High-power Supercontinuum Generation Research Articles

Structural Analysis of Nano Core PCF With Fused Cladding for Supercontinuum Generation in 6G Networks

AbstractThe Sixth Generation (6G) networks have identified the use of frequency range between 95 GHz and 3 THz with a targeted data rate of 1 Terabytes/second at the access network for holographic video applications. As is demands broadening of spectrum at the core network, this paper proposes a Supercontinuum Generation (SCG) through photonic crystal fiber (PCF) as it provides excellent broadening of the optical spectrum. Discussed in the paper is supercontinuum generation at high pumping power as per the standards specified by the International Telecommunications Union. The proposed PCF is designed with silicon nanocrystal core and the cladding microstructures is arranged in a fusion approach to effectively optimize the optical parameters such as dispersion, nonlinearity, birefringence, group‐velocity dispersion, and confinement loss. The fused cladding comprises of a flower‐cladding assembly in which air‐holes arrangement is inspired from petals in a pleated structure. Such arrangement is shown here to provide high nonlinearity and negative dispersion for high power supercontinuum generation. The novel nanocore assembly with improved structural constraints delivers a non‐linearity of 6.37 × 106 W−1 km−1 and a negative dispersion of −142.1 (ps/nm‐km) at 1,550 nm. Moreover, a supercontinuum spectrum is generated using different pulse widths ranging from 350 to 650 ps with 25 kW pump power for PCF lengths of 10 and 15 mm.

Simple method for high average power supercontinuum generation based on Raman mode locking in a quasi-CW fiber laser oscillator.

A simple generation method for a supercontinuum (SC) based on Raman mode locking (RML) in a quasi-continuous wave (QCW) fiber laser oscillator is demonstrated experimentally and analyzed in this paper. The power of the SC is adjustable by changing the pump repetition rate and duty cycle. Under the pump repetition rate of 1 kHz and duty cycle of 11.5%, an SC output with a spectral range of 1000-1500 nm is obtained at a maximum output power of 791 W. The RML is fully analyzed in terms of the spectral and temporal dynamics. RML plays a major role in this process and further enriches the generation of the SC. To the best of the authors' knowledge, this is the first report on directly generating a high and adjustable average power SC using a large-mode-area (LMA)-based oscillator, which provides a proof-of-concept experiment for achieving a high average power SC source and greatly improves the potential application value of the SC source.

Recent Development of Mid-Infrared Supercontinuum Generation in Fluoroindate Glass Fibers

Supercontinuum (SC) generation that leads to the emission of broadband radiation has been extensively studied. In particular, SC sources encompassing the wavelength range of 2–5 μm have attracted considerable interest in the last decade, and a continuous increase in the output power and spectrum width has been observed. To enable broadband and high-power SC generation, suitable nonlinear media combined with appropriate pump sources must be used, maintaining the output as spectrally flat. This paper briefly reviews the current state-of-the-art SC sources restricted to those based on fluoroindate fibers, including systems pumped with femtosecond, picosecond, and nanosecond pulses. First, the concept of SC generation in optical fibers is briefly presented. This is followed by an examination of indium fluoride optical fibers, with an emphasis on their material and waveguide properties. Furthermore, the advances in SC generation in fluoroindate fibers, including the latest results on high-power (Watt-level) continuum generation adopting different pump schemes, are also explored. A record time-averaged output power of 11.8 W with a spectrum spanning from ~1.9 to 4.9 µm has been demonstrated, which is certainly not the power limit of this technology. Finally, potential future directions of research are discussed at the end of this paper.

High power supercontinuum generation by dual-color femtosecond laser pulses in fused silica

High power supercontinuum (SC) is generated by focusing 800 nm and 400 nm femtosecond laser pulses in fused silica with a microlens array. It is found that the spectrum of the SC is getting broader compared with the case of a single laser pulse, and the spectral energy density between the two fundamental laser wavelengths is getting significantly higher by optimizing the phase matching angle of the BBO. It exceeds μJ/nm over 490 nm range which is from 380 nm to 870 nm, overcoming the disadvantage of relative lower power in the ranges far from the fundamental wavelength.

