Optical field study of near-field optical recording with a solid immersion lens

The use of a solid immersion lens (SIL) is an important technique for increasing areal density in optical recording. Here an approximate method is presented for analyzing the optical fields in a SIL above a half-space and a SIL above a multilayer recording medium. Both propagating and evanescent components are included in the distribution of fields below the SIL. An approximate closed-form expression is given for the decay of the intensity away from the SIL surface above a half-space. In the case of a SIL above a recording medium the model describes the strong oscillations that are observed in the reflected Kerr rotation and ellipticity as the medium spacing is varied. These oscillations are attributed to standing waves in the propagating field component.     

Theoretical study of near-field optical storage with a solid immersion lens

Both the reflection inside a hemisphere solid immersion lens (SIL) and the reflection inside the gap between the SIL and the optical recording medium are considered. The near-field SIL imaging theory for high numerical aperture is developed by using the vector diffraction and thin-film optics. Numerical results show that the spot size, Strehl ratio, and sidelobe intensity have an oscillatory behavior with the change of thickness of the air gap, which results from the interference effect of the transmitted field. We find that for smaller spot size, the Strehl ratio is smaller but the sidelobe intensity is larger. A certain thickness of air gap is useful for optical storage, which is less than 63 nm for the system in the simulated examples.     

Optical data storage system with a planoellipsoidal solid immersion mirror illuminated directly by a point light source

A new solid immersion mirror called the planoellipsoidal (PE) solid immersion mirror (SIM) for the near-field optical storage is proposed and developed. The PE SIM has a small aperture on the apex of the ellipsoidal surface. The intensity distribution of the transmitted field is calculated by using the vector diffraction theory. Compared with a conventional solid immersion lens (SIL), the proposed PE SIM has the following features. A PE SIM replaces three optical elements of the collimator, objective, and SIL in a conventional SIL optical storage system, so that the optical system equipped with the PE SIM is not only simple in its assembly but is also effective in making an optical head unit. The PE SIM obtains light from a point light source and focuses it directly on the recording layer, which may be useful for a compact optical data storage system. The convex ellipsoidal surface of the PE SIM can reduce the risk of the SIM touching the surface of the recording medium. In addition, the spreading of the spot size with the increase of distance is very small in the PE SIM.     

Simulation of Contaminates Around the Solid Immersion Lens in a Near-Field Optical Recording System

Accurate predictions of contamination in next-generation optical storage drives are paramount when active gap control is employed. In near-field recording devices, the read/write interface can be on the order of 20-30 nm, which means that the gap could be quite susceptible to contamination. Predictive modeling approaches for studying the behavior of contaminates in nanoscale hydrodynamic interfaces are needed. Here, we present such a model. The interface consists of a flat disk surface translating under a solid immersion lens (SIL) of hemispherical geometry. We present the computational modeling simulation results for nano-scale contaminates around the near-field SIL. The simulation shows that the discrete contaminates actually circumnavigate the SIL/disk interface during operation. We identify and discuss the external influences on the discrete contaminate particle behavior     

Wide-Field and Real-Time Super-Resolution Optical Imaging By Titanium Dioxide Nanoparticle-Assembled Solid Immersion Lens

Super-resolution optical imaging techniques can break the optical diffraction limit, thus providing unique opportunities to visualize the microscopic world at the nanoscale. Although near-field optical microscopy techniques have been proven to achieve significantly improved imaging resolution, most near-field approaches still suffer from a narrow field of view (FOV) or difficulty in obtaining wide-field images in real time, which may limit their widespread and diverse applications. Here, the authors experimentally demonstrate an optical microscope magnification and image enhancement approach by using a submillimeter-sized solid immersion lens (SIL) assembled by densely-packed 15 nm TiO₂ nanoparticles through a silicone oil two-step dehydration method. This TiO₂ nanoparticle-assembled SIL can achieve both high transparency and high refractive index, as well as sufficient mechanical strength and easy-to-handle size, thus providing a fast, wide-field, real-time, non-destructive, and low-cost solution for improving the quality of optical microscopic observation of a variety of samples, including nanomaterials, cancer cells, and living cells or bacteria under conventional optical microscopes. This study provides an attractive alternative to simplify the fabrication and applications of high-performance SILs.     

Photon tunneling in a uniaxial crystal film

A method for studying photon tunneling in uniaxial crystal films is presented. The complex refractive index and the complex angle of refraction of the evanescent wave in a crystal are calculated for the most general case. The reflectance and transmittance resulting from the tunneling effect in crystal films are discussed, and the relations among these coefficients and the optical parameters of crystal are found. These relations provide a theoretical basis for characterizing crystal films by means of photon tunneling.     

Simplified design of thin-film polarizing beam splitter using embedded symmetric trilayer stack

An analytically tractable design procedure is presented for a polarizing beam splitter (PBS) that uses frustrated total internal reflection and optical tunneling by a symmetric LHL trilayer thin-film stack embedded in a high-index prism. Considerable simplification arises when the refractive index of the high-index center layer H matches the refractive index of the prism and its thickness is quarter-wave. This leads to a cube design in which zero reflection for the p polarization is achieved at a 45° angle of incidence independent of the thicknesses of the identical symmetric low-index tunnel layers L and L. Arbitrarily high reflectance for the s polarization is obtained at subwavelength thicknesses of the tunnel layers. This is illustrated by an IR Si-cube PBS that uses an embedded ZnS-Si-ZnS trilayer stack.     

