[show abstract][hide abstract] ABSTRACT: We propose a new measurement technique to investigate the highly focused light used in optical data storage systems named immersion high resolution interference microscopy (HRIM). This system allows three-dimensional (3D) measurements of the amplitude and phase of light fields in a static scheme. In contrast to scanning techniques, HRIM allows the nondestructive investigation penetrating through the optical disc. We investigated the focusing of light in high-definition digital versatile disc (HD DVD) systems. The experimental spot sizes agree well with the theory in intensity measurements. The measured phase distributions resemble the wavefront propagation of aberration-free converging light beams. The observed phase singularity positions near the focal plane demonstrate the super-resolution capability of such measurements and give access to details of the Airy pattern. Our results prove the applicability of studying highly focused beams in advanced optical systems and its use to clarify storage mechanisms for future generations of optical memories. # 2010 The Japan Society of Applied Physics
Japanese Journal of Applied Physics 01/2010; · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: We present the first optical sensor based on Surface Plasmon Resonance (SPR) operating in the mid-infrared range. The experimental setup is based on a Kretschmann geometry with Ti/Au layers deposited on a CaF(2) prism where light excitation is provided by a Quantum Cascade Laser (QCL) source. Evidence of SPR is presented and the sensing capability of the system is demonstrated by using CO(2) and N(2) mixtures as test samples. Due to the absorption of CO(2) at this wavelength, it is shown that the sensitivity of this configuration is five times higher than a similar SPR sensor operating in the visible range of the spectrum.
[show abstract][hide abstract] ABSTRACT: We present results of numerical simulations and preliminary experiments to investigate and characterize the effect of asymmetrical coupling of normally incident light to surface plasmon polaritons (SPPs) on metallic blazed gratings. Two types of blazed gratings are investigated, a two-dimensional (2D) area-coded binary grating and a one-dimensional (1D) slanted sinusoidal grating. The 2D blazed grating, which can be fabricated with standard e-beam lithography, is shown to have the same ability as the classical 1D blazed grating to enhance the strength of the −1st(+1st) evanescent order over the +1st(−1st) counterpart, which leads to the asymmetrical excitation of two counterpropagating SPP modes on the grating surface. The 1D blazed grating, as a reference, is also studied experimentally to verify the previous theoretical predictions. In our first experiments, the observed asymmetrical coupling effect is relatively weak compared with the optimal designs due to many practical limitations. However, good agreement between theory and experiment has been obtained, and physical insight concerning the observed SPP coupling phenomena has been gained. Further measures to realize stronger asymmetrical excitation of SPPs on blazed gratings at normal incidence are discussed.
[show abstract][hide abstract] ABSTRACT: A two step process has been developed for the fabrication of diffraction limited concave microlens arrays. The process is based on the photoresist filling of melted holes obtained by a preliminary photolithography step. The quality of these microlenses has been tested in a Mach-Zehnder interferometer. The method allows the fabrication of concave microlens arrays with diffraction limited optical performance. Concave microlenses with diameters ranging between 30 microm to 230 microm and numerical apertures up to 0.25 have been demonstrated. As an example, we present the realization of diffusers obtained with random sizes and locations of concave shapes.
[show abstract][hide abstract] ABSTRACT: A surface plasmon resonance sensor has been successfully designed in the mid-infrared range. Evidence for surface plasmon resonance will be presented and early results on gas sensing performed with this sensor will be discussed.
[show abstract][hide abstract] ABSTRACT: We perform a near-field mapping of Bloch Surface Waves excited at the truncation interface of a planar silicon nitride multilayer. We directly determine the field distribution of Bloch Surface Waves along the propagation direction and normally to the surface. Furthermore, we present a direct measurement of a near-field enhancement effect under particular coupling conditions. Experimental evidence demonstrates that a approximately 10(2) near-field intensity enhancement can be realistically attained, thus confirming predictions from rigorous calculations.
