Gain switching of a Nd(+3)-doped fiber laser

Monolithic 2-µm single-frequency linearly-polarized gain-switched distributed feedback fiber laser by femtosecond laser direct-writing

We report a single-frequency, linearly polarized gain-switched, distributed feedback (DFB), 2-µm thulium doped silica fiber laser (TDFL), with an effective cavity length of 2.5 mm. The cavity is based on a heavily thulium doped non-polarization-maintaining silica fiber and composed of a π-phase-shifted fiber Bragg grating (FBG) with a total FBG length of 35 mm. The DFB FBG was written by femtosecond-laser point-by-point (PbP) method. In-band pumping scheme is chosen with a 1550 nm nanosecond pulsed erbium-doped silica fiber laser pump. Single-longitudinal, linearly polarized, gain-switched TDFL at 2002 nm, with a recorded shortest pulse duration of 4.7 ns, a repetition rate of 20 kHz, a maximum peak power of 170 W, and single pulse energy of 0.8 µJ, has been obtained, benefitting from the ultrashort DFB cavity made by the femtosecond laser direct-writing method.

Highly adaptable gain-switched fiber laser with improved efficiency

A highly adaptable fiber laser with pulse-on-demand and precision pulse-duration tuning is presented. It is based on a compact optical design combining the gain-switching technique with the all-fiber master oscillator and pump-recovery amplifier architecture. The approach of laser-pulse stability control by compensation pumping and pulse-duration control by changing the pump wavelength are introduced. In order to prove the concept, a laser setup capable of producing laser pulses with an average power of up to 30 W and a peak power of approximately 1 kW at an improved efficiency and an arbitrary repetition rate is presented.

Single-frequency gain-switched ytterbium-doped fiber laser at 1017 nm based on dynamic self-induced grating in a saturable absorber

We report on a stable single-frequency gain-switched ytterbium-doped fiber (YDF) laser at 1017 nm based on saturable absorber (SA) properties. The laser is realized by utilizing a short-length, high-concentration phosphosilicate YDF that simultaneously acts as an SA and a gain medium in a linear cavity. Despite the fact that gain switching is achieved by modulating the pump laser, single-frequency operation is sustained due to dynamic self-induced grating. By making use of high-concentration phosphosilicate YDF and selecting a suitable spectral region, grating is strongly induced along the cavity to stabilize single-mode operation. Additionally, the residual grating property in SA assures single-mode gain-switched performance at high repetition rates. Here, the laser generates pulses with 427 ns duration at 100 kHz, yielding the mean power of 12 mW with linewidth of less than 7.5 MHz.

High-power nanosecond pulse generation from an integrated Tm-Ho fiber MOPA over 2.1 μm

In this paper, we report on high-power stable nanosecond pulse generation at ~2.1 μm from an integrated Tm-Ho all-fiber master oscillator power amplifier (MOPA) system. A total output power of 128.5 W is generated from the Tm-Ho hybrid MOPA, with an average power of 99.1 W from Ho emission at 2116 nm; the corresponding pulse repetition frequency and pulse width are 161 kHz and 322 ns, respectively, leading to a peak power of 1.91 kW. The Tm-Ho integrated master oscillator is designed to operate at 1980 and 2116 nm, where the former wavelength serves as the pump of the Ho-doped fiber. Stable laser pulses are generated from both the Tm and Ho oscillators owing to mutual modulation of emission from the two lasers. The prospects for further scaling in output power at ~2.1 μm using Tm-Ho integrated MOPA system are discussed.

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.

Passive Q-switching of an all-fiber laser induced by the Kerr effect of multimode interference

A novel passively Q-switched all-fiber laser using a single mode-multimode-single mode fiber device as the saturable absorber based on the Kerr effect of multimode interference is reported. Stable Q-switched operation of an Er(3+)/Yb(3+) co-doped fiber laser at 1559.5 nm was obtained at a pump power range of 190-510 mW with the repetition rate varying from 14.1 kHz to 35.2 kHz and the pulse duration ranging from 5.69 μs to 3.86 μs. A maximum pulse energy of 0.8 μJ at an average output power of 27.6 mW was achieved. This demonstrates a new modulation mechanism for realizing Q-switched all-fiber laser sources.

Short pulsed gain-switched fiber laser with improved efficiency utilizing unabsorbed pump recovery

A simple solution for increasing the slope efficiency of a gain-switched fiber laser based on Yb-doped active fiber is presented. By adding a fiber amplifier stage, which recovers the unabsorbed pump light from the gain-switched oscillator, a significant increase in slope efficiency is achieved. The pulses at 1030-nm wavelength have an FWHM of 28 ns and a peak power of 2.3 kW.

Gain switch laser based on micro-structured Yb-doped active fiber

In this paper a near infrared gain-switched fiber laser based on oscillator stage only design with high peak power is presented. Output pulses reached 2.3 kW of peak power and duration of less than 60 ns. The dependence of the laser pulse duration on operation parameters was measured and theoretically explained. As the setup is based on flexible micro structured single polarization fiber, the laser output exhibits high polarization extinction ratio. Due to the narrow output spectrum the setup is suitable for second harmonic generation.

