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Carbon nanotubes (CNTs) possess remarkable nonlinear optical properties; a particular application is to function as a mode locker used in ultrafast fiber lasers to produce ultrashort optical pulses. Various types of CNT saturable absorbers (SAs) and ultrafast fiber lasers have been demonstrated. In this review, typical fabrication process and development of CNT SAs are discussed and we highlight the recent investigation and progress of state-of-the-art ultrafast fiber lasers covering GHz, bidirectional ultrafast fiber lasers, vectorial mode fiber lasers, comb systems, and mode-locking dynamics. Our perspectives of ultrafast fiber lasers based on CNT SAs are given finally.

We report experimental observation of polarization attractors in the form of vector dissipative solitons from a carbon nanotube mode locked fiber laser. At a time scale of 14–14,000 roundtrips, the typical polarization locked vector solitons, and other appealing attractors are shown. In addition, we observe the vector dissipative solitons operated in dual-wavelength regime with central wavelength of 1533 and 1557 nm which can be related to a fixed point polarization attractor. The results unveiled complex oscillatory behavior of dissipative solitons in the polarization domain which may help understand laser physics, nonlinear optics. The demonstrated work may underpin a new type of high energy laser source leading to possible applications in nanoparticle manipulation, micromachining, spectroscopy etc.

We demonstrated a harmonic mode-locked fiber laser by using saturable absorber based on interaction of over-coupled long period fiber grating and carbon nanotubes. Maximum repetition rate of 2.416 GHz was obtained with 15 mW output.

Bidirectional wavelength-tunable mode-locked fiber lasers have demands for many applications. In our experiment, two frequency combs from a single bidirectional carbon nanotube mode-locked erbium-doped fiber laser are obtained. Continuous wavelength tuning is demonstrated in the bidirectional ultrafast erbium-doped fiber laser for the first time. We utilized the microfiber assisted differential loss-control effect on both directions to tune operation wavelength and it presents different wavelength tuning performances in two directions. Correspondingly, the repetition rate difference can be tuned from 98.6 Hz to 32 Hz by applying strain on microfiber within 23 µm stretching length. In addition, a minor repetition rate difference variation of 4.5 Hz is achieved. Such technique may provide possibility to expand wavelength range of dual-comb spectroscopy and broad its application fields.

We examine the implication of intracavity nonlinearity for harmonic mode locking (HML) by exploiting highly nonlinear fiber in a carbon nanotube film mode-locked Er-doped fiber laser. It is found that the reasonably large nonlinearity is of benefit to increase the extent of harmonic order while the excessive nonlinearity leads to some peculiar multi-pulse patterns such as noise-like pulse and soliton rain. Via appropriate nonlinearity management, nearly 4 GHz repetition rate pulses at the 91st harmonic with 936 fs pulse duration are delivered under the pump power of 280 mW. The pulse stability is evidenced by the super-mode suppression ratio of 35.6 dB. To the best of our knowledge, it is the highest repetition rate yet reported for a passively HML fiber laser based on a film-type physical saturable absorber. Furthermore, the laser exhibits steep pumping efficiency slope of > 19 M H z / m W , which is also a record among all of the passively HML fiber lasers.

A wavelength-tunable noise-like pulse (NLP) erbium-doped fiber laser incorporating PbS quantum dot (QD) polystyrene (PS) composite film as a saturable absorber (SA) is experimentally demonstrated. The wavelength tuning is implemented via a Lyot filter consisting of a segment of polarization-maintaining fiber (PMF) and a 45° tilted fiber grating. By adjusting the polarization state of the ring cavity, the laser can deliver NLP with a continuous wavelength-tunable range from 1550.21 to 1560.64 nm. During continuous wavelength tuning, the output power varies between a range of 30.88–48.8 mW. Worthwhile noting is that the output power of 48.8 mW is the reported highest output power for wavelength-tunable NLP operation in an erbium-doped fiber laser using composite film as a saturable absorber.

