Microfiber evanescent-field photothermal gas detection using acoustic-induced mode-dependent frequency shift

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Technology
• Gas Spectroscopy

Background:

• Evanescent field photothermal gas detection offers high sensitivity.
• All-fiber frequency shifting is crucial for advanced interferometric systems.
• Few-mode fibers enable mode conversion for frequency manipulation.

Purpose of the Study:

• To experimentally demonstrate microfiber evanescent-field photothermal gas detection.
• To develop an all-fiber MHz-level frequency shift scheme for enhanced detection.
• To implement a compact and sensitive all-fiber heterodyne interferometric system.

Main Methods:

• Utilizing acousto-optic interaction in a few-mode fiber for MHz frequency shifts (0.9 and 1.83 MHz).
• Implementing all-fiber frequency shifters with high sideband rejection (>40 dB) and low insertion loss (<1 dB).
• Employing a pump-probe configuration with a 1-μm microfiber for photothermal gas detection via evanescent field modulation.

Main Results:

• Achieved a detection limit of 32 ppm (1σ) for ammonia with a fast response time of 22 μs.
• Demonstrated low instability (0.24%) within 48 pump cycles.
• Validated the effectiveness of the MHz-level frequency shift scheme in a heterodyne interferometric setup.

Conclusions:

• The developed all-fiber photothermal gas detection system offers high sensitivity and rapid response.
• The MHz-level frequency shifting technique is effective for advanced fiber optic sensing.
• This technology holds promise for applications in heterodyne detection, fiber sensors, and coherent communications.