Optoelectronic frequency-modulated continuous-wave terahertz spectroscopy with 4 THz bandwidth

Area of Science:

• Optoelectronics
• Spectroscopy
• Terahertz technology

Background:

• Terahertz (THz) spectroscopy offers significant potential across science and industry.
• Existing THz systems, particularly terahertz time-domain spectroscopy (TDS), are often complex due to femtosecond lasers and optical delay lines, hindering widespread adoption.
• There is a need for simpler, more robust THz sensing technologies.

Purpose of the Study:

• To present a novel optoelectronic, frequency-modulated continuous-wave (FMCW) terahertz sensing method.
• To demonstrate a broadband THz spectrometer with reduced complexity compared to traditional TDS systems.
• To showcase the potential of this new method for industrial non-destructive testing and material analysis.

Main Methods:

• Generation of the terahertz field using a frequency-swept optical beat signal.
• Coherent detection via photomixing with a time-delayed copy of the same beat signal.
• Inherent phase modulation of the receiver current without an external modulator.

Main Results:

• Achieved a 4 THz bandwidth and 117 dB peak dynamic range with a 200 Hz measurement rate.
• Demonstrated performance comparable to state-of-the-art terahertz-TDS systems but with significantly reduced complexity.
• Successfully performed thickness measurements of multilayer dielectric samples (down to 23 µm) with <2% uncertainty in 0.2 s, achieving high accuracy for continuous-wave terahertz spectroscopy.

Conclusions:

• The optoelectronic FMCW approach offers a powerful and simplified alternative for broadband terahertz spectroscopy.
• This technology has strong potential for industrial non-destructive testing and other real-world applications.
• The method paves the way for compact terahertz spectrometers integrating fiber optics and photonic integration.