Avalanche Photodiodes Research Articles

Performance analysis of near-earth, lunar and interplanetary optical communication links

The performance of near-Earth, lunar and interplanetary laser optical communications is investigated by using simulation models which were successfully verified in previous projects. The simulation models consider typical mission design parameters like transmit power and operation wavelength for the optical laser transmitters, different apertures of the optical telescope, varying distances between the Earth ground station and the spacecraft terminals, Geiger-mode avalanche photodiodes (APD) or superconducting nanowire single photon detection (SNSPD) receivers, atmospheric disturbances like scintillation and absorption, background noises for the uplink and downlink and appropriate pulse position modulation (PPM) orders. Typical design parameters are those of published ESA (European Space Agency) and NASA (National Aeronautics and Space Administration) missions. The investigations of laser optical communications for various system parameters and different distances between the Earth ground station and the spacecraft could also help to achieve an overview of free space and deep space optical communications for different orbit constellations for future missions with laser optical communication links.

Performance comparisons between inverted and conventional avalanche photodiodes for larger capacity applications

Performance comparisons between inverted and conventional avalanche photodiodes for larger capacity applications

Afterpulse effect in measurement-device-independent quantum key distribution.

There is no doubt that measurement-device-independent quantum key distribution (MDI-QKD) is a crucial protocol that is immune to all possible detector side channel attacks. In the preparation phase, a simulation model is usually employed to get a set of optimized parameters, which is utilized for getting a higher secure key rate in reality. With the implementation of high-speed QKD, the afterpulse effect which is an intrinsic characteristic of the single-photon avalanche photodiode is no longer ignorable, this will lead to a great deviation compared with the existing analytical model. Here we develop an afterpulse-compatible MDI-QKD model to get the optimized parameters. Our results indicate that by using our afterpulse-compatible model, we can get a much higher key rate than the prior afterpulse-omitted model. It is significant to take the afterpulse effect into consideration because of the improvement of the system working frequency.

A GaAsSb/AlGaAsSb Avalanche Photodiode With a Very Small Temperature Coefficient of Breakdown Voltage

Avalanche photodiodes (APDs) made with the material AlGaAsSb (lattice-matched to InP) exhibit very low excess noise characteristics. We demonstrate a Separate Absorption and Multiplication APD (SAM-APD) incorporating a GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.52</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> (GaAsSb) absorption region and an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.56</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.44</sub> (AlGaAsSb) avalanche region. Our GaAsSb/AlGaAsSb SAM-APD exhibits a cut-off wavelength of 1.70 μm at room temperature and a responsivity of 0.39 A/W at 1.55 μm wavelength (with no antireflection coating). Temperature dependence of the breakdown voltage was obtained from avalanche gain data from multiple devices operated at 77 to 295 K. This produced a temperature coefficient of breakdown voltage of 4.31±0.33 mV/K, a factor of 10 and 5 smaller than values for comparable InP and InAlAs SAM-APDs. The very small temperature coefficient of this work is consistent with the extremely weak temperature dependence of avalanche breakdown previously observed in AlGaAsSb diodes.

Performance investigation of DPMZM based RoF system by employing PIN and APD photodetector

Abstract As per the increasing demand of users, the wireless network fulfils significant challenges in terms of capacity, data rate, reduced environmental impact and better receiver performance. Radio over fiber (RoF) is the technique by which radio signal is modulated over the optical fiber link. The functioning of RoF is dependent on the optical modulator, optical fiber and photodetector. In this paper, dual parallel Mach–Zehnder modulator (DPMZM) is used, which gives good results against intermodulation distortion (IMD) errors. In order to investigate the receiver performance, positive-intrinsic-negative (PIN) and avalanche photodiode (APD) photodetectors are utilized at the receiver end. The analytical analysis of DPMZM based RoF system is analyzed, and the simulation model is implemented using OptSIM software, including PIN and APD photodetectors. The performance is scrutinized against various optical fiber lengths. The performance of the proposed model is analyzed and investigated by the presence of desired components and distorted (IMD) components for 1 and 5 km optical fiber distance between the control station and base station.

