Quantum Populations in Zeno Regions inside Black Holes

Schwarzschild black-hole interiors border on space-like singularities representing classical information leaks. We show that local quantum physics is decoupled from these leaks due to dynamically generated boundaries, called Zeno borders. Beyond Zeno borders black-hole interiors become asymptotically silent, and quantum fields evolve freely towards the geodesic singularity with vanishing probability measure for populating the geodesic boundary. Thus Zeno borders represent a probabilistic completion of Schwarzschild black holes within the semiclassical framework.Comment: 5 pages, 2 figures, more pedagogical presentation of our unchanged results including an introduction to Zeno region

Too Bad to Benefit?: Effect Heterogeneity of Public Training Programs

This study analyzes the treatment effects of public training programs for the unemployed in Germany. Based on propensity score matching methods we extend the picture that has been sketched in previous studies by estimating treatment effects of medium-term programs for different sub-groups with respect to vocational education and age. Our results indicate that program participation has a positive impact on employment probabilities for all sub-groups. Participants also seem to find more often higher paid jobs than non-participants. However, we find only little evidence for the presence of heterogeneous treatment effects, and the magnitude of the differences is quite small. Our results are thus - at least in part - conflicting with the strategy to increasingly provide training to individuals with better employment prospects.Program Evaluation, Active Labor Market Policy, Effect Heterogeneity, Public Training Programs, Matching

Silicon photonic, planar coupled, 4-channel WDM transmitter

Description We report on our current developments towards a silicon photonic, 4-channel wavelength division multiplexed transmitter system with planar fiber chip coupling. The optical core components consisting of the photonic chip and the connecting V-groove mounted glass fibers were assembled with sub-micrometer accuracy on a glass plate with low thermal expansion for a stable fiber chip coupling. This setup is ready to attach the DC-biasing and termination board as well as a fan-out board for 4x10 Gb/s drivers or a 4x32 Gb/s driver board. Experimental results of the optical and optoelectrical performance will be presented. Summary (500 words) Optical links using silicon photonic transmitters and wavelength division multiplexing (WDM) are the future in particle detector instrumentation, as single channel links with directly modulated laser diodes are not suitable for the projected radiation levels and data amounts anymore. Using silicon photonic modulators, the optical source can be placed in low-radiation areas and radiation hard devices are used inside the detector volume. We use 3 mm long Mach-Zehnder type modulators for our 4-channel WDM transmitter system. The wavelength demultiplexing and multiplexing is performed by planar concave gratings on-chip, so that just two optical fibers for input and output are required. The coupling is polarization sensitive and to avoid polarization controllers for each wavelength, a polarization maintaining fiber is used to launch light to the chip. An overview of the setup is shown in figure a). The WDM chip can be seen in the middle on a 770 µm high, thin-glass platform to match its surface height to the fibers. The angle polished optical fibers for a compact and stable coupling [1] are placed in V-groove chips for positioning and mounting and are located diagonally on the upper left and lower right in the picture. After positioning, all components are fixed on a microscope slide using UV-glue. The low shrinkage of the glue while curing introduces just a negligible increase of coupling loss of less than 1 dB. This might even be decreased by a smaller amount and more precise application of the glue. A side view of the setup is shown in figure b). The fibers protrude 6 mm from the V-grooves to allow for more space for wire bonding the chip to its electronics. In later setups this can be optimized for a smaller size and higher stability. Current driver electronics are made of commercial driver ICs and are rather bulky. To attach the 4x10 Gb/s version, we developed a fan-out board, shown on the left side of figure c). It converts SMA connectors for each of the four channels on one side to bondpads with a pitch of 140 µm on the other side for wire bonding to the chip. This board can be replaced by another driver board for data rates of up to 4x32 Gb/s, but with decreased voltage swing. As the transmission lines of the modulators needs termination, a second board with termination resistors will be attached on the other side of the chip. This board, shown on the right side of figure c), also includes the DC-biasing circuitry for the modulators, which consists of two bias-Tees per modulator. For illustration a silicon photonic system chip is placed between the two boards and will be replaced by the setup shown in figure a). At the time of writing this abstract, electrical tests of the individual modulators are being prepared. Full system performance tests will then be performed after bonding the electrical boards to the chip. [1] M. Schneider et al., “Planar fiber-chip-coupling using angle-polished polarization maintaining fibers”, JINST, DOI 10.1088/1748-0221/18/01/C0106

