Surface wave effect on light scattering from one-dimensional photonic crystals

Light scattering and reflection measurements using attenuated total reflection technique for s polarization of the incident light on a finite one-dimensional photonic crystal are reported. Angular specular reflection was measured experimentally to determine, the optimum thickness, the angular position of the surface mode, and the number of bi-layers of the system. It was demonstrated that the position of the surface mode inside the last film is close to the asymptotic value when the number of periods is increased. Spectral reflection measurements were made to determine experimentally the band gap width and measure the dispersion relation of the surface mode inside this band. The corresponding field amplitude was calculated (∣E∣²) showing that in resonant conditions it has a maximum near the surface. The angular dependence of the scattered light measured displays a peak caused by singles cattering and located approximately at the excitation angle of the surface electromagnetic mode. When the incident light is in resonance with the surface electromagnetic wave, it is found experimentally that the scattering of light is enhanced overall by approximately one order of magnitude in comparison with the off-resonance case.     

Waveguides formed by incoherent dark solitons

We demonstrate experimentally optical guidance of coherent light beams, using incoherent light. Such guidance is made possible by generation of partially spatially incoherent self-trapped dark beams (dark incoherent solitons) in a noninstantaneous nonlinear medium. In the one-dimensional case, the incoherent solitons induce single and Y-junction planar waveguides, whereas in the two-dimensional case, they form circular waveguides. These experiments introduce the possibility of controlling high-power laser beams with low-power incoherent light sources such as LED's or lightbulbs.     

A temporal-coherence anisotropy of unpolarized light

We analyze the anisotropic behavior of unpolarized, temporally partially coherent light. We demonstrate that unpolarized light with different intrinsic degrees of coherence can present an anisotropic behavior which is experimentally observable while it is not the case if both intrinsic degrees are equal. This behavior is analyzed in comparison with the standard anisotropy property of partially polarized light.     

Multi-point abnormal-temperature warning sensor system with?different thresholds

We propose and experimentally demonstrate a time-division-multiplexing-based (TDM-based) multi-point abnormal-temperature warning sensor system with different thresholds. A multi-channel fiber Bragg grating (FBG) serving as the wavelength selector is employed in the fiber ring laser to generate a multi-wavelength pulsed light source. The sensor array is composed of multiple uniform sensing FBGs at different positions and with different nominal wavelengths. The warning signal is obtained by only monitoring the time slot between the injected pulse and the reflected pulse. The measurement range and resolution are theoretically discussed and experimentally demonstrated.     

Band-structure determination for finite 3-D photonic crystals

The partial band structure from a finite photonic crystal is determined using a model based on light diffraction and the transfer-matrix formalism. The predictions from such a model are compared to an experimental measurement of the bands in the LU direction of a face centered cubic colloidal crystal. Then, both the theoretical predictions and the experimental measurements are compared with the usual band-structure calculation based on a plane-wave expansion with perfectly periodic boundary conditions. As in measurements performed in the past, discrepancies between the predictions of this later model and the experimentally determined bands are observed. On the contrary, using the model presented based on light propagation through a finite crystal, where no periodicity is imposed in the direction perpendicular to any of the set of planes considered to determine a specific branch of the band structure, we found a very good agreement between the experimentally determined and the predicted bandwidths.     

Prompt light particle emission in the 36Ar + 58Ni reaction at 95 MeV/nucleon

The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function of impact parameter. The results are compared with experimental data from the ³⁶Ar + ⁵⁸Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity. Received: 27 July 2000 / Accepted: 20 November 2000     

Cross spectral purity and its influence on ghost imaging experiments

Pseudo-thermal light has been widely used in ghost imaging experiments. In order to understand the differences between the pseudo-thermal source and thermal source, we propose a method to investigate whether a light source has cross spectral purity (CSP), and experimentally measure the cross spectral properties of the pseudo-thermal light source in near-field and far-field zones. Moreover we present a theoretical analysis of the cross spectral influence on ghost imaging.     

Effects of recording wavelength on three-dimensional vector holograms in photoreactive liquid crystal composites

Effects of recording wavelength on the recently proposed (Sasaki, 2008) three-dimensional vector holograms, in which the optical anisotropy is three-dimensionally modulated, are presented experimentally and theoretically. The polarization states of the interference light are three-dimensionally modulated due to both the polarization interference and optical anisotropy in the recording medium. These spatial distributions of the polarization states and the resulting diffraction properties in the three-dimensional vector holograms are strongly dependent on the recording wavelength. Theoretical consideration based on the finite-difference time-domain (FDTD) method reveals the mechanism of the optical characteristics of the three-dimensional vector holograms recorded by various kinds of light sources with different wavelengths.     

Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection

A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry-Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57 ps, the timing jitter of 340 fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.     

Synchronization of mutually versus unidirectionally coupled chaotic semiconductor lasers

Synchronization dynamics of mutually coupled chaotic semiconductor lasers are investigated experimentally and compared to identical synchronization of unidirectionally coupled lasers. Mutual coupling shows high quality synchronization in a broad range of self-feedback and coupling strengths. It is found to be tolerant to significant parameter mismatch which for unidirectional coupling would result in loss of synchronization. The advantages of mutual coupling are emphasized in light of its potential use in chaos communications.     

