Sensitivity and noise in THz electro-optic upconversion radiometers

Area of Science:

• Optics and Photonics
• Terahertz (THz) Technology
• Quantum Optics

Background:

• Room-temperature terahertz (THz) radiometers are crucial for various applications.
• Existing THz receivers often require cryogenic cooling for optimal performance.
• THz-to-optical upconversion offers a potential pathway for room-temperature THz detection.

Purpose of the Study:

• To investigate the noise characteristics of room-temperature THz radiometers employing THz-to-optical upconversion.
• To analyze the impact of different optical detection schemes on receiver noise.
• To assess the potential of these upconversion-based receivers to outperform existing THz technologies.

Main Methods:

• Utilized sum-frequency-generation (SFG) in high-quality factor (Q) whispering-gallery mode (WGM) resonators for THz-to-optical upconversion.
• Analyzed noise properties under coherent (homodyne/heterodyne) and incoherent optical detection.
• Performed theoretical predictions based on noise analysis and photon conversion efficiency.

Main Results:

• Efficient electro-optic modulation via SFG in WGM resonators does not introduce intrinsic noise.
• Coherent optical detection (homodyne/heterodyne) leads to quantum-limited noise performance, comparable to conventional amplifiers and mixers.
• The upconversion receiver demonstrates potential as a THz photon counter with optical domain counting.

Conclusions:

• Upconversion-based room-temperature THz receivers can surpass state-of-the-art cooled and room-temperature receivers.
• Performance enhancement is contingent on achieving a photon conversion efficiency greater than 1%.
• While inherently narrow, the detection bandwidth can be broadened through engineered optical coupling mechanisms.