Optical Spectrum Analyzers
| Key Specificationsa|
|Wavelength Range||350 - 1100 nm||600 - 1700 nm||1000 - 2500 nm|
(10000 - 4000 cm-1)
|1000 - 5600 nm|
(10000 - 1786 cm-1)
|Spectral Resolutionb||7.5 GHz (0.25 cm-1)|
See the Design Tab for Details
|Spectral Accuracy||±2 ppmc|
|Spectral Precision||1 ppmc|
|Wavelength Meter Resolution||0.1 ppmc|
|Wavelength Meter Accuracy||1 ppmc|
|Wavelength Meter Precision||0.2 ppmc|
- Based on a Michelson Interferometer
- View Fourier-Transformed Spectrum or Raw Interferogram in Real Time
- Four Models Available: 350 - 1100 nm, 600 - 1700 nm, 1000 - 2500 nm, and 1000 - 5600 nm
- Spectral Resolution: 7.5 GHz (0.25 cm-1)
- Includes Windows® Laptop with Pre-Installed Software
- Flat, Intuitive Interface with Tooltips for All Functions
- Quickly Perform Math Operations, Apodize, Convert Units, and More
- Routine Libraries for LabVIEW and Common Programming Languages
- Standalone "Virtual Device" Software Demo Available (See the Software Tab)
Thorlabs' Optical Spectrum Analyzers (OSAs) are general-purpose instruments that measure the optical power of a light source as a function of wavelength. Compact, accurate, and precise, these instruments are versatile enough to analyze the spectrum of a broadband telecom signal, resolve the Fabry-Perot modes of a gain chip, or measure the coherence length of a tunable external cavity laser.
Many commonly available OSAs use grating-based monochromators and suffer from slow acquisition times due to the need to mechanically scan the grating and average out noise at each wavelength. Thorlabs' OSAs acquire the spectrum via a Fourier transform, using a scanning Michelson interferometer in a push/pull configuration, as explained in the Design tab and shown in the video below. This approach dramatically improves the acquisition time, provides a full-featured OSA, and enables a high-precision wavelength meter mode with 1 part-per-million accuracy (i.e., 7 significant figures).
Thorlabs' OSAs accept FC/PC-connectorized optical fibers. Single mode and step-index multimode fibers with cores up to Ø50 µm can be used. In addition, the OSA205 can directly accept a collimated free-space input. Special designs with other fiber input receptacles are available upon request. The instruments are designed to measure CW light sources but also work in some applications where a pulsed light source is used. Please contact Technical Support to discuss custom fiber connectors and pulsed light source applications.
To reduce the presence of water absorption lines in the mid-IR region of the spectrum, the OSA203 and OSA205 feature two 1/4" ID quick-connect hose connections on the back panel, through which the interferometer can be purged with dry air or nitrogen. Thorlabs' Pure Air Circulator Unit is ideal for this task.
Introduction to OSA Design Principles, Features, and Manufacturing
|Wavelength Range||Detector Limited||350 - 1100 nm||600 - 1700 nm||1000 - 2500 nm|
(10000 - 4000 cm-1)
|1000 - 5600 nm|
(10000 - 1786 cm-1)
|Spectral Resolution||Broadband Mode||7.5 GHz (0.25 cm-1)|
See the Design Tab Above for Details
|Spectral Accuracya||±2 ppmb|
|Spectral Precisionc||1 ppmb|
|Wavelength Meter Resolution||Wavelength Meter Mode|
(Linewidth < 10 GHz)
|Wavelength Meter Display Resolutiond|| 9 Decimals|
|Wavelength Meter Accuracya||1 ppmb|
|Wavelength Meter Precisione||0.2 ppmb|
|Input Power (Max)||CW Source||10 mW (10 dBm)|
|Input Damage Thresholdf||-||20 mW (13 dBm)|
|Power Level Accuracyg||-||±1 dB|
|Optical Rejection Ratio||See the Design Tab|
Above for Details
|Level Sensitivityh||-60 dBm/nm||-70 dBm/nm||-65 dBm/nm||-40 dBm/nm|
|Input Fiber Compatibility||-||FC/PC Connectorsi|
All Single Mode Fibers, Including Fluoride Single Mode Fibers
Standard and Hybrid Step-Index Multimode Fibers with ≤Ø50 µm Core and NA ≤ 0.22
|Dimensions||-|| 320 mm x 149 mm x 475 mm|
(12.6" x 5.9" x 18.7")
|Input Voltage||-|| 100 - 240 VAC, 47 - 63 Hz, 250 W (Max)|
|Operating Temperature||-|| 10 °C to 40 °C|
|Storage Temperature||-|| -10 °C to 60 °C|
|Relative Humidity||-|| <80%, Non-Condensing|
|Time Between Updates|
|Sensitivity||Low Resolution||High Resolution|
|Low||0.5 s||1.8 s|
|Medium Low||0.8 s||2.9 s|
|Medium High||1.5 s||5.2 s|
|High||2.7 s||9.5 s|
|Sensitivity||Low Resolution||High Resolution|
|Low||1.9 Hz||0.6 Hz|
|Medium Low||1.2 Hz||0.3 Hz|
|Medium High||0.7 Hz||0.2 Hz|
|High||0.4 Hz||0.1 Hz|
|Click to Enlarge
Schematic of the optical path in Thorlabs' OSA, detailing the dual retroreflector design. We will refer to this schematic throughout this tutorial.
