Efficient double-clad thulium-doped fiber laser with a ring cavity

We have constructed a novel ring cavity for a double-clad thulium-doped fiber laser, by placing the fiber's 45 degrees angle-polished output end before the input end and relaunching the pump and the laser power into the fiber. This design can reduce reabsorption by using short fibers without loss of pump efficiency. The dependence of the laser's performance on the fiber's length and the output coupler's reflectivity is investigated experimentally and theoretically. With an 80-cm-long fiber, 2.7-W single-mode continuous-wave output is generated for 11.5 W of launched pump power.     

Tunable graphene-based Q-switched erbium-doped fiber laser using fiber Bragg grating

A graphene-based Q-switched erbium-doped fiber laser (EDFL) with a tunable fiber Bragg grating (TFBG) acting as a wavelength tuning mechanism is proposed and demonstrated. The proposed setup utilizes a newly-developed ‘ferrule-to-ferrule transfer’ technique to obtain a single graphene layer that allows for Q-switch operation in the EDFL using a highly doped-gain medium. A TFBG is used as a wavelength tuning mechanism with a tuning range of 10 nm, covering the wavelength range from 1547.66 nm to 1557.66 nm. The system has a wide repetition rate range of over 206.613 kHz from 1.387 kHz to 208.000 kHz with pulse durations of between 94.80 μs to 0.412 μs. The laser output is dependent on the pump power, with energy per pulse of 4.56 nJ to 16.26 nJ. The system is stable, with power and wavelength variations of less than 0.47 dBm and 0.067 nm. The output pulse train is free from self-mode locking and pulse jitters.     

Passively Q-switched Tm(3+)-doped silica fiber lasers

By splicing on a length of Ho(3+)-doped silica fiber onto a diode-pumped double-clad Tm(3+)-doped silica fiber, stable passive Q switching of the Tm(3+)-doped silica fiber laser is demonstrated. The formation of Q-switched pulses was found to depend on both the length and the position of the Ho(3+)-doped silica fiber that was inserted into the fiber laser cavity. For stable Q-switched pulse generation, Ho(3+)-doped silica fiber lengths shorter than twice the absorption depth must be used. For long Ho(3+)-doped silica fiber lengths, randomly generated pulses are observed at operating wavelengths longer than 2090 nm, which are attributed to intracavity pumping of the Ho(3+)-doped silica fiber.     

Wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser

An all-fiber passively wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser is presented. With a low insertion loss carbon nanotube based saturable absorber, C- and L-band tunable Q-switched lasers are achieved by tuning the transmission wavelength of one C-band tunable filter and the other L-band one, respectively. The threshold of the Q-switched operation is only 12.8 mW. The self-mode-locking effect on the Q-switching can be effectively reduced by introducing a spatial hole burning effect with two optical circulators. The tunable wavelength range of the Q-switching laser can be changed by inserting a variable optical attenuator in the laser cavity to tune the gain spectrum.     

All-fiber broadband supercontinuum source with high efficiency in a step-index high nonlinear silica fiber

We demonstrate an all-fiber broadband supercontinuum (SC) source with high efficiency in a step-index high nonlinear silica fiber, which was pumped by a 1557 nm subpicosecond-pulse laser in the normal dispersion region. The broad SC spectrum covers the spectral range from 840 to 2390 nm, and the 10 dB bandwidth from 1120 nm to 2245 nm of the SC covers one octave, assuming the peaks near 1550 nm were filtered. The SC source system is constructed by all-fiber components, which can be fusion-spliced together directly with low loss, less than 0.1 dB. Thus the SC source has high energy transfer efficiency from the pump source. The maximum SC average power of 332 mW is obtained, including the peaks near 1550 nm. The spectral density for the 10 dB bandwidth is in the range from -17.3 to -7.3 dBm/nm.     

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50?m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48?nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4?kHz as the pump power increases from the threshold power of 69.0?mW to the maximum pump power of 133.8?mW. The minimum pulse width of 4.4?μs was obtained at the maximum pump power of 133.8?mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0?mW.     

