High-Power Fiber-Coupled Laser Sources: NIR, with TEC


2000 nm, 15 mW

  • FC/PC or FC/APC Interface for Single Mode Fiber
  • High Current TEC for Temperature Regulation and Stability
  • Software Interface for Computer Control


1310 nm, 50 mW

Related Items

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Single Channel Benchtop Laser Sources Selection Guide
Spectrum Wavelength TEC Laser Type Cavity Type Output Fiber Type
Visible 405 - 675 nm No Semiconductor Fabry Perot SM, MM, or PM
405 - 685 nm Yes Semiconductor Fabry Perot SM
NIR 785 - 1550 nm No Semiconductor Fabry Perot SM or PM
705 - 2000 nm Yes Semiconductor Fabry Perot SM
1310 - 1550 nm Yes Semiconductor DFB SM
1900 - 2000 nm N/A Fiber Laser Fabry Perot SM
MIR 2.7 µm N/A Fiber Laser Fabry Perot SM
Other Fiber-Coupled Laser Sources
Stability Comparison Graph
Click to Enlarge

An illustration of the difference in the intensity noise floor between our standard FP laser sources with TEC (Item # S3FC520 shown) and our high-power FP laser sources with TEC (Item # S4FC660 shown). The noise signal from the S4FC660 shows a considerable reduction in the peak-to-peak noise amplitude, as well as suppression of high frequency components that are seen in the noise signal of the S3FC520. The S3FC520 plot is vertically offset in order to better compare the two signals. Note that the curves shown are without mode-hopping, which will occur despite temperature or current adjustment.


  • NIR Wavelengths Available from 705 to 2000 nm
  • Single Mode, FC/PC or FC/APC Fiber Interface
  • Typical Maximum Output Powers up to 100 mW
  • High-Current TEC for Temperature Regulation and Stability
  • BNC Connector for Modulating Output with Analog Input
  • USB Connector for Computer Control via Included GUI or Command Line
  • Power Level is Adjustable via Knob and BNC Modulation Input
  • Constant Current Operation
  • Interlock Circuit Provided via 2.5 mm Mono Jack

Thorlabs' NIR High-Power Fiber-Coupled Laser Sources are high-performance benchtop Fabry-Perot laser diode sources with TEC, which offer excellent stability and computer control. The internal electronics isolate the laser diode driver from noise coupling (such as that produced by nearby switching supplies). As a result, these high-power FP laser sources with TEC offer lower noise intensity compared to our standard FP sources with TEC (see graph to the right). The integrated, high-current TEC element can provide excellent temperature regulation and stability to the laser diode, as illustrated in the graphs on the Temp. Stability tab. Even when the ambient temperature changes significantly, the temperature control servo is capable of maintaining constant temperature at the laser diode head. This exceptional temperature stability produces a constant and stable power output from the device.

High-Power Laser Source
Click to Enlarge

An example of the S4FC series software GUI. Both the S4FC series and S6FC2000 high-power laser sources include software packages. See the Software tab above for details. 

For both the S4FC series and S6FC2000 laser sources, the laser diode is pigtailed to a single mode fiber. In the S4FC series sources, the fiber is terminated at an FC/PC bulkhead connector (wide and narrow key compatible). In the S6FC2000 source, the fiber is terminated at an FC/APC fiber connector (wide and narrow key compatible). The S6FC2000 features an angled fiber ferrule at the internal laser/fiber launch point to minimize reflections back into the laser diode, thereby increasing the stability of the laser diode's output. To minimize losses, we recommend using a fiber patch cable that is the same fiber type as the fiber-pigtailed laser.

These laser sources operate via constant current. The power is displayed on the S4FC sources, whereas the current is displayed on the S6FC2000 source. Also on the display panel is the temperature in °C, an on/off key, an enable button, a knob to adjust either the laser power (S4FC series) or the laser current (S6FC2000), and a trimpot to adjust the temperature (TEC current).

The back panel includes a BNC input that allows the laser diode drive current to be controlled via an external voltage source (0 - 5 V) and a remote interlock input. This input enables intensity modulation of the laser source. Using a sine wave, the output can obtain full-depth modulation at frequencies up to 100 kHz. A USB connector on the back panel enables computer communication. The included GUI provides control and readout of the laser's output power and setpoints (see Software tab). The back panel also features a remote interlock input (2.5 mm mono jack) for added safety.