730 mW, 2-8 μm supercontinuum generation and the precise estimation of multi-pulse spectral evolution in the soft-glass fibers cascaded nonlinear system

We experimentally demonstrate the 2-8 μm high-power supercontinuum generation and theoretically propose a statistical method for precise estimation of the multi-pulse spectral evolution in the ZBLAN and As2S3 fiber cascaded all-fiber structured nonlinear system. In the experiment, with the aid of the ultra-low loss fusion splice technology, high-efficiency fiber butt-coupling technology and precise thermal management technology, we obtained a record-breaking supercontinuum source with a spectrum spanning from 2 μm to 8 μm at a power of 730 mW. Considering the strong pulse splitting and soliton fission effects in fibers, to precisely estimate the multi-pulse spectral evolution in this system, we, for the first time, built a multi-pulse pump model with the Pearson product-moment correlation coefficient method based multi-pulse selection mechanism. In combination with the existing approaches and some new programmatic work, finally, we verified that the simulation results are in good agreement with the experimental one.

High-power mid-IR supercontinuum generation in fluoroindate and arsenic sulfide fibers pumped by a broadband 1.9–2.7 μm all-fiber laser source

We report the experimental demonstration of high-power supercontinuum generation in step-index fluoroindate (InF3) and chalcogenide (As2S3) fibers. A home-built fiber-based laser system with a broad spectrum spanning from 1.9 to 2.7 μm and delivering an output average power of 6.15 W was used as the pump source. A time-averaged power of 2.95 W covering the entire 2–5 μm wavelength range is obtained from an InF3 fiber. Cascading the system by adding an As2S3 fiber, the spectrum was extended up to 5.58 μm. Moreover, we present a supercontinuum with an average power of 440 mW and a spectrum extended to 4.17 μm generated by an As2S3 fiber pumped directly by a broadband (2.4–2.7 μm), silica-based laser source centered at 2.55 µm. Combined with a high degree of spectral flatness, the high-output supercontinuum power highlights the potential of the developed sources for use in a wide variety of applications.

All-Fiber High Power Supercontinuum Generation by Cascaded Photonic Crystal Fibers Ranging From 370 nm to 2400 nm

104 W supercontinuum (SC) covering 370 nm-2400 nm is reported. High power visible SC is generated by pumping cascaded photonic crystal fibers (PCF) with 1064 nm picosecond pulse. Cascaded PCFs is fabricated by fusion splicing two different PCFs together with a coupling efficiency of 75%. For the purpose of avoiding fiber fuse phenomenon in PCF, the discharge time and intensity of fusion splicer should be precisely controlled. Two components of cascaded PCFs are pumped separately by 1064 nm picosecond pulse for comparing with the impact of cascaded PCFs. As a result of pumping cascaded PCFs, 104 W SC covering 370 nm−2400 nm is generated. Visible spectra (380 nm−780 nm) accounts for 50.4% (52.4 W) by numerical integration. To best of our knowledge, it's the first time that a visible SC with over a hundred watt output and 370 nm short-wave edge is obtained experimentally.

High-power supercontinuum generation in the mid-infrared pumped by a soliton self-frequency shifted source.

We report the demonstration of a fiber-based supercontinuum source delivering up to 825 mW of average output power between 2.5 and 5.0 µm generated in all-normal dispersion regime. The pumping source consists of an amplified ultrafast Er3+:ZrF4 fiber laser providing high peak power femtosecond pulses at 3.6 µm with an average output power exceeding the watt-level. These pulses are spectrally broadened through self-phase modulation using commercial chalcogenide-based step-index fibers. Al2O3 anti-reflection coatings were sputtered on chalcogenide fiber tips to increase the launching efficiency from 54% to 82%, making this record output power possible, and thus confirming that such coatings can support watt-level pumping with intense femtosecond pulses. To the best of our knowledge, this result represents the highest average output power ever achieved from a As2Se3-based mid-IR supercontinuum source with the potential of a high degree of coherence.