Analysis of optical crosstalk within optoelectronic integrated circuits including lasers and photodetectors

Optical crosstalk from a 1.3 μm laser to a 1.55 μm photodiode on a single InP substrate, and its suppression within 1.3 μm/1.5 μm Y-junction transceiver OEICs, has been analyzed experimentally. The results indicate that the optical crosstalk suppression is limited by the accumulated light in the OEIC substrate coming mainly from the spontaneous emission of the integrated laser and from stray light at the laser–waveguide butt joint interface. For OEICs, integrating lasers and photodetectors, the achievable optical intra-chip crosstalk at present will be in the range of 30–40 dB at the required small die dimensions. Received: 16 May 2001 / / Published online: 23 October 2001     

Dispersion compensation properties of grating-based temporal-correlation Optical Coherence Tomography systems

This article explores specific dispersion compensation properties of an OCT set-up based on temporal correlation performed by using a diffraction grating. The linear dispersion term introduced by a glass plate with a thickness of up to 9 mm has been experimentally compensated optically through the position adjustment of the output imaging lens and for a light bandwidth of 100 nm. The dispersion compensation principle is described theoretically and results obtained experimentally are compared successfully with simulated ones. System limitations are discussed, especially regarding compensation of second orders of dispersion. Perspectives are given to achieve such a dispersion compensation.     

Generation of amplitude squeezed green light from a high efficiency PPKTP frequency doubler

We report on a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation of a home-made 1064 nm single-frequency Nd:YVO₄ laser with a periodically poled KTP crystal. A stable green power of 60 mW with a conversion efficiency of 75% was measured. Meantime, we investigate the quadrature amplitude noise of the green light at the same experimental setup and 0.6 dB green light squeezing was experimentally observed (taking into account the total detection efficiency of 58%, the squeezing should be 1.1 dB). The squeezing as a function of input power was also studied and we found qualitative agreement with theoretical prediction.     

Phase control algorithms for focusing light through turbid media

Light propagation in materials with microscopic inhomogeneities is affected by scattering. In scattering materials, such as powders, disordered metamaterials or biological tissue, multiple scattering on sub-wavelength particles makes light diffuse. Recently, we showed that it is possible to construct a wavefront that focuses through a solid, strongly scattering object. The focusing wavefront uniquely matches a certain configuration of the particles in the medium. To focus light through a turbid liquid or living tissue, it is necessary to dynamically adjust the wavefront as the particles in the medium move. Here we present three algorithms for constructing a wavefront that focuses through a scattering medium. We analyze the dynamic behavior of these algorithms and compare their sensitivity to measurement noise. The algorithms are compared both experimentally and using numerical simulations. The results are in good agreement with an intuitive model, which may be used to develop dynamic diffusion compensators with applications in, for example, light delivery in human tissue.     

Experimental study of light diffraction by standing ultrasonic wave with cylindrical symmetry

We report a new acousto-optic arrangement based on ultrasonic wave with cylindrical symmetry. The theory of light interaction with standing cylindrical ultrasonic wave is experimentally verified in the Fraunhofer region. A very good agreement of experimental results with numerical calculations based on the proposed theory is found. The diffraction pattern consists of ring-shaped diffraction orders which posses a fine structure. The time average light intensity of the whole zeroth diffraction order as a function of the Raman-Nath parameter is investigated. The modulation properties of presented system are examined by means of single photon counting technique. Finally, some potentially useful applications in the laser and fibre technology are suggested.     

色散选通复合成像光谱系统的实验研究

提出一种新的利用色散选通复合成像原理测量光谱空间分布的光学系统.对这个系统的成像质量、聚光本领和光谱带宽进行了理论和实验研究.探讨了它在荧光光谱和吸收光谱空间分布测量中的应用.     

Interaction between a dark spot and a two-dimensional nonlinear photonic lattice with fully incoherent white light

We study experimentally the interaction of a dark spot with a nonlinear photonic lattice with fully incoherent white light emitted from an incandescent bulb in the self-defocussing photovoltaic media when the dark spot is aimed at different positions of lattices with different lattice spacing. In this case a host of novel phenomena is demonstrated, including dark spot induced lattice dislocation-deformation, the annihilation of the dark spot and so on. Results demonstrate that the interaction between incoherent dark spot and photonic lattice is always attraction and the large-spacing photonic lattice is analogous to the continuous medium.     

Beaming effect from increased-index photonic crystal waveguides

We study the beaming effect of light for the case of increased-index photonic crystal (PhC) waveguides, formed through the omission of low-dielectric media in the waveguide region. We employ the finite-difference time-domain numerical method for characterizing the beaming effect and determining the mechanisms of loss and the overall efficiency of the directional emission. We find that, while this type of PhC waveguide is capable of producing a highly collimated emission as was demonstrated experimentally, the inherent characteristics of the structure result in a restrictively low efficiency in the coupling of light into the collimated beam of light.     

冷端温度对无极灯253.7nm共振谱线的影响

无极灯是一种长寿命、低汞害、无频闪的新型电光源,其光效在很大程度上取决于253.7nm共振谱线的辐射效率。通过原子发射光谱分析,实验研究了冷端温度对253.7nm共振谱线的影响规律。研究发现,253.7nm共振谱线的辐射效率随冷端温度变化近似呈正态分布,即无极灯工作存在一个最佳冷端温度。运用气体放电理论对实验结果进行了定性分析,对无极灯光效的提高具有指导意义。     

Optically-induced defect states in photonic lattices: formation of?defect channels, directional couplers, and disordered lattices leading to Anderson-like light localization

Formation of defect states by optical induction in one-dimensional photonic lattices fabricated in photorefractive lithium niobate is investigated experimentally. First, by using a moving narrow laser beam for defect recording, we investigate light propagation in samples containing single line defects and adjacent channel defects forming directional couplers. Then, these results are used to create lattices with randomly distributed defects, resembling a disordered optical potential. In such lattices, wave propagation is found to change from ballistic transport to transverse Anderson-like light localization as a function of induced disorder.