Tunable delay lines in silicon photonics: coupled resonators and photonic crystals, a comparison

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

A variable delay integrated receiver for differential phase-shift keying optical transmission systems

An integrated variable delay receiver for DPSK optical transmission systems is presented. The device is realized in silicon-on-insulator technology and can be used to detect DPSK signals at any bit-rates between 10 and 15 Gbit/s

Determining the electronic performance limitations in top-down fabricated Si nanowires with mean widths down to 4 nm

Silicon nanowires have been patterned with mean widths down to 4 nm using top-down lithography and dry etching. Performance-limiting scattering processes have been measured directly which provide new insight into the electronic conduction mechanisms within the nanowires. Results demonstrate a transition from 3-dimensional (3D) to 2D and then 1D as the nanowire mean widths are reduced from 12 to 4 nm. The importance of high quality surface passivation is demonstrated by a lack of significant donor deactivation, resulting in neutral impurity scattering ultimately limiting the electronic performance. The results indicate the important parameters requiring optimization when fabricating nanowires with atomic dimensions

Travelling-wave resonant four-wave mixing breaks the limits of cavity-enhanced all-optical wavelength conversion

Wave mixing inside optical resonators, while experiencing a large enhancement of the nonlinear interaction efficiency, suffers from strong bandwidth constraints, preventing its practical exploitation for processing broad-band signals. Here we show that such limits are overcome by the new concept of travelling-wave resonant four-wave mixing (FWM). This approach combines the efficiency enhancement provided by resonant propagation with a wide-band conversion process. Compared with conventional FWM in bare waveguides, it exhibits higher robustness against chromatic dispersion and propagation loss, while preserving transparency to modulation formats. Travelling-wave resonant FWM has been demonstrated in silicon-coupled ring resonators and was exploited to realize a 630-μm-long wavelength converter operating over a wavelength range wider than 60 nm and with 28-dB gain with respect to a bare waveguide of the same physical length. Full compatibility of the travelling-wave resonant FWM with optical signal processing applications has been demonstrated through signal retiming and reshaping at 10 Gb s−

Statistics of backscattering in optical waveguides

The statistics of backscattering induced by sidewall roughness in dielectric optical waveguides is experimentally investigated. We demonstrate that waveguide backscattering is a wavelength dependent random process, whose statistics follows the rules of single scattering systems, independently of shape, size and refractive index contrast of the waveguide, and of the light polarization state. The intensity of backscattering is distributed according to an exponential probability density function and its mean delay corresponds to a reflection at half the effective length of the waveguide

The first decade of coupled resonator optical waveguides: bringing slow light to applications.

A century after the first optical cavity, coupled resonator optical waveguides (CROWs) were conceived as a new way to guide light on a photonic chip. Controlling chains of coupled resonators to let light propagate through, with a reduced speed and enhanced intensity, boosting light-matter interaction while keeping information undistorted: this was the fascinating promise of CROWs, but also one of the most ambitious challenges ever set for integrated optics. The first decade of the history of CROWs is discussed in this review, from the original idea to recent applications, panning through the technological platforms that have been employed to realize these structures. Design criteria and management issues, fundamental limits, and sensitivity to fabrication tolerances are discussed to make the reader aware of the performance of state-of-the-art CROWs and to provide a realistic perspective of future applicative horizons

Roughness Induced Backscattering and Polarization Rotation in Optical Waveguides

In this contribution we experimentally investigate backscattering and polarization rotation induced by sidewall roughness in silicon-on-insulator (SOI) optical waveguides. Waveguides with different widths, different upper cladding and longitudinally tapered have been measured and compared. All the measurements have been performed by means of an advanced frequency domain interferometric technique, which allows the evaluation of both amplitude and phase of backscatter as well as its polarization

Modelling Backscattering in Optical Waveguides

The properties and the statistics of backscattering induced by sidewall roughness in optical waveguides are modelled and compared with experiments. The presented model is effectively employed to evaluate the impact of backscattering on the performance of optical circuits

A generic design platform for generic photonic foundries

A software platform able to fulfill the requirements of the new approach in photonic integration through the establishment of generic foundries is presented. The kernel is a circuit simulator able to combine the foundry building blocks described by accurate models to design and analyze complex circuits in the spectral domain