Research On Key Technologies Of Adi Based On Wavelength Modulation

With the development of aerospace and aviation industry, the higher level of measurement of absolute distance is required. The machining and fitting of the large-sized component also requires for accurate measurement of absolute distance for even large sizes. The recent measurement method of ADI based on wavelength modulation is an important one of ADI, as it can measure the big sizes with micro-meter precision. In this method, the absolute distance can be obtained by the phase difference between the measured object and the interfered laser light with stable frequency passing through a reference interferometer with precise length, which is generated by a semiconductor laser generator with modulated wavelength through.In this paper, it analyzes the error module of ADI based on the principles of ADI based on wavelength modulation and with the current equipment of measurement, and it also studies the frequency stabilization of a laser diode with use of light-induced birefringence in an atomic vapor to resolve the problems of low stability of laser light. In this paper, it also raises the issue of measurement on stability, and also builds reference interferometer of ADI based on wavelength modulation. The main contents of the research are as follows:A closed side symmetric heating structure is designed to resolve the issue of poor noise-signal ratio, long time to reach stable frequency and loss of signals caused by improper temperature control of atomic vapor. The resistance wire with reversed winding is used to control the temperature for the atomic vapor, so it can be heated timely and stably. Thus, the sublimation of the metal atoms at the side with laser light in the atomic vapor is resolved, and the noise-signal ratio can be improved, which will finally improve the feedback control during the stabilized frequency.Compared to the poor accuracy of the scanty stable frequency generated by the current semiconductor laser generator with saturated absorption frequency stabilization of the potassium, a generator with a diode with use of light-induced birefringence in a rubidium atomic vapor is constructed to improve not only the precision of the frequency stabilization but also to broaden the atomic absorption spectra, which resolves the issue of few stabilized frequencies, but also realizes the multiple stable frequencies of laser.Regarding the problem of current methods to evaluate the stability of the semiconductor laser, one sort of software is designed to measure the phase and to evaluate the stability with the nonlinear error compensation to the system with ellifit. At the same time, a reference interferometer with compact structure, with less likelihood of being impacted, and with small drift of length is designed and built up as the length reference for absolute distance measurement, so as to resolve the unstable structure of the reference interferometer.Based on the research on key technologies above, in this paper a reference interferometer with stable frequency via light-induced birefringence is built up for ADI based on wavelength modulation. The characteristic parameters of key units have been tested through experiments, and the stability of the laser generator has also been tested by the method of evaluation mentioned above. The experimental results indicate that the method of stability measurement in this paper is practicable for the evaluation of laser stability. And it also indicate that after the frequency is stabilized for the laser generated by the light-induced birefringence, its frequency stability can be kept within 1.5×10-8, and this method can stabilize the multiple frequency of the semiconductor laser fast.