Research On High-efficiency Spectral Focusing System In Near Infrared Non-invasive Biochemical Analysis

Near-infrared spectroscopy (NIRS) is one of the most potential ways in non-invasive biochemical analysis of blood. However, the absorption spectra of blood were weak, because of strong absorption of water to light in human tissue, and low contents of various chemical components in blood. Thus, it is a little difficult in non-invasive biochemical analysis with NIRS. In order to solve this problem, this paper utilizes a method which is that increasing light collection efficiency of optical system to increase the flux of spectral analysis system, and then it is benefit to improve the signal-noise ratio (SNR) of spectral instrument.First of all, the research progress of near-infrared non-invasive biochemical analysis was introduced. The current technical difficulties in this field were discussed, including weak absorption spectra of blood, interference of background and blood volume periodic change. About the first problem, the design of high-efficiency focusing optical system was proposed. Several optical systems which were composed of optical fiber, ellipsoidal reflector and compound parabolic concentrator respectively were studied.The principle of Monte Carlo simulation was presented, and combining with three layers of skin tissue, the propagation law of light in skin tissue was researched. In the wavelength range from1000nm to2350nm, the photon propagation path length, the photon visit depth, the photon scattering number, and diffuse reflectance light energy were calculated. Besides, the influence of incidence-emergence distance to emergent photons was discussed. According to the results of Monte Carlo simulation, the structure of optical fiber was designed. And with the help of optical software, diffuse reflectance light energy and illumination distribution that was collected by optical fiber were simulated.Based on the focusing characteristic of ellipsoidal reflector, coordinates of image points were calculated when object was in focal plane. Following this method, structure parameters of ellipsoidal reflector focusing well were optimized. Using ray tracing method, focusing energy feature of ellipsoidal reflector was analyzed. The light energy utilization efficiency of ellipsoidal reflector raised5.4times as against non-optical collection system.Relationship of reflection ray with structure of compound parabolic concentrator (CPC) was analyzed, as well as the structure parameters of CPC-concave mirror system were optimized. A novel double compound parabolic concentration system was put forward firstly. Focusing performance change of standard and truncated CPC was discussed, and then structure parameters collecting light well were optimized. Meanwhile, focusing situation to human diffuse reflection light of these two optical systems were studied respectively. Compared with non-optical collection system, the light energy utilization efficiency of truncated CPC-concave mirror system raised15.1times, while the light energy utilization efficiency of truncated double compound parabolic concentration system raised32.6times to human diffuse reflection light.The results show that several focusing system above can collect diffuse reflection light to detector effectively. Thus, it helps improve SNR in near-infrared non-invasive biochemical analysis of blood, along with overall analysis accuracy.