In this paper a tunable optic system is presented for use in various optical systems. In contrast to most of the tunable optical components which are composed of a waveguide, an electro-optical layer, and electrodes of different materials. The new system consists of a TiO2 waveguide with ZnO as a functional layer on top. The TiO2 layer acts as a high index waveguide, the ZnO system consists of a ZnO:Al/ZnO/ZnO:Al sandwich structure. The ZnO film is used as an electro-optical cladding for the TiO2 waveguide while the two ZnO:Al films act as transparent electrodes. Applying a voltage results in a shift of the effective refractive index of the waveguide because of the electro-optical effect of the ZnO. The TiO2 film is deposited on SiO2 by a PECVD-process from a metal organic precursor CpTiCh (cyclopentadienyl-cycloheptatrienyl-titanium). ZnO and ZnO:Al are rf-sputtered from a Zn target and ZnO:Al target, respectively. While both ZnO layers are c-oriented polycrystals, the TiO2 grows in a nanocrystalline formation without any texture. The configuration of the high index material TiO2 in combination with the transparent and electro-optical ZnO layer allows the use in integrated optical subsystems such as active couplers or active micro ring resonators. The system is designed for a wavelength of 1550 nm.
An integrated optical wavelength division multiplexer/demultiplexer for the 1.5micrometers telecommunication band is presented using a self-focusing transmission grating as the main dispersive element. The high index contrast between the primary TiO2 and the secondary Al2O3 slab waveguide enables comparatively small devices. In contrast to most other WDM principles like arrayed waveguide gratings or interferometer based devices the optical path may be folded thereby further reducing system dimensions. Plasma assisted metal organic chemical vapor deposition is used to deposit Al2O3 and TiO2 thin films onto oxidized silicon substrates from aluminium acetylacetonate Al(acac) and a prototype precursor cyclopentadienyl-cycloheptatrienyl-titanium CpTiCh, respectively. The grating is realized by an anisotropic plasma etch process. Common input and output channels (respectively input channels and common output for a multiplexer) are numerical aperture matched ridge waveguides and can be coupled to optical fibers. In spite of positioning the outgoing waveguides according to the focal points of the self-focusing grating, the grating itself is designed to meet the layout of the device. The strong impact of the desired arrangement on the grating properties (curvature, size and far field) necessitates a compromise which is found by a hybrid simulation based on the finite element analysis (FEM) and a genetic algorithm.
An optical transceiver is presented consisting of a polarization insensitive directional coupler, a hybrid integrated self-aligned laser diode and a hybrid integrated photodiode. In order to increase waveguide-fiber coupling, the fiber is connected to a tapered waveguide. The polarization insensitive directional coupler is designed for separation of the transmitting ((lambda) equals1.3 micrometers ) and the receiving ((lambda) equals1.55 micrometers ) wavelengths. The coupler is based on Al2O3 waveguides realized by MOPECVD processes. These waveguides show attenuation below 0.3 dB/cm at the wavelengths of interest after annealing at ~700 degree(s)C. The hybrid integration of the laser diode is realized by a self-aligned soldering process. Electroplated tin/gold is used as the solder, while the pre-positioning of the laser diode is achieved by a fine-placer. After self-alignment, the misalignment of the laser has to be smaller than +/- 0.5 micrometers vertical and +/- 1.5 micrometers lateral to achieve coupling losses below 3 dB. Vertical mirrors are used for guiding the signal on the chip to reduce optical losses and chip size. The waveguide-fiber coupling is optimized by a tapered waveguide during the deposition of the Al2O3 layer by a KOH-etched silicon mask. The lateral positioning of the fiber is guaranteed by the vertically etched walls of the waveguide improving the properties of the coupling facet. The depth of the fiber groove is machined by an isotropic silicon plasma etch process.
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