Coherent-mode representation of partially coherent imagery

A new method for calculating image intensity distribution in partially coherent illumination is described. The method is based on the coherent-mode representation of the cross-spectral density function of illumination field and allows considerable reduction of the computational effort needed for image intensity calculation in comparison with the direct method. The computational efficiency of the method is larger the more coherent is the illumination in a global sense. An example of calculating image intensity for Schell-model illumination is compared with theoretical results.     

复宗量厄米-高斯光束的相干模表示

基于激光的相干模分解理论，讨论了复宗量厄米_高斯(EHG)光束的模相关和相干模表示，推导出EHG光束的模相关系数的解析表达式，并给出了一种只包含有限个模式的相干模表示. 在此基础上，根据EHG光束的模结构，分析了EHG光束和常规厄米_高斯(SHG)光束M²因子的差异. 关键词： 复宗量厄米_高斯(EHG)光束 相干模分解 2因子')" href="#">M²因子 模相关系数(MCCs)     

Coherent-mode representation and orbital angular momentum spectrum of partially coherent beam

Orbital angular momentum of the coherent beam has been intensively studied and promises potential applications in free space optical communication. But the orbital angular momentum of partially coherent beam is not well known. In this communication the coherent-mode representation method is adopted to describe the partially coherent beam and the orbital angular momentum spectrum is introduced for the partially coherent beam. The characteristics of the orbital angular momentum spectrum of partially coherent beam are discussed. To study the influence of the partial coherence on the optical link, the channel capacity is studied, with two kinds of available mode separators included.     

Laguerre-Gaussian supercontinuum

We show what is believed to be the first coherent white-light optical vortices generated from supercontinuum that have the azimuthally varying phase structure consistent with a monochromatic Laguerre-Gaussian beam. Two methods of Laguerre-Gaussian supercontinuum generation are discussed and contrasted. We use a computer-generated hologram to convert a Gaussian white-light supercontinuum source into Laguerre-Gaussian supercontinuum.     

Visible cw-pumped supercontinuum

We report the experimental demonstration of a visible supercontinuum in the cw pumping regime. A 20 W ytterbium fiber laser at 1.06 microm is used to pump a photonic crystal fiber whose zero-dispersion wavelength decreases along the fiber length. Visible wavelengths are generated in the fundamental mode via trapping of dispersive waves by redshifted solitons.     

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.     

All-fiber Raman supercontinuum generator

The results on an all-fiber supercontinuum generator that exhibits a continuous wide spectrum in the range 1060–1640 nm predominantly owing to the cascade stimulated Raman scattering in a single-mode quartz fiber at a relatively high power of the combined femtosecond-picosecond pumping with a central wavelength of 1080 nm are presented for the first time. The mean power of the supercontinuum is 2.1 W.     

70 W全光纤超连续谱光源

超连续谱光源在很多领域具有广泛而重要的应用,过去40多年一直是国际研究热点之一。但一方面由于普通双包层光纤与光子晶体光纤模场不匹配会导致较高的熔接损耗和耦合损耗;另一方面受高质量超快光纤脉冲激光器输出平均功率的限制,目前超连续谱光源的最高输出平均功率只有50 W。报道了一种全光纤结构的超连续谱光源,输出平均功率为 70 W。由于整个装置采用一种新的超连续谱形成机制,较好解决了普通双包层光纤与光子晶体光纤由于模场不匹配导致的较高熔接损耗和耦合损耗;降低了对脉冲泵浦源光谱质量的要求。     

70 W全光纤超连续谱光源

 超连续谱光源在很多领域具有广泛而重要的应用,过去40多年一直是国际研究热点之一。但一方面由于普通双包层光纤与光子晶体光纤模场不匹配会导致较高的熔接损耗和耦合损耗;另一方面受高质量超快光纤脉冲激光器输出平均功率的限制,目前超连续谱光源的最高输出平均功率只有50 W。报道了一种全光纤结构的超连续谱光源,输出平均功率为 70 W。由于整个装置采用一种新的超连续谱形成机制,较好解决了普通双包层光纤与光子晶体光纤由于模场不匹配导致的较高熔接损耗和耦合损耗;降低了对脉冲泵浦源光谱质量的要求。     

Femtosecond supercontinuum characteristics control

Supercontinuum generation in the spectral range 530–1100 nm in series of photonic-crystal fibers pumped by femtosecond Ti:S laser Mira Oprima 900-F is achieved. The evolution of spectral characteristics of femtosecond supercontinuum is proofed to be dependent on pump pulse wavelength and power radiation. Polarization characteristics of supercontinuum spectral components are analyzed. We demonstrated experimentally the possibility of control of femtosecond supercontinuum generation.     

High average power supercontinuum sources

The physical mechanisms and basic experimental techniques for the creation of high average spectral power supercontinuum sources is briefly reviewed. We focus on the use of high-power ytterbium-doped fibre lasers as pump sources, and the use of highly nonlinear photonic crystal fibres as the nonlinear medium. The most common experimental arrangements are described, including both continuous wave fibre laser systems with over 100 W pump power, and picosecond mode-locked, master oscillator power fibre amplifier systems, with over 10 kW peak pump power. These systems can produce broadband supercontinua with over 50 and 1 mW/nm average spectral power, respectively. Techniques for numerical modelling of the supercontinuum sources are presented and used to illustrate some supercontinuum dynamics. Some recent experimental results are presented.     

