Medical Library

Three-core fiber-based shape-sensing application.

By using specially designed three-core fiber, a microstructured light-pattern generator for sensing 3-D shapes has been demonstrated. The square or hexagon grid-interferometric fringe pattern formed by the fiber-optic interferometric grid generator is projected onto an object\’s surface. The deformed grid pattern containing information of the object\’s surface topography is captured by a CCD camera and is analyzed using 2-D Fourier transforming profilometry. The use of the fiber-optic grid-interferogram technique greatly simplifies the holographic interferometry system, and the carrier grid interferogram can be conveniently generated without the use of excessive auxiliary components or sophisticated experimental devices; moreover, the three-core fiber can be used in very narrow places, owing to its small size. Finally, the square or hexagon grid-interferometric fringe pattern provides a data-fusion ability that could further improve the accuracy of the 3-D shape-sensing results.

Yuan L, Yang J, Guan C, Dai Q, Tian F.

Refractive and reflective behavior of polymer prisms used for surface plasmon guidance.

Two-dimensional optics with surface plasmons was realized by the use of topographically structured dielectric polymer coatings. Triangles of polymethylmetacrylate (PMMA) with lateral dimensions of some tens of micrometers on top of a silver layer act as two-dimensional prisms for surface plasmons. Refraction and internal reflection of plasmons were investigated by scanning near-field optical microscopy. The change in propagation direction can be explained by Snell\’s law when taking an effective refractive index for plasmons into account. Furthermore, intensity modulations in the PMMA elements and in the transmitted plasmon beam were observed.

Griesing S, Englisch A, Hartmann U.

Generalized wavefront phase for non-Kolmogorov turbulence.

We introduce the Lévy fractional Brownian field family to model the turbulent wavefront phase. This generalized model allows us to overcome the limitations found in a previous approach [Perez et al., J. Opt. Soc. Am. A 21, 1962 (2004)]. More precisely, our new model provides stationary phase increments over the full inertial range. Thus it successfully extends classical results to non-Kolmogorov turbulence without any approximation.

Pérez DG, Zunino L.

Enhancement of band-edge emission induced by defect transition in the composite of ZnO nanorods and CdSe/ZnS quantum dots.

A new and general approach to enhance band-edge emission at the expense of defect emission in a semiconductor nanocomposite is proposed. The underlying mechanism is based on the resonance effect between defect transition and band-to-band excitation and transfer of excited electrons between conduction band edges. With our approach, it is possible to convert defect loss into bandgap emission. As an example, we demonstrate that the bandgap emission of ZnO nanorods can be enhanced by as much as 30 times when they are compounded with CdSe/ZnS nanoparticles.

Tzeng LJ, Cheng CL, Chen YF.

Optimization of multiplexed holographic gratings in PQ-PMMA for spectral-spatial imaging filters.

Holographic gratings formed in thick phenanthrenquinone- (PQ-) doped poly(methyl methacrylate) (PMMA) can be made to have narrowband spectral and spatial transmittance filtering properties. We present the design and performance of angle-multiplexed holographic filters formed in PQ-PMMA at 488 nm and reconstructed with a LED operated at ~630 nm. The dark delay time between exposure and the preillumination exposure of the polymer prior to exposure of the holographic area are varied to optimize the diffraction efficiency of multiplexed holographic filters. The resultant holographic filters can enhance the performance of four-dimensional spatial-spectral imaging systems. The optimized filters are used to simultaneously sample spatial and spectral information at five different depths separated by 50 mum within biological tissue samples.

Luo Y, Gelsinger PJ, Barton JK, Barbastathis G, Kostuk RK.

Highly sensitive refractometer with a photonic-crystal-fiber long-period grating.

We present highly sensitive refractometers based on a long-period grating in a large-mode-area photonic crystal fiber (PCF). The maximum sensitivity is 1500 nm/refractive index unit at a refractive index of 1.33, to our knowledge the highest reported for any fiber grating. The minimal detectable index change is 2×10(-5). The high sensitivity is obtained by infiltrating the sample into the holes of the PCF to give a strong interaction between the sample and the probing field.

Rindorf L, Bang O.

Spectral-purity-enhancing layer for multilayer mirrors.

We demonstrate, both theoretically and experimentally, that special spectral-purity-enhancing multilayer mirror systems can be designed and fabricated to substantially reduce the level of out-of-band radiation expected in an extreme ultraviolet lithographic tool. A first proof of principle of applying such spectral-purity-enhancement layers showed reduced out-of-band reflectance by a factor of five, while the in-band reflectance is only 4.5% (absolute) less than for a standard capped multilayer.

van Herpen MM, van de Kruijs RW, Klunder DJ, Louis E, Yakshin AE, van der Westen SA, Bijkerk F, Banine V.

Random lasing in freely suspended dye-doped nematic liquid crystals.

Random lasing in fully disordered systems having organic and inorganic nature has been the subject of extensive studies since the beginning of the past decade. The interest mainly emerges from the unexpected role played by disorder in the laser action. The disorder was considered detrimental for the optical feedback in cavity laser, until it was demonstrated that multiple-scattering materials including a gain medium act as random laser. Here, a completely new approach is reported, where freely suspended complex fluid films doped with fluorescent molecules under optical excitation generate narrowband lasing peaks. The constellation of localized modes is selected by properly choosing the gain profile. The idea to have laser action in absence of mirrors and boundaries realizes an unparalleled tunable and moldable laser source.

Ferjani S, Barna V, Luca AD, Versace C, Strangi G.

Photonic generation of a microwave signal by incorporating a delay interferometer and a saturable absorber.

A novel approach to generate microwave signals is presented by employing a dual-wavelength erbium-doped fiber ring laser. By using a delay interferometer as a comb filter cascaded with a tunable bandpass filter and a saturable absorber formed by an unpumped polarization-maintaining erbium-doped fiber, a stable wavelength-tunable dual-wavelength single longitudinal-mode laser is achieved. A microwave signal at 20.07 GHz with a linewidth of <25 kHz is demonstrated by beating the two wavelengths at a photodetector.

Chen G, Huang D, Zhang X, Cao H.

Plasmonic electro-optic modulator design using a resonant metal grating.

A plasmonic electro-optic modulator design using an evanescently coupled resonant metal grating is numerically studied in this Letter. Owing to excitation and propagation of long-range surface plasmons between the metal grating nanowires, a deep and narrow reflection dip can be obtained. Improved modulation performance is achieved through decreased damping from large dielectric gaps between the grating nanowires. An optimized electro-optic modulator design with lower insertion loss and low operating voltage is presented.

Wu Z, Nelson RL, Haus JW, Zhan Q.