High frequency ultrasound imaging with optical arrays

Dynamically focused and steered high frequency ultrasound imaging systems require arrays with fine element spacing, wide bandwidths, and large apertures. However, these characteristics are difficult to achieve at frequencies greater than 30 MHz using conventional array construction methods. Optical schemes offer a solution. Focused laser beams incident on a suitable surface can generate and detect acoustic radiation. Precisely controlling the position and size of the beams defines points of transmission and detection, making it possible for pulse-echo image formation by synthetic aperture methods. An optical detection array was built, relying on a conventional piezoelectric transducer as an ultrasound source. The detection system, with near optimal resolution over a wide depth of field, demonstrates the potential for high frequency array implementation using optical techniques. A possible application is in pathology, where 2-D or 3-D fine resolution pulse-echo imaging can be performed in situ without the need for biopsies.     

Image fiber optic space-CDMA parallel transmission experiment using 8 x 8 VCSEL/PD arrays

We experimentally demonstrate space-code-division multiple access (space-CDMA) based twodimensional (2-D) parallel optical interconnections by using image fibers and 8 x 8 vertical-cavity surface-emitting laser (VCSEL)/photo diode (PD) arrays. Two spatially encoded four-bit (2 x 2) parallel optical signals were emitted fiom 2-D VCSEL arrays and transmitted through image fibers. The encoded signals were multiplexed by an image-fiber coupler and detected by a 2-D PD array on the receiver side. The receiver recovered the intended parallel signal by decoding the signal. The transmission speed was 64 Mbps/ch (total throughput: 512 Mbps). Bit-error-rate (BER) measurement with a laterally misaligned PD array showed the array had a misalignment tolerance of 25 microm for a BER performance of 10(-9).     

大尺度二维直线度测量仪的研制

研制出一种新的基于离轴成像技术的远距离、大范围二维直线度测量仪。仪器的直线基准为整形的十字线激光光束,光电二维位置敏感元件采用互相正交的线阵CCD,所设计的带有狭缝的离轴光学系统,避开激光十字线光束的能量中心,以使线阵CCD输出信号不会出现饱和现像,从而扩大了测量距离,保证了测量精度。该仪器能在0-20m测量范围连续测量二维直线度,其直线度可达0-70mm,精度优于0.1mm。实际的多次室外环境测量表明,该仪器可适应不同天气环境下的野外作业。     

Four-Channel, 8 x 8 Bit, Two-Dimensional Parallel Transmission by use of Space-Code-Division Multiple-Access Encoder and Decoder Modules

We experimentally demonstrate four-channel multiplexing of 64-bit (8 x 8) two-dimensional (2-D) parallel data links on the basis of optical space-code-division multiple access (CDMA) by using new modules of optical spatial encoders and a decoder with a new high-contrast 9-m-long image fiber with 3 x 10(4) cores. Each 8 x 8 bit plane (64-bit parallel data) is optically encoded with an 8 x 8, 2-D optical orthogonal signature pattern. The encoded bit planes are spatially multiplexed and transmitted through an image fiber. A receiver can recover the intended input bit plane by means of an optical decoding process. This result should encourage the application of optical space-CDMA to future high-throughput 2-D parallel data links connecting massively parallel processors.     

Industrial applications of optical techniques that measure displacements

Full-field optical techniques have reached a level of development that makes them ideal tools to solve many practical industrial problems. The areas of application include metrology; nondestructive evaluation of components; solutions to stress analysis problems, both static and dynamic; and development of sensors. In metrology, of particular significance are problems of three-dimensional (3-D) shape measurement. The shape measurement is connected to computer-aided design/computer-aided manufacturing programs, rapid prototyping, and reverse engineering. Unlike tactile machines that provide single-point data, optical methods provide high-density information, and their accuracy has reached a level comparable to tactile machines. This information makes feasible a number of new applications of high industrial interest in reverse engineering. Another area of great interest is 3-D visualization. Other areas of growth are the detection of flaws in nondestructive evaluation, problems arising from dynamic effects, refining of modeling techniques, and development of new sensors. A completely new area of application is the use of optical techniques in the field of microelectromechanical systems and in the area of nanosciences. Very recent work shows that one can go beyond the Rayleigh limit and obtain information at the nanolevel. It is possible to anticipate that a great expansion will take place in these fields in the next few years.     

Analysis and characterization of alignment for free-space optical interconnects based on singular-value decomposition

We propose a theoretical method to analyze and characterize the alignment of optical systems by using a singular-value decomposition (SVD) technique. One application of this method is to identify critical parameters for alignment systematically during alignment of two-dimensional device arrays. Another example application is to characterize the sensitivity or the accuracy of the misalignment-detection capability by evaluation of the singular values of optical systems. The information obtained through SVD-based techniques yields critical insights into the analysis of alignment.     

Improved distributed-index planar microlens and its application to 2-D lightwave components

A recent improvement of a 2-D array of distributed-index (DI) planar microlenses is presented to demonstrate a 2-D integrated optical component using a planar microlens array. These components are made by stacking planar microlens arrays and other planar optical devices. The improved planar microlens has f = 2.0 mm, a N.A. = 0.23, and its spherical aberration is very small. A fiber coupler is demonstrated. From a preliminary experiment, it is shown that the coupling loss of each channel is <0.5 dB for coupling 50-micron core DI fibers.     

