Repetition Rate Of Pulse Train Research Articles

Dual-wavelength passively Q-switched Erbium-doped fiber laser with MWCNTs slurry as saturable absorber

In this work, a compact, stable dual-wavelength Q-switched laser with a multi-walled carbon nanotubes (MWCNTs) slurry as saturable absorber (SA) which is independent of any host polymer has been demonstrated. The MWCNTs slurry is fabricated and the peak shift is investigated using Raman spectroscopy.The passively Q-switched erbium-doped fiber laser (EDFL) oscillated simultaneously at 1532.32 nm and 1556.97 nm with 24.67 nm peak separation, at threshold and maximum input power of 26mW and 74mW respectively.By increasing the input pump power from 36 mW to 74 mW, the pulse train repetition rate increases from 25 kHz to 78 kHz, while the pulse width is reduced from 17.84 us to 5.24 ?s. The generated pulse produced maximum pulse energy and maximum peak power of 11.97 nJ and 2.05 mW, respectively at maximum input pump power. The recorded signal to noise ratio is about 62 dB and shows that the proposed MWCNTs slurry based SAis able to generate dual wavelength Q-switched pulse laser with high stability pulse. Full Text: PDF ReferencesL.Liu, Z. Zheng, X. Zhao,S. Sun, Y. Bian, Y. Su, J. Liu, and J. Zhu, "Dual-wavelength passively Q-switched Erbium doped fiber laser based on an SWNT saturable absorber", Optics Communications 294, 267 (2013). CrossRef Z. Luo, M. Zhou, J. Weng, G. Huang, H. Xu, C. Ye, and Z. Cai, "Graphene-based passively Q-switched dual-wavelength erbium-doped fiber laser", Optics Letters 35, 3709 (2010). CrossRef F. Lou, R. Zhao, J. He, Z. Jia, X. Su, Z. Wang, J. Hou, and B. Zhang, "Nanosecond-pulsed, dual-wavelength, passively Q-switched ytterbium-doped bulk laser based on few-layer MoS2 saturable absorber", Photon. Res. 3, A25 (2015). CrossRef F. A. A. Rashid et al., "Using a black phosphorus saturable absorber to generate dual wavelengths in a Q-switched ytterbium-doped fiber laser", Laser Phys. Lett. 13, 1 (2016). CrossRef J. Sotor, G. Sobon, I. Pasternak, K. Krzempek, G. Dudzik, A. Krajewska, W. Strupinski, and K. M. Abramski, "Dual-wavelength fiber mode-locked laser based on graphene saturable absorber", Proc. of SPIE 8961, 89612A (2014). CrossRef S. Alwarappan, and A. Kumar, Graphene-Based Nanomaterials (Boca Rota, CRC Press 2014).N. Taib, N. Bidin, H. Haris, N. N. Adnan, M. Ahmad, and S. W. Harun, "Multi-walled carbon nanotubes saturable absorber in Q-switching flashlamp pumped Nd:YAG laser", Optics & Laser Technology 79, 193 (2016). CrossRef M. Ahmad, A. Latiff, Z. Zakaria, and S. Harun, "Q-Switched Ultrafast TDFL Using MWCNTs-SA at 2 ?m Region", International Journal of Computer and Communication Engneering 3, 446 (2014). CrossRef H. Ahmad, K. Z. Hamdan, F. D. Muhammad, S. W. Harun, and M. Z. Zulkifli, "Switchable dual-wavelength CNT-based Q-switched using arrayed waveguide gratings (AWG)", Applied Physics B 118, 269 (2015). CrossRef J. M. Dudley and J. R. Taylor, Supercontinuum Generation in Optical Fibres (New York, Cambridge University Press 2010). CrossRef H. Ahmad, M. A. M. Salim, M. R. K. Soltanian, S. R. Azzuhri, and S. W. Harun, "Passively dual-wavelength Q-switched ytterbium doped fiber laser using Selenium Bismuth as saturable absorber", Journal of Modern Optics 62, 1550 (2015). CrossRef H. Chu et al., "Dual-Wavelength Passively Q-Switched Nd,Mg:LiTaO3 Laser With a Monolayer Graphene as Saturable Absorber", IEEE Journal of Selected Topics in Quantum Electronics 21, 1600705 (2015). CrossRef Z. T. Wang, Y. Chen, C. J. Zhao, H. Zhang, and S. C. Wen, "Switchable Dual-Wavelength Synchronously Q-Switched Erbium-Doped Fiber Laser Based on Graphene Saturable Absorber", IEEE Photonics Journal 4, 869 (2012). CrossRef J. H. Liu et al., "Passively Q-switched dual-wavelength Yb:LSO laser based on tungsten disulphide saturable absorber", Chin. Phys. B 25, 034207 (2016). CrossRef Z. C. Tiu et al, "Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes", Journal of Modern Optics 61, 1133 (2014). CrossRef