Numerical study of the displacement of a three-dimensional Gaussian beam transmitted at total internal reflection. Near-field applications

Longitudinal and transverse shifts of a light beam at total internal reflection was experimentally studied by far-field measurements on the reflected field. We propose to use a scanning tunneling optical microscope (STOM) to study these shifts in transmission, and we present a theoretical model of this proposed experiment to obtain a numerical estimation of these shifts. We study the reflection and the transmission of a three-dimensional polarized incident beam. We verify the validity of our formalism by studying the Goos-Hanchen shift in reflection and by comparing our results with published ones. Then we calculate STOM images of the transmitted field distribution. On the images the well-known Goos-Hanchen shift is easily observed. But we also encounter a smaller shift, perpendicular to the plane of incidence. This transverse shift was also observed in reflection by Imbert and Levy [Nouv. Rev. Opt. 6, 285 (1975)]. We study the variations of the two shifts versus various parameters such as the angle of incidence, the optical index, and the incident polarization. Then we discuss the feasibility of the near-field observation of these shifts.     

High capacity optical beam forming for phased arrays with fiber gratings and frequency conversion for beat noise control

A new wavelength division multiplexing grating-based beam-forming architecture for phased arrays that can achieve the minimum possible number of optical interconnects is presented. A reduction in interconnect hardware of 99.6% is obtained for a 512-beam array, which is, as far as we know, the lowest number of interconnects reported to date. Analysis of the ultimate beam capacity limit of the beam former shows that the beat noise interference limitation is the most important factor. We present a new hybrid frequency-converting optical beam former that removes the fundamental beat noise limitation. This frequency downconverts the rf signal to an intermediate frequency before performing the true-time-delay equalization in the optical domain. The resulting advantage of reduced optical bandwidth per channel enables more wavelengths to be used for a given wavelength span, resulting in an increased beam capacity. A greater than sevenfold increase in beam capacity is demonstrated through the use of the frequency conversion technique, with 960 beams synthesized at 12.4 GHz, showing a 99.8% reduction in required interconnects.     

Readout signals calculated for near-field optical pickups with land and groove recording

Optical disk readout signals with a solid immersion lens (SIL) and the land-groove recording technique are calculated by use of a simplified vector-diffraction theory. In this method the full vector-diffraction theory is applied to calculate the diffracted light from the initial state of the disk, and the light scattered from the recorded marks is regarded as a perturbation. Using this method, we confirmed that the land-groove recording technique is effective as a means of cross-talk reduction even when the numerical aperture is more than 1. However, the top surface of the disk under the SIL must be flat, or the readout signal from marks recorded on a groove decays when the optical depth of the groove is greater than lambda/8.     

Compact stand-alone near-field optical microscope combined with force detection

We present a compact stand-alone near-field optical microscope combined with force detection in which manufactured atomic force microscope (AFM) microcantilevers are used for both optical and force detection. Because of the stand-alone design, the combination allows a great variety of operation modes, including the scanning tunneling optical microscope (STOM), and possibly the reflection scanning near-field optical microscope modes. The first images obtained in the AFM and the STOM mode are presented. A polarization study is carried out to confirm the optical nature of the detected signal and to discuss possible artifacts.     

Design considerations of stacked multilayers of diffractive optical elements for optical network units in optical subscriber-network applications

The detailed design process and experimental results of stacked multilayer diffractive optical elements are reported for an optical network unit used in optical subscriber-network applications. The optical network unit accepts two incoming light beams of 1.3- and 1.55-mum wavelengths through a single-mode optical fiber. A laser diode is also placed for bidirectional communications. The optical network unit consists of five diffractive optical elements that perform the following functions: collimation of incoming beams, focusing of the outgoing 1.55-mum beam, 3-dB splitting of the 1.3-mum beam, focusing of the 1.3-mum beam onto the photodiode, and collimation of the light emitted from a laser diode. Possible cost reductions as a result of mass production and the ease of alignment of the stacked diffractive optical elements could be ideal for constructing low-cost optical network units.     

Optical phased-array beam steering controlled by wavelength

A scheme for optical phased-array beam steering controlled by wavelength is proposed. In this scheme, the optical scanning device consists of arrayed optical waveguides with specific length differences, by which the desired phase slope that results in optical beam steering is formed at the ends of the waveguides and can be changed by varying the optical wavelength. By introducing the concept of irregularly spaced arrays, sidelobes can be dramatically suppressed regardless of large center-to-center interelement spacing. The absolute phase difference between adjacent elements plays a vital role in optical beam steering, and the relation between the nonuniform length difference and the corresponding center-to-center spacing among elements is found.     

