We have designed a high-efficiency broadband grating coupler for coupling between silicon-on-insulator (SOI) waveguides and optical fibers. The grating is only 13 µm long and 12 µm wide, and the size of the grooves is optimized numerically. For TE polarization the coupling loss to single-mode fiber is below 1 dB over a 35-nm wavelength range when using SOI with a two-pair bottom reflector. The tolerances to fabrication errors are also calculated.

/pdf/compact-efficient-broadband-grating-coupler-for-silicon-on-28c3jk3fhz.pdf

Compact efficient broadband grating coupler for silicon-on-insulator waveguides.

General Trojan-horse attacks on quantum-key-distribution systems, i.e., attacks on Alice or Bob's system via the quantum channel, are analyzed. We illustrate the power of such attacks with today's technology and conclude that all systems must implement active counter measures. In particular, all systems must include an auxiliary detector that monitors any incoming light. We show that such counter measures can be efficient, provided that enough additional privacy amplification is applied to the data. We present a practical way to reduce the maximal information gain that an adversary can gain using Trojan-horse attacks. This does reduce the security analysis of the two-way plug-and-play implementation to those of the standard one-way systems.

/pdf/trojan-horse-attacks-on-quantum-key-distribution-systems-24jm8wut0d.pdf

Trojan-horse attacks on quantum-key-distribution systems

We demonstrate a novel polarization splitter based on a two-dimensional grating etched in a silicon-on-insulator waveguide. The device couples orthogonal modes from a single-mode optical fiber into identical modes of two planar ridge waveguides. The extinction ratio is better than 18 dB in the wavelength range of 1530-1560 nm and the coupling efficiency is approximately 20%. The device is very compact and couples light only to transverse-electric modes of the planar waveguides. Therefore, it may be used in a polarization diversity configuration to implement a polarization insensitive photonic integrated circuit based on photonic crystal waveguides.

/pdf/a-compact-two-dimensional-grating-coupler-used-as-a-37q01f5m3m.pdf

A compact two-dimensional grating coupler used as a polarization splitter

In nondispersive media, the minimum distance that can be resolved by partial coherence interferometry (PCI) and optical coherence tomography (OCT) is inversely proportional to the source spectral bandwidth. Dispersion tends to increase the signal width and to degrade the resolution. We analyze the situation for PCI ranging and OCT imaging of ocular structures. It can be shown that for each ocular segment an optimum source bandwidth yielding optimum resolution exists. If the resolution is to be improved beyond this point, the group dispersion of the ocular media has to be compensated. With the use of a dispersion compensating element, and employing a broadband superluminescent diode, we demonstrate a resolution of 5 μm in the retina of both a model eye and a human eye in vivo. This is an improvement by a factor of 2-3 as compared to currently used instruments. © 1999 Society of Photo-Optical Instrumentation Engineers.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-4/issue-01/0000/Dispersion-effects-in-partial-coherence-interferometry--implications-for-intraocular/10.1117/1.429900.pdf

Dispersion effects in partial coherence interferometry: implications for intraocular ranging

A method is given for extracting object visibilities from data provided by a long baseline interferometer, where the beams are spatially filtered by single-mode fibers and interferograms are obtained as scans around the zero optical pathlength difference. It is shown how the signals can be corrected from the wavefront perturbations caused by atmospheric turbulence. If the piston perturbations are also removed, then the corrected data contain both spatial and spectral information on the source (double Fourier interferometry). When the piston cannot be removed, object phase and spectral information are lost, and the observable (free of detector noise bias) is the squared modulus of the coherence factor, integrated over the optical bandpass. In a fiber interferometer this quantity leads to very accurate object visibility measurements because the transfer function does not involve an atmospheric term. The analysis also holds for a more classical pupil plane interferometer which does not take advantage of the spatial filtering capability of single-mode fibers. In that case however, the transfer function includes a turbulence term that needs to be calibrated by statistical methods.

/pdf/deriving-object-visibilities-from-interferograms-obtained-75spr133sc.pdf

Deriving object visibilities from interferograms obtained with a fiber stellar interferometer

Physical Explanation of Waveguiding by Single-Mode Fibers.- Electromagnetic Fields.- Gaussian Beams.- The Fundamental Fiber Mode.- Higher-Order Modes.- Launching of Modes.- Radiation from the Fiber End.- Joints Between Fibers.- Spot Size and Width of the Radiation Pattern.- Signal Transmission Through Single-Mode Fibers.- Components for Single-Mode Fibers.- Measuring Techniques.

Ernst-Georg Neumann

Papers

Single-mode fibers