Carbon Nanotube Saturable Absorber Research Articles

Passively synchronized dual-color soliton fiber laser based on single-walled carbon nanotubes

In this work, we propose a uniquely designed fiber laser to generate dual-color soliton molecules, which are stable bound states made up of solitons with different carrier frequencies, pulse widths and soliton energies. This fiber laser consists of two resonators, which are cascaded by a pair of wavelength division multiplexers (WDMs), and a single-walled carbon nanotube saturable absorber (SWCNT-SA) is placed in the common branch shared by two sub-cavities to achieve optical soliton mode-locking. The optical solitons generated by this laser have central wavelengths of 1530.43 nm and 1547.62 nm with pulse widths of 0.832 ps and 1.198 ps, respectively. The synchronous mode-locked operation of the two sub-cavities can be easily achieved by adjusting the optical delay line (DL) in one of the resonant cavities. When the synchronized state is reached, two solitons with different central wavelengths operate synchronously and stably at a consistent repetition frequency of ∼8.1505 MHz and dual-color soliton molecules are generated. The fiber laser has the advantages of simple structure and controllable generation of soliton molecules, which provide a new idea for the design of soliton molecule ultrafast fiber laser.

Synchronized triple-wavelength fiber lasers at 1, 1.55, and 1.9 µm.

Synchronized lasers working at different wavelengths are of great significance for numerous applications, such as high-energy femtosecond pulse emission, Raman microscopy, and precise timing distribution. Here, we report synchronized triple-wavelength fiber lasers working at 1, 1.55, and 1.9 µm, respectively, by combining the coupling and injection configurations. The laser system consists of three fiber resonators gained by ytterbium-doped fiber, erbium-doped fiber, and thulium-doped fiber, respectively. Ultrafast optical pulses formed in these resonators are obtained by passive mode-locking with the use of a carbon-nanotube saturable absorber. A maximum cavity mismatch of ∼1.4 mm is reached by the synchronized triple-wavelength fiber lasers in the synchronization regime by finely tuning the variable optical delay lines incorporated in the fiber cavities. In addition, we investigate the synchronization characteristics of a non-polarization-maintaining fiber laser in an injection configuration. Our results provide a new, to the best of our knowledge, perspective on multi-color synchronized ultrafast lasers with broad spectral coverage, high compactness, and a tunable repetition rate.

C-band dual-wavelength synchronized mode-locked erbium-doped fiber laser using a common absorber

We demonstrate a C-band dual-wavelength synchronized mode-locked erbium-doped fiber laser based on a common single-wall carbon nanotube saturable absorber and two loop resonators. The synchronous mode-locked pulses laser is with a repetition rate of 16.28 MHz and durations of 1.95 ps and 1.21 ps at 1533 nm and 1562 nm, respectively. The tolerance of a cavity-length mismatch is about 830μm. The proposed dual-wavelength laser system exhibits a flexibly controlled performance and a long-term stability, which offers great potential for a number of applications, such as difference-frequency terahertz-wave generation and field-enhancement Raman microscopy.

Broadband Q-switched pulse modulation of the zeolite based single wall carbon nanotube

We reported a wide-band single walled carbon nanotube (SWCNT) saturable absorber (SA) fabricated in the one-dimensional nanochannels of ZnAPO4-5 (AFI) zeolite single crystals. The as-synthesized SA could provide Q-switched operation at both 1038.8 and 1856.5 nm in the ytterbium-, and thulium-doped fiber lasers. Owing to the polarization state in the cavities remained unchanged by the all polarization maintaining (PM) optical paths, the modulation was only related to the nonlinearity of the material. The modulation depths were characterized by the balanced twin-detector system at different wavelengths, showing excellent anisotropic optical properties, which were 5.5 % and 13.0 %, respectively. These results demonstrated that the SWCNT@AFI crystal could act as a specific polarization sensitive SA for some certain scenarios requiring seismic resistance and environmental adaptability, and was an appropriate device for short-duration pulsed fiber laser with a broad spectral coverage.

