Frequently Asked Questions
We’ve compiled answers to the most common questions about our lasers, including their features, applications, and technical specifications. Whether you’re curious about tunability, ultra-narrow linewidths, or how our lasers can be integrated into your systems, this page is designed to help. If you don’t find the answer you’re looking for, feel free to reach out to our team – we’re always here to help!
COMET – Swept Source Laser
The laser controller appears as a “Virtual Com Port” when connected via USB to a computer. This serial interface is also accessible via the RX/TX pins of the DE-9 connector at the laser housing. Communication is based on low-level serial commands. For convenience, we can provide a Python library which includes a wrapper for these low-level commands, as well as advanced functions such as sweeping and setting the laser wavelength.
The COMET supports both operation modes, namely the “steady” tuning mode and the “swept” mode. Using the “steady” mode, the laser can be tuned within the tuning range with step sizes specified by the resolution.
The COMET can sweep without mode hops over approximately 0.25 nm, which is limited due to the laser design and the maximum phase shift of the heater actuators. For a wide-range sweep, the laser sweeps in quasi-continuous way. After every 0.25 nm sweep the laser hops from one cavity mode to the next. The mode hop takes less than 0.5 ms, during which time the laser restarts at the next mode. The result is a continuous wavelength sweep, with power dips during the mode hops. To ensure predictability for repetitive sweeps, all modes are indexed, and the mode hops happen at fixed wavelengths.
The laser provides a trigger signal at the start and end of each sweep, from the 1st SMA connector on the COMET adapter. This trigger signal can be fed into the trigger input of an oscilloscope for sweep synchronization.
In addition, the 2nd SMA connector on the COMET adapter provides a high signal during mode hops, which can be used to mask data points measured during mode hops.
We can only calibrate the COMET for one value of the sweep rate. The sweep performance will be optimal for that sweep rate. Nevertheless, the user can configure the sweep rate using the included software. The sweep performance can be suboptimal if the configured sweep rate differs significantly from the calibration value.
The relation between resolution and wavelength range is given by the maximum number of wavelength entries. The reason is that a maximum of about 13k wavelength entries can be stored in the device memory. For example, a wavelength range of 50 nm with 5 pm resolution requires 10k wavelength entries, which fits in the device memory.
The relation between scan rate and resolution is given by the time interval per wavelength step. This time interval should be maximally 0.5 ms and preferably 0.1 ms for a smooth sweep, due to matching with the heater bandwidth. For example, 5 pm wavelength resolution with a time interval of 0.1 ms gives a sweep rate of 50 nm/s.
Yes, we offer a modulation input (SMA connector) to modulate the laser diode current. Modulating the laser current enables fine analog control of the laser frequency, within a limited frequency range (typically up to ~1 GHz). We advise to use the modulation input only for the “steady” tuning mode, but not for the “swept” mode.
Our standard product does not include an isolator, but we can offer a built-in isolator as an add-on.
It is perfectly fine to use the laser immediately after switching on. However, optimal laser stability is reached when the laser is in thermal equilibrium with its surroundings (e.g. a heat sink), which is in 1-hour after warming up.
ATLAS – Wavelength Tunable Laser
Yes, the ATLAS is a complete tunable laser system. However, a computer is required to operate the laser, as the laser has no hardware user control.
The laser controller appears as a “Virtual Com Port” when connected via USB to a computer. This serial interface is also accessible via the RX/TX pins of the DE-9 connector at the laser housing. Communication is based on low-level serial commands. For convenience, we can provide a Python library which includes a wrapper for these low-level commands, as well as advanced functions such as setting the laser wavelength.
No, but our COMET laser offers both wavelength tuning and continuous sweeping.
Our standard product does not include an isolator, but we offer a built-in isolator as an add-on for the product versions with a central wavelength around 1550 nm.
The default wavelength resolution can be found in the specifications of the laser. We can calibrate the laser for smaller wavelength steps, but at the expense of the wavelength range. The reason is that a maximum of about 13k wavelength entries can be stored in the device memory. Ultimately, the D/A converters used for the heater drivers limit the minimum wavelength and frequency resolution to the order of 0.01 pm or 1 MHz, respectively.
Yes, we offer a modulation input (SMA connector) to modulate the laser diode current. Modulating the laser current enables fine analog control of the laser frequency, within a limited frequency range (typically up to ~1 GHz).
This is not supported by default. However, we are open to customizing the hardware and software to your preferences.
Modulation
Yes, we offer laser drivers with a modulation input (SMA or SMB connector) to modulate the laser diode current. Modulating the laser current enables lasers frequency and amplitude modulation. This is useful, e.g., for spectroscopy and FMCW (frequency-modulated continuous-wave) technology.
The modulation bandwidth is imposed by the electronic driver. Our drivers have a typical 3-dB modulation bandwidth of a few Mhz. The modulation amplitude is limited by the laser cavity FSR, which is typically a few GHz. To avoid mode hops during modulation, we recommend modulation up to ~1 GHz.
Yes, laser frequency can be chirped when applying the desired waveform to the modulation input.
We do not offer pulsed lasers based on, e.g., mode-locking technology. We design our lasers for CW (continuous wave) emission.
Tuning
To ease wavelength tuning, we deliver our ATLAS and COMET tunable lasers with a software-based wavelength calibration, where all knobs are automatically set based on the requested wavelength. Alternatively, all tuning knobs can be controlled manually via the software. Upon request, we can provide an application note to explain tuning in more detail.
The continuous tuning range, without mode hops, depends on the laser design and the tuning method. For example, our ATLAS-1550 can be tuned mode-hop-free over a) about 4 GHz (32 pm) when tuning the diode current or phase heater only. b) about 32 GHz (250 pm) for synchronous tuning of the phase section and ring heaters and c) about 5 GHz (40 pm) when only tuning the laser temperature. Note that the laser wavelength can also be tuned over a much larger range by piece-wise mode-hop-free tuning.
Currently, we only offer lasers based on thermo-optic tuning for the cavity phase and ring resonators by using resistive heaters placed on top of the respective waveguides.
Stability
This depends very much on the laser driver and operating condition. A typical long-term measurement for our ATLAS-1550 laser can be found in this reference (see blue curve in Fig. 6). The frequency drift for this free-running laser remained within 350 MHz over 65 hours. Note that a correlation with the 24-h lab temperature cycle can be observed in this graph, which suggests that the free-running stability could be further improved with a stable ambient temperature.
This depends very much on the laser setting, the driver and the operating condition. Please contact us about your specific requirements.
Feedback sensitivity
The laser performance can be significantly affected for a back-reflection level higher than –40 dB. To avoid any effect on the laser due to undesired back-reflections, we advise connecting an isolator to the laser output..
A standard off-the-shelve fiber-optic isolator is sufficient in most cases, for example from Thorlabs (IO-G-1550-APC or IOT-G-1550A) or any other supplier.
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