Compact enough to be integrated into the cabin of a car – such as within the windshield – Velodyne’s Velarray H800 is the first lidar system that integrates two illumination modules for both short- and long-range measurements in the same unit.
Launched in 2020, the H800 combines velodyne’s micro-lidar array (MLA) with a VCSEL-based near illumination module to cover distances from 10 centimetres to 200 metres – all within a device measuring just 180 x 55 x 90mm and marketed at $500. This achievement demands cutting edge innovation and clever integration, which Yole Group experts explore in their latest report.
Therefore, this article is based on the latest LiDAR analysis proposed by Yole SystemPlus, part of Yole Group: Velodyne Short and Long Range Lidar with VCSEL and EEL. The report, provides physical analysis and cost estimations for the MLA and near-illumination modules, and details the following components: EELs, photodiodes, MEMS beamsplitter, lens, GaN driver IC, PCB and ceramic substrate, and assembly of the MLA module.
Long range detection with the micro lidar array
The measurement of obstacles at long range, up to 200m, is enabled by Velodyne’s MLA engine. The MLA measures just 14.1mm x 8.9mm x 2.05mm and contains eight edge emitting lasers (EELs), eight photodiodes and optical elements that are all assembled on the same substrate.
The EPC2715, a gallium nitride (GaN) lidar driver, generates the pulse of current for two EELs that transfer the electricity into light pulses. The power GaN transistors and the monolithic gate drivers are integrated onto the same die, which negates the need for an additional electrical component to control two lasers. This technology is specific to EPC, which designs the GaN die that is manufactured by Episil Technologies Inc.
The GaN transistor is also beneficial as it allows the generation of ultra short pulses, which is highly necessary because of the minimal space between the GaN lidar driver and other optical components – and much more difficult to achieve using silicon.
The light pulse generated by the lasers is then sent through a MEMS based beam splitter that allows the light to pass. The beamsplitter is an innovative Velodyne-specific component based on MEMS technology that enables integration at a very close distance to the lasers, lens and photodiodes.
A dual axis oscillating mirror integrated outside of the illumination module deﬂects the laser beam through an emitting lens, and receives the returned echoes through a condenser lens. The dual-axis mirror is the first such mirror to be used in an automotive lidar system and is smaller than the more commonly seen rotating mirrors. The returned light is then sent towards the mirror side of the beam splitter, which directs the light toward the silicon avalanche photodiode (APD) where the light is converted to electrical current. The duration between the pulse transmission and the detection gives the distance between the lidar and the obstacle.
VCSEL-based near illumination module
While Velodyne’s integration within the long-range illumination module is highly innovative, the true cutting-edge element exists within the near-field illumination module. The system employs similar technology as seen in Apple’s facial recognition software, but at much higher powers, and is the first VCSEL-based system to exist in an automotive setting.
The VCSEL-based module sits on a PCB above the long-range illumination module. It overcomes the difficulties in detecting obstacles at short range with traditional EEL-based systems and allows measurements from 10cm to 20m.
The VCSEL pulses are generated by four VCSEL dies assembled in parallel on a PCB. A diffractive optical element (DOE), the similar component used in Apple’s iPhone lidar, creates a structured light dot pattern. The returned echo pulses received by the dual axis oscillating mirror are then sent towards the photodiodes in the MLA. The same eight photodiodes are used to detect the echo from the EELs and the VCSELs, requiring extremely precise alignment of the optical elements.
To generate the high-power light needed to emit light further than VCSELs used in smartphones, the VCSEL dies use a five-junction emission structure – the first company to adopt this design. In general, VCSELs generate light from a single layer, but stacking multiple junctions allows VCSELs to better amplify optical power, increasing gain. This is because fewer distributed Bragg reflector layers need to be deposited on the VCSEL to trap light and enable laser gain. Fewer layers lower the internal resistance, and subsequently boosts efficiency. This, in turn, reduces the electrical power needed to attain a particular optical power.
Velodyne uses the OSRAM 5J multijunction VCSEL 905nm, which uses dies from US-headquartered Vixar, the first company to commercialise multi-junction VCSEL technology and a subsidiary of OSRAM. The dies measure 0.78mm x 0.78mm x 0.11mm.
Multi-junction VCSEL technology has only recently become available because it requires epitaxially fabricating low resistance, low optical loss tunnel junctions that connect each junction. But as demand for higher power, more efficient VCSELs increased, Ams Osram built this capacity.
This innovative technology opens the doors for creating much more powerful illumination profiles at a reduced size, which could have implications for other applications. Will we see this technology within smartphones in the future?
As vehicle manufacturers demand smaller, aesthetic systems that match the sleek look of their cars, lidar manufacturers are demanding innovative components while finding new ways to integrate them. A more efficient dual-axis oscillating mirror, a MEMs-based beam splitter, multijunction VCSEL dies, and the same photodiode detection of light from both illumination systems are just a few of the innovations that have enabled Velodyne to take a massive step in this direction. In the near future, we could see Velodyne branch out into other applications where size and aesthetic are important, such as robotics.
Download Yole SystemPlus’s report to determine the structure and manufacturing processes of these components through a more detailed physical analysis, including teardown, cross-sectional analysis, circuit delayering, and scanning electron microscopy.
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About the authors
Sylvain Hallereau is Principal Technology & Cost Analyst at Yole SystemPlus, part of Yole Group (Yole).
Working in close collaboration with the laboratory teams, Sylvain produces reverse engineering & costing reports while also contributing to custom projects, especially focused on solid-state lighting components, sensors, biotechnology devices, and ICs. Together, they define the objectives of the analysis and the most relevant methodology to gain a detailed understanding of the structure of the device. Sylvain then analyzes the results to describe the technology choices made by the leading semiconductor companies and the related process flows and also calculates the cost structure.
In parallel, based on his significant technical and industrial knowledge, Sylvain supports the development of the semiconductor device activities and the related team at Yole SystemPlus. He also contributes to the strategies of this department.
Sylvain daily runs a strategic watch within the semiconductor community. Through his investigations, his aim is to identify innovative components and new manufacturing processes. In this way, Sylvain supports Yole SystemPlus with the setting up of new methodologies for analysis and the updating of advanced simulation tools, especially those developed internally by Yole SystemPlus’s experts.
Sylvain regularly contributes to numerous media articles, using his technology and industry expertise to analyze and comment on the latest innovations. He holds a master’s degree in Microelectronics from the University of Nantes (France).
Pierrick Boulay is a Senior Technology & Market Analyst in the Photonics and Sensing Division at Yole Intelligence, part of Yole Group. He works in the fields of Solid-State Lighting and Lighting Systems, carrying out technical, economic, and marketing analyses. In addition, he leads the automotive activities within the company.
Pierrick has authored several reports and custom analyses on topics such as automotive lighting, LiDAR, sensing for ADAS vehicles, and VCSELs. Prior to Yole, Pierrick has worked in several companies where he developed his knowledge of lighting and automotive. In the past, he has primarily worked in R&D departments on LED lighting applications.
Pierrick holds a Master of Science in Electronics at ESEO (Angers, France).