Near-infrared Supercontinuum Generation Research Articles

Numerical simulation of all-normal dispersion visible to near-infrared supercontinuum generation in photonic crystal fibers with core filled chloroform

This study proposes a photonic crystal fiber made of fused silica glass, with the core infiltrated with chloroform as a new source of supercontinuum (SC) spectrum. We numerically study the guiding properties of the fiber structure in terms of characteristic dispersion and mode area of the fundamental mode. Based on the results, we optimized the structural geometries of the CHCl3-core photonic crystal fiber to support the broadband SC generations. The fiber structure with a lattice constant of 1 μm, a filling factor of 0.8, and the diameter of the first-ring air holes equaling 0.5 μm operates in all-normal dispersion. The SC with a broadened spectral bandwidth of 0.64 to 1.80 μm is formed by using a pump pulse with a wavelength of 850 nm, 120 fs duration, and power of 0.833 kW. That fiber would be a good candidate for all-fiber SC sources as cost-effective alternative to glass core fibers.

Supercontinuum generation in nanostructured core gradient index fibers

We report on near-infrared supercontinuum generation in a submeter-long single-mode, nanostructured core fiber. The fiber core is composed of few thousand pure silica and germanium-doped silica glass nanorods with diameter of 200 nm each. The nanorods’ distribution is calculated based on the Maxwell–Garnett effective medium approach to mimic effective parabolic refractive index distribution in the fiber core. The standard stack-and-draw method was used to scale down the fiber structure and obtain subwavelength nanorods in the core. Size and distribution of individual nanorods are essential to determine modal and dispersion properties of the fiber without assistance of air holes in the fiber cladding. We study supercontinuum generation performance in this nanostructured core fiber pumping with low-cost microchip laser operating at 1550 nm with 1 ns pulse length and pulse energy of 0.4 µJ. A modulation instability-driven supercontinuum is generated in the fiber, covering a wavelength span of 1400–2300 nm. Due to possibility of dispersion engineering and all-solid structure the nanostructured fibers offer new possibilities for development of low-cost all-fiber supercontinuum light sources for the near-infrared range and cascaded ultrabroadband supercontinuum all-fiber systems.

Near-infrared supercontinuum source by intracavity silica-based highly-nonlinear fiber.

Near-infrared supercontinuum generation by using silica-based highly-nonlinear fiber placed inside of the ring-cavity of an erbium-doped fiber laser pulsed by mode-locking is experimentally demonstrated. Only one erbium-doped fiber amplifier is employed to generate supercontinuum with a spectral width as long as 830nm (from 1205 to 2035nm) and a spectral power higher than -30 dBm/nm. To generate supercontinuum, it is not necessary a second amplifier to raise the power of the laser pulses coupled into the nonlinear fiber. Moreover, all the devices employed are commercial and available at any photonics laboratory. To the best of our knowledge, this is the first demonstration of this kind of device by pumping the nonlinear fiber in the third window of communications.

A dispersion engineered silica-based photonic crystal fiber for supercontinuum generation in near-infrared wavelength region

We report computational modeling of photonic crystal fibers in silica glass for near-infrared supercontinuum generation. Optical parameters like chromatic dispersion, nonlinearity and the effective area of the fundamental mode have been computed and tailored by using a full vectorial finite element method. At pump wavelength of 1300 nm, a flat-top dispersion profile has been obtained with very low dispersion value + 0.6402 ps/nm/km in the anomalous region. The reported structure offers high nonlinear coefficient 26.27W−1. km−1with effective mode area 4.78 μm2 at the pump wavelength. An ultra-broadband supercontinuum spanning, from 0.67 μm up to 2.4 μm can be easily achieved by the proposed fiber of 37 cm length using a 63 fs secant laser pulse source with 8 kW peak power in the near-infrared wavelength region. Such type of fiber can be advantageous in the field of near-infrared spectroscopy, optical communication, gas sensing, medical, frequency metrology, optical coherence tomography, and food quality control.

Influences of position of ytterbium-doped fiber and ASE pump on spectral properties of random fiber laser.

The influences of the position of the ytterbium-doped fiber and the parasitic lasing in the amplified spontaneous emission (ASE) pump source on the spectral properties of the random fiber laser are analyzed and discussed in this paper. The experimental results show that putting ytterbium-doped fiber in the random fiber laser's cavity and using an ASE pump source with parasitic lasing are beneficial for the generation of high-order Stokes. A near-infrared supercontinuum with 20 dB bandwidth of more than 500 nm can be generated directly from a random fiber laser, which proved that a random laser fiber cannot only works as a traditional random fiber laser, but also can be a novel, simple, low-cost, low-coherence and robust near-infrared supercontinuum generation method.

