Soliton Self-frequency Shift Research Articles

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

Highly sensitive nonlinear temperature sensor based on soliton self-frequency shift technique in a microstructured optical fiber

A novel fiber-optic soliton self-frequency shift (SSFS) temperature sensor fabricated using an in-house-made microstructured optical fiber was proposed. Based on this sensor, SSFS-based sensing was systematically investigated with the variation of average pump power and pump wavelength. By detecting the central wavelength shift of the 3-dB bandwidth of the soliton with the change in temperature, the sensing performance of the proposed sensor was evaluated experimentally and theoretically, subject to the average pump power and pump wavelength. At the generation of the fundamental soliton, when the pump wavelength was fixed, the higher the average pump power, the higher the temperature sensitivity. When the average pump power was fixed, the longer the pump wavelength, the higher the temperature sensitivity. The maximum temperature sensitivity of the proposed sensor was 1.759 nm/℃ at an average pump power of 300 mW and pump wavelength of 1600 nm. This temperature sensor exhibited excellent properties, such as high sensitivity, a simple structure, an easy fabrication process, good mechanical strength, and low cost, rendering it highly applicable in fields such as food quality control, environmental monitoring, and biomedical testing.

Temporal optical rogue waves in high power short-cavity Yb-doped random fiber laser

A high power short-cavity random fiber laser employing the gain mechanism of the Yb-doped fiber and the half-open cavity structure and the temporal optical rogue waves (RWs) behavior are observed and investigated in the paper. The record output power without the stimulated Raman scattering (SRS) is promoted to 26.6 W in the Yb-doped random fiber lasers (YDRFL) with the Ge-doped fiber (GDF) length of 120 m. The stochastic pulses and temporal optical RWs are observed and demonstrated in the short cavity YDRFL for the first time. It is found that the proportion of RWs depends on the GDF length and can also affect the stability of output lasing and the M2 factor distribution. The M2 factor distribution demonstrated a special longitudinal mode instability phenomenon. The experimental phenomenons display that the multiple high order SRS stokes lights and the visible light radiations are generated by the soliton self-frequency shift and Cherenkov radiation in the YDRFL with shorter GDF length. The research results reveal that achieving the relative stable output power requires the greater pump power for the shorter GDF length, although decreasing the GDF length will promote the maximum output power of the YDRFL without the SRS.

Fiber-based source of 500 kW mid-infrared solitons.

Fiber-based sources delivering high-energy few-cycle pulses at high repetition rates are currently being developed in the near-infrared spectral range, thanks to the wide availability of telecommunication-grade optical fibers and components. Similar sources in the middle-wave infrared (mid-IR) spectral domain, however, are scarce, although such sources are of high interest for applications such as high-precision frequency metrology and molecular spectroscopy or as a seed source to reach further into the mid-IR via coherent nonlinear processes. Here we report on the design of a fiber-based source of 50-nJ energy 90 fs duration pulses up to 2950 nm, corresponding to 500 kW peak power. To obtain this level of peak power we exploit multi-solitonic fission and soliton self-frequency shift in large mode area fibers excited by picosecond pulses emitted at 2 µm from a megahertz repetition rate fiber laser. We leverage mature silica-based fiber technology up to 2.4 µm and restrict the use of fluoride fiber to the very last frequency-shifting stage. The level of instantaneous power and ultra-short duration achieved in this Letter pave the way to all-fiber format generation of an ultra-broadband coherent continuum in the mid-IR with profound implications for applications such as high-resolution molecular spectroscopy and imaging.

Numerical demonstration of mid-infrared temperature sensing by soliton self-frequency shift in a fluorotellurite microstructured fiber

Numerical demonstration of mid-infrared temperature sensing by soliton self-frequency shift in a fluorotellurite microstructured fiber

Mid-infrared soliton self-frequency shift in chalcogenide glass.

Emerging applications in the mid-infrared (MIR) stimulate the growth and development of novel optical light sources. Soliton self-frequency shift (SSFS) in soft glass fiber currently shows great potential as an efficient approach toward the generation of broadly tunable femtosecond pulses in the MIR. In this work, we demonstrate a highly efficient tunable soliton source based on SSFS in chalcogenide glass. We show a simple and fully fiberized system to generate these continuously tunable Raman solitons over a broad spectral range of 2.047-2.667 µm, which consumes no more than 87 pJ per pulse. The spectral measurements suggest that the generated pulses are as short as 62 fs with a maximum power conversion efficiency of 43%. This result is realized thanks to an 8 cm long As2S3 microstructure optical fiber tapered into a microwire. Thanks to their broad transparency, their high nonlinearity, and their adjustable chromatic dispersion, chalcogenide microwires are promising components for the development of compact and highly efficient MIR optical sources with low power consumption.

