Single-walled 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.

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.

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.

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.

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.

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.

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.

Passively Q-switched laser with specific chiral SWCNTs selected by N-CS as saturable absorber at [formula omitted

The single-wall carbon nanotubes (SWCNTs) with the specific chirality (6, 5) and (7, 5) were sorted out by the density gradient ultracentrifugation (DGU) method. 2D photoluminescence excitation–emission map and the Raman spectrum confirmed the successful chirality-selection. The nonlinear optical performance of the chirality-selected SWCNTs was investigated by an open-aperture Z-scan setup. By employing the prepared SWCNTs saturable absorber (SWCNTs-SA), the minimum pulse duration of 115 ns with a pulse repetition rate of 550 kHz was obtained in the passively Q-switched (PQS) laser operation.

Diameter-selected single-walled carbon nanotubes for the passive Q-switching operation at 2 μm

In this paper, we proposed the diameter-selected single-walled carbon nanotubes (SWCNTs) via the simple liquid phase separation for the pulsed 2 μm laser operation as the saturable absorber (SA). The nonlinear absorption properties of the prepared SWCNTs based SA at 2 μm were investigated. The modulation depth and the saturation intensity were 8% and 6.5 kW/cm2, respectively. By employing the diameter-specified SWCNTs SA, a stable passively Q-switched Tm:YLF laser was demonstrated at 2 μm for the first time. The maximum repetition rate of 35.9 kHz and the shortest pulse duration of 920 ns were achieved with the output coupler of T = 3%. The experiment results indicated that the diameter selection of SWCNTs could be a promising method to improve the Q-switching characteristics.

21 fs Cr:LiSAF laser mode locked with a single-walled carbon nanotube saturable absorber

We report the shortest femtosecond pulses directly generated from a solid-state laser that is mode locked by using a single-walled carbon nanotube saturable absorber (SWCNT-SA). In the experiments, we used a 660nm diode-pumped, low-threshold extended-cavity Cr:LiSAF laser operating around 850nm with a repetition rate of 47.9MHz. The SWCNT-SA mode-locked Cr:LiSAF laser produced 21fs pulses with a time-bandwidth product of 0.56 by using only 210mW of pump power. Pump-probe spectroscopy measurements showed that the SWCNT-SA exhibited saturable absorption with slow and fast decay times of 2.7ps and 0.4ps. The single-pass modulation depth and saturation fluence of the SWCNT-SA were further determined as 0.3% and 45 μJ/cm2 at the pump wavelength of 850nm.

Fluorite-type Tm3+:KY3F10: A promising crystal for watt-level lasers at ∼1.9 μm

Tm3+-doped cubic potassium yttrium fluoride, KY3F10, is a promising laser crystal for efficient watt-level lasers at ∼1.9 μm because of the relatively easy crystal growth by the Czochralski method, advantageous thermo-optical properties, high available Tm3+ doping levels and very efficient cross-relaxation mechanism. A compact diode-pumped 8 at.% Tm3+:KY3F10 laser generated 1.85 W at 1891 nm with a slope efficiency of 65.2% and a laser threshold of 450 mW. A negative thermal lens was detected in this crystal owing to the negative dn/dT coefficient (−8.9 × 10−6 K−1). Passive Q-switching of the Tm3+:KY3F10 laser by single-walled carbon nanotube saturable absorber was demonstrated yielding 13.2 μJ/490 ns pulses at a repetition rate of 58 kHz.

Passively mode-locked Yb-doped all-fiber oscillator operating at 979 nm and 1032 nm with the single wall carbon nanotubes as SA

We report on an all-fiber passively mode-locked ytterbium-doped (Yb-doped) fiber laser with single polymer composite saturable absorber (SA) based on the single wall carbon nanotubes (SWCNTs) with diameters of 0.8 nm. The SWCNTs are mixed with sodium carboxymethylcellulose (NaCMC) to form SWCNTs SA film. The non-saturable absorption coefficient, modulation depth and saturable intensity of the SWCNTs SA are measured to be 29%, 12% and 0.12 MW/cm2, respectively. By using the SWCNTs as SA, a passively mode-locked Yb-doped fiber laser has been achieved at 979 nm with pulse duration of 228 ps and repetition rate of 15.47 MHz. To our knowledge, this is the first time ever reported in an all-fiber Yb-doped mode-locked fiber laser using SWCNTs as SA at 980 nm, which overcome the difficulties of low gain and serious re-absorption effects in the quasi-three-level system. In order to verify the saturation absorption performance of the SWCNTs, mode-locking experiment in quasi-four-level system is also carried out around 1030 nm and the stable and uniform mode-locked pulses are obtained. A mode-locked fiber laser at 1032 nm is realized with a pulse width of 485 ps and repetition rate of 8.78 MHz. It is sufficiently manifested that SWCNTs with diameters of 0.8 nm have excellent saturable absorption performance as optical mode-locking elements in ultrafast photonic applications.

