Design of angle-tuned wedge narrowband thin film filter

• Transmitting intensity distribution of wedge filter has been calculated.
• The negative wedge angle can improve the transmitting spectrum characteristics.
• The negative wedge angle can decrease the facular broadening in oblique incidence.
• The tunable wavelength range of the filter can increase 10 nm with -0.8° wedge angle.

As a tunable optical filter, angle-tuned thin film narrowband filter is widely used in dense wavelength division multiplexing (DWDM) system. In oblique incidence, the transmitting facular broadens obviously, which will cause a decrease in transmissivity and rectangular degree of the filter. The transmitting spectrum characteristics and the transmitting facular broadening are also influenced by the non-parallel incident and emergent interfaces' wedge angle of the wedge filter. In the present paper, the transmitting intensity distribution in different incident angle of the wedge filter has been calculated, and the influences of the wedge angle to the transmissivity and the half bandwidth are also analyzed. The proper wedge angle and incident orientation will improve the characteristics of the transmitting spectrum. A 100 GHz DWDM angle-tuned wedge filter was fabricated which has a wedge angle of 0.8°. Compared with the parallel angle-tuned filter, the wedge filter can enhance the transmissivity and the rectangular degree in oblique incidence and its tunable wavelength range will increase 10 nm.