We have previously written about many of the technical aspects of laser diode design, such as cooling systems, electrical power sources, and diode structure. It is critical to remember that automotive lidar systems operate principally outdoors, meaning an important consideration is the surrounding environment. For automotive lidar, there are four main factors to consider when selecting and designing the laser diode that lies at the heart of the lidar system.
Laser Eye Safety: A lidar system must be safe for use in the presence of pedestrians, animals, and other drivers. Lidar systems typically use short pulses (1-20ns) of infrared light which is invisible to the human eye. Since you cannot see the infrared light, there is no blink reflex and light that passes through the aqueous area gets focused by the lens onto the retina. This can cause damage by burning the retina. Methods to address eye safety include using longer wavelengths (>1400nm) that are absorbed more by the aqueous area behind the cornea and cannot transmit to the retina. Hence, more, eye-safe energy can be used at the longer SWIR wavelengths (1400-3000nm) than at the shorter NIR wavelengths (850nm to 1400nm) which are not absorbed. Lidar systems using NIR wavelengths can be optimized to keep exposed energy levels within the eye-safe limit by using shorter pulses and lower brightness. Learn more about eye-safety requirements and technology in this white paper.
Ambient Light: Lidar operates by projecting and receiving a beam of light, and that means ambient light of the same wavelength creates a background signal that reduces signal-to-noise. Solar emission is broadband, but after passing through the atmosphere, it varies with wavelength. There are dips in the solar energy at 905nm and 1500nm and the solar spectrum is 10x quieter at 1500nm than 905nm. One way to maximize the signal-to-noise ratio is to operate at one of the wavelengths that matches the notches in the solar energy spectrum.
Ambient Temperature: Lidar systems are used in a range of environments with different temperatures. Changes in temperature impact the efficiency of diodes and shift the wavelength of a laser. Temperature control is critical to maintain performance. Lasertel lasers diode can be customized with integrated thermal management solutions to control the temperature of the diode. Lasertel offers both VCSEL and edge-emitting lasers. VCSELs have a wavelength temperature coefficient of 0.07nm/°C while edge emitters have a wavelength temperature coefficient of 0.3nm/°C. However, edge emitters are twice as efficient and can offer higher output power with lower waste heat. Lasertel diodes and package design can be optimized to operate over a large temperature range. Download our white paper to learn more about the advantages of VCSEL and edge-emmiting lasers.
Terrain: An automotive lidar system must be rugged to resist damage from the shocks and vibrations caused by traveling over rough terrain. Lasertel's laser diode systems are monolithic structures secured with hard-soldered connections. These lasers are used in fighter jets and have been tested to withstand the toughest of environments.
Keeping these issues in mind is critical when designing a safe and effective lidar system. Optimizing the performance of a lidar system requires the use of an optimized laser diode source. Lasertel gives customers the creative control to define the laser that will work best for their specific application and lidar system. The lidar system must perform over a range of environmental conditions and the selection of the optimal laser source is critical. Lasertel is capable of fabricating completely customized edge-emitting and VCSEL laser diodes from the basic chips up to the device housing with supporting drive electronics.
Contact Us early in the design process to discover how a custom-made Lasertel diode laser can elevate the performance of your lidar system.
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