4-bit DAC based 6.9Gb/s PAM-8 UOWC system using single-pixel mini-LED and digital pre-compensation.

Low-cost underwater wireless optical communication (UOWC) systems are attractive for high-speed connections among unmanned vehicles or devices in various underwater applications. Here we demonstrate a high-speed and low-cost UOWC system using a low-resolution digital to analog converter (DAC), a single-pixel mini-sized light-emitting diode (mini-LED), and digital pre-compensation (DPC). The enabled DPC scheme comprises digital pre-distortion (DPD), digital pre-emphasis (DPE), and digital resolution enhancer (DRE), which pre-compensate for mini-LED nonlinearity, the bandwidth limitation of the mini-LED and avalanche photodiode detector, and DAC resolution limitation, respectively. The simulation results show that the in-band signal-to-quantization noise ratio can be increased by 6.8 dB using DRE based on a 4-bit DAC. To further improve the system capacity, we tune the level of DPE in order to optimize the trade-off between the residual inter-symbol interference and signal-to-noise ratio. With the combination of optimized DPE and DRE, we obtain a 21.1% higher data rate compared with full DPE only and demonstrate the transmission of 6.9 Gb/s PAM-8 signal over a 2-m distance underwater based on a single-pixel mini-LED and 4-bit DAC. This paper reports a cost-effective UOWC system first using a low-resolution DAC and DPC, which offers a promising path toward low-cost underwater optical wireless networks.

Self-Assembly Nanopillar/Superlattice Hierarchical Structure: Boosting AlGaN Crystalline Quality and Achieving High-Performance Ultraviolet Avalanche Photodetector.

As a burgeoning wide-band gap semiconductor material, AlxGa1-xN alloy has attracted great attention for versatile applications due to its superior properties. However, its poor crystalline quality has restricted the employment of AlGaN on electronic devices for a long time. Herein, we proposed a nanopillar/superlattice hierarchical structure for AlGaN epitaxy to boost the crystalline quality. The scale-controllable AlN nanopillar template is fabricated from a nickel self-assembly process. AlGaN initiates the epitaxial laterally overgrowth mode based on the nanopatterned template. In addition, the AlxGa1-xN/AlyGa1-yN superlattice structure could effectively block the propagation of threading dislocation segments. The kinetics of the dislocation and epitaxy process in the hierarchical structure is intuitively demonstrated and analyzed. Consequently, the dislocation density of AlGaN grown by this method is significantly reduced by more than 30 times compared to the AlN template. No threading dislocation segments were observed in the 4 μm TEM field of view. Moreover, based on the hierarchical structure, we also fabricated an AlGaN ultraviolet avalanche photodiode (APD). The APD exhibits superior performance, achieving a maximum gain of 1.3 × 105 and high responsivity of 1.46 A/W at 324 nm. The reliability of the nanopillar/superlattice AlGaN epitaxial procedure is anticipated to shed new light on the nitride semiconductor material, further bringing a breakthrough to wide-band gap electronic devices.

Narrow bandgap Al0.15In0.85As0.77Sb0.23 for mid-infrared photodetectors.

Mid-IR is a useful wavelength range for both science and military applications due to its low atmospheric attenuation and ability to be used for passive detection. However, many solutions for detecting light in this spectral region need to be operated at cryogenic temperatures as their required narrow bandgaps suffer from carrier recombination and band-to-band tunneling at room temperature leading to high dark currents. These problems can be alleviated by using a separate absorption, charge, and multiplication avalanche photodiode. We have recently demonstrated such a device with a 3-µm cutoff using Al0.15In0.85As0.77Sb0.23, as the absorber, grown on GaSb. Here we investigate Al0.15In0.85As0.77Sb0.23 as a simple PIN homojunction and provide metrics to aid in future designs using this material. PL spectrum measurements indicate a bandgap of 2.94 µm at 300 K. External quantum efficiencies of 39% and 33% are achieved at 1.55 µm and 2 µm respectively. Between 180 K and 280 K the activation energy is ∼0.22 eV, roughly half the bandgap of Al0.15In0.85As0.77Sb0.23, indicating thermal generation is dominant.

