Dispersion-managed Fiber Laser Research Articles

206 MHz fully stabilized all-PM dispersion-managed figure-9 fiber laser comb

High-repetition-rate optical frequency combs are useful for precision spectroscopy because of their high power per comb mode, but conventional high-repetition-rate lasers do not have a broad enough spectrum. In this study, a fully stabilized polarization-maintaining figure-9 mode-locked fiber laser with a high repetition rate of 206 MHz and a broad spectrum was demonstrated by employing simultaneous control of cavity dispersion and length. The laser exhibited a 3 dB spectral bandwidth of 88 nm and a compressed pulse width of 66 fs. Additionally, fCEO and frep phase locking were implemented, resulting in low (0.21 rad) in-loop carrier-envelope-offset frequency phase noise. To the best of our knowledge, this is the widest spectrum bandwidth and shortest pulse duration directly obtained from an all-PM figure-9 fiber laser oscillator to date. The combination of high repetition rate and broad spectral range makes this system very useful for a wide range of applications, especially in the field of precision spectroscopy.

Build-up dynamics of different pulse types in a dispersion-managed Yb-doped fibre laser

We present a dispersion-managed mode-locked ytterbium fibre laser based on the nonlinear polarization evolution technique. Four single-pulse states could be generated by changing group delay dispersion values from anomalous (−0.0038 ps2) to normal (0.051 ps2) with a grating pair. In the normal dispersion regime, the pulse width was gradually decreased with the decrease of the net dispersion. In the anomalous dispersion region, the typical soliton was obtained, which time-bandwidth product could be calculated as 0.526. In addition, the dynamics of four states were also investigated by using the dispersive Fourier transformation technique. Different pulse evolution dynamics were observed from chaotic state to mode-locking.

Dynamic behaviors of special noise-like pulses and rogue waves in an L-band ultrafast fiber laser

We demonstrate a composite regime of the special noise-like pulses (NLPs) and rogue waves (RWs) in an L-band dispersion-managed fiber laser. Apart from stable ultrashort pulses, the fiber laser can easily generate unique NLPs with clear peak on broad spectrum at high pump power and proper polarization state. In this regime, these tiny pulses with irregular intervals experience random fluctuations, making the dynamic evolutions of these pulse envelopes look like the endless undulating mountains along the hundreds of intra-cavity roundtrips. In addition, the real-time observation based on the time-stretch technique shows that there are the unique lacking pieces and changeable pulse durations in this NLPs regime. Besides, the chaotic pulse packets with intensity fluctuations are observed at the proper condition, showing the typical statistical distribution with L shape, which can be called as the typical RWs. It is believed that these results will facilitate the further understanding of the nonlinear characteristics of the NLPs and RWs in ultrafast fiber lasers.

Design of a 10 W Level Dispersion-Managed High-Power Ultrafast Mid-Infrared Fiber Laser System

Design of a 10 W Level Dispersion-Managed High-Power Ultrafast Mid-Infrared Fiber Laser System

Formation and statistical properties of rogue wave in dispersion-managed fiber lasers

Rogue wave in ultrafast fiber lasers is a hot research topic of nonlinear optics, which is generally monitored at the fixed cavity positions, despite its dramatic intra-cavity evolution. The shot-to-shot statistical properties change significantly if the chaotic pulse experiences strong changes along the cavity, which is rarely considered in the past. Here, we simulate the dynamic evolution of the rogue wave in the dispersion-managed fiber laser. Attributing to the temporal structure change induced by the dispersion, the rogue wave within the noise-like pulse appears in a limited cavity region while disappears in the rest parts. It is also demonstrated that the dispersion is capable of manipulating rogue waves in the pulse trains outside the cavity. Our results offer insightful views on the properties of chaotic waves in ultrafast lasers.

Systematic exploration and characterization on the influence of dispersion to pulse characteristics in Tm-doped NPE mode-locked fiber oscillator

We present a systematic and experimental exploration on the influence of the second-order and third-order dispersion on pulse characteristics in an ultra-high numerical aperture (UHNA) fiber dispersion-managed, Tm-doped and nonlinear polarization evolution (NPE) mode-locked fiber laser cavity; and obtained the detailed regularity of the variation of the key parameters for mode-locked pulse, including pulse duration, pulse spectral profile, and pulse signal-to-noise ratio (SNR) with dispersion. In this process, we find that there are two interesting second-order dispersion points of −0.207 ps2 and 0.09 ps2, in which the pulse SNRs can be optimized to as high as 79 dB and 78 dB, respectively, considerably higher than that in other positions. Besides, the experimental results show that the value of third-order dispersion can not only impact the pulse spectrum but also monotonously affect the quality of pulse SNR. To the best of our knowledge, this is the first report on the detailed analysis of the effects of both the second and the third-order dispersion values on the pulse characteristics in 2-μm mode-locked fiber laser cavity and it will be an important reference to the realization of a Tm-doped mode-locked laser with high pulse contrast.

