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Supercontinuum generation. (a) Set-up used for supercontinuum generation, HNLF- Highly Nonlinear fiber and EDFA (Erbium doped fiber amplifier. (b) seed laser source (f 1 - 9.63GHz) and generated supercontinuum.
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There is an increasing demand for all-fiber passively mode-locked lasers with pulse repetition rates in the order of gigahertz for their potential applications in fields such as telecommunications and metrology. However, conventional mode-locked fiber lasers typically operate at fundamental repetition rates of only a few megahertz. In this paper, w...
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Context 1
... meter [1]. By amplifying the FFPL output to an average power of approximately 25dBm using an erbium doped fiber and launching the amplified pulses into 30m of highly nonlinear dispersion shifted fiber (HNL-DSF) with a nonlinear coefficient of 20W 1 .km 1 , zero dispersion at 1576nm and normal dispersion at the seed wavelength (1560nm). In Fig. 8(a) the experimental set-up employed for the supercontinuum generation is shown. Figure 8(b) shows the optical spectra of the seed FFPL and the generated supercontinuum. Further work is required before these laser sources can be employed as supercontinuum sources for many real applications in particular for optical frequency metrology ...
Context 2
... Fig. 8(a) the experimental set-up employed for the supercontinuum generation is shown. Figure 8(b) shows the optical spectra of the seed FFPL and the generated supercontinuum. Further work is required before these laser sources can be employed as supercontinuum sources for many real applications in particular for optical frequency metrology where highly coherent, octave spanning supercontinuum is required. ...
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Citations
... In 2011, Yamashita et al. utilized ultrahigh-gain Erbium-ytterbium co-doped phosphosilicate fibers and successfully established 5 mm long short cavity with high repetition rate pulses [13]. However, depositing SWCNTs film on fiber ferrule mirrors and the special gain glass materials required in the cavity are complicate to fabricated and expensive. ...
We demonstrated a short-cavity mode-locked erbium-doped fiber laser based on single walled carbon nanotube polymer composite film saturable absorber with a maximum fundamental repetition rate of 270.5 MHz. To the best of our knowledge, this is the highest fundamental repetition rate among mode-locked erbium-doped ring fiber lasers based on nanomaterial polymer composite films. Samples with non-saturable loss range from 13.2% to 60% and modulation depth from 1.63% to 7.08% are prepared by controlling carbon nanotube concentration and film thickness. We systematically investigate the impacts of saturable absorbers on mode-locking repetition rate. Our results show that when the laser repetition rate continuously increases from 15.45 MHz to 270.5 MHz, samples with higher non-saturable loss will push forward the mode-locking threshold and eventually lose mode-locking. In addition, the increased modulation depth will enhance the pulse shaping ability and result in a shorter pulse. Our results may help for high repetition rate mode-locked fiber laser design and improve the laser characteristics. The demonstrated laser may support applications such as frequency comb, etc.
... 12) Previous works have shown that ultrahigh repetition rates can be obtained by using short fiber Fabry-Perot resonators. [13][14][15] Ring lasers can get rid of standing waves and spatial hole burning effect that always happen in linear lasers, however, it is challenging for realizing high repetition rate ring lasers. ...
We demonstrate a 783 MHz fundamental repetition rate mode-locked Er-doped all-fiber ring laser with a pulse width of 623 fs. By using carbon nanotubes saturable absorber, a relatively low self-starting pump threshold of 108 mW is achieved. The laser has a very compact footprint less than 10 cm × 10 cm, benefiting from the all-active-fiber cavity design. The robust mode-locking is confirmed by the low relative intensity noise and a long-term stability test. We propose a new scheme for generating high repetition rate femtosecond optical pulses from a compact and stable all-active-fiber ring oscillator.
... In recent times, the demand for high-repetition pulsed lasers has surged [19][20][21][22] as they enable more effective data acquisition and faster material processing speed. Consequently, researchers have developed harmonic mode-locking techniques in fibre lasers [23], short-cavity solid-state lasers [24], mode locked integrated external-cavity surface-emitting lasers [25], and Er 3+ doped fibre-ferrule cavities [26]. Among these, nanophotonic devices fabricated from erbium-ion (Er 3+ ) doped glass [27,28] stand out as potential cost-effective solutions, given the maturity and robustness of the material. ...
We show theoretically and numerically that mode-locking is feasible with a coupled-cavity system with gain and loss, notably, without any natural saturable absorber. We highlight that in the vicinity of the exceptional point, system Q exhibits substantial modulation even with minor refractive index changes and a minimal Kerr effect contribution. Leveraging this unique behavior, we propose an unprecedented approach wherein the lossy auxiliary cavity functions as an efficient artificial saturable absorber, thus facilitating mode-locking. This approach is not only novel, but also presents considerable advantages over conventional systems where both gain and saturable absorption are contained within a single microcavity. These benefits include reduced operational power and ease of post-adjustment, achievable through the manipulation of the coupling strength between the two microcavities.