Performance analysis of PPM FSOC system with APD detector considering atmospheric turbulence channel and fiber coupling

In a free-space optical communication system with an avalanche photodiode (APD) detector, the average bit error rate (ABER) is studied based on pulse position modulation (PPM) considering Gamma–Gamma atmospheric turbulence and fiber coupling efficiency (FCE). By analyzing the shot noise and thermal noise, the approximate analytical expression of the ABER of binary PPM is theoretically derived. Then, the approximate analytical expression of ABER union bound is derived for L-ary PPM. The FCE has a greater impact on the ABER of the APD detection system than it does on the PIN detection system. By adopting the adaptive optics technology, compared with the PIN detection system, the communication performance of the APD detection is greatly improved. Moreover, the optimal average APD gain of the APD detection system is strongly correlated to the detector temperature but weakly dependent on the atmospheric turbulence intensity, FCE, number of wavefront compensation terms, average received photon number, and receiving aperture size. By optimizing the receiving aperture and designing an accurate temperature control system, the communication performance of the APD detection system can be further improved.

High signal-noise ratio avalanche photodiodes with dynamic biasing technology for laser radar applications

In this work, a high signal-noise ratio (SNR) dynamic biasing InGaAs/InAlAs avalanche photodiode (APD) is demonstrated experimentally and first applied in a laser radar system. Combining with the dynamic biasing technology, the APDs are operated in an unexploited voltage range between linear mode and Geiger mode, which, in this work, is defined as a transition zone. Surprisingly, it is found that the excess noise of dynamic biasing APDs decreases with the gain in this transition zone. As expected, the maximum useful gain is as high as 620 in the dynamic biasing mode, which shows a greater promotion than that of the DC biasing mode (17.5). Compared with the traditional DC biasing mode, the optimal SNR for dynamic biasing mode is improved by 14 dB without the degradation of response time as the peak optical power is 525 nW. Moreover, when SNR = 10, the peak optical power for the dynamic biasing mode is 43.4 nW, which shows a 57.5-fold (17.6 dB) reduction in comparison with the DC biasing mode (2495 nW). Therefore, we believe this new optical receiver will pave a new way in high-sensitivity and high-speed light detection.

Advances in Mid-Infrared Single-Photon Detection

The current state of the art of single-photon detectors operating in the mid-infrared wavelength range is reported in this review. These devices are essential for a wide range of applications, such as mid-infrared quantum communications, sensing, and metrology, which require detectors with high detection efficiency, low dark count rates, and low dead times. The technological challenge of moving from the well-performing and commercially available near-infrared single-photon detectors to mid-infrared detection is discussed. Different approaches are explored, spanning from the stoichiometric or geometric engineering of a large variety of materials for infrared applications to the exploitation of alternative novel materials and the implementation of proper detection schemes. The three most promising solutions are described in detail: superconductive nanowires, avalanche photodiodes, and photovoltaic detectors.

Biaxial strain modulated valence-band engineering in III-V digital alloys

Some III-V digital alloy avalanche photodiodes exhibit low excess noise. These alloys have low hole ionization coefficients due to presence of small 'minigaps', enhanced effective mass and large separation between light-hole and split-off bands in the valence band. In this letter, an explanation for the formation of the minigaps using a tight binding picture is provided. Furthermore, we demonstrate that decreasing substrate lattice constant can increase the minigap size and mass in the transport direction. This leads to reduced quantum tunneling and phonon scattering of the holes. Finally, we illustrate the band structure modification with substrate lattice constant for other III-V digital alloys.

High-speed waveguide Ge/Si avalanche photodiode with a gain-bandwidth product of 615 GHz

