Wavelength flattened directional couplers for mirrorsymmetric interferometers

In the context of guided optics, we derive, analytically and geometrically, a rigorous general criterion to design wavelength insensitive interferometers with mirror symmetry, which are needed for wavelength multiplexing/demultiplexing. The criterion is applied to a practical case, resulting in an interferometer that works on a band wider than 70 nm.Comment: 21 pages, 9 figure

Design Scheme for Mach-Zehnder Interferometric CWDM Wavelength Splitters/Combiners

We propose an analytical approach to design flattened wavelength splitters with cascaded Mach-Zehnder interferometers when wavelength dependence of the directional couplers cannot be neglected. We start from a geometrical representation of the action of a doubly point symmetrical filter, assuming no wavelength dependence of the couplers. Next we derive the analytical formulas behind its working principle and we extend them to the wavelength dependent case. We also show how the geometrical representation allows to broaden the class of working structures

Exact analytic expressions for electromagnetic propagation and optical nonlinear generation in finite one-dimensional periodic multilayers

Translation Matrix Formalism has been used to find an exact analytic solution for linear light propagation in a finite one-dimensional (1D) periodic stratified structure. This modal approach allows to derive a closed formula for the electric field in every point of the structure, by simply imposing a convenient form for the boundary conditions. We show how to apply this result to Second Harmonic Generation (SHG) in the undepleted pump regime.Comment: 24 pages, 7 figure

New silicon photonics integration platform enabled by novel micron-scale bends

Even though submicron silicon waveguides have been proposed for dense integration of photonic devices, to date the lightwave circuits on the market mainly rely on waveguides with micron-scale core dimensions. These larger waveguides feature easier fabrication, higher reliability and better interfacing to optical fibres. Single-mode operation with large core dimensions is obtained with low lateral refractive index contrast. Hence, the main limitation in increasing the level of integration and in reducing the cost of micron-scale waveguide circuits is their mm- to cm-scale minimum bending radius. Fortunately, single-mode rib waveguides with a micron-scale silicon core can be locally transformed into multi-mode strip waveguides that have very high lateral index contrast. Here we show how Euler spiral bends realized with these waveguides can have bending radii below 10 {\mu}m and losses below 0.02 dB/90{\deg} for the fundamental mode, paving way for a novel densely integrated platform based on micron-scale waveguides.Comment: 14 pages, 29 Refs., 5 Fig

Wavelength-flattened directional couplers: a geometrical approach

A new approach to design a wavelength-insensitive optical power splitter is presented. First, a coupledmode theory is cast in operatorial form. This allows us to solve the equivalent of coupled differential equations as simple limits. The operators are then represented on a generalized Poincaré sphere, and the resulting graphical tool is applied to different structures, giving a clear interpretation of previous results in literature as well as hints on how to find improved solutions

Universal charts for optical difference frequency generation in the terahertz domain

We present a universal and rigorous approach to study difference frequency generation in the terahertz domain, keeping the number of degrees of freedom to a minimum, through the definition of a suitable figure of merit. The proposed method relies on suitably normalized charts, that enable to predict the optical-to-terahertz conversion efficiency of any system based on wave propagation in quadratic nonlinear materials. The predictions of our approach are found to be in good agreement with the best experimental results reported to date, enabling also to estimate the d22 nonlinear coefficient of high quality GaSe.Comment: 3 pages in 2 columns format, 3 figures. GaSe analysis has been corrected. Fig. 3 has been replace

The role of nonlinear optical absorption in narrow-band difference frequency terahertz-wave generation

We present a general analysis of the influence of nonlinear optical absorption on terahertz generation via optical difference frequency generation, when reaching for the quantum conversion efficiency limit. By casting the equations governing the process in a suitably normalized form, including either two-photon- or three-photon-absorption terms, we have been able to plot universal charts for phase matched optical-to-terahertz conversion for different values of the nonlinear absorption coefficients. We apply our analysis to some experiments reported to date, in order to understand to what extent multiphoton absorption could have played a role and also to predict the maximum achievable conversion efficiency at higher peak pump intensities.Comment: 16 pages, 2 figures. Some correction and some explanation adde

Exploiting the optical quadratic nonlinearity of zincblende semiconductors for guided-wave terahertz generation: a material comparison

We present a detailed analysis and comparison of dielectric waveguides made of CdTe, GaP, GaAs and InP for modal phase matched optical difference frequency generation (DFG) in the terahertz domain. From the form of the DFG equations, we derived the definition of a very general figure of merit (FOM). In turn, this FOM enabled us to compare different configurations, by taking into account linear and nonlinear susceptibility dispersion, terahertz absorption, and a rigorous evaluation of the waveguide modes properties. The most efficient waveguides found with this procedure are predicted to approach the quantum efficiency limit with input optical power in the order of kWs.Comment: 8 pages in two columns format, 6 figures, 2 Table