A graphene-based electro-absorption modulator has been integrated into a passive polymer waveguide platform for the first time. The opto-electronic properties of the structure are investigated with numerical simulations and measurements of a fabricated device. The graphene layers transferred to the polymer substrate were analyzed by means of Raman spectroscopy and the results indicate a high crystalline quality of the two-dimensional material. The voltage-dependent transmission through a 25 µm long device has been measured in the telecommunications-relevant wavelength range between 1500 nm and 1600 nm yielding an extinction ratio of 0.056 dB/µm
Photonic devices and new functions based on HHI's hybrid integration platform PolyBoard are presented providing lowloss thin-film-element-based light routing, an on-chip micro-optical bench and mechanically flexible chips comprising optical and electrical waveguides. The newly developed transfer and integration of graphene layers enables the fabrication of active optoelectronic devices in the intrinsically passive polymer waveguide networks with bandwidths in the GHz range. These novel functionalities in combination with the mature thermo-optic components of the PolyBoard platform such as tunable lasers, switches and variable attenuators pave the way towards new applications of photonic integrated circuits in communications and sensors.
A microwave plasma reactor for diamond growth that allows for highly controllable process conditions is presented. The position of the diamond substrate within the reactor can be accurately controlled. Thus, equilibration of plasma conditions can be carried out after changes in process parameters. With this approach, sharp layer transitions among doped, undoped, and isotopically controlled diamond films can be obtained. In addition to the sample transfer, the growth temperature is maintained through a substrate heater, and a clean reactor environment is realized by a load‐lock sample exchange system. The plasma conditions are constantly monitored by optical emission spectroscopy. Using this system, the growth of nanoscopic sandwich structures is demonstrated with controlled isotopic ratios down to ≈10 nm thickness and N(V) layers below 50 nm are obtained on (001)‐oriented diamond. Growth rates and doping efficiencies depending on the used methane concentration are presented. Characterization with continuous‐wave optically detected magnetic resonance yields an average contrast of 4.1% per nitrogen vacancy (NV) orientation in layers with a thickness below 100 nm. Depending on the used methane concentration, surface morphology and NV doping homogeneity are influenced as observed by photoluminescence and atomic force microscopy measurements.
Graphene with its high carrier mobility as well as its tunable light absorption is an attractive active material for highspeed electro-absorption modulators (EAMs). Large-area CVD-grown graphene monolayers can be transferred onto arbitrary substrates to add active optoelectronic properties to intrinsically passive photonic integration platforms.In this work, we present graphene-based EAMs integrated in passive polymer waveguides. To facilitate modulation frequencies in the GHz range, a 50 Ω termination resistor and a DC blocking capacitor are integrated with graphene EAMs for the first time.Large signal data transmission experiments were carried out across the O, C and L optical communications bands. The fastest devices exhibit a 3-dB bandwidth of more than 4 GHz. Our analytical model of the modulation response for the graphene-based EAMs is in good agreement with the measurement results. It predicts that bandwidths greater than 50 GHz are possible with future device iterations.Owing to the absorption properties of the graphene layers, the devices are expected to be functional at smaller wavelengths of interest for optical interconnects and data communications as well, offering a novel flexibility for the integration of high-speed functionalities in optoelectronic integrated circuits. Our work is the first step towards an Active Optical Printed Circuit Board, hiding the optics completely inside the board and thus removing entry barriers in manufacturing. We believe this will lead to the same success as observed in Active Optical Cables for short range optically wired connections.
Vertical diamond Schottky diodes with blocking voltages VBD > 2.4 kV and on-resistances R On < 400 mΩcm 2 were fabricated on homoepitaxially grown diamond layers with different surface morphologies. The morphology (smooth asgrown, hillock-rich, polished) influences the Schottky barrier, the carrier transport properties, and consequently the device performance. The smooth as-grown sample exhibited a low reverse current density JRev < 10 -4 A/cm 2 for reverse voltages up to 2.2 kV. The hillock-rich sample blocked similar voltages with a slight increase in the reverse current density (JRev < 10 -3 A/cm 2 ). The calculated 1D-breakdown field, however, was reduced by 30 %, indicating a field enhancement induced by the inhomogeneous surface. The polished sample demonstrated a similar breakdown voltage and reverse current density as the smooth as-grown sample, suggesting that a polished surface can be suitable for device fabrication. However, a statistical analysis of several diodes of each sample showed the importance of the substrate quality: A high density of defects both reduces the feasible device area and increases the reverse current density. In forward direction, the hillock-rich sample exhibited a secondary Schottky barrier, which could be fitted with a modified thermionic emission model employing the Lambert W-function. Both polished and smooth sample showed nearly ideal thermionic emission with ideality factors 1.08 and 1.03, respectively. Compared with literature, all three diodes exhibit an improved Baliga Figure of Merit for diamond Schottky diodes with VBD > 2 kV.
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