Gain-switched Laser Research Articles

Nd3+-doped transparent tellurite ceramics bulk lasers

We report on the laser emission of the polycrystalline ceramic obtained from the full and congruent crystallization of the parent glass 1Nd3+:75TeO2-12.5Bi2O3-12.5Nb2O5 composition. In particular, the current work underlines the importance of carefully controlling the heat treatment in order to solely crystallize the Bi0.8Nb0.8Te2.4O8 cubic phase and consequently avoid the formation of the BiNbTe2O8 orthorhombic phase that would be detrimental for optical purpose. The structure, microstructure and photoluminescence properties of the resulting transparent tellurite ceramics are characterized. The continuous-wave and gain-switching laser performances reveal that the emission remains perfectly single transversal mode in the range of pump powers explored. The maximum output power achieved was ~28.5 mW, for a pump power threshold of ~67 mW, and with associated efficiency and slope efficiency of ~22.5% and ~50%, respectively. These data definitely stand among the best results obtained so far for bulk laser tellurite materials and thus demonstrate the potential of such polycrystalline transparent ceramics as optically active materials. Finally, the laser emission characteristics in pulsed regime, at low and high repetition rates, are also provided: more than 6.5 W of peak power at a repetition rate of 728 kHz can be obtained.

Gain-Switched 2-μm Fiber Laser System Providing Kilowatt Peak-Power Mode-Locked Resembling Pulses and Its Application to Supercontinuum Generation in Fluoride Fibers

A fast gain-switched Tm-doped fiber laser and amplifier system providing stable 17-ns pulses with a 0.64-mJ energy and 35.6-kW peak power at 25 kHz is demonstrated. Then, self-starting mode-locked resembling pulses with duration of <;200 ps, recorded within the gain-switched pulse envelope, were achieved in the same laser cavity. By amplifying the pulse train in a Tm-doped fiber amplifier, an average output power of 6.8 W at a ~15-ns full width at half maximum gain-switch envelope and a ~36.9-μJ subpulse with a peak power of up to 115.6 kW were demonstrated. To the best of our knowledge, this is the shortest gain-switched and mode-locked-like pulse as well as the highest peak-power that has been demonstrated in this type of laser system. A mid-infrared supercontinuum generation with a total output power of 2.45 W and a cutoff wavelength at 4.4 μm is also reported.

Stable pulse generation in a bias-pumped gain-switched fiber laser

We demonstrate gain-switched fiber laser with bias pumping plays an important role in regulating chaotic relaxation spikes. Under certain conditions the profile of output pulse from gain-switched fiber laser can keep the same shape as that of pump pulse. Bias pumping technique may have significance in increasing output stable pulse energy in gain-switched fiber laser. Gain-switched fiber laser with bias pumping may be interesting for some applications in micro-processing and thin film removal.

State-switchable and wavelength-tunable gain-switched mid-infrared fiber laser in the wavelength region around 2.94 μm.

We demonstrate a gain-switched singly Ho3+-doped ZBLAN fiber laser for the first time in the wavelength region around 2.94 μm which circumvents the strong water vapor lines. Four switchable gain-switched temporal states with 1/n (n = 4,3,2,1) pump repetition rates are first observed. The influences of pump power (pulse energy), repetition rate, duty cycle (pulse duration), and laser wavelength on their characteristics are studied, respectively. The results indicate that high pump repetition rate, large pump duty cycle, and short laser wavelength are beneficial for obtaining more gain-switched temporal states. For the case (n = 1), the increased pump repetition rate contributes to the increased pulse duration while decreased pulse energy and peak power. While μs-level pump pulse duration variation has an almost negligible effect on them. By introducing a plane ruled grating, the wavelength tuning was performed yielding a tuning range of 105 nm from 2895.5 nm to 3000.5 nm which just overlays the peak region of liquid water absorption. Finally, further optimizing of laser performances is discussed as well. This demonstration is helpful for preliminarily designing, prior to constructing a mid-infrared gain-switched laser which can find direct applications in laser surgery.

