VCSEL - Vertical Cavity Surface Emitting Laser
VCSELs are LASER light sources. They have been used for quite some time in fiber optic communications. In the last few years, they have become popular as structured light generating sources in mobile phone applications. The acronym VCSEL derived from the name Vertical Cavity Surface Emitting Laser is an indication about why VCSELs are so popular for emerging high volume applications.
Surface Emitting versus Edge Emitting Laser
VCSEL for Emerging Applications
In a VCSEL, the laser light emits from the surface of the semiconductor versus the edge of the device. VCSELs have vertical lasing cavities with the ‘mirror’ structures built into the semiconductor wafer fabrication process itself. VCSELs are created at the wafer-level using highly cost-effective and easily miniaturized semiconductor fabrication processes. The resultant VCSELs are therefore less expensive and can be smaller than traditional EEL laser diodes.
This miniaturization and cost optimization has made VCSELs attractive for a wide range of high-volume emerging applications that require coherent, collimated light sources. VCSELs are capable of delivering laser capabilities to small spaces cost effectively.
VCSEL – Vertical Cavity Surface Emitting Laser
Structured Light versus Time of Flight
Structured Light
Uses an optical projector (generator) to project a specific pattern upon a scene. The scene is then captured by a digital camera or cameras and the image is processed using image processing algorithms to extra scene features and depth information.
Advantages
- Highly accurate within the working distances supported by the system
- The system is more robust against interference from other sensors
- Light sensor processing is in the MHz frequency range (microsecond) allowing the light pattern to be captured with existing high-volume, low-cost camera modules
Disadvantages
- Complex image processing required
- Sensitive to double reflection (for example: glass table tops and mirrors)
Time-of-Flight
Advantages
- Accurate over greater working distances
- Pulsed light allows for higher optical intensity while staying under the eye-safety limit
- (Typically) lower power consumption for the light source
- Simple, compact
- Fast distance algorithm because the distance can be
Disadvantages
- Interference from other ToF sensors
- Background light and multi-path reflections
- Not as accurate for low dynamic range applications
Rise in popularity of VCSELs
VCSELs have been around for a long time having been used in the photonics market for high-speed communication since the early 2000’s. Apple’s introduction of the 3D camera Face ID feature brought the VCSEL to the high-volume and cost conscious mobile phone market in 2017.
Cellphone Market Adoption of VCSELs Drives Economies of Scale
Following Apple’s success with the Face ID feature, Huawei soon followed with a 3D camera feature that also utilized a VCSEL projector. Overtime, the major mobile phone manufacturers, including Oppo, Vivo, Xiaomi, Samsung, and LG, all added 3D cameras with VCSEL projector capability.
The mobile market’s adoption of VCSELs has made this technology small, accessible and highly cost-effective.
VCSEL Illuminator Advantages
Cameras detect light (photons) that are reflected from objects in the field of view of the camera. Some illumination source is required to “light up” the scene to capture a low-noise, high-quality image. There are many historically available illumination sources such as incandescent bulbs, florescent tubes, and Xenon flashes. All of these illumination sources are bulky, expensive and power hungry compared to the leading illumination sources of today.
Today’s Illumination Source Candidates
Today, three primary light sources compete for use in mobile, automotive, metaverse (AR/VR), and industrial applications. These three sources are LEDs, VCSELs, and Edge-Emitting-LASERs (EELs).
LED – Light Emitting Diode
- Incoherent light
- Lambertian emission of light from all facets
VCSEL – Vertical Surface Emitting LASER
- Coherent light
- Symmetrical beam emission
- Low divergence of the optical beam
- No astigmatism
- Mirrors realized vertically at the wafer-level leading to disruptive cost savings versus EEL
EEL – Edge Emitting LASER
- Coherent light
- Elliptical, astigmatic optical beam emission
- Mirrors are formed by cleaving wafers and coating the ends – a more expensive and time-consuming process versus how VCSELs are manufactured
VCSELs are a Superior Infrared Red Light Source
| LED | EEL | VCSEL | |
| Output Power | Up to 1W CW (typical) | 100mWs CW | >3W CW, >30W pulsed |
| Wall-Plug Efficiency | ~25% | >45% | >35% |
| Beam Divergence & Quality | 180 degrees circular, No speckle | 11-40 degrees, Elliptical, Speckle | ~17 degrees, Circular, No Speckle |
| Wavelength Stability | Broadband emission and 0.3nm/C | 0.3nm/C | 0.07nm/C |
| Pulse Speed | 10s to 100s Nanoseconds | Nanoseconds | Nanoseconds |
| Packaging | Lowest cost, mature, surface-mount | Complex, larger, Low z-height a plus | Lower cost, Surface Mount |
VCSELs deliver LASER Diode benefits at LED price points.
VCSEL Driver – VCSEL Drivers – Triad Semiconductor IC solutions for driving VCSEL Light Sources
The Rise in VCSEL Popularity & Affordability
VCSELs were first introduced in the 1970’s. They have been used for decades in the photonics industry as the light source for optical communications. With the advent of Apple’s Face ID on the iPhone X in September 2017, VCSELs became sought-after technology in the mobile phone industry. The iPhone Face ID feature used a VCSEL dot projector to project a pseudo-random pattern of infrared dots onto the user’s face. This dot pattern helped to provide 3D depth information about the user’s face allowing the iPhone to compute a ‘signature’ of the user’s face to serve as the biometric information needed to unlock the iPhone.
After Apple introduced Face ID based on VCSEL projectors, the rest of the mobile phone market scrambled to add similar features all based on VCSEL-based dot projectors. The mobile phone industry drive huge production volumes. This mass adoption of VCSEL technology rapidly advanced VCSEL manufacturing capabilities and dramatically lowered the cost of VCSEL solutions.
With VCSELs enjoying the economies-of-scale benefits afforded by the mobile phone industry’s adoption, VCSELs rather quickly became highly cost effective solutions to deliver LASER-like performance to a vast number of applications.
VCSEL Applications
- Data Center Optical Communication – Historic use case
- Smartphone dot projector for 3D face detection biometrics
- Gas Sensors
- Structured Light Generators
- Line Generators
- Infrared Illuminator
- Automotive Driver Monitoring System (DMS) Illumination
- Automotive Occupancy Sensor Illumination
- Factory Automation Photoelectric Sensors – Red VCSELs shine here
- Medical Wearables – improved pulse oximetry
- Medical Lasing for plastic surgery and beauty applications
- Time-of-Flight Ranging Systems
- Infrared (IR) Flash
- UV-C disinfecting
- 3D LIDAR
- Ambient Lighting
- Automotive Intelligent Forward Lighting
- Automotive Adaptive driving beams
- High-speed near infrared (NIR) flash for high-speed industrial imaging
- Industrial 3D scanning
- Horticulture
- Medical Sensing Illumination
VCSEL Driver Solutions
VCSEL Driver Solutions by Triad Semiconductor