Femtosecond Er-Doped All-Fiber Laser with High-Density Well-Aligned Carbon-Nanotube-Based Thin-Film Saturable Absorber.

We have studied the ultrafast saturation behavior of a high-density well-aligned single-walled carbon nanotubes saturable absorber (HDWA-SWCNT SA), obtained by a high-pressure and high-temperature treatment of commercially available single-wall carbon nanotubes (SWCNTs) and related it to femtosecond erbium-doped fiber laser performance. We have observed the polarization dependence of a nonlinear optical saturation, along with a low saturation energy level of <1 fJ, limited to the detector threshold used, and the ultrafast response time of <250 fs, while the modulation depth was approximately 12%. We have obtained the generation of ultrashort stretched pulses with a low mode-locking launching threshold of ~100 mW and an average output power of 12.5 mW in an erbium-doped ring laser with the hybrid mode-locking of a VDVA-SWNT SA in combination with the effects of nonlinear polarization evolution. Dechirped pulses with a duration of 180 fs were generated, with a repetition rate of about 42.22 MHz. The average output power standard deviation was about 0.06% RMS during 3 h of measurement.

Multi-gigahertz mode-locked femtosecond Yb:KLuW waveguide lasers

We demonstrate multi-gigahertz continuous-wave mode-locking of a Yb:KLuW waveguide laser. A femtosecond-laser-inscribed Yb:KLuW channel waveguide in an extended laser cavity delivers a fundamentally mode-locked laser near 1030 nm. A tunable few-centimeter-long cavity containing a single-walled carbon nanotube saturable absorber as mode-locker generates self-starting femtosecond pulses with average output powers exceeding 210 mW at repetition rates of 2.27, 2.69, and 3.55 GHz. The laser cavity, which includes a wedged waveguide, is extended by using a lens pair that controls the laser fluence on the saturable absorber for reliable mode-locked operation without instability. The presented laser performance, mode-locked up to 3.55 GHz, highly suggests the potential of crystalline Yb:KLuW waveguides for realizing high-power ultrafast lasers with higher GHz repetition rates in a quasi-monolithic cavity.

The generation and observation of pulses with switchable single/dual wavelengths and tunable bandwidth from a SWNT mode-locked Er-doped fiber laser

Mode-locked pulse outputs with switchable single/dual wavelengths and widely tunable spectral bandwidth are demonstrated by fully exploiting multiple soliton formation mechanisms combining single-wall carbon nanotube, intracavity loss tuning and nonlinear polarization rotation. An isolator with single-polarization fiber pigtails is additionally inserted in a ring fiber laser cavity to introduce polarization-dependent loss modulation for gain profile tuning and nonlinear polarization rotation. Mode-locked by a home-made single-wall carbon nanotube saturable absorber, switchable single/dual-wavelength pulses centered in the 1530- or/and 1550-nm gain regions of erbium-doped fiber are experimentally observed by tuning the intracavity loss to tilt the gain profile. Moreover, the spectral bandwidths of single-wavelength pulses centered in the 1530- and 1550 nm regions could be continuously tuned from 2.4 to 4.0 nm, and 2.7 to 9.0 nm, respectively. Such widely tunable spectral bandwidths are attributed to hybrid mode-locked mechanisms combining the nonlinear polarization rotation and single-wall carbon nanotube. Our results give a deep insight into the well-controlled gain profile tuning and provide a relatively simple setup and method to obtain bandwidth-tunable, wavelength-switchable pulse outputs, showing the potential to meet various requirements of ultrafast laser applications.

