Optical fibre-grating pulse compressors

This article reviews the current state-of-the-art of optical pulse compressors based on the optical fibre-grating pair. As this technique has become a standard laboratory procedure providing pulses with duration shorter than those directly generated from mode-locked lasers, we review the basic mechanism of the method, the role played by additional non-linear effects (such as stimulated Raman scattering), describe the current results, with emphasis to our own work, and point out the limitations of the technique.     

Optical pulse compression using the temporal Radon-Wigner transform

The temporal Radon-Wigner transform (RWT), which is the squared modulus of the fractional Fourier transform (FRT) for a varying fractional order p, is here employed as a tool for pulse compression applications. To synthesize the compressed pulse, a selected FRT irradiance is optically produced employing a photonic device that combines phase modulation and dispersive transmission. For analysis purposes, the complete numerical generation of the RWT with 0 < p < 1 is proposed to select the value of p required for pulse compression. To this end, the amplitude and phase of the signal to be processed should be known. In order to obtain this information we use a method based on the recording of two different FRT irradiances of the pulse. The amplitude and phase errors of the recovered signal, which are inherent to the recording process, are discussed in connection with the RWT production. Numerical simulations were performed to illustrate the implementation of the proposed method. The technique is applied to compress signals commonly found in fiber optic transmission systems, such as chirped gaussian pulses, pulses distorted by second and third-order dispersion and nonlinear self-modulated pulses.     

Optical pulse compression: bulk media versus hollow waveguides

Optical pulse-compression systems based on bulk materials and hollow waveguides are compared by use of coupled-mode theory. Our analysis reveals an intuitive picture of the temporal and spatial nonlinear processes involved in pulse compression. Further, simple formulas are derived that give an estimate of the spatial distortions and of the self-phase modulation induced by Kerr nonlinearity. Finally, a parameter regime is identified in which self-focusing in bulk media is suppressed, resulting in a substantial improvement in the spatial beam quality of the compressed pulses.     

Optical pulse compression and breaking in nonlinear fibre couplers

The analysis of a curved, fibre coupler with a Kerr-type nonlinear medium between the fibres is presented. The nonlinear fibre coupler is seen to produce compression of optical pulses. A new feature, that of optical pulse breaking, is presented as well.     

Optical pulse compression of ultrashort laser pulses in a multi-hollow-core fiber

By numerical simulations and analysis, we proposed a fiber with multi-hollow-core structure for optical pulse compression of high energy ultrashort laser pulses. In this scheme, different parts of a high-energy flat-top pulse are coupled into different hollow cores of such fiber and each of the cores functions as an independent traditional hollow-core fiber compressor. After the multi-hollow-core fiber, the output beams are collimated and compressed to few-cycle level. Then they can be focused to ultra-high intensity. This method can easily be scaled to compressing pulses of large beam size with high energy without limit in principle.     

Optical pulse compression to 5 fs at a 1-MHz repetition rate

We report on the characterization and compression of the white-light continuum produced by injection of a 13-fs pulse from a cavity-dumped self-mode-locked Ti:sapphire laser into a single-mode fiber. Pulses as short as 5 fs were generated at repetition rates up to 1 MHz.     

Optical pulse compression of ultrashort laser pulses in an argon-filled planar waveguide

We investigate the possibility of optical pulse compression of high energy ultrashort laser pulses in an argon-filled planar waveguide, based on two level coupled mode theory and the full 3D nonlinear Schr?dinger equation. We derive general expressions for controlling the spatial beam profile and the extent of the spectral broadening. The analysis and simulations suggest that the proposed method should be appropriate for optical pulse compression of ultrashort laser pulses with energies as high as 600 mJ.     

Optical pulse compression using the combination of phase modulation and high-order dispersion compensation

Optical pulse compression using high-order dispersion compensation is proposed and theoretically analyzed. Firstly, the required dispersion profile for the high-order dispersion compensation is derived, according to the linear chirp and the nonlinear chirp of a phase-modulated continuous-wave (CW) laser source. With the use of the high-order dispersion compensation, such as the combination compensation of the second order dispersion (SOD) and the fourth order dispersion (FOD), an efficient pulse compression having a less time-bandwidth product and a greater peak power is realized. A sampled fiber Bragg grating (FBG) with both the SOD and the FOD is then designed using the equivalent chirp and the reconstruction algorithm. Finally, in the numerical simulation an optical pulse with a time-bandwidth product of 0.79 is generated via high-order dispersion compensation that is performed by using the sampled FBG.     

Limit for pulse compression by pulse splitting

We have detected a fundamental pulse-compression limit for high-nonlinear fibers in the normal dispersion regime near the zero-dispersion wavelength. The desired generation of a broadband continuum by self-phase modulation is limited by already small amounts of third-order dispersion (TOD), which results in pulse splitting above a critical pulse power. We investigate the critical fiber length in dependence on pulse- and fiber parameters.     

Adaptive femtosecond pulse compression

A practical adaptive method for femtosecond optical pulse compression is demonstrated experimentally for the first time to our knowledge. The method is robust and capable of handling the general case of pulse compression, in which the input pulses are completely uncharacterized or partially characterized.     

