Single-mode semiconductor lasers fabricated by standard photolithography for direct modulation

Area of Science:

• Optoelectronics
• Semiconductor device physics

Background:

• Semiconductor lasers are crucial for optical communication.
• Surface gratings offer a method for laser mode control.
• Optimizing grating design is key to enhancing laser performance.

Purpose of the Study:

• To investigate the impact of surface higher-order gratings on semiconductor laser characteristics.
• To evaluate lasers with different grating orders (20th and 37th) at 1.55 µm.
• To determine the optimal grating placement for single-mode operation and dynamic response.

Main Methods:

• Fabrication of semiconductor lasers with surface higher-order gratings using standard photolithography.
• Characterization of output power, modal properties, and far-field profiles.
• Analysis of dynamic modulation responses and bandwidth.

Main Results:

• Single-mode operation achieved for lasers with 20th- and 37th-order gratings at 1.55 µm.
• 20th-order gratings resulted in lower threshold currents and higher slope efficiencies compared to 37th-order gratings.
• Vertical far-field profiles were affected by grating proximity to the output facet, but single-mode operation remained robust to grating position within the waveguide.
• A -3 dB bandwidth of 9 GHz at 100 mA was achieved, representing a significant advancement for this laser type.

Conclusions:

• Surface higher-order gratings are effective for achieving single-mode operation in semiconductor lasers.
• Grating order significantly influences laser efficiency and threshold.
• Laser performance is optimized by careful consideration of grating placement relative to the output facet.