Soliton Spectral Tunneling Research Articles

Controlled generation of soliton spectral tunneling by double pulses injection.

Numerical simulations of a simple and direct method to generate soliton spectral tunneling (SST) based on two input pulses are reported in the paper. An intense pump pulse and a weak probe pulse with a time delay are transmitted in a photonic crystal fiber with three zero-dispersion wavelengths. Our results demonstrate that the distance and the state of soliton tunneling are obviously influenced by the probe-pump delay. Therefore, the velocity and efficiency of SST can be effectively regulated by varying the relative time delay, thus affecting the SST formation. This scenario appears promising for designing a "soliton ejector", in which real-time control of the soliton ejection process can be achieved through phase modulation between pulses.

Influence of dispersion slope on soliton spectral tunneling in photonic crystal fiber

We report a numerical investigation of how the dispersion slope affects the soliton spectral tunneling (SST) in a photonic crystal fiber with three zero dispersion wavelengths. It is discovered that a larger dispersion slope makes group-velocity mismatch between the initial soliton and the transferred wave thereby suppressing the SST effect, while a proper decrease of the dispersion slope enhances the SST effect to widen a supercontinuum range. Besides, we find a soliton-like leaking dispersion wave, which can sustain information and energy for a short time within a particular spectral range.

Temperature-assisted broadly tunable supercontinuum generation in chalcogenide-glass-based capillary optical fiber

We propose an alternative technique for generating a tunable supercontinuum in a liquid-filled chalcogenide capillary optical fiber exhibiting three zero-dispersion wavelengths. To investigate the tunable supercontinuum, a nonlinear Schrödinger equation is solved to understand the soliton pulse dynamics. Utilizing temperature-assisted dispersion tailoring, the generation of dispersive waves that are tunable within a broad wavelength range of 3630–4650 nm and 2230–2560 nm is reported, with detailed investigations of various spectrograms confirming the predictions of dispersive waves through phase-matching characteristics. Also, temperature-controlled soliton spectral tunneling is numerically predicted in the same fiber and depends on the spectral width of the normal dispersion region between two anomalous regions.

Impact of potential barriers on soliton spectral tunneling in photonic crystal fiber

We report the effect of the potential barriers on soliton spectral tunneling (SST) in photonic crystal fibers (PCFs) with three zero-dispersion wavelengths. Our numerical simulations show that the generation and condition of SST can be well controlled by regulating the potential barrier of the PCFs. Through adjusting the width and position of the potential barrier, we can control the status and location of the switched solitons. In addition, we get the leakage dispersive wave, which may carry energy and information in the specific spectrum range for a short time. We illustrate a new understanding of SST, which may inspire some applications in information security in the near future.

Supercontinuum manipulation based on the influence of chirp on soliton spectral tunneling**Project supported by the National Natural Science Foundation of China (Grant Nos. 61275137 and 61571186) and the Natural Science Foundation of Hunan Province, China (Grant No. 2018JJ2061).

The soliton spectral tunneling (SST) effect, as a soliton spectral switching phenomenon, enables a soliton to tunnel through a spectrally limited regime of normal dispersion in the fiber with multiple zero dispersion wavelengths (ZDWs). Since initial chirp can affect the behavior of pulse evolution, we numerically study the influence of chirp on the SST in the process of supercontinuum (SC) occurring in a photonic crystal fiber (PCF) with three ZDWs. The linear chirp is imposed by a phase modulation of input pulse while maintaining a constant pulse duration. Interestingly, it is found that the spectral range and flatness can be flexibly tuned by adjusting the initial chirp value. More specifically, positive chirp facilitates soliton self-frequency shifting (SSFS), making the soliton quickly transfer from one anomalous dispersion regime to another accompanied by the generation of dispersive waves (DWs). In this case, the SST effect further expands the spectral range by enhancing both the red-shift of the fundamental soliton and the blue-shift of DWs, thus generating a broader SC. However, negative chirp suppresses the SST effect, resulting in a smoother SC at the expense of bandwidth. Therefore, the findings in this work provide interesting results relating to the influence of initial chirp on the SST to generate a considerably smoother and broader SC, which is extremely useful in many applications, such as wavelength conversion and SC generation.

