Developments | ICW Laser Driver

The development of this alternative laser driving scheme has been triggered by the quest for lowering the overall heat dissipation of cw-QCL devices and reducing the complexity and footprint of the driving electronics. The concept of intermittent continous wave (icw) driving solves many technical issues and offers an elegant and versatile solution for an efficient laser scanning. It is an ongoing development that was initiated in 2012. The timeline of these activities are shown below:
 

2012 | the 1st prototype

The main goal was to enable the packaging of cw-DFB-QCLs into TO-8 housings, and thus support their usage in mobile applications. The concept foresees the complete turn-off of the drive current between individual scans and a freely selectable duty-cycle. Our custom-built, fully integrated, largely analog, yet flexible laser driver eliminates the need for any external electronics for current modulation, lowers the demands on power supply performance, and allows shaping of the tuning current in a wide range [1].

 

2016 | FPGA laser driver and DAQ system;

We exploit the benefits of the time-division multiplexed (TDM) icw driving concept and the real-time signal pre-processing capabilities of a commercial System-on-Chip (SoC, Red Pitaya). This offers a universal solution for operating a wide range of multi-wavelength QCL device types and allows stacking for the purpose of multiple laser configurations. Its adaptation to the various driving situations is enabled by numerous  FPGA functionalities that were developed on the SoC, such as flexible generation of a large variety of synchronized trigger signals and digital inputs/outputs (DIOs). The same SoC is used to sample the spectroscopic signal at rates up to 125 MS/s with 14-bit resolution.  The on-board averaging of consecutive spectral scans in real-time results in optimized memory bandwidth and hardware resource utilisation, and facilitates autonomous system operation [2].

This laser driver along with the DAQ system is used in the spectrometers produced by the Empa spin-off company MIRO Analytical AG.

Laser modulation schemes: a) Standard modulation, where a sawtooth waveform is added to the sub-threshold DC laser current (top). For a sufficiently small modulation, the emission wavelength follows the current (bottom). b) Intermittent modulation with reduced duty cycle. The laser current is only applied during the scan. The enhanced temperature chirp at the beginning of the scan causes a large tuning.

 

2020 | Faster and better

A more powerful programmable board (Alpha250, Koheron), built around an FPGA, which features a faster sampling rate (250 MS/s) and a higher bandwidth (100 MHz) analog front end with dual-channel 14-bit ADCs and 16-bit DACs [3].

 

2022 | Switch-scan tuning of Vernier QCLs

This driver is specially developed for rapid switching between multiple (up to six) Vernier clusters combined with high-resolution spectral scanning within the individual clusters. Within one measurement cycle of this scheme, the current levels of the front and back heaters of the QC-XT device are stepwise modified to switch between the Vernier clusters. In parallel, we acquire many spectral scans by driving the laser in the iCW regime with a much faster repetition rate than the switching rate [4].

Driving scheme for QC-XT lasers. The schematic depicts one Vernier cycle (typically 360 ms duration). Switching between the Vernier clusters occurs at every heater-current step (top and middle panels). In parallel, the laser is repeatedly scanned within each spectral window by iCW driving with 150-μs-long current pulses (bottom panel). Typically, 200 scans were acquired per cluster and spectral data obtained from the last 100 pulses was averaged (visualized as colored laser pulses).

 

2024 | Time-multiplexed single driver / multi-laser scheme

Stay tuned. Coming soon!

  1.  Fischer, M. et al. Intermittent operation of QC-lasers for mid-IR spectroscopy with low heat dissipation: tuning characteristics and driving electronics", Opt. Express 22, 7014–7027, (2014). 
    Publication Link

  2.  Liu, C. et al. Laser driving and data processing concept for mobile trace gas sensing: Design and implementation, Rev. Sci. Instrum. 89 (6), 065107, (2018). 
    Publication Link

  3.  Bereiter, B. et al. High-precision laser spectrometer for multiple greenhouse gas analysis in 1 mL air from ice core samples, Atmos. Meas. Tech., 13, 6391–6406, (2020).
    Publication Link

  4. Brechbühler, R. et al., Rapid Detection of Volatile Organic Compounds by Switch–Scan Tuning of Vernier Quantum-Cascade Lasers, Anal. Chem. 95(5), 2857–2864, (2023).
    Publication Link 

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