Encyclopedia … combined with a great Buyer's Guide!

Surface-emitting Semiconductor Lasers

Acronyms: VCSEL, VECSEL, PCSEL (see below for the distinction of those)

Definition: semiconductor lasers where the generated light propagates in the direction perpendicular to the wafer surface

Alternative term: vertically emitting semiconductor lasers

More general term: semiconductor lasers

More specific terms: vertical cavity surface-emitting lasers, vertical external cavity surface-emitting lasers, photonic crystal surface-emitting lasers

Opposite term: edge-emitting semiconductor lasers

German: oberflächenemittierende Halbleiterlaser

Categories: optoelectronicsoptoelectronics, laser devices and laser physicslaser devices and laser physics


Cite the article using its DOI: https://doi.org/10.61835/jtz

Get citation code: Endnote (RIS) BibTex plain textHTML

Semiconductor lasers can generally be grouped into two classes:

  • Edge-emitting lasers, where the laser light propagates parallel to the wafer surface of the semiconductor chip and is reflected or coupled out at a cleaved edge.
  • Surface-emitting lasers, where the light propagates in the direction perpendicular to the semiconductor wafer surface.

This article covers only surface-emitting lasers, providing an overview on different types (with the details of those being explained in other articles). Surface-emitting lasers can further be distinguished according to different criteria:

Monolithic vs. External-cavity Lasers

In any case, many monolithic lasers or gain chips for VECSELs can be fabricated together on a single wafer, which is sliced into many pieces.

Monolithic surface-emitting lasers may also be fabricated as two-dimensional laser arrays (e.g. VCSEL arrays) for generating much higher total output powers.

Vertical Cavity vs. In-plane Cavity

Vertical emission (i.e., an output laser beam perpendicular to the wafer surface) can fundamentally be achieved in two different ways:

Vertical-cavity Lasers

In vertical-cavity lasers, the intracavity laser light also essentially propagates in directions perpendicular to the wafer surface. The output beam is obtained simply by partial transmission through an output coupler mirror.

Practically, that approach implies that the path length in the semiconductor gain medium is rather short – on the order of micrometers. The laser resonator may also be very short for a monolithic device (VCSEL), or much longer for an external-cavity laser (VCSEL). In any case, the available round-trip laser gain is quite limited, typically to at most a few percent. It is therefore necessary to realize a laser resonator with relatively low losses, i.e., using Bragg mirrors with high reflectivity.

In-plane Lasers

There are (so far less common) lasers where the intracavity laser light essentially propagates in a plane along the wafer surface. That approach allows one to combine some of the advantages of edge-emitting and surface-emitting lasers: The active area and thus the output power can be much higher, also the round-trip gain due to the longer propagation length in the gain medium. This creates the potential of generating watt-level output power in combination with spatially single-mode emission, i.e., high beam quality.

There are different ways of implementing an in-plane laser, which may also be called horizontal cavity surface-emitting laser (HCSEL):

  • One may use a structure similar to a edge-emitting laser, i.e. with a waveguide structure along the wafer surface, but complemented with an additional structure which reflects the output light upward in order to achieve vertical emission of the output.
  • Another realization is the photonic crystal surface-emitting laser (PCSEL), where the in-plane laser resonator is realized with a photonic crystal structure. The same structure also reflects some of the light such as to form the output beam. Here, one may even achieve single-frequency operation, which is important, for example, for applications in 3D sensing and optical data transmission.

Electrical vs. Optical Pumping

One of the most important attractions of semiconductor lasers is that most of them can be electrically pumped. That is the most convenient and cheap way of providing the required power. This approach is also realized in most of the surface-emitting semiconductor lasers.

However, in some cases one uses optical pumping – usually with radiation from another semiconductor laser – because that also has some advantages:

  • It is substantially simpler to produce the semiconductor structure if one does not require electrical contacts. Also, optical pumping eliminates the requirement of sufficiently high electrical conductivity, so that undoped semiconductor media can be used, which are often also advantageous in terms of light absorption. One may thus produce devices with substantially simpler technology.
  • Optical pumping allows one to ideally distribute the energy input in the spatial dimensions. In particular, it is easy to uniformly pump a larger area, whereas electrical pumping with a ring electrode around an active area properly works only for a limited ring diameter. Otherwise, one would need transparent electrodes, which are difficult to realize.

The advantages of optical pumping are particularly realized in high-power VECSELs. These can work with much larger active areas than electrically pumped VCSELs and thus produce much higher output powers, while still maintaining diffraction-limited beam quality due to the external cavity.

