Xinrong Wang

Helicon plasma deposition of a TiO2/SiO2 multilayer optical filter with graded refractive index profiles

Thirty one layer TiO2/SiO2 optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices of TiO2, SiO2 and TiO2–SiO2 composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter.

Microstructure and optical properties of amorphous TiO2-SiO2 composite films synthesized by helicon plasma sputtering

Abstract Composite films of TiO 2 –SiO 2 have been deposited on Si(100) wafers and glass (BK7) substrates by helicon plasma sputtering at room temperature. The results of X-ray diffraction and high resolution transmission electron microscopic observation showed that all of the composite films have an amorphous structure. The observation of scanning electron microscopy exhibited that the surfaces of all of the composite films have dense smooth morphology. The refractive index and the transmittance of the composite films varied gradually in the whole composition range of the TiO 2 –SiO 2 binary system. TiO 2 –SiO 2 composite films exhibited a transmittance of more than 90% compared with that of the glass (BK7) substrate. The relationship between refractive index and TiO 2 content for the composite films can be described using the Lorentz–Lorenz model

Brilliant and tunable color of carbon-coated thin anodic aluminum oxide films

When a thin anodic aluminum oxide (AAO) film on an Al substrate is uniformly coated with carbon by chemical vapor deposition, the saturation of interference color is substantially enhanced and, as a result, the coated AAO film exhibits a brilliant color. Such remarkable saturation enhancement is predominantly due to the carbon deposited on the inner walls of nanochannels of the AAO film, which efficiently screens the reflected light from AAO–Al interface. The brilliant carbon-coated AAO film is useful for weather-resistant decorative purposes and holds promise as an effective broadband optical limiter for nanosecond laser pulse.

Design and experimental approach of optical reflection filters with graded refractive index profiles

A novel optical multilayer filter with graded refractive index profiles using a quarterwave stack was designed. This filter exhibits a high reflectance band, a sharp cutoff and a wide transmittance region as the result of sidelobe suppression. A 31 layer TiO2/SiO2 high reflectance filter with a graded refractive index profile was fabricated by helicon plasma sputtering on BK7 and Si (100) substrates. The deposition system was operated under ambient gas pressure of 1.8×10−1 Pa at room temperature. The measured transmittance of the spectrum was in good accord with calculated results. Transmission electron microscopic observations confirmed the expected microstructure of the filter.

Optical properties of titania/silica multilayer filters prepared by helicon plasma sputtering

Seven-layer optical multilayer filters with alternating layers of titania and silica were fabricated by helicon plasma sputtering at room temperature. The reflectance of the filters around the design wavelengths of 800 and 1300 nm are up to 95.80% and 95.32%, respectively. Their reflected bands have the full widths at half maximum of about 360 and 600 nm, respectively. The measured transmittance spectra correspond well with the calculated results based on the optical multilayer film theory with measured refractive indices of 2.44 and 1.48 for TiO2 and SiO2, respectively. Microstructures of the TiO2 and SiO2 films and TiO2/SiO2 multilayer films were investigated.

Design and preparation of a 33-layer optical reflection filter of TiO2–SiO2 system

Multilayer optical reflection filters with several kinds of graded refractive index profiles were designed. The effects of the number of layers of multilayer films and grading functions of refractive index profiles on the optical filter characteristics were examined by using simulation. A 33-layer optical reflection filter with a linear refractive index profile was found to be optimal in terms of both optical performance and manufacture. The designed 33-layer TiO2–SiO2 reflection filter was fabricated by helicon plasma sputtering. The optical performance of the prepared multilayer film agreed well with that of the designed filter. The measured transmittance spectrum exhibited a sharp cutoff stop band around a central wavelength of 1340 nm and a wide pass region with high transmittance of about 90%. The reflectance of the stop band was greater than 99.0% in the wavelength region from 1208 to 1518 nm.

Stepwise graded refractive-index profiles for design of a narrow-bandpass filter

A combination of stepwise graded refractive-index profiles and a cavity structure is used for designing narrow-bandpass filters of TiO(2)/SiO(2) multilayer films upon BK7 glass substrates. Symmetrical profiles of stepwise graded refractive indices result in high transmittance of passbands for the designed filters. The bandwidth of the narrow-bandpass filter is controlled by adjustment of parameters such as the thickness and the number of layers in the multilayer stack. This design is proposed as a new and simple method for coating synthesis of optical filters.

Design and Synthesis of a 33-Layer Narrow Bandpass Filter with Graded Refractive Index Profiles

A novel bandp ass filter consisting of graded refractive index profiles and a three-cavity stack was designed. It exhibits good optical characteristics, i.e., high transmittance (>99%) at the designated wavelength of 1550±25 nm and high reflectance (>99%) in wavelength regions of 1400±50 nm and 1780±100 nm. This designed 33-layer TiO 2 -SiO 2 film with graded refractive index profiles was prepared by helicon plasma sputtering. The measured transmittance spectrum exhibited good agreement with the designed spectrum. The microstructure of this multilay er film was investigated using electron microscopy.