Reflective fiber optic probeAs a key component for receiving signals in fiber optic sensors, it plays an increasingly important role in today's industrial detection, medical diagnosis, and scientific research fields. It has achieved precise measurement of various physical quantities such as displacement, morphology, temperature, and even biological tissue characteristics, thanks to its unique advantages of non-contact, high sensitivity, and resistance to electromagnetic interference. This article will delve into the working principle, core structure, technological evolution, and wide application scenarios of reflective fiber optic probes.

1、 Core working principle: Precision sensing based on light intensity modulation

Based on total internal reflection and intensity modulation of light. Its typical system consists of a light source, emitting optical fiber, probe, reflecting surface (measured object), and photodetector.

The workflow begins with the light emitted by the light source being coupled into the emitting fiber, transmitted through the fiber, and emitted from its end face, illuminating the reflective surface of the object being measured. The reflected light is captured by the receiving fiber and transmitted back to the photodetector for conversion into an electrical signal. The final output signal strength has a specific functional relationship with the distance between the probe end face and the reflection surface. By accurately measuring changes in light intensity, information such as displacement and surface condition of the measured target can be inferred.

Research has shown that the output characteristic curve can usually be divided into three regions: the front slope region, the peak region, and the back slope region. The signal in the front slope area grows linearly and is suitable for high-precision displacement measurement at the micrometer level; The signal in the back slope area decays with the square of distance and can be used for measurements with lower sensitivity requirements but larger range. The performance of the probe, such as measurement range, sensitivity, and linearity, is greatly influenced by factors such as fiber parameters, reflection surface characteristics, and the axial spacing between the transmitting and receiving fibers.

2、 Structural Design and Technological Evolution: From Foundation to Optimization

The performance of a reflective fiber optic probe depends on its structural design. In the early days, a simple Y-shaped branch structure was common, connecting the light source and detector to the same probe. To further improve performance, researchers have conducted continuous innovative optimizations.

1. Structure and Materials

Basic reflection probes are often composed of fiber bundles, such as a common FRP reflection probe, whose probe end consists of 7 optical fibers (6 receiving and 1 transmitting) inside a stainless steel protective shell. The standard fiber core diameter is 200 μ m, and the interface is SMA905. In order to improve the receiving efficiency of reflected light, the end face of the receiving fiber is often ground into a D-shaped cross-section.

2. Innovative structure and compensation technology

In order to overcome the effects of light source fluctuations, environmental interference, etc., high-precision probes have made important improvements in their structure:

Dual output and ratio measurement: One improvement is to adopt a new structure with two output terminals. By calculating the ratio of the two output signals as the final output, the impact of fluctuations in light source intensity and differences in measured surface roughness can be significantly reduced, thereby improving anti-interference ability and measurement accuracy.

Special optical fibers and irregular structures: Research attempts to use standardized quartz optical fibers combined with mass-produced large core diameter thin clad special quartz optical fibers to form same core or different core structure probes, in order to seek the best balance between performance and cost. More in-depth theoretical research and design have proposed innovative structures such as concave stepped fiber optic probes. By accurately analyzing the influence of misalignment and different reflection surfaces on light intensity modulation characteristics, traditional probes have been systematically optimized.

3、 Future prospects

With the development of new materials, new processes, and intelligent algorithms,Reflective fiber optic probeIt is evolving in the following directions:

Integration and Intelligence: The probe will be more closely integrated with miniature light sources, detectors, and processing circuits, and combined with artificial intelligence algorithms to perform real-time analysis of reflected spectra or signal patterns, achieving real-time state judgment and fault prediction.

Multi functional and multi parameter sensing: A single probe will be able to simultaneously decouple multiple physical quantities such as temperature, pressure, displacement, etc., or combine spectral analysis capabilities to provide richer information about the measured target.

Structural innovation and performance limit breakthrough: Based on rigorous mathematical models (such as light field models) and biomimetic design, new probe structures will continue to emerge, constantly breaking through the theoretical limits of measurement sensitivity, resolution, and linear range.