A. K. Rüßeler
J. Matthes
F. Kurth
L. Zhao
G.-A. Hoffmann
M. Jupé
A. Wienke
D. Ristau

Combining miniaturization, high precision and active switching capability to develop cost-efficient thin-film filters for hybrid integration

Humboldt meets Leibniz: Emerging Topics in Optics and Photonics
12.-14. Juni
Type: Konferenzbeitrag
Miniaturization and cost-reduction are two trends in research on optics and photonics, driven by ubiquitous applications like tele- and data communication as well as the broad spectrum of sensor applications. Hybrid integration is one approach to transfer the advantages of precise photonic components into the compact and cost-efficient format of a micro-platform. For this platform, we unlock versatile, passive thin-film filter features like precise wavelength multiplexing or beam splitting with special filter characteristics. Our interference filters are produced by means of ion beam sputtering (IBS), coated on 3” silicon wafers with a sacrificial layer. During the IBS process, in situ monitoring with a high resolution broadband monitor controls the deposition process, to achieve high layer thickness accuracy. After deposition, the optical coating is laser segmented into thousands of elements with possible sizes between 25 µm and few millimeters in the areal extend. By removing the sacrificial layer with a water-based process, we reduce the thickness of the elements down to its functional layers and obtain substrate-free, miniaturized thin-film filters. Furthermore, we benefit from interdisciplinary collaboration within the cluster of excellence PhoenixD as well as different materials and production techniques to develop actively switchable filters. Polymer layers with embedded poled chromophores exhibit a refractive index, which changes linearly depending on an applied electric field. They also offer a high transparency in the wavelength region around 910 - 980 nm, which is not addressed by silicon photonics. In addition, they offer high surface quality suitable for optical coatings. The solvent compatibility of the polymer opens up versatile and cost-efficient processing methods under mild conditions. We are currently using spin coating, but highly scalable techniques like a roll-to-roll process with polymer ink would also be conceivable for this material. We demonstrate the integration of the poled chromophore layers into IBS coatings. In our cavity thin-film filter designs, with transparent conductive oxide layers as electrodes on each surface of the filter, high electric field strengths above 10{\^}6 V/m are already achieved when voltages below +- 60 VDC are applied. Our design exploits electro-optic activity of the poled chromophores to change the resonance wavelength of the cavity and thereby induces a spectral shift of the transmission peak. For a given laser wavelength, this phenomenon enables a switching capability between a reflective and transmitting state. This way, our research approach opens up the possibility of a highly integrated filter-based switch on a micro-platform.