Attosecond pulse trains driven by IR pulses spectrally broadened via supercontinuum generation in solid thin plates**Project supported by the National Key R&D Program of China (Grant No. 2017YFB0405202), the Major Program of the National Natural Science Foundation of China (Grant No. 61690221), the Key Program of the National Natural Science Foundation of China (Grant No. 11434016), and the National Natural

We utilized a set of fused silica thin plates to broaden the spectrum of 1 kHz, 30 fs Ti:sapphire amplified laser pulses to an octave. Following the compression by chirped mirror pairs, the generated few-cycle pulses were focused onto an argon filled gas cell. We detected high order harmonics corresponding to a train of 209 as pulses, characterized by the reconstruction of attosecond beating by interference of two-photon transition (RABITT) technique. Compared with the conventional attosecond pulse trains, the broad harmonics in such pulse trains cover more energy range, so it is more efficient in studying some typical cases, such as resonances, with frequency resolved RABITT. As the solid thin plates can support high power supercontinuum generation, it is feasible to tailor the spectrum to have different central wavelength and spectral width, which will make the RABITT source work in different applications.

30-W supercontinuum generation based on ZBLAN fiber in an all-fiber configuration

We report an all-fiberized 30-W supercontinuum (SC) generation in a piece of ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The pump source is a thulium-doped fiber amplifier (TDFA) with broadband output spectrum spanning the 1.9 to ∼2.6 μm region. The used ZBLAN fiber has a core diameter of 10 μm, and was directly fusion-spliced to the pigtail of the TDFA without using a traditional mode field adapter (MFA) or a piece of transition fiber. Such a low-loss and robust fusion splice joint, together with a robust AlF3-fiber-based endcap, enables efficient and high-power SC generation in the ZBLAN fiber. An SC with an average power up to 30.0 W and a spectral coverage of 1.9–3.35 μm with 20-dB bandwidth of 1.92–3.20 μm was obtained. Moreover, an SC with a broader spectrum was achieved by raising the pump pulse peak power (via reducing the duty ratio of the pump laser pulse). An SC with an output power of 27.4 W and a spectral coverage of 1.9–3.63 μm (with 20-dB bandwidth of 1.92–3.47 μm) was obtained, as well as an SC with output power of 24.8 W and a spectral coverage of 1.9–3.70 μm (with 20-dB bandwidth of 1.93–3.56 μm). The power conversion efficiency was measured as >69%. To the best of the authors’ knowledge, this research demonstrates the record output power of SC lasers based on ZBLAN fibers, paving the way for broadband and efficient multi-tens-of-watts SC generation in soft-glass fibers.

High-power supercontinuum generation by noise-like pulse amplification in Yb-doped fiber amplifier operating in a nonlinear regime.

In this paper, we report on a supercontinuum generation by amplifying noise-like pulses (NLPs) in a nonlinear Yb-doped fiber amplifier. The NLP source is a homemade Yb-doped all-fiber ring oscillator based on nonlinear polarization rotation mode-locking method. NLPs possess a repetition rate of 11.57MHz, energy of 16.5nJ, and 3dB spectral bandwidth of 42nm. The intensity autocorrelation function of NLPs has a broad pedestal and a narrow central spike. The pedestal and the spike have temporal widths of 63ps and 92fs, respectively. The NLPs are amplified by a Yb-doped fiber nonlinear power amplifier to achieve output power of 7.5W. Nonlinear effects in the amplifier drastically broaden the spectrum of NLPs and generate high-power supercontinuum light with 10dB spectral bandwidth of 1130nm (from 1037 to 2167nm). The presented supercontinuum generation system is an all-fiber compact structure and has the advantage of not requiring long single-mode, nonlinear, or photonic crystal fibers.

Ultra-efficient, 10-watt-level mid-infrared supercontinuum generation in fluoroindate fiber.

A 10-watt-level mid-infrared supercontinuum (SC) spanning 0.8-4.7μm with ultra-high-power conversion efficiency is generated in a piece of fluoroindate (InF3) fiber. The pump laser is a master oscillator power amplifier system seeded by a mode-locked fiber laser operating at 1956nm with pulse repetition rate and pulse duration of 33MHz and 60ps, respectively. A piece of InF3 fiber is fusion spliced to the output end of the pump light source with a low fusion splicing loss of 0.12dB. An endcap made of multimode aluminum fluoride fiber is used to protect the fiber tip from possible optical or thermal damage. Benefiting from the fiber endcap as well as the low-loss splicing joint between silica and InF3 fiber, high-power SC generation is achieved with maximal output power of 11.3W. Furthermore, the long wavelength edge of the obtained SC spectrum is extended to 4.7μm. This Letter, to the best of our knowledge, not only demonstrates the first 10-watt-level SC generation in InF3 fibers, but also achieves record power conversion efficiency of 66.5% among reported 10-watt-level fluoride-fiber-based SC laser sources.

