In order to create thermally tunable filter, we fabricate integrated micro-ring resonators with specific
polymers. Their high index contrast (Δn ~ 0.15 at the wavelength of 1550 nm) allows to make small size
waveguides (typically with cross sections of 1.2 × 1.5 μm2). We study the impact of different ring radii and
gaps on the response of filters. Compared to the state of the art with polymers, we have obtained ring
resonators with good characteristics. These results and the high thermo-optic coefficient of polymers
enable us to plan the creation of thermally tunable resonators. For that purpose, we develop a thermal
model of the polymer waveguide behaviour in order to minimize the electrical consumption of a tunable
filter. First experiments of thermal tunability of the micro-ring filter are also reported to work on a range of
40 °C giving a 5 nm shift of the dropped wavelength.
Polymers are increasingly attractive for the creation of optical integrated circuits particularly owing to a high thermo-optical
coefficient (-10-4 °C-1) which allows to design optical functions tunable according to temperature. For example,
tunable filters or multiplexers are attractive in telecom applications for bringing broadband services to subscribers.
Moreover, the large available range of refractive index, leads to large scale of integration, lowering the fabrication costs
and could be an alternative solution to semiconductor or inorganic dielectric technologies. In this work, optical functions
were created using standard photolithography and Reactive Ion Etching (RIE). Photolithography was used with particular
conditions to improve pattern resolution. Firstly, the details of making optical polymer waveguides and wavelength
micro-ring based filters are given. Optical loss measurements of waveguides and optical characterisation of micro-ring
resonators are also shown for which the results are in agreement with the modelling. Secondly, the same micro-ring
resonators were observed with the temperature change and we noticed that the variation of resonance wavelength is
about 0.2 nm.°C-1. This is just what is needed for the creation of tunable filters or multiplexers without electrical high
power, considering the very small size of the component.
Polymers are attractive to realize integrated circuits specially because they are very simple to process and are promising for low cost devices. Moreover, beside low cost technology, the large possible range of refractive index, could lead to large scale of integration, lowering the fabrication costs. In some cases, it could be an alternative solution to semiconductor or inorganic dielectric technologies. With usual UV photolithography technology, this work shows that it is possible to perform small guides in order to provide relatively high circuit densification. The refractive index contrast, between optical core and cladding, can be as high as 0.07 instead of 0.02 for the higher contrast in silica Ge doped waveguides. Recently, this contrast has been increased to 0.11 at the wavelength of 1550nm. These materials make possible the patterning of guides having radius of curvature smaller than 200μm. Such curvatures open the way to functions based on microrings that potentially lead to compact wavelength multiplexers. With the view to control the fabrication of polymer waveguides, some features of the process are reported here. For example, shortcomings such as unsuitable film worm aspects are described and solutions are given with requirements assigned to rough materials. Mechanical and thermal properties of polymers have to be adjusted to withstand integrated circuit processing. This paper also presents results concerning the realization of integrated passive microring resonators with this technology.
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