Shaping device for high retangle factor tunable thin-film filter

The beam divergence angle of the incident collimator will change the transmitting characteristics of the angle-tuned thin-film filter, which insert loss will increase and passband will decrease. With the incident angle is increasing, the phenomena will be more and more obviously. According to the Lagrange-Helmholtz principle, the beam expander has been designed to compress the divergence angle of the incident beam. The double filtering technology has also been used to enhance the retangle factor of the thin-film filter. The experiment results show that the shaping system can effectively eliminate the influence of the divergence angle to the thin-film filter.