VISIIIBLES BLUE

High-Performance SLEDs
for the BLUE Spectral Range

GaN

Next Generation of
Gallium Nitride-based design

450 nm

A true-blue SLED.
Low Speckle. High Sharpness.

Collimation

Efficient beam collimation and waveguide coupling.

VISIIIBLES BLUE

High-Performance SLEDs
for the visible BLUE range

GaN

Next Generation of
Gallium Nitride-based design.

450 nm

A true-blue SLED.
Low Speckle. High Sharpness.

Collimation

Efficient beam collimation and waveguide coupling.

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.

Moreover: based on the broad spectrum and high spatial coherence, EXALOS SLEDs offer high directionality (or low etendue) and high sharpness in image generation, outperforming existing LED- and laser-based projection systems.

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
The SLED is available as TO-56 and 14-pin Butterfly packages. Special form factors and advanced solutions for next generation devices are available on request.

FEATURES

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450 nm

A true-blue SLED.

Available as TO-56 and BTL-14 versions.
With VISIIIBLESBLUE EXALOS developed a next generation SLED in the blue spectral range (λ > 450 nm) to ultimately provide another essential element of the ideal SLED-based RGB illumination source.

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.

Characteristics *

Output Power & Current

VISIIIBLES BLUE achieve 10 mW @ 100 mA with the latest wafers (2019).

Wavelength and ASE Power
* These characteristics are relative to a particular device under test.
Device to device variations may occur on a different set of samples.

FEATURES

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The Next Generation of
GaN-based SLED design.

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.

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Learn More about the EXALOS material system

EXALOS Gallium Nitrid Epitaxial Structure

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.

Challenges for BLUE & GREEN SLEDs

T he development of a market-ready blue or even green SLEDs, especially the high indium content of the QWs, has to overcome great challenges.
The high Indium contents have a negative impact on the device performance caused by the higher lattice mismatch. This leads to a reduction of the critical QW thickness and, thus, to a reduced gain, higher defect formation as well as higher internal electric fields on substrates with polar orientation (c-plane).
The risk of decomposition of In-rich QWs is high.

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.

The confinement factor decreases with the wavelength.
Modal gain curves extracted from the 2-parameter fitting model for the four L-I curves discussed above. The solid line shows the modal gain curve obtained from a direct measurement of a blue SLED operating at 440 nm with similar epitaxial layer structure as the 450-nm structure
1 A. Castiglia et al., “Recent progress on GaN-based superluminescent light-emitting diodes in the visible range”, SPIE Photonics West 2018

From our Blog

Gallium Nitride:
The new driving force of the photonics industry
VISIIIBLESBLUE

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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Superior Image Quality

Low Speckle. High Sharpness. Efficient Beam Collimation.

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

Due to their operational principles, SLEDs combine the best characteristics of lasers and LEDs and therefore promise important benefits for illuminating MEMS-mirror scanning architectures, LCOS-based displays and holographic spatial modulator.

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.

Furthermore, he light output can be conveniently collimated into parallel beams or focused to µm-scale spot sizes and shows high degree of linear polarization, which can in turn lead to 50% savings in optical output power when used for illumination of LCOS-based micro-displays.2
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.

Read More

SPECIFICATIONS

VISIIIBLES BLUE 450 nm

Maximum Ratings *

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

Preliminary Specification: This product is under development. The data sheet contains preliminary data. Additional data may be added at a later date. EXALOS reserves the right to change specifications at any time without notice in order to supply the best possible product.

Operating characteristics
(TO-56 module) *

Tcase: 25 °C

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

Preliminary Specification: This product is under development. The data sheet contains preliminary data. Additional data may be added at a later date. EXALOS reserves the right to change specifications at any time without notice in order to supply the best possible product.

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

VISIIIBLES RGB

Revolutionary “Speckle-free” Lasers
for Head-Mounted and Head-Up Displays

VISIIIBLES RED

635 nm

Hitting the Sweet Spot of higher eye sensitivity and power consumption

VISIIIBLES GREEN

510 nm

A visible GaN-based
GREEN SLED.
The first of its kind.

VISIIIBLES BLUE

450 nm

A high-performance
GaN-based BLUE SLED.

EXALOS AG is a privately held Swiss technology company, developing industry-leading Superluminescent Light Emitting Diodes and Swept Laser Sources for the medical imaging, fiber optic gyroscope, test equipment, space, military and sensor industries.

EXALOS offers the widest range of visible SLEDs, including the world’s only true BLUE & GREEN SLEDs, SLED-based Transceivers for Fiber Optic Gyroscope and Current Sensing applications.

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