2,806 research outputs found
Narrow-Linewidth Distributed Feedback Channel Waveguide Laser in AlO:Er
We report on the fabrication and characterization of a distributed feedback channel waveguide laser in erbium-doped aluminium oxide on a standard thermally oxidized silicon substrate. Holographically-written surface-relief Bragg gratings have been integrated with the aluminium oxide waveguides via reactive ion etching of a silicon dioxide overlay film. The laser operates at a wavelength of 1545.2 nm and exhibits a threshold of 2.2 mW absorbed pump power, while it produces a maximum output power of 3 mW. The emission is TE polarized and has a Lorentzian linewidth of 1.70±0.58 kHz, which corresponds to a Q-factor of 1.14×E11
Modal characteristics of a flexible cylinder in turbulent axial flow from numerical simulations
High-Q distributed-Bragg-grating laser cavities
Applying Bragg gratings in Al2O3 channel waveguides, we demonstrate distributed Bragg reflectors with Q-factors of 1.02x10e6. An integrated Al2O3:Yb3+ waveguide laser with 67% slope efficiency and 47 mW output power is achieved with such cavities
Characterization of thermally treated PECVD SiON layers.
PECVD Silicon Oxynitride (SiON) layers with different refractive indices (1.472-1.635) were grown and characterized. The as-deposited layers have good thickness uniformity (~1%) and a high homogeneity of the refractive index (~ 5x10-4) over the wafer area. For telecommunication application, however, the optical losses of the as-deposited layers are unacceptably high. Therefore, the loss reduction upon annealing as well as the impact of the elevated temperature on the remaining layer properties has been studied. Annealed waveguides with optical losses as low as 0.2 dB/cm at λ = 1550 nm have been realized
Dual parallel modulation schemes for low-distortion analog optical transmission
The use of two integrated-optical modulators operated in parallel to attain low-distortion analog optical transmission is examined. This static feedforward approach achieves significantly improved linearity at the expense of small increases in the required optical power and moderate increases in the required drive voltage. A novel variation that uses the unique characteristics of an integrated-optical modulator to correct the dominant quadratic distortion of a directly modulated laser is proposed
The diurnal evolution of the urban heat island of Paris: a model-based case study during Summer 2006
The urban heat island (UHI) over Paris during summer 2006 was simulated using the Advanced Regional Prediction System (ARPS) updated with a simple urban parametrization at a horizontal resolution of 1 km. Two integrations were performed, one with the urban land cover of Paris and another in which Paris was replaced by cropland. The focus is on a five-day clear-sky period, for which the UHI intensity reaches its maximum. The diurnal evolution of the UHI intensity was found to be adequately simulated for this five day period. The maximum difference at night in 2 m temperature between urban and rural areas stemming from the urban heating is reproduced with a relative error of less than 10%. The UHI has an ellipsoidal shape and stretches along the prevailing wind direction. The maximum UHI intensity of 6.1 K occurs at 23:00 UTC located 6 km downstream of the city centre and this largely remains during the whole night. An idealized one-column model study demonstrates that the nocturnal differential sensible heat flux, even though much smaller than its daytime value, is mainly responsible for the maximum UHI intensity. The reason for this nighttime maximum is that additional heat is only affecting a shallow layer of 150 m. An air uplift is explained by the synoptic east wind and a ramp upwind of the city centre, which leads to a considerable nocturnal adiabatic cooling over cropland. The idealized study demonstrates that the reduced vertical adiabatic cooling over the city compared to cropland induces an additional UHI build-up of 25%. The UHI and its vertical extent is affected by the boundary-layer stability, nocturnal low-level jet as well as radiative cooling. Therefore, improvements of representing these boundary-layer features in atmospheric models are important for UHI studies
Tolerance and application of polarization independent waveguide for communication devices
A polarization independent optical waveguide structure has been developed and optimized towards minimized dependence on deviations in the processing parameters and very low processing complexity. The tolerance analysis was based on typical parameters of the silicon oxynitride technology. The optimized waveguide structure meets the criterion of a channel birefringence within 5x10-5 taking the processing tolerance into account. Moreover, it was found that the channel birefringence is thickness independent (within the 10-5 criterion) over a range of up to 200 nm. The optimized waveguide, fulfilling also the remaining demands of the application, has been applied for the realization of a passband flattened add-drop multiplexing device with 0.4 nm free spectral range and 0.03 nm TE-TM shift
Use of integrated optical waveguide probes as an alternative to fiber probes for sensing of light backscattered from small volumes
We show that for light collection from thin samples, integrated probes can present a higher efficiency than conventional fiber probes, despite having a smaller collection area. Simulation results are validated by experiments
Arrayed-waveguide-grating light collector for on-chip spectroscopy
We present a novel arrayed-waveguide-grating (AWG) device with improved external (biomedical) signal collection for use in on-chip spectroscopy. The collection efficiency of the device is compared to that of a standard AWG. We also present experimental results on the collection efficiency and size of the collection volume
Multiperiodicity in the large-amplitude rapidly-rotating Ceph ei star HD 203664
We perform a seismic study of the young massive Cephei star HD 203664
with the goal to constrain its interior structure. Our study is based on a time
series of 328 new Geneva 7-colour photometric data of the star spread over
496.8 days. The data confirm the frequency of the dominant mode of the star
which we refine to c d. The mode has a large amplitude of
37 mmag in V and is unambiguously identified as a dipole mode () from
its amplitude ratios and non-adiabatic computations. Besides , we discover
two additional new frequencies in the star with amplitudes above :
c d and c d or one of their daily
aliases. The amplitudes of these two modes are only between 3 and 4 mmag which
explains why they were not detected before. Their amplitude ratios are too
uncertain for mode identification. We show that the observed oscillation
spectrum of HD 203664 is compatible with standard stellar models but that we
have insufficient information for asteroseismic inferences. Among the
large-amplitude Cephei stars, HD 203664 stands out as the only one
rotating at a significant fraction of its critical rotation velocity ().Comment: 7 pages, 5 figures, accepted for publication in A&A (Astronomy &
Astrophysics
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