Superluminescent Diodes for OCT


Superluminescent Diode (SLD) Light Source for OCT Systems

  • 1325nm SLD, Bandwidth > 100 nm
  • Fiber-Coupled Power > 10 mW
  • SM Fiber Pigtail with FC/APC Connector
  • Integrated Optocal Isolator, Thermistor, and TEC Element

SLDs are the light source of choice in Spectral Domain Optical Coherence Tomography (SD-OCT) imaging because the emission spectrum is broad and the emitted light has a short coherence length. In addition to SLD1325, Thorlabs offers an extended broadband SLD light source for OCT applications.


  • Integrated Optical Isolator for Enhanced Output Stability
  • FC/APC Terminated Fiber Pigtail Minimizes Optical Feedback
  • Integrated TEC and Thermistor for Temperature Control
  • Hermetically Sealed 14-Pin Butterfly Package

When the limits on current, temperature, and output power are adhered to, the lifetime of the SLD1325 will exceed 5000 hours. We strongly recommend adherence to the operating conditions marked on each package. While optimal performance is achieved by utilizing the recommended settings, we recognize users can adjust the spectral characteristics of the SLD by deviating from these recommended settings. For instance, operating at lower temperatures will cause a shift of the central wavelength to shorter wavelengths. It is imperative, however, that as the temperature is reduced, the injection current is also reduced so as not to exceed the recommended output power as noted on the package.

Operation and Warranty

The SLD should be operated in a constant current constant temperature mode, which is relatively simple with the proper SLD mount and drivers. Thorlabs recommends the following equipment for use with the SLD1325:

  • LM14S2 – Butterfly Laser Diode Mount (see SLD Mount tab)
  • ITC4001 – Combination Laser Diode and TEC Controller (see SLD Driver tab)

When purchased alone, the SLD1325 comes with a standard 1 year warranty. If purchased with the LM14S2 Butterfly Mount and ITC4001 Combination Laser Diode and TEC Controller, Thorlabs provides a 2 year warranty for the SLD1325.


SLD Specifications

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. All devices will exceed the bandwidth and power specifications listed below.

Item #SLD1325
Central Wavelength 1325 nm
Bandwidth (FWHM) >100 nm
Fiber-Coupled Power > 10 mW
Maximum SLD Injection Current 780 mA
Maximum Voltage 4 V
Operating Temperature Range 0 - 40 °C

Additional Specifications

Item #SLD1325
Isolation of Integrated Isolator >30 dB
Fiber Pigtail SMF-28e+
Fiber Length ~1 m
Fiber Connector FC/APC
Return Loss of FC/APC Connector >50 dB
Max Thermoelectric Cooler Current 4 A
Max Thermoelectric Cooler Voltage 4 V
Thermistor Resistancea 10 kΩ
  • Steinhart - Hart Coefficients: C1 = 1.1291x10-3,
    C2 = 2.3413x10-4, and C3 = 0.8767x10-7

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.


SLD Mount


  • Laser Diode Mount for 14-pin Butterfly Package
  • ZIF Mounting Socket
  • Laser Enabled LED Indicator
  • User Defined Pin Out Configuration

The LM14S2 is designed to for use with all lasers and two-port electro-optic devices in a 14-pin butterfly package. The top surface has heat sink fins and a recessed region to mount the laser diode, resulting in a low profile package. The LM14S2 also includes a laser diode TEC Lockout feature* that disables the laser when the TEC Controller is not active. The LM14S2 supports maximum laser and TEC current of 5 A each. The mount supports thermoelectric cooling, however the Thermal Electric Cooler (TEC) and/or Thermistor sensor has to be integrated into the optoelectronic device. This mount also features a Zero Insertion Force (ZIF) socket, a remote safety interlock connection, and an LED to indicate that the laser diode is enabled.