光纤-光栅对激光脉冲压缩

本文报道用2m单模保偏光纤实现脉冲光谱加宽,经光栅对补偿后,将40ps脉冲压缩到小于10ps的实验结果,分析了影响光脉冲压缩质量的原因。实验结果与理论较好地吻合。     

Optical pulse compression to 3.4 fs in the monocycle region by feedback phase compensation

We compensated for chirp of optical pulses with an over-one-octave bandwidth (495-1090 nm; center wavelength of 655.4 nm) produced by self-phase modulation in a single argon-filled hollow fiber and generated 3.4-fs, 1.56 optical-cycle pulses (500 nJ, 1-kHz repetition rate). This was achieved with a feedback system combined with only one 4-f phase compensator with a spatial light modulator and a significantly improved phase characterizer based on modified spectral phase interferometry for direct electric-field reconstruction. To the best of our knowledge, this is the shortest pulse in the visible-to-infrared region.     

Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

We demonstrate the use of a deformable-mirror pulse shaper, combined with an evolutionary optimization algorithm, to correct high-order residual phase aberrations in a 1-mJ, 1-kHz, 15-fs laser amplifier. Frequency-resolved optical gating measurements reveal that the output pulse duration of 15.2 fs is within our measurement error of the theoretical transform limit. This technique significantly reduces the pulse duration and the temporal prepulse energy of the pulse while increasing the peak intensity by 26%. It is demonstrated, for what is believed to be the first time, that the problem of pedestals in laser amplifiers can be addressed by spectral-domain correction.     

Stationary rescaled pulse in dispersion-decreasing fiber for pedestal-free pulse compression

By using the concept of a stationary rescaled pulse (SRP), we analyze an adiabatic soliton compression system based on dispersion-decreasing fiber (DDF). We show that a SRP can exist in a DDF with a linearly decreasing dispersion profile and that the SRP resembles a linearly chirped sech2 pulse. According to the analysis, we show numerically that pedestal-free pulse compression is possible by using the SRP.     

Multiwavelength pulse generator using time-lens compression

We demonstrate a novel method of generating a multiwavelength pulse train by use of time-lens compression. In addition to pulse compression, this time lens simultaneously displaces the pulses according to their center wavelengths, resulting in a temporally evenly spaced multiwavelength pulse train. We further demonstrate a new aberration-correction technique based on the temporal analog of a spatial correction lens to improve the quality of the compressed pulses. Through the use of cw distributed-feedback lasers and electro-optic phase modulators, the all-fiber system allows complete tunability of temporal spacing, spectral profile, and repetition rate.     

全固态高重复频率磁脉冲压缩发生器

设计制作了全固态高重复频率磁脉冲压缩发生器,最高重复频率5 kHz,脉宽70 ns,通过调节初始储能电容上的电压可在500 阻性负载上获得4~40 kV连续可调的输出电压。通过分析简化的磁压缩末级回路,分析了预脉冲产生的过程,得出了预脉冲的电压表达式,选取适当的磁芯相对磁导率,经过求解,得出在磁开关未饱和电感一定时预脉冲随负载阻值变化的曲线簇,从曲线中可以看出：随着负载的阻值的增大,预脉冲的峰值绝对值也增大;在负载恒定的情况下,增大磁开关未饱和电感的大小可以显著地减小负载两端预脉冲的峰值绝对值,这要求磁开关磁芯有更高的相对磁导率。     

高功率微波脉冲压缩技术实验研究

 建立了利用储能切换法实现微波脉冲压缩的实验装置并进行了实验研究。在输入脉冲功率为2.7MW,脉冲宽度为1.4μs的情况下,脉冲压缩功率增益近40,输出微波脉冲功率为106MW,脉宽为13～14ns。实验结果表明输出功率增益与气压和气体成分没有明显的联系,气体击穿的分散性可能是导致输出功率增益波动的主要原因。     

高功率微波脉冲压缩技术实验研究

建立了利用储能切换法实现微波脉冲压缩的实验装置并进行了实验研究。在输入脉冲功率为2.7MW,脉冲宽度为1.4μs的情况下,脉冲压缩功率增益近40,输出微波脉冲功率为106MW,脉宽为13～14ns。实验结果表明输出功率增益与气压和气体成分没有明显的联系,气体击穿的分散性可能是导致输出功率增益波动的主要原因。     

Microwave pulse compression using diffraction gratings

Electromagnetic pulse compressors employing gratings of high breakdown strength in the autocollimation regime at the center frequency of the pulse for p polarization are investigated theoretically. A theory is devised on the basis of a numerical solution of the electromagnetic field equations in an integral-equation formulation. The case of the aberrationless approximation of the compression of a bell-shaped pulse with a quadratically modulated phase is considered analytically. A numerical experiment demonstrates the presence of strong distortions in the pulse after compression, which are caused by the cubic and higher terms in the expansion of the frequency dependence of the phase acquired by the wave in the compressor. The conditions for optimal pulse compression with allowance for aberrations are investigated. Zh. Tekh. Fiz. 68, 82–90 (February 1998)     

全固态高重复频率磁脉冲压缩发生器

设计制作了全固态高重复频率磁脉冲压缩发生器,最高重复频率5 kHz,脉宽70 ns,通过调节初始储能电容上的电压可在500 阻性负载上获得4~40 kV连续可调的输出电压。通过分析简化的磁压缩末级回路,分析了预脉冲产生的过程,得出了预脉冲的电压表达式,选取适当的磁芯相对磁导率,经过求解,得出在磁开关未饱和电感一定时预脉冲随负载阻值变化的曲线簇,从曲线中可以看出:随着负载的阻值的增大,预脉冲的峰值绝对值也增大;在负载恒定的情况下,增大磁开关未饱和电感的大小可以显著地减小负载两端预脉冲的峰值绝对值,这要求磁开关磁芯有更高的相对磁导率。