... In the conventional mode-locked laser, the generation of ultrafast pulses at GHz rate is, however, technically challenging. This is because the pulse repetition rate of a mode-locked laser is inversely proportional to the laser cavity length, and for GHz-rate pulses the cavity length of a few centimeters is required, which leads to some intrinsic difficulties in heat dissipation and intracavity dispersion management, limiting the achievable pulse energy and ultrafast performance of such short-cavity lasers [7,8]. ...
We demonstrate a compact ultrafast fiber laser system that can deliver 1.87 GHz pulse train at 1550 nm with a pulse energy of 52 pJ and an ultrashort pulse duration of 57 fs. While an acousto-optic mode-locking fiber laser was used as the seed light source at GHz rate, a stage of Er-doped fiber amplifier boosted the laser power to ∼320 mW, giving a pulse energy of ∼170 pJ. Then, a pulse compression setup was constructed, providing a high compression ratio of ∼10 with a total efficiency of ∼32%. In the cascaded compression configuration, multiple fiber samples with alternately normal and anomalous dispersion were fused together, providing efficient nonlinear spectral broadening while suppressing excessive pulse broadening over propagation. This GHz-rate ultrafast fiber laser, with compact configuration, broad optical spectrum, and high time-resolving ability could be used as the seed light source for constructing high-rate, high-power ultrafast laser systems and may find a few applications in optical measurements and microwave photonics.
... 提出国 际 相 干 放 大 网 络 工 程 (International Coherent Amplification Network，ICAN)计划，旨在利用数万路光纤激光阵列实现单脉冲能量 大于10 J、重复频率大于10 kHz、脉宽100~200 fs的超强激光脉冲，将应用于新一代粒子加速器驱动源探索。 该重大工程的实现依赖啁啾脉冲放大(chirped pulse amplification, CPA)和相干合成技术发展。在此重大科 学研究背景下，大功率GHz重复频率飞秒光纤激光逐渐受到了关注。在平均功率提升方面，得益于大模场光 纤制造与放大技术发展，单路全光纤超快激光器的性能指标达到了一个新的高度，单路高重复频率超快光纤 激光器已经实现千瓦级平均功率输出 [22] [28] 和基于脉冲重复频率倍增 [29] [31] 通 过进一步优化腔内色散管理的集成器件，在环形腔内首次实现了重复频率为1 GHz、脉冲宽度为64 fs的掺镱 飞秒光纤激光。此后，该课题组 [32] 通过"光积木"的方式搭建了类似结构的高重复频率"固态光纤激光器" ， 将GHz重复频率光纤激光器的时间抖动降低至阿秒量级。2023年，上海理工大学袁帅教授课题组 [33] 采用类似 的环形腔结构，通过进一步优化腔内色散管理，直接产生48 fs的超短脉冲，实现了1 GHz基本重复频率的"固 态光纤激光器" 。 这些成果表明NPR技术结合腔内器件优化的方式在GHz重复频率飞秒光纤激光器研究中取得 了显著进展。有别于NPR技术，南方科技大学沈平教授课题组 [34] 设计了一种无隔离器、基于SESAM被动锁模 的环形腔结构， 获得了基本重复频率为1.048 GHz、 脉冲宽度为177 fs的掺镱飞秒光纤激光。 另一方面， 在NALM 光纤激光器中，谐振腔需要一定长度的光纤来积累足够的非线性相移差以实现锁模。因此，目前报道的全光 纤NALM激光器，通常只能实现约200 MHz的基本重复频率 [35] 。直到最近，中国科学院上海光学精密机械研 究所冯衍研究员课题组 [36] 提出了一种嵌套光纤环形腔结构，此结构在NALM内采用由两个光纤耦合器熔接构 成的环形内腔进行模式滤波，通过巧妙地匹配内、外腔的自由光谱范围，将"9"字腔光纤激光器的重复频 率成功倍增至GHz量级，并呈现出高相干、低噪声的特性，为实现GHz基本重复频率的光纤激光器提供了一 种新的有效途径。基于NPR、NOLM/NALM环形腔结构的GHz基本重复频率光纤激光器由于在环形腔内方便 进行精细的色散管理，通常能够实现更低的激光噪声性能。然而，由于环形腔内集成器件(如法拉第旋转器) 的体积受限，因此环形腔结构进一步实现更高重复频率飞秒光纤激光仍有较大挑战。 为了进一步实现大于1 GHz基本重复频率锁模，采用超短线性腔结构是优选技术路线。在基于线性腔结 构的光纤激光器中，超短谐振腔通常由可饱和吸收体、高掺杂浓度增益光纤和高反射率腔镜组成。脉冲的 重 复频率与腔内光纤长度成反比，通过缩短光纤可以有效提高锁模激光的重复频率。这种谐振腔结构为实现高 重复频率锁模激光提供了一种简单而有效的途径。东京大学Yamashita教授课题组利用碳纳米管作为锁模器件 并基于线性谐振腔结构高重复频率光纤激光器进行了一系列研究。2005年，该课题组 [37] 基于2 cm长的法布里 -珀罗(Fabry-Pé rot , FP)谐振腔结构实现了5 GHz亚飞秒锁模脉冲输出。2011年，该课题组 [38] 将1.5 μm波段 的脉冲基本重复频率提升至19.45 GHz，研究了GHz重复频率脉冲产生超连续谱的现象。2014年，该课题组 [39] 基于保偏铒镱共掺光纤，实现了基本重复频率为12 GHz的保偏谐振腔光纤激光器，其光谱中心波长为1535 nm、输出脉宽为2 ps、输出功率为5 mW。除了碳纳米管等可饱和吸收体，SESAM作为一种成熟的商用锁模 器件， 具有使用便捷、 易实现锁模自启动等优势， 受到广泛青睐。 2007年， 美国国家标准与技术研究院Newbury 等人 [40] 基于SESAM锁模在1.54 ...
... Techniques such as active mode-locking [7], passively harmonic modelocking [8,9], dissipative four-wave mixing [10] and mode filtering [11] could achieve a very high repetition rate, however, they exhibit a higher instability in terms of output performance compared to fundamentally passive mode-locking [12]. Previous works have shown that ultrahigh repetition rates can be obtained by using short fiber Fabry-Perot resonators [13][14][15], however, is still challenging for ring lasers. ...