Note that the fiber bulkhead and patch cable ferrule must be cleaned prior to connecting a patch cable. For instructions, please refer to the operating manual. The laser must be off when connecting or disconnecting fibers from the device, particularly for power levels above 10 mW. For applications that require several laser sources, consider the temperature-stabilized four-channel fiber coupled laser source.

Common Specifications
Display Accuracy ±5% of Actual
S4FC Series
Laser Adjustment
Default Laser Threshold to Max
Option 0 mA Current to Max
Laser Adjustment
Default Laser Threshold to Max or Min
Option 0 mA Current to Max or
Jumps to Min
Laser Adjustment Resolutiona S4FC Series: 0.01 mW
S6FC2000: 0.1 mA 
Temperature Adjustment Range 20 °C to 30 °C
Temperature Setpoint Resolution 0.01 °C
Modulation Inputb 0 to 5 V (0 to Full Power)
Modulation Input Impedance 1 kΩ
Modulation Input Connectorc BNC
Modulation Bandwidthd ≤100 kHz, Sine Wave
Output Fiber Connector FC/PC or FC/APCe,
2.2 mm Wide-Key Slot
Operating Temperature 15 to 35 °C
Storage Temperature 0 to 50 °C
Input Power 85 - 264 VAC; 50 - 60 Hz
USB Connectorc Type B
  • While Laser is Enabled
  • Modulation Input voltage directly corresponds to output power, where 5 V = Max Power and 0 V = 0 mW when the front panel knob is set to 0 mW. The maximum voltage will be less than 5 V when using the default laser adjustment range (Laser Threshold to Max).
  • The maximum USB and BNC cable length is 3 meters in order to avoid a susceptibility to RF interference according to IEC61000-4-3.
  • Waveforms other than sine waves contain components with higher frequency than the overall frequency of the waveform, which may not be followed.
  • Only the S6FC2000 is offered with an FC/APC connector.
Laser Source and Fiber Specifications
Item # Wavelength Internal Fiber Spectruma
(Click for
Output Powerb
Laser Power
Min Typical 15 min 24 hr
S4FC705d 705 ± 10 nm SM600 3B 13 mW 15 mW ≤0.022 dB
≤0.087 dB
S4FC785d 785 ± 10 nm 780HP 3B 98 mW 100 mW ≤0.022 dB
≤0.087 dB
S4FC808d 808 ± 10 nm SM800-5.6-125 3B 28 mW 30 mW ≤0.087 dB
≤0.087 dB
S4FC820d 820 ± 10 nm 3B 78 mW 80 mW ≤0.022 dB
≤0.150 dB
S4FC852d 852 ± 10 nm 3B 28 mW 30 mW ≤0.022 dB
≤0.065 dB
S4FC915d 915 ± 10 nm 3B 38 mW 40 mW ≤0.013 dB
≤0.022 dB
S4FC940d 940 ± 10 nm 3B 28 mW 30 mW ≤0.022 dB
≤0.087 dB
S4FC1064d 1064 ± 10 nm HI1060 3B 48 mW 50 mW ≤0.087 dB
≤0.132 dB
S4FC1310 1310 ± 20 nm SMF-28 Ultra 3R 48 mW 50 mW ≤0.004 dB
≤0.009 dB
S4FC1550 1550 ± 20 nm 3B 48 mW 50 mW ≤0.004 dB
≤0.009 dB
S6FC2000d 2000 ± 20 nm SM2000 1M 10 mW 15 mW ≤0.043 dB
≤0.087 dB
  • Spectral plots are typical and actual spectra may vary from lot to lot. Measurements were obtained with an optical spectrum analyzer. For further information, please contact Tech Support.
  • Specified at Temperature Set Point of 25 °C
  • At 75% of maximum output power. The stability spec was obtained after a 1 hour warm-up period.
  • This laser source may experience mode-hopping that cannot be tuned out with temperature or current adjustment. Therefore, power stability should be interpreted as the maximum power drift over that period.

The stability data below was obtained using an S4FC660 Laser Source. The performance is representative of both our S4FC sources and our S6FC2000 source.

