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We report a continuous-wave high-output power and narrow-linewidth all-fiber laser at 1550 nm with the master oscillator power amplifier (MOPA) configuration. An all-fiber distributed feedback seed laser was boosted by three cascaded fiber amplifiers. In the experiment, we adopted a large-mode-area (LMA) Er3+:Yb3+-co-doped polarization-maintaining fiber to increase nonlinear thresholds and avoided the broadening of the laser linewidth. A linear-polarization fiber laser with average output power of 20 W, linewidth of 0.88 kHz, and power jitter less than 2% was finally achieved.

Spectral broadening due to amplified spontaneous emission (ASE) in a fiber amplifier is experimentally and theoretically investigated in this paper. By measuring and analyzing the variation in linewidth and noise of the fiber amplifier, the influence of ASE on laser linewidth is studied. The analysis shows that the ASE will cause broadening of the laser linewidth as noise, and the noise is introduced as an additive term rather than a multiplicative one.

A dynamic nonlinear error compensation method for the interferometers is proposed to meet the design demands of the tracker. It makes the system reach high precise measurement when the target is moving with high speed. With the passive compensation method of the optical path, part of the errors are eliminated. Thus, the periods of the signals could be counted accurately. A dynamic compensation method is proposed for the displacement in less than one period. By tracking the peak values and valley values of the interference signals in one cycle, the zero offsets error and unequal amplitude error can be compensated; then the quadrature phase shift error could be compensated by tracking the intersection of the two compensated signals. By tracking the signals and renewing the compensation parameters, the signals even with random nonlinear errors can get high-precision subdivision. Experiment results show that the system can get nanometer accuracy even the target is moving at high velocity. The system has better adaptability to different environment and anti-jamming capability.

An efficient single resonant extracavity optical parametric oscillator is demonstrated based on a Type II noncritical phase matching KTA crystal. Under a pump power of 0.6 W and a pulse width of 13 ns, the average power of 86 mW at 3.467 mu m is obtained with the pulse width of 6 ns and repetition rate of 100 Hz, corresponding to a conversion efficiency as high as 14% from 1.064 to 3.467 mu m. The beam spatial profile for 3.467 pm is near TEM(00) mode. The average power of 123 mW is also obtained with a multitransverse mode at the repetition rate of 200 Hz and an average power of 2.3 W of the pump laser. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2204-2207, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26247

A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened through nonlinear effects of PCF.

an all-digital design method consisting of a laser drive circuit for gradually modulating the frequency, pulse width, and amplitude of the output of semiconductor laser is demonstrated. field programmable gate arrays (fpgas) and accurate delaying chip are used to generate the pulse. the repetition rate and pulse width of the laser pulse gradually adjust from 1 to 10 khz and 700 ps to 3 ns, respectively. furthermore, the time of the rising and falling edges for the laser pulse is less than 800 ps.

To achieve high peak current with narrow pulse width, the circuit model is analyzed based on a fast and high-power metallic oxide semiconductor field effecttransistor (MOSFET) as the high speed switch of the resistor-capacitor (RC) charge and discharge circuits. It is easy to obtain a narrow high-current pulse by adopting the narrow triggering pulse to control the on-off state of the MOSFET switch, and using the driving pulse to modulate the exponential decay pulse in the RC discharge loop. The procedure for the high speed MOSFET switch is then discussed. To make the speed of the MOSFET switch as quick as possible, the push-pull driving circuit for the grid of the MOSFET is brought forward and the circuit for producing the narrow trigger pulse is designed. The experimental result shows that the full width at half maximum (FWHM) of the trigger pulse is about 500 ps when the narrow trigger pulse is connected with the discharge return circuit. Measured results demonstrate that the RC discharge loop produces a narrow high-current pulse, with a peak current of up to 92.5 A and FWHM of 6.2 ns. After adjusting relevant parameters, the peak current could reach up to 115.9 A. However, the corresponding pulse width is broadened. Finally, influencing factors on the narrow pulse width for the discharge loop are briefly analyzed.

