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The European X‐ray Free Electron Laser (EuXFEL) offers intense, coherent femtosecond pulses, resulting in characteristic peak brilliance values a billion times higher than that of conventional synchrotron facilities. Such pulses result in extreme peak radiation levels of the order of terawatts cm−2 for any optical component in the beam and can exceed the ablation threshold of many materials. Diamond is considered the optimal material for such applications due to its high thermal conductivity (2052 W mK−1 at 300 K) and low absorption for hard X‐rays. Grating structures were fabricated on free‐standing CVD diamond of 10 µm thickness with 500 µm silicon substrate support. The grating structures were produced by electron‐beam lithography at the Laboratory for Micro‐ and Nanotechnology, Paul Scherrer Institut, Switzerland. The grating lines were etched to a depth of 1.2 µm, resulting in an aspect ratio of 16. The characterization measurements with X‐rays were performed on transmissive diamond gratings of 150 nm pitch at the P10 beamline of PETRA III, DESY. In this paper, the gratings are briefly described, and a measured diffraction efficiency of 0.75% at 6 keV in the first‐order diffraction is shown; the variation of the diffraction efficiency across the grating surface is presented. [ABSTRACT FROM AUTHOR]

In the under‐screen fingerprint recognition of smart cell phones, the tiny image signals are easily deteriorated by the protective membranes of screens. To solve this issue, an optical waveguide comprising two stage dual‐function gratings is proposed to supply extra lighting. The first stage is formed by two adjacent gratings possessing a cross angle of 120°, which serve as couplers and beam splitters to trap and split the incident light into two paths within the optical waveguide film, respectively. The second stage gratings, possessing a 60° included angle to the first stage, act as beam orientators and expanders by consecutively redirecting a portion of the light beams towards the sensing zone. By covering the waveguide film outside on an organic light emitting diode display screen and setting a camera and a laser under the screen, this slim construction shows high efficiency and large area under‐screen fingerprint recognition with high signal contrast. The design inspires a novel method for efficiently and flexibly controlling photons by arranging a series of gratings with the proper orientations and locations on a chip, which is highly demanded in displays and optical communication. [ABSTRACT FROM AUTHOR]

A broadband, high efficiency polarized beam splitter (PBS) metagrating based on integrated resonant units (IRUs) to enable simultaneous polarization analysis, spectral dispersion, and spatial imaging in the near infrared (NIR) is developed. A PBS metagrating with a diameter of 60 mm is the key technology component of the high‐resolution multiple‐species atmospheric profiler in the NIR (HiMAP‐NIR), which is a spaceborne instrument concept crafted to be a core payload of NASA's new generation Earth System Observatory. HiMAP‐NIR will enable the aerosol profiling in Earth's planetary boundary layer (from surface to2 km altitude) by simultaneously measuring four spatial‐spectral‐polarimetric images from 680 to 780 nm. Through detailed optimization of hybridized resonant modes in IRUs, the PBS metagrating shows a diffraction efficiency of 70% (or better) for all four linear‐polarized incident light, and polarization contrasts between orthogonal states are 0.996 (or better) from 680 to 780 nm. It meets the stringent performance required by the HiMAP‐NIR exploiting a new paradigm for the broad applications of metasurfaces. [ABSTRACT FROM AUTHOR]

For the High‐Energy‐Density (HED) beamline at the SASE2 undulator of the European XFEL, a hard X‐ray split‐and‐delay unit (SDU) has been built enabling time‐resolved pump/probe experiments with photon energies between 5 keV and 24 keV. The optical layout of the SDU is based on geometrical wavefront splitting and multilayer Bragg mirrors. Maximum delays between Δτ = ±1 ps at 24 keV and Δτ = ±23 ps at 5 keV will be possible. Time‐dependent wavefront propagation simulations were performed by means of the Synchrotron Radiation Workshop (SRW) software in order to investigate the impact of the optical layout, including diffraction on the beam splitter and recombiner edges and the three‐dimensional topography of all eight mirrors, on the spatio‐temporal properties of the XFEL pulses. The radiation is generated from noise by the code FAST which simulates the self‐amplified spontaneous emission (SASE) process. A fast Fourier transformation evaluation of the disturbed interference pattern yields for ideal mirror surfaces a coherence time of τc = 0.23 fs and deduces one of τc = 0.21 fs for the real mirrors, thus with an error of Δτ = 0.02 fs which is smaller than the deviation resulting from shot‐to‐shot fluctuations of SASE2 pulses. The wavefronts are focused by means of compound refractive lenses in order to achieve fluences of a few hundred mJ mm−2 within a spot width of 20 µm (FWHM) diameter. Coherence effects and optics imperfections increase the peak intensity between 200 and 400% for pulse delays within the coherence time. Additionally, the influence of two off‐set mirrors in the HED beamline are discussed. Further, we show the fluence distribution for Δz = ±3 mm around the focal spot along the optical axis. The simulations show that the topographies of the mirrors of the SDU are good enough to support X‐ray pump/X‐ray probe experiments. [ABSTRACT FROM AUTHOR]

The authors demonstrate that the bits of a Compact Disc -- Read Only Memory (CD-ROM) can be read without a photodiode (PD). A commercial CD-ROM drive was used and left unmodified except a beam splitter was removed which would route the light to a PD. This allowed for the reflected light to be incident on the laser within the laser package itself. By monitoring fluctuations in the voltage across the laser diode under constant-current injection, it was possible to read and interpret the bits from a spinning CD-ROM. [ABSTRACT FROM AUTHOR]

We present a cost-effective dual polarization quadrature phase-shift coherent receiver module using a silica planar lightwave circuit (PLC) hybrid assembly. Two polarization beam splitters and two 90° optical hybrids are monolithically integrated in one silica PLC chip with an index contrast of 2%-Δ. Two four-channel spot-size converter integrated waveguide-photodetector (PD) arrays are bonded on PD carriers for transverse-electric/ transverse-magnetic polarization, and butt-coupled to a polished facet of the PLC using a simple chip-to-chip bonding method. Instead of a ceramic sub-mount, a lowcost printed circuit board is applied in the module. A stepped CuW block is used to dissipate the heat generated from trans-impedance amplifiers and to vertically align RF transmission lines. The fabricated coherent receiver shows a 3-dB bandwidth of 26 GHz and a common mode rejection ratio of 16 dB at 22 GHz for a local oscillator optical input. A bit error rate of 8.3 × 10-11 is achieved at a 112-Gbps back-to-back transmission with off-line digital signal processing. [ABSTRACT FROM AUTHOR]

A novel polarisation beam splitter (PBS) with a high extinction ratio in a broad band has been proposed and realised by cascading a bent directional coupler and a low-loss transverse-magnetic (TM)-pass polariser based on a subwavelength grating. The realised PBS has a footprint as small as 3 × 22.5 μm, a high extinction ratio (>20 dB) and a low excess loss (∼1 dB) are obtained over a broad band of ∼60 nm for both transverse-electric and TM polarisations. [ABSTRACT FROM AUTHOR]

A polarisation-independent Bragg grating wavelength filter using polarisation rotation is reported. A rib waveguide Bragg grating structure and second-order mode are used to generate the polarisation rotation. A device connected to polarisation beam splitter (PBS) to obtain a polarisation-independent device is fabricated. The measured diffraction wavelength peaks were almost the same for both input polarisations. [ABSTRACT FROM AUTHOR]