[show abstract][hide abstract] ABSTRACT: With help of liquid crystal polymers (LCP) a polarization sensitive diffuser has been realized. By using convex microstructures made of LCP and an index matching layer, two distinct functions depending on the orientation of the device and the polarization state of the input light are realized. For one polarization the light pass through the device with no changes and for the perpendicular polarization, the light is diffused by the microstructures.
[show abstract][hide abstract] ABSTRACT: Based on liquid crystal polymers (LCP) a compact micro-optical polarizer with high efficiency has been designed and realized. By using cylindrical microlens arrays made of LCP and index matching layer, a complete separation of both polarization components of the unpolarized input light is achieved. Combined with a patterned twisted nematic (TN) cell, allowing a rotation of only one polarization component, a polarizer with high efficiency (72,5% (measured) is realized. Simulations and measurements are presented.
[show abstract][hide abstract] ABSTRACT: In nature strong colors play an important role in scaring away predators or finding a mate. Often, the strongest and brightest colors arise from coherent scattering and reflection on periodic structures on a length scale of several micro- or nanometers. Until recently, many theoretical combinations of diffractive structure and interference layers have been investigated and nearly nothing has been done on combinations of refractive structures and multilayer interferences. Only a few realizations have been achieved. We constructed and studied optical systems that mimic nature and are fabricated completely from organic materials. In this study we concentrate on combinations of Bragg reflectors and microlenses. Fabrication was carried out by spin-coating of organic interference layers and soft replication of microlenses. We studied reflection properties of such structures and discuss herein their behavior under different illumination conditions. To provide deeper insight, a model based on ray tracing is used that allows simulation of main characteristics. Particular optical configurations exist where the reflected color is insensitive to observation angles, while others have only one preferred direction of response.
Japanese Journal of Applied Physics 01/2008; · 1.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: Polymeric multilayer Bragg structures are combined with diffractive gratings to produce artificial visual color effects. A particular effect is expected due to the angular reflection dependence of the multilayer Bragg structure and the dispersion caused by the grating. The combined effects can also be used to design particular filter functions and various resonant structures. The multilayer Bragg structure is fabricated by spin-coating of two different low-cost polymer materials in solution on a cleaned glass substrate. These polymers have a refractive index difference of about 0.15 and permit multilayer coatings without interlayer problems. Master gratings of different periods are realized by laser beam interference and replicated gratings are superimposed on the multilayer structure by soft embossing in a UV curing glue. The fabrication process requires only polymer materials. The obtained devices are stable and robust. Angular dependent reflection spectrums for the visible are measured. These results show that it is possible to obtain unexpected reflection effects. A rich variety of color spectra can be generated, which is not possible with a single grating. This can be explained by the coupling of transmission of grating orders and the Bragg reflection band. A simple model permits to explain some of the spectral vs angular dependence of reflected light.
[show abstract][hide abstract] ABSTRACT: We investigate the effect of defects in the metal-coating layer of a scanning near-field optical microscopy (SNOM) probe on the coupling of polarization modes using rigorous electromagnetic modeling tools. Because of practical limitations, we study an ensemble of simple defects to identify important trends and then extrapolate these results to more realistic structures. We find that a probe with many random defects will produce a small but significant coupling of energy between a linearly polarized input mode and a radial/longitudinal polarization mode, which is known to produce a strongly localized emitted optical field and is desirable for SNOM applications.
Journal of the Optical Society of America A 06/2006; 23(5):1096-105. · 1.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: The optical properties of plano-convex refractive microlenses with low Fresnel Number (typically FN < 10) are investigated. It turns out that diffraction effects at the lens aperture limit the range of the effective focal length. The upper limit of the focal length is determined by the diffraction pattern of a pinhole with equal diameter. In addition achromatic microlenses can be realized because refraction and diffraction have opposing effects on the focal length. Gaussian beam propagation method has been used for simulation. The presented results are of relevance for applications, where microlenses with small apertures and long focal lengths are used, for example, Shack Hartmann wavefront sensors or confocal microscopes.
