applications, and quantum communications. Furthermore, this special issue covers a range of advances on theory and simulation, design and fabrication, and optical detector characterization methodologies.

64×64 InGaAs/InP三维成像激光焦平面探测器

针对900~1 700 nm波长无扫描激光三维成像雷达的需求，研制了一种规模为6464的线性模式雪崩焦平面阵列（LM-APD-FPA），它由InGaAs/InP雪崩光电二极管阵列与CMOS专用读出电路（ASIC）组成。该器件采用飞行时间（TOF）测距的方式工作，APD光敏芯片将脉冲激光信号转化成脉冲光电流，读出电路对其进行放大、阈值比较后实现激光探测并在每个单元获取光脉冲的飞行时间，将其转化成二进制编码信号后串行输出。测试结果表明，6464 LM-APD-FPA有效像元最小可探测光功率值约为400 nW，时间分辨率为1 ns。用该探测器在激光雷达系统上实现了无扫描单脉冲激光三维成像，表明了线性模式激光焦平面探测器可用于激光三维成像领域。

Comparison of flash lidar detector options

Three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks are compared. The tasks are combinations of two collection types (3-D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on Geiger mode avalanche photodiodes (GMAPD), linear mode avalanche photodiodes (LMAPD), and optical time-of-flight lidar, which combine rapid polarization rotation of the image and dual low-bandwidth cameras to generate a 3-D image. We choose scenarios to highlight the strengths and weaknesses of various lidars. We consider HgCdTe and InGaAs variations of LMAPD cameras. The InGaAs GMAPD and the HgCdTe LMAPD cameras required the least energy to 3-D map both scenarios for bare earth, with the GMAPD taking slightly less energy. We comment on the strengths and weaknesses of each receiver technology. Six bits of intensity gray levels requires substantial energy using all camera modalities.

Development of Gated Pinned Avalanche Photodiode Pixels for High-Speed Low-Light Imaging

This work explores the benefits of linear-mode avalanche photodiodes (APDs) in high-speed CMOS imaging as compared to different approaches present in literature. Analysis of APDs biased below their breakdown voltage employed in single-photon counting mode is also discussed, showing a potentially interesting alternative to existing Geiger-mode APDs. An overview of the recently presented gated pinned avalanche photodiode pixel concept is provided, as well as the first experimental results on a 8 × 16 pixel test array. Full feasibility of the proposed pixel concept is not demonstrated; however, informative data is obtained from the sensor operating under −32 V substrate bias and clearly exhibiting wavelength-dependent gain in frontside illumination. The readout of the chip designed in standard 130 nm CMOS technology shows no dependence on the high-voltage bias. Readout noise level of 15 rms, full well capacity of 8000, and the conversion gain of 75 µV are extracted from the photon-transfer measurements. The gain characteristics of the avalanche junction are characterized on separate test diodes showing a multiplication factor of 1.6 for red light in frontside illumination.

High performance waveguide-coupled Ge-on-Si linear mode avalanche photodiodes.

We present experimental results for a selective epitaxially grown Ge-on-Si separate absorption and charge multiplication (SACM) integrated waveguide coupled avalanche photodiode (APD) compatible with our silicon photonics platform. Epitaxially grown Ge-on-Si waveguide-coupled linear mode avalanche photodiodes with varying lateral multiplication regions and different charge implant dimensions are fabricated and their illuminated device characteristics and high-speed performance is measured. We report a record gain-bandwidth product of 432 GHz for our highest performing waveguide-coupled avalanche photodiode operating at 1510nm. Bit error rate measurements show operation with BER< 10-12, in the range from -18.3 dBm to -12 dBm received optical power into a 50 Ω load and open eye diagrams with 13 Gbps pseudo-random data at 1550 nm.

Pixel multiplexing technique for real-time three-dimensional-imaging laser detection and ranging system using four linear-mode avalanche photodiodes.

The avalanche-photodiode-array (APD-array) laser detection and ranging (LADAR) system has been continually developed owing to its superiority of nonscanning, large field of view, high sensitivity, and high precision. However, how to achieve higher-efficient detection and better integration of the LADAR system for real-time three-dimensional (3D) imaging continues to be a problem. In this study, a novel LADAR system using four linear mode APDs (LmAPDs) is developed for high-efficient detection by adopting a modulation and multiplexing technique. Furthermore, an automatic control system for the array LADAR system is proposed and designed by applying the virtual instrumentation technique. The control system aims to achieve four functions: synchronization of laser emission and rotating platform, multi-channel synchronous data acquisition, real-time Ethernet upper monitoring, and real-time signal processing and 3D visualization. The structure and principle of the complete system are described in the paper. The experimental results demonstrate that the LADAR system is capable of achieving real-time 3D imaging on an omnidirectional rotating platform under the control of the virtual instrumentation system. The automatic imaging LADAR system utilized only 4 LmAPDs to achieve 256-pixel-per-frame detection with by employing 64-bit demodulator. Moreover, the lateral resolution is ∼15 cm and range accuracy is ∼4 cm root-mean-square error at a distance of ∼40 m.

Demonstration of the over dynamic range of MPPC by high intensity pulsed light illumination

Abstract The dynamic range of Multi-Pixel Photon Counter (MPPC) is considered to be limited by the total pixel number of MPPC, while it can be extended if the length of the pulsed incident light is larger than the width of the output avalanche pulse of MPPC, because single pixel could be triggered more than once. However, in this paper we demonstrated that the amplitude of the output signal of MPPC can reach several times larger than the equivalent amplitude of MPPC when all the pixels are fired, even if the length of the pulsed light is much smaller than the width of the output avalanche pulse of MPPC. The experimental phenomenon is described in detail. One possible explanation of this phenomenon is that the non-high electrical field region in the MPPC also has its own gain but smaller than the gain in the high electrical field region. The non-high electrical field region should be working in the linear mode like a linear mode avalanche photodiode (APD). The gain in the non-high electrical field region is of the order of 100 by estimation.

Linear Mode Avalanche Photodiode With High Responsivity Integrated in High-Voltage CMOS

A fully integrable avalanche photodiode fabricated in a 0.35-μm standard high-voltage CMOS process is presented. The device achieves a high unamplified responsivity (M = 1) of 0.41 A/W and a maximum responsivity (M = 6.6 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ) of 2.7 · 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> A/W for 5-nW optical power using a 670-nm laser source. The maximum bandwidth of 850 MHz was measured at 500-nW and 5-μW optical power which results in a responsivity bandwidth product of 17.4-GHz · A/W for a gain of M = 50.