Structure and Principle of Fiber Optic Displacement Sensor

Fiber optic displacement sensors measure the position or movement of a target by detecting changes in the intensity of light reflected from the target surface through optical fibers.Working PrincipleA fiber optic displacement sensor typically consists of a transmitting fiber, a receiving fiber, and a detector. Light from a source, such as a laser or LED, is transmitted through the transmitting fiber and directed onto the target surface. The light reflected from the target is collected by the receiving fiber and sent to a photodetector, which converts the light intensity into an electrical signal proportional to the displacement of the target . The sensor operates on the principle that the intensity of reflected light varies with the distance between the probe tip and the target. When the target moves closer to the probe, the amount of light captured by the receiving fibers decreases, and when the target moves away, the received light intensity increases. This relationship is highly sensitive in a specific range, known as the front slope of the performance curve, allowing precise measurement of small displacements .Sensor ConfigurationsExtrinsic sensors: Use the fiber only to transmit and receive light, with the sensing occurring outside the fiber. The alignment of transmitting and receiving fibers relative to the target can be adjusted to optimize sensitivity .Intrinsic sensors: The fiber itself acts as the sensing element, where changes in light properties such as intensity, phase, or wavelength occur within the fiber due to displacement or strain . Advanced designs, such as pentafurcated fiber bundles, improve linearity, sensitivity, and measurement range by arranging a central transmitting fiber surrounded by concentric rings of receiving fibers .AdvantagesFiber optic displacement sensors offer non-contact measurement, compact size, flexibility, and immunity to electromagnetic interference, making them suitable for confined or harsh environments, such as turbines or high-voltage areas . They are widely used for measuring surface deformation, vibration, material thickness, and precise distances in industrial and aerospace applications. In summary, the principle of a fiber optic displacement sensor relies on detecting variations in reflected light intensity caused by target movement, which is converted into an electrical signal to quantify displacement accurately.