Generation of megawatt soliton at 1680 nm in very large mode area antiresonant fiber and application to three-photon microscopy

The spectral window around 1700 nm is interesting for in-depth multiphoton microscopy of intact tissues due to reduced scattering and absorption in this wavelength range. However, wide adoption of this excitation range will rely on the availability of robust and cost-effective high peak power pulsed lasers operating at these wavelengths. Here, we report on a fiber-based femtosecond laser providing up to 95 nJ, 85 fs pulses at 1800 nm. The laser system makes use of a fiber-based chirped pulse amplifier emitting at 1560 nm followed by an in-house fabricated very large mode area antiresonant fiber for soliton self-frequency shift. Megawatt-peak power pulses at the repetition rate of 1 MHz are available directly at the output of the flexible fiber. We illustrate the potential of the source for biological microscopy by recording three-photon-excited fluorescence images of mouse nervous tissue. The flexible fiber tailored to propagate megawatt solitons in the biologically relevant window around 1700 nm opens the way to deep brain imaging of freely moving animals via miniaturized endomicroscopes.

Highly stable sub-nanosecond Nd:YAG pump laser for optically synchronized optical parametric chirped-pulse amplification.

We developed an optically synchronized highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration. The 1064 nm seed pulses generated by soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were stabilized by controlling input pulse polarization. The seed pulses were amplified to 200 mJ by diode-pumped amplifiers with a high stability of only <0.2% (rms). With an external LBO doubler, the system generated 330 ps green pulse energy of 130 mJ at 532 nm with a conversion efficiency of 65%. The pulse duration was further extended to 490 ps by adjusting Nd:YAG crystal temperature. To the best of our knowledge, these results present a longer pulse duration with higher stability than previous Nd:YAG lasers with sub-nanosecond optical synchronization.

Generation of mid-infrared supercontinuum by designing circular photonic crystal fiber

A circular photonic crystal fiber (C-PCF) based on As2Se3 is designed, which has three zero dispersion wavelengths and flat dispersion. Using this fiber, a wide mid-infrared supercontinuum (MIR-SC) can be generated by launching a femtosecond pulse in the first anomalous dispersion region. The simulation results show that the MIR-SC is formed by soliton self-frequency shift and direct soliton spectrum tunneling on the long wavelength side and self-phase modulation, soliton fission on the short wavelength side. Further, optical shocking and four-wave mixing (FWM) are not conducive to the long-wavelength extension of MIR-SC, while the number and intensity of fundamental solitons have a greater effect on the short-wavelength extension of MIR-SC. The generation of optical shocking waves, FWM waves and fundamental solitons can be obviously affected by changing the fiber length and input pulse parameters, so that the spectrum range and flatness can be adjusted with great freedom. Finally, under the conditions of 4000 W pulse peak power, 30 fs pulse width, 47 mm fiber length, and 0 initial chirp, a wide MIR-SC with a coverage range of 2.535 μm–16.6 μm is obtained. These numerical results are encouraging because they demonstrate that the spread of MIR-SC towards the red and blue ends can be manipulated by choosing the appropriate incident pulse and designing optimized fiber parameters, which contributes to applications in such diverse areas as spectroscopy, metrology and tomography.

A shower of mid-infrared Raman solitons at designed wavelength of ∼3 μm from a tapered fluorotellurite fiber

Optical temporal soliton generation in optical fibers and resonators has achieved great breakthroughs and found significant applications in many fields. Despite recent advances on optical soliton generation in optical fibers, it remains challenging to realize a shower of Raman solitons at a certain wavelength in optical fibers, i.e. put all the generated Raman solitons at a same wavelength on demand. Here we propose and experimentally demonstrate a shower of mid-infrared Raman solitons at designed wavelength of 3 μm from a tapered fluorotellurite fiber pumped by a 1960 nm picosecond fiber laser. Tapered fluorotellurite fibers have an untapered region length of ∼49 cm and a tapered transition region length of ∼1 cm. The fiber segment at the end of the tapered region has a 2nd zero-dispersion wavelength of ∼3 μm. Firstly, multiple Raman solitons with different wavelengths are generated in the untapered region pumped by the 1960 nm picosecond laser. Then, as Raman solitons propagate into the tapered region, the redshift of all the generated Raman solitons with different wavelengths are accelerated due to the dramatic increase of the nonlinear coefficient. Finally, as Raman solitons move out from the tapered region, all the accelerated Raman solitons are stopped around 3 μm owing to the occurrence of soliton self-frequency shift cancellation, causing the generation of a shower of mid-infrared Raman solitons around 3 μm. This phenomenon may find applications in super-efficient nonlinear light generation and signal processing.

