We have developed a proprietary Triple Junction laser diode at eye-safe 1550nm based on AlInGaAs/InP material systems for LiDAR and laser range finding applications. Three monolithic laser structures with tunnel junction layers are designed to reduce mechanical stress with superior heat dissipation. It achieves 3x output power and 2x wall plug efficiency of a single junction with low operating voltage and high slope efficiency at 1W/A. A 1550nmTriple Junction laser diode allows a LiDAR or laser rangefinder to achieve the longest detection range compared to a single junction or 905nm laser diode. Here we demonstrate the high reliability of Triple Junction high power laser diodes at 1550nm for adoption in various applications. The life test was performed on Triple Junction samples with 95μm aperture and 2.5mm cavity length in a TO9 package. They were driven at average power of 700mW in pulse width of 100 μsec and 10% duty cycle at 60°C. Such stressed electrical and thermal condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated over 1000 hours of life test on 17 devices. Based on Arrhenius conditions the estimated MTTF (mean time to failure) is 75k hours at 20°C and 17k hours at 50°C operating temperature, which is respectively 9.3x and 2.5x more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C and it shows no sign of COD (catastrophic optical damage). Under a high stress CW operating condition at 5W, Triple Junction laser diodes exhibit thermal rollover but return to normal performance under pulsed operation.
Semiconductor optical amplifier (SOA) has drawn much attention due to its critical need in coherent detection scheme such as FMCW (frequency-modulated continuous-wave) in automotive LiDAR (Light Detection and Ranging). Coherent detection provides more features than ToF (Time of Flight) such as speed and direction for autonomous vehicles. Instead of a bulky and expensive fiber laser, a coherent laser source with high gain SOA can achieve small form factor with Si PIC (Photonic Integrated Circuit). Here we present a proprietary SOA structure based on AlInGaAs material system with multiple quantum wells on InP substrate. The SOAs with curved and tilted straight waveguides were developed and tested. The saturated output power of such SOA at 1550nm and 1310nm can reach higher than 350mW and 450mW with high wallplug efficiency. The small signal gain exceeds 40dB for both 1310nm and 1550nm. The low anti-reflection (AR) coating can achieve 0.01% reflectivity, and the noise figure and near-field mode fields of various SOA configurations are presented and compared. An array of four SOA waveguides at 127m or 500m pitch can deliver total output power over 2 Watts with proper heat sinking. SOA arrays can also be processed as individually addressable with electrical and optical isolations. Such high-performance SOA array offers the design freedom to LiDAR systems with various scanning strategies such that long range detection can be realized. Gain chip, RSOA (Reflective SOA) based on the curved waveguide for external cavity laser configurations is tested and discussed. Self-alignment features can be built onto the SOA chipset to achieve integration of Si PIC for minimal footprint and low-cost mass production.
We present an industry-leading semiconductor optical amplifier (SOA) platform that exhibits top performance at both 1550nm and 1310nm used in FMCW (frequency-modulated continuous-wave) LiDAR (Light Detection and Ranging) for autonomous vehicles. The SOA structure is based on a proprietary AlInGaAs material system with multiple quantum wells on InP substrate. The SOAs with curved and tilted straight waveguides were developed and tested. The saturated output power of such SOA at 1550nm and 1310nm can reach higher than 450mW and 600mW. The small signal gain exceeds 40dB for both 1310nm and 1550nm SOA. An array of four SOA waveguides at 127um or 500um pitch can deliver total output power over 2 Watts. SOA arrays can also be processed as individually addressable with electrical and optical isolations. Such high performance offers the design freedom to LiDAR systems with various scanning strategies such that long range detection can be realized. The low anti-reflection (AR) coating can achieve 0.01% reflectivity, and the noise figure and near-field mode fields of various SOA configurations are presented and compared. Gain chip based on the curved waveguide for various laser configurations is tested and discussed. The SOA chips and arrays can be integrated into a Silicon Photonic Integrated Circuit (Si PIC) to minimize the total footprint of a LiDAR system and overall cost. They include self-alignment features for the ease of integration and high coupling efficiency on Si PIC.
KEYWORDS: Semiconductor lasers, LIDAR, Reliability, Fiber lasers, Industry, Current confinement, High power lasers, Failure analysis, Diodes, Design and modelling
We have developed the world-leading Triple Junction laser diode based on AlInGaAs/InP material systems for LiDAR applications. The monolithic laser structure with tunnel junction layers is designed to reduce the stress and improve the heat dissipation. It has 3x the output power and 2x the wall plug efficiency of a single junction laser due to its low operating voltage and high slope efficiency at 1W/A. A single Triple Junction laser diode at eye-safe 1550nm allows a LiDAR to achieve over 200m detection range in all-weather conditions. It can drastically improve and simplify the LiDAR design compared to other laser choices such as 905nm or fiber lasers. For mass adoption by the automotive industry here we demonstrate the high reliability required for Triple Junction high power laser diodes at 1550nm. The life test was performed on 95um aperture Triple Junction with 2.5mm cavity length in a TO9 package. They were driven at an average power of 700mW with the pulse width of 100 micro-seconds and 10% duty cycle at 90°C. Such stressed electrical and temperature condition is almost 20 times higher than standard operation for automotive LiDAR. We have accumulated for more than 1000 hours of life test on 30 devices. Based on Chi squared distribution analysis and Arrhenius equation the estimated MTTF (mean time to failure) is 248k hours at 20°C and 57k hours at 50°C operating temperature, which is respectively 31x and 7 more than the required 8k hours in automotive applications. We also tested Triple Junction laser diodes up to 100°C without performance degradation and without COD (catastrophic optical damage).