We demonstrate a nonlinearity managed passively harmonic mode-locked Er-doped fiber laser using carbon nanotubes film. Lowering the pulse energy via careful nonlinearity management results in 3.4GHz pulse generation with only 250mW pump power.

We have demonstrated a bidirectional wavelength-tunable mode-locked fiber laser. The wavelength can be continuously tuned from 1567.3 to 1561.21 nm in the clockwise direction and from 1567.25 to 1561.19 nm in the counter-clockwise direction.

We demonstrate an L-band wavelength-tunable passively mode-locked fiber laser using a single long-period fiber grating (LPFG) as a narrow-band optical attenuator (NBOA). Through bending the LPFG, the central wavelength can be continuously tuned from 1582.02 to 1597.29 nm, while the output power only varies from 1.465 to 1.057 mW, approximately a rate of 22 µW/nm variation. This is the first time that LPFG is functioned as a NBOA in mode-locked fiber lasers, showing the great advantage of less impact on output power variation reduction. Besides, the total cavity length is 5.08 m, which is the shortest length yet reported in wavelength-tunable mode-locked fiber lasers. The wavelength tuning could also be realized at harmonic mode locking with tuning range of 14.69 nm under 5th harmonic.

We report on an in-fiber Brewster device with a 45° tilted fiber grating (TFG) directly written by a plane-by-plane femtosecond laser inscription method. Up to 10 dB polarization-dependent loss was achieved, proving effective polarizing functionality. Furthermore, we employ it as an in-line polarizer to successfully mode lock a fiber laser through the nonlinear polarization rotation technique. A stable soliton pulse train has been generated at 1563.64 nm with a pulse width of 624 fs and pulse energy of 0.42 nJ. With proper polarization adjustment, the laser also can operate in a noise-like regime. The parameters of this kind of 45°-TFG can be flexibly customized owing to the high flexibility and controllability of the femtosecond laser-inscription approach. In particular, such in-fiber polarizing devices inscribed by femtosecond laser inscription without removing the fiber coating are extremely robust for fiber lasers working at a broad wavelength region including the mid-infrared.

We demonstrated a wavelength-tunable passively mode-locked erbium-doped fiber laser based on carbon nanotube and intermodal interference of the microfiber. Continuously tuning range from 1569.6 nm to 1561.57 nm is achieved under single pulse operation.

We demonstrate a multi-wavelength mode-locked Yb-doped fiber laser by incorporating a pair of polarization maintaining 45° tilted fiber gratings (PM-45°TFG) based Lyot filter. Thanks to the functions of the polarizer and the comb filtering introduced by the Lyot filter, dissipative soliton (DS) pulses centered at 1035.26 nm, 1044.93 nm, 1055.62 nm, 1066.11 nm and 1076.63 nm can be generated respectively by finely tuning the intracavity polarization controllers (PCs). Moreover, the laser also can operate in a multi-wavelength regime via appropriately adjusting the pump power and polarization orientation. The high nonlinearity induced by the long cavity length leads to the generation of h-shaped mode-locked pulse with a repetition rate of 566.27 kHz. In the absence of any disturbance, the laser can operate steadily, that can potentially be used in various fields including wavelength division multiplexing systems etc.

We demonstrate a pump-controlled wavelength switchable Yb-doped fiber laser (YDFL) by nonlinear polarization rotation (NPR) for the first time. The polarizer replaced by a 45° tilted fiber grating (45°-TFG) combines with a section of polarization maintaining fiber (PMF) to form a fiber-based birefringent filter. Stable dissipative soliton (DS) with center wavelength of 1068.39 nm is generated under the mode-locked threshold of 277 mW. The operating wavelength switching between 1046.51 nm and 1067.90 nm can be realized via increasing the pump power simply while keeping the polarization controllers (PCs) in a fixed state. The laser maintains stable mode-locking operation at each wavelength, which can be regarded as a type of multi-wavelength ultrafast light source with precise control and integration potential.