FMCW LiDAR – The hottest topic in the current photonics industry

While the challenges to fully developing FMCW (frequency modulated continuous wave) LiDAR technology appear steep, the commercial value of integrating the device on a single chip holds the promise of such significant cost reduction and technical advantage, that, on the one part, it is seen as absolutely essential for the implementation of advanced autonomous drive, and on the other, as opening the flood gates to device ubiquity as a key enabling technology across a vast range of new applications.

FMCW Lidar

In this blog, the most recent developments in FMCW LIDAR will be reviewed, together with wider ecosystem dynamics, especially packaging challenges, as they point to future roadmap development.

Our pursuit in this respect requires that we first grasp the difference between FMCW LiDAR, and the incumbent, favored, and it must be said, extremely successful technology known as ToF LiDAR (time of flight). The latter has its origins in research carried out over the past 20 years, but only comparatively recently has it really come into its own. Indeed, it is said to have caused a photonics revolution. At one end of the spectrum it has reduced the cost of high-end devices from tens of thousands of dollars to hundreds and even less, but perhaps even more importantly, allowed for the lighter, smaller devices now present in a growing number of consumer products, including high-end smart phones. Technically speaking, what has marked a break-through advantage over earlier devices is its mechanical simplicity. Unlike previous scanning systems, ToF requires no moving parts. A simplified technical overview is presented in the diagram below.

Figure 1. Time of flight LiDAR 3D: Range, Azimuth, Elevation

FMCW Lidar2Near infrared light pulses (905nm) hit an object before bouncing back to a sensor. Return time is measured, allowing distance to be calculated. Over the course of a large number of such pulses the result is a three-dimensional depth map. This entire process is extremely quick: a maximum range of 200m takes less than 1.5ns.

In terms of manufacturing advantage, the critical difference with earlier LiDAR generations is that it allows for the production of solid-state devices, which, absent of moving parts, tends towards comparative ease of packaging, improved cost effectiveness, higher reliability and integration at very small scales; small enough to fit into many wearable or portable IoT devices. Another advantage is that ToF requires considerably less computer processing power since the necessary algorithms are much more straightforward. Thirdly, there is the comprehensive nature of what is captured with a single shot, and, by exceeding 150 frames per second, easily enables the real-time imaging necessary for high levels of safety. Finally, whatever the limits of the technology for automotive use, overall ToF has and remains significant in facilitating still higher levels of industrial and commercial uptake over the short and medium-term.

Reviewing the disadvantages of ToF devices, our consideration should be understood as providing a focus of exactly what kind of technical challenges FMCW LiDAR seeks to resolve, as equally, explaining why ToF LiDAR faces a potentially up-hill struggle in serving the automotive market over the longer-term. Other than on-going (and significant) challenges in the cost of volume manufacture, technical issues include a higher rate of IR decay, sensitivity to interference from sunlight and other ToF LiDAR devices, and utilizing a spectrum potentially unsafe to the human eye.

Figure 2 presents a simplified schematic outlining the principles behind a FMCW LiDAR device, together with a list of potential functioning advantages.

Figure 2.  Frequency Modulated Continuous Wave LiDAR 4D, Plus Doppler

FMCW Lidar3

  • Immunity to sunlight and other device interference through coherent detection.
  • Operating in the 1550nm spectrum, eye safety is far less an issue.
  • Ranges up to 300m at high resolution.
  • Twenty times greater sensitivity to object velocity.
  • 1000 times lower power consumption.
  • Extremely rapid target discrimination.
  • Data enables behavior prediction.

In terms of how FMCW LiDAR basically works, modulated light is split into two; one portion is transmitted to the target area (Tx) while the second is kept local (LO) to the device. The laser light that hits various objects is bounced back (Rx), subsequently detected and interferometrically recombined with the LO. Frequency differences (the heterodyne beat) instantaneously creating a 4D map.

Looking to demands on packaging technology needed for large scale commercialization, seven clear challenges stand out.

  1. Identifying the best light source, both laser type and materials used. Considerations here must include optical coherence. While optical transceivers operate at distances no more than 1cm, these devices must utilize laser technologies that can work at distances of at least 300m and beyond.
  2. Photonic chip integration. High levels of, and degrees in hybrid component integration, especially the light source and detector, coupling efficiencies, yet all the while enabling ultra-low-loss and scalability. The is perhaps the most critical issues as it requires combining two state-of-the-art techniques, a sophisticated FMCW ranging and a solid-state beam steering mechanism, into one simple integrated solution.
  3. Device construction and dependability. Unlike data center transceivers, these devices must withstand constant and occasionally severe vibration and operate at temperatures that range from -44°C to 85°
  4. Heat management. Developing detectors that do not require external cooling and signal amplifiers that do not get too hot.
  5. Device/power optimization in respect to photon range and photons detected.
  6. A manufacturing assembly process that meets stringent automotive standards, yet takes advantage of breakthroughs such as non-hermetic sealing.
  7. Vastly lowered packaging costs. At the moment the latter make FMCW automotive technology prohibitively expensive, accounting as they do, for over 80 per cent of device price.

While daunting, these challenges are far from insurmountable. On the one hand there is the confidence that comes from the industry’s collective ability to build on the principles of coherent transceiver technology—including current developments in co-packaged optics—and, on the other, complementary efforts among automotive manufacturers to set out a rolling target of desired and identified development parameters. That as many as two dozen different kinds of device are currently being validated globally, is indicative of the diversity—and energies—currently being devoted to FMCW LiDAR development.

With decades of experience in developing sequential generations of LiDAR, from bread-box size to smart phone size, Palomar’s global Innovation Centers have a wide repertoire supporting SMEs in both ToF and FMCW prototyping and packaging, as well as serving large multinationals who chose to outsource aspects of their research and development.

For more information on Palomar’s experience with LiDAR packaging, visit: https://www.palomartechnologies.com/applications/automotive#automotive

Download our Innovation Center brochure: https://www.palomartechnologies.com/advancing-lidar-packaging-assembly

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Dr. Anthony O'Sullivan
Strategic Market Research Specialist
Palomar Technologies