[show abstract][hide abstract] ABSTRACT: We present theoretical and experimental results on switching and tuning of a two-dimensional photonic crystal resonant microcavity by means of a silicon AFM tip, probing the highly localized optical field in the vicinity of the cavity. On-off switching and modulation of the transmission signal in the kHz range is achieved by bringing an AFM tip onto the center of the microcavity, inducing a damping effect on the transmission resonance. Tuning of the resonant wavelength in the order of several nanometers becomes possible by inserting the AFM tip into one of the holes of the Bragg mirror forming the microcavity in the propagation direction.
[show abstract][hide abstract] ABSTRACT: We present all-optical tuning and switching of a microcavity inside a two-dimensional photonic crystal waveguide. The photonic crystal structure is fabricated in silicon-on-insulator using complementary metal-oxide semiconductor processing techniques based on deep ultraviolet lithography and is completely buried in a silicon dioxide cladding that provides protection from the environment. By focusing a laser onto the microcavity region, both a thermal and a plasma dispersion effect are generated, allowing tuning and fast modulation of the in-plane transmission. By means of the temporal characteristics of the in-plane transmission, we experimentally identify a slower thermal and a fast plasma dispersion effect with modulation bandwidths of the order of several 100 kHz and up to the gigahertz level, respectively.
[show abstract][hide abstract] ABSTRACT: High Resolution Interference Microscopy (HRIM) is a technique that allows the characterization of amplitude and phase of electromagnetic wave-fields in the far-field with a spatial accuracy that corresponds to a few nanometers in the object plane. Emphasis is put on the precise determination of topological features in the wave-field, called phase singularities or vortices, which are spatial points within the electromagnetic wave at which the amplitude is zero and the phase is hence not determined. An experimental tool working in transmission with a resolution of 20 nm in the object plane is presented and its application to the optical characterization of various single and periodic nanostructures such as trenches, gratings, microlenses and computer generated holograms is discussed. The conditions for the appearance of phase singularities are theoretically and experimentally outlined and it is shown how dislocation pairs can be used to determine unknown parameters from an object. Their corresponding applications to metrology or in optical data storage systems are analyzed. In addition, rigorous diffraction theory is used in all cases to simulate the interaction of light with the nano-optical structures to provide theoretical confirmation of the experimental results.
[show abstract][hide abstract] ABSTRACT: A confined, evanescent nano-source based on the excitation of Surface Plasmon Polaritons (SPP) on structured thin metal films is proposed. With the help of a suitable cavity, we numerically demonstrate that it is possible to trap SPP over a spatial region smaller than the diffraction limit. In particular, the enhanced plasmonic field associated with the zero-order cavity mode can be used as a virtual probe in scanning near-field microscopy systems. The proposed device shows both the advantages of a localized, non-radiating source and the high sensitivity of SPP-based sensors. The lateral resolution is limited by the lateral extension of the virtual probe. Results from simulated scans of small objects reveal that details with feature sizes down to 50 nm can be detected.
[show abstract][hide abstract] ABSTRACT: We present results of the optical characterization of silicon photonic crystal waveguides and microcavities that are completely buried in a silicon dioxide cladding and are fabricated by deep ultraviolet (UV) lithography. The advantages of buried waveguides and deep UV lithography are discussed. Transmission spectra and loss factors for photonic crystal waveguides, as well as quality factors for resonant microcavities, are obtained. The observed characteristics are in good agreement with three-dimensional simulations.
Journal of Applied Physics 08/2005; · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: A study of the optical properties of microfabricated, fully-metal-coated quartz probes collecting longitudinal and transverse optical fields is presented. The measurements are performed by raster scanning the focal plane of an objective, focusing azimuthally and radially polarized beams by use of two metal-coated quartz probes with different metal coatings. A quantitative estimation of the collection efficiencies and spatial resolutions in imaging both longitudinal and transverse fields is made. Longitudinally polarized fields are collected with a resolution approximately 1.5 times higher as compared with transversely polarized fields, and this behavior is almost independent of the roughness of the probe's metal coating. Moreover, the coating roughness is a critical parameter in the relative collection efficiency of the two field orientations.
Journal of the Optical Society of America A 08/2005; 22(7):1432-41. · 1.67 Impact Factor