A high energy and high efficiency extracavity KTiOAsO(4) (KTA) optical parametric oscillator (OPO) with excellent stability and beam quality, which is pumped by a Q-switched single-longitudinal-mode Nd:YAG laser, has been demonstrated based on a type II non-critical phase matching (NCPM) KTA crystal. The maximum pulse energy of 10 mJ at 3.467 mu m is obtained with the repetition rate of 10 Hz and pulse width of 2 ns, corresponding to an optical-optical conversion efficiency of 14% from 1.064 mu m to 3.467 mu m. After one hour of investigation, the OPO output stability better than 4.5% rms has been obtained.

Based on the linear frequency modulation (LFM) of semiconductor laser, a laser ranging system is built. The ranging precision of the system is about micron dimension with the repetition frequency of 100 kHz and a distance of 1–10 m. We analyzed the ranging precision experimentally. As the bandwidth increases, the ranging precision becomes higher and higher. When the bandwidth is fixed, as the distance increases, the signal-to-noise ratio (SNR) will decrease, which reduces the precision.

A photoconductive semiconductor switch (PCSS) would work in a nonlinear mode under high biased electrical field. The experimental results of nonlinear critical state have shown that both the biased voltage and the laser energy may have working thresholds to turn on the nonlinear modes. The relation between the biased voltage (aid the laser energy is inverse ratio, i.e., higher biased field need lower laser energy for nonlinear mode, and vise versa. At the nonlinear critical point, the output of PCSS is unstable, as both the linear and nonlinear pulse may occur. As the laser energy and biased field increase, the PCSS would work in the nonlinear mode steadily. (C) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 56-59 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOT 10.1002/mop.24001

A novel ultra-wideband electromagnetic pulse generating method based on the photoconductive semiconductor switches (PCSS) is presented. Gallium arsenide is used to develop the PCSS for an ultrashort electromagnetic pulse source. The pulse generated by such PCSS is within picosecond (ps) time scale, and can yield power pulse with an voltage over 10 kV. The experimental results show that the pulses are stable, with the peak-peak amplitude change of 6% and the time jitter within several picoseconds. The radiations of the PCSS triggered by the picosecond laser and fenitosecond laser pulse series illustrate that the electromagnetic pulses would have high repetition of more than 80 MHz and frequency bandwidth of DC-6 GHz. The radiations of "lock-on " mode of the PCSS are also analyzed here. (c) 2007 Wiley Periodicals, Inc.

This report presents the experiments to study the characteristics of the picosecond ultra-wideband pulses coherent radiation. The testing involves bow-tie horn antennas for both the transmitting and receiving antenna. Sixteen channels of electrical pulses with 290 ps duration and jitter

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

This study presents an eye-safe, single-mode, nanosecond-pulsed, and all-fiber laser source with master-oscillator-power-amplifier configuration at 1 550 nm that is suitable for high-resolution three-dimensional (3D) imaging light detection and ranging (LIDAR) system. The output peak power of 7.6 kW is obtained at the 1.2-ns pulse width and 50-kHz repetition rate. The single-mode pulse laser output ensures the range precision and imaging results of the LIDAR system. The laser is used as a transmitter for the 3D imaging LIDAR system. The detailed characteristics of the LIDAR system and the results of the 3D imaging are presented.

An all fiber laser with master-oscillator-power-amplifier (MOPA) configuration at 1064nm/1550nm for the high-resolution three-dimensional (3D) imaging light detection and ranging (LIDAR) system was reported. The pulsewidth and the repetition frequency could be arbitrarily tuned 1ns~10ns and 10KHz~1MHz, and the peak power exceeded 100kW could be obtained with the laser. Using this all fiber laser in the high-resolution 3D imaging LIDAR system, the image resolution of 1024x1024 and the distance precision of ±1.5 cm was obtained at the imaging distance of 1km.

We present a novel high-energy, single-mode, all-fiber-based master-oscillator-power-amplifier (MOPA) laser system operating in the C-band with 3.3-ns pulses and a very widely tunable repetition rate, ranging from 30 kHz to 50 MHz. The laser with a maximum pulse energy of 25 \muJ and a repetition rate of 30 kHz is obtained at a wavelength of 1548 nm by using a double-clad, single-mode, Er:Yb co-doped fiber power amplifier.

