Spectral-interferometric study of nonlinear-spectronic similariton

By means of spectral interferometry we study properties of similaritons formed in a single-mode optical fiber without gain. Nonlinear-spectronic character of such similaritons leads to linearization of their chirp and spectral-temporal similarity, which may be useful for applications in ultrafast optics.     

基于10 m光子晶体光纤的放大自相似锁模振荡器研究

基于单根10 m大模场面积保偏光子晶体光纤, 搭建了带有色散图的放大自相似振荡器; 通过仔细调节腔内色散量的大小以及位于色散补偿端的端镜前的狭缝位置和大小, 实现了稳定的锁模运转, 获得了抛物线形脉冲输出. 输出脉冲的重复频率为8.6 MHz, 脉冲宽度为6.2 ps, 光谱宽度为3.84 nm, 平均功率820 mW, 对应单脉冲能量95 nJ. 这是第一次在自相似振荡器中直接获得重复频率在10 MHz 以下的脉冲输出, 95 nJ也是目前自相似振荡器直接输出的最高脉冲能量. 通过数值模拟证实了在第一个光栅的零级反射处和狭缝滤波后可以分别实现抛物线型脉冲和高斯脉冲的两种锁模脉冲输出.     

Asymptotic characteristics of parabolic similariton pulses in optical fiber amplifiers

The fundamental asymptotic nature of parabolic similariton pulses in normal-dispersion fiber amplifiers is experimentally demonstrated. With frequency-resolved optical gating characterization measurements with a fixed input pulse energy, the output parabolic pulse characteristics are shown to be invariant with the input pulse profile and duration and to be completely determined only by the amplifier parameters.     

Regenerative 40 Gbit/s wavelength converter based on similariton generation

We present an all-optical regeneration technique based on spectral filtering of self-similar parabolic pulses (similaritons). In particular, we demonstrate numerically and experimentally that ghost pulses, which occur in the zero bit slots of telecommunication pulse trains, can be effectively suppressed. These results are obtained with a 40 Gbit/s pulse train.     

Diagnostics of femtosecond laser pulses based on generation of nonlinear-dispersive similariton

We propose and test experimentally a method, alternative to the autocorrelation technique, for determination of the duration of femtosecond laser pulses. The method is based on generation of nonlinear-dispersive similariton in a passive optical fiber (without gain) and measuring its spectral width (or duration) determined by the power of the initial pulse.     

Experimental demonstration of similariton pulse compression in a comblike dispersion-decreasing fiber amplifier

Self-similar propagation of linearly chirped hyperbolic-secant pulses in a comblike decreasing-dispersion fiber amplifier has been observed experimentally for the first time to our knowledge. The scheme takes advantage of an exact solution of the generalized nonlinear Schr?dinger equation with distributed coefficients.     

Analytic investigation on the similariton transmission control in the dispersion decreasing fiber

By means of the similarity transformation, we discuss the generalized nonlinear Schrödinger equation exhibiting inhomogeneous dispersion, nonlinearity and gain or loss at the same time. Explicit bright and dark multi-similariton solutions are obtained. Based on them, we investigate transmission control using the dispersion decreasing fiber with potential applications to the design of high-speed optical devices and amplifiers and pulse compressors, and the development of tunable sources of amplitude modulated light.     

Self-phase modulation via similariton solutions of the perturbed NLSE Modulation instability and induced self-steepening

The perturbed nonlinear Schrodinger equation (PNLSE) describes the pulse propagation in optical fibers, which results from the interaction of the higher-order dispersion effect, self-steepening (SS) and self-phase modulation (SPM). The challenge between these aforementioned phenomena may lead to a dominant one among them. It is worth noticing that the study of modulation instability (MI) leads to the inspection of dominant phenomena (DPh). Indeed, the MI triggers when the coefficient of DPh exceeds a critical value and it may occur that the interaction leads to wave compression. The PNLSE is currently studied in the literature, mainly on finding traveling wave solutions. Here, we are concerned with analyzing the similarity solutions of the PNLSE. The exact solutions are obtained via introducing similarity transformations and by using the extended unified method. The solutions are evaluated numerically and they are shown graphically. It is observed that the intensity of the pulses exhibits self steepening which progresses to shock soliton in ultra-short time (or near t = 0). Also, it is found that the real part of the solution exhibits self-phase modulation in time. The study of (MI) determines the critical value for the coefficients of SS, SPM, or high dispersivity to occur.     

Broadband terahertz spectroscopy

An overview of the major techniques to generate and detect THz radiation so far,especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser,has been presented.And also,this paper,in particularly,focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy (THz-TDS) with the help of ultra-short pulsed laser.The time-dom...     

