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Industry Pushes New Technologies, Applications for Lidar

EuroPhotonics
Dec 2017
ANA GONZALEZ AND JOSE POZO, EUROPEAN PHOTONICS INDUSTRY CONSORTIUM

Digitalization of the world requires detection tools able to recognize objects and precisely measure distances quickly. Lidar-based monitoring systems are a key part of this current technological revolution because their high accuracy and speed can be used to make digital 3D representations of the target. In the media, most lidar applications discussed are related to autonomous driving, but lidar also currently finds application in robotics and industrial markets, construction (geographical survey) and the military (payload). However, the technology today is too bulky and its current pricing too high for it to massively enter the markets.

Ultracompact pulsed fiber laser for lidar applications.
Ultracompact pulsed fiber laser for lidar applications. Courtesy of MWTechnologies.

Currently, automotive lidar is used exclusively in autonomous vehicle research. Lidar and radar technologies are similar, but radar uses an antenna to emit radio signals while a lidar device has specialized optics and lasers for receiving and transmission. While radar is more convenient when the detection distance is more important than the actual 3D image of the target, lidar devices allow a quality that’s superior to radar images because of the laser’s shorter wavelength. However, lidar systems are sensitive to inclement weather.

Working principles

Lidar uses a light pulse — from 10 µm to the UV — to illuminate the surface and target, and measures the time it takes to return to its source. This amount of time is used to measure the distance to the target. The laser beam is then moved across a certain angular range, generating a detailed image. As the laser moves along, it must continuously change its wavelength, enabling the processing circuit to differentiate between the reflected and outgoing light. This requires a precise movement of mirrors within the laser cavity. The mechanism controlling this movement is one of the reasons why today’s lidar systems are so bulky and expensive.

Classification of lidar systems

For lidar systems, a frequency stable transmitter (~1 ms−1) is usually required. And a Doppler receiver is most often employed to measure the frequency shift of the backscattered radiation. These Doppler receivers can operate in heterodyne or direct detection.

Coherent systems generally use optical heterodyne detection, which is more sensitive than direct detection. This allows such systems to operate at a much lower power and are classed “eye-safe.” This makes them usable with little safety precautions, although at the expense of more complex transceiver requirements.

In both types of lidar detection (direct and heterodyne), there are two main pulse models — micropulse and high-energy systems. Micropulse systems require a high-capability computer for processing data. High-energy systems are used to measure a variety of atmospheric parameters such as the density, temperature, wind and humidity.

A 308-nm LEAP excimer laser for high-power lidar for ozone and water.

A 308-nm LEAP excimer laser for high-power lidar for ozone and water. Courtesy of Coherent.

Original lidar sensors consisted of a single photodiode, but currently they can scan in all directions to achieve an accuracy of ±3 cm and a range of 100 m. They can consist of a line of photodiodes in which multiple laser emission channels would be employed (for an automotive approach to PIN or APD), or an array of photodiodes used in the flash lidar. Light sources — typically diodes, but recently fiber lasers have been incorporated — operate in pulsed mode with a measurement distance accuracy of 10 cm.

Spinning lidar can be achieved by rotating the entire system or by using a MEMS micromirror. Rotating the lidar system is the most common solution today, as it provides a 360-degree view; however, this also leads to bulky systems. Using micro-mirrors, the size and price of the lidar system can be reduced, but the field is also significantly reduced (<180 degrees).

Recent technologies for these systems involve solid-state lidar by self-sweeping lasers, in which the semiconductor laser has been integrated with a grating mirror that considerably reduces the power consumption, weight, size and cost.

NIR light sources from 905 to 1550 nm are usually employed for lidar applications because less light is absorbed into the atmosphere, and because it works below the maximum permissible exposure to the eyes. However, lidar can be used for more applications by varying the wavelength of the light source to fit the target. It can use ultraviolet, visible or NIR light to image objects, and can focus on a wide range of materials, including nonmetallic objects, rocks, rain, chemical compounds, aerosols, clouds and even single molecules. Suitable combinations of wavelengths can allow for remote mapping of atmospheric contents by identifying wavelength-dependent changes in the intensity of the returned signal.

