JEOS:RP - Journal of the European Optical Society Rapid publications
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Axial spectral scans of polarization dependent third harmonic generation in a multimode photonic crystal fiber
Get PDFWe demonstrate a nondestructive axial scanning technique for the spectrally resolved analysis of femtosecond nonlinear-optical transformation in photonic crystal fibers. This technique is applied to map the generation of a polarization-switched third harmonic of femtosecond Cr:forsterite laser pulses in a multimode silica photonic crystal fiber. Obtained results confirmed the intermodal phase-matching to be responsible for the observed polarization dependent multipeak third-harmonic generation. The axial scans revealed, that it is necessary to distinguish between the low and high energy excitation regime of the fiber sample. The proposed technique allows to measure the spectra of nonlinear signals generated in a photonic crystal fiber as a function of the propagation distance without cutting the fiber
High-efficiency wide-band metal-dielectric resonant grating for 20fs pulse compression
Get PDFMore than 95% average efficiency TE-polarization diffraction over a 200 nm wavelength range centered at 800 nm is obtained by a metal-dielectric grating structure with non-corrugated mirror. 98% maximum –1st order diffraction efficiency and a wide band top-hat spectrum are demonstrated experimentally opening the way to the high-efficiency Chirped Pulse Amplification of femtosecond pulses as short as 20 fs
Computing Zernike polynomials of arbitrary degree using the discrete Fourier transform
Get PDFThe conventional representation of Zernike polynomials R_n^m(rho) gives unacceptable results for large values of the degree n. We present an algorithm for the computation of Zernike polynomials of arbitrary degree n. The algorithm has the form of a discrete cosine transform which comes with advantages over other methods in terms of computation time, accuracy and transparancy. As an application we consider the effect of NA-scaling on the lower-order aberrations of an optical system in the presence of a very high order aberration
Polarization and coherence for vectorial electromagnetic waves and the ray picture of light propagation
Get PDFWe develop a complete geometrical picture of paraxial light propagation including coherence phenomena. This approach applies both for scalar and vectorial waves via the introduction of a suitable Wigner function and can be formulated in terms of an inverted Huygens principle. Coherence is included by allowing the geometrical rays to transport generalized Stokes parameters. The degree of coherence for scalar and vectorial light can be expressed as simple functions of the corresponding Wigner function
Enhanced transmission through arrays of subwavelength holes in gold films coated by a finite dielectric layer
Get PDFEnhanced transmissions through a gold film with arrays of subwavelength holes are theoretically studied, employing the rigid full vectorial three dimensional finite difference time domain method. Influence of air-holes shape to the transmission is firstly studied, which confirms two different resonances attributing to the enhanced transmission: the localized waveguide resonance and periodic surface plasmon resonances. For the film coated with dielectric layers, calculated results show that in the wavelength region of interest the localized waveguide resonant mode attributes to sensing rather than the periodic gold-glass surface plasmon mode. Although the detected peak is fairly broad and the shift is not too pronounced, we emphasize the contribution for sensing from the localized waveguide resonant mode, which may opens up new ways to design surface plasmon based sensors
Tolerancing of single point diamond turned diffractive optical elements and optical surfaces
Get PDFSingle point diamond turning has an increasing importance with the production of the surfaces for different optical systems such as infrared systems, prototype production of mobile phone cameras or head mounted displays with plastic lenses or master manufacturing for the injection moulding of plastic lenses for mass products.
Tolerances which occur during single point diamond turning of aspheric surfaces and diffractive elements or during polar coordinate laser plotting of Computer-generated holograms will be treated. In both cases we expect similar tolerances, because the work piece is rotated in both diamond turning and laser plotting. The purpose is to understand the typical tolerances and to simulate their influence to the aberrations in the optical system. © The Author. All rights reserved [DOI: 10.2971/jeos.2007.07028
Microlenses with annular amplitude and phase masks
Get PDFWe present theoretical and experimental investigations of microlenses with both amplitude and phase masks. The light field in the focal region has been measured with a high resolution Mach-Zehnder interferometer with z-scan. The experimental results show good agreement with simulation. We show that we can obtain effects as diverse as squeezing or expansion in longitudinal and lateral directions, focal point splitting and focal shift. These effects may be of interest for applications such as Shack-Hartmann wavefront sensing, integral imaging, optical tweezers and confocal microscopy
High sensitivity photonic crystal pressure sensor
Get PDFA two-dimensional photonic crystal microcavity coupled with a waveguide is proposed to realise a high sensitive force sensor, designed on a GaAs membrane. A theoretical model is developed to evaluate the change of the refractive index induced by the application of the force onto a sensing surface. A linear calibration curve is obtained relating the resonant drop position to the applied force
Quantitative analysis of the thermal distortions in a 100 W CW Nd:YAG ceramic slab laser.
Get PDFMaking use of an interferometric diagnostic system, we analyze the thermo-mechanical distortions taking place in the slab shaped ceramic Nd:YAG active medium of a 100 W class laser. These distortions are collected in different pumping regimes, both in static situations and during transient warm-up, and compared to the results of computer simulations. This procedure enables us to determine the relevance of different stress causes and thus to increase the specific power extraction of the active slab module
Third Order Bragg Grating Filters in Small SOI Waveguides
Get PDFThird order grating filters fabricated in small Silicon-on-Insulator rib waveguides are demonstrated. Variations in grating etch depth and duty cycle are considered, and a maximum experimental reflection of 42% is demonstrated for gratings of 1500microm in length, with a grating period of approximately 689nm and an etch depth of 200nm. Agreement with modeling is shown to be good