Patterning of multilayer dielectric optical coatings for multispectral CCDs

The development of optical sensors for spacecraft applications requires that all components be as lightweight as possible. One method to reduce the weight of a multispectral optical system is to eliminate beamsplitting optics and multiple detectors by patterning a filter array directly onto a CCD. However, techniques commonly used in the production of these filter arrays result in decreased image resolutions. This can greatly impact the performance of sensors used for applications such as planetary probes. To address this issue, we have studied the patterning of multilayer dielectric optical coatings in a small scale, two dimensional array, which will allow development of a four color sensor with a resolution one-half that of monochromatic sensors (compared to one-fourth or less for a four color striped array). We have developed ion milling techniques for the preparation of optical filter arrays which are patterned on a scale as small as 7.5 μm, enabling each pixel of a CCD to have its own associated filter. This paper presents details of the fabrication of these multispectral arrays, and discusses problems associated with pixel-sized filters.     

Two-dimensional image transmission through a single optical fiber by wavelength-time multiplexing

Serial transmission of image data through an optical fiber is inefficient in the utilization of the channel capacity of the fiber. Parallel image transmission techniques, on the other hand, generally limit the transmission length to a few meters. A novel approach is introduced with which 2-D image data can be transmitted efficiently at high speed over a single optical fiber using wavelength-time multiplexing. Several system configurations designed for different types of input are presented.     

Extracting mode components in laser intensity distribution by independent component analysis

With increasingly sophisticated laser applications in industry and science, a reliable method to characterize the intensity distribution of the laser beam has become a more and more important task. However, traditional optic and electronic methods can offer only a laser beam intensity profile but, cannot separate the main mode components in the laser beam intensity distribution. Recently, independent component analysis has been a surging and developing method in which the goal is to find a linear representation of a non-Gaussian data set. Such a linear representation seems to be able to capture the essential structure of a laser beam profile. After assembling image data of a laser spot, we propose a new analytical approach to extract laser beam mode components based on the independent component analysis technique. For noise reduction and laser spot area location, wavelet thresholding, Canny edge detection, and the Hough transform are also used in this method before extracting mode components. Finally, the experimental results show that our approach can separate the principal mode components in a real laser beam efficiently.     

Two-Dimensional Image Transmission Based on the Ultrafast Optical Data Format Conversion between a Temporal Signal and a Two-Dimensional Spatial Signal

We have experimentally demonstrated a two-dimensional (2-D) image transmission based on the ultrafast optical data format conversion between a temporal signal and a spatial signal with an ultrashort optical pulse. In the proposed system we adopt a spectral holography technique to transmit a one-dimensional (1-D) spatial signal and use a spatial-domain time-frequency transform to realize a transform between 1-D and 2-D spatial signals. By use of these techniques, a low-optical-loss transmission system can be constructed. To demonstrate a 2-D image transmission with this technique, we achieved experimentally transmission of the alphabet letter T as a 3 x 3 pixel 2-D spatial image.     

White-light implementation of the Wigner-distribution function with an achromatic processor

A temporally incoherent optical processor that combines diffractive and refractive components is proposed for performing two different operations simultaneously: an achromatic image along an axis and an achromatic one-dimensional Fourier transformation along the orthogonal axis. These properties are properly employed to achieve the achromatic white-light display of the Wigner-distribution function associated with a one-dimensional real signal, with high redundancy and variable scale.     

Plastic modules for free-space optical interconnects

A combined optoelectronic and optomechanical packaging technique for the construction of snap-together free-space optical interconnect systems is described. The modules integrate relaying and routing functions by use of transparent optical molded plastic, which can achieve sufficient alignment precision that further adjustment is not required during system assembly. Methods to integrate the optoelectronic chips, such as vertical-cavity surface-emitting laser and receiver arrays with these plastic optical modules are described. Other chips can also be integrated to form optoelectronic multichip modules. These modules can also be designed to accommodate coupling to or from optical fiber arrays. A test-bed system to demonstrate the concept was assembled to a lower precision by use of conventional machining techniques.     

Fluorescence intensity ratio stereoscopic transform

A novel approach to 3-D information processing of 2-D cell images is presented, called fluorescence intensity ratio stereoscopic transform (FIRST). Here, we describe its basic principle of image processing and show the results for the ratio of total internal reflection fluorescence (TIRF) to fluorescence intensity. A simple, intuitive transform algorithm would help us to easily obtain a clear stereoscopic image from two 2-D cell images with different fluorescence intensity. For this purpose, nonlinear evanescent-field (EF) imaging of cell-membrane surface and its intracellular structures by using on-chip grating coupler is achieved. This method enabled us to obtain cell images with different signal-to-background ratio and resolution under microfluidic environments. Specifically, we manipulated optic pathway to partially illuminate microscale objects within the microfluidic channel. These findings imply this method will enable selectively to detect optical signals of biomolecular interaction within the cell membrane in a controlled manner. Furthermore, we believe this approach will help to develop an optofluidic sensor for individually detecting dynamic behaviors of intracellular molecules in living cells under microfluidic cell culture environments.     

