液芯光纤喇曼光谱的研究

本文叙述了利用液芯光纤技术获得最佳自发喇曼光谱的方法和条件。用16mW He-Ne激束为泵光浦源,获得了较高强度的溴苯自发喇曼光谱。首次用测量喇曼信号强度的方法,计算出光纤衰损系数α,从而获得了最大喇曼光谱所对应的最佳光纤长度。本文以15OmW Ar离子(488nm)激光器为光源,用Spex1403喇曼系统,得到了丰富的溴苯喇曼光谱,比用普通方法获得的喇曼光谱强度高两个数量级。实验结果与理论计算基本符合。     

Tunable and low bending loss of liquid-core fiber

The liquid-core fiber with relatively high refractive index difference between the core and cladding is proven to be bending insensitive. The single mode condition and bending loss of the fiber with a mixture of toluene and chloroform as its core material are studied. The results show that the bending loss of this fiber is not only much smaller than the conventional silica single mode fiber but also can be tuned by the temperature and liquid mixture ratio. This kind of fiber may find its potential applications in all-optical network.     

四磺酸基苯基卟啉荧光增强苯的高阶受激拉曼散射

报道了在液芯光纤内利用四磺酸基苯基卟啉荧光增强苯的高阶受激拉曼散射实验研究. 实验表明:利用荧光效应显著增强苯的高阶受激拉曼谱线的强度;高阶Stokes谱线的阈值明显降低;随着Stokes谱线阶数的增加,Stokes谱线宽度变窄. 用3.55 mJ小能量激光实现了液芯光纤内生物分子荧光增强受激拉曼散射. 此技术对实现宽带受激辐射、种子激光、生物大分子结构研究和生物分子的非生物利用等领域有广阔的应用前景. 关键词： 受激拉曼散射 荧光 液芯光纤     

多模液芯光纤干涉的实验研究

本文介绍了多模液芯光纤干涉的一些性质,干涉条纹的最大可见度条件.给出了干涉传感的二种测量结果.     

Asymmetrical spectral broadening of SRS and its temperature dependence in a phenylethanol liquid-core wave-guide optical fiber

Spectral broadening of stimulated Raman scattering has been studied in a phenylethanol liquid-core wave-guide optical fiber by using a frequency-doubled Q-switched Nd: YAG laser. Four orders of Stokes lines were observed. All the Stokes lines were asymmetrically broadened favoring the lower frequencies. Both the red-shifted broadening and the blue-shifted broadening increased with the rise of the temperature of the Raman medium. The asymmetric broadening was discussed to be mainly due to the effect of the cascaded stimulated Rayleigh-wing scattering.     

液芯光纤方法研究溶剂对分子拉曼光谱强度的影响

液芯光纤可以大幅度提高拉曼光谱强度. 本文用液芯光纤方法测量了CCl4 在CS2 和C6H5Br中不同浓度下459 cm-1,314 cm-1和218 cm-1的拉曼光谱强度,验证了一些溶剂使某些分子拉曼光谱增强的溶剂效应.     

Stimulated Raman Stokes scattering influenced by all-trans-β -carotene in liquid-core optical fiber

We demonstrate stimulated Raman Stokes (SRS) scattering of carbon disulfide (CS₂) influenced by a natural dye named all-trans-β-carotene in a liquid-core optical fiber (LCOF). These Stokes emissions can acquire the extra effects of seeding or suppression, both of which result from the optical properties of the carotenoids. Then, the efficient control of the selective developments of the Stokes lines by the natural dyes is available in LCOFs. Especially, the low threshold of the high-order Stokes lines, such as the 2nd Stokes line of CS₂, can be more easily obtained through the seeding effect. The saturation intensity of the 1st Stokes line can be suppressed more when the concentration of all-trans-β-carotene in CS₂ becomes high. Simultaneously, the threshold of the 1st Stokes line increases with the addition of the carotenoids. This result is expected to be worthy of new SRS-based fiber light sources for bio-medicine applications such as photodynamic therapy.     

