Stephen Crouch 19th Coherent Laser Radar Conference
CLRC 2018, June 18 – 21 1
Advantages of 3D Imaging Coherent Lidar for Autonomous
Driving Applications
Stephen Crouch Blackmore Sensors and Analytics, Inc.
136 Enterprise Blvd., Bozeman, MT, 59718
Abstract: Blackmore has developed the first real-time, 3D imaging lidar product based
on frequency modulation and coherent detection for autonomous driving applications.
Units began shipping to automotive customers in late 2017. The technology provides
long range performance (>300m), impressive point throughput (300k to 1.2M points
per second per scanned beam), total interference immunity, and a unique ability to
measure radial velocity on each 3D data point. In addition, continuous wave
transmission is an ideal fit for integrated photonics and solid-state scanning solutions
such as optical phased arrays. These advantages highlight an incredible market
opportunity for coherent lidar systems in automotive and other consumer applications
where direct detection lidar fails to meet system requirements. Technology building
blocks in high-throughput processing, integrated photonics and optical phased array
technology, all under development at Blackmore, will be presented in addition to
exciting mobile, geo-registered 3D point cloud data results.
Keywords: Coherent Laser Radar, 3D Imaging, Autonomous Driving, Range-Doppler Imaging
1. Introduction
Autonomous transportation systems have seen a spike in interest in recent years. Successful research
and pilot programs by industry leaders such as Waymo have demonstrated the possibility of autonomous
systems to make transportation safer, more efficient, and easier to access [1]. A variety of sensors
including cameras, radars, ultra-sonics, and lidar work together through complicated artificial
intelligence (AI) stacks to complete the necessary navigation and avoidance tasks. Of these sensors,
lidar is the most nascent and highest cost. Yet experts agree that lidar technology is critical to the success
of the “self-driving” revolution.
Automotive lidar market leader Velodyne distributes a lidar sensor based on pulsed, time-of-flight
ranging operated at 905nm wavelength. While this sensor has proven to be indispensable for this task,
the limited range performance (<100m typical), high cost, and issues with sunlight interference have
triggered a market for better lidar technology. According to released specifications, the pulse energy
per measurement of a Velodyne system is approximately 300nJ [2].
The most capable automotive lidar systems to-date have transitioned to 1550nm wavelength sources. At
this wavelength, the systems can emit significantly higher optical power [3]. This allows manufacturers
to make more measurements at longer ranges (~200m). While systems such as Luminar have succeeded
in hitting most automotive OEM specifications, the inefficient use of optical power via fiber laser
amplifiers underlines a questionable pathway to scalability. In some cases, manufacturers have claimed
to use in excess of 10uJ per pulse leading to time averaged optical powers of >10 watts per system [4].
In the search for optimal lidar solutions, many have dismissed coherent detection as “impossible" from
both technical and cost perspectives. However, Blackmore's products prove that coherent systems have
an important role in autonomous vehicle sensor suites. The presented technology represents a step for
coherent laser radar (lidar) into mass market applications.
2. Coherent Lidar Operational Advantages
Coherent lidar has several operational advantages that have been demonstrated in over 18 months of on-
vehicle, mobile lidar operation. These advantages include range performance, interference rejection, and
Mo9
Stephen Crouch 19th Coherent Laser Radar Conference
CLRC 2018, June 18 – 21 2
direct velocity measurement. The long-range performance of Blackmore’s lidar system is shown in
Figure 1 where the data was collected with a real-time processing and geo-registration.
Figure 1. A few seconds of lidar data is accumulated to demonstrate the fill factor and range of a
coherent lidar imaging system.
The range demonstrated in Figure 1corresponds to a system operating with a 100mW continuous wave
output power and 305kHz repetition frequency. The observable range extends beyond 450m for brighter
diffuse targets. System parameters are included in a proprietary link budget model for a 10% diffuse
reflector which shows good agreement with traditional models and supports good SNR at a 200m range
[5-7].
Figure 2. Blackmore’s link budget model is compared to classic coherent detection papers and shows
good agreement.
Coherent systems are very sensitive to the doppler effect. While operating with this effect can be
technically challenging, signal processing solutions enable excellent velocity precision (<0.25 m/s) over
very short measurement time intervals (3.3 us). The rapid measurement of range and velocity sets this
approach apart from automotive radar systems that need to operate on timescales of tens of millisecond
to effectively resolve similar Doppler frequencies. Example Doppler imagery is shown in Figure 3.
Vehicle Location
In-N-Out Burger Sign
Stephen Crouch 19th Coherent Laser Radar Conference
CLRC 2018, June 18 – 21 3
Figure 3. (TOP) A series of frames is from Blackmore’s automotive lidar system is shown. Points are
colored by velocity showing clear resolution of motion components on the moving target. (BOTTOM)
Mobile lidar data showing pedestrian tracks when colored by the Doppler data field.