All-normal dispersion supercontinuum vs frequency-shifted solitons pumped at 1560 nm as seed sources for thulium-doped fiber amplifiers.

We present a direct comparison between two types of femtosecond 2 µm sources used for seeding of an ultrafast thulium-doped fiber amplifier based on all-normal dispersion supercontinuum and soliton self-frequency shift. Both nonlinear effects were generated in microstructured silica fibers, pumped with low-power femtosecond pulses at 1.56 µm originating from an erbium-doped fiber laser. We performed a full characterization of both nonlinear processes, including their shot-to-shot stability, phase coherence, and relative intensity noise. The results revealed that the solitons show comparable performance to supercontinuum in terms of relative intensity noise and shot-to-shot stability, despite the anomalous dispersion regime. Both sources can be successfully used as seeds for Tm-doped fiber amplifiers as an alternative to Tm-doped oscillators. The results show that the sign of chromatic dispersion of the fiber is not crucial for obtaining a stable, high-quality, and low-noise spectral conversion process when pumped with sub-50 fs laser pulses.

Spectral Evolution in Fiber Lasers With Soliton Self-Frequency Shift Effect

The generation and evolution process of red shifting in a ultrafast fiber laser with the soliton self-frequency shift are investigated by numerical simulation. And the effect of different parameters including the pump strength, the length of dispersion shift fiber, the modulation depth of saturable absorber and the initial field on the red shifting are analyzed for the first time to our knowledge. By optimizing these parameters, a soliton with the maximum red shifting beyond the laser's gain bandwidth is obtained. In addition, within a narrow parameter range, we have also achieved a novel red-shift period-doubling bifurcated soliton with a periodic switching central wavelength.

Pure quartic solitons in dispersion-engineered aluminum nitride micro-cavities.

Pure quartic soliton (PQS) is a new class of solitons demonstrated in recent years and provides innovations in nonlinear optics and its applications. Generating PQSs in micro-cavities offers a novel way to achieve coherent microcombs, presenting a promising application potential. Here we numerically investigate the PQS generation in a dispersion-engineered aluminum nitride (AlN) micro-cavity. To support PQS, a well-designed shallow-trench waveguide structure is adopted, which is feasible to be fabricated. The structure exhibits a dominant fourth-order dispersion reaching up to -5.35×10-3 ps4/km. PQSs can be generated in this AlN micro-cavity in the presence of all-order-dispersion and stimulated Raman scattering. Spectral recoil and soliton self-frequency shift are observed in the PQS spectrum. Furthermore, we find that due to the narrow Raman gain spectrum of crystalline AlN, the PQS evolves directly to chaos rather than turning into a breather. The threshold pump power with which the PQS turns into chaos is also theoretically calculated, which squares with the simulation results.

Study on soliton self-frequency shift in a Tm-doped fiber amplifier seeded by a Kelly-sideband-suppressed conventional soliton

We experimentally present mid-infrared Raman soliton self-frequency shift (SSFS) process in a Tm-doped fiber amplifier using sideband-suppressed conventional solitons as seed pulses. The strong Kelly sidebands of the soliton oscillator were efficiently suppressed (more than 21 dB) using a home-made all-fiber Lyot filter (AFLF). As a result, the Raman solitons with a continuously tunable wavelength of 1.95-2.34 µm were achieved, with a high soliton energy conversion of >93% over the range of 1.95-2.24 µm. The conversion efficiency and tunable range of Raman solitons were both significantly improved, comparing to the same amplifier seeded with sideband-unsuppressed pulses.

Higher-order correction terms to the nonlinear amplification or absorption, the nonlinear refractive index, and the intrapulse Raman scattering.

In this paper we have investigated through the numerical solution of the basic equation as well as through the dynamic model the influence of higher-order correction terms to the nonlinear amplification (absorption) and to the nonlinear refractive index on the self-frequency shift of Raman dissipative solitons. We have found a nonlinear dependence of the self-frequency shift of Raman dissipative solitons on the parameter describing intrapulse Raman scattering in the presence of the saturation of the nonlinear gain. With the increase of the absolute value of the saturation of the nonlinear gain, the maximum absolute value of the frequency shift decreases and its position moves to larger values of the parameter describing intrapulse Raman scattering. The increase in the value of the nonlinear gain leads to an increase in the maximum absolute value of the frequency shift, without changing its position. We have also observed the nonlinear dependence of the absolute value of the frequency shift on the parameter describing intrapulse Raman scattering in the presence of higher-order correction term to the nonlinear refractive index. The discovered nonlinear dependence of the self-frequency shift on the value of the saturation of the nonlinear gain as well as on the higher-order correction term to the nonlinear refractive index can be used for the better understanding and control of the spectral characteristics of Raman dissipative solitons. The dynamic model correctly describes all the features of the observed phenomena.

