| Recently, the application fields of optical thin film expand constantly. And these applications require very high performance for optical thin film component, therefore put forward a severe challenge to thin film engineers, and at the same time, accelerate the development of thin film technology. Because of the importance of optical monitor in optical coating system, many institutes and companies have done a good many researches for it and achieved many achievements applied in practical optical coating system. At the aspect of optical monitoring, several leading companies in the world who product optical coating system, such as Leybold, Veecoo, Shincoron and Optorun, make optical monitors with high performance. However, the optical monitor made in China is far below worldwide level. Therefore, we analyzed the optical monitoring system in detail, and thereby, designed high precision optical monitor by ourselves. The jobs we've done include:1 .In this paper, optical thin film technology, the current state of the research on optical monitor, the goal and significance of the research and the theory of optical monitoring are introduced firstly. It is also pointed out that the developing trend of optical monitor- digitalization.2.Before designing practical optical monitor, we analyze the principle of the key component of optical monitor- the lock-in amplifier, then simulate phase sensitive detection (PSD) by computer at the first time in China. We simulate out the main signal with wide band noise and frequency noise. Then simulate PSD operation with the main signal and a simulated reference signal. As a result, the impact of these twokinds of noises on optical monitor is obtained. In order to solve the problems in designing optical monitor, we've made several other simulations. Firstly, combining the simulation and the required time delay of the practical optical monitor, we can decide the order and time delay of the low pass filter in PSD. Secondly, we also simulate the PSD with a square wave to be the reference signal. And thirdly, we make sure that inserting band pass filter before the multiplier of PSD has no significance in enhancing the signal noise ratio of the system by further simulation.3.The precision and stability of the system is decided by the combining effect of the noises in the system. By analyzing the noises in light path and circuit in the system of optical monitor, we chose the current source with high stability to be the power supply for light source, designed frequency-stabilized chopper and low noise circuit for receiving optical signal, and designed digital lock-in amplifier with excellent performance of noise restraint, thereby built up high precision optical monitor, increase the monitoring spectrum range of the monitor and improved the precision and stability of the system to ±0.05% and ±0.1%. We also achieved auto stop in the process of optical coating by programming of computer and PLC, thereby avoid the deficiency of manual operation and increased the ratio of qualified product and repetitiveness of optical coating.4.Applied in optical coating practically, the optical monitor shows us high precision and stability.By analysis and design upwards, we've designed high precision optical monitor and improved the precision and stability of the system greatly, thereby built up the convenience for increasing the ratio of qualified product and enhancing the quality of optical thin film. At the end of this paper,, we pointed out the further job we need to do to improve the precision and stability of the optical monitor.
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