Thorlabs' Fourier Transform Optical Spectrum Analyzer (FT-OSA) utilizes two retroreflectors, as shown in the figure to the right. These retroreflectors are mounted on a voice-coil-driven platform, which dynamically changes the optical path length of the two arms of the interferometer simultaneously and in opposite directions. The advantage of this layout is that it changes the optical path difference (OPD) of the interferometer by four times the mechanical movement of the platform. The longer the change in OPD, the finer the spectral detail the FT-OSA can resolve.
After collimating the unknown input, a beamsplitter divides the optical signal into two separate paths. The path length difference between the two paths is varied from 0 to ±40 mm. The collimated light fields then optically interfere as they recombine at the beamsplitter.
The Detector Assembly shown in the figure to the right records the interference pattern, commonly referred to as an interferogram. This interferogram is the autocorrelation waveform of the input optical spectrum. By applying the Fourier Transform to the waveform, the optical spectrum is recovered. The resulting spectrum offers both high resolution and very broad wavelength coverage with a spectral resolution that is related to the optical delay range. The wavelength range is limited by the bandwidth of the detectors and optical coatings. The accuracy of our system is ensured by including a frequency-stabilized (632.991 nm) HeNe reference laser, which acts to provide highly accurate measurements of beam path length changes, allowing the system to continuously self-calibrate. This process ensures accurate optical analysis well beyond what is possible with a grating-based OSA.
Each OSA model has a spectral resolution of 7.5 GHz, or 0.25 cm-1. The resolution in units of wavelength is dependent on the wavelength of light being measured. For more details, see the Resolution and Sensitivity section below. In this context, the Spectral Resolution is defined according to the Rayleigh Criterion and is the minimum separation required between two spectral features in order to resolve them as two separate lines. These spectral resolution numbers should not be confused with the resolution when operating in the Wavelength Meter mode, which is considerably better.
The Thorlabs FT-OSA utilizes a built-in, actively stabilized Reference HeNe laser to interferometrically record the variation of the optical path length. This reference laser is inserted into the interferometer and closely follows the same path traversed by the Unknown Input light field. To reduce the presence of water absorption lines in the mid-IR region of the spectrum, the OSA203 and OSA205 feature two quick-connect hose connections (1/4" ID) on the back panel, through which the interferometer can be purged with dry air or nitrogen. Thorlabs' Pure Air Circulator Unit, which uses hosing that can be directly inserted into these connectors, is ideal for this task.
Interferogram Data Acquisition
The interference pattern of the Reference Laser is used to clock a 16-bit Analog-to-Digital Converter (ADC) such that samples are taken at a fixed, equidistant optical path length interval. The HeNe reference fringe period is digitized and its frequency multiplied by a phase-locked loop (PLL), leading to an extremely fine sampling resolution. Multiple PLL filters enable frequency multiplication settings of 16X, 32X, 64X, or 128X. At the 128X multiplier setting, data points are acquired approximately every 5 nm. The multiple PLL filters enable the user to balance the system parameters of resolution and sensitivity against the acquisition time and refresh rate.
A high-speed USB 2.0 link transfers the interferogram for the device under test at 6 MB/s with a ping-pong transfer scheme, enabling the streaming of very large data sets. Once the data is captured, the OSA software, which is highly optimized to take full advantage of modern multi-core processors, performs a number of calculations to analyze and condition the input waveform in order to obtain the highest possible resolution and signal-to-noise ratio (SNR) at the output of the Fast Fourier Transform (FFT).