Passively Q-switched erbium doped fiber laser based on graphene and carbon nanotube saturable absorbers

A passively Q-switched erbium-doped fiber laser (EDFL) was experimented on by employing graphene, single walled carbon nanotubes (SWCNT) and multi-walled carbon nanotube (MWCNT) saturable absorbers (SA). The SA film was obtained by embedding the graphene, SWCNT and MWCNT into polyvinyl alcohol (PVA). The graphene SA was prepared by dipping a PVA thin film into the graphene solution while carbon nanotubes SAs were prepared using the casting method and placed in the ring cavity to produce a stable pulse laser. Graphene, SWCNT and MWCNT SAs were operating at wavelengths of 1558.92 nm, 1557.98 nm and 1558.51 nm, respectively, whereas the continuous wave was 1560.72 nm at the input pump power of 56 mW. The pulse energy, output power, repetition rate and pulse width were compared in graphene, SWCNT and MWCNT SAs. The shortest pulse width retrieved in graphene, SWCNT and MWCNT were 3.90 µs, 3.62 µs 4.43 µs and produced at the repetition rate of 115.00 kHz, 130.70 kHz, and 89.13 kHz, respectively. In comparison to graphene and SWCNT SAs, MWCNT SAs exhibit the best performance in terms of output power of 2.19 mW and high pulse energy of 24.57 nJ in passively Q-switched EDFL.

Mode-locked fiber laser of 3.5 µm using a single-walled carbon nanotube saturable absorber mirror

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

Ultrafast all-anomalous-dispersion Er-doped large-mode-area fiber lasers

Ultrafast Er-doped large-mode-area (LMA) fiber lasers are demonstrated in the all-anomalous-dispersion regime. With the assistance of a home-made carbon nanotube saturable absorber, stable and chirp-free solitons are always observed for output coupling ratios (OCRs) varying from 10% to 90%, leading to the simultaneous achievement of the maximum pulse energy and minimum pulse duration at the OCR of 70%. To validate the universality of the all-anomalous-dispersion mode-locking, an all-fiber saturable absorber based on nonlinear multimode interference effect is incorporated into the LMA fiber laser cavity, which can also generate chirp-free solitons. The influences of gain fiber dispersion on solitons are numerically simulated, revealing that the dispersion consistency of fibers in the laser cavity is in favor of generating stable and chirp-free solitons even at an ultrahigh OCR. This work paves the way for ultrafast Er-doped LMA fiber lasers in the all-anomalous-dispersion regime, which provides an alternative route to further improve the stability and output pulse energy of ultrafast LMA fiber lasers, i.e. ensuring the dispersion consistency and hence enlarging the OCRs.

SWCNT-SA mode-locked Tm,Ho:LCLNGG laser.

Sub-100 fs pulse generation from a passively mode-locked Tm,Ho-codoped cubic multicomponent disordered garnet laser at ∼2 µm is demonstrated. A single-walled carbon nanotube saturable absorber is implemented to initiate and stabilize the soliton mode-locking. The Tm,Ho:LCLNGG (lanthanum calcium lithium niobium gallium garnet) laser generated pulses as short as 63 fs at a central wavelength of 2072.7 nm with an average output power of 63 mW at a pulse repetition rate of ∼102.5 MHz. Higher average output power of 121 mW was obtained at the expense of longer pulse duration (96 fs) at 2067.6 nm using higher output coupling. To the best of our knowledge, this is the first report on mode-locked operation of the Tm,Ho:LCLNGG crystal.

Sub-100 fs mode-locked Tm:CLTGG laser.

We report on the first sub-100 fs mode-locked laser operation of a Tm3+-doped disordered calcium lithium tantalum gallium garnet (Tm:CLTGG) crystal. Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 69 fs were achieved at a central wavelength of 2010.4 nm with an average power of 28 mW at a pulse repetition rate of ∼87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW.

High-Order Mode Mode-Locked Fiber Laser Based on Few-Mode Saturable Absorber

We presented two kinds of high-order mode (HOM) mode-locked fiber lasers based on few-mode (FM) saturable absorbers for direct HOM oscillation. One is a ring fiber laser based on a carbon nanotube (CNT) saturable absorber (SA), in which the combination of a long period fiber grating (LPFG) and a mode selective coupler (MSC) is used for the cycle of mode conversion between LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes. The other is a linear-cavity laser using a FM-based SESAM with the HOM oscillation, in which a MSC is used for mode conversion inside the cavity. The presented mode-locked fiber lasers can achieve the saturable absorption of the HOM and the cylindrical vector beams (CVBs). And we also compared the nonlinear saturation absorption characteristics of two SAs operating at LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes.

