Carbon Nanotube-based Saturable Absorber Research Articles

Coherent optical gyroscope on the basis of the bidirectional ultra-short pulse Erbium ring fiber laser

A gyroscopic effect has been studied in the bidirectional ultra-short pulse erbium-doped fiber ring laser hybridly mode-locked with a co-action of a Single-Walled Carbon Nanotube-based saturable absorber (SWCNT-SA) and Nonlinear Polarization Evolution introduced by means of the short-segment polarizing fiber. Owing to the Kerr nonlinearity contribution through self-phase modulation and self-steepening effects to the carrier-to-envelope phase slip of both clockwise (CW) and counterclockwise (CCW) solitons, wideband controllable tuning of a gyroscope bias point has been demonstrated by means of an appropriate adjustment of either intracavity polarization or pump power. Angular velocity detected ranges from 0.12 deg/s to 360 deg/s while the highest rotation sensitivity reaches 7 kHz/(deg/s) for 0.79 m2 single-coil ring gyroscope being in agreement with the calculated scale factor value. The gyroscope dead band with upper limit of ≈5.15 deg/s corresponding to the beat-note frequency of ≈15 kHz has been detected during clockwise rotation of the gyroscope. The highest gyroscope resolution of ≈0.01 deg/s=38 deg/h has been estimated on the basis of the bias point drift measurement.

Broadband Metallic Carbon Nanotube Saturable Absorber for Ultrashort Pulse Generation in the 1500–2100 nm Spectral Range

Herein, we report on the possibility of ultrashort laser pulse generation in the broadband spectral range using a saturable absorber based on free-standing metallic carbon nanotube thin film. Erbium, thulium, and holmium-doped all-fiber lasers were mode-locked with a single saturable absorber containing a 300 nm thick material layer. Subpicosecond pulses were generated at 1559, 1938, and 2082 nm. Our work validates the broadband operation of metallic carbon nanotube-based saturable absorbers and highlights the suitable performance of nanomatematerial for ultrafast photonic applications.

Optical characteristics and application of carbon-nanotube-based saturable absorber with a spiral scheme

A carbon-nanotube-based saturable absorber (CNT-SA) with a spiral scheme is proposed, which is obtained by twining CNT-polymer filaments around a microfiber. The proposed CNT-SA possesses many advantages, such as high thermal damage threshold, excellent oxidation resistance, and long-distance evanescent field interaction. Nonlinear absorption of this CNT-SA is measured, giving saturable absorption and saturable intensity of ∼5.02% and ∼172.2 MW cm−2, respectively. Based on the CNT-SA, an Er-doped fiber laser is achieved. The experimental results open up venues to create a new type of SA for ultrafast lasers.

Metallic carbon nanotube-based saturable absorbers for holmium-doped fiber lasers.

In 2003, carbon nanotubes opened a new field of research on nanomaterial-based mode-locked fiber lasers. They maintain popularity in the ultrafast laser community due to their broadband operation, relatively high damage threshold, and tunable optical properties. Here we show that metallic carbon nanotube-based thin film fabricated by vacuum filtration technique can be used as a saturable absorber in holmium-doped fiber laser operating in anomalous and normal dispersion regimes. Scaling the absorbers modulation depth by adjusting the film thickness was observed. The Fourier transform limited 6.65 nm wide optical solitons in anomalous dispersion regime were generated. Utilizing stretched-pulse regime greatly improves the laser performance - 212 fs pulses reach the energy of 3.79 nJ.

Effects of spectral filtering on pulse dynamics in a mode-locked fiber laser with a bandwidth tunable filter

We investigate numerically the impact of spectral filtering on pulse characteristics in anomalous dispersion erbium-doped fiber laser mode-locked with carbon nanotube-based saturable absorber. The laser can operate only in a single-pulse state without a filter, while it will transit to bound soliton states once the saturation energy of the gain fiber and the bandwidth of the filter are carefully chosen, respectively. Further analyzation shows that the operation of a single-pulse lasing from dissipative soliton to conventional soliton can be selectively targeted by changing the bandwidth of the filter through the loss and frequency narrowing effects. Laser performances, such as spectrum structure, pulse duration, pulse energy and peak power in both the frequency and the time domains, will all be affected. This paper provides a guidance for the mode-locked fiber laser and proposes a feasible way to control the pulse dynamics.