A very low noise and low distortion detector amplifier with automatic gain control provides a large dynamic range, allows optimal use of the ADC, and ensures excellent signal-to-noise (SNR) for up to 10 mW of input power. For low-power signals, the system can typically detect less than 100 pW from narrowband sources. The balanced detection architecture enhances the SNR of the system by enabling the Thorlabs FT-OSA to use all of the light that enters the interferometer, while also rejecting common mode noise.
Interferogram Data Processing
The interferograms generated by the instrument vary from 0.5 million to 16 million data points depending on the resolution and sensitivity mode settings employed. The FT-OSA software analyzes the input data and intelligently selects the optimal FFT algorithm from our internal library.
Additional software performance is realized by utilizing an asynchronous, multi-threaded approach to collecting and handling interferogram data through the multitude of processing stages required to yield spectrum information. The software's multi-threaded architecture manages several operational tasks in parallel by actively adapting to the PC's capabilities, thus ensuring maximum processor bandwidth utilization. Each of our FT-OSA instruments ships complete with a laptop computer that has been carefully selected to ensure that both the data processing and user interface operate optimally.
Wavelength Meter Mode
When narrowband optical signals are analyzed, the FT-OSA automatically calculates the center wavelength of the input, which can be displayed in a window just below the main display that presents the overall spectrum. The central wavelength, λ, is calculated by counting interference fringes (periods in the interferogram) from both the input and reference lasers according to the following formula:
Here, mo is the number of fringes for the Reference HeNe laser, m is the number of fringes from the Unknown Input, no is the index of refraction of air at the reference laser wavelength, nλ is the index of refraction of air at the wavelength λ, and λo is the vacuum wavelength of the HeNe reference laser (632.991 nm).
The resolution of the FT-OSA operating as a Wavelength Meter is substantially higher than the system when it operates as a broadband spectrometer because the system can resolve a fraction of a fringe up to the limit set by the phase-locked loop multiplier (see the Interferogram Data Acquisition section above). In practice, the resolution of the system is limited by the bandwidth and structure of the Unknown Input, noise in the detectors, drift in the Reference HeNe, interferometer alignment, and other systematic errors. The system has been found to offer reliable results as low as ±0.1 pm in the visible spectrum and ±0.2 pm in the NIR/IR (see the Specs tab for details).
The software evaluates the spectrum of the unknown input in order to determine an appropriate display resolution. If the data is unreliable, as would be the case for a multiple peak spectrum, the software disables the Wavelength Meter mode so it does not provide misleading results.
Wavelength Calibration and Accuracy
The FT-OSA instruments incorporate a stabilized HeNe reference laser with a vacuum wavelength of 632.991 nm. The use of a stabilized HeNe ensures long-term wavelength accuracy as the dynamics of the stabilized HeNe are well-known and controlled. The instrument is factory-aligned so that the Reference HeNe and Unknown Input beams experience the same optical path length change as the interferometer is scanned. The effect of any residual alignment error on wavelength measurements is less than 0.5 ppm; the input beam pointing accuracy is ensured by a high-precision ceramic receptacle and a robust interferometer cavity design. No optical fibers are used within the scanning interferometer. The wavelength of the Reference HeNe in air is actively calculated for each measurement using the Eldén formula with temperature and pressure data collected by sensors internal to the instrument.
For customers operating in the visible spectrum, the influence of relative humidity (RH) on the refractive index of air can affect the accuracy of the measurements. To compensate for this, the software allows the assumed RH value to be set manually. The effect of the humidity is negligible in the infrared.
|Distance from Peak||Dynamic Range|
|0.2 nm (25 GHz)||30 dB|
|0.4 nm (50 GHz)||30 dB|
|0.8 nm (100 GHz)||30 dB|
|4 nm (500 GHz)||39 dB|
|8 nm (1000 GHz)||43 dB|
The ability to measure low-level signals close to a peak is determined by the optical rejection ratio (ORR) of the instrument. It can be seen as the filter response of the OSA, and be defined as the ratio between the power at a given distance from the peak and the power at the peak.
