Broadband 2 µm ASE Source

  • High-Power ASE Source Based on Tm-Doped Fluoride Fiber
  • 50 mW Output Power and 100 nm Spectral Width
  • Single Mode Fiber Output
  • Integrated Output Isolator for Added Stability


The typical power spectral density (PSD) of the ASE1900 has a 100 nm width measured 20 dB below the peak.

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 Custom Options for the ASE1900
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The green curve is the typical PSD of the ASE1900. Custom versions with wavelength-shifted PSDs are also available. The wavelength limits are approximated by the dashed blue and red curves. Contact Tech Support to request a custom version. Please note that there is a lead time for custom versions, and their power and spectral widths will differ from those of the ASE1900, which is available from stock.


  • Turnkey ASE Source Based on Thulium-Doped Fluoride Fiber
  • User-Adjustable Optical Output Power up to 50 mW Maximum (Typical)
  • 1870 nm Nominal Center Wavelength
  • Ideal for Fiber Component Testing in the 2 µm Region
  • Included Drivers Enable Remote Operation via USB Type-B Port on Back Panel
  • Optical Output via 2.0 mm Narrow-Key FC/APC Connector
  • Contact Tech Support to Request Custom Sources with Slightly Red- or Blue-Shifted Spectra

Thorlabs’ ASE1900 is an amplified spontaneous emission (ASE) source operating around 1900 nm that provides turnkey operation and single mode optical fiber output for test and measurement applications. It is based on a Tm-doped fluoride fiber to maximize the ASE, and the optical output has a 50 mW typical maximum power. An integrated isolator minimizes back reflections into the source for additional output power stability. The optical emission has an 1870 nm nominal center wavelength and is unpolarized. The broad spectral width, measured 20 dB below the peak, is 100 nm. Please see the Specs tab for more information. Thorlabs also offers Tm-doped fiber lasers with emission wavelengths at 1900 nm, 1950 nm, and 2000 nm.

There are several advantages to using an ASE source like the ASE1900 instead of a thermal emitter, such as a Globar. These include being able to focus the emission to a diffraction-limited spot, which is important for microscopy, optical coherence tomography (OCT), and other applications. The emission can also be collimated over long distances, which benefits applications that include high-resolution Fourier transform infrared (FTIR) spectroscopy. A few examples of trace gases with absorption lines within the ASE1900's emission band include NO, H2O, NH3, CO2 and HCl.

The electronic platform of the ASE1900 includes an integrated high-precision and low-noise constant current source and thermoelectric-cooler-based temperature control unit. These components are fully controlled by a microcontroller, which also monitors the system for fault conditions. To prevent damage, the microcontroller disables the output if the analog input exceeds the system limits. The current driving the pump laser can be adjusted by the user, which allows the user to change the power of the ASE output. Each ASE1900 is shipped with test data measurements of optical output power as a function of the pump drive current (L-I curve). 

Remote Control
Included drivers permit full remote control of the source by a PC via a USB type B port on the back panel. The drivers can also be downloaded from the Software tab. Please see the manual for information about the command line interface, commands, and syntax.

A remote interlock connector located on the back panel enables users to connect a remotely actuated switch to disable emission from the ASE1900 in the event of an open laboratory door or other unsafe event.

