Over the last several years, there's been a veritable revolution in LiDAR. In large part, this has been spurred by the ever-looming boom of autonomous vehicles, where LiDAR is increasingly used as a method of sensing obstacles. There's also been a resultant increase in affordable LiDAR, making it more accessible to a broad range of designers.
The next step in LiDAR evolution is, according to some, the utilization of solid-state LiDAR.
In this article, I'll introduce the basic concepts behind typical LiDAR, go over how solid-state LiDAR differs, and then take a look at who's working on developing solid-state LiDAR options.
The Problem with Rotating LiDAR Sensors
Most current-generation LiDAR technology bounces a pulsed laser off of a rotating mirror to distant targets and then records the time for the reflected pulse to return. This technique provides a full 360°-coverage of an area. Depending on the optics and resolution of the receiver, it can provide a scan sector beam width that varies from a one-channel, one-pixel high 0° field of view, to a multi-channel, 32-pixel, 45° field of view.
Of course, as we'll see in this article, a 45° field of view may be typical (for now) but it's certainly not the limit.
Image of a rotating LiDAR unit. Image courtesy of Renishaw.
With many high-precision moving parts, these mechanical LiDARs are expensive, sensitive to vibration, and difficult to miniaturize. Additionally, if mounted inconspicuously at the front of a car (rather than at the top, as Waymo originally showcased), the body of the car would eliminate as much as 50% of the LiDAR's field of view.
To fully incorporate a unit into a car, automakers need a cheaper, more robust option.
One way of dealing with this issue is to incorporate multiple less expensive sensors. Multiple companies are now researching and developing solid-state LiDARs that are robust and inexpensive. While they have a limited field of view, their low price points allow vehicle makers to integrate several units into a car for a fraction of the cost of a single current-gen solid-state LiDAR.
Methods of Implementing Solid-State LiDAR
Solid-state LiDARs use a system, detector, and sometimes a MEMS mounted in a non-rotating housing to bathe a scene in pulsed-laser light and record the reflected pulses. There are several ways to accomplish this task:
Crossed Array Scanning
With this method, laser light is pulsed sequentially from a vertical array, while sequentially being detected by a horizontal array. This crossed configuration produces a resolution that is the product of the number of laser emitters and the number of photodiode detectors. The hardware keeps track of the laser position, the detector position, and the time for the light to return to generate a three-dimensional point cloud of the environment.
Image courtesy of LeddarTech
MEMS-Based Solid-State LiDAR
With a MEMS-based solution, a single powerful laser pulse is used along with a mirror to create the same effect as the laser array shown above. As the mirror is manipulated to create a scanning laser pulse, a sensor array detects the reflected light and generates the three-dimensional point cloud of the environment.
Image courtesy of LeddarTech
The Israeli company Innoviz has a solid-state LiDAR called the InnovizPro that you can purchase and immediately place on your car. It is based on the MEMS technology and has an expected price of a few thousand dollars.
Their upcoming InnovizOne, an automotive-grade LiDAR, is expected to be available in 2019 for just a few hundred dollars. An Innoviz press release first publicized at CES in January stated that high-volume customers could see prices as low as $100 per unit.
Image courtesy of Innoviz.tech
When interviewed via email, Innoviz CEO and Co-Founder, Omer Keilaf, stated that their LiDAR "is designed to deliver extremely rich, high-density output in the form of a high-resolution point cloud, enabling [them] to extrapolate advanced object detection capabilities. With extremely high data intensity, Innoviz's LiDAR is able to build additional layers of information and thereby offer superior levels of object detection, classification and tracking."
Innoviz provides a full software stack solution that includes object detection, classification, and tracking. The object classification and tracking are especially important for automotive applications where a changing environment poses serious threats to pedestrian and driver safety.
See the Innoviz LiDAR in action performing SLAM (Simultaneous Localization and Mapping) in the video below.
LeddarTech's LeddarVu, etc.
LeddarTech also has solid-state LiDAR solutions that are designed to be placed at multiple locations on an automobile to provide complete coverage. LeddarTech has multiple units available already for under $1000.
The LeddarVu platform utilizes "patented signal processing and algorithms" to create solid-state LiDAR sensors with versatility.
The Vu8, a solid-state LiDAR module developed on the LeddarVu platform. Image courtesy of LeddarTech
LeddarTech's software implementation also allows for object detection and classification.
Additionally, their website offers a significant number of resources to help users to better understand the technology. For example, LeddarTech's whitepaper on their optical time-of-flight sensing tech (PDF) explains their use of software-implemented algorithms in processing sensor data. This educational approach can help engineers better understand the technology in the LeddarTech LiDAR units.
Quanergy claims to have "the world's first affordable solid-state LiDAR sensor" in their S3 model, which was unveiled way back in January of 2016. While the original LiDAR modules from half a decade ago would typically cost tens of thousands of dollars, the S3's price point was initially announced to be $250.
The S3 LiDAR sensor. Image courtesy of Quanergy.
The S3 can fit in the palm of one hand and its lasers have a 120 ° arc. Quanergy touts the fact that the S3 has no moving parts which they assert will improve reliability. This is just one of many ways companies like Quanergy are hoping to ease friction between LiDAR design and implementation in the automotive industry, which requires high levels of reliability for the sake of safety.
Inexpensive, solid-state LiDAR units are on the market now from multiple manufacturers. As time progresses, their cost will continue to drop and their capabilities will continue to improve.
How long will it be before this technology is modified for home use? From electric wheelchairs and drones to motorcycles and other mobile platforms, there are plenty of applications—aside from autonomous cars— that could benefit from environmental awareness and mapping.
Have you worked with LiDAR before? Would you use solid-state LiDAR in a project if you could? Let us know in the comments below.