Watt-Level Nanosecond 4.42-<inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m Raman Laser Based on Silica Fiber

We report the demonstration of a 4.42-μm silica-fiber-based Raman laser delivering a record average output power of 1.4 W and operating in a single transversal mode. The Raman laser is based on a hydrogen-filled hollow-core silica fiber, which is pumped by a nanosecond erbium-doped fiber laser at 1.56 μm. In spite of a large quantum defect of a 1.56-4.42-μm conversion, the Raman laser demonstrates no heat-initiated problems. Due to the implementation of a linearly polarized pump and virtually all-polarization-maintaining configuration of the Raman laser, the quantum efficiency has reached 53%, which is a theoretical limit imposed by optical losses (1.1 dB/m) at 4.42 μm in a state-of-the-art revolver hollow-core silica fiber. The developed laser demonstrates the prospects of gas fiber Raman lasers to serve as pump sources for high-power supercontinuum generation in the mid-infrared spectral range. Such sources can find numerous scientific and biomedical applications.

High Power, Tunable, Continuous-Wave Fiber Lasers in the L-Band Using Cascaded Raman Amplifiers

We demonstrate a high power, all-fiber, tunable laser source that can operate in the L-band region. A low power, tunable input laser is amplified with a recently proposed, high efficiency, 6th order cascaded Raman amplifier. The proposed system is scalable and overcomes the limitations of Erbium and Erbium-Ytterbium co-doped fiber lasers for power scaling. A tunable Erbium-Ytterbium co-doped fiber ring laser generating ~0.5W of power and tunable in the 1560-1590 nm wavelength range is utilized as the seed source. The output from the seed laser is amplified to ~24 W using 6th order cascaded Raman amplification. A high power Yb laser operating at 1117nm is used as the pump laser for driving the Raman conversions. The operating wavelength of the demonstrated laser in the eye-safe, atmospherically transparent region enables high power free-space applications. In addition, this source enables other interesting applications such as high power supercontinuum generation with conventional silica fibers.

Broadband and top-flat mid-infrared supercontinuum generation with 3.52\xa0W time-averaged power in a ZBLAN fiber directly pumped by a 2-\xb5m mode-locked fiber laser and amplifier

Supercontinuum generation from 1.87 to 4.03 µm in a ZBLAN fiber is reported. A home-made passively mode-locked thulium-doped fiber laser and amplifier, providing 21.4-ps pulses at 81 MHz is used as a pump. The continuum output power is 3.52 W, of which 1.45 and 0.88 W corresponds to wavelengths longer than 3 and 3.5 µm, respectively. A spectrum flatness of 2 dB over a bandwidth of 1710 nm, from 2.02 to 3.73 µm, is also reported. This represents, to our knowledge, the best power conversion in the mid-infrared region and the best spectral flatness for high power supercontinuum generation in ZBLAN fibers directly pumped by 2-µm CW mode-locked fiber lasers and amplifiers.

Filamentation and supercontinuum emission with flattened femtosecond laser beam by use of microlens array in fused silica

