Asymmetric propagation and limited wavelength translation of optical pulses through a linear dispersive time-dynamic system.
TL;DR: The analytical and numerical investigations reveal that optical pulses show asymmetric behavior while propagating in opposite direction through a linear, dispersive, gain-loss-assisted bulk medium whose refractive index is time-varying.
Abstract: We study optical pulse propagation through a linear, dispersive, gain-loss-assisted bulk medium whose refractive index is time-varying. To analyze the dynamics, we have used a novel technique of time transformation that provides universal formulas of pulse propagation. Our analytical and numerical investigations reveal that optical pulses show asymmetric behavior while propagating in opposite direction through such a medium, in both the temporal and spectral domains. Moreover, the wavelength shift during this process is the most interesting outcome which is limited in range, but could be tuned by varying the refractive index with time. Phenomena that are observed in this Letter are novel and realizable in practical devices such as coupled waveguides where the refractive index is a function of time.
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Abstract: Abstract Opening a new door to tailoring electromagnetic (EM) waves, temporal boundaries have attracted the attention of researchers in recent years, which have led to many intriguing applications. However, the current theoretical approaches are far from enough to handle the complicated temporal systems. In this paper, we develop universal matrix formalism, paired with a unique coordinate transformation technique. The approach can effectively deal with temporally stratified structures with complicated material anisotropy and arbitrary incidence angles. This formulation is applied to various practical systems, enabling the solution of these temporal boundary related problems in a simple and elegant fashion, and also facilitating a deep insight into the fundamental physics.
15 citations
TL;DR: In this article, the formation of a BIC has been shown using the interaction between proximity resonances undergoing avoided resonance crossing in a simple fabrication, feasible gain-loss assisted microcavity.
Abstract: We propose a framework to study the topological properties of an optical bound state in the continuum (BIC). Here, the formation of a BIC has been shown using the interaction between proximity resonances undergoing avoided resonance crossing in a simple fabrication, feasible gain-loss assisted microcavity. Similar to a Friedrich-Wingten (FW)-type BIC, the formation of an ultrahigh-quality ($Q$) mode due to the precise destructive interference between resonances has been reported. The enhancement in the $Q$ factor was found to be more than four orders of magnitude greater than the other participating resonances. Furthermore, multiple such FW-type high-$Q$ operating points from the same set of proximity resonances have been identified. Upon further inspection, we report the formation of a special-BIC line in the system parameter space connecting the locations of these operating points. Further, we closely investigate the light dynamics of systems near single and multiple quasi-BICs. Aiming to develop a scheme to enhance the performance of optical sensing in a microcavity, we study the sensitivity of transmission coefficients and quality factor to sense even ultrasmall perturbations in the system configuration. Our proposed scheme would open up a vast potential for an enhanced desired optical response in enhanced nonlinear applications, low-threshold nano- and microlasers, and device-level sensors.
8 citations
TL;DR: In this paper, an asymmetric behavior of optical pulses during their propagation through a time-varying linear optical medium is reported, and the peak power and accumulated chirp of the output pulse in both propagation directions are also opposite in nature, irrespective of their initial state.
Abstract: We report an asymmetric behavior of optical pulses during their propagation through a time-varying linear optical medium. The refractive index of the medium is considered to be varying with time and complex, such that a sufficient amount of gain and loss is present to realize their effect on pulse propagation. We have exploited the universal formula for optical fields in time-varying media. Numerically simulated results reveal that pulses undergo opposite temporal shifts around their initial center position during their bi-directional propagation through the medium along with corresponding spectral shifts. Moreover, the peak power and accumulated chirp (time derivative of accumulated phase) of the output pulse in both propagation directions are also opposite in nature, irrespective of their initial state. Numerically simulated behavior of the pulses agrees well with the analytical solutions.
1 citations
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TL;DR: In this article, the influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified for monolithic integrated interferometric wavelength converters.
Abstract: Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber.
855 citations
TL;DR: By achieving an indirect interband photonic transition, it is shown that the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive.
Abstract: We demonstrate electrically driven nonreciprocity on a silicon chip. By achieving an indirect interband photonic transition, we show that the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive. Our structure is characterized by a nonsymmetric scattering matrix identical to a linear magneto-optical device.
668 citations
TL;DR: In this paper, the authors demonstrate numerically that the wavelength conversion of light is possible by the simple dynamic refractive index tuning of an optical cavity in a photonic crystal, and they also clarify the mechanism and conservation rule for this conversion process.
Abstract: We demonstrate numerically that the wavelength conversion of light is possible by the simple dynamic refractive index tuning of an optical cavity in a photonic crystal. We also clarify the mechanism and conservation rule for this conversion process. In addition, we discuss the observability of this phenomenon in realistic cavities. Our results indicate that this linear adiabatic wavelength conversion process can be observed for various high-$Q$ microcavities.
194 citations
TL;DR: This work employs the recent concept of gradient index metamaterials to demonstrate a waveguide with asymmetric propagation of light, independent of polarization, based on the principle of momentum symmetry breaking at interfaces with phase discontinuities.
Abstract: Optical diodes are fundamental elements for optical computing and information processing. Attempts to realize such non-reciprocal propagation of light by breaking the time-reversal symmetry include using indirect interband photonic transitions, the magneto-optical effect, optical nonlinearity or photonic crystals. Alternatively, asymmetric reciprocal transmission of light has been proposed in photonic metamaterial structures for either circularly or linearly polarized waves. Here we employ the recent concept of gradient index metamaterials to demonstrate a waveguide with asymmetric propagation of light, independent of polarization. The device blocks both transverse electric and magnetic polarized modes in one direction but transmits them in the other for a broadband spectrum. Unlike previous works using chiral properties of metamaterials, our device is based on the principle of momentum symmetry breaking at interfaces with phase discontinuities. Experiments in the microwave region verify our findings, which may pave the way to feasible passive optical diodes.
95 citations
TL;DR: In this article, a light pulse propagating through a Si-based photonic-crystal waveguide is adiabatically blueshifted when the refractive index of the Si is reduced on a femtosecond time scale.
Abstract: We demonstrate by experiment and theory that a light pulse propagating through a Si-based photonic-crystal waveguide is adiabatically blueshifted when the refractive index of the Si is reduced on a femtosecond time scale. Thanks to the use of slow-light modes, we are able to shift a 1.3-ps pulse at telecom frequencies by 0.3 THz with an efficiency as high as 80% in a waveguide as short as 19 µm. An analytic theory reproduces the experimental data excellently, which shows that adiabatic dynamics are possible even on the femtosecond time scale as long as the external stimulus conserves the spatial symmetry of the system.
81 citations