VISIIIBLES BLUE
High-Performance SLEDs
for the BLUE Spectral Range
GaN
Gallium Nitride-based design
450 nm
Low Speckle. High Sharpness.
Collimation
VISIIIBLES BLUE
High-Performance SLEDs
for the visible BLUE range
GaN
Next Generation of
Gallium Nitride-based design.
450 nm
Low Speckle. High Sharpness.
Collimation
With VISIIIBLESBLUE EXALOS provides a high perfomance SLED with low etendue and low speckle noise for the visible blue spectral range.
Based on our next-generation Gallium Nitride design the high-performance SLED provides a wavelength of 450 nm.
EXALOS VISIIIBLESRGB SLED technology offers strong benefits, like high color gamut, high efficiency and effective collimation. Perfect for the next generation of projection technology, e. g. augmented reality displays, illuminating micro- or head-up displays, for holography, metrology or spectroscopy.
Thanks to the low temporal coherence – a unique characteristic of SLEDs – VISIIIBLESBLUE are free of speckle, associated with laser-based projection displays.
VISIIIBLESBLUE are the key solution for small footprint AR/MR Micro Displays, direct Retina projection or holographic solutions, which will change the interaction between humans and information in the near future.
Features
- Next Generation of EXALOS´ GaN-based design
- Low speckle, broadband output
- Enabling sharp images
- High directionality, low etendue beam
- Diffraction-limited (single spatial mode)
- Polarized output
- Energy efficient
- High damage threshold
- Perfect for compact size applications, free-space
or fiber coupled architectures
VISIIIBLES BLUE are designed for:
- Holographic Displays
- Near-to-eye Displays for AR/VR/MR, e.g. Smart Glasses
- Color-sequential LCOS, DLP, SLM and Scanning MEMS Mirrors
- Micro Displays
- Military & Industrial HUDs
- Pico Projectors
- Machine Vision
- Metrology
- Microscopy
FEATURES
1 / 3
Following the rapid development experienced by III-nitride materials in recent years after EXALOS´ first demonstration of a blue SLED in 2009, the performance has been continuously improving. Today´s commercially available devices can compete with LDs in terms of output power and with emission in the true-blue spectral range and can outperform than in terms of image quality for projection applications.
With the provided specifications (see below) and a very high coupling efficiency into single-mode optical fibers (>50%) plus long lifetime and temperature stability comparable to LDs VISIIIBLES BLUE are now mature for all kinds of speckle-free display applications, especially the next generation of upcoming Smart Glasses for Augmented Reality.
Comparison of speckle noise in the far-field pattern of a blue LD (a) and SLED (b).
(c) Directional emission from 5.6mm TO-packaged blue SLED.
VISIIIBLES BLUE achieve 10 mW @ 100 mA with the latest wafers (2019).
Device to device variations may occur on a different set of samples.
FEATURES
2 / 3
I n 2009 EXALOS introduced the first blue-violet (420nm) SLED based on III-nitride compound semiconductors, which was developed in collaboration with the Ecole Polytechnique Fédérale de Lausanne (EPFL). With with VISIIIBLESBLUE the III-N semiconductor technology has evolved towards efficient and reliable devices that can comfortably operate in spectral regions beyond 450 nm and reaches with VISIIIBLESGREEN even the green spectral range (λ > 510 nm).
With more than a decade of experience and our industry-leading research team, EXALOS was able to overcome the challenges of this design for blue light emissions (see below).
The breakthrough resulted from extensive modelling/simulation, iterative epitaxial designs and improvements in the modal gain of the semiconductor structure.
Based on an innovative design and improved growth conditions for the active region, the waveguide and cladding layers, EXALOS was able to optimize the crystal quality, the optical loss in the light guiding layers and the electrical injection efficiency.