General Specifications
AC Input 100 - 240 VAC, 50 - 60 Hz
Input Power 20 VA (Max)
Fuse Ratings 500 mA
Fuse Type IEC60127-2/III (250 VA, Slow Blow Type "T")
Fuse Size 5 mm x 20 mm
Dimensions (W x H x D) 5.77" x 12.17" x 3.07"
(146.5 mm x 309.1 mm x 77.9 mm)
Weight 1.96 kg (4.32 lbs) Unit Weight
4.13 kg (9.1 lbs) Shipping Weight
Operating Temperature 15 to 35 °C
Storage Temperature 0 to 50 °C
Connections and Controls
Interface Control Optical Encoder with Pushbutton
Enable Select Keypad Switch Enable with LED Indicator
Power On Key Switch
Display LCD, 16x2, Alphanumeric Characters
Input Power Connection IEC Connector
Interlock 2.5 mm Mono Phono Jack
Communications Port USB 2.0 Compatible
Com Connection USB Type B Connector
Required Cable 2 m USB Type A to Type B Cable
(Replacement Item # USB-A-79)
Item # ASE1900
Parameter Min Typical Max
Emission Center Wavelength 1860 nm 1870 nm 1880 nm
Emission Bandwidth (-20 dB) 80 nm 100 nm -
Drive Current - - 450 mA
Output Power at Maximum Drive Current 40 mW 50 mW 70 mW
Polarization Unpolarized
Power Stability (Ambient Temperature ±2 °C) <±1% Over 24 Hours (After 15 minute Warm Up)
Relative Intensity Noise (RMS, 10 Hz - 1 MHz) 0.05% (Typical)
Output Fiber Type SMF-28 Ultra or Equivalent
Output Fiber Mode Field Diameter (Estimated)
11 µm @ 1900 nm
Output Fiber NA 0.14
Output Fiber Connector 2.0 mm Narrow Key FC/APC
ASE1900 Standard Spectrum
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Click for Raw Data
The typical standard PSD of the ASE1900 has a center wavelength of 1870 nm. Contact Tech Support to request a custom unit with a slightly higher or lower center wavelength. 
ASE1900 Stability
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Click for Raw Data
The ASE1900's output power has a typical 1.2% peak-to-peak stability. 
ASE1900 Stability
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Click for Raw Data
Provided with each ASE1900 is a data sheet with a unit-specific output power vs. current (L-I) plot, similar to the example shown above. This plot relates the pump laser diode's driving current, which is user-adjustable, to the optical power of the ASE. 
ASE1900 Front Panel
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Figure 1: ASE1900 Front Panel
Front Panel of the ASE1900
Callout Description
F1 Control Knob
F2 Key-Lock Power Switch
F3 ASE Enable / Disable Button
F4 LED Indicator
F5 Single Mode Fiber Output via FC/APC Connector
F6 LCD with Backlight
 LCD of ASE1900
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Figure 2: Display of the ASE1900

Generation of ASE
The ASE1900's design is based on a fluoride optical fiber doped with thulium (Tm), which is a rare earth element that absorbs light in specific wavelength bands and emits light in other wavelength bands. When a high-power laser diode with an emission wavelength matched to one of thulium's absorption bands is coupled to the input of the Tm-doped fiber, the Tm ions absorb the pump light and then emit light centered at a longer wavelength. The emission wavelength band is on the order of 100 nm wide. If the optically-pumped Tm-doped fiber is placed between two wavelength-selective reflectors, the narrow-band optical feedback they provide induces lasing. The width of the laser emission much narrower than the width of the Tm emission band lasing suppresses ASE from outside of laser's wavelength band. Thorlabs' Tm-doped fiber lasers use this approach. In the case of the ASE1900, an optical isolator is placed at the output end of the fiber. This minimizes back reflections into the source that could induce lasing, and the result is a broad and high-intensity output spectrum. This emission has low temporal coherence, which provides the benefit of reduced speckle when compared with a laser, and high spatial coherence, which allows the beam to be focused down to a diffraction-limited spot.

Connector Cleaning
Optical patch cords used to connect to the front panel of the instrument, shown in Figure 1, should have their end faces cleaned every time a new connection is made. The end faces of the internal fiber connectors can easily be damaged by the use of dirty fiber ends. If damage occurs, the instrument will need to be sent back for repair. Your benchtop source comes with a fiber cleaning card that can be used for cleaning the fiber connector on patch cables. If you require additional connector cleaners, Thorlabs offers the FCC-7020 Fiber Cleaning Cloth Spool. Alternatively, a lint-free cloth moistened with isopropyl alcohol or methanol can be used. Never use acetone. The optical connectors on the front panel may be cleaned using a 2.5 mm bulkhead cleaner such as the FBC250. This allows the user to clean the fiber end-face without removing it from the internal bulkhead adapter.

Enabling Optical Emission from the ASE1900
Enabling optical emission requires proper configuration of the ASE1900's key switch, enable button, and interlock. These components are identified on the Front & Back Panels tab. Turn the key clockwise to power the unit. The enable button must then be pressed to enable the emission. An LED indicator on the front panel allows the user to easily determine the activation state. The LED is extinguished when the unit is not activated. After the enable button is pressed, the LED rapidly blinks in warning during the 3 second delay before the fiber ASE source turns on. When the ASE source is fully enabled, the LED glows a steadily. For added safety, there is an interlock located on the back panel that must be shorted in order for the output to be enabled. An interlock pin is installed at the factory, but the pin can be removed and the interlock port easily used to disable the source in response to opening of lab doors or other unsafe conditions.

Liquid Crystal Display (LCD)
The LCD on the front panel of the ASE1900 is shown in Figure 2. The display is divided in quadrants, with the type of the source (ASE) shown on the top left and the rounded center wavelength shown on the top right. The current driving the pump laser diode is shown on the bottom left and its temperature is on the bottom right.