Simultaneous generation and real-time observation of loosely bound solitons and noise-like pulses in a dispersion-managed fiber laser with net-normal dispersion

We demonstrate the coexisting dynamics of loosely bound solitons and noise-like pulses (NLPs) in a passively mode-locked fiber laser with net-normal dispersion. The total pulse number of the single soliton bunch under the NLP operation regime almost increases linearly with increasing pump power, whereas the average pulse spacing decreases accordingly. Furthermore, pulse-to-pulse separation between adjacent soliton pulses in one soliton bunch keeps in the range of hundreds of picoseconds, which decreases from left to right with the change of time. Besides, the real-time observation has been performed by utilizing the time-stretch method, showing that each one of the loosely bound solitons on the NLP operation is actually composed of chaotic wave packets with random intensities. These findings obtained will facilitate the in-depth understanding of nonlinear pulse behaviors in ultrafast optics.

Numerical modeling and experimental investigation of ultrafast pulses generation from all-polarization-maintaining dispersion-managed nonlinear polarization evolution Yb-doped fiber laser.

We investigate an all-fiber all-polarization-maintaining dispersion-managed ultrafast fiber laser mode-locked by nonlinear polarization evolution in polarization-maintaining fibers both numerically and experimentally. We find that the laser can operate in different regions among a wide net dispersion, including dispersion-managed solitons, dispersion-managed dissipative solitons, bound state solitons and noise-like pulses. The laser generates the dispersion-managed soliton pulses with a maximum 3 dB bandwidth of 37.84 nm, which can be further compressed to 161.37 fs. Moreover, pulses generation simulation under different net dispersion condition has been carried out. Nonlinear pulse evolution dynamics in laser cavity has been analyzed through numerical simulation as well. The results are basically consistent with the experimental ones.

Experimental observation of shaking soliton molecules in a dispersion-managed fiber laser.

Recent progress in real-time spectral interferometry enables access to the internal dynamics of optical multisoliton complexes. Here, we report on the first, to the best of our knowledge, experimental observation of shaking soliton molecules by means of the dispersive Fourier transform technique. Beyond the simplex vibrating soliton pairs, multiple oscillatory motions can jointly involve in the internal dynamics, reminiscent of the shaking soliton pairs. Both quasi-periodically and chaotically evolving phase oscillations are approached in the sense of different oscillatory frequencies. In addition, the shaking soliton pair combined with sliding phase dynamics is also observed, and is interpreted as the superposition of two different internal motions. All of these results shed new light on the internal dynamics of soliton molecules with higher degrees of freedom, as well as enrich the framework toward multisoliton complexes.

GaSe saturable absorber for mode-locked Yb-doped fiber laser at 1.04 µm

Transition-metal dichalcogenides, such as tungsten disulfide (WS2) and molybdenium disulfide (MoS2), are highly anisotropic layered materials and have attracted growing interest from basic research to practical applications due to their exotic physical property that may complement graphene and other semiconductor materials. GaSe nanosheets are found to exhibit broadband nonlinear saturable absorption property, and saturable absorbers are fabricated by depositing GaSe nanosheets on side-polished fibers. Attributing to the weak evanescent field and long interaction length, the GaSe nanosheets are not exposed to large optical intensity, which allows the saturable absorber to work at the high-power regime. The saturable absorbers are used to mode locked dispersion-managed soliton fiber lasers.

