We investigate the beam splitting phenomena under the case that light is incident obliquely on thin film Fabry-Perot filter and the dispersion diagram of Fabry-Perot filter is shown; Gaussian beam propagating in the structure is analyzed by Fourier decomposition in angular field, transmitted band is calculated by characteristic matrix arithmetic in optical thin film theory. At last, the thin film Fabry-Perot filter device was fabricated by e-beam deposition in vacuum and measured from 782 to 787 achieved by the tunable Ti-sapphire laser. We show the variation of the distance between the splitting spots at different wavelengths by the image of splitting beams we detected, demonstrating the distance achieve maximum at the peak transmittance wavelength because of the largest group delay. And the experimental result is in good agreement with our interpretation.
Based on the difference of photonic band structures between TE and TM polarization modes in periodic multiplayer and the combining effect of one-dimensional (1D) hybrid dual-periodical photonic crystals (PCs), a novel method to design polarization band-pass filters used in wavelength division multiplexing system is presented. Such the polarization band-pass filters can be fabricated by dual-periodical TiO2/SiO2 thin film PC structures and theoretical calculation shows that they can have excellent optical properties with TM polarization transmission and TE polarization reflectance. And we try to physically discuss and explain the relation between the parameters of PC heterostructures and the optical characteristics of the filters, such as the number of TM polarization passbands, peak transmittance, half-band width and rejection and so on.
The tunable optical filter used for WDM system was fabricated by employed the birefringence of liquid crystal. When the driver voltage changed, the refractive index of the liquid crystal was altered, which inverted to change the effective thickness of the cavity of the filter based on the Fabry-Perot etalon, so the peak of the transmittance was shifted and the filter achieved the tunable performance. The experiment result of the device was achieved to the tunable range from 1534.5nm to 1562.5nm and the full width of the half maximum is nearly 0.8nm and was in agreement with the design one.
A simple and low-cost solution for interleaver used in optical communication, based on multi-cavity Fabry-Perot optical thin film filters, is presented. The analyses on this kind optical interleaver reveal the influencing factors that would affect the thin film interleaver performance, including the cavity's spacer thickness, ambient temperature variation, dispersion for the refractive index of deposited material depending on wavelength and the numbers of cavity that is important for passband flatness and isolation. The interleaver achieved to 100GHz-spaced channels, at wavelength around C band, with adjacent channel's cross-stalk less than —25dB and the minimum insertion loss nearly 0.4dB or so.