The high power supercontinuum from femtosecond filamentation has attracted great attention for recent years due to its various applications. In our previous researches, we have used microlens array to obtain filament-array in fused silica and to generate the high spectral power supercontinuum. To further improve the ability to generate the high power supercontinuum by using microlens array, in this work we adopt flattened femtosecond laser beam with a flat-top energy distribution to generate filament-array in fused silica and supercontinuum. By using a laser beam shaping system consisting of aspherical lenses, the Gaussian intensity distribution of initial femtosecond laser beam is converted into a flat-top distribution. The flattened laser beam is focused by a microlens array into a fused silica block, and consequently a filament array is formed in the block. Our experimental results show that compared with the filaments formed by a Gaussian laser beam, the filaments formed by the flattened beam have a uniform distribution and almost the same onset due to the initial uniform energy distribution across the section of the laser beam. Furthermore, the spectral stability of supercontinuum emission is used to evaluate the damage of the fused silica block. It is demonstrated that the flattened beam with a pulse energy of 1.9 mJ does not induce permanent damage to the fused silica block, while the Gaussian beam with a relatively low pulse energy of 1.46 mJ leads to the damage to the block. Therefore, a higher incident laser pulse energy is allowed in the case of flattened laser beam, and consequently stronger supercontinuum generation than in the case of the Gaussian laser beam can be expected. In our experiments, the relative spectral intensity of flattened beam generated supercontinuum in the visible range is about twice higher than that for the Gaussian beam case. The conversion efficiencies of the supercontinuum for the two kinds of laser beams are further analyzed. The conversion efficiencies are 49% and 55% for the cases of Gaussian and flattened beams respectively. In this work, we demonstrate the formation of filament array with uniform distribution in fused silica, and, as a proof of principle, we also demonstrate the high power supercontinuum generation with high conversion efficiency from the filamentation, by using flattened femtosecond laser beam as the incident laser and microlens array as the focusing element. This approach provides a way to obtain a high power femtosecond supercontinuum source which is of great importance in many applications such as some absorption spectroscopies based on coherent supercontinuum light.

Intense and Collimated Supercontinuum Generation Using Microlens Array

A method of high power supercontinuum (SC) generation is proposed, in which femtosecond pulses are focused into a transparent medium using a microlens array (MLA). The MLA combining a telescopic system is used to form long-path multiple filaments inside the medium, and another symmetrically arranged telescopic system and MLA are used to collimate of the emitting multiple SC beams from filaments. The reshaped stable SC beam shows a Gaussian intensity transverse distribution and similar spectra and chirp properties with that generated by single filament, while the pulse energy can be increased by more than two orders.

Amplified spontaneous emission pulses for high‐power supercontinuum generation

The authors demonstrate an incoherent light source based on a reflective semiconductor optical amplifier as pump for high-power supercontinuum generation for the first time. The obtained power level is about 160 mW and 20 dB spectral bandwidth is around 170 nm.

Studies of the modal properties of circularly photonic crystal fiber (C-PCF) for high power applications

The guiding properties of a new type of photonic crystal fibers where air-holes are arranged in a circular pattern (C-PCF) with a silica matrix have been investigated. The dispersion properties of the fiber with different spacing of circle and air-hole diameter have been studied in detail. It is shown that C-PCFs with smaller values of radius and higher air-filling fraction can be used as dispersion compensating fiber. A comparison between fibers with circular and triangular lattice has also been performed, taking into account the dispersion properties and the effective area in the wavelength range between 1200nm and 1600nm. C-PCF can better compensate the inline dispersion for both single wavelength and broadband wavelength applications which is a unique property not observed by regular triangular-lattice or square-lattice PCFs. The fiber provides higher effective area, making it a better candidate for high power accumulations in the core of the fiber. The fiber also shows red-shifting of the first zero dispersion wavelength (ZDW), flatter dispersion slope and lower Group Velocity Dispersion (GVD) in the normal dispersion region thereby making it a better candidate for high power nonlinear applications like super-continuum generation, soliton pulse propagation etc. With the above advantages, we have considered a series study of these circular-lattice structures for various geometrical parameters and temporal pulses in order to explore the characteristics of broadband supercontinuum generation. This design study for high power supercontinuum generation will be very helpful for potential application of new sources in various fields like astronomy, climatology, spectroscopy optical tomography and sensing etc. to name a few.

High-power supercontinuum generation using high-repetition-rate ultrashort-pulse fiber laser for ultrahigh-resolution optical coherence tomography in 1600 nm spectral band

We describe the generation of a high-power, spectrally smooth supercontinuum (SC) in the 1600 nm spectral band for ultrahigh-resolution optical coherence tomography (UHR-OCT). A clean SC was achieved by using a highly nonlinear fiber with normal dispersion properties and a high-quality pedestal-free pulse obtained from a passively mode-locked erbium-doped fiber laser operating at 182 MHz. The center wavelength and spectral width were 1578 and 172 nm, respectively. The output power of the SC was 51 mW. Using the developed SC source, we demonstrated UHR-OCT imaging of biological samples with a sensitivity of 109 dB and an axial resolution of 4.9 µm in tissue.