苯乙醇液芯光纤受激喇曼散射的红移和蓝移展宽

本文首次用调QYAG激光器的倍频光(λ=532.1nm)在苯乙醇液芯光纤中产生受激喇曼散射,观察到了4阶斯托克斯线和2阶反斯托克斯线.讨论了引起红移为主的斯托克斯线展宽的原因.     

偏振光纤中受激四光子混频及其应用

本文给出了双折射光纤中不同模式和偏振组合时受激四光子混频的频移和双折射的关系。文中对正交分泵受激四光子混频应用于光纤总色散的测量进行了实验研究。     

Reduced threshold of a stimulated four-wave mixing process in an optical fiber

The possibility for all-optical control of the effective parametric Stokes gain was demonstrated in an optical fiber. For the first time the threshold reduction induced by the interference of two different four-wave mixing processes which share a common Stokes wave was used as a control mechanism.     

Nondegenerate four-wave mixing in a birefringent optical fiber pumped by a dye laser

An efficient nondegenerate four-wave-mixing process in a highly birefringent optical fiber pumped by a dye laser is reported. The output beam from a dye laser (at ~610 nm) was found to mix with the accompanying superfluorescent light (from 575 to 600 nm) in a birefringent fiber to generate a distinct frequency-shifted beam, which could be Stokes or anti-Stokes radiation, depending on which mode of the fiber was excited. The frequency shift was comparable with that observed in the well-known pump-divided degenerate process, as confirmed by the theory.     

Terahertz-wave generation by surface-emitted four-wave mixing in optical fiber

We propose a novel terahertz-wave source through the four-wave mixing effect in a conventional single-mode optical fiber pumped by a dual-wavelength laser whose difference frequency lies in the terahertz range. Surface-emitted geometry is employed to decrease absorption loss. A detailed derivation of the terahertz-wave power expression is presented using the coupled-wave theory. This is a promising way for realizing a reasonable narrow-band terahertz-wave source.     

Observation of photoacoustic/photothermal effect with a liquid-core optical ring resonator

Photothermal/photoacoustic(PT/PA) spectroscopy provides useful knowledge about optical absorption, as well as the thermal and acoustical properties of a liquid sample. For microfluidic biosensing and bioanalysis where an extremely small volume of liquid sample is encapsulated, simultaneous PT/PA detection remains a challenge. In this work, we present a new optofluidic device based on a liquid-core optical ring resonator(LCORR) for the investigation of PT and PA effects in fluid samples. A focused 532 nm pulsed light optically heats the absorptive fluid in a capillary to locally create a transient temperature rise, as well as acoustic waves. A1550 nm CW laser light is quadrature-locked to detect the resonance spectrum shift of the LCORR and study thermal diffusion and acoustic wave propagation in the capillary. This modality provides an optofluidic investigative platform for biological/biochemical sensing and spectroscopy.     

Necessary conditions for nonlinear excitation of a high-order mode in a single-mode optical fiber

The necessary conditions for nonlinear excitation of higher-order modes in a single-mode step-index optical fiber are analyzed. The cutoff conditions for such an optical waveguide are investigated taking into account Kerr nonlinearity. The minimal power of optical pulses required for fulfilling the necessary conditions for nonlinear excitation of higher-order modes in a single-mode step-index fiber is calculated as a function of the normalized frequency. The allowed ranges of variation of the normalized frequency and optical-radiation power are estimated. It is demonstrated that the conditions necessary for nonlinear excitation of a higher-order mode in a step-index single-mode optical fiber can be created for optical pulses shorter than 500 fs.     

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber has been observed. It is shown that in a nonbirefringent single-mode fiber the phase matching that is necessary for stimulated four-wave mixing can be accomplished with a combination of self-phase modulation and cross-phase modulation induced by a pump-laser pulse.     

