GaSb surface grating distributed feedback interband cascade laser emitting at 3.25 µm.

Area of Science:

• Semiconductor Lasers
• Infrared Photonics
• Materials Science

Background:

• Interband cascade lasers (ICLs) are crucial for mid-infrared applications.
• Achieving high-quality surface gratings and stable single-mode operation in ICLs remains a challenge.
• Distributed feedback (DFB) mechanisms are essential for wavelength control and single-mode emission.

Purpose of the Study:

• To design, grow, and fabricate a second-order distributed feedback interband cascade laser (DFB-ICL) emitting at 3.25 µm.
• To investigate the use of a GaSb cap layer for improved surface grating quality.
• To evaluate the laser's performance in terms of threshold current, output power, tuning range, and single-mode stability.

Main Methods:

• Coherent epitaxy of a GaSb cap layer on the laser structure.
• Fabrication of a second-order surface grating using GaSb and gold.
• Design and simulation using couple-wave theory.
• Device fabrication with 2-mm-long cavities and 4.5-µm-wide ridges.
• Characterization of continuous-wave (CW) performance at various temperatures.

Main Results:

• A high-quality GaSb/gold surface grating was successfully fabricated.
• Simulations predicted sufficient coupling strength and inter-modal loss difference.
• The fabricated DFB-ICL exhibited a CW threshold current of 60 mA and a maximum output power of 24 mW at 20°C.
• Stable single-mode operation with high side-mode suppression ratios (>20 dB) was achieved over a tuning range of >20 cm⁻¹.
• Output power remained at 5 mW even at 55°C.

Conclusions:

• The novel GaSb cap epitaxy approach enables high-quality surface gratings for DFB-ICLs.
• The fabricated 3.25 µm DFB-ICL demonstrates excellent performance, including stable single-mode emission and broad continuous tuning.
• This work contributes to the development of advanced mid-infrared laser sources for various applications.