Lidar technology in use

Lidar is a high-end technology that currently touts the highest performance of 3D information gathering. Existing markets for lidar include the military and professional sectors, either for geographical surveys or in the construction world. However, the scope of sectors in which lidar finds application is very broad. Because of its high technical performance, lidar is rapidly becoming a key device for autonomous vehicles and robotics. Market volumes are very low, but average selling price can exceed $100,000.

Non-European companies such as Continental, Quanergy and Velodyne are leading the lidar systems market. However, there are numerous others around the world that are also now employing these systems. Among them are photonics developer and manufacturer Coherent Inc., which, among other components and systems, makes IR laser diodes and excimer laser systems that can be used for climate-relevant observation.

Finisar Corp.’s vertical-cavity surface-emitting laser (VCSEL) technology brings together the advantages of laser light with surface-normal emission, versus edge emission from other laser sources. This enables true wafer-scale manufacturing, test and packaging of efficient, high-power lasers. It leverages and builds upon the manufacturing and supply chain efficiencies of similar semiconductor processes and products (e.g., compound semiconductor RF amplifiers and LEDs). VCSELs have the advantage of wavelength stability over temperature, scalable output power, and high reliability under high optical powers, all in a small, easy-to-package dye. Such lasers are also directionally focused with a high-quality circular beam profile that makes them 10 times more efficient than an LED in similar packaging.

“VCSEL technology has quickly moved from relatively obscure data communications applications to very visible, mainstream consumer mobile and automotive applications in the span of just a few years. But this wouldn’t have happened without the deep investment in the technology that we and a select few others have committed over the past 10 to 15 years,” said Craig Thompson, Finisar’s vice president of New Markets. “There are very compelling applications of 3D camera and sensor technology enabled by high-quality, high-power VCSELs that will bring the technology into mainstream everyday use very soon.”

Other companies in the lidar systems market: MWTechnologies develops ultracompact pulsed fiber lasers for lidar applications; Keopsys is focused on the development of high-performance fiber lasers and amplifiers (the company has developed a pulsed fiber laser for lidar applications that covers the complete range of eye-safe wavelengths); and Fastree3D produces flash lidar camera modules that enable vehicles and machines to recognize and locate fast-moving objects in real time.

A Fastree3D 3DK hardware development kit.

A Fastree3D 3DK hardware development kit. This technology includes an array of 60×1 pixels, four illumination sources, on-chip preprocessing to provide real time per-pixel reliability, and choice between different data types (distance, speed, motion). Courtesy of Fastree3D.

The lidar market is expanding and emerging, as evidenced by the huge interest in new developments for key components and current system improvements. Market value is expected to reach $2.3B by 2022, and $7B by 2030, mainly for autonomous driving applications1. Innovative technologies that improve solid-state lidar are emerging, as well, and European companies are projected to take a leading role in the initial introduction of this technology into the market.

Meet the authors Ana González is the project leader at the European Photonics Industry Consortium (EPIC). Her expertise lies in the development of systems based on integrated photonic circuits, packaging and assembly, and the investigation of applications such as chemical/biological sensing and Datacom. In addition, she has been involved in technology transfer and business development processes. She received a bachelor’s degree in chemistry from the University Autonomous of Barcelona and a Ph.D. from the Catalan Institute of Nanoscience and Nanotechnology. Jose Pozo is the director of technology and innovation at EPIC. He has 15 years’ background in photonics technology and market knowledge, and a large network within the industrial and academic photonics landscape. He is a member of the board of the IEEE Photonics Society Benelux. He holds a Ph.D. in electrical engineering from the University of Bristol in England and an M.Sc. and B.Eng. in telecom engineering.

Reference

1. P. Cambou et al. Market and technology briefing: Lidar technology and applications, Yole Développement.

GLOSSARY
lidar
An acronym of light detection and ranging, describing systems that use a light beam in place of conventional microwave beams for atmospheric monitoring, tracking and detection functions. Ladar, an acronym of laser detection and ranging, uses laser light for detection of speed, altitude, direction and range; it is often called laser radar.
heterodyne
The interaction between two oscillations of unlike frequencies that forms other oscillations, specifically those with a frequency equal to the frequency difference of the former oscillations.
lidar3Dindustrialroboticsmilitary & defenseautonomousradarUVdetectorsphotodiodesheterodyneMicroPulseMEMSContinentalQuanergyVelodyneFinisar Corp.VCSELMWTECHNOLOGIESKeopsysEuropeAmericasAna GonzálezEPICJose PozoEPICinsights

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