Optimal linear operation point control of silicon-based Mach-Zehnder modulator.

Area of Science:

• Photonics and Optical Engineering
• Semiconductor Device Physics
• Microwave Engineering

Background:

• Silicon Mach-Zehnder modulators (MZMs) are crucial for microwave photonics links.
• Achieving optimal linear operation is essential for minimizing distortion and maximizing dynamic range.
• Existing methods for bias stabilization may not guarantee the highest linearity.

Purpose of the Study:

• To propose and demonstrate an automated control system for biasing silicon carrier-depletion MZMs.
• To identify the optimal linear operation point for enhanced performance in microwave photonics links.
• To improve the spurs-free dynamic range (SFDR) beyond traditional quadrature biasing.

Main Methods:

• Superposing a low-frequency two-tone dither signal with the RF modulation signal.
• Extracting fundamental harmonic (FH) and third-order intermodulation distortion (IMD3) components.
• Sweeping bias voltage and optical path difference to find the point of maximum SFDR.
• Implementing SFDR measurements at 500 MHz to validate linearization.

Main Results:

• The control system successfully identified an optimal linear operation point for the MZM.
• The achieved SFDR at the optimal point was 107.5 dB·Hz^2/3 at 500 MHz.
• This represents a 6 dB improvement in SFDR compared to the quadrature point.

Conclusions:

• The developed control system effectively achieves automatic optimal biasing for silicon MZMs.
• The system significantly enhances the linearity and SFDR of microwave photonics links.
• This approach offers a practical method for improving the performance of optical modulation systems.