Single stage Yb-doped fiber laser based on gain switching with short pulse duration

A simple solution for producing nanosecond laser pulses can be obtained using gain-switched fiber lasers. In this paper, we present an optimized single stage gain-switched ytterbium-doped fiber laser. Three fiber lengths were tested to show the impact of length on the laser output pulse. A pulse as short as 28 ns at 1.4 kW peak power and a maximum peak power of nearly 2 kW at 41 ns pulse duration was achieved. The laser possess a linear polarized output, very good beam quality of M2 < 1.1, and a spectral bandwidth of 0.11 nm.

The all-fiber cladding-pumped Yb-doped gain-switched laser

Gain-switching is an alternative pulsing technique of fiber lasers, which is power scalable and has a low complexity. From a linear stability analysis of rate equations the relaxation oscillation period is derived and from it, the pulse duration is defined. Good agreement between the measured pulse duration and the theoretical prediction is found over a wide range of parameters. In particular we investigate the influence of an often present length of passive fiber in the cavity and show that it introduces a finite minimum in the achievable pulse duration. This minimum pulse duration is shown to occur at longer active fibers length with increased passive length of fiber in the cavity. The peak power is observed to depend linearly on the absorbed pump power and be independent of the passive fiber length. Given these conclusions, the pulse energy, duration, and peak power can be estimated with good precision.

Gain-switched all-fiber laser with narrow bandwidth

Gain-switching of a CW fiber laser is a simple and cost-effective approach to generate pulses using an all-fiber system. We report on the construction of a narrow bandwidth (below 0.1 nm) gain-switched fiber laser and optimize the pulse energy and pulse duration under this constraint. The extracted pulse energy is 20 μJ in a duration of 135 ns at 7 kHz. The bandwidth increases for a higher pump pulse energy and repetition rate, and this sets the limit of the output pulse energy. A single power amplifier is added to raise the peak power to the kW-level and the pulse energy to 230 μJ while keeping the bandwidth below 0.1 nm. This allows frequency doubling in a periodically poled lithium tantalate crystal with a reasonable conversion efficiency.

Gain-switched Yb-doped fiber laser for microprocessing

The gain-switched fiber laser presents the simplest construction among pulsed lasers in the nanosecond region and consequently is also very robust. These properties make it potentially appropriate for industrial applications, especially in some types of microprocessing. However, careful design of such lasers is important in order to reach the required pulse parameters (peak power and pulse duration). To design and optimize a gain-switched fiber laser for microprocessing, a numerical model using time and spatial dependencies was developed and reported in this paper. The effects of pump power and laser length on the pulse duration and peak power were investigated by modeling gain-switched operation. Further, the results of modeling were compared to data from an experimental setup based on a Yb³⁺-doped gain-switched fiber laser, revealing good agreement.

Gain-switched CW fiber laser for improved supercontinuum generation in a PCF

We demonstrate supercontinuum generation in a PCF pumped by a gain-switched high-power continuous wave (CW) fiber laser. The pulses generated by gain-switching have a peak power of more than 700 W, a duration around 200 ns, and a repetition rate of 200 kHz giving a high average power of almost 30 W. By coupling such a pulse train into a commercial nonlinear photonic crystal fiber, a supercontinuum is generated with a spectrum spanning from 500 to 2250 nm, a total output power of 12 W, and an infrared flatness of 6 dB over a bandwidth of more than 1000 nm with a power density above 5 dBm/nm (3 mW/nm). This is considerably broader than when operating the same system under CW conditions. The presented approach is attractive due to the high power, power scalability, and reduced system complexity compared to picosecond-pumped supercontinuum sources.

Nonlinearly coupled, gain-switched Nd:YAG second harmonic laser with variable pulse width

An all-solid-state, gain-switched, green laser is developed using a side diode-array pumped Nd:YAG laser and a KTiOPO(4) (KTP) crystal as an intracavity frequency doubler. The effect of nonlinear coupling on the pulse width of the fundamental is studied and is found to be in good agreement with the experimental measurement. In this preliminary experiment, a peak power of 40 W at 532 nm corresponding to a pulse width of 409 ns is obtained for an average pump power of 2 W. Compared to a Q-switched laser, it is simple and does not require a high voltage RF driver or saturable absorbers in its operation. The laser may be useful where relatively longer nanosecond pulses are required such as eye surgery, micromachining, and underwater communication.

Mode-locked fiber laser gyroscope based on a distributed-feedback semiconductor laser amplifier

A mode-locked fiber laser gyroscope is reported that uses a distributed-feedback semiconductor laser amplif ier as the gain medium. Stable mode-locked optical pulses were obtained without gain competition, and the pulse interval could be measured with much-improved accuracy as a function of rotation rate. The rms noise equivalent rotation rate was measured to be 0.4 deg/ radicalh.

Frequency-modulated cavity-dumped Nd-doped fiber laser

A cw-pumped Nd-doped single-mode double-clad fiber laser coiled around a resonant piezoelectric ceramic ring and coupled to an empty external cavity with strong feedback is described. Intensity laser pulses with durations in the 1-2-micros range are observed as the pump power or the ring drive voltage is increased, yielding peak powers as much as 25 times greater than average powers. The effect is attributed to strong phase modulation of the fiber laser by the piezoelectric ring, which induces FM laser oscillation. The external cavity acts as a frequency-dependent reflector, thus effectively cavity dumping the fiber laser as the oscillation frequency is swept through the narrow transparent windows of the external cavity.