If the ORR is not higher than the optical signal-to-noise ratio of the source to be tested, the measurement will be limited by the OSA's response, rather than reflecting a true property of the tested source. The table to the right provides some example values for the optical rejection ratio of the OSA203 at 1550 nm with the following settings: High Resolution, Low Sensitivity, Average = 4, Apodization = Hann. All OSA models show similar behavior if the distance from the peak is measured in GHz (units of frequency).
Absolute Power and Power Density
The vertical axis of the spectrum can be displayed as Absolute Power or Power Density, both of which can be displayed in either a linear or logarithmic scale. In Absolute Power mode, the total power displayed is based on the actual instrument resolution for that specific wavelength; this setting is recommended to be used only with narrow spectrum input light. For broadband devices, it is recommended that the Power Density mode is used. Here the vertical axis is displayed in units of power per unit wavelength, where the unit wavelength is based upon a fixed wavelength band and is independent of the resolution setting of the instrument.
Click to Enlarge
OSA Resolution vs. Wavelength of the Unknown Input
The resolution shown here was calculated using the formula to the left, using Δk
= 1 cm-1
for Low Resolution Mode and Δk
= 0.25 cm-1
for High Resolution Mode. Although the formula is valid for all OSA models, the usable wavelength range of each model is limited by the bandwidth of the detectors and optical coatings.
Resolution and Sensitivity
The resolution of this type of instrument depends on the optical path difference (OPD) between the two paths in the interferometer. It is easiest to understand the resolution in terms of wavenumbers (inverse centimeters), as opposed to wavelength (nanometers) or frequency (terahertz).
Assume we have two narrowband sources, such as lasers, with a 1 cm-1 energy difference, 6500 cm-1 and 6501 cm-1. To distinguish between these signals in the interferogram, we would need to move away 1 cm from the point of zero path difference (ZPD). The OSA can move ±4 cm in OPD, and so it can resolve spectral features 0.25 cm-1 apart. The resolution of the instrument can be calculated as:
where Δλ is the resolution in pm, Δk is the OPD in cm-1 (minimum of 0.25 cm-1 for this instrument) and λ is the wavelength in µm. The resolution in pm as a function of wavelength, converted using this formula, is shown in the graph to the right.
The resolution in the OSA can be set to High or Low. In high resolution mode, the retroreflectors translate by the maximum of ±1 cm (±4 cm in OPD), while in low resolution mode, the retroreflectors translate ±0.25 cm mechanically (±1 cm in OPD). The OSA software can be configured to cut the length of the interferogram that is used in the calculation of the spectrum in order to reduce the resolution to the level the user wishes.
The sensitivity of the instrument depends on the electronic gain used in the sensor electronics. Since an increased gain setting reduces the bandwidth of the detectors, the instrument will run slower when higher gain settings are used. The figures below show the dependency of the noise floor on the wavelength and OSA model.
The OSA is also designed so that it samples more points/OPD when the translation of the retroreflector assembly is slower. The data sampling is triggered by the reference signal from the internal Reference HeNe laser. A phase-locked loop multiplies the HeNe period up to 128 times for the highest sensitivity mode. This mode can be very useful when the measured light is weak and broadband, causing only a very short interval in the interferogram at the ZPD to contain all the spectral information. This portion of the interferogram is normally referred to as the zero burst.
Click to Enlarge
Noise Floor in Absolute Power Mode
Absolute Power mode is recommended for narrowband sources.
Click to Enlarge
Noise Floor in Power Density Mode
Power Density mode is recommended for broadband sources.
Thorlabs' OSA205 is the only model that directly supports free-space optical inputs. For the OSA201, OSA202, and OSA203, we recommend using a reflective collimator to collect the output from a fiber end. For details on both of these options, please read below.
OSA205: Directly Compatible with Free-Space Beams
The OSA205 features a built-in free-space optical input, allowing it to directly accept collimated light beams. The mechanical aperture of the OSA205 is Ø6 mm, and it includes four 4-40 taps for compatibility with our 30 mm cage systems. When the free-space door is open, a red alignment beam is emitted that should be made collinear and antiparallel to the unknown input for optimal measurement accuracy. For a demonstration, please refer to the video in the Overview tab at 2:54.
Beam Height Adjustment
The bottom of the OSA205 contains three M4 taps that accept the specially designed Ø1" pedestal posts included with the unit. By securing these pedestal posts with a CF125 or CF175 clamping fork, the enclosure can be fixed to an optical table. The M4 taps should not be used to mount the unit on Ø1/2" posts. Because the OSA weighs ~20 lbs (~10 kg), Ø1/2" posts will not provide adequate support.