Dual-Wavelength Pumped Highly Birefringent Microstructured Silica Fiber for Widely Tunable Soliton Self-Frequency Shift

We report the design of a microstructured silica-based fiber for widely tunable soliton self-frequency shift, suitable for pumping with two most common fiber laser wavelengths: 1.04 and 1.55 μm. Depending on the pump source, the output spectrum can be continuously tuned up to 1.67 (pump at 1.04 μm) or 1.95 μm (pump at 1.55 μm) in the same 1.5 m-long fiber sample, with pump-to-soliton conversion efficiency higher than 20%. The fiber is highly birefringent, which results in an excellent polarization extinction ratio of the soliton, reaching 26 dB. The shifted solitons have a high degree of coherence confirmed by pulse-to-pulse interference measurement. The available soliton tuning range covers the wavelengths inaccessible for fiber lasers, e.g., 1.3 μm and 1.7, highly important for multi-photon microscopy and imaging. Our work shows that it is possible to design and fabricate one universal optical fiber that supports soliton shift when pumped at two different wavelengths separated by over 500 nm.

High-order analytical formulation of soliton self-frequency shift

We derive an analytical formulation of the Raman-induced frequency shift experienced by a fundamental soliton. By including propagation losses, self-steepening, and dispersion slope, the resulting formulation is a high-order (HO) extension of the well-known Gordon’s formula for soliton self-frequency shift (SSFS). The HO-SSFS formula agrees closely with numerical results of the generalized nonlinear Schrödinger equation, but without the computational complexity and required computation time. The HO-SSFS formula is a useful tool for the design and validation of wavelength conversion systems and supercontinuum generation systems.

Temperature Sensing in a Silica Microstructured Optical Fiber Based on Soliton Self-Frequency Shift

This article presented an investigation of nonlinear temperature sensing based on soliton self-frequency shift (SSFS) in an in-house fabricated microstructured optical fiber (MOF), and the sensing performance was evaluated by detecting the peak wavelength shift of soliton with the variation of temperature. Both theoretical simulation and experimental research were carried out and there was a good correspondence between the two results. The experimental sensitivity was as high as 0.451 nm/°C at 400 mW with a resolution of 0.2653 °C. Our work is a proof of concept of the optical fiber nonlinear phenomenon of SSFS to sensing technology. This temperature sensor does not involve additional fiber modification, and it has potential applications in biomedical, security, and harsh industrial environment.

Elliptically-Polarized Soliton Self-Frequency Shift in Isotropic Optical Fiber

Solitons are prevalent in various nonlinear physical systems. Optical solitons in optical fibers are exceptionally intriguing due to the multitude of both linear and nonlinear optical effects that are involved during their propagation. Here we demonstrate elliptically-polarized soliton self-frequency shift (SSFS) in a novel isotropic fiber, photonic-crystal (PC) rod. We combine three methodologies, i.e., experimental, numerical, and analytical, to elucidate the fundamental aspects of this novel physical process. Our results show that wavelength-shifted, elliptically-polarized solitons can be generated through the elliptically-polarized SSFS in PC rod. Our research sheds new light on the soliton physics.

Soliton dynamics in an all-normal-dispersion photonic crystal fiber with frequency-dependent Kerr nonlinearity

We explore high-order soliton evolution in a composite all-normal dispersion photonic crystal fiber with frequency-dependent doping nonlinearity that can vary from positive to negative and vanish at a specific wavelength, named the zero-nonlinearity wavelength (ZNW). The change in frequency dependence of doping nonlinearity dramatically adjusts the position of the ZNW and the nonlinear strength acting on the supercontinuum spectral component. As the negative (positive) frequency dependence decreases (increases), one of two generated fundamental solitons via the combined action of negative nonlinearity and normal dispersion first has a gradually boosting soliton self-frequency shift (SSFS), and then a more suppressed SSFS, but is finally limited within an increasingly small spectral range while the other has a gradually decreasing SSFS toward the ZNW and radiates a broader and stronger phase-matched dispersive wave (DW) in the nonsolitonic region. Note that the collision between two fundamental solitons plays a significant role in regulating their temporal and spectral shift as well as energy redistribution. Furthermore, the numeric sign of the frequency dependence of doping nonlinearity provides another potential tool in controlling the spectral shift direction of fundamental solitons and DWs.