18 results
Filters
Settings
Now showing1 - 10 of 18
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Optical push broom effect by a moving refractive index front in a silicon Bragg waveguideHere we report the first experimental demonstration of signal trapping by a refractive index front in a silicon waveguide with a periodic perturbation, the so-called optical push broom effect. The refractive index front generated by a fast pump pulse captures and confines the energy of a CW signal propagating with smaller group velocity near to the band gap of a Bragg grating introduced in the waveguide. The energy of the CW signal is shifted in frequency, accelerated to the front velocity and thus accumulated inside the front. In the experiment a 2 ps free carrier front was generated via two photon absorption of the pump in the silicon waveguide. It collects approximately a 30 ps long packet of the CW signal inside it. The presented effect can be utilized to compress signals in time and space.Publicationtype: Journal Article20 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fourier optics with linearly tapered waveguides: light trapping and focusing(American Institute of Physics (AIP), 2021-06-23); ; ; An optical pulse asymptotically reaching zero group velocity in tapered waveguides can ultimately stop at a certain position in the taper accompanied by a strong spatial compression. This phenomenon can also be observed in spatiotemporal systems where the pulse velocity asymptotically reaches the velocity of a tapered front. The first system is well known from tapered plasmonic waveguides where adiabatic nano-focusing of light is observed. Its counterpart in the spatiotemporal system is the optical push broom effect where a nonlinear front collects and compresses the signal. Here, we use the slowly varying envelope approximation to describe such systems. We demonstrate an analytical solution for the linear taper and the piecewise linear dispersion and show that the solution in this case resembles that of an optical lens in paraxial approximation. In particular, the spatial distribution of the focused light represents the Fourier transform of the signal at the input.Publicationtype: Journal Article132 249 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Pulse time reversal and stopping by a refractive index front(American Institute of Physics (AIP), 2020-08-14); ; ; We discuss how dynamic light stopping and pulse time reversal can be implemented in dispersive waveguides via indirect photonic transitions induced by moving refractive index fronts. The previous concepts of light stopping/time reversal either require complex local variation of the device's refractive index or rely on the strict phase matching condition, which imposes limitations on the amount of manipulated information. Until now, only single pulses or continuous waves were manipulated experimentally. Our scheme is not limited by a strict phase matching condition and does not require local index variations, thus it can manipulate broadband signals in a single step process. Here, we present several numerically integrated results for pulse time reversal and stopping/storage via indirect front-induced transitions. The presented results are experimentally feasible using existing photonic waveguide technologies.Publicationtype: Journal ArticleScopus© Citations 11 210 276 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Front induced transitions: Refractive index fronts in dispersive waveguides(SPIE, 2020-03); ; ; ; Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation leading to the change of signal frequency and wavenumber. The interaction of light with such fronts allows frequency conversion, light stopping, optical delays as well as bandwidth and pulse duration manipulation. We will present theoretical and experimental examples of signal transmission, reflection and trapping by the front and highlight special situations such as light stopping, time reversal or optical push broom effect. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrödinger equation which follows from the slowly varying envelope approximation of the wave equation. In particular, for highly dispersive waveguides a temporal evolution of the spatial wave envelopes are considered in contrast to conventional spatial evolution of temporal envelopes. Further, we will present an overview of experimental results and estimate the maximal achievable effects for each of the application in different waveguide systems.Publicationtype: Conference Paper65 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optical push broom in a silicon waveguide(2020-03); ; ; ; We report on light trapping by a moving refractive index front inside a silicon waveguide, the so-called optical push broom effect. The front generated by a fast pump pulse collects and traps the energy of a signal wave with smaller group velocity tuned near to the band gap of the waveguide with hyperbolic dispersion. The energy of the signal wave is accumulated inside the front and distributed in frequency. The presented effect can be utilized to compress signals in time and space.Publicationtype: Conference Paper78 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Optical reflection from a free carrier-induced front in a slow light waveguide(SPIE, 2020-02-26); ; ; ; Dynamic manipulation of light has received considerable attention in recent years. The process of an optical signal undergoing a transition between two modes of a photonic structure is referred to as a photonic transition. We show that a signal wave interacting with a free carrier front in a slow light waveguide experiences indirect photonic transitions leading to reflection from the moving front. Theory and experimental results are presented. The front induced dynamic frequency conversion is also compared to the frequency shifting based on other nonlinear effects like cross-phase modulation and four wave mixing.Publicationtype: Conference Paper137 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Front induced transitions in slow light and dispersive waveguidesMoving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation. The interaction of light with that front allows frequency conversion, light stopping, optical delays, and bandwidth and pulse duration manipulation. Here, we present examples of signal transmission, reflection, trapping and stopping. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrödinger equation which follows from the slowly varying envelope approximation of the wave equation.Publicationtype: Conference Paper81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Linear Schrödinger equation for front-induced transitions close to the band edgeA moving refractive index front can induce an indirect transition between states before or after the front. A linear Schrödinger equation can be used to describe the transition of a slowly varying signal envelope at the front. In waveguides with weak dispersion usually spatial evolution of the pulse temporal profile is tracked. However, we show that for waveguides with strong dispersion it is beneficial to track temporal evolution of the pulse spatial profile. Simulation examples close to the band edge of a photonic crystal waveguide are presented. We also compare the numerical results with the theoretical predictions from the phase continuity criterion.Publicationtype: Conference Paper53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Front-induced transitions(2019-11-01); ; ; Refractive index fronts propagating in waveguides are special spatiotemporal perturbations. The interaction of light with such fronts can be described in terms of an indirect transition where the frequency and wavenumber of a guided mode both are changed. In recent years, front-induced transitions have been used in dispersion-engineered waveguides for frequency conversion, optical delays, and bandwidth and pulse duration manipulation. These concepts have originated from different research areas of photonics, such as nonlinear fibre optics, slow-light waveguides, plasma physics, moving media and relativistic effects. Here, we discuss these concepts, providing a unifying theoretical description and highlight the potential of this exciting research field for light manipulation in guided optics.Publicationtype: Review Article240 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Linear Schrödinger equation with temporal evolution for front induced transitions(2019-07-22); ; ; The nonlinear Schrödinger equation based on slowly varying approximation is usually applied to describe the pulse propagation in nonlinear waveguides. However, for the case of the front induced transitions (FITs), the pump effect is well described by the dielectric constant perturbation in space and time. Thus, a linear Schrödinger equation (LSE) can be used. Also, in waveguides with weak dispersion the spatial evolution of the pulse temporal profile is usually tracked. Such a formulation becomes impossible for optical systems for which the group index or higher dispersion terms diverge as is the case near the band edge of photonic crystals. For the description of FITs in such systems a linear Schrödinger equation can be used where temporal evolution of the pulse spatial profile is tracked instead of tracking the spatial evolution. This representation provides the same descriptive power and can easily deal with zero group velocities. Furthermore, the Schrödinger equation with temporal evolution can describe signal pulse reflection from both static and counter-propagating fronts, in contrast to the Schrödinger equation with spatial evolution which is bound to forward propagation. Here, we discuss the two approaches and apply the LSE with temporal evolution for systems close to the band edge where the group velocity vanishes by simulating intraband indirect photonic transitions. We also compare the numerical results with the theoretical predictions from the phase continuity criterion for complete transitions.Publicationtype: Journal Article301