To adjust the OSA205 for different beam heights, the simplest solution is to use a periscope. Alternatively, the unit can be raised on a well-supported optical breadboard, as shown in the photo below.
OSA205 on Aluminum Breadboard
In this photo, an MB3045/M Aluminum Breadboard, mounted on five Ø1.5" posts, is being used to raise the OSA205. The two silver clamping forks on the left, visible underneath the enclosure, fasten the unit to the raised breadboard.
OSA201, OSA202, and OSA203: Use a Reflective Collimator
To send a free-space input into the OSA201, OSA202, or OSA203, we recommend using a reflective collimator and a Ø50 µm core, 0.22 NA multimode fiber to collect light and transport it to the instrument, as shown below. A single mode patch cable can also be employed to collect the light. This may provide more precise results, but the alignment procedure is far more difficult (see Data Acquisition with a Single Mode Fiber Patch Cable, below, for details).
When using the OSA203 with wavelengths above 2 µm, we recommend using Fluoride Single Mode Fibers as they offer very good transmission in the mid-IR. Our standard silica fibers can also be used, but since their attenuation is high above 2 µm, it is important to minimize attenuation by choosing a fiber with the shortest usable length (1 m is preferred). For more information about fiber transmission above 2 µm, please contact firstname.lastname@example.org.
A list of parts used in this setup is available in the tables below. Mouse over the photo to see the corresponding part highlighted in the tables.
|OSA202||Optical Spectrum Analyzer||1|
|M42L01||Ø50 µm Core FC/PC|
Multimode Patch Cable
|LMR05||Ø1/2" Fixed Optic Mount||1|
|TR2||Ø1/2" Optical Post||1|
|P6||Ø1/5" Optical Post||1|
Thorlabs' OSA can be used to study free-space light sources using a folding mirror pair and the RC08FC-P01 reflective collimator. In this example, a 1532 nm HeNe laser is coupled into the OSA202 Optical Spectrum Analyzer.
The 1523 nm HeNe laser can be attached to the optical table using a P6 Ø1.5" post and a C1503 Kinematic V-Clamp Mount. The folding mirror pair consists of two Ø1/2" PF05-03-P01 silver mirrors mounted in POLARIS-K05 mirror mounts. The Polaris mounts should be mounted on RS3P8E Ø1", 3" long posts held to the table with CF125 clamping forks. Mount the RC08FC-P01 reflective collimator using an LMR05 fixed mount, a TR2 Ø1/2" post, and a UPH1.5 post holder. The beam height should be kept as low as possible in order to provide the best alignment stability.
In this example, two output fibers were used: an M42L01 Ø50 µm core multimode FC/PC-to-FC/PC patch cable and a P1-SMF28E-FC-1 single mode FC/PC-to-FC/PC patch cable. Initial coupling alignment should be conducted using the multimode fiber. Once the system is aligned for good coupling efficiency using the multimode fiber, the MM patch cable can be replaced by an SM patch cable, if desired. The system will then need to be retweaked for optimal coupling efficiency.
Our HLS635 635 nm, 1 mW portable alignment laser, which is a battery-powered 635 nm laser source, can be used to roughly align the system. At the start of the alignment, place both the HeNe laser and the reflective collimator at the same optical height as the folding mirror pair; this will minimize the amount of vertical adjustment of the beam path needed.
Mount the collimator and laser parallel to the hole pattern in the table. Plug the laser into the output fiber to run the light backwards through the system. Place the first mirror onto the table so that the laser beam exiting the reflective collimator is incident on it at 45°, with the beam exiting the mirror parallel to the optical table's holes. Then, place the second mirror similarly, so that the beam is indicent on the output aperture of the laser. At this point, the clamping forks can be used to secure the post of each mirror mount to the table, and the system should be close to proper alignment.
Next, turn on the HeNe laser and view the two laser beams along the optical path using a VRC4 IR viewing card. Adjust the mirrors so that the beams are incident on the same spot on the card at each point along the optical path. In the photo to the right, the small bright beam is from the HeNe laser, while the large red beam is from the alignment laser, incident on the back side of the card.
Next, measure the power of the free-space beam using the PM200 touch screen power meter and S122C sensor head. In this example, the free-space power of the laser was measured to be 1.55 mW.
Next, set up the PM200 power meter with the S155C fiber-coupled sensor to measure the output power in the fiber while the alignment of the system is fine tuned.