Item #LM14S2
Maximum Current 5 A
Polarity of Optoelectronic Device AG
Polarity of Monitor Diode Floating
Maximum TEC Current 5 A
Temperature Sensor Thermistora
Temperature Rangeb 0 to 70 °C
Temperature Coefficient of Heat Sink 3 °C/W
Dimensions 3.5" x 3.5" x1.25"
  • Integrated into the optoelectronic packag
  • Depends on the optoelectronic package being used


The LM14S2 eliminates the restriction of fixed pin configuration mounts by using swapable configuration cards that plug into a connector located on the bottom of the mount. Two cards are included with the LM14S2. One card is pre-configured for both Type 1 and Type 2 lasers, see the Specs tab for definitions of these types. The second card is a user configurable card (LM14S2-UA) designed to allow custom wiring of the mount. Additional cards are available and can be ordered separately.

In addition to the configurable pin out feature, a Bias-T adapter is included, allowing for RF modulation of butterfly lasers specifically designed with this capability.

The LM14S2 is pin for pin compatible with all Thorlabs' benchtop laser diode and TEC controllers, and most of our platform laser and TEC controllers as well, eliminating the need for custom made interface cables.


SLD Driver


  • Combination Controller: Low Noise SLD or LD Driver and High Stability Temperature Controller
  • Internal Function Generator for Analog Modulation
  • External Modulation Input
  • Analog Monitor Output for the Laser Current
  • Reliable Protection for Optoelectronic Devices
  • Power Efficient by Active Power Management
  • Operates With All Polarities of SLD, Laser Diode, and Photodiode

The ITC4001 Diode Current and TEC Controller provides current and temperature control in one unit. It has been designed to provide a precise, stable current for laser diodes with injection currents of 1 A up to 20 A and an excellent temperature stabilization of 0.002 °C within 24 hrs. Many enhanced features, like the Quasi-Continuous Wave (QCW) operation mode, easy auto PID setting, and diverse laser diode and TEC element protection, together with a new design, make the ITC4000 series an ideal choice for most applications.

Intuitive User Interface
The ITC4001 device is controlled via front panel keys and intuitive operation menus on a large and easy-to-read graphic LCD display (Please see the ITC4001 Display Screens tab for sample screens) Additionally, the ITC4001 can be controlled by a SCPI compatible USB Interface. A higher setting and measurement resolution is offered via remote control operation, since the front panel resolution is limited by the resolution of the display.


SLDs or laser diodes can be driven in constant current (CC) or constant power (CP) mode with this driver (the recommended mode for an SLD is constant current). All pin configuration types are supported. The SLD or laser diode is always driven with respect to ground. In comparison to driver designs that require a floating ground, this grounded operation of the SLD or laser diode offers advantages regarding noise, transient suppression, and stability.

Constant Current
In CC mode, the current to the SLD or laser is held precisely at the prescribed level. This mode is used when the lowest noise and highest response speed is required. Most applications in this mode require the temperature of the SLD or laser to be stabilized.

Constant Power
In CP mode, the internal photodiode integrated into most laser diode packages is used to actively stabilize the laser's output power, which is adjusted by a feedback circuit. An adjustment of the full scale photodiode current in CP mode is provided in order to compensate for the differences in the photodiode currents between different laser diodes.

Safety Features

  • Interlock
  • Laser Current Limit
  • Soft Start
  • Short Circuit when Laser Off
  • Open Circuit Detection
  • Temperature Window Protection
  • TEC Current Limit
  • Short Circuit when TEC Off
  • No Sensor Protection
  • Over Temperature Protection

Current Limit
A precisely adjustable current limit ensures that the maximum laser current cannot be exceeded. Thorlabs has intentionally provided limited access to this feature to prevent accidental adjustment. An attempt to increase the laser drive current above the pre-set limit will result in a visible and short audible indicator. Even when utilizing the external modulation feature, the current limit set-point cannot be exceeded.

Current Source
If the connection between the current source and laser diode is interrupted, the current source automatically switches off the current output. The open current circuit condition is indicated by the LED "OPEN" and a short acoustic warning. The separate laser ON key switches the laser current on and off. When switched off, an electronic switch within the LDC200C short circuits the laser diode for added protection. After being switched on, a soft start ensures a slow increase of the laser current without voltage peaks. Even in the case of line failure, the laser current remains transient-free. Voltage peaks on the AC line are effectively suppressed by electrical filters, shielding of the transformer, and careful grounding of the chassis.


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