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The advantages of the TRUMPF VCSEL

What is a VCSEL laser and what are its advantages compared to other laser diodes? What is the structure that makes the special functionality of VCSEL arrays possible in the first place? On this page you can also learn more about the two types of VCSELs as well as everything you need to know about the typical industrial and consumer applications of the laser diodes.

What is a VCSEL (vertical cavity surface emitting laser)?

A VCSEL (Vertical cavitiy surface emitting laser) is a laser diode that vertically emits light in a cone-shaped beam from the surface of a fabricated wafer. VCSELs offer many benefits in comparison with conventional edge-emitting lasers where light is emitted on one or two edges of the chip. Whether for the industry or the consumer market, VCSELs are available in different wavelengths. The standard wavelengths are in the range of 760 nm, 850 nm and 940 nm.

What are the advantages of VCSELs?

Optimized beam profile

The round beam, which can even be Gaussian in shape, the low beam divergence and the different light modes (multimode and single-mode) make VCSELs perfect for a variety of applications.

Perfect for high-tech applications

With their high modulation speeds, beam quality and energy efficiency, VCSEL arrays are ideally suited for high-tech applications such as 3D sensing, LiDAR or optical data communication.

Saves on space and costs

The vertically emitting lasers can save on installation space and arrays with many emitters can be achieved with just one chip. This means high volume production and testing can be achieved at wafer level

High energy efficiency

The power input of the VCSELs in the very low milliwatt range enables very efficient operation in mobile applications, or even when used in data centers, while at the same time significantly reducing power consumption.

Short rise and fall times

Thanks to short rise and fall times, very fast pulse operation is possible with VCSEL. This is particularly important for use in optical data communication and Time-Of-Flight (ToF) systems.

Narrow bandwidth spectral light emission

VCSELs enable spectral light emission with an extremely narrow bandwidth.

Simple vertical integration

With the vertical light emission, additional features such as polarization-stabilizing elements or micro-optics can be easily integrated.

This is how a VCSEL works

A VCSEL is made up of many epitaxial layers built on top of each other. The top layer is a contact layer for power input. The first of the two mirrors is below this. This is carbon-doped and is composed of multiple layers of AlGaAs with varying levels of aluminum. The reflectivity of the upper mirror is usually around 99 percent.

The oxidation layer comes after the upper mirror. This consists of material with a high aluminum content, which is partially passivated by wet oxidation. The inner (non-passivated) part of the oxidation layer is used for current constriction and optical guidance. The oxidation layer is responsible for defining many important electro-optical parameters of a VCSEL.

The active region contains the quantum wells. This serves to boost the power.

Below the active region is the second mirror, which is silicon-doped and significantly thicker than the upper mirror. This serves to reflect as much light as possible back into the active region. The reflectivity of the lower mirror is usually around 99.9 percent.

Single-mode VCSEL vs. multimode VCSEL: what are the differences?

Technology image single-mode and multimode VCSEL laser, TRUMPF Photonic Components

Currently, there are two types of VCSEL: single-mode VCSELs and multimode VCSELs. A single-mode VCSEL produces a light beam with high spectral purity and exhibits lower divergence and higher coherence than a multimode VCSEL. While single-mode VCSELs are especially common in many industrial sensor applications, the compact multimode VCSELs are most commonly used in mobile consumer applications and highly integrated sensors.

What are the typical applications of VCSEL arrays?

Time-of-Flight (ToF)

Whether for distance sensor systems, laser autofocus or for high-precision depth sensors, the compact VCSEL arrays are suitable for measuring from distances of few millimeters up to several meters, and are particularly suitable for smartphone applications.

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Structured light

With VCSELs, which cast a pattern of light onto a surface in the form of dots, preset patterns can be precisely projected and identified. This is why light diodes play an important role in facial recognition when it comes to unlocking a smartphone, for security recognition when making mobile payments or when opening doors.

Industrial sensors

Whether with oxygen sensors that detect particles in the environment or optical encoders that are used for high-precision positioning, single-mode VCSELs in a hermetically sealed TO housing can withstand even the harshest operating conditions.

LiDAR

VCSEL arrays are very well suited to LiDAR applications. The very low rise and fall times of the optical pulses make ultra-short pulsing with high peak powers possible, in turn contributing to higher distance measuring. The system performance can be significantly increased by the addressability of the different segments on the VCSEL arrays. VCSELs will therefore have an important role in the future of autonomous driving.

Optical data communication with fiber optics

VCSEL and photodiode solutions allow a coded signal to be sent which is received at the other end and then decoded into an electrical signal. The components' high performance and reliability is crucial.

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Industrial heat treatment (VCSEL heating systems)

Many industrial applications such as joining, welding, drying, sealing, softening or heating can be achieved with high-power VCSEL heating systems. Beam sources based on VCSEL arrays are able to heat large surfaces with directed wavelength-selective infrared radiation.

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