First, use the tip/tilt controls on one of the folding mirrors to find a maximum signal level. Next, turn the vertical adjustment screw on that mirror mount a quarter-turn, and then use the other folding mirror to find the new maximum. If this power level is higher than the original maximum, then continue this process until an absolute maximum is reached. If the power level was lower than the original level, repeat the same process, but turn the adjustment screw on the first mirror mount in the opposite direction.
Repeat this process for the horizontal adjustment, and then iterate between horizontal and vertical adjustments until an absolute maximum power level is reached. As shown by the final power measurement to the right, in this setup, a maximum coupling efficiency of ~80% was reached.
Finally, plug the M42L01 patch cable into the OSA to acquire data.
Data Acquisition with a Single Mode Fiber Patch Cable
In some circumstances, using a single mode fiber patch cable may increase the accuracy of the OSA wavelength meter, due to reduced variations in the optical path length inside the fiber. The alignment procedure is similar with single mode fiber, except that single mode fiber is much more sensitive to errors in alignment. The system should be fully aligned using multimode fiber before switching to single mode fiber. Much smaller adjustments should be made with the folding mirror pair during single mode alignment, and a lower coupling efficiency should be expected.
Here, a P1-SMF28E-FC-1 patch cable is being used to take data.
Here is a screenshot of the OSA software taking data for this experiment. It shows the spectrum of the laser (top), as well as the OSA's wavelength meter.
The 1523 nm HeNe laser line corresponds to the 2s2 → 2p1 transition in Ne I, which has an energy corresponding to a vacuum wavelength of 1523.48765 nm*. In this example, the OSA202 measured a center vacuum wavelength of 1523.488 nm, which is within the specified ±2 pm accuracy of the OSA wavelength meter.
* Information from the NIST Atomic Spectra Database.
Software for the Optical Spectrum Analyzer and CCD Spectrometers
Includes a GUI for control of the OSA, as well as a "virtual device" mode ideal for evaluating the software prior to purchase.
A graphical user interface allows easy operation from a PC connected via USB 2.0 to the FT-OSA. The PC records the interferometric signal from the FT-OSA, which is then fast Fourier transformed (FFT) to yield the resulting spectra.
Monochromatic light may be viewed with sub-picometer resolution by utilizing the wavelength meter mode of the FT-OSA. Broadband emission can also be viewed through the OSA's software, which has built-in zoom and peak analysis features. A peak discriminator can select bands that exceed a user-defined intensity and display them according to their wavelength (nm), wavenumber (cm-1), or frequency (GHz). The instrument has a spectral resolution of 7.5 GHz (0.25 cm-1) and a spectral accuracy better than 2 ppm (parts per million). In wavelength meter mode, the accuracy improves to 1 ppm.
The FT-OSA software is pre-installed on the laptop computer included with the purchase of the instrument.
The software has a customizable graphical user interface for acquiring, inspecting, manipulating, and analyzing spectra and interferograms. The software makes it easy to locate and track spectral peaks or valleys, measure the optical input power over any wavelength range, calculate an absorption spectrum in real time, or track a large number of parameters over time. In addition, the software features a virtual device function that lets users manipulate virtual spectra and test out the features of the software.
A device interface library, containing a multitude of routines for data acquisition, instrument control, and spectral processing and manipulation, is also provided with the instrument. The library can be used to develop customized software for the user's own application using LabVIEW, C, C++, C#, Java, or other programming languages. Each OSA ships with a set of LabVIEW routines to assist with writing your own applications.
The screen shots below were taken using the included software. Each trace utilized a 1550 nm laser diode and demonstrates some of the various measurements that are possible with the optical spectrum analyzer.
The software provided with our OSAs is also compatible with our line of Compact CCD Spectrometers.
Click to EnlargeFigure 1:
The peak and total optical power of a 1550 nm gain chip operating well below threshold.
Click to EnlargeFigure 2:
The ASE spectrum of the same 1550 nm gain chip shown in Figure 1. The ripple is caused by Fabry-Perot modes in the chip.
Click to EnlargeFigure 3:
1550 nm gain chip in an external cavity laser. The software is set up to display the spectrum and the optical power. The wavelength meter mode window is also activated.
Click to EnlargeFigure 4:
A trace of the acetylene absorption spectrum. The 1550 nm gain chip was used in ASE mode as the source, with the valley search function activated.