The highest electrical-to-optical efficiencies, partly well above 60%, are achieved by some electrically pumped lasers, and that kind of efficiency is hardly achievable with optical pumping. At least, the optical-to-optical efficiency of an optically pumped laser can be quite high, and despite the overall lower power conversion efficiency, the thermal handling can be simplified, since the pump laser does not need to have a very high beam quality and can thus be of a robust type.

Basic Advantages

The concept of surface-emitting semiconductor lasers offers various advantages, comparing with edge-emitting lasers:

  • For a given optical output power, the emitting area is substantially larger, which implies correspondingly low optical intensities. Therefore, the challenge of catastrophic optical damage (COD), which is a limiting factor for many edge-emitting lasers, is effectively eliminated.
  • The technical difficulties of carefully processing the cleaved outer sides of semiconductor gain chips are also eliminated, since the light does not go through those edges. Overall, the fabrication is tentatively simpler and thus potentially faster and cheaper.
  • It can also be convenient that many gain chips, which are fabricated together on a large wafer, may be tested even before separating them.
  • The often very short laser resonator makes it relatively easy to achieve single-mode emission, and this over a wide range of operation parameters like pump power and temperature.
  • The emission wavelength is often not determined by the gain maximum of the semiconductor material, but by an optical resonance. That often leads to a substantially smaller temperature coefficient of the emission frequency.

More to Learn

Encyclopedia articles:


The RP Photonics Buyer's Guide contains ten suppliers for surface-emitting semiconductor lasers. Among them:


[1]K. Iga et al., “Surface emitting semiconductor lasers”, IEEE J. Quantum Electron. 24 (9), 1845 (1988); https://doi.org/10.1109/3.7126
[2]M. Kuznetsov et al., “High-power (> 0.5-W CW) diode-pumped vertical-external-cavity surface-emitting semiconductor lasers with circular TEM00 beams”, IEEE Photon. Technol. Lett. 9 (8), 1063 (1997); https://doi.org/10.1109/68.605500
[3]M. Imada et al., “Coherent two-dimensional lasing action in surface-emitting laser with triangular-lattice photonic crystal structure”, Appl. Phys. Lett. 75 (3), 316 (1999); https://doi.org/10.1063/1.124361
[4]K. Iga, “Surface-emitting laser – its birth and generation of new optoelectronics field”, J. Sel. Top. Quantum Electron. 6 (6), 1201 (2000); https://doi.org/10.1109/2944.902168
[5]S. Hoogland et al., “Passively mode-locked diode-pumped surface-emitting semiconductor laser”, IEEE J. Photon. Technol. Lett. 12 (9), 1135 (2000); https://doi.org/10.1109/68.874213
[6]A. C. Tropper et al., “Vertical-external-cavity semiconductor lasers”, J. Phys. D: Appl. Phys. 37, R75 (2004) (a good review); https://doi.org/10.1088/0022-3727/37/9/R01
[7]D. Lorenser et al., “Towards wafer-scale integration of high repetition rate passively mode-locked surface-emitting semiconductor lasers”, Appl. Phys. B 79, 927 (2004); https://doi.org/10.1007/s00340-004-1675-3
[8]Y. Kurosaka et al., “On-chip beam-steering photonic-crystal lasers”, Nature Photonics 4 (7), 447 (2010); https://doi.org/10.1038/nphoton.2010.118
[9]K. Hirose et al., “Watt-class high-power, high-beam-quality photonic-crystal lasers”, Nature Photonics 8 (5), 406 (2014); https://doi.org/10.1038/nphoton.2014.75
[10]S. Noda et al., “Photonic-crystal surface-emitting lasers: review and introduction of modulated-photonic crystals”, IEEE J. Sel. Top. Quantum Electron. 23 (6), 4900107 (2017); https://doi.org/10.1109/JSTQE.2017.2696883
[11]M. Yoshida et al., “Double-lattice photonic-crystal resonators enabling high-brightness semiconductor lasers with symmetric narrow-divergence beams”, Nature Materials 18 (2), 121 (2019); https://doi.org/10.1038/s41563-018-0242-y
[12]T. Inoue et al., “Design of photonic-crystal surface-emitting lasers with enhanced in-plane optical feedback for high-speed operation”, Opt. Express 28 (4), 5050 (2020); https://doi.org/10.1364/OE.385277

(Suggest additional literature!)

Questions and Comments from Users

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

Spam check:

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.


Share this with your network:

Follow our specific LinkedIn pages for more insights and updates: