Finisar’s Vertical Cavity Surface Emitting Laser (VCSEL) technology brings together the advantages of low cost and optical efficiency within a small footprint.
VCSELs are high efficiency semiconductor lasers that direct the maximum amount of light where it is needed. There are a few variables that lead to overall system optical efficiency and for VCSELs to be the IR source of choice for 3D sensing and 2D imaging systems.
- Laser Wall-Plug Efficiency (WPE): WPE is a measure of the output power out of the laser device, as a percentage of the electrical power into the device. VCSEL technology has improved in WPE in recent generations and now it is possible to achieve >40% WPE.
- Usable light power: Not all light that is emitted from an IR source (laser or LED) is usable. Usable light needs to be focused onto a specific ‘field of illumination’ (FOI). Lenses, diffusers, mirrors and other optical elements lead to loss. Light can also leak from the package. VCSELs emit a stable, focused and circular beam vertically from the topside of the device, allowing the optical engineer to capture and use most of the emitted light from the device. This is particularly beneficial when comparing to LEDs which emit in all directions and require optics to control, which introduces additional power loss.
- Usable light wavelength: An efficient optical sensing or imaging system is made up of a projector (such as a VCSEL) and receiver (CMOS image sensor or Photodiode array for example). The wavelength of the light used by the system matters. A receiver will be most sensitive at a specific wavelength. The system also needs to reject other wavelengths that might contribute noise. Often times a filter is applied to the receiver to only let specific wavelengths through. An efficient optical sensing system will reject much of the spectrum from a broadband light source like LEDs. A VCSEL, on the other hand, provides a very narrow, pure wavelength that is very stable over temperature, especially compared to edge-emitting lasers.