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Superluminescent Diode (SLD) Light Sources for OCT Systems
1325 nm SLD, >100 nm Bandwidth
An Image of the Anterior of the Eye Taken with the SLD830S-A10 in a Modified Ganymede ll OCT System
830 nm SLD, Gain Ripple ≤0.15 dB
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The SLD1325 Superluminescent Diode Mounted in a CLD1015 Compact Laser Diode Driver with TEC
Superluminescent Diodes (SLDs) are the light source of choice in Spectral Domain Optical Coherence Tomography (SD-OCT) imaging. The broad spectrum and short coherence length of the emitted light improves the depth resolution in OCT images. Thorlabs offers SLDs designed for OCT applications with center wavelengths of 830 nm or 1325 nm. Each SLD is shipped with an individualized product data sheet, which includes information on the spectrum and operating parameters of the device. Raw test data for each SLD is also available upon request; please contact Tech Support with inquiries.
Thorlabs' 830 nm SLDs have a center wavelength of 830 nm, a typical 3 dB bandwidth of 20 nm, near-Gaussian spectrum, and extremely low gain ripple, which are important features for producing high-quality OCT images at this wavelength. Two versions are available; the SLD830S-A10 has a typical fiber-coupled power output of 13 mW, while the SLD830S-A20 has a typical fiber-coupled power output of 22 mW. The ripple is guaranteed to be no larger than 0.15 dB (RMS), with a typical value of 0.03 dB.
The SLD1325 has a center wavelength of 1325 nm. It was designed with a broad bandwidth of >100 nm, which supports improved depth resolution in SD-OCT systems. For additional information about the relationship between the OCT system resolution and SLD bandwidth, see the Resolution SD-OCT tab. This SLD is packaged with an integrated TEC and thermistor for temperature control, as well as an optical isolator for enhanced optical stability.
Thorlabs is able to provide low-ripple SLDs with custom wavelengths or higher power diodes. Please note that the engineering design and wafer manufacturing costs involved make the purchase of low quantities very costly. For a quote on custom SLDs, please contact Tech Support.
These SLDs should be operated in a constant current, constant temperature mode, which is relatively simple with the proper SLD mount and drivers. To mount and drive these SLDs, Thorlabs recommends using the CLD1015 Compact Laser Diode Driver.
As with most active semiconductor devices, standard anti-static handling procedures must be adhered to in order to prevent an electrical discharge that could destroy the device.
In addition to the butterfly-packaged SLDs available below, Thorlabs offers an extended broadband SLD light source for OCT applications.
Note, these specifications are given as guidelines. The characterization sheet shipped with each SLD provides the min, max, and recommended operating parameters and specifications specific to that device. The ASE Power specification is the output from the fiber pigtail.
Center Wavelength Calculation
The center wavelength for these SLDs is determined by taking the weighted average of the intensity profile. For a given Optical Spectrum Analyzer (OSA) trace:
Theoretical axial resolution for a Spectral Domain OCT System utilizing a 1325 nm light source with 100 nm bandwidth in air, assuming an ideal source with Gaussian spectral distribution.
The theoretical axial (depth) resolution of a Spectral Domain OCT imaging system is
Here, Δz, is the axial resolution (FWHM of the autocorrelation function) while Δλ is the FWHM of the power spectrum of the SLD light source. The index of refraction (n) of air is ~1, so for a central wavelength (λ) of 1325 nm and a spectral bandwidth of 100 nm, the theoretical axial resolution would be approximately 7.7 µm (see plot). This equation assumes an ideal source with Gaussian spectral distribution. To reduce side-lobe artifacts that may arise from utilizing non-Gaussian sources, we recommend applying a spectral filter to the detected interferogram. Depending on the filter applied, the actual resolution may be reduced.
For applications that require higher resolutions than can be obtained with a single SLD, it is possible to combine a pair of SLDs with different central wavelengths to produce a light source with an extended spectral range. For more information on these types of light sources, please see our Extended Broadband Source.
Butterfly Package, Type 1
These superluminescent laser diodes are designed to be used in OCT Systems that require an illumination source with extremely low typical gain ripple of 0.03 dB (RMS) and a relatively flat spectrum over a 20 nm wide 3 dB bandwidth. They are available with a typical fiber-coupled output power of 13 mW or 22 mW.
The specifications in the table below are typical. Each SLD is shipped with an individualized data sheet that includes dominant wavelength, output power, operating current, and other information specific to that device.
Images of (a) the lens, (b) the anterior, and (c) the retina of the eye obtained using a Ganymede II SD-OCT System modified to integrate an SLD830S-A10 as a light source. The images each have an in-tissue depth of 6.2 mm and were taken using a 36 kHz A-scan rate.
The SLD1325, with a typical center wavelength of 1325 nm, is designed to have an extremely broad bandwidth of >100 nm (FWHM), making it ideal for high-axial-resolution SD-OCT applications (see the Resolution SD-OCT tab above for more information). This SLD is packaged with an integrated TEC and thermistor for temperature control, as well as an optical isolator for enhanced optical stability. In addition to the SLD1325 sold here, Thorlabs offers an extended broadband SLD light source for OCT applications.
The SLD should be operated in a constant current constant temperature mode, which is relatively simple with the proper SLD mount and drivers. To mount and drive the SLD1325, Thorlabs recommends using the CLD1015 Compact Laser Diode Driver.
Note that the specifications in the table to the right are given as guidelines. The characterization sheet shipped with each SLD provides the min, max and recommended operating parameters and specifications specific to that device. All devices will exceed the bandwidth and power specifications listed below.