Report No. 14: Gutachten zur Erwerbstätigenentwicklung in Deutschland: Erstmals mehr als 40.000.000 Erwerbstätige

Kurzgutachten im Auftrag der Initiative Neue Soziale Marktwirtschaft, Bonn 2007 (11 Seiten)

Planar fiber-chip-coupling using angle-polished polarization maintaining fibers

We report on our latest developments of a planar fiber-chip-coupling scheme, using angle polished, polarization maintaining (PM) fibers. Most integrated photonic chip components are polarization sensitive and a suitable way to launch several wavelength channels to the chip with the same polarization is the use of PM fibers. Those impose several challenges at processing and handling to achieve a stable, permanent, and low-loss coupling. We present the processing of the fibers in detail and experimental results for our planar and compact fiber-chip-coupling technique. Summary High performance optical links using wavelength division multiplexing (WDM) are the future in detector instrumentation to increase data transmission bandwidth and reduce fiber count. A key component of such a system is a compact and efficient fiber-chip-coupling, connecting a photonic chip to the optical glass fibers. As most components of integrated photonic chips are polarization sensitive, one can use lossy on-chip polarization-insensitive couplers and polarization controllers or use polarization maintaining (PM) fibers to feed the required polarization directly from the lasers without the need of further manipulation. Our fiber-chip-coupling uses optical single mode glass fibers, whose tip is polished to a certain angle, so that light is reflected radially out of the fiber by total internal reflection at a defined angle, as shown in figure a). The fiber is positioned parallel to the chip surface with the tip above an on-chip grating coupler, so that the radially emitted light hits the grating coupler, which diffracts the light into an on-chip waveguide for further on-chip routing [1, 2]. PM fibers, however, are not axially symmetric due to the strain rods close to the fiber core to introduce birefringence (figure b)). Therefore fiber-chip-coupling becomes more challenging, as the angle of in-axis rotation has to be very well defined. For our process the angle is adjusted for the polishing process with an error of less than 0.3°. To achieve this, a special setup was developed (figure c)), which allows a precise fiber rotation before gluing the fibers to a fiber holder for polishing. For alignment, the front facet of a cleaved PM fiber with its core, cladding, and, most important, strain rods is imaged by a camera with a microscope objective. The camera picture is analyzed by a machine vision system, extracting the contours of the fiber and the strain rods, calculating the rotation angle and indicating if the angle is in an acceptable range. To display the glass strain rods inside the cladding glass, special lighting and contrast enhancement is required. The following polishing process is essential for a low-loss coupling, as the angle of the polished surface to the fiber axis and the surface quality are equally important. To maintain the polishing angle, a special polishing fixture with a parallelogram guidance was developed and 3D-printed (figure d). Several silicon carbide grinding discs and diamond suspensions with decreasing grain sizes were used for polishing. After removing the polished fibers from their respective holders, a final thermal cleaning and fine polishing step was used to get a smooth mirror surface. We will present the setup to initially adjust the PM fibers for polishing, the optimized polishing process providing a recipe to reproduce the results, as well as measurement results of fiber-chip-coupling experiments. [1] D. Karnick et al., ”Optical Links for Detector Instrumentation: On-Detector Multi-Wavelength Silicon Photonic Transmitters” JINST, DOI 10.1088/1748-0221/12/03/C03078 [2] D. Karnick et al., “Efficient, easy-to-use, planar fiber-to-chip coupling process with angle-polished fibers”, 67th ECTC, DOI 10.1109/ECTC.2017.24