Power Stability
Click to Enlarge

A demonstration of the long-term stability of the S4FC660 Laser source, shown over the course of 25 hours. The device is capable of maintaining a constant laser diode temperature, and thus constant output power, over long periods of operation. To obtain the detector signal, the S4FC660 output power was set to 75% of maximum and passed through ND filters reducing the power to 1 mW. The resultant beam was directed into a DET100A (previous generation) detector which was then connected to an oscilloscope via a T-adapter and high-impedance terminator.
Temperature Regulation
Click to Enlarge

The graph above demonstrates the ability of the S4FC660 to maintain steady temperature regulation even with large changes in the environmental temperature. Even when the environment changes by 20 °C, the S4FC660 is able to maintain a steady and regulated temperature of the laser diode, yielding a consistent power output. To obtain the detector signal, the S4FC660 output power was set to 75% of maximum and passed through ND filters reducing the power to 1 mW. The resultant beam was directed into a DET100A (previous generation) detector which was then connected to an oscilloscope via a T-adapter and high-impedance terminator.

Modulation In

BNC Female

BNC Female

0 to 5 V Max, 1 kΩ

Remote Interlock Input

2.5 mm Mono Phono Jack


2.5 mm Phono Jack

Terminals must be shorted either by included plug or user device, i.e. external switch, for laser mode "ON" to be enabled.


USB Type B

USB Type B

Computer Interface

S4FC Software Package

Version 2.0.1

Includes a GUI for control of Thorlabs S4FC Benchtop Laser Sources. To download, click the button below.

Software Download

S6FC Software Package

Version 1.1.0

Includes a GUI for control of Thorlabs S6FC2000 Benchtop Laser Source. To download, click the button below.

Software Download

GUI Interface
Each software package allows the user to control the settings and the display features of the benchtop laser source. The Options window in the S4FC software and the Settings tab in the S6FC software include several helpful features for controlling the device, including setting an output limit, starting the device from the last setting (instead of at 0 mW or threshold power), adjusting the device by current, dimming the display intensity, or enabling the temperature LED to blink when the device is not at its temperature setpoint (making it visually easier to observe when the laser is not at thermal equilibrium).

The controls tab can be used to select the temperature setpoint, interlock status, and to enable the laser's output. In the S4FC software, the power of the device can be adjusted and will be displayed when the enable button is activated. In the S6FC2000 software, the current of the device can be adjusted and will be displayed when the enable button is activated.

Click to Enlarge
The control panel of the software when the laser source is connected. An example of the S4FC series GUI is shown.

Click to Enlarge

The Controls tab of the software when the laser source is connected and the laser not yet enabled. An example of the S6FC2000 GUI is shown.

Laser Safety and Classification

Safe practices and proper usage of safety equipment should be taken into consideration when operating lasers. The eye is susceptible to injury, even from very low levels of laser light. Thorlabs offers a range of laser safety accessories that can be used to reduce the risk of accidents or injuries. Laser emission in the visible and near infrared spectral ranges has the greatest potential for retinal injury, as the cornea and lens are transparent to those wavelengths, and the lens can focus the laser energy onto the retina. 

Laser Glasses Laser Curtains Blackout Materials
Enclosure Systems Laser Viewing Cards Alignment Tools
Shutter and Controllers Laser Safety Signs

Safe Practices and Light Safety Accessories

  • Laser safety eyewear must be worn whenever working with Class 3 or 4 lasers.
  • Regardless of laser class, Thorlabs recommends the use of laser safety eyewear whenever working with laser beams with non-negligible powers, since metallic tools such as screwdrivers can accidentally redirect a beam.
  • Laser goggles designed for specific wavelengths should be clearly available near laser setups to protect the wearer from unintentional laser reflections.
  • Goggles are marked with the wavelength range over which protection is afforded and the minimum optical density within that range.
  • Laser Safety Curtains and Laser Safety Fabric shield other parts of the lab from high energy lasers.
  • Blackout Materials can prevent direct or reflected light from leaving the experimental setup area.
  • Thorlabs' Enclosure Systems can be used to contain optical setups to isolate or minimize laser hazards.
  • A fiber-pigtailed laser should always be turned off before connecting it to or disconnecting it from another fiber, especially when the laser is at power levels above 10 mW.
  • All beams should be terminated at the edge of the table, and laboratory doors should be closed whenever a laser is in use.
  • Do not place laser beams at eye level.
  • Carry out experiments on an optical table such that all laser beams travel horizontally.
  • Remove unnecessary reflective items such as reflective jewelry (e.g., rings, watches, etc.) while working near the beam path.
  • Be aware that lenses and other optical devices may reflect a portion of the incident beam from the front or rear surface.
  • Operate a laser at the minimum power necessary for any operation.
  • If possible, reduce the output power of a laser during alignment procedures.
  • Use beam shutters and filters to reduce the beam power.
  • Post appropriate warning signs or labels near laser setups or rooms.
  • Use a laser sign with a lightbox if operating Class 3R or 4 lasers (i.e., lasers requiring the use of a safety interlock).
  • Do not use Laser Viewing Cards in place of a proper Beam Trap.


