Haixing Chen

Wavelength-division multiplexed thin-film filters used in tilted incident angles of light

The properties of wavelength-division multiplexed (WDM) narrowband filters used in tilted collimated light are described. The wavelength shift for s polarization in a low-index-spacer filter is larger than that for p polarization when the filter is tilted, but it is smaller in a high-index-spacer filter. Therefore the passbands of the tilted filter can be centered at the same wavelength for two polarization modes by use of high- and low-index materials, as appropriate, as spacers or by selection of a moderate-index material instead of a spacer. With such spacers, WDM filters used for incident angles of 20 degrees or even greater are constructed. Experimental results agree with the computed ones.

Tunable optical filter based on liquid crystal Fabry-Perot etalon

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.

Optical interleaver based on multicavity Fabry-Perot thin film filter

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 cavitys 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 channels cross-stalk less than —25dB and the minimum insertion loss nearly 0.4dB or so.

Superprism Effect in Thin Film Fabry-Perot Filter

For the sake of achieving remarkable superprism effect, we investigate in thin film Fabry-Perot filter which possess drastic change in phase and large group delay around wavelength of peak transmittance. The group delay and spatial dispersion shift are simulated numerically; while the device is fabricated and tested with the maximum spatial separation shift reach to 65�m . We also analyze Gaussian beam propagating in the device to give the interpretation of the spot splitting phenomenon in this experiment. Compared with the traditional prism, the total thickness of our structure is only 3.3�m , and shows a very large deflection angle about 30 ◦ /nm.

Beam splitting phenomena in Fabry-Perot filter

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.