We have demonstrated 783-MHz, the highest fundamental repetition rate from a mode-locked all-fiber ring laser with a pulse width of 623 fs. By using carbon nanotubes (CNT) saturable absorber (SA), a relatively low self-starting pump threshold of 108 mW is achieved. The laser has a very compact footprint less than 10 cm × 10 cm, benefiting from the all-active-fiber cavity design. The robust mode-locking is confirmed by the low relative intensity noise (RIN) and a long-term stability test. We propose a new scheme for generating high repetition rate femtosecond optical pulses from a compact and stable all-fiber ring laser.
... To achieve a GHz repetition rate mode-locked fiber laser, one method is to shorten the cavity length. In this way, a ∼ 20 GHz repetition rate has been achieved within a 5 mm linear cavity [8]. However, such a technique usually poses challenges to the gain media and fiber components. ...
We demonstrate a 1.5 GHz harmonic mode-locked erbium-doped fiber laser by incorporating gold nanofilm as a saturable absorber (SA). The high-quality gold nanofilm SA fabricated by the physical vapor deposition method possesses a high modulation depth of 12.9% and a low saturation intensity of 1.69 MW/cm2 at 1.56 µm, facilitating the generation of harmonic mode-locking. The fundamental mode-locked operation was obtained at 1564.7 nm, with a pulse duration of 586 fs and a repetition rate of 34.235 MHz. At the pump power of 610 mW, 44th-order harmonic mode-locking with a repetition rate of 1.506 GHz was achieved, which is the highest yet reported in mode-locked fiber lasers using gold nanomaterials as SAs. Moreover, the gold nanofilm-based harmonic mode-locked fiber laser shows relatively high signal-to-noise ratios, high output power, and good stability. These results highlight the advantage of the gold nanofilm-based SA in realizing high repetition rate laser sources.
... Passively mode-locked fiber lasers have widespread applications such as communications [1,2], manufacturing and processing [3,4], biomedical diagnostics [5,6], and other fields due to their competitive properties such as compact structure, high repetition frequency, high pulse energy, ultrashort pulse width, and high peak power [7][8][9][10]. It is noteworthy that two-dimensional (2D) materials are preferred for the saturable absorber (SA) as the pivotal device of passively mode-locked fiber laser on account of their superior properties such as high damage threshold, ultrafast recovery time, broad spectral absorption, and rapid response time [11][12][13][14]. ...
In this study, germanene-nanosheets (NSs) were synthesized by liquid-phase exfoliation, followed by an experimental investigation into the nonlinear saturable absorption characteristics and morphological structure of germanene. The germanene-NSs were employed as saturable absorbers, exhibiting saturation intensity and modulation depth values of ${22.64}\;{{\rm MW/cm}^2}$ 22.64 M W / c m 2 and 4.48%, respectively. This demonstrated the feasibility of utilizing germanene-NSs passively mode-locked in an erbium-doped fiber laser (EDFL). By optimizing the cavity length, improvements in the output of EDFL characteristics were achieved, resulting in 883 fs pulses with a maximum average output power of 19.74 mW. The aforementioned experimental outcomes underscore the significant potential of germanene in the realms of ultrafast photonics and nonlinear optics.
