In this paper, we report a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguides (PhCWs), which have both been exploited as tunable delay lines. The two structures were fabricated on the same silicon-on-insulator (SOI) technological platform, with the same fabrication facilities and evaluated under the same signal bit-rate conditions. We compare the frequency- and time-domain response of the two structures; the physical mechanism underlying the tuning of the delay; the main limits induced by loss, dispersion, and structural disorder; and the impact of CROW and PhCW tunable delay lines on the transmission of data stream intensity and phase modulated up to 100 Gb/s. The main result of this study is that, in the considered domain of applications, CROWs and PhCWs behave much more similarly than one would expect. At data rates around 100 Gb/s, CROWs and PhCWs can be placed in competition. Lower data rates, where longer absolute delays are required and propagation loss becomes a critical issue, are the preferred domain of CROWs fabricated with large ring resonators, while at data rates in the terabit range, PhCWs remain the leading technology

In this study, the sensitivity and the linearity of the un-coated and TiO 2 -coated microfiber knot resonator (MKR) have been analyzed. The MKR is very sensitive to humidity changes since its refractive index is strongly humidity dependent. As a result, shifts occur in the resonance wavelength and there are also changes in output power. The un-coated MKR showed a sensitivity of 1.3 pm/%RH, in terms of the resonance wavelength, and a sensitivity of 0.0626 dB/%RH for the transmitted output power. The sensitivity increased greatly after the deposition of a porous TiO 2 nanoparticle coating on the MKR. The TiO 2 -coated MKR showed an improved sensitivity of 2.5 pm/%RH, with respect to the resonance wavelength, and 0.0836 dB/%RH for the transmitted output power. This MKR sensor has the potential for use in a variety of humidity sensing applications.

We report, for the first time to our knowledge, direct spectral measurements of nonlinear spectral broadening caused by nonlinear propagation through Bragg gratings written on integrated AlGaAs waveguides. The spectral broadening is associated with pulse compression from 400 to 80 ps. The high nonlinearity of AlGaAs enables high-repetition-rate, low-peak-power sources to be used, facilitating easy spectral measurements.

Editorial Integrated optics -new material platforms, devices and applicationsThe objective of the two special issues of Lasers and Photonics Reviews (LPR) on Integrated Optics (of which this is the second part) is to get an idea of the state-of-the-art of this fascinating field through reports of leading scientists and engineers about the latest developments. Our intention is that the broad range of materials, devices, circuits and applications of Integrated Optics is represented by selected examples. We shall not repeat what has already been said in our editorial for the first special issue, which appeared in January 2012. Instead of this, we move immediately to commentary on the content of this second special issue with essential parts of the review abstracts printed in italics.For a number of years, nonlinear integrated optics based on quasi-phase-matched second order nonlinear interactions in materials such as periodically poled lithium niobate (PPLN) and other ferroelectrics, but also in periodically orientation patterned semiconductors, has become progressively more important. It is possible nowadays to convert, with a high efficiency level, the frequency of coherent radiation in integrated nonlinear devices almost arbitrarilyand only limited by the fundamental absorption bands of the substrate materials. Considerable flexibility has been achieved by "ferroelectric domain engineering", which is usually carried out by applying structured external fields to the materials to be poled. However, light-mediated methods can also be used -with major advantages for the fabrication of sub-micrometer domain structures. This exciting development is reviewed by Charlie Y. J. Ying, Alistair C. Muir, Christopher E. Valdivia, Hendrik Steigerwald, Collin L. Sones, Robert W. Eason, Elisabeth Soergel, and Sakellaris Mailis (University of Southampton, United Kingdom; University of Bath, United Kingdom; Cyrium Technologies Inc., Canada; University of Bonn, Germany) in their article on "Light-mediated ferroelectric domain engineering and micro-structuring of lithium niobate crystals". They also show that domain patterns can be transferred into topographical structures by domain selective etching. In this way a wide range of micro-structures of excellent quality has been demonstrated.The state-of-the-art of high-refractive-index-contrast single-crystalline thin lithium niobate (LiNbO 3 , LN) films as a new platform for high-density integrated optics is reviewed by Gorazd Poberaj, Hui Hu, Wolfgang Sohler, and Peter Günter (ETH Zürich, Switzerland; University of Paderborn, Germany). In their paper on "Lithium niobate on insulator (LNOI) for micro-photonic devices" the authors show how sub-micrometer thick, single-crystalline LN films can be fabricated, even as a full wafer of 3 inch (75 mm) diameter, by "ion-slicing" and crystal-or PCB-bonding to a SiO 2 -coated LN substrate. Moreover, several microand nano-structuring techniques have been used to develop micro-and nano-photonic devices. Among them are LNOI photonic wires (cross-s...

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