强度法测量光纤数值孔径（Measurement of optical fiber numerical aperture by intensity method）.doc

强度法测量光纤数值孔径（Measurement of optical fiber numerical aperture by intensity method） National key construction of fiber optic cable experiment and training -- optoelectronic technology major 28 Measurement of optical fiber numerical aperture by practical five strength method First, the purpose of the experiment 1. to understand the working principle and characteristics of transmissive optical fiber sensors 2. to understand and master the method of measuring fiber optic numerical aperture by transmission fiber optic sensor 3. learn how to make optical fiber sensors Two 、 experimental principle 1, experimental principle (1) fiber numerical aperture NA (Numerical Aperture) defined, when the light beam to two different interfaces, will produce emission and refraction. The cladding interface at the core, the critical angle of C (i.e., the refraction angle is the angle of incidence PI /2) according to the law of Snell refraction can be drawn: 12 arcsin n n C?? (5-1) where: N1 is the refractive index of the fiber core, N2 is the refractive index of the cladding, if the light emitted from the light source through the air after coupling into the fiber, then meet the maximum incident condition of total reflection optical angle of C sin (2): meet the 22211 sin n n n c c??????? (5-2) maximum theoretical numerical aperture (defined optical fiber numerical aperture optical fiber said light collecting capability size): NA max = 2221 n n = n? 1? 2 (5-3) in the formula: n = 121 n? N? N 1, the gradient of optical fiber, optical fiber is the axis of the refractive index n is 2, the refractive index of the cladding. (2) another definition of the numerical aperture of fiber numerical aperture by far field intensity method is the effective numerical aperture defined by far-field intensity method (NAeff). NAeff is determined by measuring the far field intensity distribution of optical fibers. It is defined as the optical far-field intensity of radiation pattern on strong values down to the ma