Single-frequency Q-switched erbium-doped fiber ring laser by combination of a distributed Bragg reflector laser and a Mach-Zender interferometer

A single-frequency Q-switched erbium-doped fiber ring laser is implemented for producing a single frequency with 25-Mhz laser linewidth, Q-switched pulses with a high peak power at 1557.5 mm. The single longitudinal mode is selected by a distributed Bragg reflector fiber laser, and a fiberoptic Mach-Zehnder interferometer acts as a Q-switch. The peak power and the average power of the Q-switched pulses vary with the repetition rate.     

Tunable graphene Q-switched erbium-doped fiber laser with suppressed self-mode locking effect

Self-mode locking effect in a wideband tunable graphene-based passively Q-switched erbium-doped fiber laser has been observed experimentally. Q-switching is achieved by using graphene as a saturable absorber, while a tunable bandpass filter with a narrow bandwidth is used to obtain wideband tunability. We propose to suppress the modulation on each pulse from self-mode locking by introducing three subring resonators constructed with three 3 dB couplers into the laser ring cavity. Moreover, the laser output characteristics with respect to pump power are studied in detail. A stable Q-switched erbium-doped fiber laser with a tunable range from 1522 nm to 1568 nm is demonstrated experimentally.     

Pure antimony film as saturable absorber for Q-switched erbium-doped fiber laser

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of Sb on a polyvinyl alcohol (PVA) film through physical vapour deposition (PVD) process. A 1 × 1 mm area of the film SA is cut and integrated into between two fiber ferrules inside the laser cavity for intra-cavity loss modulation. Self-starting and stable Q-switched pulses are obtained within a pump power range from 60 to 142 mW. Within this range, the repetition rate increases from 70.82 to 98.04 kHz, while pulse width decreases from 7.42 to 5.36 μs. The fundamental frequency signal-to-noise ratio of the pulse signal is 74 dB, which indicates the excellent stability of the pulses. The maximum output power and pulse energy are 8.45 mW and 86.19 nJ, respectively. Our demonstration shows that Sb film SA capable of generating stable pulses train operating at 1.55-micron region.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Q-switched mode-locking of an erbium-doped fiber laser using cavity modulation frequency detuning

We present the results of an investigation regarding a Q-switched mode-locked fiber laser scheme based on a cavity modulation frequency detuning technique. The approach is based on undamped laser relaxation oscillations occurring due to frequency detuning in the fundamental cavity resonance frequency. Through a range of experiments with an erbium-doped, fiber-based, ring-cavity laser, this approach has been shown to be capable of generating high-quality Q-switched mode-locked pulses from an optical fiber-based laser. The maximum frequency detuning range for a stable Q-switched mode-locking operation has been observed to vary depending on the pump power used. We found that the highest pulse peak power was obtained at the frequency detuning threshold at which the operation changed from the mode-locking to the Q-switched mode-locking regime.     

Passively Q-switched fibre laser utilizing erbium-doped fibre saturable absorber for operation in C-band region

In this paper, a stable and robust all-fibre passively Q-switched erbium-doped fibre laser (EDFL) emitting at 1558?nm is described. The proposed laser utilizes an 11?cm long erbium-doped fibre as saturable absorber (SA). The fibre SA features a linear optical absorption of about 13?dB in the Q-switched EDFL operating regime. By elevating the input pump power from the threshold of 60?mW to the maximum available power of 142?mW, a pulse train with a maximum repetition rate of 86?kHz, minimum pulse width of 3.39?µs, maximum average output power of 10.5?mW, maximum pulse energy of 122?nJ and maximum peak power of 36?mW are obtained. The signal to noise ratio (SNR) of the spectrum is measured to be around 70?dB. This fibre SA is simple, reliable, compact and alignment free. Thus it is suitable for making a portable pulse laser source.     

