Study On Linear Tuning Filters Based On Interference Thin Film Filters

Tunable optical filters based on thin-film interference filters are extensively researched due to the good characteristics of thin-film interference filters such as narrow bandwidth, low insertion loss and fine temperature stability.In this paper, a new linear tuning filter based on the angle-tuned thin-film interference filter is design for the first time. The idea of the linear tuning filter is to design a mechanism including a stepping motor to make the central wavelength of the filter and rotary angle of stepping motor become linearity. So it is very convenient to measure central wavelength of the filter. It can determine the central wavelength of the linear tuning filter directly through step count of stepping motor.Theoretically, through transfer matrix method of multilayer thin-film interference filter and parameters of the mechanism, the relationship between central wavelength of the filter and rotary angle of stepping motor is calculated with a three-cavity thin-film interference filter. Then, the influence on linearity of the linear tuning filters is analyzed with different parameters of the mechanism.Experimentally, a linear tuning filter's set including a finished product narrowband thin-film interference filter and control circuit of stepping motor has been designed. Then, making use of LED in 1550nm as broadband light source, the spectrum curve is achieved after light through the linear tuning filter. Linearity of the tuning filter is analyzed through the spectrum curve. In the end, the experimental results show that the linearity of the linear tuning filter is less than ± 0.4nm with a tuning range of 1548nm~1560nm by means of optimizing parameters of the mechanism.