Laser Classification

Lasers are categorized into different classes according to their ability to cause eye and other damage. The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic, and related technologies. The IEC document 60825-1 outlines the safety of laser products. A description of each class of laser is given below:

Class Description Warning Label
1 This class of laser is safe under all conditions of normal use, including use with optical instruments for intrabeam viewing. Lasers in this class do not emit radiation at levels that may cause injury during normal operation, and therefore the maximum permissible exposure (MPE) cannot be exceeded. Class 1 lasers can also include enclosed, high-power lasers where exposure to the radiation is not possible without opening or shutting down the laser.  Class 1
1M Class 1M lasers are safe except when used in conjunction with optical components such as telescopes and microscopes. Lasers belonging to this class emit large-diameter or divergent beams, and the MPE cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. However, if the beam is refocused, the hazard may be increased and the class may be changed accordingly.  Class 1M
2 Class 2 lasers, which are limited to 1 mW of visible continuous-wave radiation, are safe because the blink reflex will limit the exposure in the eye to 0.25 seconds. This category only applies to visible radiation (400 - 700 nm).  Class 2
2M Because of the blink reflex, this class of laser is classified as safe as long as the beam is not viewed through optical instruments. This laser class also applies to larger-diameter or diverging laser beams.  Class 2M
3R Class 3R lasers produce visible and invisible light that is hazardous under direct and specular-reflection viewing conditions. Eye injuries may occur if you directly view the beam, especially when using optical instruments. Lasers in this class are considered safe as long as they are handled with restricted beam viewing. The MPE can be exceeded with this class of laser; however, this presents a low risk level to injury. Visible, continuous-wave lasers in this class are limited to 5 mW of output power.  Class 3R
3B Class 3B lasers are hazardous to the eye if exposed directly. Diffuse reflections are usually not harmful, but may be when using higher-power Class 3B lasers. Safe handling of devices in this class includes wearing protective eyewear where direct viewing of the laser beam may occur. Lasers of this class must be equipped with a key switch and a safety interlock; moreover, laser safety signs should be used, such that the laser cannot be used without the safety light turning on. Laser products with power output near the upper range of Class 3B may also cause skin burns.  Class 3B
4 This class of laser may cause damage to the skin, and also to the eye, even from the viewing of diffuse reflections. These hazards may also apply to indirect or non-specular reflections of the beam, even from apparently matte surfaces. Great care must be taken when handling these lasers. They also represent a fire risk, because they may ignite combustible material. Class 4 lasers must be equipped with a key switch and a safety interlock.  Class 4
All class 2 lasers (and higher) must display, in addition to the corresponding sign above, this triangular warning sign.  Warning Symbol