High-sensitivity and high-bandwidth receivers are always demanded for high-speed optical link systems. As a key element, an avalanche photodiode (APD) is often regarded as one of the most attractive options for achieving high sensitivity owing to the potential high internal gain. In this paper, a 48-GHz waveguide Ge/Si avalanche photodiode operating at the O-band (1310 nm) is designed with a lateral reach-through structure and fabricated with simplified processes. The fabricated APD shows a high primary responsivity of 0.93 A/W at the unit-gain voltage of−4.7V. It has an avalanche gain of 12.8 and a record gain-bandwidth product of∼615GHzwith an input optical power of−15dBmwhen operating at a bias voltage of−14V. The present Ge/Si APD is used successfully for high-speed data receiving, showing a sensitivity improvement about 7.6 dB for KP4-FEC operation (i.e., BER=2.4×10−4) with 50 Gbps non-return-to-zero (NRZ) data, compared with the case of using the reference PIN PD on the same chip. The sensitivity of the receiver with the present APD for NRZ signals is about−21.3dBm,−17.8dBm, and−12.6dBmfor KP4-FEC operation with different data rates of 50 Gbps, 80 Gbps, and 100 Gbps, while the sensitivity for four-level pulse amplitude modulation signals is about−13.2dBmand−11.3dBmfor KP4-FEC operation with different data rates of 25 and 50 Gbaud. Such high-performance APDs pave the way to achieve high-speed and high-sensitivity data transmissions.

Photon arrival sequence analysis of laser heterodyne signal with a Geiger-mode APD array

A heterodyne detection mechanism with Geiger-mode avalanche photodiode detector arrays is proposed for optical systems to achieve high sensitivity and good anti-interference. In contrast to the conventional processing method of photon arrival sequence, where the step of incoherent accumulation is canceled, the beat frequency is only obtained in this paper by the coherent superposition of phase-matched sequences, which can alleviate or even reduce the effect of the initial phase drift between the frames of the beat frequency signal. After phase matching of the beat signal, the power spectral density intensity of coherent superposition is greater than that of incoherent accumulation.

Study of the characteristics of germanium avalanche photodiodes in the photon counting mode

A study was made of the characteristics of photodetectors for fiber-optic communication lines using quantum cryptographic systems – germanium avalanche photodiodes operating in the photon counting mode. In particular, it was established at what highest temperature the implementation of the photon counting mode is possible, and the influence of temperature and overvoltage on the sensitivity of photodiodes is also considered. An experimental setup has been developed for the research. It has been determined that the highest ambient temperature at which LFD-2 germanium avalanche photodiodes operate in the photon counting mode is 243 K. It has also been found that the highest sensitivity of germanium avalanche photodiodes corresponds to the optical radiation wavelength range of 1310÷1490 nm. Lowering the temperature leads to an increase in the sensitivity of germanium avalanche photodiodes. It was found that the dependence of the signal-to-noise ratio on overvoltage has a maximum corresponding to overvoltage ΔU = 0.1 V. Lowering the temperature led to an increase in sensitivity and signal-to-noise ratio. Since there was no shift in the maximum dependence of the signal-to-noise ratio on the overvoltage, it was therefore concluded that when the avalanche photodiode operates in the photon counting mode, in order to ensure maximum sensitivity, it is necessary to select the overvoltage corresponding to the maximum signal-to-noise ratio. The results obtained can be used in quantum cryptographic systems, technical means of protecting information transmitted over fiber-optic communication lines, and for the metrology of single-photon radiation sources.

Joint Frame Detection and Channel Parameter Estimation for OOK Free-Space Optical Communications

We consider a free-space optical (FSO) communication link for packet-based transmissions over a turbulence fading channel. The modulation format is on-off keying (OOK) and a unique-word (UW) composed by a known synch pattern is periodically inserted in the data stream to identify the start of frame. Since an avalanche photo-diode (APD) is used for direct detection of the OOK symbols, the photocurrent signal provided by the APD is plagued by a mixture of thermal and shot noise with signal-dependent power. Our goal is the detection of the UW position in the received stream, along with the estimation of the unknown channel attenuation and noise variances. The aforementioned problem has recently been studied by ignoring any information conveyed by data symbols surrounding the UW. In this work, further investigation is conducted in order to determine the maximum likelihood (ML) solution that, in addition to the UW, exploits all the information-bearing symbols belonging to the observation window. The relevant Cramér-Rao bound (CRB) is also evaluated to establish the ultimate accuracy achievable in the estimation process. Since the true ML estimator leads to a computationally intractable multi-dimensional optimization problem, we develop suitable approximations that enable accurate frame synchronization with affordable complexity. We also present an iterative solution to refine the channel and noise power estimates provided by the UW detection procedure. Numerical simulations demonstrate the superiority of the proposed synchronization and estimation schemes with respect to existing alternatives.