Based on the technique of master oscillator power amplifier (MOPA), a two-stage ytterbium-doped fiber amplifier (YDFA) with all-fiber structure is theoretically simulated. The seed signal operating at the wavelength of 1064 nm has the characteristic of high repetition rate (10 MHz), ultrashort pulse duration (10 ps), low signal power input (20μW) and single longitudinal mode. The gain (and amplification stimulation emission power) is calculated at the different pump powers and gain fiber lengths of YDFA pumped by 975 nm. In addition, the amplifications at the different signal power inputs (1-25μW) are also simulated. The numerical results can be used to optimize the YDFA.

Experimental investigation of single and dual pulses in a passively Q-switched Nd:YAG microchip laser with a Cr4+:YAG saturable absorber has been reported. The dual pulses consist of a main and a satellite pulse with respective spectra, intensities, and durations. It is found that the preponderant oscillating mode gives birth to the main pulse, and the other oscillating mode corresponds to the satellite pulse. Our results demonstrate that the dual-pulse emission results from double-longitudinal-mode oscillation in high pump regime.

The nonlinear error of a homodyne interferometer is presented: the amplitudes, the phase and the offsets. An improved compensation method is introduced since the conventional Heydeman modal' calculation is very time-consuming. First, the "zero drift" problem is solved with the polarization phase-shifting technology; second, a fast algorithm based on the Heydeman method is introduced to calculate the errors; and third, electronic circuit is used to remove the nonlinear errors timely. The test result shows that the nonlinearity of the homodyne interferometer could be reduced to subnanometer over the measuring range of 20cm, and the accuracy can be improved more than tenfold by the dynamic compensation method.

A high energy dual-wavelength extracavity KTA optical parametric oscillator (OPO) with excellent stability and beam quality, which is pumped by a Q-switched single-longitudinal-mode Nd:YAG laser, has been demonstrated based on a type II noncritical phase matching (NCPM) KTA crystal. The maximum pulse energy of 10.2 mJ with the output stability of better than 4.1% rms at 3.467 μm is obtained at the repetition rate of 10 Hz and pulse width of 2 ns, and the 11.9 mJ of 1.535 μm radiation is obtained simultaneously. This extracavity NCPM KTA OPO is very useful when high energy, high beam quality and smooth time domain are needed., {"references":["S. T. Yang and S. P. Velsko, \"Frequency-agile kilohertz repetition-rate\noptical parametric oscillator based on periodically poled lithium\nniobate,\" Opt. Lett. 24, 133-135 (1999).","K. L. Vodopyanov and P. G. Schunemann, \"Broadly tunable noncritically\nphase-matched ZnGeP2 optical parametric oscillator with a 2-╬╝J pump\nthreshold,\" Opt. Lett. 28, 441-443 (2003) .","M. Henriksson, M. Tiihonen, V. Pasiskevicius and F. Laurell, \"Midinfrared\nZGP OPO pumped by near-degenerate narrowband type-I\nPPKTP parametric oscillator,\" Appl. Phys. B 88, 37-41 (2007).","X. J. Wang and Z. Y. Xu, \"Single-longitudinal-mode operation of a 1 W\ncombined actively and passively Q-switched Cr, Nd:YAG laser,\" Opt.\nExpress 13, 6693-6698 (2005).","R. F. Wu, K. S. Lai, H. F. Wong, W. J. Xie, Y. L. Lim, E. Lau, \"Multiwatt\nmid-IR output from a Nd:YALO laser pumped intracavity KTA OPO,\"\nOpt. Express 8, 694-698 (2001).","A. Dergachev, D. Armstrong, A. Smith, T. Drake, M. Dubois, \"3.4-╬╝m\nZGP RISTRA nanosecond optical parametric oscillator pumped by a\n2.05-╬╝m Ho:YLF MOPA system,\" Opt. Express 15, 14404-14413\n(2007).","P. Schlup, G. W. Baxter and I. T. McKinnie, \"Single-mode near midinfrared\nperiodically poled lithium niobate optical parametric oscillator,\"\nOpt. Commun. 176, 267-271 (2000).","M. Henriksson, M. Tiihonen, V. Pasiskevicius, F. Laurell, \"ZnGeP2\nparametric oscillator pumped by a linewidth-narrowed parametric 2 ╬╝m\nsource,\" Opt. Lett. 31, 1878-1880 (2006).","X. L. Dong, B. T. Zhang, J. L. He, H. T. Huang, K. J. Yang, J. L. Xu, C.\nH. Zuo, S. Zhao, G. Qiu, Z. K. Liu, \"High-power 1.5 and 3.4 ╬╝m\nintracavity KTA OPO driven by a diode-pumped Q-switched Nd:YAG\nlaser,\" Opt. Commun. 282,1668-1670 (2009).\n[10] D. L. Fenimore, K. L. Schepler, U. B. Ramabadran and S. R. McPherson,\n\"Infrared corrected Sellmeier coefficients for potassium titanyl\narsenate,\" J. Opt. Soc. Am. B 12, 794-796 (1995)."]}

