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Advanced SLEDs
for the Near Infrared Range

Made by EXALOS

EXALOS offers a wide variety of Superluminescent Light Emitting Diodes (SLED) for the Near Infrared Range (NIR) at different wavelengths ranging from 750 to 1700 nm, with different output power and bandwidth values.

Since 2003, EXALOS has shipped more than 500,000 NIR SLEDs. EXALOS products are used extensively in Medical and Industrial Imaging, Navigation, Optical Sensing, Metrology, and Scientific applications.

For a list of all available SLEDs and their specifications, please visit our SLED Product page.

Our high-performance SLEDs come in various packages or form factors, including:

Cooled 14-pin Butterfly and Dual-In-Line (DIL) packages
Add “Cooled 9-pin Butterfly packages”
Cooled and Uncooled 5-pin Butterfly packages
Low-cost uncooled TOSA packages
Uncooled free-space TO-56 packages

EXALOS SLEDs provide efficient beam collimation and waveguide coupling.

The operation and Lifetime/Reliability of SLEDs are similar to that of Laser Diodes.

EXALOS has a long track record of creating innovative, industry-leading light sources:

20+ years with InP devices,
15+ years with Gallium Arsenid (GaAS) devices
10+ years with Gallium Nitrid (GaN) devices.

Learn more

What are SLEDs - Technology Overview

What are SLEDs?

Broadband "Laser Diodes" with a beam-like output

Incoherent "Laser Diodes"

Speckle-free "Laser Diodes"

S Superluminescent Emitting Diodes (SLEDs, SLDs) are semiconductor devices that emit broadband light through electrical current injection. SLEDs are a hybrid between LEDs, which emit broadband light in all directions, and semiconductor laser diodes, which emit narrowband light with a well-defined laser beam. In this sense, SLEDs can be understood as broadband laser diodes with a beam-like output.

Broadband means that SLEDs emit an optical spectrum that is broad in the wavelength or frequency domain. The spatial domain is correlated to the frequency domain through the Fourier transform. A light source that is broadband in the frequency domain is therefore narrowband in the spatial domain, meaning it is having a short coherence length (see below). In this sense, SLEDs can be also understood as incoherent laser diodes.

Light from any light source can interfere with light from the same or another light source, but only within its coherence length. Reflections from surfaces, which are never perfectly flat and even, cause so-called “speckles” when the path differences between the interfering light waves are smaller than the coherence length of the light.

Speckles are random dark and white interference patterns that are perceived as noise. Narrowband laser diodes typically generate speckle noise because of their large coherence length. In this sense, SLEDs can be understood as speckle-free laser diodes.

Broadband Light Generation in SLEDs

SLEDs – Comparison to LEDs and Laser Diodes

SLEDs have distinctive optical characteristics that essentially makes them a desirable hybrid between the properties of laser diodes and LEDs.

Performance comparison of LD, LED and SLEDs

Hardware Architecture Comparison

Superluminescence Emission Regime

The total optical power emitted by an SLED depends on the injected current. Unlike laser diodes, the output intensity does not exhibit a sharp threshold but it gradually increases with current (see image below).

A soft knee in the power vs. current curve defines a transition between a regime dominated by spontaneous emission (typical for surface emitting LEDs) and one that is dominated by amplified spontaneous emission (i.e. superluminescence).

The maximum value of the current that allows a safe operation of the device depends on the model and ranges between 70 mA and > 500 mA for the most powerful devices.

Full CAST

High-Performance SLEDs for the complete Near Infrared Range

from

nm

EXALOS provides SLEDs with flexible characteristics and different spectra for the full NI Range:

Fibre & Connectors

EXALOS SLEDs can be offered with many industry standard Single-Mode Fiber and Polarization-Maintaining fiber, and come standard with FC/APC connectors.

Military Standards

EXALOS’ has qualified SLEDs for Space and other Military Applications. These qualifications include testing in accordance with MIL-STD-883 and Telcordia. In addition to the standard qualification tests, specific EXALOS’s SLEDs have successfully passed Gama-Radiation testing.

See all EXALOS SLED Products / Specifications

EXALOS SLED Technology

Combining the advantages of Laser Diodes and LEDs.