Development of Er^3+-doped high-purity tellurite glass fibers for gain-switched laser operation at 27 μm

We present low-loss tungstate-tellurite fibers doped with Er3+ for laser operation near 2.7 μm. Two “ultra-dry” preforms with cores of TeO2-WO3-La2O3-Bi2O3 glasses doped with 0.4 and 4 mol% of Er2O3 and undoped TeO2-WO3-La2O3 claddings were produced. High-quality multimode fibers were fabricated and characterized. Photoluminescence spectra of about 2.7 μm (4I11/2 → 4I13/2 transition) and about 1.6 μm (4I13/2 → 4I15/2 transition) were measured under excitation by diode pumping at 975 nm (4I15/2 → 4I11/2 transition). The production test and the theoretical investigation of gain-switched laser generation showed potential applicability of the designed samples in the spectral range of interest. Prospective application of single-mode fibers based on the developed glass preforms was also simulated. A feasibility of pulse train generation was demonstrated even for a rough choice of parameters, which is very encouraging for experimental implementation.

Ultra-low repetition rate gain-switched thulium-doped fibre laser at 2 μm

Ultra-low repetition rate nanosecond pulsed seed lasers are beneficial for scaling both the pulse energy and the peak power in rare-earth doped fibre amplifiers. We report the generation of nanosecond laser pulses at 1958 nm with low repetition rates of down to 100 Hz in an all-fibre gain-switched thulium-doped fibre laser. Temporal characteristics of the generated 1958 nm laser pulses with repetition rates in the range from 100 Hz to 10 kHz are investigated in detail. It is found that the needed threshold pump energy decreases with increasing repetition rate. The experimental results are shown to be in good agreement with the results of the theoretical discussion.

Numerical Study of Transient Oscillation in Gain-Switched InGaN-Based Laser Diodes

The pulse working of gain-switched laser diodes (LDs) provides more power than continuous-wave (CW) emission. Similar to the CW emission, the pulse emission affects by the structural properties and different loss mechanisms of the active region. In this paper, both of these parameters are investigated in InGaN-based LDs, numerically. It is found that the thickness of the InGaN quantum well (QW) have an influence on the transient pulse, and at high enough injection currents, the thinner QW with a higher loss in CW mode can produce a stronger transient peak emission. The study of loss mechanisms in these structures indicates that the cause of the strong emission in thinner QW is mainly from the higher carrier concentration inside the active layer, which decreases significantly by Auger recombination and carrier leakage. The results of this paper can help to have a better understanding about pulse emission power from InGaN-based LDs.

Corrections to “On-Chip Investigation of Phase Noise in Monolithically Integrated Gain-Switched Lasers” [May 1, 2017 731-734

In the above letter equations (2) and (6) are incorrect due to an additional $S$ present within the bracketed term.

The Degree of Temporal Synchronization of the Pulse Oscillations from a Gain-Switched Multimode Semiconductor Laser.

Langevin noise leads to inhibition of the temporal synchronization of the pulse oscillations from a gain-switched multimode semiconductor laser, resulting in the power reduction in optical beat detection. In this paper, the degree of the temporal synchronization of the pulse oscillations was examined by numerically estimating the output energy in THz time-domain spectroscopy (THz-TDS) using multimode semiconductor laser rate equations that include Langevin noise. The degree was estimated to be 95.5% from the ratio of the averaged THz-TDS output energy for the case where Langevin noise was included to that for when Langevin noise was excluded. Therefore, a gain-switched multimode semiconductor laser can be regarded as equivalent to optical pulses oscillating simultaneously in all modes in actual applications including optical beat detection.

Efficient Wavelength-Tunable Gain-Switching and Gain-Switched Mode-Locking Operation of a Heavily Er3+-Doped ZBLAN Mid-Infrared Fiber Laser

We report on an efficient wavelength-tunable gain-switched and gain-switched mode-locked Er3+-doped double-clad fiber laser with a linear cavity. Stable gain-switching and gain-switched mode-locking were achieved with slope efficiencies of 28.6% and 34.5% with respect to launched pump power, respectively. The gain-switched laser pulses were generated with a maximum average output power of around 110 mW, pulse width of 661.2 ns, and calculated peak power of ∼16.5 W at a repetition rate of 10 kHz. At the same repetition, the gain-switched mode-locked laser pulses were generated with a maximum average output power of around 514 mW, subpulse repetition rate of ∼30.7 MHz, and peak power of higher than 154 W at a repetition rate of 10 kHz when the wavelength was tuned to 2.78 μ m. This is, to the best of our knowledge, the first demonstration of a gain-switched self-started mode-locked fiber laser near 3 μ m.