In viewing mode, the display provides continually updated temperature and current readings. In adjustment mode, the control knob, which is located to the left of the display can be used to change the current and temperature setpoints. There is a timeout on the adjustment mode, which will revert the display back to viewing mode and is intended to prevent accidental adjustment of any of the parameters. Upon timeout, the selected values will be locked in.

Control Knob
The driving current of the pump laser and the temperature setpoint of the thermoelectric cooler can be set by using the control knob on the front panel of the ASE1900. The control knob utilizes an intelligent speed control to enable both fine and coarse adjustments to parameter values. Rotating the knob slowly will increment values at the maximum resolution. To increase the step size used to increment the value, rotate the knob more quickly.

Adjusting the Pump Laser's Current (to Change the Output Power of the ASE)
Before adjusting the current, please refer to the L-I plot on the data sheet that is provided with the ASE1900. These data describe how the ASE output power scales with the current driving the pump laser.

To adjust the current, first press the control knob once. The current value in bottom left location of the display will start blinking. Adjust the control knob until the desired current value is shown. The current cannot be adjusted beyond an upper limit that is programmed at the factory. Press the knob again to enter the temperature-adjustment mode, or press the knob twice to return the display to viewing mode. The current display updates in real-time as it adjusts to its new current setting. On system shut down, the selected current setting is remembered.

Adjusting the Pump Laser's Temperature
Please note that the default temperature setpoint programmed at the factory ensures optimal operation of the ASE source and maximizes the optical output power. This default setpoint value is included in the test data sheet that is provided with the ASE1900. Changing the pump laser diode’s temperature from this optimal value can significantly reduce the output power below its specified value.

To adjust the temperature, if the display is in the viewing mode, press the control knob twice. If the display is in the current-adjustment mode, press the control knob once. The temperature setpoint will be shown blinking in the bottom-right corner of the display. Rotate the control knob to increase or decrease the temperature setpoint over a range of 20.00 °C to 30.00 °C with a resolution of 0.01 °C. After the desired temperature is selected, press the knob once to return the display to viewing mode. The system will quickly settle into the new operating temperature, typically after less than a minute.

Standby Mode
In standby mode, the ASE source is still enabled and operates with the minimum possible laser diode drive current. As the system utilizes a constant-current control, there will always be a minimum current to maintain the current control loop. The output optical emission is typically very low, or nonexistent.

To enter standby mode, press the knob once to enter the display’s current-adjustment mode from viewing mode. Rotate the knob fully counterclockwise until the pump laser’s driver current setpoint is reduced to its minimum value. Press the knob twice to enter display mode, or wait for the timeout to return the display to viewing mode.

ASE1900 Front Panel
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ASE1900 Front Panel
ASE1900 Back Panel
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ASE1900 Back Panel
Front Panel of the ASE1900
Callout Description
F1a Control Knob
F2b Key-Lock Power Switch
F3 ASE Enable / Disable Button
F4c LED Indicator
F5 Single Mode Fiber Output via FC/APC Connector
F6 LCD with Backlight
  • Control knob and LCD are used to select, then adjust the driving current and thermoelectric cooler setpoint of the pump laser diode. Please note that the changing the default temperature setpoint, which has been optimized and programmed at the factory, can significantly reduce the power of the ASE below its specified value.
  • To remove key, first rotate it to position 0.
  • Blinks for 3 s as a warning prior to enabling emission and glows steadily when emission is enabled.
Back Panel of the ASE1900
Callout Description
B1a Cooling Fan
B2 USB Type B Connector for Remote Control Interface with PC
B3b 2.5 mm Phono Jack for Interlock Input Remote Interlock Interlock Pin
B4 Fuse Tray
B5 AC Power Cord Connector
  • Do not block.
  • A shorting pin is installed at the factory and can be removed and replaced with the user's plug.


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

Drivers for the ASE1900

Version 2.12.18

Includes drivers required to control our ASE1900 ASE source remotely in a command-line Windows® environment.

Software Download


  • Benchtop ASE Source
  • Test Data Sheet
  • USB Memory Stick with Drivers
  • Fiber Connector Cleaning Card
  • FBC250 Connector and Bulkhead Cleaner
  • Two Keys
  • Region-Specific AC Power Cord
  • Operating Manual

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.
  • Thorlabs recommends the use of laser safety eyewear whenever working with laser beams with non-negligible powers (i.e., < Class 2) 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

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ASE1900 Support Documentation
ASE1900Tm-Doped Fiber ASE Source, 50 mW, 1900 nm Band