Tunable spectral enhancement of fiber supercontinuum

We demonstrate tunable spectral enhancement of the supercontinuum generated in a microstructured fiber with a fiber long-period grating. The long-period grating leads to phase distortion and loss that, with subsequent high-intensity propagation in uniform fiber, evolves into an enhancement around the grating's resonant wavelengths. Wavelength tunability is achieved by varying the temperature or the ambient refractive index, and the spectral peak can be extinguished by immersing the grating in index-matching oil.     

Coherent fiber supercontinuum for biophotonics

Biophotonics and nonlinear fiber optics have traditionally been two independent fields. Since the discovery of fiber‐based supercontinuum generation in 1999, biophotonics applications employing incoherent light have experienced a large impact from nonlinear fiber optics, primarily because of the access to a wide range of wavelengths and a uniform spatial profile afforded by fiber supercontinuum. However, biophotonics applications employing coherent light have not benefited from the most well‐known techniques of supercontinuum generation for reasons such as poor coherence (or high noise), insufficient controllability, and inadequate portability. Fortunately, a few key techniques involving nonlinear fiber optics and femtosecond laser development have emerged to overcome these critical limitations. Despite their relative independence, these techniques are the focus of this review, because they can be integrated into a low‐cost portable biophotonics source platform. This platform can be shared across many different areas of research in biophotonics, enabling new applications such as point‐of‐care coherent optical biomedical imaging.     

All-fiber high-energy supercontinuum pulse generator

An all-fiber supercontinuum generator with a record-high pulse energy of 40 μJ is presented. The generator is based on a nanosecond ultralong high-energy mode-locked Yb-doped fiber laser with an additional amplification stage. The supercontinuum spectrum belongs to the wavelength range 500–1750 nm, and a relatively uniform spectral distribution of the intensity is observed in the interval 1125–1550 nm. The mean power of the supercontinuum is greater than 1.5 W. The simulation of such a generator yields the integrity of the supercontinuum pulse on the nanosecond time scale and shows that the pulse can be characterized by a certain energy in contrast to the multipulse complicated trains of supercontinuum corresponding to the femtosecond and picosecond pumping.     

Coherence properties of the supercontinuum source

Mutual–temporal coherence of the supercontinuum (SC) generation has been experimentally investigated using a diffraction grating based interferometer. A broadband SC generation was produced in a pyrex glass plate with a 1.6-μm coherence length at 550-nm center wavelength. The degree of mutual coherence of 0.34 was measured for a wavefront shift for zero and first diffraction orders of half of the beam diameter. A design of SC source with the capability of manipulating the amplitudes and phases of optical frequency components within the SC pulse is presented for coherence applications.     

177.6 W全光纤超连续谱光源

超连续谱光源在众多科学领域具有广泛而重要的应用, 近年来一直是国际研究热点. 回顾了利用连续光激光器和脉冲光激光器抽运光子晶体光纤产生超连续谱光源的形成机制以及近几年来两种机制下高功率超连续谱光源所取得的进展, 分析了在提高超连续谱光源输出平均功率过程中需要克服的难题. 报道了国防科学技术大学通过优化超连续谱光源的整体结构, 攻克了低损耗熔接、光纤端面抗损伤、热处理以及非线性效应的有效控制等关键技术, 成功研制出一种全光纤结构、输出平均功率为177.6 W的超连续谱光源, 光谱范围覆盖1064-2000 nm, 10 dB光谱带宽约740 nm, 光-光转换效率高达56%, 功率水平为国际领先.     

7 W all-fiber supercontinuum source

Combine a section of photonic crystal fiber and a picosecond fiber laser to realize an all-fiber supercontinuum source. The picosecond laser exhibits 20 W average output power, 14 ps pulse duration at 480MHz repetition rate. Approximately 7 W supercontinuum with over 1100 nm spectral range is obtained with an optical-optical conversion efficiency of 34%. Further improvements for higher average power are discussed in this paper.     

Spectral anomalies in supercontinuum focused waves

The diffraction-induced spectral anomalies in the focal plane of an apertured spherical wave with supercontinuum flat-top power spectrum are investigated. Coherent broadband radiation (also incoherent white light) demonstrates a strong blue shift in the vicinity of the optical axis, and discrete spectral gaps with overall red shift arise out of this central region. Unlike narrow-band light, the spectral switch effect fades away with ultra-broad spectra.     

Few-cycle solitons in supercontinuum generation dynamics

We review several propagation models that do not rely on the slowly-varying-envelope approximation (SVEA), and can thus be considered as fundamental models addressing the formation and propagation of few-cycle pulsed field structures and solitary waves arising in the course of intense ultrashort optical pulse evolution in nonlinear media and beyond octave-bandwidth optical spectrum broadening. These generic models are: the modified-Korteweg-de Vries (mKdV), the sine-Gordon (sG), and the mixed mKdV-sG equations. To include wave polarization dynamics, the vector extensions of both mKdV and sG equations are introduced. Multi-octave-spanning supercontinuum generation and few-cycle soliton structures are highlighted from numerical simulations.     

Fiber supercontinuum generator with wavelength-tunable pumping

The initial results of the experimental and numerical study of a fiber supercontinuum generator based on a wavelength-tunable femtosecond Yb:KYW laser are presented. It is demonstrated that a variation in the pumping wavelength in the vicinity of the zero-dispersion wavelength of a microstructured fiber at about 1040 nm allows for a wide-range variation in the supercontinuum spectral width at a constant mean pumping power. The experimentally measured strong dependence of the supercontinuum spectral width (from 70 to 390 nm) on the pumping wavelength (1040–1049 nm) at a pulse energy of about 1 nJ and a pulse duration of 250 fs is qualitatively reproduced in the simulation.