Imaging of resonant quenching of surface plasmons by quantum dots

In scanning tunneling microscopy (STM), confinement of surface plasmons to the optical cavity formed at the metallic tunneling gap stimulates the emission of light. We demonstrate that quantum dots (QDs) found in such a cavity give rise to discrete, observable transitions in the tunneling luminescence spectrum due to the resonant extinction of the plasmon. The observed resonances represent a fingerprint of the QD and occur at the optical band gap owing to the nearly simultaneous transfer of carriers from both sides of the tunneling gap to the QD. The resonant quenching of surface plasmons enables a new imaging technique, dubbed plasmon resonance imaging, with a spatial resolution potentially similar to that of STM and the energy resolution of optical spectroscopies. This detection and imaging strategy is not restricted to QDs, being of great interest to an entire spectrum of nanostructures, from molecular assemblies and biomolecules to carbon nanotubes.     

Optical intensity distribution of a plano-convex solid immersion mirror

Ignoring the effect of the small aperture, we deduce the optical field distribution of the so-called plano-convex solid immersion mirror with a small aperture on the apex (PC-SIM) by using the vector diffraction theory. The simulation results show that a PC-SIM, like a solid immersion lens (SIL), can achieve high resolution. Unlike the SIL, the PC-SIM can effectively reduce the spreading of the spot size with increasing distance from the interface. The size and intensity of the spot are related not only to the refractive index of the solid immersion medium but also to the structure parameter of the PC-SIM. The size of a spot smaller than a quarter wavelength can be obtained simply by optimizing the structure parameter of a PC-SIM but not by decreasing the size of the small aperture.     

Planar-structure microscope-lens for simultaneous acoustic and optical imaging

A new type of combined acoustic and optical microscope lens with a planar structure is proposed. It can meet the demand for simultaneously obtaining both an acoustic image and its optical counterpart. The lens is composed by uniting a Fresnel-zone-type acoustic lens developed by the authors with a rod-type gradient-index optical lens (SELFOC). An acoustic beam is converged to a focal point in water by an acoustic planar lens that is composed of annular grooves formed on the end of the SELFOC rod. An optical beam, emitted by a He-Ne laser source and guided into the rod, converges due to the gradient of the refractive index and focuses on a spot in water. By designing the length of the rod properly, the focal spot of the optical beam is set to coincide with that of an acoustic beam. The design and fabrication of the lens are described, and results of some preliminary experiments for simultaneous observation of acoustic and optical images of the same portion of a specimen are shown.     

Tunneling of quasiparticles between two weakly coupled systems of superfluid helium

Quasiparticle tunneling in a weakly coupled system of liquid helium is theoretically studied, in analogy with normal electron tunneling of superconductor junctions. Chemical potential difference in this case is to be created across the junction by a superfluid flow parallel to the junction. Calculation shows that a collimated beam of quasiparticles would show several divergences of tunneling current at specific angles of incidence or at specific values of superfluid velocity, while no divergence is expected for the integrated current, which is an important difference from the case of superconductor junctions.     

Dynamic null steering in an ultrawideband time-steered array antenna

We develop a method for forming squint-free wideband nulls in the antenna pattern of an ultrawideband array antenna. The technique uses an optical dispersive-prism beam former to provide time-delayed microwave signals to each antenna element for forming a squint-free main beam. The amplitude-modulated optical carrier is propagated through a set of optical links. Each link feeds an array element and includes an amount of dispersion proportional to element position. Tuning the wavelength of the optical carrier controls the microwave signal's arrival-time delay gradient across the array. A dispersive-prism tapped delay-line microwave filter is used to frequency shape a nulling signal. The wideband nulls do not significantly distort the main beam and are steered independently of the main beam. The technique is applied to sidelobe nulling for a transmitter and for jammer suppression for a receiver array.     

吲哚俘精酸酐实现三值偏振全息光学存储器

针对三值光计算机需要直接存储线偏振光束的问题,利用光致各向异性材料吲哚俘精酸酐对偏振态敏感的特性,提出了一种基于吲哚俘精酸酐/PMMA 薄膜的三值偏振全息数字存储方法,并建立了相应的光学存储器模型.该存储器系统采用He-Ne 激光器为记录和读出光源,以双层液晶和偏振器为核心的编码器作为三值数据的输入部件,以双CCD 为核心的解码器作为数据输出器件,采用傅里叶变换全息记录的方法,在吲哚俘精酸酐/PMMA薄膜上实现三值数字光学存储.该存储器系统可望实现直接并行存储用光束的正交线偏振态和无光态表示的三值数字信息,以及以页面为单位的并行寻址和读写操作.     

Optical actuation of micromechanical tunneling structures with applications in spectrum analysis and optical computing

An efficient method for optically actuating a micromechanical cantilever is presented for the first time to our knowledge. Measurable responses can be obtained for moderate light sources if electron tunneling occurs between the cantilever tip and a metallic contact below it. The small deflection of the cantilever that is due to light pressure is sufficient then to produce large tunneling current variations. On the basis of this effect several applications such as a miniaturized spectrum analyzer and one-step optical computing units for addition, integration, or differentiation of one-dimensional or two-dimensional optical signals are presented.