压电水听器线阵与DFB光纤水听器线阵的分析

分布反馈式(Distributed Feedback,DFB)光纤激光水听器因其多方面优越的性能近些年发展迅速,国内已对由其组成的线阵进行了成功的湖试.为检验更大规模DFB光纤激光水听器线阵的实用性能及与传统压电水听器线阵的性能区别,在某湖进行了实验,获得了传统压电水听器线阵和8元DFB光纤水听器线阵的相关数据.分析了...     

Timing jitter reduction and single-frequency operation in an acousto-optic Q-switched Cr,Nd:YAG laser

A laser-diode-pumped watt-level single-frequency combined actively and passively Q-switched (CAPQ) laser with a wavelength of 1064 nm that simultaneously uses a codoped Cr(4+),Nd(3+):YAG crystal as the gain medium and mode selector is presented. The optimum repetition period of the CAPQ laser is approximately 1.5 times the natural repetition period of the passively Q-switched laser. The averaged timing jitter is approximately 400 ns in the CAPQ laser and the repetition rate of the CAPQ laser is experimentally shown to reach a time instability of 0.2% over 10(6) pulses. The output is a stable single frequency with a linewidth of 400 MHz at 20 W pump power.     

Divergence temporal dynamics of a Q-switched laser

I address the influence of the direct coupling of the average lattice strains to the active ions on the pulse shape and the far-field beam spreading of a Q-switched laser. Calculations are made for the Cr(3+): sapphire system. The dynamic behavior of laser divergence as the pulse develops is studied without and with an internal aperture. The results can be used to search for similar effects in lasers involving other ions, such as Ti(3+) and Cr(4+).     

Kinetic modeling of Q-switched high-power ytterbium-doped fiber lasers

We present a kinetic model for Q-switched, cladding-pumped, high-power Yb-doped fiber lasers that are based on the rate equation, in a difference equation form, of ion population and propagation equations for both pumping and signal light. The effects of fiber-laser parameters, such as doping, length, pump power, and repetition rate on pulse characteristics are analyzed. This model is used to analyze the performance of Q-switched multicore fiber lasers and to show the output pulses with enhanced characteristics.     

Modeling and optimization of Q-switched double-clad fiber lasers

The numerical modeling of actively Q-switched fiber lasers is systematically presented. On the basis of typical Q-switched ytterbium-doped double-clad fiber lasers under forward and backward pump, the dynamic characteristics of pulse energy, pulse width, population inversion, and stored energy at tens-of-kilohertz repetition rates are studied by using the traveling-wave method. The laser performance is further investigated for different fiber core diameters, doping rates, cavity lengths, fiber losses, signal and pump wavelengths, reflectivities of output coupler, and switching speed of an acousto-optic modulator; the laser optimization is also quantitatively discussed. Some simulation results are also compared with previous experimental results.     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

All-fiber quasi-continuous wave supercontinuum generation in single-mode high-nonlinear fiber pumped by submicrosecond pulse with low peak power

We demonstrate quasi-continuous wave supercontinuum generation in a single-mode high-nonlinear fiber (HNLF) in 1.55 μm band, which is pumped by the amplified passively Q-switched submicrosecond pulse. The pump wavelength is in the normal dispersion region of HNLF and near to the zero-dispersion wavelength. The broad SC spectral range from 1200 to 2260 nm is obtained with the low pump peak power of 17.8 W. The 20 dB bandwidth of 922 nm from 1285 to 2207 nm is obtained with the assumption that the peak near 1560 nm is filtered. The spectrum density for the 20 dB bandwidth is from -27.5 to -7.5 dbm/nm.     

Switchable dual-wavelength fiber laser mode-locked by monolayer graphene on D-shaped fiber

A switchable mode-locking fiber laser is demonstrated by means of a monolayer graphene saturable absorber (SA) based on a D-shaped fiber. The monolayer graphene, which is grown by chemical vapor deposition, is transferred onto the D-shaped fiber and then the light–graphene interaction via the evanescent field of the fiber is enhanced greatly. Using such a graphene-based SA, the single-wavelength mode locking can be switched from 1531.5 to 1559.1 nm by appropriately adjusting the polarization controller (PC). In addition, the stable dual-wavelength mode-locking operation is also observed at the proper state of PC.