KEYWORDS: Semiconductor lasers, LIDAR, Signal to noise ratio, Receivers, Indium gallium arsenide, Reflectivity, Eye, Avalanche photodetectors, Visibility, Direct detection LIDAR, Time of flight imaging
We benchmark long range ToF LiDAR with laser emitter at 905nm vs. 1550nm. Based on IEC eye safety standards, a high-power laser diode at 1550nm with 100W peak power can deliver 80 times more photon count compared to 905nm out of a LiDAR emitter. Considering detection distance, target reflectivity, and atmospheric media loss, a LiDAR with such power output at 1550nm can outperform 905nm by more than 60 times in SNR and 24 times higher in detection probability at a distance longer than 200m. At longer range of 250m, a single 1550nm emitter can function nicely in both clear sky and low visibility conditions with 20% target reflectivity. To achieve such high performance at 1550nm an innovative multi-junction laser structure has been developed. We present a triple junction high-power laser diode at 1550nm based on AlInGaAs/InP materials. The laser stacks three AlInGaAs lasers epitaxially connected by two tunnel junctions and grown on InP substrate. The monolithic laser structure with tunnel junction layers is designed in a way to reduce the stress and improve the heat dissipation. Each tunnel junctions is formed with an n-type InGaAs layer and a ptype InGaAs layer. The active area of each junction comprises AlInGaAs barrier and quantum well layers. The design leads to three times the output power of a single junction laser and reaches 1W/A slope efficiency. Over 100W peak optical power at 100A with a 350m aperture and 10 nsec pulse width is demonstrated. A low operating voltage is achieved with such triple junction design, thus the wall-plug efficiency is two times better. Given the required detection distance over 200m, a long-range LiDAR with a triple-junction 1550nm laser diode may enable high-speed autonomous vehicles with confidence.
We present a triple junction high power laser diode at 1550nm based on AlInGaAs/InP material system. The device was developed, fabricated, and tested. The laser stacks three AlInGaAs lasers epitaxially connected by two tunnel junctions and grown on InP substrate. The monolithic laser structure with tunnel junction layers is designed in a way to reduce the stress and improve the heat dissipation. Each tunnel junctions is formed with an n-type InGaAs layer and a p-type InGaAs layer. The active area of each junction comprises AlInGaAs barrier and quantum well layers. The design leads to three times the output power of a single junction laser and reaches 1W/A slope efficiency. We demonstrate over 100W peak optical output power at 100A with a 350m aperture and 10 nsec pulse width. A low operating voltage can be achieved with such triple junction design, thus the wall-plug efficiency is two times better. The monolithic triple junction with overall small source size allows efficient optic or fiber coupling, and is an ideal source for applications such as long range LiDAR. Using this new triple junction 1550nm laser diode we benchmark against 905nm in a single-emitter LiDAR for performance comparison. By considering eye safety standards, distance, target reflectivity, and atmospheric loss, the photon budget of 1550nm triple junction can be 80 times more than 905nm. With such advantage, a LiDAR with the new 1550nm triple junction can outperform 905nm by more than 60 times in SNR and more than 24 times in detection probability at a distance longer than 200m.
Ion implantation of semiconductors results in the introduction of vacancies, interstitials, antisites and complexes involving these defects. The donor to gallium vacancy and the free electron to gallium vacancy transitions occurs at 1.4745 and 1.4785 eV respectively in the photoluminescence (PL) spectrum of irradiated n-type gallium arsenide (GaAs) slightly doped with silicon, when the samples temperature is 4K. We have implanted 4 micrometers thick GaAs films grown on bulk GaAs with carbon, oxygen and arsenic ions in order to determine the VGa introduction rate using PL. The particle energy was chosen such that the stopping range covered 2 to 20 micrometers . The production rate is in agreement with Rutherford scattering theory, in which only primary knock out processes are considered when the stopping range is much greater than the epilayer thickness, but less than the theory when the particles are implanted in the epilayer. Since vacancies are created by both primary and secondary ion collisions and removed by recombinations, the data suggests that secondary ion collisions and recombinations are unimportant at high energies when the particles go right through the samples, or that their effects cancel out. At low energies, when implantation occurs, the combined data suggests that vacancies are removed through recombinations at a faster rate than they are produced by secondary ions collisions.
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