Frequently Asked Questions
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 on the EXALOS’s website, where typical performance data and product datasheets can be downloaded, after filling in our download form.
EXALOS offers a wide variety of standard SLEDs with wavelengths ranging from 400 to 1750 nm with different powers and bandwidths. The SLEDs are available in standard 14-pin dual-in-line (DIL) or Butterfly packages as well as low-cost TOSAs (pigtailed) and TO-56 cans (window devices) packages.
In addition to our standard products, EXALOS can also provide devices with custom performance and custom housing/packaging solutions.
Please contact our Sales team, moc.s1685481245olaxe1685481245@sela1685481245s1685481245, 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 general specifications and typical performance curves for EXALOS’ standard products?
The general specifications and typical performance curves can be accessed from the summary table under the sub-menu of “PRODUCTS” Menu or from the links listed below.
- SLED Modules
- SLED Driver Boards
- Broadband Light Sources
- Swept Sources
- OCT Engines
- Balanced Receivers
Please contact the EXALOS Sales team ( moc.s1685481245olaxe1685481245@sela1685481245s1685481245 ) with any questions.
At what wavelengths does EXALOS offer SLEDs?
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 SLED product page 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, moc.s1685481245olaxe1685481245@sela1685481245s1685481245 , for more information.
Are EXALOS products supplied with an optical connector? Which type?
Are EXALOS SLEDs supplied with a monitor photodiode?
Which fiber is used as standard fiber?
The default optical fiber is a single-mode fiber, for example SMF-28 for the long-wavelength range (1250-1750 nm), HI-780 for the short-wavelength range (700-950 nm), 1060-XP for wavelength range (980-1230 nm) , S405-XP for the visible range (400-680 nm), or other single-mode fibers for other wavelengths. Please contact Sales team (moc.s1685481245olaxe1685481245@sela1685481245s1685481245) for more information.
Where can I buy EXALOS products?
Please contact the EXALOS Sales team, moc.s1685481245olaxe1685481245@sela1685481245s1685481245, for more information on our products or a quotation. A list of international sales offices can be found on our contact page.
What are the key advantages of an SLED?
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 occur. An example of this type is the reduction of speckle effects in imaging applications when replacing the laser with an 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, 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 SLEDs will continue to grow as designers become more aware of the performance 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 backreflections 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 OCT
SLEDs 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. Several companies are now offering OCT instrumentsquipment for both medial 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.
Does EXALOS provide a laser diode controller or a TEC driver?
More information can be found on our website www.exalos.com.
Are EXALOS products thermally stablized?
All SLED modules in a 14-pin butterfly or DIL form factor feature an integrated thermo-electric cooler (TEC) and a standard 10-kOhm NTC temperature sensor such that the SLED chip can be stabilized to a set temperature with an accuracy of 0.01 °C.
Lower-cost SLED modules offered as TOSAs (fiber-pigtailed) or TO cans (free space) typically do not have an integrated TEC and require external heat sinking and temperature stabilization. Heat sinking is also required for butterfly and DIL modules.
What is the maximum drive current?
Some devices, especially uncooled SLEDs, may also have a maximum specified output power as the maximum drive current at lower chip temperatures may result in excessive optical output power values that can damage the output facet of the device. The maximum drive current for short-wavelength GaAs devices is typically in the range of 120-250 mA while many long-wavelength InP devices can be operated up to 500-600 mA.
How can I use the Monitor Photo Diode (MPD)?
Typically, the MPD current is in the range of 0.1-1.5 mA. EXALOS recommends to use a low-impedance termination (TIA gain) of max. 100 Ohm for the MPD current. If larger electrical control signals are required, a low-noise voltage amplifier shall be used.
How should I control the SLED temperature?
All standard EXALOS products packaged in DIL or Butterfly package contain a Thermo Electric Cooler (TEC) inside the package and a negative temperature coefficient (NTC) thermistor is placed in close proximity to the SLED chip.
Employing a suitable external heat sink and control electronics allows for the stabilization of the chip temperature against environmental variations. Unless otherwise specified, the default chip temperature for short-wavelength SLEDs (400-1100 nm) is 25 °C while it is 20 °C for long-wavelength SLEDs (1250-1750 nm).
Please download our Applications Notes for more details.
Where is the TEC located and how is the heat dissipated?
Why is the Butterfly package better for high power devices than DIL?
Are SLEDs sensitive to optical feedback?
However, optical feedback of lower than -30dB is generally recommended in order to fully guarantee the specifications. Higher values of optical feedback can induce modifications to the spectral density distribution and reduce output power. The use of an optical isolator with isolation > 30dB over the operational wavelength band is recommended. Without an optical isolator, the use of angled fiber connectors is necessary for optimal device performance.
It is worth noting that the degree of sensitivity to back-reflection also depends on the state of polarisation of the returned light.
Please download our Applications Notes for more details.
Are SLEDs temperature sensitive?
Can EXALOS SLEDs be modulated? What is the maximum modulation frequency?
When the SLED is used on the EXALOS driver boards, the modulation frequency is limited to 50 Hz as these driver boards have been optimized for lowest-noise performance. Higher modulation frequencies may be realized upon request.
Does the Monitor Photo Diode (MPD) current depend on the reverse bias voltage?
Unless specified otherwise in the datasheet of the particular SLED, EXALOS recommends a reverse voltage of -1 V to -5 V to ensure that the photodetector is not driven into saturation and is providing a rather linear relationship between optical output power and MPD current.
What is spectral ripple?
For example in spectral-domain OCT, spectral ripple and related secondary coherence peaks can generate horizontal lines in the OCT image.
EXALOS SLEDs exhibit a low amount of spectral ripple due to an advanced chip design. Even at high power levels, the spectral ripple is typically less than 0.1 dB, corresponding to a secondary peak suppression of around 35 dB.
What is the coherence length of an SLED?
For OCT applications it is common to describe the imaging performance of the system by plotting the point spread function (PSF) of the electrical power signal as a function of OPD (or imaging depth). Here, the coherence length is equivalent to the 6-dB drop of the PSF amplitude (on a 20-log vertical scale) from the maximum.
The coherence length is proportional to the square of the center wavelength of the SLED and inversely proportional to the width of the optical ASE spectrum. The coherence length also depends on the shape of the ASE spectrum. For example, a 840-nm SLED having a flat-top ASE spectrum with a FWHM of 50 nm has a coherence length of 7.4 microns (in air), while a 650-nm SLED with a Gaussian ASE spectrum and a FWHM of 10 nm has a coherence length of 18.6 microns.
At twice the center wavelength (1300 nm), a 4-times broader spectrum (40 nm FWHM) is required to achieve the same coherence length.
What is the lifetime of EXALOS products?
All our SLEDs offer excellent reliability and fully comply with the Telcordia GR-468 or other MIL standards.
Typical tests that are carried out include verification of mechanical integrity and bond strength, temperature cycling, robustness against electro-static discharge (ESD) and hermiticity of sealed modules.
Why is the ripple high in the 1400nm range?
However, these dips are typically not residual reflections from the SLED module but are absorption lines of OH molecules that are present in the optical beam path, for example the water vapor in the air when working with free-space beam optics.
Even fiber-coupled SLED modules may show such absorption lines when the spectrum is measured with an optical spectrum analyzer (OSA) that is operated in standard air. Reducing the humidity level of the ambient air or operating the OSA in dry air or nitrogen will remove those absorption lines.