Numerical simulation and analysis about the influence of the time modulation of the pump laser caused by mode beating on optical parametric process are presented with OPA and OPG as examples. It is shown that the output power of the generated beams from optical parametric process is modulated in the time domain and exhibits large power fluctuations, when a Q-switched laser oscillating on several random longitudinal modes is used as the pump laser. Irregular spike sequences of the generated beams are observed. We also find that the output power of the light from optical parametric process becomes more stable and exhibits a less fluctuation, when the number of the longitudinal modes (n) increases.

Two common approaches to generate ultra-short electromagnetic pulse are presented in this paper. One is that using a high-speed avalanche transistor and another is that using a laser triggering photoconductive semiconductor switch (PCSS). An ultra-short electromagnetic pulse with the rise time of 190 picosecond (ps), the pulse duration of 290 ps and the amplitude of 2.2 kV, is radiated by an ultra-wide band (UWB) antenna. It is noted that the ultra-wide frequency spectrum provided by the ultra-short electromagnetic pulses with duration of picosecond can be used to distinguish different targets. The radiated pulse would transmit and be reflected by various targets within the detection range. By analyzing the reflected signal, the corresponding reflection material can be discerned. The experiment is set up to distinguish the iron metal and concrete wall respectively. The results show that such ultra-short pulse technology has an excellent ability to distinguish objects.

A passively Q-switched ytterbium-doped double-clad fiber laser with SESAM as a saturable absorber is demonstrated experimentally. This system showed up to 18.7mW output power, up to 29.4 kHz repetition rate, a maximum pulse energy of 0.636μJ and a minimum pulse duration of 3.148 μs. The characteristics of pulse were investigated, and the theoretical analysis agree well with the experimental results.

A two-dimensional linear array fiber amplifier based on the master oscillator power amplifier (MOPA) configuration is constructed and employed as the laser source of a high resolution 3D imaging LIDAR system. Each branch of the linear array system comprises a dual-stage Yb3+-doped large-mode-area double-clad fiber amplifier. The amplified pulse is of 2.3 ns temporal duration and 30 kHz repetition rate with an average power of 8.5 W when the pump power is 20 W. The optical–optical conversion efficiency is 41.8%. Furthermore, the SRS effect can be suppressed effectively. The M2 values of the output beam are 1.35 and 1.33 in the x- and y-axis directions, respectively.

A compact all-fiber sub-nanosecond narrow-linewidth Yb-doped fiber amplifier with a controllable repetition rate has been investigated. Tunable temporal pulses ranging from sub-nanoseconds to 10 ns with repetition rates from 10 kHz to 1 MHz are obtained by controlling the waveform of the injected electrical-pulse signal. Due to the practical requirements of our intended applications, a distributed feedback semiconductor laser with a wavelength of 1064 nm, pulse duration of 802 ps, repetition rate of 500 kHz and average power of 20 μW is used to seed a dual-stage single mode Yb-doped fiber amplifier. The characteristics of the amplified pulses are measured and exhibit a temporal duration of 810 ps with an average power of 31.2 mW. The gain of the amplified pulse is about 32 dB at the maximum output power. A notable feature of the amplifier pulses is that the spectral linewidth can be maintained to less than 0.1 nm during the dual-stage amplifier process. The noise level lies more than 22 dB below the peak value of the amplified spectrum, which represents an excellent signal-to-noise ratio.