As described above (“What are SLEDs?”) Superluminescent Light Emitting Diodes have distinctive optical characteristics that essentially bridge the gap between the properties of Laser Diodes and LEDs (* see benefit comparison below).

SLEDs emit an optical spectrum that is broad in the wavelength or frequency domain, which translates to a low temporal coherence or short coherence length. Conversely, they exhibit high directionality or spatial coherence.

Thanks to this special behaviour, SLEDs combine the spatial coherence of a laser diode and the temporal incoherence of an LED.

The spatial coherence translates into a small beam divergence, which enables the coupling of the output into a single-mode fibre with an efficiency similar to that of laser diodes. Typically more than 50 percent of the power from a single facet can be coupled into a single-mode fibre. The low temporal coherence is advantageous for applications where interferences cause problems such as speckle or ghost signals – perfect for any kind of projection technology (read more in our Blog: Quality Comparison of Light Sources for Holographic Projection).

At the same time, SLEDs are much more powerful than standard LEDs and are particularly useful for applications that require high power densities. When biased with several hundreds of milliamperes, they typically have single-mode output powers of the same order of magnitude as single-mode laser diodes of several tens of milliwatts.

Comparison of the optical properties of LEDs, SLEDs and LDs.

Show Comparison

	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

More about SLEDs

Bridge the Gap

By combining the best features of lasers and LEDs, SLEDs bridging an important application gap.

SLEDs can be used in fiber optic pressure sensors for static strain (load) or dynamic strain (vibration) measurements as well as temperature measurements in structures such as suspension bridges.

More about SLEDs

Bridge the Gap

By combining the best features of lasers and LEDs, SLEDs bridging an important application gap.

SLEDs can be used in fiber optic pressure sensors for static strain (load) or dynamic strain (vibration) measurements as well as temperature measurements in structures such as suspension bridges.

Superluminescent LEDs Enter the Mainstream

The combination of valuable features of Superluminescent LEDs are essential for a variety of applications and finding commercial use.

Read More

Comparison of SLED, laser diode and LED architectures

In the case of lasers, an optical waveguide and reflective facets are used to create a laser cavity (resonator), and amplified stimulated emission creates an edge-emitting device with a narrow band output.

LEDs, on the other hand, have no amplified gain and emit light in all directions through spontaneous emission only. SLEDs, however, utilize an optical waveguide to exploit the process of amplified spontaneous emission (ASE) and single pass again, as opposed to multiple round-trips in a laser diode.

A broad range of possible energy transitions is something that also applies to a semiconductor laser, for example a Fabry-Perot (FP) laser diode (LD), or to a light-emitting diode, a LED.

FP laser diodes use the broadband gain of the semiconductor material, an optical waveguide and reflecting facets of the LD chip to build a laser cavity (resonator). Starting from spontaneous emission that is amplified along the waveguide of the LD, light travels back and forth (multiple roundtrips) inside the laser cavity, resulting in constructive amplification of cavity modes through stimulated emission. Consequently, the optical spectrum of a FP laser diode exhibits a comb of distinct longitudinal modes of the laser cavity.

SLEDs exploit the process of amplified spontaneous emission (ASE) where light of spontaneous emission is amplified only in a single pass through an optical waveguide as compared to amplification over multiple roundtrips in an LD. For this reason SLEDs typically have lower output powers for the same electrical drive current as compared to LDs, which also means that their wall-plug efficiency is lower.

Furthermore, any kind of optical cavity is avoided in a SLED, resulting in a broadband spectrum with no or little amplitude modulation (spectral ripple).

LEDs do not feature any optical waveguide and are therefore not edge-emitting devices with a “laser beam” like LDs or SLEDs. Instead, LEDs emit in all directions light from spontaneous emission only (as compared to ASE).

The total output power of LEDs can be considerably high, however due to the wide emission angles the optical power density (intensity) is lower as compared to SLEDs or laser diodes. For the same reason, coupling into single-mode optical fibers is rather impractical with LEDs and coupling efficiencies are very poor. LEDs produce light with an optical spectrum that might be even wider than that of a SLED because the process of amplified spontaneous emission along the waveguide results in spectral narrowing.

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Advanced SLEDs
for the Near Infrared Range