Broadband interference filters

The characteristics of two-component broadband interference filtering coatings are calculated for the middle-infrared spectral range. Up to now, these characteristics have been obtained only for four-component interference coatings.     

Broadband space-variant Fresnel processor

We present a radically new class of optical setup working with white-light illumination, namely, a chromatically compensated processor operating in the Fresnel domain. The optical configuration is a hybrid (diffractive-refractive) three-lens system that exhibits an intermediate achromatic Fresnel plane and an output image plane without chromatic distortion. As a first application of this optical arrangement we develop a parallel space-variant color pattern-recognition experiment with white light.     

光学薄膜的宽带膜厚监控装置

装置是由配有微机的快速扫描分光光度计组成,在镀膜时不断测量膜层的光谱透射率曲线以监控膜厚,并作了监控三层膜的试验。 装置的性能:测量波长宽度333nm;波长点数:50点;透射率精度:±1％;光谱透射率扫描速度:12c/s。     

声学宽带多焦点聚焦

针对声学宽带多焦点聚焦的问题,设计出结构简洁的声学人工结构。通过控制细槽深度,对反射声波的波前进行任意操控。数值仿真结果验证了所设计的声人工结构的聚焦效果。这种人工结构还允许对焦点的相对位置及数目进行精确而自由的调控,当尺寸大于波长的障碍物存在时仍可通过合理设计来产生聚焦效果。该方案具有设计简洁及焦点可控等优点,有望在生物医学及无损检测等场合产生广泛应用。     

Broadband attosecond pulse shaping

We use semiconductor (Si) and metallic (Al, Zr) transmission filters to shape, in amplitude and phase, high-order harmonics generated from the interaction of an intense titanium sapphire laser field with a pulsed neon gas target. Depending on the properties of the filter, the emitted attosecond pulses can be optimized in bandwidth and/or pulse length. We demonstrate the generation of attosecond pulses centered at energies from 50 to 80 eV, with bandwidths as large as 45 eV and with pulse durations compressed to 130 as.     

宽带光子晶体插分滤波器

 通过使用正方格介质柱二维光子晶体设计了带有环形谐振器的一种插分滤波器ADF(add drop filter)结构,该结构具有1个输入端口和2个输出端口,采用时域有限差分法研究了带有1个环形谐振器和2个环形谐振器的ADF结构传输性能。结果表明：该ADF结构在第三通信窗口具有优良的滤波作用,能够根据需要将电磁波信号沿着波导向前后上下4个方向传输,ADF结构还具有可调性开关波长、宽频带、高传输率等特点,在光子晶体集成化、光器件制作等方面具有潜在价值。     

Broadband optimal contrast resolution beamforming

This paper proposes a novel receive beamformer architecture for broadband imaging systems that uses unique finite impulse response (FIR) filters on each channel. The conventional delay-and-sum (DAS) beamformer applies receive apodization by weighting the signal on each receive channel prior to beam summation. Our proposed FIR beamformer passes the focused receive radio frequency (RF) signals through multi-tap FIR filters on each receive channel prior to summation. The receive FIR filters are constructed to maximize the contrast resolution of the system’s spatial response. The broadband FIR beamformer produces spatial point spread functions (PSFs) with narrower mainlobe widths and lower sidelobe levels than spatial PSFs produced by the conventional DAS beamformer.We present simulation results showing that FIR filters of modest tap lengths (3-7) can yield marked improvement in image contrast and point resolution. Specifically we show that 7-tap FIR filters can reduce sidelobe and grating lobe energy by 30 dB and improve contrast resolution by as much as 20 dB compared to conventional apodization profiles. This improvement in contrast resolution comes at the expense of a decrease in beamformer sensitivity. We investigate the effects of phase aberration and show in simulation results that the multi-tap FIR beamformer outperforms the unaberrated DAS beamformer by 8-12 dB even in the presence of moderate aberration characterized by a root-mean-square strength of 28 ns and a full-width at half-maximum correlation length of 3.6 mm. We show experimental results wherein multi-tap FIR filters decrease sidelobe energy in the resulting 2D spatial response while achieving a narrow mainlobe. We also show results where the FIR beamformer improves the contrast to noise ratio (CNR) in simulated B-mode cyst images by more than 4 dB. Our algorithm has the potential to significantly improve ultrasound beamforming in any application where the system response is reasonably well characterized. Furthermore, this algorithm can be used to increase contrast and resolution in one-way beamforming systems such as acousto-optic and opto-acoustic imaging.