Research On The Measurement Of Phase Properties Of Optical Coating

With the development of femosecond laser technology and broad band optical fiber communication, the design of thin films with different phase characteristics has attracted more and more concerns. However, the traditional methods for measuring the optical properties of thin film can not meet the requirement of phase characteristics testing. In this thesis, a new white-light Michelson interferometric system is proposed. In which a fiber-optic spectrometer is employed to record interferometric information, and a picomotor is appended to drive the sample. With this system group delay (GD) can be retrieved directly, and high accuracy maintained by avoiding the numerical error. The main contents are arranged as follows:1. Mesuring system of phase properties of optical thin film. After the study of the limitations and disadvantages of former testing system, a novel white-light Michelson interferometric system is developed. Compared with former experimental facility, some new features are appended in our system to improve the measuring accuracy and the stability of system. Moreover, the repeatability and stability of light source are measured, and the errors caused by environmental noise, white-light source, beam splitter and fiber-optic spectrometer are discussed respectively.2. Calculation methods of phase properties of optical thin film. Several calculation methods of phase and GD including windowed Fourier transform, node fitted and wavelet transform based on single shot interferogram are discussed in this thesis. To overcome the shortcomings and limitations of former methods, one two-dimension time domain scanning method is proposed to retrieve the GD directly, by which the error amplifying effect brought by derivation can be can avoided and the testing accuracy of group delay dispersion (GDD) increased. Finally, both advantages and limitations are analyzed for all these methods which provide foundation and orientation for the follow testing work.3. Phase information measurement of optical thin film. A series of experiments are carried out for the measurement on the reflective phase of single layer and on the GDD of dispersion compensation mirrors (including chirped mirror and G-T cavity resonator) using our novel white-light interferometic system. Compared with the measuring curves given by Spectra Physics, the accuracy of our method and stability of our system are verified. Besides, the system is expanded to measure the group refractive index of bulk material and the piezoelectricity properties of PZT thin film. The results are also given to demonstrate the higher testing accuracy and good repeatability of our system over a broad spectral range.