All-fiber high-average power nanosecond-pulsed master-oscillator power amplifier at 2 μm with mJ-level pulse energy.

We present a high-power nanosecond-pulsed Tm-doped fiber amplifier at 1.971 μm based on a master-oscillator power amplifier (MOPA) configuration. When the repetition rate is 500 kHz and the pulse width is 63.3 ns, the average power reaches 238 W, the peak power reaches 7.06 kW, and the pulse energy is 0.477 mJ. When the pulse train's repetition rate is 300 kHz with a pulse width of 63.7 ns, the average power reaches 197 W, the peak power reaches 9.73 kW, and the pulse energy is 0.66 mJ. When the pulse train's repetition rate is 200 kHz with a pulse width of 58.2 ns, the average power reaches 150 W, the peak power reaches 12.1 kW, and the pulse energy is 0.749 mJ. The spectral linewidths of the pulse trains are 0.15, 0.14, and 0.10 nm for 500 kHz repetition rate, 300 kHz repetition rate, and 200 kHz repetition rate, respectively. To the best of our knowledge, this is the first demonstration of high-power nanosecond-pulsed MOPA at 2 μm with the maximum average power reaching 238 W, the maximum peak power reaching 12.1 kW, and the maximum pulse energy reaching 0.749 mJ.

Structure of picosecond pulses of a -switched and mode-locked diode-pumped Nd : YAG laser

The pulse duration of a diode-pumped Nd : YAG laser, in which -switching with mode-locking (QML regime) is achieved using a spherical mirror and a travelling-wave acousto-optic modulator, is directly measured with a streak camera. It is found that the picosecond pulses can have a non-single-pulse structure, which is explained by excitation of several competing transverse modes in the -switching regime with a pulse repetition rate of . In the case of cw mode-locking (without -switching), a new (auto-QML) regime is observed, in which the pulse train repetition rate is determined by the frequency of the relaxation oscillations of the laser field while the train contains single picosecond pulses.

Multiwavelength pulse generation using a SESAM-based mode-locked fiber laser together with Fabry–Perot filter

A simple and compact configuration of multiwavelength pulse generator is proposed and experimentally demonstrated, using a SESAM-based passively mode-locked fiber laser together with fiber Fabry–Perot filter. By optimizing the dispersion of fiber ring cavity, a flat rectangular optical spectrum with 3 dB bandwidth of 8.1 nm is obtained, with power fluctuation of <0.5 dB. Inserting a fiber Fabry–Perot filter at the output of passively mode-locked fiber laser, we can simultaneously obtain 40 channels with 0.2 nm wavelength spacing, under the condition of <3 dB power uniformity. After wavelength-division demultiplexing and optic-to-electronic conversion, the full width at half maximum (FWHM) of single channel pulse is measured to be 30 ps while the repetition rate of pulse train is 20.3 MHz.

Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization.

We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing.

Graphene-deposited microfiber photonic device for ultrahigh-repetition rate pulse generation in a fiber laser.