High-order mode lasing in all-FMF laser cavities

We experimentally demonstrate two kinds of all few-mode fiber (FMF) ring lasers with high-order mode (HOM) oscillation in the laser cavity. One kind is a switchable-wavelength all-FMF HOM laser with an output of tunable optical vortex beams (OVBs); the other is a Q-switched all-FMF HOM laser with an output of pulsed cylindrical vector beams (CVBs). The lasers are composed of all-FMF components and few-mode erbium-doped fiber. A Sagnac interferometer made of a 3 dB FMF coupler functions as the wavelength selector, and switchable multiwavelength tunable OVBs are experimentally realized. Carbon nanotube-based saturable absorbers and the nonlinear polarization rotation technique are used to achieve Q-switched CVB lasers. This is the first report, to our knowledge, on the generation of switchable-wavelength and Q-switched HOM beams in all-FMF laser cavities.

Wavelength and pulse duration tunable ultrafast fiber laser mode-locked with carbon nanotubes

Ultrafast lasers with tunable parameters in wavelength and time domains are the choice of light source for various applications such as spectroscopy and communication. Here, we report a wavelength and pulse-duration tunable mode-locked Erbium doped fiber laser with single wall carbon nanotube-based saturable absorber. An intra-cavity tunable filter is employed to continuously tune the output wavelength for 34 nm (from 1525 nm to 1559 nm) and pulse duration from 545 fs to 6.1 ps, respectively. Our results provide a novel light source for various applications requiring variable wavelength or pulse duration.

Generation regimes of bidirectional hybridly mode-locked ultrashort pulse erbium-doped all-fiber ring laser with a distributed polarizer.

We report on the stable picosecond and femtosecond pulse generation from the bidirectional erbium-doped all-fiber ring laser hybridly mode-locked with a coaction of a single-walled carbon nanotube-based saturable absorber and nonlinear polarization evolution that was introduced through the insertion of the short-segment polarizing fiber. Depending on the total intracavity dispersion value, the laser emits conservative solitons, transform-limited Gaussian pulses, or highly chirped stretched pulses with almost 20 nm wide parabolic spectrum in both clockwise (CW) and counterclockwise (CCW) directions of the ring. Owing to the polarizing action in the cavity, we have demonstrated for the first time, to the best of our knowledge, an efficient tuning of soliton pulse characteristics for both CW and CCW channels via an appropriate polarization control. We believe that the bidirectional laser presented may be highly promising for gyroscopic and other dual-channel applications.

Switchable dual-wavelength CNT-based Q-switched using arrayed waveguide gratings (AWG)

In this paper, a dual-wavelength synchronously pulsed fiber laser Q-switched by carbon nanotube-based saturable absorber with switchable wavelength spacing enabled using arrayed waveguide grating (AWG) is proposed and demonstrated. By just switching the channels of the AWG, discrete tuning in wavelength spacing of the dual-wavelength Q-switched laser operation can be attained over several nanometers, ranging from 1.6 to 4.0 nm in a stable dual-wavelength regime without employing any modulation technique or intracavity spectral filters. Our experimental results show that the fiber laser can generate Q-switched microsecond pulses with a wide repetition rate range, starting from 12.0 kHz to a maximum value of 54.9 kHz. This proposed system is also reasonably simple to realize at low cost.

Self-Starting Harmonic Mode-Locked Thulium-Doped Fiber Laser with Carbon Nanotubes Saturable Absorber

We report a ring cavity passively harmonic mode-locked thulium-doped fiber laser (TDFL) using a newly developed single-wall carbon nanotube-based saturable absorber. The TDFL generates the 25th harmonic mode-locked stretched pulse train with a high repetition rate of 213 MHz and a pulse duration of 710 fs. The laser operates at 1901.6 nm with an average power of 1.89 mW, which corresponds to the pulse energy of 0.008 nJ, at 1552 nm pump power of 719 mW. The peak-to-background ratio is measured to be 60 dB, which indicates the stability of the laser.

