Coherence of supercontinua generated by ultrashort pulses compressed in optical fibers

Femtosecond fiber lasers together with nonlinear fibers are compact, reliable, all-fiber supercontinuum sources. Maintaining an all-fiber configuration, however, necessitates pulse compression in an optical fiber, which can lead to nonlinearities for subhundred femtosecond, nanojoule pulses. In this work we show that using large-mode-area fibers for pulse compression mitigates the nonlinearity, resulting in compressed pulses with significantly reduced satellite pulses. Consequently, supercontinua generated with these pulses are shown to have as much as a 10 dB increase in coherence fringe contrast. By using a hybrid highly nonlinear fiber-photonic crystal fiber, the continuum can be extended to visible wavelengths while still maintaining high coherence.     

啁啾脉冲堆积用于光脉冲整形

报道了一种利用100 ps啁啾脉冲堆积产生2．2 ns任意整形脉冲的脉冲整形系统。采用掺Yb~(3 )光纤锁模振荡器得到稳定的锁模光脉冲序列,将该锁模脉冲通过啁啾光纤光栅展宽并通过1 nm带宽的高斯形光谱滤波器滤波,得到标准的100 ps高斯形啁啾脉冲序列,将此脉冲选单经过光纤延迟线组成的32路脉冲堆积器,得到了精度为32 bit的重复频率为1 Hz的2．2 ns任意整形光脉冲。研究了堆积脉冲的特性,分析了宽带啁啾堆积整形脉冲的光谱时间扫描特性对激光驱动惯性约束聚变打靶束匀滑的优化作用。实验测得了该系统输出的2．2 ns整形光脉冲具有小于50 ps的上升沿,与100 ps啁啾脉冲的时间抖动小于4 ps。     

Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb³⁺-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 × 10⁷ at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse.     

Femtosecond laser pulse generation with a fiber taper embedded in carbon nanotube/polymer composite

We propose and demonstrate a new saturable absorber based on a fiber taper embedded in a carbon nanotube/polymer composite. Greater than a 10% reduction in absorption (due to saturation) is directly measured for our saturable absorber. Using an embedded fiber-taper saturable absorber, we built an all-fiber mode-locked ring laser, which produces 594 fs/1.7 nJ pulses with a repetition rate of 13.3 MHz.     

Multifunctional high-performance 10-J level laser system

In this letter,we report a multifunctional high-performance Nd:glass laser system.Laser pulses from an all-fiber front end are first amplified by a regenerative amplifier to 10 mJ level,and then further amplified in a four-pass amplifier.The laser system can provide 10.3-J,3-ns laser pulses at 1053-nm wavelength.The shot-to-shot energy stability is better than 1.5%(RMS).The output laser beam is near diffraction limit.Binary amplitude masks are used to maintain a flat top near-field profile with a 71%fill factor.After the frequency conversion process,7 and 5.5 J pulses at 526.5 and 351 nm are obtained,respectively.     

Fiber Optic Raman Distributed Temperature Sensor Based on an Ultrashort Pulse Mode-Locked Fiber Laser

Optics and Spectroscopy - The testing of an all-fiber erbium ultrashort pulsed laser in a distributed fiber temperature sensor as a source of probing pulses has been performed. Among the prospects...     

Simple method for the complete characterization of an optical pulse

A novel and simple method to measure the amplitude and the phase of optical pulses is presented. The technique basically involves modulating the optical pulse train in a particular manner and then directly examining the resultant optical spectrum. This experimental measurement technique, which is extremely accurate and sensitive and can be implemented with an all-fiber setup, permits direct measurement of the phase of the optical signal in the frequency domain. Experimental results demonstrate the use of this measurement technique for characterizing optical pulses at 10 GHz from a gain-switched laser diode.     

High-power chirped-pulse all-fiber amplification system based on large-mode-area fiber gratings

We describe the fabrication of chirped gratings in a specially developed photosensitive large-mode-area fiber and report the use of these components in a picosecond all-fiber chirped-pulse-amplification circuit. We demonstrate the generation of microjoule energy pulses with peak powers in excess of 500 kW, which we believe to be a record peak power from an all-fiber system.     

Single-frequency terahertz source pumped by Q-switched fiber lasers based on difference-frequency generation in GaSe crystal

We demonstrate a unique terahertz (THz) source that is compact, utilizes recently developed all-fiber Q-switched lasers, and is based on difference-frequency generation in a GaSe crystal. A single piezo simultaneously Q switched the two fiber lasers by using stress-induced birefringence, to achieve the temporal overlap of pulses from the two fiber lasers. These correlated pulses then combine in the GaSe crystal to produce coherent and highly monochromatic THz pulses. The peak power for this THz source can reach 0.53 mW, corresponding to an average power of 0.43 microW and a conversion efficiency of 4.75 x 10(-7). The estimated linewidth of this THz source can be as narrow as approximately 35 MHz or 1.17 x 10(-3) cm(-1).     

All-fiber integrated 10 GHz repetition rate femtosecond laser source based on Raman compression of pulses generated through spectral masking of a phase-modulated diode

We report the development of a 10?GHz repetition rate all-fiber integrated femtosecond source tunable around 1.55?μm. A phase modulator and sharp spectral filter are used to convert the output of a tunable CW diode to a 10?GHz pulse train. These pulses are compressed using Raman soliton adiabatic compression in a 21?km long length of fiber to generate sub-300-fs duration pulses at a 10?GHz repetition rate. By tuning the wavelength of the diode and appropriate filtering, similar performance was achieved over a 20?nm bandwidth.     