We report on the generation of a high-repetition-rate pulse in a fiber laser using a graphene-deposited microfiber photonic device (GMPD) and a Fabry-Perot filter. Taking advantage of the unique nonlinear optical properties of the GMPD, dissipative four-wave mixing effect (DFWM) could be induced at low pump power. Based on DFWM mode-locking mechanism, the fiber laser delivers a 100 GHz repetition rate pulse train. The results indicate that the small sized GMPD offers an alternative candidate of highly nonlinear optical component to achieve high-repetition rate pulses, and also opens up possibilities for the investigation of other abundant nonlinear effects or related fields of photonics.

Theoretical study of the periodic quantum phase modulation of the dipole response in atomic He

Based on the laser-induced-phase model, periodic quantum phase modulation of the dipole response in atomic He is studied theoretically. The two-level system of the transition 1s2→1s2p with a delay width of 1.8 × 109 s-1 and an energy difference of 21.2 eV between the excited state and the ground state is used in the calculation. The system is excited by attosecond laser pulse from high harmonic generator, and the spectral response of the system is of single isolated symmetric Lorentzian absorption line. After the excitation, near infrared (NIR) femtosecond laser pulse train with a repetition rate of 5 GHz, central frequency 780 nm, and pulse duration of 100 fs, is utilized to periodically modify the spontaneous decay of the excited 1s2p level. The incremental phase step Δφ depends on the intensity of the NIR laser pulse, while the initial offset phase φ can be controlled independently by partially overlapping the first NIR pulse with the excitation. Simulated results show that the Lorentzian absorption line is transformed into comb-like spectral structure with equal gap depending on the repetition rate of the NIR pulse train. The line shape of each comb tooth is symmetric Lorentzian line by setting φ = Δφ/2 = π/2, while it is Fano line by setting φ = Δφ = π. The location of the comb structure is mainly dependent on the energy difference between the excited state and the ground state, while it can be slightly tuned by controlling the incremental phase step Δφ. We develop an analytic description of the comb-like spectral structure by Fourier analysis, depending on both the atomic and the phase-control properties. The analytical expressions can be readily used to estimate the exact experimental parameters. The universality of this mechanism allows the spectral modulation in arbitrary atomic system at arbitrary frequency, including the hard X-ray regime, by using reference transitions in highly charged ions. The generalization of this approach should thus not only enable relative frequency measurement and relevant applications at extremely high frequencies, but also open the way for pulse shaping at arbitrary frequencies.

Laser Driver for a Photoinjector of an Electron Linear Accelerator (February 2014)

The presented laser driver for a photoinjector of an electron linear accelerator delivers 10-ps long laser pulses with the energy of \(1.85~\mu \) J at the wavelength of 262 nm. Laser pulses irradiating with the repetition rate of 10 MHz form the rectangular 800- \(\mu \) s long pulse trains with 18.5-W mean power inside them. The pulse train repetition rate is 10 Hz. Short-lived absorption centers accumulating in BBO fourth-harmonic generator crystal cause significant distortion of the pulse train envelope. The envelope remains rectangular due to precompensating of these distortions in the fiber acousto-optical modulator with fast varying transmission.

Soliton generation from a fundamentally mode-locked fiber laser with a feed-forward path

We demonstrate for the first time to our knowledge, the soliton generation from a mode-locked erbium-doped fiber laser using a novel saturable absorber (SA), which is realized by combining a dual-drive modulator and an intensity feed-forward path. The laser is fundamentally mode-locked under high-frequency RF signal modulation. Experimentally, the actively mode-locked laser produces a 16.7 MHz repetition rate pulse train with a 1.4 ps pulse width, and the spectrum bandwidth is 2.17 nm. The results demonstrate that the SA supports soliton pulse shaping in the cavity at the fundamental frequency.

