Continuous-wave THz vector imaging system utilizing two-tone signal generation and self-mixing detection.

Area of Science:

• Terahertz (THz) Imaging
• Photonics
• Semiconductor Devices

Background:

• Traditional heterodyne and homodyne THz detection require complex local oscillator references and phase rotation.
• Thicker samples in THz imaging can lead to 2π phase ambiguity, complicating data interpretation.
• Existing THz imaging systems often lack the simplicity needed for real-time applications.

Purpose of the Study:

• To propose and demonstrate a continuous-wave vector THz imaging system.
• To achieve simultaneous amplitude and phase measurement without complex referencing.
• To overcome the 2π phase ambiguity issue in THz imaging.

Main Methods:

• Utilized photonic generation of two-tone THz signals using a uni-traveling-carrier photodiode and electro-optic modulator.
• Employed a Schottky barrier diode detector as a self-mixer for signal detection.
• Implemented a vector imaging approach for simultaneous amplitude and phase retrieval.

Main Results:

• Achieved a 50-dB signal-to-noise ratio at 325 GHz with a 100-μs integration time.
• Demonstrated a low phase fluctuation of 0.012 radians.
• Successfully performed two-dimensional THz phase contrast imaging.

Conclusions:

• The proposed system simplifies THz vector imaging by eliminating the need for local oscillator references and phase rotation.
• The self-mixing detection scheme effectively avoids 2π phase ambiguity.
• The system's simple receiver configuration is highly advantageous for developing real-time THz vector imaging systems, especially with emerging 2D THz image sensors.