Impact of the self-steepening effect on soliton spectral tunneling in PCF with three zero dispersion wavelengths

This work presents a numerical investigation of the self-steepening (SS) effect on the soliton spectral tunneling (SST) effect in a photonic crystal fiber (PCF) with three zero dispersion wavelengths. Interestingly, the spectral range and flatness can be flexibly tuned by adjusting the SS value. When the SS coefficient increases, the energy between solitons and dispersion waves is redistributed, and the red-shifted soliton forms earlier in the region of long wavelength anomalous dispersion. As a consequence, the SST becomes more obvious. The findings of this work provide interesting insights in regard to the impact of the SST effect on tailored supercontinuum generation.

Probe-controlled soliton frequency shift in the regime of optical event horizon.

In optical analogy of the event horizon, temporal pulse collision and mutual interactions are mainly between an intense solitary wave (soliton) and a dispersive probe wave. In such a regime, here we numerically investigate the probe-controlled soliton frequency shift as well as the soliton self-compression. In particular, in the dispersion landscape with multiple zero dispersion wavelengths, bi-directional soliton spectral tunneling effects is possible. Moreover, we propose a mid-infrared soliton self-compression to the generation of few-cycle ultrashort pulses, in a bulk of quadratic nonlinear crystals in contrast to optical fibers or cubic nonlinear media, which could contribute to the community with a simple and flexible method to experimental implementations.

Highly coherent mid-IR supercontinuum by self-defocusing solitons in lithium niobate waveguides with all-normal dispersion.

We numerically investigate self-defocusing solitons in a lithium niobate (LN) waveguide designed to have a large refractive index (RI) change. The waveguide evokes strong waveguide dispersion and all-normal dispersion is found in the entire guiding band spanning the near-IR and the beginning of the mid-IR. Meanwhile, a self-defocusing nonlinearity is invoked by the cascaded (phase-mismatched) second-harmonic generation under a quasi-phase-matching pitch. Combining this with the all-normal dispersion, mid-IR solitons can form and the waveguide presents the first all-nonlinear and solitonic device where no linear dispersion (i.e. non-solitonic) regimes exist within the guiding band. Soliton compressions at 2 μm and 3 μm are investigated, with nano-joule single cycle pulse formations and highly coherent octave-spanning supercontinuum generations. With an alternative design on the waveguide dispersion, the soliton spectral tunneling effect is also investigated, with which few-cycle pico-joule pulses at 2 μm are formed by a near-IR pump.

Analysis of Cascaded Soliton Spectral Tunneling Effect in Segmented Fibers With Engineered Dispersion

The cascaded soliton spectral tunneling (SST) effect is proposed and numerically investigated in multiple optical fiber segments, which work together to transfer the soliton pulse over a wide wavelength span. A triple-cladding fiber and a solid core step-index photonic crystal fiber are carefully studied and demonstrated to have three zero-dispersion wavelengths (ZDWs), which can evoke the SST effect individually and therefore are good candidates for the cascaded SST effect. Such a cascaded SST scenario can be applied to optical wavelength conversions, and the transferred wavelength could be flexible tuned by tailoring the position of ZDWs. Numerical simulations in both fiber segments are shown, and a soliton transfer over 570 nm is demonstrated with two fiber segments. Meanwhile, soliton pulse compression and supercontinuum generation are also observed to accompany each SST effect.

