article · Journal of Modern Optics
This research examines modulational instability within a nonlinear optical coupler composed of two tunnel-coupled waveguides, where one channel consists of standard dielectric material and the other possesses negative refraction. The investigation accounts for higher order cubic and quintic nonlinear responses, using linear stability analysis to assess how these effects shape the gain spectrum. Calculations were performed across anomalous, normal, and near-zero dispersion regimes for both focusing and defocusing conditions. The findings show that the resulting instability gain spectra comprise multiple regions that are symmetrical around the zero point. Additionally, specific spectra display high cut-off frequencies alongside narrow spectral widths, which provides an effective mechanism for generating high-repetition-rate optical pulse trains.
Understanding how light interacts across conventional and metamaterial channels helps physicists control optical signal behaviour. By charting how higher order nonlinearities govern instability spectra, this work provides foundational insights that can aid the design of optical systems capable of producing ultra-fast pulse trains, which are critical for precision optical processing and high-speed signal generation.
The findings could ultimately inform the development of high-repetition-rate pulse generators for laser manufacturers and high-capacity telecommunications systems. However, because the results stem purely from theoretical linear stability analysis rather than experimental prototypes, the work represents early-stage basic research that remains distant from direct commercial implementation.
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We are motivated by recent studies in medium formed by two tunnel-coupled waveguides. One of the waveguides is manufactured from an ordinary dielectric, while the second has negative refraction. We present an investigation of the gain spectrum permitting modulation instability in the nonlinear optical coupler with a negative-index metamaterial channel whose non-linear response includes third- and fifth-order terms. The principal motivation for our analysis stems from the impact of the inevitable presence of the effective cubic–quintic nonlinearity. We emphasize the influence of higher order nonlinear terms, over the MI phenomena, and the outcome of its development achieved by using linear stability analysis. Gain spectrum investigation has been carried out for both anomalous and normal dispersion regime in the focusing and defocusing cases of nonlinearity and near-zero dispersion regime where higher order linear dispersive effects emerge. Our results show that the MI gain spectra consist of multiple spectral region which are symmetric to the zero point. Moreover, some spectra have a high cut-off frequency but a narrow spectral width, which is obviously beneficial to the generation of high-repetition-rate pulse trains.
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DOI: 10.1080/09500340.2014.949320
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