Fiber Vector Bend Sensor Based on Multimode Interference and Image Tapping

Area of Science:

• Optoelectronics and Photonics
• Fiber Optic Sensing Technology
• Interferometry and Wave Phenomena

Background:

• Traditional fiber bend sensors often rely on complex grating structures or imaging processing.
• Multimode interference (MMI) devices offer potential for simplified optical sensing.
• Accurate and directional bend sensing is crucial for various industrial and medical applications.

Purpose of the Study:

• To demonstrate a grating-less fiber vector bend sensor.
• To develop a method for determining both the bend radius and direction using MMI.
• To simplify the analysis of bend-induced light distribution changes.

Main Methods:

• A standard single-mode fiber was spliced to a multimode fiber to create an MMI device.
• A seven-core fiber was spliced to the MMI device to tap out light intensity distribution.
• Relative light intensities from seven output single-mode fibers were compared to determine bend parameters.

Main Results:

• The sensor successfully detected bend direction and radius without complex imaging.
• A 10 µm bend displacement in the X-direction caused a 4.6 dB power imbalance between outputs C4 and C7.
• A similar displacement in the Y-direction resulted in a 7.0 dB imbalance between outputs C3 and C4, while C4/C7 remained constant.

Conclusions:

• The demonstrated grating-less fiber vector bend sensor effectively utilizes multimode interference.
• The seven-core fiber readout simplifies bend analysis, enabling determination of both radius and direction.
• This technology offers a promising approach for high-sensitivity, directional fiber optic sensing.