The Doppler field allows more reliable measurement of scene activity with lower latency. This
translates into more efficient artificial intelligence for vehicle navigation by using velocity-based scene
segmentation, tracking, and object identification. Ultimately this increases the measurement certainty
and overall “value” of each 3D data point.
3. The Pathway to Scalability
The discussion in sections 1 and 2 highlights a stark contrast between the optical power requirements
for pulsed/direct-detect and CW/coherent scanned lidar approached. The >10x difference in optical
power efficiency of coherent detection on a per measurement basis is an important consideration in
discussing the scalability of lidar designs. High optical powers will not translate to small, mass
manufacturable chip designs.
Optical fiber communications points to a solution. This space has long targeted coherent detection as
the preferred implementation for high bandwidth, long-haul, power efficient systems [8]. Many of the
same technology building blocks such as narrow linewidth lasers and balanced receivers, along with
broader supply chain capacity, can be leveraged in the construction of scalable coherent lidar systems.
An example of InP chips from on of Blackmore’s recent wafer runs is shown in Figure 4. These chips
represent a major subsystem for future automotive lidar design at Blackmore and a step towards “lidar
on a chip”.
Non-mechanical beamsteering is often cited as a long-term requirement for automotive lidar. The low
optical power requirements offer a match with integrated photonics for non-mechanical beamsteering
where high peak powers are not acceptable. Blackmore is working with Sandia National Labs to develop
silicon photonics based non-mechanical beamsteering devices for use in future systems. While these
systems are indeed challenging to realize and require special attention to insertion loss mechanisms, the
opportunity to realize complete “lidar chipsets” is clear. Ultimately, lidar sensors need to be chip-scale
to ever realize the low cost and volume potential of the automotive market.
Stationary Receding
+3.5m/s -3.5m/s
Illumination Direction
Velocity = Doppler
Stephen Crouch 19th Coherent Laser Radar Conference
CLRC 2018, June 18 – 21 4
Figure 4. A set of InP chips with several lidar subsystem building blocks is shown in testing. The
chips were developed in conjunction with Fraunhofer HHI and JePPIX.
As a final technical point, the author notes that coherent detection has significantly less susceptibility to
interference from sunlight or other lidar system due to spatial, spectral, temporal, and other filter options
that make interference an impossibility. As automotive lidar scales to the broader market, this advantage
will prove to be invaluable as interference rejection in coherent lidar is inherent and does not require
expensive optical bandpass filters which may degrade across temperature and field of view. In a safety
critical application, performance must be guaranteed across the broadest possible operational set. This
includes immunity to interference.
4. Conclusions
The requirements for automotive lidar are challenging for any optical technology to address. However,
coherent detection offers a unique set of capability and scalability advantages that will support
significant future investment as other technologies fail. The low optical power requirements relative to
pulsed, direct-detect systems will be the major differentiator as the automotive industry pivots to
coherent lidar. Through prototype systems and technology investments, Blackmore has demonstrated a
roadmap for driving coherent laser radar towards mainstream applications.
5. References
[1] T. Higgins and C. Dawson, “Waymo Orders Up to 20,000 Jaguar SUVs for Driverless Fleet,” Wall Street
Journal, 27-Mar-2018.
[2] Velodyne. “HDL-64E, Resource Manual, Laser Safety Parameters,” November 7, 2007.
[3] “Encyclopedia of Laser Physics and Technology - eye-safe lasers, retina, corneal injuries, erbium, thulium.”
[Online]. Available: https://www.rp-photonics.com/eye_safe_lasers.html.
[4] Jeff Hecht. “Under the Hood of Luminar's Long-Reach Lidar.” IEEE Spectrum. July 5, 2017.
[5] R. G. Frehlich and M. J. Kavaya, “Coherent laser radar performance for general atmospheric refractive
turbulence,” Appl. Opt., AO, vol. 30, no. 36, pp. 5325–5352, Dec. 1991.
[6] C. M. Sonnenschein and F. A. Horrigan, “Signal-to-Noise Relationships for Coaxial Systems that Heterodyne
Backscatter from the Atmosphere,” Appl. Opt., AO, vol. 10, no. 7, pp. 1600–1604, Jul. 1971.
[7] J. Y. Wang, “Detection efficiency of coherent optical radar,” Appl. Opt., AO, vol. 23, no. 19, pp. 3421–3427,
Oct. 1984.
[8] F. Corporation, “Finisar Introduces Industry’s Smallest Coherent Optical Assembly for High-Density Line
Card and Transceiver Designs at OFC 2018,” 13-Mar-2018. [Online]. Available: http://globenewswire.com/news-release/2018/03/13/1421255/0/en/Finisar-Introduces-Industry-s-Smallest-Coherent-Optical-Assembly-for-High-
Density-Line-Card-and-Transceiver-Designs-at-OFC-2018.html.