... The peak powers of the compressed pulses achieved in this work, labeled as red stars in Fig. 2, are compared to other state-of-the-art nonlinear temporal compression approaches for GHz repetition rates. [70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] A few important features differentiate our work from the adjacent values in Fig. 2. For example, the average power at 20 GHz repetition rate in our work is ∼ 4× lower than that of Refs. 18 and 19. ...
Frequency combs with mode spacing of 10–20 GHz are critical for increasingly important applications such as astronomical spectrograph calibration, high-speed dual-comb spectroscopy, and low-noise microwave generation. While electro-optic modulators and microresonators can provide narrowband comb sources at this repetition rate, a significant remaining challenge is a means to produce pulses with sufficient peak power to initiate nonlinear supercontinuum generation spanning hundreds of terahertz (THz) as required for self-referencing. Here, we provide a simple, robust, and universal solution to this problem using off-the-shelf polarization-maintaining amplification and nonlinear fiber components. This fiber-integrated approach for nonlinear temporal compression and supercontinuum generation is demonstrated with a resonant electro-optic frequency comb at 1550 nm. We show how to readily achieve pulses shorter than 60 fs at a repetition rate of 20 GHz. The same technique can be applied to picosecond pulses at 10 GHz to demonstrate temporal compression by 9× and achieve 50 fs pulses with a peak power of 5.5 kW. These compressed pulses enable flat supercontinuum generation spanning more than 600 nm after propagation through multi-segment dispersion-tailored anomalous-dispersion highly nonlinear fibers or tantala waveguides. The same 10 GHz source can readily achieve an octave-spanning spectrum for self-referencing in dispersion-engineered silicon nitride waveguides. This simple all-fiber approach to nonlinear spectral broadening fills a critical gap for transforming any narrowband 10–20 GHz frequency comb into a broadband spectrum for a wide range of applications that benefit from the high pulse rate and require access to the individual comb modes.
... Under the combined actions of selfphase modulation, stimulated Raman scattering, and four-wave mixing, a supercontinuum is generally obtained by pumping a high-nonlinearity fiber (HNLF) with amplified ultrashort pulses, but it would lift the noise floor because of the amplified spontaneous emission, which is unable to be suppressed outside the cavity [6][7][8][9][10]. In comparison, pumping a HNLF with ultrashort pulses directly output from oscillators is an effective method [11][12][13][14][15]. Generally, pulses with a high repetition rate feature a high sampling speed for applications; however, due to the limited average power of the oscillator, a compromise is usually required between the pulse energy and repetition rate of the laser [16,17]. In particular, to generate an octave-spanning supercontinuum in the 1 µm region, sub-100 fs pulses serving as an unamplified pump source are necessary when the repetition rate is in the multi-100 megahertz region, given that the output power of a mode-locked fiber laser is typically below 1 W [11][12][13][14]. ...
... Taking advantage of polarization-maintaining fiber and semiconductor saturable absorber (SESAM) mode-locking, a 1.08 GHz fundamentally mode-locked bidirectional Yb-doped fiber laser was demonstrated by Ou et al. [19], whose mode-locking threshold is 432 mW, but the output pulse width (177 fs) is much higher than 100 fs. By implementing highly doped phosphate fiber into linear cavity configurations and using SESAM mode-locking, it is easy to reach a repetition rate at a multi-gigahertz level at very low initiating pump power, but the pulse durations are usually in the picosecond range, because those cavities are typically without dispersion management [16,17,20,21]. By employing an output coupler as a dispersion compensator, a modified version of a linear Yb-doped fiber laser that generates ∼200 fs pulses was proposed by Chen et al. [22] at a repetition rate of 3 GHz. ...
Supercontinuum generation via direct pumping of unamplified high-repetition-rate, sub-100 fs pulses with a pulse energy lower than 50 pJ is superior in noise performance and features a high acquisition speed. We demonstrate a novel, to the best of our knowledge, gigahertz-repetition-rate, mode-locked Yb-doped fiber laser, where the hybrid mode-locking approach is employed. The laser has a low initiating threshold of 300 mW and a broad mode-locking range of 600 mW (300–900 mW) in terms of pump power. The shortest obtained pulse width of the laser after compression is 95 fs, and the highest output pulse energy is 92.9 pJ at a fundamental repetition rate of 1.15 GHz. Moreover, the laser’s output polarization states are switchable, and it has a polarization extinction ratio of 17.9 dB.