Ultraviolet to near-infrared supercontinuum generation in a yttrium orthosilicate channel waveguide formed by ion implantation

We report on the ultraviolet to near-infrared supercontinuum generation in a 3-mm-long yttrium orthosilicate channel waveguide implanted by oxygen. The generated broadest spectrum spans 575 nm (at −30 dB points) from 430 to 1005 nm when pumping the waveguide at 800 nm and spans 115 nm (at −30 dB points) from 345 to 460 nm when pumping the waveguide at 400 nm, respectively. The nonlinear refractive index of the ion implanted region is quantified by fitting our spectra to nonlinear pulse propagation simulations around 800 nm. Our analysis shows that the nonlinear refractive index of yttrium orthosilicate waveguide after ion implantation and thermal treatment is about half the value of the bulk crystal. Our research findings indicate that ion implantation is a promising method to fabricate channel waveguides for low-threshold supercontinuum generation.

Design of All-Normal Dispersion Microstructured Optical Fiber on Silica Platform for Generation of Pulse-Preserving Supercontinuum Under Excitation at 1550 nm

We investigated numerically the possibility of all normal dispersion fiber design for near-infrared supercontinuum generation based on a standard air-silica microstructure. The design procedure includes finding of target dispersion profile and subsequent finding of appropriate geometrical fiber design by inverse dispersion engineering. It was shown that the tailoring of dispersion profile could increase the spectral width of generated supercontinuum while maintaining perfect spectral flatness. Conditions necessary for wide and flat supercontinuum generation as well as restrictions imposed by chosen materials were discussed. As a result of design and optimization procedure, an air-silica design was found providing normal dispersion up to $\text{3}\;\mu {\text{m}}$ . Simulation results with 10 nJ, 100 fs pulses demonstrate supercontinuum generation up to 1.3 octave; whereas pumping with 30 nJ, 100 fs pulses could provide 1.8 octavse supercontinuum.

Temperature-dependent bending loss characteristics of W-type photonic crystal fibres: design and analysis

The temperature-dependent bending loss characteristics of two solid-core W-typephotonic crystal fibres have been reported by employing full-vectorial finite element method. The bending loss characteristics of W-type-I photonic crystal fibrestructure have been found better than that of the W-type-II photonic crystal fibre structure. The proposed photonic crystal fibrestructures show significant nonlinearity and hence can be used in telecommunication and nonlinear applications such as visible to near-infrared supercontinuum generation. Macro-bend insensitive nature of the proposed photonic crystal fibres makes them suitable candidates for fibre-to-the-home applications.

Visible to near-infrared supercontinuum generation in yttrium orthosilicate bulk crystal and ion implanted planar waveguide.

This paper reports on the supercontinuum generation in yttrium orthosilicate bulk crystal and 6-mm-long ion implanted planar waveguide. The waveguide is fabricated by 6 MeV oxygen ions implantation with fluence of 5 × 1014 ions/cm2 at room temperature. The yttrium orthosilicate bulk crystal and waveguide are pumped using a mode-locked Ti:Sapphire laser with a center wavelength of 800 nm. The generated broadest supercontinuum spans 720 nm (at −30 dB points) from 380 to 1100 nm in bulk crystal and 510 nm (at −30 dB points) from 490 to 1000 nm in ion implanted waveguide, respectively. Compared to the bulk crystal, the ion implanted waveguide requires almost three orders of magnitude lower pump power to achieve a similar level of broadening. The supercontinuum is generated in the normal dispersion regime and exhibits a relatively smooth spectral shape. Our research findings indicate that ion implantation is an efficient method to produce waveguide in yttrium orthosilicate crystal for low-threshold supercontinuum generation.

Effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier**Project supported by the National Natural Science Foundation of China (Grant Nos. 11404404 and 11274385) and the Outstanding Youth Fund Project of Hunan Province and the Fund of Innovation of National University of Defense Technology, China (Grant No. B120701).

The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.