Repetition-Rate-Switchable and Self-Mode-Locked Pulses Generation From a Gain-Switched Thulium-Doped Fiber Laser and Their Amplification Properties

We report on repetition-rate-switchable and self-mode-locked pulses generation from a gain-switched thulium-doped fiber laser. Stable pulse trains were gain-switched by a home-made, pulsed Erbium/Ytterbium codoped fiber amplifier. The pulse repetition rate (PRR) of stable output pulse trains can be switched as 1/4, 1/3, and 1/2 times of that of the pump pulse train. Besides, the gain-switched mode-locked pulses were also achieved in the same cavity. By following three-stage thulium-doped fiber amplifiers, the average output power of the stable gain-switched pulses was scaled to 115 W with the PRR of 100 kHz, corresponding to a pulse energy of about 1.15 mJ. The amplification properties of the gain-switched mode-locked pulses were also characterized and discussed.

Broadband tunable integrated CMOS pulser with 80-ps minimum pulse width for gain-switched semiconductor lasers

High power pulsed lasers with tunable pulse widths are highly favored in many applications. When combined with power amplification, gain-switched semiconductor lasers driven by broadband tunable electric pulsers can meet such requirements. For this reason, we designed and produced a low-cost integrated CMOS pulse generator with a minimum pulse width of 80 ps and a wide tuning range of up to 270 ns using a 40-nm microelectronic process technique. We used this pulser to drive a 1.3-µm semiconductor laser diode directly, and thereafter investigated the gain-switching properties of the laser system. The optical pulses consist of a spike followed by a steady state region. Tuning the width of the electrical pulse down to approximately 1.5 ns produces optical pulses consisting only of the spike, which has a minimum pulse-width of 100 ps. Moreover, the duration of the steady state can be tuned continuously by tuning the electrical pulse width, with a peak power of approximately 5 mW. The output voltage of the electric pulser has a tuning range of 0.8–1.5 V that can be used to directly drive semiconductor laser diodes with wavelengths in the near-infrared spectrum, which are suitable for power amplification with rare-earth doped fiber amplifiers.

High repetition rate gain-switched 194 μm fiber laser pumped by 156 μm dissipative soliton resonance fiber laser

A dissipative soliton resonance (DSR) mode-locked Er:Yb fiber laser has been used to pump a thulium fiber laser to generate gain-switched pulses at high repetition rates. Here 412ns long DSR pulses with a center wavelength of around 1.56μm at a repetition rate of 410kHz have been fed to a thulium fiber laser, resulting in generation of gain-switched pulses at 1.94μm. The minimum pulse width achieved was 256ns with an average power of 4.6W at 66% slope efficiency. Gain-switched pulses at 520kHz and 750kHz were generated through changing the pump pulse repetition rate by modifying the DSR cavity. To the best of our knowledge, this is the first demonstration of a high repetition rate gain-switched thulium fiber laser pumped by a DSR mode-locked fiber laser. As DSR pulses can be generated with high seed average power and energy independent of the operating wavelength regime as well as mode-locking technique, the proposed method can be applied to generate gain-switched pulses at high repetition rates and various wavelengths without the need of any optical or electrical modulators.

Tunable Passively-Synchronized 1-μm Q-Switched and 1.5-μm Gain-Switched Dual-Wavelength Fiber Laser Based on an Er/Yb Codoped Fiber

A wavelength-tunable passively-synchronized 1-μm Q-switched and 1.5-μm gain-switched dual-wavelength pulsed fiber laser has been demonstrated with a single gain fiber for the first time to our knowledge. The realized dual-wavelength co-oscillation is based on a dual ring-cavity configuration with a common Er/Yb co-doped fiber (EYDF). The Q-switched 1-μm pulses are generated through the saturable absorption effect of unpumped EYDF aided by a 1.5-μm oscillation cavity, whereas the 1.5-μm pulses are produced by the gain-switching of Er3+ ions induced by the 1-μm Q-switched pulses. A tuning range of 11.7 nm from 1045.3 to 1057 nm and 29.7 nm from 1535 to 1564.7 nm are obtained at stable synchronized pulse operation for 1 and 1.5-μm spectral bands, respectively.

On-Chip Investigation of Phase Noise in Monolithically Integrated Gain-Switched Lasers

Phase noise in gain-switched lasers is investigated theoretically using the semiconductor laser rate equations and compared with the experimental results from monolithically integrated devices. The phase noise of a gain-switched laser is modelled both with and without injection-locking using the rate equations for a single-mode laser. Phase noise is found to increase with gain-switching, and decrease when injection-locked to a master laser. This trend is then observed experimentally on-chip with monolithically integrated devices without the use of an isolator.