Microjoule level femtosecond optical pulses with double-cladding fiber-based nonlinear chirped-pulse amplification

An all-fiber high-energy nonlinear chirped-pulse amplification system with two-stage double-cladding fiber amplifiers is presented in this paper. It generates pulses with the energy up to 10 μJ at 20 kHz repetition rate and total accumulated nonlinear phase shift as large as 12.8π. The pulses can be compressed to 137 fs with the compensation of mismatched third-order dispersion by self-phase modulation in the fiber amplifiers.     

Wide-spectrally-tunable CW and femtosecond linear fiber lasers with ultrabroadband loop mirrors based on fiber circulators

It is demonstrated for the first time that the fiber circulator-based loop reflectors exhibit an extremely wide spectral range. Fiber reflectors based on a commercially available circulator for a wavelength of 1064 nm provide a reflectance of greater than 90% (50%) in a spectral band with a width of 75 (180) nm. The application of such a reflector in a linear CW Yb laser in combination with the second prism reflector allows the smooth tuning of the laser wavelength in the range with a width of greater than 90 nm. The application of two ultrabroadband circulator-based reflectors in the linear all-fiber all-positive-dispersion mode-locked Yb laser makes it possible to generate unique combined femtosecond-picosecond pulses whose shortest component has a duration of less than 190 fs. The spectrum of ultrashort pulses is smoothly tuned in the range 1065–1115 nm owing to the prism reflector.     

Short-pulse, all-fiber, Raman laser with dispersion compensation in a holey fiber

The use of Raman gain in conventional fiber followed by dispersion compensation in a holey fiber in a synchronously pumped laser configuration allowed compression by a factor of 8.5 of output pulses at a selected wavelength with respect to the pump pulses. We obtained 2-ps output pulses at 1.14 microm from a totally fiber-integrated laser pumped with 17-ps pulses at 1 microm. Higher pulse compression should be possible with nonlinear chirp compensation. Ultrashort-pulse, all-fiber Raman lasers at wavelengths shorter than 1.3 microm are feasible.     

All-fiber actively Q-switched fiber laser tuned by a pair of temperature controlled fiber Bragg gratings

We report an all-fiber actively Q-switched erbium-doped fiber laser, where the linear laser cavity mirrors are composed of two fiber Bragg gratings (FBGs). The laser oscillation wavelength could be tuned by this pair of temperature controlled FBGs. The Q-switching is achieved by an all-fiber phase modulation device. Using this system, we could obtain stable Q-switched laser pulses output, which could be optimized by tuning the reflection wavelengths of the two FBGs to be adjacent to each other. Instead of being modulated by the FBG filter in high-speed oscillation, this fiber laser system is operating in the Q-switched regime using an all-fiber phase modulator, producing a more stable laser output spectrum.     

Wavelength-Tunable Rectangular Pulses Generated from All-Fiber Mode-Locked Laser Based on Semiconductor Saturable Absorber Mirror

The wavelength-tunable rectangular mode-locking operation is demonstrated in an all-fiber laser based on semiconductor saturable absorber mirror.As the dissipative soiiton resonance signature,the puJse duration varies from 580 ps to 2.1 ns as a function of the increasing pump power.Correspondingly,the maximum pulse energy is9.11 nJ.Moreover,it is found that the wavelength tunable operation with a range of approximately 10 nm could be obtained by properly adjusting the polarization controllers.The characteristics of the rectangular pulses at different wavelengths are similar to each other.The demonstration of the wavelength tunable rectangular pulses would be beneficial to some applications for many fields such as spectroscopy and sensing research.     

Pulse-shaping control of spectral transformations of ultrashort pulses in photonic-crystal fibers

We experimentally demonstrate that the initial pulse width and spectral phase of ultrashort laser pulses may significantly influence the solition dynamics of such pulses in a photonic-crystal fiber. These findings suggest new solutions for the transmission, shaping, stretching, amplification, and spectral transformation of ultrashort pulses in all-fiber laser technologies.     

All-fiber laser seeded femtosecond Yb:KGW solid state regenerative amplifier

A high efficiency compact Yb:KGW regenerative amplifier using an all-fiber laser seed source was comprehensively studied. With thermal lensing effect compensated by the cavity design, the compressed pulses with energy of 1 m J at 1 k Hz and 0.4 m J at 10 k Hz in sub-400-fs pulse duration using chirped fiber Bragg grating(CFBG) stretcher were demonstrated.A modified Frantz–Nodvik equation was developed to emulate the dynamic behavior of the regenerative amplifier. The simulation results were in good agreement with the experiment. Numerical simulations and experimental results show that the scheme can be scalable to higher energy of multi-m J, sub-300 fs pulses.     

Erbium-doped fiber laser simultaneously mode locked on more than 24 wavelengths at room temperature

We demonstrate simultaneous mode locking of more than 24 wavelengths at 3 GHz in an actively mode-locked erbium-doped fiber laser operating at room temperature. The multiwavelength operation is achieved when a frequency shifter and an all-fiber 50-GHz periodic filter are inserted into a ring cavity. Active mode locking is performed with an amplitude modulator, and pulses with a FWHM of 30 ps are obtained.     

All-fiber,octave-spanning supercontinuum

We present an all-fiber supercontinuum source based on a passively mode-locked erbium fiber laser and a small-effective-area, germanium-doped silica fiber. The parallels between this system and the continuum generated in microstructured fibers with 800-nm pulses are discussed, and the role of dispersion is investigated experimentally. We construct a hybrid fiber by fusion splicing lengths of different-dispersion fiber together, generating more than an octave of bandwidth.     

Experimental demonstration of a passive all-fiber Q-switched erbium- and samarium-doped laser

Self-Q-switched operation of the all-fiber laser using erbium and samarium fibers in the cavity is realized experimentally. This passively Q-switched all-fiber laser produces very stable pulses with energy of 142 nJ and duration of 450 ns. The experimental results were well reproduced by the results obtained through the numerical integration of a rate-equations model.