Mid-Infrared Q-Switched and Mode-Locked Fiber Lasers at 2.87 <italic>μ</italic>m Based on Carbon Nanotube

We report Q-switching and mode-locking operations in a Ho3+/Pr3+ co-doped ZBLAN fiber laser at 3- μ m mid-infrared waveband using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The SWCNTs were produced by catalytic chemical vapor deposition method and then deposited on the surface of a flat gold-coated mirror to form the SWCNT-SA. The modulation depth and saturation intensity of the SWCNT-SA are 16.5% and 1.66 MW/cm2, respectively. Stable Q-switched laser pulses operating at 2865.6 nm were obtained at a launched pump power of 530.6 mW. The resulting pulses have a measured repetition rate and pulse width of 178.6 kHz and 1.21 μs, respectively. The maximum pulse energy is calculated to be 0.36 μJ. By slightly adjusting the position of the SWCNT-SA, stable continuous-wave mode-locked pulses at 2865.2 nm were also achieved. Our work demonstrates that SWCNTs are promising SAs for 3- μ m midinfrared pulsed lasers.

Dry-transfer technique for polymer-free single-walled carbon nanotube saturable absorber on a side polished fiber

We fabricate single-walled carbon nanotube saturable absorbers on a side-polished fiber by a dry transfer technique. We demonstrate that this method allows for the easy and robust implementation of polymer-free carbon nanotube film for an evanescent field interaction in the fiber laser cavity. The high-quality single-walled carbon nanotubes are synthesized by the aerosol CVD method with absorption maximum tuned to an erbium doped fiber laser emission line. The Q-switch and mode-lock regimes as well as the harmonic mode-lock regime with the 79th order are successfully demonstrated with this approach. Critical power for damage threshold is estimated.

Wideband tunable passively Q-switched fiber laser at 28 μm using a broadband carbon nanotube saturable absorber

We propose and demonstrate a widely tunable passively Q-switched Ho3+/Pr3+-codoped ZrF4-BaF2-LaF3-AlF3-NaF fiber laser operating in the 2.8 μm mid-infrared (MIR) waveband based on a single-walled carbon nanotube (SWCNT) saturable absorber (SA). The SWCNTs have diameters ranging from 1.4 to 1.7 nm. The modulation depth and saturation intensity of the SWCNT SA measured at 2850 nm are 16.5% and 1.66 MW/cm2, respectively. Stable Q-switched pulses with the shortest pulse duration of 1.46 μs and the maximum pulse energy of 0.43 μJ are achieved at a launched pump power of 445.6 mW. The combined use of a broadband SWCNT SA and a plane ruled grating ensures a broad continuously tuning range of 55.0 nm from 2837.6 to 2892.6 nm. The output powers, emission spectra, repetition rates, and pulse durations at different tuning wavelengths are also characterized and analyzed. Our results indicate that SWCNTs can be excellent broadband SAs in the 3 μm MIR region. To the author’s knowledge, this is the first demonstration of a widely tunable carbon-nanotube-enabled passively Q-switched fiber laser operating in the 2.8 μm MIR waveband.

Sub-80 fs mode-locked Tm,Ho-codoped disordered garnet crystal oscillator operating at 2081 nm.

We demonstrate a mode-locked (ML) femtosecond laser based on the disordered garnet crystal Tm,Ho:CNGG. Employing a single-walled carbon nanotube saturable absorber, pulses as short as 83 and 76fs at 2081nm are achieved without and with external compression, respectively. The latter represents, to the best of our knowledge, the shortest pulse duration obtained from any Ho-doped or Tm,Ho-codoped laser. The average power amounts to 67mW at a repetition rate of 102MHz. By analyzing the soliton ML regime, the nonlinear refractive index of Tm,Ho:CNGG is estimated to be ∼1.1×10-19 m2/W.