Understanding Soliton Spectral Tunneling as a Spectral Coupling Effect

Concept of spectral soliton coupling is proposed to explain the group-velocity-matching dispersive wave generation and the soliton spectral tunneling effect. Soliton eigen state is found corresponding to a spectral phase profile under which the soliton phase shifts induced by the dispersion and the nonlinearity are instantaneously counterbalanced. A local but non-eigen soliton pulse will shed off energy and form radiations at other wavelengths, during the coupling to the soliton eigen state. Group-velocity-mathing between the local and generated wave is necessary not only as it produces a coupler-like phase profile which supports soliton coupling but also because it physically supports a soliton phase matching condition, which means the generated wave has a soliton state phase matched to the local exciting pulse. Examples in realistic photonic crystal fiber structures are also presented.

Enigmas of optical and matter-wave soliton nonlinear tunneling

The method of mathematical analogies opens the possibility to study optical and matter-wave solitons in parallel and, due to the evident complexity of experiments with matter wave solitons, offers remarkable possibilities in studies of the BEC systems by performing experiments in the nonlinear optical systems and vice versa. We discuss previous misinterpretations of the binding soliton energy and investigate all possible scenarios of nonlinear soliton tunneling of Schrödinger solitons including soliton splitting on a potential barrier, leading to partial reflection and partial transmission, sub-barrier soliton tunneling and over-barrier soliton reflection. We reveal the most significant modifications of soliton tunneling scenarios due to increasing the binding energy, and show that the self-compressing soliton resembles more the classical particle case than a quantum mechanical behavior. The enhancement of the soliton binding energy is of decisive importance in the testing of a long-standing theoretical result which predicts that an optical soliton can tunnel between two regions of anomalous dispersion across a forbidden region of normal dispersion (enhanced soliton spectral tunneling effect).

Role of dispersion profile in controlling emission of dispersive waves by solitons in supercontinuum generation

We study the supercontinuum process in optical fibers numerically for a variety of dispersion profiles to investigate how a specific dispersion profile controls the emission of dispersive waves. We conclude that the number of zero-dispersion points in the dispersion profile of a fiber is an excellent predictor of the dispersive-wave peaks when it is pumped with femtosecond pulses in the anomalous dispersion regime. Our study reveals that two or more such peaks can form on the same side of the input wavelength in specially designed and practically achievable dispersion profiles. We show that dispersive waves are emitted even in the case of normal dispersion where soliton fission does not occur. We suggest that a phenomenon related to soliton spectral tunneling is responsible for this radiation. Distinct dispersive peaks may also appear when an optical pulse, launched in the normal dispersion region, later begins to propagate in the anomalous dispersion regime because of its spectral broadening. Several dispersion profiles are numerically employed to show how the soliton fission process creates non-solitonic radiation even under normal dispersion pumping. A time-domain picture clearly shows this radiation when the conventional phase matching condition is satisfied. We also propose a realistic photonic crystal fiber with a dispersion profile that supports dispersive-wave generation in the normal-dispersion region. Our study should prove useful for experiments designed to control the generation of blue light by launching femtosecond pulses into optical fibers.

Soliton Spectral Tunneling in Dispersion-Controlled Holey Fibers

We design a number of index-guiding holey fibers with relatively simple structure which possess suitable dispersive properties for the observation of soliton spectral tunneling. Although the fabrication tolerances for these fibers are demanding, numerical simulations show that tunneling across a normal dispersion region of 150 nm width when pumped in the near infrared is in principle possible using just a few meters of these fibers.

Theoretical analysis of the self-frequency shift near zero-dispersion points: Soliton spectral tunneling

Soliton dynamics under the action of higher-order dispersion and the Raman effect is analyzed. Though we consider a wide variety of parameters, a particularly interesting phenomenon occurs when the presence of cubic and quartic dispersion results in two regions of anomalous group velocity dispersion (GVD) separated by a region of normal dispersion. In this case a sharp switching of the soliton frequency from one anomalous GVD region to the other may exist. During such a transformation, the center of the soliton spectrum passes through the normal GVD region. We show that this switching occurs due to the phase matching between the soliton and the resonance frequency in the two anomalous GVD regions.