High-Power Ultraflat Near-Infrared Supercontinuum Generation Pumped by a Continuous Amplified Spontaneous Emission Source

A high-power ultraflat near-infrared supercontinuum (SC) is generated in a section of photonic crystal fiber (PCF) pumped by an amplified spontaneous emission (ASE) source instead of continuous-wave (CW) and pulsed lasers. A low-power ASE seed at 1 $\mu\hbox{m} $ is amplified to be 90.9 W by two fiber amplifiers and then emitted from a 10- $\mu\hbox{m} $ -core fiber. Using this ASE source to pump a section of 100-m-long PCF, a 49.5-W near-infrared SC is obtained, and the 5-dB spectral bandwidth is 760 nm, covering from 1062 to 1822 nm. This is the reported highest power of ASE-pumped SC source. A comparative experiment is taken with a 122-W CW laser at 1090 nm to pump the same PCF. A 56.2-W SC source is generated with 5-dB spectral width of 605 nm from 1082 to 1687 nm. The conversion efficiency to SC is higher, and the spectrum is broader and flatter using the ASE source as the pump. Conclusively, pump incoherence can aid the SC generation and spectral flatness.

Spectral coherence in all-normal dispersion supercontinuum in presence of Raman scattering and direct seeding from sub-picosecond pump

Intensity stability and wavelength correlations of near-infrared supercontinuum generation are studied in all-normal flattened dispersion, all-solid soft glass photonic crystal fiber. We use dispersive Fourier transformation method to measure shot-to-shot resolved spectra under pumping from a sub-picosecond, fiber-based chirped pulse amplification (CPA) system. For the first time to our knowledge, we demonstrate how unconverted radiation from pump, propagating in the photonic cladding of the fiber, improves the measured degree of coherence in the spectrum and influences its wavelength correlation by seeding of multiple four-wave-mixing / Raman scattering components. The presented results suggest a convenient and simple way of stabilizing of shot-to-shot coherence in sub-picosecond fiber laser pumped, normal-dispersion supercontinuum sources by direct, pump-related seeding.

Effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier

Theoretical and experimental research on the effect of initial chirp on near-infrared supercontinuum generation by a nanosecond pulse in a nonlinear fiber amplifier is carried out. The complex Ginzburg—Landau equation is used to simulate the propagation of the pulse in the fiber amplifier and the results show that pulses with negative initial chirp produce the widest supercontinuum and pulses with positive initial chirp produce the narrowest supercontinuum when the central wavelength of the pump lies in the normal dispersion region of the gain fiber. A self-made line width narrowing system is utilized to control the initial chirp of the nanosecond pump pulse and a four-stage master oscillator power amplifier configuration is adopted to produce a high power near-infrared suppercontinuum. The experimental results are in good agreement with simulations which can provide some guidance on further optimization of the system in future work.

Analysis of the scalability of single-mode near-infrared supercontinuum to high average power

The scalability of single-mode near-infrared supercontinuum (SC) generation directly from a fiber amplifier is analyzed considering thermal and nonlinear effects, fiber end facet damage, pump as well as fiber combiner limits, and damage to the ytterbium-doped fiber. For fiber amplifiers with 3 ns input pulse width and gain fiber with 30 μm core diameter under optimized conditions, the safety temperature limit of the fiber coating prevents the average output power of the near-infrared SC from further scaling while the damage to the ytterbium-doped fiber restricts the scaling of the peak power of the near-infrared SC to a higher value. The results may provide some guidance on future work and the realization that kilowatt level near-infrared SC generation from a fiber amplifier with an average spectral power density of above 1 W nm−1 is possible.

Near-infrared supercontinuum generation in an all-normal dispersion MOPA configuration above one hundred watts

177.6 W near-infrared supercontinuum generation in a nonlinear fiber amplifier is first demonstrated. An all-normal dispersion master oscillator power amplifier (MOPA) configuration is adopted and an all-fiber structure is realized. The supercontinuum stretches from 1064 to 2000 nm with a 10 dB spectral width of 740 nm and 56% optical to optical conversion efficiency. The average spectral power density across the whole continuum is more than 150 mW nm−1 and the effective pulse energy is above 0.3 mJ, which paves the way for high-power supercontinuum generation at a level of hundreds of watts.

Recent developments in high power near-infrared supercontinuum generation based on photonic crystal fiber

High power supercontinuum generation has witnessed rapid developments during the past few years. The mechanism and the latest achievements in high power supercontinuum generation are reviewed both for the continuous wave pump regime and the pulsed pump regime. The challenges in scaling the average power of supercontinuum generation are analyzed. Some of our works on high power supercontinuum generation are summarized, and perspectives for the future development are discussed.