Stimulated rayleigh-kerr and raman-kerr scattering in a liquid-core hollow fiber system

By using a liquid-core multimode hollow fiber system with a long gain-length (2.5 or 7 m), a superbroadening stimulated scattering added to the pump line and/or the several orders of Stokes-stimulated Raman scattering lines of the core medium can be observed. This kind of stimulated scattering is related to the optical Kerr (reorientation) effect and Raman-induced Kerr effect in a liquid consisting of anisotropic molecules. Experimental studies of hollow fiber filled with different liquid samples (carbon disulfide, benzene, carbon tetrachloride) are reported. A theoretical approach based on a photon scattering model of optical Kerr effect and Raman-induced Kerr effect is proposed to explain the principal features of our experimental results. The significance of stimulated Kerr scattering studies and their potential applications are discussed.     

Investigations of Yb-doped optical fiber using selective laser excitation

The method of tunable site-selective laser excitation was used for a study of the spectral and fluorescence characteristics of Yb³⁺ optical centers in laser optical fiber. Decay curves and positions of fluorescence spectra maxima at different wavelengths of selective laser excitation and positions of excitation spectra maxima at different fluorescence selective registration provide new information on lifetimes and Stark energy distribution among inhomogeneously broadened Yb³⁺ lines. The obtained Stark splitting energy distribution diagram demonstrates the tuneability of Yb³⁺ laser oscillation wavelength under tunable excitation of a pump laser.     

Action potential-induced fluorescence changes resolved with an optical fiber carrying excitation light

With the use of a single, implantable, optical fiber, to excite fluorescence and detect changes from voltage-sensitive dyes, transmembrane potential changes were measured without the need for a clear line-of-sight path between the excitation light, the tissue, and the detector. In a previous study, we were required to use signal averaging and could detect only cardiac action potentials from frog. In the present study we improved this system so that unaveraged cardiac action potentials were resolved with high fidelity, and action potentials from single nerve axons were detected. Endeavors to optimize the signal-to-noise ratio resulted in the selection of a larger core fiber with a rounded tip, styryl dyes, and filters based upon fluorescence spectra of the dyes when bound to membrane (rather than in solution). The frog gave signals nearly comparable in magnitude and signal-to-noise ratio to those seen with systems that use a fluorescence microscope. Action potential-induced signals could be detected in single lobster axons with the intracellular injection of a dye. The improvement in the signal-to-noise ratio allowed the use of a reduced-intensity excitation illumination which produced less bleaching of the dye.     

Performance study of a liquid-core Bragg fiber sensor in presence of a defect layer

Performance parameter of a Bragg fiber waveguide based resonant sensor in presence of a defect layer in cladding regions is theoretically studied. The Bragg fiber waveguide consists of a liquid-core surrounded by alternate high and low refractive indices materials in cladding regions. Reflectivity of the proposed waveguide based resonant sensor is formulated using transfer matrix method for a non-homogeneous multilayer cylindrical system. The waveguide shows a band gap region with a narrow defect mode in the band gap region under the considered wavelength range. Instead of taking a whole band gap as a sensing signal, here the defect peak is taken as the sensing signal. It is observed that the intensity of defect mode is more sensitive for core refractive index than the intensity of traditional band gap region (lobe). This study shows that the higher sensitivity can be achieved by creating the defect at a position in cladding region where the intensity of transmitted light lies between 40% and 90%. Presence of a defect layer is able to increase the detection accuracy of the sensor and, hence increase the overall performance of this sensor.     

Selective excitation and coupling of high-order optical modes of a microstructured optical fiber by using a fiber-end microtip

We present the selective excitation and coupling of high-order optical modes in microstructured optical fibers (MOFs) by using a fiber-end microtip. After the self-growing of a microtip on the end face of a standard single-mode fiber, it is demonstrated that a fine tuning of the relative displacement between the microtip and MOF can greatly improve the excitation and coupling efficiency of high-order optical modes of the MOF. A 6.85?dB improvement in coupling efficiency of the second-order mode of a homemade small-hole MOF is experimentally achieved, and a sensitivity-enhanced measurement of the refractive index in MOF microholes is demonstrated.