September 28, 2021

Environmental Conditions that Impact Laser Diode Design for Automotive Lidar

We have previously written about many 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 outdoors, meaning a vital consideration is the surrounding environment. When selecting and designing the laser diode, you should consider four main factors for the automotive 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 (1-20 ns) of infrared light, invisible to the human eye. Since you cannot see the infrared light, there is no blink reflex, and the light that passes through the aqueous area gets focused by the lens onto the retina, which can cause damage by burning the retina. Methods to address eye safety include using longer wavelengths (> 1400 nm) which are absorbed more by the aqueous area behind the cornea and therefore cannot transmit to the retina. Eye-safe energy can be used at longer wavelengths (1400 nm – 3000 nm) rather than at shorter wavelengths (850 nm to 1400 nm), which are not absorbed. Lidar systems using shorter 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 technical white paper

Ambient Light: Lidar operates by projecting and receiving a beam of light, which 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 905 nm and 1500 nm, and the solar spectrum is 10x quieter at 1500 nm than 905 nm. One way to maximize the signal-to-noise ratio is to operate at one wavelength that matches the notches in the solar energy spectrum.

Ambient Temperature: Lidar systems are used in a range of environments and temperatures. Temperature changes shift the wavelength of a laser. Temperature control is critical to maintaining performance. Leonardo laser diodes can be customized with integrated thermal management solutions to control the temperature of the diode. Leonardo offers both VCSEL and edge-emitting lasers. The 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. The laser diode package can be designed and optimized to operate over an extensive temperature range. Download our white paper to learn more about the advantages of VCSEL and edge-emitting lasers. 

Terrain: An automotive lidar system must be rugged to resist the shocks and vibrations caused by traveling over rough terrain. Leonardo'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. Leonardo 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 selecting the optimal laser source is critical. Leonardo can fabricate completely customized edge-emitting and VCSEL laser diodes from the bare chips up to the device housing with supporting drive electronics.

Contact Us early in the design process to discover how a custom-made Leonardo diode laser can elevate the performance of your lidar system.

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