Main Street Autonomy

Laser sources

There are basically three commonly used types of lasers:

Laser type Typical wavelength(s) Beam quality (M²) Coherence / FMCW-ready Power per element Cost Array?
VCSEL 850–940 nm Very good, circular Low–mid linewidth Low (mW–tens mW) Low Excellent: monolithic 2D arrays (10²–10⁵ emitters), fine pitch, easy eye-safety
Edge-emitting diodes 905 nm, 1350–1550 nm Good (often elliptical) Mid–high Mid (100 mW–W class with bars) Mid Good: 1D bars/arrays (dozens–hundreds)
Fiber/ECDL 1550 nm Excellent High (kHz–100 kHz LW) — best for FMCW High (W class via fiber amps) High Poor as dense arrays; usually single source + split/steer

Table 3 — Summary of laser types

Vertical cavity surface-emitting lasers (VCSELs) are very cheap and you can make a bunch of them on a chip in a chip-scale solid state array. They are called “vertical cavity” because the beam comes out perpendicular to the chip. You make them by depositing several layers of material on the chip. The main drawback is that they are low peak power.

Edge-emitting laser diodes are a mature technology and are cheap enough to be 1D arrays.

Fiber lasers produce high quality light that is highly coherent. But they are quite expensive so you can probably just afford one or two per lidar. Some lidars split one laser between many lidar heads, as in the case of Baraja’s lidar. Not only are fiber lasers more coherent, they can output millions of times greater power than edge-emitting diode lasers and VCSELs as well as much shorter pulses. Having shorter pulses is very advantageous for pulsed lidar as it improves the range resolution. Some fiber lasers can also vary the wavelength in highly linear chirps, allowing use in FMCW lidars.

The development of these lasers is highly driven by the telecommunications industry where they are used in fiber optics, so the lidar industry sort of profits from that for free.