Monte Carlo Simulation of High-Speed MWIR HgCdTe e-APD

High-speed avalanche photodiodes (APDs) have attracted great interest for their potential applications in weak signal detection and free-space communication. In this article, the bandwidth characteristics of mid-wavelength infrared (MWIR) Hg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Te electron-APDs (e-APDs) are investigated by the Monte Carlo method. The simulated gain, excess noise, and carrier velocity agree well with the previously reported experimental data. Moreover, the transport process of photogenerated carriers is described in detail. Meanwhile, the effects of different absorption region thickness as well as the incident wavelengths on the device bandwidth are studied, and the trend of the bandwidth with bias voltage is explained. Finally, a structure with gradient <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${p}$ </tex-math></inline-formula> -region is proposed to further increase the bandwidth.

High-Performance Lateral Avalanche Photodiode Based on Silicon-on-Insulator Structure

In this work, a silicon-on-insulator (SOI)-based lateral avalanche photodiode (APD) is proposed and fabricated. The device features lateral separate-absorption-multiplication (SAM) and electron-only injection. The bandwidth is optimized with the effective blocking of the deep photogenerated carriers by SOI structure. The device stability is also improved by additional shallow P-well region near the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -region which can eliminate the edge breakdown induced by the curvature effect. Simulation results demonstrate that avalanche region (high electric field zone) is confined at the lateral PN <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> junction. Experimental fabrication and characterizations are further realized, and this SOI-based lateral APD device exhibits high responsivity (1.92 A/W at 7.8 V for 300 nm), low dark current (below 5 V), large bandwidth (12.4 GHz at 8.2 V), and low breakdown voltage (~7.8 V). The demonstrated device performance as well as the simple structure and good process compatibility can be attractive in future photo-detecting and advanced sensing applications.

Improvement of parameters of micro-pixel avalanche photodiodes

The paper is concerned with the parameter study of a new generation of micro-pixel avalanche photodiodes (MAPD) with deeply buried pixel structure, also named silicon photomultipliers (SiPM) or multi-pixel photon counter (MPPC). The new MAPD of type MAPD-3NM was manufactured in the frame of collaboration with Zecotek Company. Measurements were carried out and discussed in terms of the important parameters such as the current-voltage and capacitance-voltage characteristic, gain, the temperature coefficient of breakdown voltage, breakdown voltage, and gamma-ray detection performance using an LFS scintillator. The obtained results showed that the newly developed MAPD-3NM photodiode outperformed the previous generation in most parameters and can be successfully applied in space application, medicine, high-energy physics, and security. New proposals are also discussed, for further improvement of the parameters of the MAPD photodiodes that will be produced in the coming years.

Efficient design and implementation of a distributed temperature sensor for field apparatus

The signal acquisition and processing ability of distributed temperature sensor based on Raman scattering (DTS-Raman) directly determines the accuracy, spatial resolution, temperature resolution, and other key indicators of the entire system. Real-time and effective processing is the key to ensuring the practicability of the field system. Owing to the long distance of the DTS system, the energy of the weak Raman scattering is further reduced when it reaches the avalanche photodiode detector because of fiber loss, which results in a decrease in the signal-to-noise ratio (SNR) and an increase in the temperature measurement error. To improve the SNR and ensure the accuracy of the demodulation temperature, the signal acquisition and processing module must be able to perform real-time and fast processing of large amounts of data. The existing processing structure based on the acquisition board requires a special personal computer and host processing software, which limits the application of DTS system. Therefore, a real-time acquisition and processing scheme based on field-programmable gate array is proposed in this paper. A set of cyclic shift register sequence (CSRS) with Ping-Pang functions is designed to improve the storage efficiency. According to the period of the laser source, the accumulated results stored in the CSRS and echo pulse data are accumulated and shifted in real time to realize circular utilization of storage resources. A DTS-Raman system prototype and test platform are built to verify the effects of the proposed scheme. The experimental results show that the scheme can realize a temperature accuracy within in real time and has a high resource utilization efficiency.