# High Performance GaSb-Based DBR Laser with On-Chip Integrated Power Amplifier via Gain-Match Design
###### Abstract  
We reported on a single-longitudinal-mode operated distributed Bragg reflector laser diode emitting at 1950 nm with an on-chip integrated power amplifier. Second-order Chromium-Bragg gratings are carefully designed and fabricated at the end of the ridge waveguide. Achieving a stable single-mode operation with a large injecting current range of 800 mA from 15 \({}^{\circ}\)C to 40 \({}^{\circ}\)C. The maximum side-mode suppression ratio (SMSR) is up to 42 dB. To increase the output power, an on-chip integrated master oscillator power amplifier (MOPA) is also introduced. MOPA-DBR lasers with different matching configurations between the gain peak and Bragg wavelength are fabricated, resulting in various amplification consequences. The best device is realized with 40 nm red-shifted between Bragg wavelength and photoluminescence (PL) peak. A power amplification of 5.6 times is achieved with the maximum output power of 45 mW. Thus, we put up the feasibility and key design parameters of on-chip integrated power amplification DBR lasers towards mid-infrared. GaSb-based diode lasers; single-longitudinal mode; distributed Bragg reflector; power amplifier +
Footnote †: journal: Applied sciences  
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Footnote 0: Accepted: 23 December 2024  
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can still form stable FP multimode oscillation, but output powers are very low, and the output power of #1 laser is less than 1 mW. The output power of the #3 laser without grating region still remains as low as 3 mW. DBR laser (#2) with a cavity  
Figure 8: Fundamental mode transmission angle corresponding to the width of ridge waveguide and wavelengths from 1.9 \(\upmu\)m to 1.95 \(\upmu\)m.
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length of 1500 \(\upmu\)m and a grating region length of 200 \(\upmu\)m achieves an output power of 8 mW, which can be used as a comparison device for the next three groups of lasers with different grating periods. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **MO Length (\(\upmu\)m)** & **PA Length (\(\upmu\)m)** & **Grating Period (\(\upmu\)m)** & **Grating Length (\(\upmu\)m)** \\ \hline \#1 & 800 & 0 & 540 & 220 \\ \#2 & 1500 & 0 & 540 & 220 \\ \#3 & 800 & 1800 & 0 & 220 \\ \#4 & 800 & 1800 & 534 & 220 \\ \#5 & 800 & 1800 & 537 & 220 \\ \#6 & 800 & 1800 & 540 & 220 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: MOPA-DBR lasers with various structural parameters. Figure 9: Current–Voltage (**a**) and Power–Current (**b**) characteristics curves of MOPA lasers with different grating periods at room temperature. As shown in Figure 9, the #3 DBR laser shows a threshold voltage of 0.766 V and a series resistance of 0.29 \(\Omega\). The #4, #5, and #6 MOPA-DBR lasers show a threshold current of 300 mA, an average threshold voltage of 0.776 V (#4 for 0.767 V, #5 for 0.772 V, and #6 for 0.790 V) and average series resistance of 0.33 \(\Omega\) (#4 for 0.32 \(\Omega\), #5 for 0.32 \(\Omega\), #6 for 0.35 \(\Omega\)), which means high stability of the fabrication process. In comparison to DBR lasers, there exists a higher slope efficiency of 0.024 W/A. The #4 laser achieves the highest output power of 20 mW, which is 2.5 times higher than DBR lasers; the #6 laser achieves the highest output power of 35.2 mW, which is 4.4 times higher than DBR lasers; the #5 laser achieves the highest output power of 45 mW, which is 5.6 times higher than DBR lasers, which indicates the on-chip integrated tapered PA waveguides efficiently achieve the function of power amplification. The kink and mode-hopping in the P-I curve of the #5 laser at currents around 1.5 A are due to the competition between the FP mode and Bragg mode. The gain peak is located below Bragg mode at a current range of less than 1.5 A. When the injected current is higher than 1.5 A, the large mode gain at the Bragg wavelength ensures the stable operation of the single-mode laser, and the P-I curve increases linearly. The mode-hopping between FP mode and Bragg mode is accompanied by significant energy jumps.