@inproceedings{BuchmannZhangScharfenorthetal.2016, author = {Buchmann, Jens and Zhang, Edward and Scharfenorth, Chris and Spannekrebs, Bastian and Villringer, Claus and Laufer, Jan}, title = {Evaluation of Fabry-Perot polymer film sensors made using hard dielectric mirror deposition}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15289}, pages = {920 -- 928}, year = {2016}, abstract = {Fabry-Perot (FP) polymer film sensors offer high acoustic sensitivity, small element sizes, broadband frequency response and optical transmission to enable high resolution, backward mode photoacoustic (PA) imaging. Typical approaches to sensor fabrication involve the deposition of stacks of alternating dielectric materials to form interferometer mirrors, which are separated by a polymer spacer. If hygroscopic soft dielectric materials are used, a protective polymer layer is typically required. In this study, methods for the deposition of water-resistant, hard dielectric materials onto polymers were explored to improve the robustness and performance of the sensors. This involved the optimisation of the fabrication process, the optical and acoustic characterisation of the sensors, and a comparison of the frequency response with the output of an acoustic forward model. The mirrors, which were separated by a 20 μm Parylene spacer, consisted of eight double layers of Ta2O5 and SiO2 deposited onto polymer substrates using temperature-optimised electron vapour deposition. The free spectral range of the interferometer was 32 nm, its finesse FR = 91, and its visibility V = 0.72. The noise-equivalent pressure was 0.3 kPa (20 MHz bandwidth). The measured frequency response was found to be more resonant at 25 MHz compared to sensors with soft dielectric mirrors, which was also in good agreement with the output of a forward model of the sensor. The sensors were used in a PA scanner to acquire 3-D images in tissue phantoms.}, language = {en} } @inproceedings{MeisterSchwedaDziedzinaetal.2010, author = {Meister, Stefan and Schweda, Dawid and Dziedzina, Marcus and Al-Saadi, Aws and Franke, B{\"u}lent A. and Scharfenorth, Chris and Grimm, Bernd and Dufft, Daniela and Schrader, Sigurd and Eichler, Hans J.}, title = {Single cavity filters on end-faces of optical fibers}, publisher = {Society of Photo-Optical Instrumentation Engineers (SPIE)}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:526-opus4-15214}, pages = {253 -- 261}, year = {2010}, abstract = {We have developed thin film Fabry-Perot filters directly coated on optical fibers to archive a high level of integration with a reduction of optical elements. Such band-pass filters can be used in fiber optical sensor systems, and for fiber communication, e.g. CWDM applications. The filters cavities consist of a single spacer and two dielectric mirrors. The dielectric mirrors are deposited by PVD directly on end-faces of single-mode optical fibers. Dielectric as well as polymeric materials were applied as the spacer layer. Polymeric spacer layers were deposited by dip coating. The influence of the mirror reflectivity on the transmission band of the Fabry-Perot filters was investigated. Furthermore, the optical performance of filters with first order (λ/2) as well as higher order spacers was analyzed. The experimental results are compared with numerical analysis of Fabry-Perot cavities on the end-face of cylindrical waveguides. The spectral characteristic of the filters are calculated using a software solving Maxwell´s equations by a FDTD method. The layer design of the filters and the deposition process were optimized for maximum transmission and narrow bandwidth of the transmission peak. Passive band-pass filters on fiber end-faces were designed, fabricated and characterized for transmission wavelengths of 945 nm, 1300 nm, as well as 1550 nm. Bandwidths as narrow as 1 nm could be achieved for 945 nm.}, language = {en} }