Preparation of Fiber Optics for the Delivery of High-Energy High-Beam-Quality Nd:YAG Laser Pulses

Recent improvements in design have made it possible to build Nd:YAG lasers with both high pulse energy and high beam quality. These lasers are particularly suited for percussion drilling of holes of as much as 1-mm diameter thick (a few millimeters) metal parts. An example application is the production of cooling holes in aeroengine components for which 1-ms duration, 30-J energy laser pulses produce holes of sufficient quality much more efficiently than with a laser trepanning process. Fiber optic delivery of the laser beam would be advantageous, particularly when one is processing complex three-dimensional structures. However, lasers for percussion drilling are available only with conventional bulk-optic beam delivery because of laser-induced damage problems with the small-diameter (approximately 200-400-mum) fibers that would be required for preserving necessary beam quality. We report measurements of beam degradation in step-index optical fibers with an input beam quality corresponding to an M(2) of 22. We then show that the laser-induced damage threshold of 400-mum core-diameter optical fibers can be increased significantly by a CO(2) laser treatment step following the mechanical polishing routine. This increase in laser-induced damage threshold is sufficient to propagate 25-J, 1-ms laser pulses with a 400-mum core-diameter optical fiber and an output M(2) of 31.     

ZnO 1-D nanostructures: Low temperature synthesis and characterizations

ZnO is one of the most important semiconductors having a wide variety of applications in photonic, field emission and sensing devices. In addition, it exhibits a wide variety of morphologies in the nano regime that can be grown by tuning the growth habit of the ZnO crystal. Among various nanostructures, oriented 1-D nanoforms are particularly important for applications such as UV laser, sensors, UV LED, field emission displays, piezoelectric nanogenerator etc. We have developed a soft chemical approach to fabricate well-aligned arrays of various 1-D nanoforms like nanonails, nanowires and nanorods. The microstructural and photoluminescence properties of all the structures were investigated and tuned by varying the synthesis parameters. Field emission study from the aligned nanorod arrays exhibited high current density and a low turn-on field. These arrays also exhibited very strong UV emission and week defect emission. These structures can be utilized to fabricate efficient UV LEDs.     

Optik braucht Vakuum

Optics needs Vacuum — Challenges in Vacuum Optics Many applications in high technology use optical signals, optical information or laser radiation in vacuum as a part of manufacturing or characterization processes. These optical signals often have to be transferred into or out of a vacuum system. This article shows basic requirements and specifications for assemblies that connect optical elements and vacuum components hermetically. Four different, common joining methods are presented that fulfill both optical and vacuum requirements. The ability of these joining methods to preserve the properties of the individual components is discussed. After pointing out strengths and weaknesses of the joining methods, typical specifications profiles for each method are derived. It is concluded, that vacuum optics holds proper solutions for every application and its specific requirements.     

Binocular three-dimensional motion detection: contributions of lateral motion and stereomotion

When an object moves along a trajectory in three-dimensional (3-D) space, there are potentially two orthogonal components that could be used to detect its motion: stereomotion resulting from the difference or disparity between the images in the right and left eyes, and lateral motion from the sum or average of the image motions in the right and left eyes. Using a suprathreshold search task for a target moving amid 3-D distractors, we found a range of 3-D trajectories for which increasing the stereomotion component did not improve detection. However, with larger stereomotion components, performance improved. The addition of random-motion noise to only the lateral motion component adversely affected the detection of both lateral motion and stereomotion. These data suggest that the visual system uses the average of the monocular image motions for the detection of a range of 3-D trajectories. In addition, a mechanism sensitive to the changing disparity may also be used but only for a very restricted range of 3-D motions.     

Stream cipher based on pseudorandom number generation with optical affine transformation

We propose a new, to our knowledge, stream cipher technique for two-dimensional (2-D) image data that can be implemented by iterative optical transformation. The stream cipher uses a pseudorandom number generator (PRNG) to generate a pseudorandom bit sequence. The proposed method for the PRNG is composed of the iterative operation of 2-D affine transformation achieved by optical components and by modulo-n addition of the transformed images. We expect efficient execution of the method by optical parallel processing. We verify the performance of the proposed method in terms of security strength and clarify problems on optical implementation by the optical fractal synthesizer.     

Effect of illumination in an integral imaging system with large depth of focus

We present the characteristics of integral imaging systems with large depth of focus (DOF) by use of two kinds of illumination: plane illumination and diffusing illumination. For each system, we perform ray analysis based on ray optics. To check the visual quality through optical experiments, we use an average image of observed images picked up at various positions within a large DOF. The synthesized elemental images for a three-dimensional (3-D) object with two character patterns were displayed in an optical system and its reconstruction experiments are performed. Experimental results show that use of diffusing illumination can improve visual quality of reconstruction 3-D images in depth-priority integral imaging.