Design of spectrometers and polarization splitters using adiabatically connected slab waveguides

The design of fully integrated prism spectrometers and polarization splitters in adiabatically connected slab waveguides with two different thicknesses, using principles of geometrical optics, is presented. In addition, the design of mirrors to connect these devices to input and output waveguides is discussed. The proposed structures will be fabricated, using two wet-etching steps, in a Si3N4 layer in-between a buffer and cladding SiO2 layer

Statistical uncertainties and systematic errors in weak lensing mass estimates of galaxy clusters

Upcoming and ongoing large area weak lensing surveys will also discover large samples of galaxy clusters. Accurate and precise masses of galaxy clusters are of major importance for cosmology, for example, in establishing well calibrated observational halo mass functions for comparison with cosmological predictions. We investigate the level of statistical uncertainties and sources of systematic errors expected for weak lensing mass estimates. Future surveys that will cover large areas on the sky, such as Euclid or LSST and to lesser extent DES, will provide the largest weak lensing cluster samples with the lowest level of statistical noise regarding ensembles of galaxy clusters. However, the expected low level of statistical uncertainties requires us to scrutinize various sources of systematic errors. In particular, we investigate the bias due to cluster member galaxies which are erroneously treated as background source galaxies due to wrongly assigned photometric redshifts. We find that this effect is significant when referring to stacks of galaxy clusters. Finally, we study the bias due to miscentring, i.e., the displacement between any observationally defined cluster centre and the true minimum of its gravitational potential. The impact of this bias might be significant with respect to the statistical uncertainties. However, complementary future missions such as eROSITA will allow us to define stringent priors on miscentring parameters which will mitigate this bias significantly.Comment: 14 pages, 7 figures; accepted for publication in MNRA

Time domain beam propagation method for the simulation of temporal solitons in periodic media

A time domain beam propagation method for the simulation of optical pulses propagating through Kerr-nonlinear structures is presented. The method is verified by simulation of the known solitary wave solutions in nonlinear periodic medi

Light Turning Mirrors in SiON Optical Waveguides for Hybrid Integration with CMOS Photo-detectors

A new method is proposed for hybrid integration of SiON optical waveguides and standard CMOS photo-detectors based on anisotropic etching of 45° facets in a Si substrate. After removal of anisotropically etched Si structures in cladding SiO2, the fabricated total-internal-reflection mirrors can direct the output of the waveguides to photo-detectors placed on top of the chip. The metal-free fabrication process, designed to create these mirrors, is convenient for batch production. Fourier optics based simulations predict that the reflection efficiency of the mirrors is 68.5 %. The far field pattern obtained from the fabricated device is similar to the simulated one

The abundance and spatial distribution of ultra-diffuse galaxies in nearby galaxy clusters

Recent observations have highlighted a significant population of faint but large (r_eff>1.5 kpc) galaxies in the Coma cluster. The origin of these Ultra Diffuse Galaxies (UDGs) remains puzzling, as the interpretation of the observational results has been hindered by the subjective selection of UDGs, and the limited study of only the Coma (and some examples in the Virgo-) cluster. We extend the study of UDGs using 8 clusters in the redshift range 0.044<z<0.063 with deep g- and r-band imaging data taken with MegaCam at the CFHT. We describe an automatic selection pipeline for quantitative identification, tested for completeness using image simulations of these galaxies. We find that the abundance of the UDGs we can detect increases with cluster mass, reaching ~200 in typical haloes of M200~10^15 Msun. The cluster UDGs have colours consistent with the cluster red sequence, and have a steep size distribution that declines as n~r_eff^-3.4. Their radial distribution is significantly steeper than NFW in the outskirts, and is significantly shallower in the inner parts. They follow the same radial distribution as the more massive quiescent galaxies in the clusters, except within the core region of r<0.15XR200 (or <300 kpc). Within this region the number density of UDGs drops and is consistent with zero. These diffuse galaxies can only resist tidal forces down to this cluster-centric distance if they are highly centrally dark-matter dominated. The observation that the radial distribution of more compact dwarf galaxies (r_eff<1.0 kpc) with similar luminosities follows the same distribution as the UDGs, but exist down to a smaller distance of 100kpc from the cluster centres, indicates that they may have similarly massive sub-haloes as the UDGs. Although several scenarios can give rise to the UDG population, our results point to differences in the formation history as the most plausible explanation.Comment: 12 pages, 11 figures. Accepted for publication in A&A after minor revisio

Design of 1480-nm diode-pumped Er3+-doped integrated optical amplifiers

Erbium-doped Y2O3 integrated optical amplifiers are designed for low-threshold operation and 3 dB amplification. The most important design parameter for minimal threshold, the erbium concentration, is found to have an optimum value of 0.35 at% for a given waveguide structure with 1.0 dB cm-1 background loss. The corresponding threshold power is 7 mW. The pump power to obtain 3 dB gain is found to be 22 mW for an amplifier with an optimum erbium concentration of 0.6 at% and 2.8 cm length. At 30 mW pump power the maximum gain is shown to be 5 dB.\ud \ud Designing is done using a comprehensive numerical model of an erbium-doped integrated optical amplifier. In the model two-dimensional intensity-dependent overlap integrals are used, which allow arbitrary erbium dopant profiles and waveguide crosssections. Concentration-dependent effects such as quenching and upconversion are also included in the model.\ud \ud Input parameters for the model are determined from measurements on an unoptimized Er: Y2O3 optical waveguide amplifier. Amplification simulations and gain measurements of the unoptimized waveguides are found to be in close agreement, providing a sound basis for the design calculations

45° light turning mirrors for hybrid integration of silica optical waveguides and photo-detectors

For hybrid integration of an optical chip with an electronic chip with photo diodes and electronic processing, light must be coupled from the optical chip to the electronic chip. This paper presents a method to fabricate metal-free 45° quasi-total internal reflecting mirrors in optical chips that enable 90° out-of-plane light coupling between flip-chip bonded chips. This method is fully compatible with fabrication of conventional optical chips. The mirrors are created using anisotropic etching of 45° facets in a Si substrate followed by fabrication of optical structures. After removal of the mirror-defining Si structures by isotropic etching, the obtained air-optical structure interface directs the output of the waveguides to out-of-plane photo detectors that are mounted flip-chip on the optical chip. Simulations show a reflection efficiency of 72.3 %, while experimentally 47% was measured on a not fully optimized first batch

The Electron Glass in a Switchable Mirror: Relaxation, Aging and Universality

The rare earth hydride YH$_{3-\delta}$ can be tuned through the metal-insulator transition both by changing $\delta$ and by illumination with ultraviolet light. The transition is dominated by strong electron-electron interactions, with transport in the insulator sensitive to both a Coulomb gap and persistent quantum fluctuations. Via a systematic variation of UV illumination time, photon flux, Coulomb gap depth, and temperature, we demonstrate that polycrystalline YH$_{3-\delta}$ serves as a model system for studying the properties of the interacting electron glass. Prominent among its features are logarithmic relaxation, aging, and universal scaling of the conductivity