In fields such as spectral measurement and material testing, the matching quality between the reflective fiber probe and the light source directly determines the measurement accuracy and signal stability. High quality matching can improve optical transmission efficiency and reduce noise interference, while improper matching may lead to signal attenuation, spectral distortion, and other problems. The following practical matching techniques are shared based on the characteristics of the probe and the type of light source.
Core premise: Accurate adaptation of wavelength range
Wavelength matching is the foundation, and it is necessary to ensure that the emitted wavelength of the light source falls within the effective transmission range of the probe. According to the product specifications of wyoptics, reflective fiber optic probes can be divided into ultraviolet/visible (185-1100nm), visible/near-infrared (380-2500nm) and other types based on wavelength. For example, deep ultraviolet probes (FIB-UV series) are suitable for the 200-1100nm spectrum, while infrared probes (FIB-IR series) cover the 380-2500nm range. When matching, it is necessary to avoid the wavelength of the light source exceeding the probe range. For example, ultraviolet light sources cannot be paired with infrared optical fibers, otherwise the signal will be severely attenuated due to fiber absorption. For special scenarios such as fluorescence measurement, a 600 micron core diameter anti ultraviolet probe can achieve dual functions of excitation and sensing, requiring a light source with corresponding excitation wavelength.
Targeted matching strategy for light source types
The characteristic differences of different light sources require targeted matching of probe parameters:
Laser diode (LD): It has the characteristics of narrowband, high brightness, and strong directionality, and is suitable for high-precision measurement. When matching, a probe with a smaller core diameter (100-200 μ m) should be selected to reduce spot diffusion and improve focusing accuracy. Experiments have shown that the combination of laser and adaptive probe can improve measurement accuracy by 25%. Attention should be paid to laser power control to avoid exceeding the probe's tolerance threshold. The light intensity can be adjusted through an adjustable attenuator.
LED light source: Wide spectrum, high reliability but weak directionality, suitable for broad-spectrum qualitative analysis. Multi core probes with larger core diameters (400~600 μ m) (such as the 7-core series) should be selected to increase the light receiving area and compensate for the lack of directionality. At the same time, priority should be given to selecting anti UV or deep UV probes that are compatible with the wide wavelength output of LEDs.
Broadband light source (halogen lamp, xenon lamp): Provides continuous spectrum, suitable for non-destructive testing, spectral imaging and other scenarios. A wideband fiber optic probe, such as the XSR series (185~1100nm), is required to ensure effective transmission of the entire spectrum. For near-infrared measurement, a combination of ARCoptix's 20W broadband light source and diffuse reflection probe can be used, combined with an integrating sphere to improve the signal-to-noise ratio.
Key parameter optimization: core diameter, number of cores, and optical path design
The probe core diameter and number of cores need to be adjusted according to the light source power and measurement requirements: low-power light sources should be paired with small core diameter probes (100-200 μ m) to avoid light energy dispersion; High power light sources can choose large core diameter probes to prevent fiber optic overheating and damage. Multi core probes (such as 7-core probes) are more suitable for strong signal demand scenarios than 2-core probes, and can enhance the efficiency of reflected light collection.
The design of the optical path also affects the matching effect: it is necessary to optimize the incident angle and spot size of the light source to ensure efficient coupling of light into the fiber; Use a bracket to fix the distance between the probe and the sample, ensuring measurement repeatability. For precision systems such as active fiber ring cavities, piezoelectric ceramic tuning of fiber Bragg gratings can be used to automatically match the wavelength of the light source with the probe, improving the ability to resist environmental interference.
Key points of calibration and environmental adaptation
Double calibration is required after matching: calibrate the stability of the light source intensity with a spectrometer, calibrate the system response with a standard reflector, and establish a correspondence between reflectivity and measured values. In terms of environment, stable light sources and probes should be selected for high temperature and vibration scenarios, such as infrared quartz fiber, which has better temperature resistance than ordinary fiber; Electromagnetic interference environment needs to strengthen optical path shielding to reduce external interference.