Tunable multidimensional multiplexed Q-switched pulse outputs from a linear fiber laser with a bidirectional loop

A simple all-fiber linear cavity to emit multidimensional multiplexed pulses is developed by combining fiber birefringence filter and bidirectional loop. Without unidirectional components, single polarization fiber and polarization maintaining fiber pigtails function as a bidirectional birefringence filter. Q-switched by a home-made single-wall carbon nanotube saturable absorber with the insertion loss of 16 dB, tunable wavelength/direction multiplexed Q-switched pulses were observed in the 1530-nm gain region of Er-doped fiber. When the pump power increased from 63 to 237 mW, the repetition rates of clockwise and counter-clockwise dual-wavelength Q-switched pulses respectively increased from 59 to 106 kHz and 60 to 106 kHz. Correspondingly, their output powers respectively increased from 139 to 579 μW and 107 to 512 μW. Meanwhile, by carefully adjusting the intracavity polarization controller under the same pump power of 237 mW, the switchable wavelength numbers and continuous spectral shift of wavelength multiplexed Q-switched microsecond pulses were observed. The feasibility of tunable wavelength/direction multiplexed Q-switched pulse generation is experimentally demonstrated for the first time to the best of our knowledge. Our results highlight a novel wavelength/direction multiplexed method for tunable multiple pulse emission using a simple linear fiber laser cavity, indicating high potential for continuously tunable microwave and THz generation and so on.

Single-walled carbon-nanotube saturable absorber assisted Kerr-lens mode-locked Tm:MgWO4 laser.

We demonstrate sub-100-fs Kerr-lens mode-locking of a Tm:MgWO4 laser emitting at ∼2µm assisted by a single-walled carbon-nanotube saturable absorber. A maximum average output power of 100 mW is achieved with pulse duration of 89 fs at a pulse repetition rate of ∼86MHz. The shortest pulse duration derived from frequency-resolved optical gating amounts to 76 fs at 2037 nm, corresponding to nearly bandwidth-limited pulses. To the best of our knowledge, these are the shortest pulses generated from any Tm-doped tungstate crystal and the first report on saturable absorber assisted Kerr-lens mode-locking of a Tm laser at ∼2µm.

Conventional Soliton and Noise-Like Pulse Generated in an Er-Doped Fiber Laser with Carbon Nanotube Saturable Absorbers

Conventional soliton (CS) and noise-like pulse (NLP) are two different kinds of pulse regimes in ultrafast fiber lasers, which have many intense applications. In this article, we experimentally demonstrate that the pulse regime of an Er-doped fiber laser could be converted between conventional soliton and noise-like pulse by using fast response saturable absorbers (SA) made from different layers of single-wall carbon nanotubes (CNT). For the monolayer (ML) single-wall CNT-SA, CS with pulse duration of 439 fs at 1560 nm is achieved while for the bilayer (BL) single-wall CNT, NLP at 1560 nm with a 1.75 ps spike and a 98 ps pedestal is obtained. The transition mechanism from CS to NLP is investigated by analyzing the optical characteristics of ML and BL single-wall CNT. The further theoretical simulation illustrates that CNT-SA enables the switching between CS and NLP in anomalous dispersion regime in Er-doped fiber lasers.

