Tunnel diode-based distributed feedback (DFB) broad-area diode lasers with excellent results for LiDAR applications
Fig. 1. High-current nanosecond pulsed electronic driver integrated with a soldered and bonded 1 mm long DFB BA laser for LiDAR applications.
Fig. 2. Characteristics of DFB BA lasers with stripe widths of 50 μm and 200 μm at 10 ns pulses. Left: Light-current characteristics at 10 kHz. Right: Time-averaged optical spectra of these lasers, operated at 25 °C and 50 °C at 100 kHz repetition frequency.
Fig. 3. Vertical far-field intensity distribution of DFB BA lasers with stripe widths of 50 μm and 200 μm.
High-power diode lasers delivering short optical pulses in the nanosecond range are ideal components for different applications, including free-space communication, spectroscopy, metrology, material processing, and light detection and ranging (LiDAR). For LiDAR systems that need to detect distant objects in different atmospheres, a high signal-to-noise ratio (SNR) is crucial. An effective strategy to improve the SNR is to use wavelength-stabilized narrowband lasers.
Distributed feedback (DFB) lasers are known for their stability, low noise, and narrow linewidth, and they are widely used in optical communications. They have the advantage over distributed Bragg reflector (DBR) lasers that the Bragg grating is extended across the entire length of the electrically driven cavity. Therefore, their chip area is smaller and they are potentially cheaper. However, achieving high peak powers requires high currents and special electronics. One way to deal with this is to stack laser diodes with intermediate tunnel junctions. Although this approach increases the voltage, it reduces the required current. By using a high-order vertical mode, the absorption in the highly doped tunnel junctions can be minimized, resulting in a high slope efficiency.
For the first time, FBH has succeeded in fabricating DFB broad-area (BA) lasers utilizing two tunnel junctions and three active regions. DFB BA lasers with a cavity length of 1 mm and stripe widths of 50 μm and 200 µm have been compared in terms of their electro-optical performance and beam quality. An increase in optical power was demonstrated by enlarging the stripe width from 50 µm to 200 µm under nanosecond pulses (Fig. 2). The laser with a 200 µm stripe width achieved a high optical pulse power of 100 W in 10 ns long pulses at an injection current of 63 A. The narrow optical spectrum of both lasers is centered at around 886 nm, revealing the effect of the 41th order surface Bragg grating (Fig. 2). The spectral bandwidth is 0.2 nm (full width at half maximum), and the thermal tuning rate is only 64 pm/K. Fig. 3 shows the vertical far fields of the lasers.
This work was partly funded by Research Fab Microelectronics Germany (FMD) under Ref. 16FMD02 and by the German Federal Ministry of Education and Research (BMBF) grant 13N15566 as part of WiVoPro.
Publications
[1] N. Ammouri, H. Christopher, J. Fricke, A. Ginolas, A. Liero, A. Maaßdorf, H Wenzel, A. Knigge, “Wavelength-stabilized ns-pulsed 2.2 kW diode laser bar with multiple active regions and tunnel junctions”, Electron. Lett. 59, 1-3 (2023), doi: 10.1049/ell2.12680.
[2] H. Christopher, N. Ammouri, A. Maaßdorf, J. Fricke, A. Ginolas, J. Glaab, A. Liero, C. Zink, M. Ekterai, H. Wenzel, A. Knigge, “2 kW Pulse Power from Internal Wavelength Stabilized Diode Laser Bar for LiDAR Applications”, Proc. SPIE 12403, 1240302 (2023), doi: 10.1117/12.2649630.
[3] A. Knigge, N. Ammouri, H. Christopher, M. Beier, J. Fricke, A. Maaßdorf, A. Ginolas, J. Glaab, A. Liero, H. Wenzel, “High power, internally wavelength stabilized diode lasers with epitaxially-stacked multiple active regions for LiDAR applications”, Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) 2023, doi: 10.1109/CLEO/Europe-EQEC57999.2023.10231959.
[4] N. Ammouri, H. Christopher, J. Fricke, A. Ginolas, A. Liero, A. Maaßdorf, H Wenzel, A. Knigge, G. Tränkle, “Distributed feedback broad area lasers with multiple epitaxially stacked active regions and tunnel junctions”, Optics Letters 48, 6520 (2023), doi: 10.1364/OL.510521.