In this paper, photovoltaic and photoconductive responses were observed respectively in different individual
single-walled carbon nanotube based devices of similar device configurations. Under IR lamp illumination in vacuum,
photocurrent at zero voltage bias was found in one device while resistance change instead of photovoltaic effects was
observed in the other device. The photocurrent was found to decrease as the temperature decreased from room
temperature to 78K; on the contrary, the photoconductive effect was enhanced as the temperature decreased. Schottky
barriers are suggested to be asymmetric for the photovoltaic device while symmetric for the photoconductive device. The
barrier heights of the photovoltaic device were also calculated based on hot electron emission mode of Schottky barrier.
Planar lightwave circuits based on silicon are playing important roles in integrated optical systems. Integrated waveguide turning mirror (IWTM) is essential component for the compactness of optical devices. We design an integrated waveguide turning mirror with a 90 degree(s) directional change in SOI, which diminishes the primary loss from the displacement of waveguide and mirror and has very low mirror surface roughness. In this paper, the theory, design and fabrication of this IWTM are introduced. A beam splitter using the structure is fabricated to test the performances, and expected results are obtained.
Low-cost optical switch is one of the most important components for fiber-based local area networks. In this paper electrostatic driven self-aligned optical switch was developed for the application in optical networks. A convenient wet etching by KOH solution was used to fabricate the structure in (100) silicon wafer in the optical switch. The cantilever, vertical mirror and V-grooves were formed in the bulk silicon directly, which makes the batch process and assembly simpler and more operable. A displacement of 30 microns of the mirror was achieved by the electrostatic force between the silicon block and the aluminum pad. An obvious advantage of the electrostatic driven way is that the operation has no power consumption. Operating frequency of 200 Hz was accepted as the working frequency, which indicated that the switching time can be less than 5 ms. Coupling alignment demonstrated that the insertion losses can be less than 2 dB in the ON-OFF positions.
Ge/Fe multilayers, which were prepared by electron beam evaporation, were annealed at temperatures between 200 and 450 degree(s)C, and the formations have been investigated. It was found that the structure of the surface layer and the interior is quite different. With the results of X-ray diffraction patterns and Mossbauer spectra, the different compound phases were found at different annealing temperature.
For improving underwater visibility for robots, a method is presented using a special intervallic series of light pulses, two acts of emitting and receiving are performed by two specially designed optical shutters, and the control signals are delay synchronized. Calculations show that the received backscattering light can be reduced and so the visible distance increased. This method has several advantages which can make it practical for underwater robots and other actual uses. Its feasibility has been demonstrated in the experiments, while only in principle due to the limitation of the experimental conditions at present.
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