VCSELs

A VCSEL, or vertical-cavity surface-emitting laser, is a type of semiconductor laser diode in which the laser cavity is defined vertically with respect to the substrate. The active region, typically a quantum well or multiple quantum wells, is sandwiched between two highly reflective mirrors known as distributed Bragg reflectors. Emission exits the device perpendicular to the chip surface, producing a nearly circular, low-divergence beam that can be focused with simple optics. Lateral confinement is often achieved with an oxide layer (oxide confinement) or other methods, enabling efficient single-mode operation in some devices.

VCSELs are grown epitaxially, with GaAs-based implementations for red and near-infrared wavelengths and InP-based implementations for 1.3–1.55 µm devices. The cavity length is a few microns, and the top and bottom DBRs provide high reflectivity to form the vertical laser cavity. They can be manufactured in two-dimensional arrays, offering high total output power and convenient testing at the wafer level. Oxide apertures help define the emission region, enabling low-threshold operation and stable beam quality.

Advantages of VCSELs include high coupling efficiency to optical fiber, low threshold currents, very low beam divergence, and compatibility with standard semiconductor processing, which supports relatively low-cost production and high reliability. They are widely used in short-reach optical communications, such as data-center links and consumer electronics, with 850 nm devices for multimode fiber and 1310–1550 nm devices for longer-reach systems. Additional applications include sensing, LIDAR, precision alignment, and display or projector illumination.

Historically, VCSELs emerged in the late 1980s and 1990s and have since matured through advances in efficiency, temperature stability, and high-speed modulation. Ongoing research explores tighter single-mode operation at longer wavelengths and enhanced integration with other photonic and electronic platforms.