The market-leading Gallium Nitride technology allows EXALOS to finally provide true-blue and even green SLEDs with a single-lateral mode that have the highest reported values of power and wall-plug efficiency to date. The achieved bandwidth (FWHM) reaches 10 nm at 20 mW of output power and spectra do not show signs of optical feedback or unwanted ripple.
Thanks to these performance parameters, VISIIIBLESBLUE are a key solution for small footprint AR/MR Micro Displays, direct Retina projection or holographic systems.
The EXALOS GaAs/GaN material system
While the development of blue and green SLEDs is usually based on the AlGaInN alloy system, the highly efficient SLEDs for the red spectral region, Made by EXALOS, are based on AlGaInP alloys – similar to edge-emitting LDs.
Learn More about the EXALOS material system
EXALOS´ blue and green SLED technology is based on III-nitride compound semiconductors. The active region of these devices is realized with strained InGaN QWs.
The advanced device structures are based on epitaxial layers grown by metal organic chemical vapour deposition on free-standing GaN substrates (see below). They rely on the light emission from multiple InGaN quantum wells (QWs) sandwiched in the middle of a low Indium content InGaN waveguiding layer, positioned in between lower refractive index AlGaN cladding layers. The latter provide optical confinement and are p- and n-doped for electrical injection.
The peak wavelength is dependent on the amount of indium introduced in the InGaN quantum wells present in the active region. The higher the Indium content of the QWs, the longer the emitted wavelength. Blue SLEDs require QWs with moderate indium content (typically of the order of 10 to 15%). Increasing the emission wavelength to 500 nm and beyond, to produce a true-green light source, requires values above 20%.
Based on an innovative epitaxial layer design, EXALOS was able to successfully increase the Indium concentration of the InGaN MQW layers to a stable design.
Consequently, the modal gain for blue and green SLED structures is rather low and higher injection currents are needed to reach the ASE regime.
Additionally, the refractive index difference between active region and surrounding waveguide layers is rapidly decreasing with longer wavelengths, even over few nanometers!
Additionally, the refractive index difference between active region and surrounding waveguide layers is rapidly decreasing with longer wavelengths, even over few nanometers!
Finally, the modal gain, which strongly influences the output power of SLED, also decreases rapidly with the higher wavelength.
Growing Indium-rich quantum wells is challenging
Consequently a shorter wavelength design needs to face the following challenges:
- High crystal strain, low uniformity.
- Increasing lattice mismatch to GaN layers.
The reduction of the critical QW thickness and, thus, to a reduced gain, leads to a higher defect formation as well as higher internal electric fields on substrates with polar orientation (c-plane). Consequently, the modal gain for green SLED structures is rather low and higher injection currents are needed to reach the ASE regime.
- Decomposition of In-rich QWs
The risk of decomposition needs to reduce growth temperature of the upper layers. The crystal quality deteriorates and p-doping becomes more challenging. - Reduced wave function overlap of electrons & holes due to polarization fields (quantum-confined Stark effect, QCSE)
Indium-rich QWs result in a reduced material gain at longer wavelengths and thus a lower efficiency.
Challenges of the low optical confinement
The output power of SLEDs is strongly influenced by modal gain. The main challenge results from the reduced modal gain at increasing wavelength. The refractive index contrast between the waveguide and surrounding waveguide layers is rapidly decreasing, even over few nanometers. The lower optical confinement factor leads to a higher internal loss coefficient caused by increasing free-carrier absorption.
The modal gain also decreases rapidly with the wavelength.
Obviously, red, blue, and green SLEDs operate in completely different regimes with respect to the modal gain. The modal gain for red SLEDs is very high.
For blue SLEDs it is significantly smaller, and for green SLEDs it is another 50% smaller at the same current density compared to blue SLEDs. This explains why the typical operating current is very different for the three RGB colors. 1
A detailed analysis of the modal gain in these structures shows that optimizing the confinement factor and achieving better carrier injection efficiency may lead to significantly lower drive current and therefore a higher device efficiency.