Q-switched Yb-doped fiber laser operating at 1073 nm using a carbon nanotubes saturable absorber

A stable passive Q-switched Ytterbium-doped fiber laser (YDFL) operating at 1073-nm region is demonstrated using single-walled carbon-nanotubes (SWCNTs) as a saturable absorber (SA). The SA is prepared using polyvinyl alcohol (PVA) as a host polymer and integrated in the YDFL ring cavity by sandwiching the SWCNT/PVA thin film between two fiber connectors. A stable pulse train is achieved with 17.1-kHz repetition rate, 6.45-μs pulse width, and 3.1-nJ pulse energy at the threshold 980-nm pump power of 95.4 mW. As the pump power increases to 117.5 mW, the pulse train repetition rate also rises to 23.6 kHz. The shortest pulse width of 3.11 μs and pulse energy of 4.4 nJ are achieved at the maximum pump power of 117.5 mW

Q-switched erbium-doped fibre laser using graphene-based saturable absorber obtained by mechanical exfoliation

A stable passively Q-switched erbium-doped fibre laser (EDFL) operating at 1536.5 nm is developed, using a 1 m long erbium-doped fibre as a gain medium and a simple graphene-based saturable absorber (SA). Using mechanical exfoliation, a single layer of graphene is obtained and deposited on the end facet of an optical fibre ferrule, which is then connected to another ferrule to form the SA. The SA is integrated into an EDFL cavity to achieve a stable pulse train at the threshold pump power of 42.3 mW. When the pump power increases from 42.3 to 63.5 mW, the pulse train repetition rate increases from 10.3 to 32.4 kHz, while the pulse width varies from 10.7 to 31.0 μs. The highest energy, 166.2 nJ, is achieved at the pump power of 42.3 mW.

Simulation analysis of an improved optical triangular-shaped pulse train generator based on quadrupling RF modulation incorporating fiber dispersion-induced power fading

We report an improved approach to generate optical triangular-shaped pulse train using quadrupling RF modulation and fiber dispersion-induced power fading. In the proposal, quadrupling RF modulation (via a dual-parallel Mach–Zehnder modulator) is employed to generate four primary optical sidebands (±2nd and ±6th) in spectrum. Then a piece of single mode fiber is connected as the dispersive media. Because of the power degradation induced by fiber dispersion, the undesired 8th order harmonic in optical intensity can be removed. It is found that when the modulation index is adjusted to a proper value (m=4.438), optical intensity with its expression corresponding to the Fourier expansion of idea triangular-shaped waveform can be found. Since the quadrupling RF modulation technique is employed, repetition rate of the target pulse train is four times of the driving frequency, which makes pulse train generation with higher repetition rate or smaller pulse duration possible.

High-repetition-rate pulse generation and compression in dispersion decreasing fibers

Optical pulse generation and compression have been numerically studied in anomalous dispersion decreasing fibers. We show that evolution of modulation instability (MI) observed with chirped wave packets in tapered fibers produces the mechanism for generation of ultrashort pulses with high repetition rates. The role of MI and Raman self-scattering has been also discussed. The simulations show that pulse chirping enhances self-Raman scattering at early stages of pulse propagation and improves compression of the generated pulses. It is also shown that the presence of amplitude and frequency modulation of the seed wave provide essential impact on the pulse train formation. The new method for increasing the pulse train repetition rate through frequency modulation of the seed wave has been proposed.

Femtosecond laser induced structural changes in fluorozirconate glass

Fluorozirconate glasses, such as ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), have a high infrared transparency and large rare-earth solubility, which makes them an attractive platform for highly efficient and compact mid-IR waveguide lasers. We investigate the structural changes within the glass network induced by high repetition rate femtosecond laser pulses and reveal the origin of the observed decrease in refractive index by using Raman microscopy. The high repetition rate pulse train causes local melting followed by rapid quenching of the glass network. This results in breaking of bridging bonds between neighboring zirconium fluoride polyhedra and as the glass resolidifies, a larger fraction of single bridging fluorine bonds relative to double bridging links are formed in comparison to the pristine glass. The distance between adjacent zirconium cations is larger for single bridging than double bridging links and consequently an expansion of the glass network occurs. The rarified glass network can be related to the experimentally observed decrease in refractive index via the Lorentz-Lorenz equation.

