Mid-infrared Soliton Research Articles

Mid-infrared ultrafast soliton molecules from a few-cycle Cr:ZnS laser

Soliton molecules, or soliton bound states, are envisioned to make far-reaching changes in both fundamental research and applications. Here, we report on the generation and precision manipulation of soliton molecules based on a Kerr-lens mode-locked single-crystal Cr:ZnS laser at 2.4 µm. In the classical soliton regime, self-starting near-transform-limited pulses with a duration of 37 fs, less than 5 optical cycles, have been obtained at a repetition frequency of 173 MHz and an average output power of 572 mW. By fine-tuning the cavity group-delay dispersion profile, bi-soliton states with pulse durations between 55 fs and 98 fs with temporal separations between 348 fs and 604 fs have been observed and characterized. These are the shortest pulse duration and separation of soliton molecules reported so far in the mid-infrared region, to the best of our knowledge. With the ability of precision manipulation of soliton molecules generated on a sub-100-fs timescale, the tunable mid-infrared soliton molecule source paves the way for applications in the fields of telecommunications and ultrafast laser technologies.

Efficient Mid-Infrared Soliton Self-Frequency Shift and Dispersive Wave in a Chalcogenide Fiber

Efficient Mid-Infrared Soliton Self-Frequency Shift and Dispersive Wave in a Chalcogenide Fiber

Numerical Demonstration of Mid-Infrared Soliton Self-Frequency Shift in Chalcogenide Microstructured Fiber

Numerical Demonstration of Mid-Infrared Soliton Self-Frequency Shift in Chalcogenide Microstructured Fiber

Numerical demonstration of widely tunable femtosecond soliton generation in chalcogenide microstructured fibers

We numerically investigated widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm in designed chalcogenide fibers with two rings of air holes. The core was made of Ge15Sb15Se70 glass and the cladding glass was composed of Ge20As15S65. By using a 4.1 µm fiber laser with a pulse width of 100 fs as the pump light and 1 m long chalcogenide microstructured fibers as the nonlinear media, widely tunable femtosecond solitons spanning from 4.1 to 7.2 µm were observed, and the pulse width of these tunable Raman solitons remained below 150 fs. The efficiencies of the mid-infrared soliton could be up to over 80%, ranging from 4.1–6.8 µm. Through numerical simulations, we also observed red-shifted dispersive waves varying from 10.2 to 8.9 µm. Our simulated results show that the designed chalcogenide microstructured fibers are promising nonlinear media for generating tunable mid-infrared light sources.

Route from single-pulse to multi-pulse states in a mid-infrared soliton fiber laser.

State-of-the-art ultrafast mid-IR fiber lasers deliver optical solitons with durations of several hundred femtoseconds. The Er- or Ho-doped fluoride gain fibers generally used in these lasers have strong anomalous dispersion at ∼3 µm, which generally forces them to operate in the soliton regime. Here we report that a pulse-energy clamping effect, caused by the buildup of intracavity nonlinearities, limits the shortest obtainable pulse durations in these mid-infrared soliton fiber lasers. Excessive intra-cavity energy results in soliton instability, collapse and fragmentation into a variety of stable multi-pulse states, including phase-locked soliton molecules and harmonically mode-locked states. We report that the spectral evolution of the mid-IR laser pulses can be recorded between roundtrips through stretching their second-harmonic signal in a 25-km-length of single-mode fiber. Using a modified dispersive Fourier transform set-up, we were able to perform for the first time spectro-temporal measurements of mid-IR laser pulses both in the pulsed state and during pulse collapse and fragmentation. The results provide insight into the complex nonlinear dynamics of mid-IR soliton fiber lasers and open up new opportunities for obtaining a variety of stable multi-pulse mode-locked states at mid-IR wavelengths.

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 61405172, 61405173, and 61275093), the Natural Science Foundation of Hebei Province, China (Grant No. F2014203194), the College Science Research Program of Hebei Province, China (Grant No. QN20131044), and the Program of Independent Research for

Raman soliton self-frequency shifted to mid-infrared band (λ > 2 μm) has been achieved in an air-silica microstructure fiber (MF). The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and the λZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti:sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, mid-infrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches 0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.

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.

Tunable Soliton Generation in a Birefringent Tellurite Microstructured Optical Fiber

We report on the multiple midinfrared soliton generation based on a birefringent tellurite microstructured optical fiber pumped in the deep anomalous dispersion regime at 2 $\mu \text{m}$ . The wavelengths of the solitons can be continuously shifted to the longer wavelength region by the Raman-induced frequency shift effect. The central wavelength of the first soliton polarized parallel to the fast axis can be tuned as wide as 680 nm from 2050 to 2730 nm by adjusting the pump power. After the pump polarization is operated at 45° to the fast axis, two soliton pairs can be generated by the optical trapping effect.

Mid-infrared soliton and Raman frequency comb generation in silicon microrings.

We numerically study the mechanisms of frequency comb generation in the mid-infrared spectral region from cw-pumped silicon microring resonators. Coherent soliton comb generation may be obtained even for a pump with zero linear cavity detuning, through suitable control of the effective lifetime of free carriers from multiphoton absorption, which introduces a nonlinear cavity detuning via free-carrier dispersion. Conditions for optimal octave spanning Raman comb generation are also described.