General FAQs

GENERAL QUESTIONS
What are the main differences between a laser diode and superluminescent light emitting diodes (SLEDs)?
What are the key advantages of superluminescent light emitting diodes (SLEDs)?
What are the advantages of SLEDs in FOG?
What are the advantages of SLEDs in Optical Coherence Tomography (OCT)?
What are the advantages of SLEDs in fiber based sensors?
Which wavelength of high power LEDs does EXALOS offer?
How can I select the right EXALOS SLED product for my application?
Where can I find the typical performance for EXALOS SLED products?
Where can I find the EXALOS product specifications?
Which fiber is used as standard fiber?
Are EXALOS SLEDs supplied with a photo detector diode?
Are EXALOS products supplied with an optical connector? Which type?
Are SLEDs available in TO-can case?
Are devices available with Polarization Maintaining Fiber (PMF)?
Where can I buy EXALOS products?

GENERAL QUESTIONS

What are the main differences between a laser diode and superluminescent light emitting diodes (SLEDs)?
Superluminescent light emitting diodes (SLEDs) are unique semiconductor light emitters in the sense that they combine the spatial coherence properties of lasers with the temporal incoherence, short coherence length, of a LED. They are sometimes referred to as a "diode lasers operated below threshold", "high power LEDs" or "super LEDs".

The high spatial coherence translates into a small divergence angle of the light beam emitted by the SLED chip. This enables a high coupling efficiency into fiber pigtails. Typically, 50% of the power emitted from the SLED chip is coupled into a single-mode fiber.

The temporal incoherence (short coherence time) is equivalent to a short coherence length. Short coherence length means that when light from high power light emitting diodes (LEDs) is split into two beams and one of the beams is delayed with respect to the other by more than the coherence length, the two beams will not interfere with each other any longer when recombined. In the spectral domain, this property manifests itself as a broadband spectrum, i.e. light is emitted over a wide range of wavelengths.

In contrast, the spectrum of a laser is monochromatic, i.e. light is emitted only within a very narrow wavelength band, resulting in a long coherence length.

What are the key advantages of superluminescent light emitting diodes (SLEDs)?
Superluminescent light emitting diodes (SLEDs) provide a broadband optical power spectrum (low temporal coherence or small coherence length) at high power levels coupled into single-mode fiber. The small coherence length is particularly useful in all applications, where unwanted interference effects may affect the system performance. An example is the reduction of speckle effects in imaging applications when replacing the laser with a Superluminescent light emitting diode (SLED)

In addition, SLEDs have a small form factor, are rugged and can be manufactured cost efficiently, while still offering superb performance. These unique properties enable SLEDs to be used in a number of different applications.

Due to their improved spectral performance, short coherence length, higher power levels and extended range of wavelengths, SLEDs are seeing a growth in the number of applications. These new applications range from scientific research to commercial applications. The applications for Superluminescent light emitting diodes (SLEDs) will continue to grow as designers become more aware of the performance, coherence length, and cost improvements in today's SLEDs.

What are the advantages of SLEDs in FOG?
The low temporal coherence is advantageous in applications where unwanted interference effects within the system can be a problem. An example is the Fiber Optic Gyroscope (FOG). Here, undesired interference effects from back reflections at the interface between internal fiber optic components and scattering effects along the fiber loop can be significantly reduced when replacing the laser source with an SLED.

What are the advantages of SLEDs in Optical Coherence Tomography (OCT)
SLEDs, sometimes referred to as high power light emitting diodes (LEDs), also provide advantages in interferometric applications where the short coherence length of the SLED enables the localization of a reflective point with high accuracy.

The SLEDs short coherence length property enables high-resolution imaging systems such as Optical Coherence Tomography (OCT) equipment to be built. Advances in Superluminescent light emitting diode (SLED) technology allow for greater accuracy in Optical Coherence Tomography (OCT) and several companies are now offering Optical Coherence Tomography (OCT) instruments for both medical and industrial applications.

What are the advantages of SLEDs in fiber based sensors?
Further, SLEDs are being employed in fiber optic sensing systems based on Fiber Bragg Gratings (FBG). In the simplest case, an SLED is illuminating an array of FBGs that have been written along a single optical fiber. Each FBG is characterized by its own Bragg wavelength and can be identified in the system by spectrally resolving the return signal using an Optical Spectrum Analyzer. Strain and/or temperature changes at the location of individual FBGs are measured as shifts in the Bragg wavelength of the corresponding FBG. The wide bandwidth of SLEDs allows a large number of FBGs to be addressed simultaneously.

In addition, optical component manufacturers are increasingly using SLEDs for the characterization of WDM components as they offer the best choice between measurement speed, accuracy and cost.

Which wavelength SLEDs does EXALOS offer?
EXALOS's portfolio of SLEDs covers wavelengths ranging from 730 to 900 nm and from 1250 to 1700 nm.

How can I select the right EXALOS SLED product for my application?
The most common criteria for selecting the right SLED for a given application are output power, central wavelength and spectral bandwidth. Our standard products are listed online where typical performance data and product datasheets can be downloaded.

EXALOS offers a wide variety of standard SLEDs with wavelengths ranging from 730 to 1700 nm with different powers and bandwidths. A variety of housings & packaging options, including standard 14-pin dual-in-line (DIL), butterfly and low-cost TOSAs (pigtailed) and TO-56 cans (window devices) are available.

In addition to our standard products, EXALOS can also provide devices with custom performance and custom housing/packaging solutions. Please contact our Sales team, sales@exalos.com, to discuss your specific requirement. Our Sales and Applications team will work with you to determine the product best suited for your particular application.

Where can I find the typical performance for EXALOS SLED products?
Datasheets for our standard products containing typical performance data can be downloaded from EXALOS's website.

In addition to our standard products, EXALOS can also provide devices with custom performance and custom housing/packaging solutions. Please contact our Sales team, sales@exalos.com, to discuss your specific requirement. Our Sales and Applications team will work with you to determine the product best suited for your particular application.

Where can I find the EXALOS product specifications?
Choose a product and the product specifications for our standard products can be downloaded after form completion.

In addition to our standard products, EXALOS can also provide devices with custom performance and custom housing/packaging solutions. Please contact our Sales team, sales@exalos.com, to discuss your specific requirement. Our Sales and Applications team will work with you to determine the product best suited for your particular application.

Which fiber is used as standard fiber?
Standard pigtailed EXALOS products employ Single Mode Fiber (SMF). Please contact EXALOS Sales, sales@exalos.com, for non-standard fiber pigtails.

Are EXALOS SLEDs supplied with a photo detector diode?
Yes, all EXALOS products come with an internal integrated Monitor Photo Diode (MPD), unless otherwise specified. Please ask for the Application Notes for more detail on the MPD.

Are EXALOS products supplied with an optical connector? Which type?
All standard SLEDs are supplied with a fiber length of approximately 1 meter and are connectorized with an angle-polished FC/APC connector. Other connector types are available on request.

Are SLEDs available in TO-can case?
Yes, we offer several SLED types as pigtailed TOSA devices or mounted in TO﷓56 cans as standard. Please refer to our product overview for a complete list. Exalos can also perform custom packaging in different TO cans.

Are devices available with Polarization Maintaining Fiber (PMF)?
Yes. Please contact EXALOS Sales, sales@exalos.com, for more information.

Where can I buy EXALOS products?
Standard EXALOS products can be bought through our Sales team (sales@exalos.com), or from our network of suppliers worldwide. Contact one of our international sales offices.