Multilayer Thin-film Filters Research Articles

Comparison of antireflection surfaces based on two-dimensional binary gratings and thin-film coatings

A comparison of antireflection surfaces based on the two-dimensional binary gratings and thin-film coatings is presented. First, a two-dimensional hybrid binary grating is proposed and analyzed by use of a vector-based implementation of the rigorous coupled-wave analysis method. The optimum parameters of the structure are determined and the effects that changing them have on spectral characteristics of the structure are studied. Then this structure is compared with multilayer thin-film antireflection filters. These filters are designed by genetic algorithm and needle methods, which are powerful methods for multilayer filter design. The comparison results show that the sensitivity of the grating to changes in the incident wavelength is high. However, a reflectance of the order of 10(-3)% at the design wavelength can be achieved. The sensitivity of designed antireflection thin-film filters to wavelength changes is lower, however, and the minimum achievable reflectance is higher.

Model for analyzing manufacturing-induced internal stresses in 50-GHz DWDM multilayer thin-film filters and evaluation of their effects on optical performances

The manufacture of a high-quality reliable thin-film filter (TFF) requires a detailed understanding of the stresses created within the device during fabrication. The ability to systematically approximate the internal stress effect on optical performance is of crucial importance to provide fabrication guidance and improve manufacturing yield. This paper analyzes the internal stress distributions in the substrate and thin-film layers of a 50-GHz TFF and examines the relation of these stresses to the filter's optical characteristics. A linear model along the thickness direction is introduced based upon Townsend's theory of multilayer structures. The analytical results for the key optical parameters are in good agreement with measurements on fabricated filters. This model analyzes the effects of process parameters, such as the substrate type, its coefficient of thermal expansion, and the final substrate thickness on the optical performance of the transmission spectrum center wavelength, transmission passband ripple and isolation, the chromatic dispersion, and polarization-mode dispersion.

Silver–silica transparent metal structures as bandpass filters for the ultraviolet range

We designed and produced silver–silicon dioxide multilayer thin-film bandpass filters for the ultraviolet range by applying the concept of ‘transparent metals’. To calculate the transmission of the designed metallodielectri cfi lters we used the transfer matrix method for lossy structures. We fabricated our multilayer metallodielectric films using radiofrequent sputtering and characterized them by spectral transmission measurements. We achieved satisfactory suppression of undesired visible and infrared parts of the spectrum even for a small number of layer pairs.

Center wavelength shift dependence on substrate coefficient of thermal expansion for optical thin-film interference filters deposited by ion-beam sputtering.

Single-layer films of Ta2O5 and multilayer thin-film filters of Ta2O5 and SiO2 were deposited by ion-beam-sputter deposition. Postdeposition annealing of the structures resulted in increased optical thickness of the films, resulting in an upward shift in the wavelength of the transmission-reflection spectra. Modeling of the single-layer films by means of the effective media approximation indicates an increase in the void fraction of the film after annealing. This increase is consistent with an observed decrease in refractive index and an increase in physical film thickness. The multilayer structures, deposited on substrates of varying coefficient of thermal expansion (CTE), were annealed at various temperatures, and the change in the center wavelength was measured. The measured change is dependent on the annealing temperature and the substrate CTE, indicating that the increase in the void fraction is caused in part by thermally induced stress during the annealing process. A simple model is proposed that relates the void fraction present in the films after annealing with the substrate CTE and the annealing temperature.

High‐gain broadband optical‐waveguide amplifiers

AbstractA novel wideband and high‐gain waveguide‐amplifier structure, which consists of a folded geometry erbium‐ytterbium co‐doped phosphate glass waveguide integrated with a cascaded multilayer medium thin‐film filter (CMMTFF), is proposed. This CMMTFF consists of some different filter‐unit cells with different central wavelengths and bandwidths, and each of them can suppress a certain gain peak at a specific wavelength. The gain characteristics of this new optical amplifiers is obtained. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 64–66, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20208

Spot-size and incident angle dependence of filtering characteristics of narrow pass-band dielectric multilayer filters

We present the spot size and incident angle dependence of filtering characteristics of dielectric multilayer thin-film filters. Experimental results on amplitude responses and dispersion characteristics of narrow pass-band (50GHz) SiO2/Ta2O5 filters are presented, which are in good agreement with theory. Although noticeable deterioration on amplitude filter responses has been seen, the chromatic dispersion is reduced with decreasing the spot size of input light.

FiEnd filters: passive multilayer thin-film optical filters deposited on fibre ends

Multilayer thin-film filters have been deposited on the end faces of optical fibres. Single and double cavity bandpass filters and low-ripple long-pass filters have been made with good optical quality. Reflections are reduced by depositing on bevelled end faces.

Fabrication of multilayer thin film filters on support screens and their properties

A fabrication technology of multilayered and monolayered thin-film filters on rigid support screens with meshes of mm order is suggested. Filters on fine porous polymer membranes with through pores and with the properties of multilayer aluminium filters are also treated. The main field of application of these filters is VUV and soft-X-ray radiation equipment.

Design and Performance of WDM Transmission Systems at 6.3 Mbits/s

One- and two-way 6.3 Mbit/s optical transmission systems employing wavelength-division-multiplexing (WDM) are designed for application to telephone networks. Multiplexing at two wavelengths, 1200 and 1300 nm, as well as that at 810 and 890 nm, is found to be effective after taking the application fields and present fabrication techniques for optical multiplexers into account. Requirements for optical multiplexers are clarified through SNR design in which crosstalk is dealt with effectively. Optical multiplexers composed of newly developed dielectric multilayer thin-film filters are designed to meet the systems' requirements, and good transmission quality is confirmed for the systems by experiments.

Dielectric multilayer thin-film filters for WDM transmission systems

Dielectric multilayer thin-film (DMF) filters for a wavelength-division-multiplexing (WDM) system are discussed. It was found that a 23-layer 3-cavity bandpass-type DMF-filter made of TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> is most suitable for this type of system. An optical multi/demultiplexer employing this type of bandpass DMF-filter is applicable to a two-way WDM transmission system.

Modern Instrumentation for the Optical Control of Thin Film Fabrication in High Vacuum

The demand for a flexible measurement and control instrument for the fabrication of optically effective thin film coatings by evaporation in a high vacuum chamber has led to the development of a modular instrument. The spectral range covers the visible and the near infrared region. It can be used below 10-2 lux and does not need lethal high voltages for its operation. It can be used with a remote controlled monochromator and it is thus possible to program the instrument for different wavelengths. The operation as a control instrument for the production of multilayer thin film filters will be described. Certain problems connected with large scale fabrication of optically effective thin film coatings and the methods to solve them will be discussed.