VCSELs provide a compact, efficient optical source for a wide range of applications. VCSELs are built as dies that can be mounted directly on printed circuit boards, packaged into components, or as vertically integrated solutions in custom packaging complete with other components such as photodiodes, drivers, TIAs, and signal controllers.
Both single mode and multimode VCSELs are available. Single mode VCSELs are limited in the amount of power they can generate and, as such, are typically only used for sensing applications. Multimode VCSELs, however, can be used in applications including datacomm at data rates up to 50 Gbps as well as precision sensing applications such as encoders and 3D imaging.
Two other commonly used optical sources are Light Emitting Diodes (LED) and Edge Emitting Lasers (EEL). As can be seen, LEDs spread their power output over a wide angle and across a spectrum of wavelengths. Even with optics, LEDs experience higher power loss compared to lasers. EELs, while coherent, produce an elliptical, astigmatic beam, and therefore require more expensive optics to focus the light. In addition, EELs emit from the side, limiting them to a linear implementation.
There are many applications with requirements that cannot be met with an LED and need the coherency and wavelength stability of a laser. For example, high-end encoders need a coherent light source to create an interference pattern through a diffraction grating. Similarly, object detection and motion sensors using self-mixing techniques need an output with a highly stable wavelength to accurately measure Doppler shifts.
Multi-element VCSEL arrays are scalable by changing the size of the array and can be customized to achieve more than 1 W of CW optical power. Typically, with a higher maximum power output, greater range is possible for sensing applications. Higher output power also yields a better signal-to-noise ratio (SNR), further improving precision. In addition, VCSELs exhibit low change in wavelength with changes in temperature. This allows for simpler packaging without the need for thermoelectric coolers in the system while still allowing for a narrow enough range of filters that result in a good SNR.
VCSELs serve as an overall more cost-efficient optical source compared to EELs in range sensing applications. To compensate for their elliptical output, EELs require more complex optics to focus and shape light. VCSELs also have a lower operating voltage than stacked junction EELs, and their array-based nature provides more inherent reliability. For example, with an array of 200 VCSELs, if one fails, the system still has 199 light sources. In contrast, EEL-based systems are limited to a linear implementation and are vulnerable to catastrophic failure; if the EEL optical source fails, the entire subsystem fails. A VCSEL’s emission wavelength is also more stable over temperature compared to edge emitters, thus eliminating the need for thermoelectric coolers usually needed with edge emitters.
EELs also cannot be tested until the end of the production process, resulting in lower yields and higher cost. VCSELs, by their nature, can be tested during various manufacturing stages to maximize yield and reliability.
VCSEL packaging has low parasitics and is extremely thermal efficient, offering better heat dissipation than EELs for the same power. In addition, VCSELs can be pulsed at high frequency to maximize precision without any significant degradation due to laser heating and thermal effects.