Non-Lagrangian approach for coupled complex Ginzburg-Landau systems with higher order-dispersion

It is known that after a particular distance of evolution in fiber lasers, two (input) asymmetric soliton like pulses emerge as two (output) symmetric pulses having same and constant energy. We report such a compensation technique in dispersion managed fiber lasers by means of a semi-analytical method known as collective variable approach (CVA) with including third-order dispersion (TOD). The minimum length of fiber laser, at which the output symmetric pulses are obtained from the input asymmetric ones, is calculated for each and every pulse parameters numerically by employing Runge-Kutta fourth order method. The impacts of intercore linear coupling, asymmetric nature of initial parameters and TOD on the evolution of pulse parameters and on the minimum length are also investigated. It is found that strong intercore linear coupling and asymmetric nature of input pulse parameters result in the reduction of fiber laser length. Also, the role of TOD tends to increase the width of the pulses as well as their energies. Besides, chaotic patterns and bifurcation points on the minimum length of the fiber owing to the impact of TOD are also reported in a nutshell.

Self-organized structures of bound states in a 2 μm dispersion-managed mode-locked fiber laser

We report on the experimental generation of various self-organized structures of bound states in a near zero-dispersion mode-locked fiber laser. When the pump power is fixed at 492 mW, appropriately adjusting polarization controllers, the switching of the cavity feedback results in the evolution from the single pulse to the dispersion-managed soliton (i.e., stretched-pulse) pair. With the increase of pump power, bound states composed of more than two pulses can also be observed. Our results of the self-organized structures might enlarge the data-carrying capacity of current fiber-optical communication systems and benefit the investigation of nonlinear dynamics of bound states in fiber lasers at 2 μm.

Various soliton molecules in fiber systems.

Generation and propagation of various soliton molecules (SMs) in fiber systems are reviewed. SMs can survive either in fibers or fiber lasers. A dispersion-managed (DM) fiber link is the only platform for SM demonstration, while various fiber lasers can support different SMs. The fundamental unit of SMs can be conventional solitons generated in an anomalous dispersion regime, stretched pulses in DM fiber lasers, parabolic pulses, or gain-guided solitons in a normal dispersion regime. SMs with typically close soliton separation are presented. In addition, we demonstrate a new kind of SM with nanosecond soliton separation. The narrow spectral filtering is required for the generation of SMs with such long-distance interaction.

Generation of high-energy pulses in dispersion-managed Tm-doped fiber laser

设计了一种基于色散管理的掺铥光纤激光器。通过调节泵浦功率以及腔内偏振态，首先实现了稳定的展宽脉冲输出，中心波长和脉冲宽度分别为1 939.4 nm和482 fs。最大输出功率为15 mW，对应的单脉冲能量为0.52 nJ。增加泵浦功率到645 mW时，通过适当调节偏振控制器可以实现类噪声脉冲锁模，中心波长为1 940.1 nm。所实现的锁模脉冲具有飞秒量级的尖峰以及皮秒量级的基底。最大输出功率为20.4 mW，相对应的单脉冲能量为0.7 nJ。相比于传统孤子，采用色散管理所实现的锁模脉冲具有更高的脉冲能量。此外，所设计的掺铥光纤激光器可作为理想的主振荡功率放大以及啁啾脉冲放大结构的种子源，进一步提高脉冲能量，拓展2 μm高能光纤激光器的实际应用。

Dispersion-managed soliton fiber laser with random dispersion, multiphoton absorption and gain dispersion

We address the generation and interaction of dispersion-managed dissipative solitons (DMDSs) in a model of fiber lasers with the cubic-quintic nonlinearity, multiphoton absorption and gain dispersion. Both anomalous and normal segments of the dispersion map include random dispersion fluctuations. Effects of the gain dispersion, higher-order nonlinearity and randomness on the generation of DMDS are demonstrated. The solitons exhibit breather-like evolution, and are found to be robust, up to a certain critical level of the random-dispersion component, which is sufficiently high. The roles of multiphoton absorption, gain dispersion and nonlinearity on the DMDS are also identified in the absence of randomness. Pair wise interactions of solitons lead, most typically, to their merger, with breaking of the left-right symmetry. The outcome of the collisions is more sensitive to the initial temporal separation between the solitons than to their phase difference.

Numerical study of multiple noise-like pulsing in a dispersion-managed figure-eight fibre laser

We study numerically noise-like pulsing in a long passively mode-locked figure-eight fibre laser with a polarization-imbalanced nonlinear optical loop mirror (NOLM) and a strong dispersion map. Contrary to the common scenario where a single noise-like pulse develops, it is found that multiple small bunches tend to form in the cavity, sharing roughly the same characteristics, which are determined by the dispersion parameters. The wave packets are subject to ample periodic variations of their duration and peak intensity as they pass through sections of opposite dispersion signs, displaying a breathing dynamics analogous to the one undergone by solitons in stretched-pulse fibre lasers. Multiple noise-like pulsing operation can be understood by considering the strong compression and corresponding intensity increase of small bunches as they travel through the NOLM, which yields higher transmission through the NOLM and thus smaller cavity losses for these small units than for larger wave packets. The present results could serve as a basis for a deeper study of the dynamics taking place in partially mode-locked fibre sources, which is particularly complex when multiple bunches of radiation coexist and interact in the cavity.