Octave spanning supercontinuum generation with a few-mode fiber

We propose and demonstrate the generation of a supercontinuum with a few-mode fiber. Due to the accommodation of a few-mode fiber in LP01 and LP11 modes, the system was engineered to detect the octave spanning supercontinuum in both modes. A mode-locked laser with 5.2 nm spectral bandwidth at a central wavelength of 1557 nm, 0.92 ps pulse width, 13.36 MHz repetition rate, and 61.3 dB peak-to-pedestal extinction ratio was implemented with a carbon nanotube saturable absorber. This mode-locked laser was employed as a seed laser for the consecutive generation of supercontinuum with a 500 m few-mode fiber. The laser modes were adjusted with a mode filter to propagate in either LP01 or LP11 modes, which were accessed with a charge-coupled device camera. A fair comparison between a few-mode fiber and a single-mode fiber was made for supercontinuum generation in the LP01 mode. Despite the fact that the few-mode fiber has lower optical power than the single-mode fiber due to higher attenuation, this fiber provides flexible design of laser modes. This work demonstrates the first attempt to generate a supercontinuum with a few-mode fiber, whereby the broad tunable soliton and associated dispersive wave sources for both laser modes were comprehensively studied.

Tunable bound solitons from carbon nanotube saturable absorber

In this report we investigate the generation of Bound Solitons (BS) by using Carbon nanotubes (CNT) Saturable Absorber (SA) by using an Erbium (Er) doped fibre laser. In this study two cases are presented, one with a tunable intracavity filter and another without. When we did not use a tunable filter, we could generate two types BS in CNT. When we used a tunable filter, we could still generate two BS, but this time they were wavelength tunable and were longer in time domain due to introduction of filter. To best of our knowledge this is the first time when wavelength and time tunable BS are presented by using a saturable absorber. This will open more avenues where these BS could be applied notability telecommunication and material processing.

68 MHz Fundamental Repetition Rates for Mode-Locked Erbium Doped Fiber Laser based Carbon Nanotube Saturable Absorber

A carbon nanotube thin film as saturable absorber in a cavity design of mode-locked fiber laser is reported in this work. Measured by power dependent absorption setup, 22% modulation depth of the saturable absorber is estimated which is ideal for stabilizing the mode-locked operation. Based on the scanning image from atomic force microscope (AFM), Single wall carbon nanotube components are identified existed in the thin film. The laser cavity employed a ~40 cm long erbium doped fiber as a gain medium which corresponds to the laser wavelength of 1550 nm (telecommunication wavelength region). Total length cavity of the fiber laser is about 3.1 m where shorter cavity design is required for higher repetition rate. This proposed system result in a firm soliton spectrum at centre wavelength of ~1561 nm with ~0.7 mW average output power and pulse duration of 410 fs. The pulses are generated at fundamental repetition rate of 68 MHz without any distortion and excellent spectral quality.

Wavelength-tunable bidirectional passively Q-switched Er-doped fiber laser incorporating a single-walled carbon nanotube and tunable bandpass filter.

We demonstrated a continuously wavelength-tunable bidirectional passively $ Q $Q-switched fiber laser based on a single-walled carbon nanotube saturable absorber and a bandpass filter (BPF). By tuning the commercial BPF, the $ Q $Q-switched pulse can be obtained in the same cavity at the same pump power in clockwise (CW) and counter-clockwise (CCW) directions. The central wavelength can be continuously tuned from 1520.88 to 1568.56 nm in the CW direction, and from 1520.96 to 1568.64 nm in the CCW direction. A wide tuning range of 48 nm is achieved for two directions in the passively $ Q $Q-switched fiber laser. During the tuning process of the fiber laser, the output pulses with the same central lasing wavelength can be obtained in both oscillation directions owing to the BPF. By increasing the pump power from 130 to 350 mW, the cavity delivers a $ Q $Q-switched pulse with the central wavelength of 1560 nm whose repetition rate changes from 9.64 to 59.18 kHz for the CW direction. In the CCW direction, the repetition rate of the $ Q $Q-switched pulse changes from 10.26 to 61.03 kHz. To the best of our knowledge, it is the first time that continuous wavelength-tunable passively $ Q $Q-switched pulses have been achieved in a bidirectional erbium-doped fiber laser.