By using a next generation GaN-based design and overcoming the intrinsic challenges of the current materials, EXALOS provides market-ready high-performance SLED for the blue spectral range.
FEATURES
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Modern holographic displays can reconstruct 3D images with full wavefront information and in high quality, free from discontinuous motion parallax, crosstalk and lack of accommodation depth cue.
The key factor for image quality is the used light source. A high degree of coherence is required to realize artifact free, sharp presentation. 1
Consequently, a light source with high spatial coherence and low temporal coherence is ideal for a holographic display in order to obtain high quality images with good sharpness and minimum speckle. sLEDs … are suitable light sources for this purpose. 1
The high spatial coherence typical of SLED emission – which corresponds to a directional light beam output – leads to a reduced complexity of collimation optics required in the optical subsystems. The low temporal coherence – resulting from the large spectral bandwidth – obviates the need for bulky dephasers used to reduce undesirable speckle noise.
SLEDs: The optimal hybrid light source
Benefits for modern display applications, compared to LEDs and Lasers:
| LED | SLED | LD | |
| Optical Spectrum |  Broadband |
Broadband |
 Narrowband |
| Temporal Coherence | Low |
Low |
High |
| Speckle Noise Generation | Low |
Low |
High |
| Directionality | Low |
High |
High |
| Polarization | High |
High |
Low |
| Spatial Coherence | Low |
High |
High |
| Coupling into Single-Mode Fibers | Poor |
Efficient |
Efficient |
| Polarization State | Random |
Linear |
Linear |
1 Coherence properties of different light sources and their effect on the image sharpness and speckle of holographic displays (2017).
Yuanbo Deng & Daping Chu. Scientific Reports Volume 7, Article number: 5893 (2017) / DOI:10.1038/s41598-017-06215-x
Published with Open Access under Creative Commons Attribution 4.0 International License
External Link: www.nature.com – Scientific Reports
2 RGB Superluminescent Diodes for AR Micro-Displays
Marco Rossetti, Antonino Castiglia, Marco Malinverni, Christian Mounir, Nicolai Matuschek, Marcus Duelk, Christian Vélez
SID 2018 Digest.
From our Blog
Quality Comparison of potential light sources
for Holographic Projection
The test from Yuanbo Deng & Daping Chu, published in Scientific Reports 7: 5893, compares the Coherence properties of 5 light sources and their effect on the image sharpness and speckle of holographic displays.
SPECIFICATIONS
Product number EXS210014-01
Package TO-56 / uncooled
Max. Output Power ( P )
10 mw
Reverse Voltage ( VR )
-2 V
Max. Forward Current ( IF )
200 mA
Max. Forward Voltage ( VF )
7.0 V
Centre wavelength ( λ )
435 nm
Min
450 nm
Typ
465 nm
Max
Bandwidth FWHM
3 nm
Min
5 nm
Typ
Power ex-window
5 nm
Typ
10 nm
Typ
20 nm
Max
Reverse Voltage
-2 V
Max
VISIIIBLES BLUE 450 nm
14-pin Butterfly module
EXALOS offers the next-generation SLED with 450 nm also as 14-pin module with SM Fibre connector (3.3 / 125 µm Nufern S405-XP). The module provides a typical electro-optical performance (TSLED= 25 °C) of 3 mW with a bandwidth of 6 nm.
Product number EXS210099-02
Package 14-BFL
VISIIIBLES BLUE 635 nm
14-pin Butterfly module
EXALOS offers the next-generation SLED with 450 nm also as 14-pin module with SM Fibre connector (3.3 / 125 µm Nufern S405-XP). The module provides a typical electro-optical performance (TSLED= 25 °C) of 3 mW with a bandwidth of 6 nm.
Product number EXS210099-02
Package 14-BFL
HIGH-PERFORMANCE LIGHT SOURCES
MADE IN SWITZERLAND
HIGH-PERFORMANCE LIGHT SOURCES
MADE IN SWITZERLAND