Optimization of Pulsed-DEER Measurements for Gd-Based Labels: Choice of Operational Frequencies, Pulse Durations and Positions, and Temperature

In this work, the experimental conditions and parameters necessary to optimize the long-distance (≥ 60 Å) Double Electron-Electron Resonance (DEER) measurements of biomacromolecules labeled with Gd(III) tags are analyzed. The specific parameters discussed are the temperature, microwave band, the separation between the pumping and observation frequencies, pulse train repetition rate, pulse durations and pulse positioning in the electron paramagnetic resonance spectrum. It was found that: (i) in optimized DEER measurements, the observation pulses have to be applied at the maximum of the EPR spectrum; (ii) the optimal temperature range for Ka-band measurements is 14-17 K, while in W-band the optimal temperatures are between 6-9 K; (iii) W-band is preferable to Ka-band for DEER measurements. Recent achievements and the conditions necessary for short-distance measurements (<15 Å) are also briefly discussed.

Asynchronous single-shot characterization of high-repetition-rate ultrafast waveforms using a time-lens-based temporal magnifier

We demonstrate asynchronous, single-shot characterization of an ultrafast, high-repetition-rate pulse source using a time-lens-based temporal magnifier. We measure a 225 GHz repetition-rate pulse train from a microresonator-based frequency comb. In addition, we show that such a system can be used as a frequency compressor for real-time, high-speed RF spectral characterization.

Periodic Time-Domain Modulation for the Electrically Tunable Control of Optical Pulse Train Envelope and Repetition Rate Multiplication

An electrically tunable system for the control of optical pulse sequences is proposed and demonstrated. It is based on the use of an electrooptic modulator for periodic phase modulation followed by a dispersive device to obtain the temporal Talbot effect. The proposed configuration allows for repetition rate multiplication with different multiplication factors and with the simultaneous control of the pulse train envelope by simply changing the electrical signal driving the modulator. Simulated and experimental results for an input optical pulse train of 10 GHz are shown for different multiplication factors and envelope shapes.

Passively Q-switched mode-locking Erbium-doped fiber laser with net-normal dispersion using nonlinear polarization rotation technique

We experimentally demonstrate a passively Q-switched mode-locking (QML) operation in an Erbium-doped fiber ring laser with net normal dispersion by using nonlinear polarization rotation technique. A 2 m long section of dispersion compensating fiber (DCF) with extra large positive dispersion was inserted into the cavity to ensure the fiber laser working in the region of net positive dispersion. By carefully adjusting the polarization controller, both uniform dissipative mode-locking pulses with fundamental repetition rate and QML pulse trains with tunable repetition rate from 71.58 to 98.83 kHz are achieved. It is found that the QML operation is caused by the interaction between the polarization state of the pulse and the intracavity polarizer.

Optical arbitrary waveform generation

Optical arbitrary waveform generation will allow waveforms to be synthesized at optical frequencies but with the flexibility currently available at radiofrequencies. This technique is enabled by combining frequency comb technology, which produces trains of optical pulses with a well-defined frequency spectrum, with pulse shaping methods, which are used to transform a train of ultrashort pulses into an arbitrary waveform. To produce a waveform that fills time, the resolution of the shaper must match the repetition rate of the original pulse train, which in turn must have a comb spectrum that is locked to the shaper. Here, we review the current efforts towards achieving optical arbitrary waveform generation and discuss the possible applications of this technology.

Timing Jitter Reduction of a Mode-Locked VECSEL Using an Optically Triggered SESAM

A technique for actively stabilizing the repetition rate of a mode-locked vertical external-cavity surface-emitting laser is presented using an optically triggered semiconductor saturable absorber mirror. This method enables a significant reduction of the timing jitter measured in the frequency range [100 Hz, 10 MHz] and makes this kind of externally locked laser suitable for high-speed sampling of microwave signals. The experimental demonstration shows jitter reduction by a factor of 16 from 8 ps down to 423 fs for a 1.68-GHz repetition rate pulse train. The hold-in locking bandwidth and stabilization efficiency are shown to be a function of the average power and modulation index of the optical control signal.