Hagen Renner

Comment on "Nonreciprocal light propagation in a silicon photonic circuit".

We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.

Measurement of the birefringence of UV-written channel silica waveguides by magnetooptic polarization-mode coupling

We report the measurement of the birefringence in integrated-optical waveguides using magnetooptical coupling between the two principal polarizations of the fundamental mode. We demonstrate this measurement technique for directly ultraviolet (UV)-written channel waveguides in silica on-silicon and silica-on-silica. The dependence of the waveguide birefringence on the UV-writing power and UV polarization is investigated. The results are compared with the birefringence of etched waveguides in comparable material systems. An analytical formula for the form birefringence in buried channel waveguides is developed, and measured data are compared with theoretical results.

Leaky-mode loss in coated depressed-cladding fibers

A simple formula for the leaky-mode loss in realistic depressed-cladding (DC) fibers is presented. It takes the finite dimension of the substrate cladding and the presence of the coating into account. The losses show oscillations versus both the wavelength and the width of the substrate cladding. Additional small humps occurring in the transmission curves of cutoff measurements are well explained.<<ETX>>

Numerical survey on Bragg reflectors in silicon-on-insulator waveguides

We present a numerical survey of wavelength-selective Bragg reflectors in silicon-on-insulator waveguides. By an appropriate choice of grating period, duty cycle, etch depth and grating length, usable gratings can be designed.

Methods for experimental characterization of UV-written gratings and waveguides

This paper reviews the present status of methods for the experimental characterization of UV sensitivity of waveguide materials, of UV-written or UV-modified waveguides, of Bragg-gratings and long-period gratings and of grating devices. Methods for the measurement of UV-induced waveguide losses and of birefringence are also discussed.

UV-writing of two-mode sections into single-mode fibers for hosting mode-converting Bragg gratings

A waveguide section intended to host mode-converting optical elements has to be two-moded, at least. However, waveguides of interest such as telecommunication fibers are single-moded in general. In this letter, we demonstrate the UV-writing of two-mode sections in originally single-mode fibers. We discuss the particular properties of mode-converting Bragg gratings written into such two-mode fiber sections.

Up and down UV-trimming of planar directional waveguide couplers: modeling

In contrast to etched channel waveguide couplers, directional couplers UV-written into a photosensitive layer can be both down and up trimmed by UV post-illumination of the waveguide cores and of the separating photosensitive region, respectively. Theoretically, the coupling length can be corrected by 10%-40% several times, before the third supermode starts to propagate.

Photonic glass for high contrast structural color

Non-iridescent structural colors based on disordered arrangement of monodisperse spherical particles, also called photonic glass, show low color saturation due to gradual transition in the reflectivity spectrum. No significant improvement is usually expected from particles optimization, as Mie resonances are broad for small dielectric particles with moderate refractive index. Moreover, the short range order of a photonic glass alone is also insufficient to cause sharp spectral features. We show here, that the combination of a well-chosen particle geometry with the short range order of a photonic glass has strong synergetic effects. Using a first-order approximation and an Ewald sphere construction the reflectivity of such structures can be related to the Fourier transform of the permittivity distribution. The Fourier transform required for a highly saturated color can be achieved by tailoring the substructure of the motif. We show that this can be obtained by choosing core-shell particles with a non-monotonous refractive index distribution from the center of the particle through the shell and into the background material. The first-order theoretical predictions are confirmed by numerical simulations.

Thermo-Optic Phase-Profile Shaping of Bragg Gratings in Planar Silica Channel Waveguides

Bragg gratings in planar channel waveguides equipped with arrays of heating elements on top of them are presented. The latter allow for applying user-defined temperature distributions along the gratings and thereby quasi-arbitrary changes of the phase of the coupling coefficient of the grating. In this way, tunable second- and higher-order dispersion compensators can be realized as well as tunable single- or multichannel transmission filters.

High-precision magneto-optic birefringence measurements of UV-written planar silica waveguides and gratings

The birefringence of UV-written planar devices in silica-on-silicon or silica-on-silica is a critical design parameter, in particular when Bragg gratings are involved such as in add-drop-multiplexers.