Enhancement of thermal damage threshold of carbon-nanotube-based saturable absorber by evanescent-field interaction on fiber end

We present a scheme of fiber-connector-type carbon-nanotube-based saturable absorber (CNT-SA) with enhanced thermal damage threshold, in which the CNTs are deposited on the fiber connector end in a ring pattern for evanescent-field interaction instead of direct interaction. The thermal damage threshold of such CNT-SA is found to be increased by around 130% compared with an evenly deposited one. An all-fiber Fabry-Perot (FP) linear cavity passively mode-locked laser is further constructed incorporating the prepared CNT-SA, where the optical power is confined in a relatively short laser cavity to investigate the thermal damage threshold and the performance of the CNT-SA. Stable output pulses with a fundamental repetition rate of 211.84 MHz and a pulse width of 680 fs are generated from the fiber laser. The mode-locking operation can be maintained an intra-cavity average power of 30 mW, indicating that the CNT-SA can withstand a relatively high optical power without performance degradation.

Self-starting harmonic mode-locked Tm-Bi co-doped germanate f iber laser with carbon nanotube-based saturable absorber

We report a ring cavity passively harmonic mode-locked fiber laser using a newly developed thuliumbismuth co-doped fiber (TBF) as a gain medium in conjunction with a carbon nanotube (CNT)-based saturable absorber. The TBF laser generates a third harmonic mode-locked soliton pulse train with a high repetition rate of 50 MHz and a pulse duration of 1.86 ps. The laser operates at 1 901.6 nm with an average power of 6.6 mW, corresponding to a pulse energy of 0.132 nJ, at a 1 552 nm pump power of 723.3 mW.

Short linear-cavity Q-switched fiber laser with a compact short carbon nanotube based saturable absorber

A novel all fiber short linear-cavity Q-switched Erbium doped fiber (EDF) laser with a compact short carbon nanotube based saturable absorber (CNT-SA) is presented. The fiber laser cavity is only 10.5 cm. It is constructed by connecting a 6.5-cm high concentration EDF and the CNT-SA in a linear-cavity formed by two fiber Bragg gratings. With the short cavity, no self-mode-locking effect on the Q-switch operation occurs. Moreover, higher pulse-repetition-rate and shorter pulse duration are not only achieved but also the stability of the laser cavity is improved.

Wide Pulse-Repetition-Rate Range Tunable Nanotube $Q$-Switched Low Threshold Erbium-Doped Fiber Laser

A novel all-fiber wide pulse-repetition-rate range tunable nanotube Q-switched low threshold erbium-doped fiber (EDF) laser is demonstrated. By connecting a compact and low insertion loss carbon nanotube-based saturable absorber and a section of high concentration EDF in a simple linear laser cavity, Q-switched laser, with a threshold of 29.85 mW, a pulse-repetition-rate tunable range of 14.5-141.4 kHz, and a minimum pulse duration of 330 ns, are achieved. With this laser structure, the self-mode-locking effect on the Q-switch operation can be effectively suppressed.

Observation of timing jitter reduction induced by spectral filtering in a fiber laser mode locked with a carbon nanotube-based saturable absorber

A self-starting passively mode-locked fiber laser with a carbon nanotube-based saturable absorber and a fiber-based bandpass filter (BPF) is proposed. Incorporation of a BPF into the cavity leads to a great reduction of its timing jitter from 84.8 to 29.1 fs (10 Hz-3 MHz). This happens because the filtering effect can weaken the fluctuation of the central wavelength induced by the quantum noise, being one of the important contributions to timing jitter in the optical amplifying process.

Carbon nanotube films for ultrafast broadband technology

Mode-locked sub-picosecond operation of Yb-, Er- and Tm:Hodoped fiber lasers operating at 1.05 microm, 1.56 microm and 1.99 microm, respectively, is demonstrated using the same sample carbon nanotube-based saturable absorber mirror. A mesh of single-walled carbon nanotubes was deposited on an Ag-mirror using a one-step dry-transfer contact press method to combine broadband saturable absorption and high reflectance properties. The novel fabrication method of the polymer-free absorber and device parameters determined using nonlinear reflectivity measurement are described in detail. To our knowledge the observed operation bandwidth of approximately 1 microm is the broadest reported to date for a single carbon nanotube-based saturable absorber.