[Spectrum analysis of modulated polarized light in phase retardation measurement]

The fundamental principle of light modulation is presented. The characteristic of light modulator is discussed both in time and frequency domains. Fourier transform spectrum of the intensity shows that the intensity distribution of outgoing light is the superposition of a series of Dirac functions in the frequency domain. The corresponding intensity distribution curves are also presented. A novel method for phase retardation measurement based on modulated polarized light is introduced. The spectrum analysis indicates that the perfect compensation condition can be satisfied only when the odd frequency components disappear. Under this condition, the phase retardation to be detected can be directly obtained from the compensation quantity of the compensator. This method is a direct measurement which is clearly superior to those indirect methods, especially in terms of high accuracy and low error. Based on the theoretical analysis, relevant experiments were conducted. And experimental results with high precision were obtained.