1、 Key points of core structure design

The basic structure of a reflective fiber optic probe consists of four parts: the transmitting fiber, the receiving fiber, the probe housing, and the optical lens. The design of each component needs to take into account both functional implementation and adaptability. The transmitting fiber is responsible for transmitting excitation light signals, and the core diameter needs to be selected according to the detection requirements. The commonly used specifications are 50 μ m-200 μ m. If the core is too thin, it will cause insufficient optical power, and if it is too thick, it will affect the focusing accuracy of the light spot; The receiving fiber is used to collect reflected light, usually using the same specification core as the transmitting fiber and arranged in a circular or coaxial manner. The circular arrangement is beneficial for improving the receiving efficiency, while the coaxial arrangement can reduce the detection blind spot.

The probe housing should meet the requirements of mechanical protection and optical compatibility, and be made of aluminum alloy or engineering plastic material. The surface should be anodized or insulated to prevent electromagnetic interference; The front end of the housing needs to reserve a lens installation interface to ensure that the coaxiality error between the lens and the fiber end face does not exceed 0.1mm. As a key component for optical signal focusing and receiving, quartz material is preferred to reduce optical loss, and the focal length needs to be matched according to the detection distance. For short distance detection (1-5mm), a convex lens with a focal length of 2-5mm is selected, and for long distance detection (5-50mm), a gradient refractive index lens can be used to reduce light spot diffusion.

2、 Key Performance Optimization Strategies

（1） Improve detection accuracy

The detection accuracy is mainly affected by the size of the light spot and the signal-to-noise ratio of the optical signal. Optimize the fiber optic layout by adopting a combination structure of "center emission+ring reception", which can focus the reflected light on the center of the receiving fiber end face and reduce edge interference caused by stray light; Coating an anti reflective film on the surface of the lens and optimizing the film system parameters for working wavelengths (such as visible light 400-760nm, near-infrared 760-1100nm) can increase the light transmittance to over 95% and reduce light loss. At the same time, control the roughness Ra of the fiber end face to be ≤ 0.1 μ m to avoid signal attenuation caused by end face scattering.

（2） Expand the scope of testing

Optimize the fiber numerical aperture (NA) and lens parameters for different detection distance requirements. When conducting short distance detection, use optical fibers with NA=0.2-0.3 and a small focal length lens to control the spot diameter within 0.1-0.5mm, thereby improving the resolution at close range; When conducting long-distance detection, optical fibers with NA=0.4-0.5 are used to increase the light receiving angle, combined with telephoto lenses to reduce light spot diffusion, which can expand the effective detection distance to over 50mm. In addition, by adjusting the ratio of the number of transmitting and receiving optical fibers, the detection range and signal strength can be balanced.

（3） Enhance environmental adaptability

In harsh environmental applications, it is necessary to strengthen probe sealing and anti-interference design. Adopting an IP67 sealing structure, with dual protection of O-ring and sealant to prevent dust and liquid from entering; The shell is made of electromagnetic shielding material to reduce the interference of external electromagnetic radiation on optical signals. At the same time, high-temperature resistant optical fibers and lens components are selected to cover the working temperature range of the probe from -40 ℃ to 120 ℃, meeting the stringent requirements of industrial scenarios.