Demonstration of record-low injection-current variable optical attenuator based on strained SiGe with optimized...

Area of Science:

• Photonics and Optoelectronics
• Semiconductor Devices
• Materials Science

Background:

• Variable optical attenuators (VOAs) are crucial components in optical communication systems for signal power management.
• Existing silicon (Si) VOAs face limitations in achieving low injection current and high-speed modulation.
• Strained silicon-germanium (SiGe) offers potential for enhanced optoelectronic properties compared to pure Si.

Purpose of the Study:

• To develop and demonstrate a strained SiGe VOA with a lateral pin junction for improved performance.
• To optimize the lateral pin junction design for reduced injection current and enhanced free-carrier absorption.
• To evaluate the VOA's attenuation, RF response, and suitability for high-speed WDM signal transmission.

Main Methods:

• Fabrication of a strained SiGe VOA incorporating a lateral pin junction.
• Optimization of the spacing between p+ and n+ regions in the lateral pin junction to manage injection current and propagation loss.
• Characterization of optical attenuation, injection current, radio frequency (RF) response, and Wavelength Division Multiplexing (WDM) signal transmission.

Main Results:

• Achieved 20-dB attenuation with a record-low injection current of 20 mA/mm in the strained SiGe VOA.
• Demonstrated 1.5 times lower current density compared to conventional Si VOAs.
• Exhibited superior RF response and enabled 2-GHz switching and error-free transmission of a 4 × 12.5 Gbps WDM signal.

Conclusions:

• The strained SiGe VOA with an optimized lateral pin junction offers a significant improvement in attenuation efficiency and speed.
• The enhanced free-carrier absorption in strained SiGe and optimized junction design contribute to the record-low injection current.
• This technology is well-suited for efficient and fast optical signal modulation in advanced WDM systems.