Lidar stands for Light detection and ranging, and is similar in many respects to radar. It depends on emitting a very short pulse of light in a specific direction, often in the nanosecond or picosecond regime, and measuring the time required for the reflection to be detected. Since light travels at roughly 1 foot per nanosecond, the temporal precision of measurement is quite high. The specific direction of emission is accomplished through some form of beam steering, usually of a laser beam, and generally in an eye-safe portion of the spectrum.
Lidar is becoming ever more important in automotive design, for it has the potential to “visually” detect position and distance of other objects in the vicinity of a moving vehicle, and provide warning of collision with ample time and distance to prevent it.
Since the distances are large in this application, the reflected signal levels are very often quite low. As a result lenses with very aggressive F-numbers are required to provide adequate signal to noise ratio (SNR).
SMA has experience in designing compact, wide-angle LIDAR receiver optics. Fields of view in excess of 110 degrees horizontally and 25 degrees vertically have been designed with F-numbers in the range of F/0.8 for use in the mid-IR spectral range. These optics generally require special detector arrays, sometimes with special focal plane arrays of light-directing elements. The lenses themselves are usually injection-molded plastic elements of aspheric design in order to achieve a very wide field of view and very low F-number simultaneously.