Posted Comments:
user  (posted 2023-11-29 04:31:26.86)
Your collimation overview states: "To observe interference fringes, the coherence length of the incident light must be longer than the change in optical path length caused by the shear plate being used. See the Specs tab for the approximate change in optical path length, ΔOPL, for each shear plate offered here. Broadband sources, such as Superluminescent Diodes (SLDs) and LEDs, will not create interference fringes due to their low coherence lengths." But unless I missed it, I can't find the coherence length listed for any of the fiber coupled laser sources. Please help.
ksosnowski  (posted 2023-11-29 02:17:22.0)
Thanks for reaching out to Thorlabs. On the Specs tab you can view the sample spectra for these lasers. The S4FC series uses fabry-perot emitters. These spectra are not Lorentzian, but rather a set of discrete narrow peaks corresponding to the cavity modes. When you look at the interferogram of such a laser, you would see beating effects between the modes, which makes it not-so-straightforward to determine its coherence length. Due to this, the typical coherence is much shorter than expected if taking a rough estimate of the spectral width from our plots. A laser with external cavity like DFB or VHG will have a much narrower spectrum and better coherence.
Filip Milojkovic  (posted 2022-10-27 16:01:34.283)
Hi does S4FC852 have an integrated optical isolator? I can't see it in the specifications. Thanks in advance
ksosnowski  (posted 2022-10-27 04:51:53.0)
Thanks for reaching out to Thorlabs. The S4FC series do not include an internal isolator on the output port.
Tahseen Kamal  (posted 2019-12-03 10:39:49.89)
Hi, I encountered some issues while trying to use the GUI. As there is minimal instructions on the software, I am unsure how to handle them. If you could help would be great. 1. I tried using my Dell laptop which has Windows 10 pro installed. The software kept crashing. 2. Then I used another PC with windows 7 and the GUI worked. But there was communication delays I guess. It happened that I changed the power quickly and then the device went to lock mode despite the GUI showing the Lock was "off". 3. Also, when I changed the power and the beam looked brighter on the card, the GUI was showing 0 mW as power on the top right display. Hope to get some support on this. Thanks.
asundararaj  (posted 2019-12-05 01:57:24.0)
Thank you for contacting Thorlabs. I have reached out to you directly to troubleshoot this further.
Ben Garber  (posted 2019-05-22 13:31:58.193)
If there's a specific intermediate wavelength we need (e.g. 813nm), can you provide a laser of one of the existing models that can provide that?
YLohia  (posted 2019-05-23 08:32:10.0)
Hello, thank you for contacting Thorlabs. Custom items can be requested by clicking the "Request Quote" button above. I have reached out to you directly to discuss the possibility of offering this.
user  (posted 2018-11-02 11:13:13.69)
Sorry, can you tell me the noise current of the source:S4FC785?
YLohia  (posted 2018-11-05 09:43:29.0)
Hello, thank you for contacting Thorlabs. The noise current measurement for the S4FC785 is 7.92 uA.
user  (posted 2018-10-30 12:25:02.19)
What is the 'a.u.' in the diagram Noise Comparison meaning?
mmcclure  (posted 2018-10-30 09:12:56.0)
Hello, thank you for your inquiry. "a.u." is an abbreviation of "arbitrary units".
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NIR High-Power Fiber-Coupled Laser Sources

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
S4FC705 Support Documentation
S4FC705Fabry-Perot Benchtop Laser Source, 705 nm, 15 mW, FC/PC
S4FC785 Support Documentation
S4FC785Fabry-Perot Benchtop Laser Source, 785 nm, 100 mW, FC/PC
S4FC808 Support Documentation
S4FC808Fabry-Perot Benchtop Laser Source, 808 nm, 30 mW, FC/PC
Lead Time
S4FC820 Support Documentation
S4FC820Fabry-Perot Benchtop Laser Source, 820 nm, 80 mW, FC/PC
S4FC852 Support Documentation
S4FC852Fabry-Perot Benchtop Laser Source, 852 nm, 30 mW, FC/PC
7-10 Days
S4FC915 Support Documentation
S4FC915Fabry-Perot Benchtop Laser Source, 915 nm, 40 mW, FC/PC
S4FC940 Support Documentation
S4FC940Fabry-Perot Benchtop Laser Source, 940 nm, 30 mW, FC/PC
Lead Time
S4FC1064 Support Documentation
S4FC1064Fabry-Perot Benchtop Laser Source, 1064 nm, 50 mW, FC/PC
S4FC1310 Support Documentation
S4FC1310Fabry-Perot Benchtop Laser Source, 1310 nm, 50 mW, FC/PC
S4FC1550 Support Documentation
S4FC1550Fabry-Perot Benchtop Laser Source, 1550 nm, 50 mW, FC/PC
S6FC2000 Support Documentation
S6FC2000Fabry-Perot Benchtop Laser Source, 2000 nm, 15 mW, FC/APC