Impact of Raman scattering on pulse dynamics in a fiber laser with narrow gain bandwidth

We examine theoretically the multi-pulse dynamics in a dispersion-managed fiber laser, in which the pulse’s spectral width is controlled by a pass-band filter. We show that in the domain of stable states with very narrow spectral width, i.e. which is one order of magnitude smaller than the bandwidth of the Raman gain of the intra-cavity fiber system, the Raman scattering (RS) significantly alters the multi-pulse dynamics. RS is found to have a greater impact in the immediate vicinity of some critical values of the pump power of the intra-cavity gain medium, where processes of pulse fragmentation occur. As a result, all the borders between the zones of stability of the multi-pulse states are altered, i.e. either shifted or suppressed.

Route to Larger Pulse Energy in Ultrafast Fiber Lasers

Principles of pulse shaping aiming larger pulse energy in fiber lasers are reviewed. From conventional solitons generated in the anomalous dispersion regime, stretched pulses in dispersion-managed fiber lasers, similaritons in normal dispersion regime, dissipative solitons in large normal dispersion regime, and amplifier similaritons in fiber lasers with narrow bandwidth filtering to dissipative-soliton-resonance (DSR) pulses in fiber lasers, scaling of pulse energy from picojoule level to microjoule is successfully achieved. DSR is a possible way to achieve endless pulse energy, which is limited by the available pump power and material damage threshold. Properties of DSR pulses are reviewed. Specifically, we experimentally and numerically demonstrate tilt-top DSR pulses in a normal dispersion mode-locked fiber laser. Two fronts of the tilt-top pulses exhibit different intensity, and the intensity disparity maintains while the pulses extend with increasing gain. The tilt-top DSR pulses have rectangular spectral pedestal and a peak. The spectral peak deviates from the center of the rectangle spectral pedestal. Further results show that the asymmetry of two fronts is closely related to the wavelength deviation of spectral peak. Numerical simulations reveal the importance of the saddle-type spectral filtering on asymmetric DSR pulse generation.

All-fiber polarization-maintaining erbium-doped dispersion-managed fiber laser based on a nonlinear amplifying loop mirror

In this paper, we build a mode-locked all-polarization-maintaining figure-of-8 erbium-doped fiber oscillator based on a nonlinear amplifying loop mirror. The fiber oscillator can generate 1.6ps chirped pulses that can be de-chirped to 500fs at 1550nm with a pulse energy of 0.8nJ and a repetition rate of 12MHz. It can be further amplified up to 10nJ and compressed down to 100fs with a pre-chirp managed nonlinear amplification setup. Such an oscillator and amplifier configuration has the advantages of self-starting and long-term operation, and it is highly suitable for subsequent frequency conversion, which is desirable for many applications in ultrafast microscopy and precision spectroscopy.

102-nm, 44.5-MHz inertial-free swept source by mode-locked fiber laser and time stretch technique for optical coherence tomography.

A swept source with both high repetition-rate and broad bandwidth is indispensable to enable optical coherence tomography (OCT) with high imaging rate and high axial resolution. However, available swept sources are commonly either limited in speed (sub-MHz) by inertial or kinetic component, or limited in bandwidth (<100 nm) by the gain medium. Here we report an ultrafast broadband (over 100 nm centered at 1.55-µm) all-fiber inertial-free swept source built upon a high-power dispersion-managed fiber laser in conjunction with an optical time-stretch module which bypasses complex optical amplification scheme, which result in a portable and compact implementation of time-stretch OCT (TS-OCT) at A-scan rate of 44.5-MHz, axial resolution of 14 µm in air (or 10 µm in tissue), and flat sensitivity roll-off within 4.3 mm imaging range. Together with the demonstration of two- and three-dimensional OCT imaging of a mud-fish eye anterior segment, we also perform comprehensive studies on the imaging depth, receiver bandwidth, and group velocity dispersion condition. This all-fiber inertia-free swept source could provide a promising source solution for SS-OCT system to realize high-performance volumetric OCT imaging in real time.