研究目的
To develop a grating-less fiber vector bend sensor based on multimode interference and image tapping for detecting both bend radius and direction using standard fiber components and simple optical power detection.
研究成果
The fiber vector bend sensor successfully detects bend radius and direction using MMI and image tapping with simple fabrication and interrogation. It demonstrates high sensitivity with minimal bend detection (e.g., 0.382° bend angle) and large dynamic range. The sensor is promising for applications in fine mechanics, health monitoring, and structural monitoring. Future work will focus on arbitrary bend directions and effects of multiple bends and torsion.
研究不足
The transition of powers is not linear with displacement, limiting the interrogation complexity for arbitrary bend directions. Mechanical backlash and delay in the fine stage cause uncertainty (±2 μm). The MMI is sensitive to multiple bends and twists, which can alter the image. A highly coherent laser source is required for long MMIs to avoid resolution drop. Future work may involve piezo-controllers for precise movement and machine learning for complex fiber forms.
1：Experimental Design and Method Selection:
The sensor uses a standard single mode fiber (SSMF) spliced to a multimode fiber (MMF) to create a multimode interference (MMI) device. A seven-core fiber (7CF) is spliced to the MMF end to tap out the MMI image, connected to a fan-out device for output to single mode fibers and photodiodes. Simulations were performed using PhotonDesign software (FIMMWAVE and BEAMPROP) to model the MMI and bending effects.
2：Sample Selection and Data Sources:
Fibers used include SSMF (Corning SMF28 Ultra), MMF (FG105LCA), and 7CF (Fibercore SM-7C1500), all with 125 μm cladding diameter. Light source is a laser diode at 1550 nm.
3：List of Experimental Equipment and Materials:
Equipment includes a fiber fusion splicer, fiber cleaver, laser diode, infrared camera (Princeton NIRVana 640ST), objective lens, 3-axis fine stages, metal pin for bending, photodiodes, and power meter. Materials are the specified fibers and fan-out device (Fibercore FAN-7C).
4：Experimental Procedures and Operational Workflow:
The MMF is spliced to SSMF and cleaved at 12,000 μm. The 7CF is marked, spliced to MMF, and connected to the fan-out device. The system is initialized by adjusting positions for uniform power distribution. Bending is induced by pulling a metal pin in X and Y directions with displacements from 0 to 40 μm in 10 μm steps, and power outputs are measured.
5：Data Analysis Methods:
Power measurements from photodiodes are normalized and compared. Simulations use mode overlap integrals to calculate coupling efficiencies. Data is analyzed to determine bend sensitivity and direction based on power imbalances.
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single mode fiber
SMF28 Ultra
Corning
Used as the input fiber to launch light into the multimode fiber for creating the MMI device.
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multimode fiber
FG105LCA
Acts as the multimode interference device where the light distribution changes with bending.
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seven-core fiber
SM-7C1500
Fibercore
Taps out the MMI image by splicing to the multimode fiber, with seven cores for discrete power detection.
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fan-out device
FAN-7C
Fibercore
Connects to the seven-core fiber to separate the seven outputs into individual single mode fibers for power measurement.
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infrared camera
NIRVana 640ST
Princeton
Used to capture the MMI image for verification and analysis before tapping.
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laser diode
Provides light source at 1550 nm for the experiment.
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fiber fusion splicer
Used to splice fibers together in the sensor setup.
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fiber cleaver
Used to cleave the multimode fiber to the desired length.
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photodiodes
Detect optical power from the output single mode fibers for bend analysis.
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power meter
Measures the optical power with accuracy ±0.01 dBm.
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3-axis fine stages
Used to position and adjust the fibers and bending pin during the experiment.
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