Widely wavelength tunable gain-switched Er3+-doped ZBLAN fiber laser around 2.8 μm.

In this paper, we demonstrate a wavelength widely tunable gain-switched Er3+-doped ZBLAN fiber laser around 2.8 μm. The laser can be tuned over 170 nm (2699 nm~2869.9 nm) for various pump power levels, while maintaining stable μs-level single-pulse gain-switched operation with controllable output pulse duration at a selectable repetition rate. To the best of our knowledge, this is the first wavelength tunable gain-switched fiber laser in the 3 μm spectral region with the broadest tuning range (doubling the record tuning range) of the pulsed fiber lasers around 3 μm. Influences of pump energy and power on the output gain-switched laser performances are investigated in detail. This robust, simple, and versatile mid-infrared pulsed fiber laser source is highly suitable for many applications including laser surgery, material processing, sensing, spectroscopy, as well as serving as a practical seed source in master oscillator power amplifiers.

Intensity fluctuation of a gain-switched semiconductor laser for quantum key distribution systems.

Security certification of quantum key distribution (QKD) systems under practical conditions is necessary for social deployment. This article focused on the transmitter, and, in particular, investigated the intensity fluctuation of the optical pulses emitted by a gain-switched semiconductor laser used in QKD systems implementing decoy-BB84 protocol. A large intensity fluctuation was observed for low excitation, showing strong negative correlation between the adjacent pulses, which would affect the final key rate. The fluctuation decreased and the correlation disappeared as excitation increased. Simulation with rate equations successfully reproduced the experimental results and revealed that the large fluctuation originates from an intrinsic instability of gain-switched lasers driven periodically at a rate comparable to the inverse of carrier lifetime, as in GHz-clock QKD systems. Methods for further reduction of the intensity fluctuation were also discussed.

Picosecond high-power 355-nm UV generation in CsLiB6O10 crystal.

We report third-harmonic generation (THG) at 355 nm in CsLiB6O10 (CLBO) by using sum-frequency mixing process. As a fundamental laser source, we employ a hybrid master oscillator power amplifier (MOPA) system seeded by a gain-switched laser diode (GS-LD) at 1064 nm to produce narrow spectral picosecond pulses. Both CLBO and walk-off compensated prism-coupled CLBO device generate over 30-W output of 355-nm UV lights, which means walk-off effect in CLBO is negligible in the picosecond laser system. The maximum THG conversion efficiency from the fundamental reaches about 48%, which is 1.2 times higher than that of LiB3O5 (LBO). Theoretical THG outputs with CLBO and LBO are numerically calculated in order to verify the validity of these experimental results in detail.

Gain-switched monolithic fiber laser with ultra-wide tuning range at 2 μm.

We demonstrate a gain-switched thulium-doped fiber laser (TDFL) built in an all-fiber format producing nanosecond pulses with variable wavelength in the 2 μm waveband. The laser features tunable operation in an ultra-wide spectral region of 1765 - 2055 nm (24 THz). The nearly 300 nm tunability doubles the record tuning range of existing gain-switched fiber lasers, and to the best of our knowledge, presents the broadest tuning range that has been reported for a monolithic pulsed rare earth doped fiber laser to date. The TDFL can operate at a repetition rate of 2.5 - 100 kHz with a pulse width as short as ~200 ns. Influences of various system parameters on the laser performance are investigated in detail.

Monolithic all-fiber repetition-rate tunable gain-switched single-frequency Yb-doped fiber laser.

We report a monolithic gain-switched single-frequency Yb-doped fiber laser with widely tunable repetition rate. The single-frequency laser operation is realized by using an Yb-doped distributed Bragg reflection (DBR) fiber cavity, which is pumped by a commercial-available laser diode (LD) at 974 nm. The LD is electronically modulated by the driving current and the diode output contains both continuous wave (CW) and pulsed components. The CW component is set just below the threshold of the single-frequency fiber laser for reducing the requirement of the pump pulse energy. Above the threshold, the gain-switched oscillation is trigged by the pulsed component of the diode. Single-frequency pulsed laser output is achieved at 1.063 μm with a pulse duration of ~150 ns and a linewidth of 14 MHz. The repetition rate of the laser output can be tuned between 10 kHz and 400 kHz by tuning the electronic trigger signal. This kind of lasers shows potential for the applications in the area of coherent LIDAR etc.