A low-cost technique using commercial UV grade silica fibers to construct microlens array that is suitable for mass-production of long-period gratings is reported. The growth rate of gratings fabricated using these arrays is much faster than the conventional amplitude masks. Our previous work had shown that this technique was 400% more efficient than the metal mask technique. Further improvement of this grating writing technique using plano-convex microlens array is reported in this paper. Under the same writing conditions, long-period gratings with absorption peaks of 1.5 dB and 17 dB were fabricated by using a microlens array and a plano-convex microlens array, respectively.

This paper presents unified VLSI architectures which can efficiently realize some widespread one-dimensional (1-D) and two-dimensional (2-D) real discrete trigonometric transforms, including the discrete Hartley transform (DHT), discrete sine transform (DST), and discrete cosine transform (DCT). First, succinct and unrestrictive Clenshaw's recurrence formula along with the inherent symmetry of the trigonometric functions are adequately employed to render efficient recurrences for computing these 1-D RDTT. By utilizing an appropriate row-column decomposition approach, the same set of recurrences can also be used to compute both of the row transform and column transform of the 2-D RDTT. Array architectures, basing on the developed recurrences, are then introduced to implement these 1-D and 2-D RDTT. Both architectures provide substantial hardware savings as compared with previous works. In addition, they are not only applicable to the 1-D and 2-D RDTT of arbitrary size, but they can also be easily adapted to compute all aforementioned RDTT with only minor modifications. A complete set of input/output (I/O) buffers along with a bidirectional circular shift matrix are addressed as well to enable the architectures to operate in a fully-pipelined manner and to rectify the transformed results in a natural order. Moreover, the resulting architectures are both highly regular, modular, and locally-connected, thus being amenable to VLSI implementations.

Analytical solutions have been obtained for the electromagnetic scattering by a modified Luneberg lens with the permittivity of arbitrary parabolic function. They are expressed by four spherical vector wave functions for radially stratified medium which were introduced for the Luneberg lens by C. T. Tai. They consist of the confluent hypergeometric function and a "generalized" confluent hypergeometric function, in which the parameters for the permittivity of arbitrary parabolic function are involved. The characteristics of the modified Luneberg lens are numerically investigated using exact solutions in comparison with that of the conventional Luneberg lens. The bistatic cross section, the forward cross section and the radar cross section are studied in detail. The near-field distribution is also investigated in order to study the focal properties of the Luneberg lens. The focal shifts defined by the distance between the geometrical focal point and the electromagnetic focal point are obtained for various ka (k is the wave number and a is the radius of the lens). The focal shift normalized to the radius of the sphere becomes larger as ka is smaller. However it drops down rapidly for ka5 when the peak of the electric field amplitude appears on the surface of sphere.

To improve the resolution of the color CRTs, we propose a new electrostatic lens system which has two additional electrodes between the focus electrode and the anode electrode. The anode voltage and focus voltage are supplied on these additional electrodes. The numerical simulation shows that the system can reduce the third order aberration coefficients almost up to 31% of the conventional system. And the experiments show that the typical beam spot diameter is improved by nearly 20% of the conventional system.

This paper summarizes our recent efforts in modelocking Ti:sapphire lasers with semiconductor saturable absorber mirrors (SESAMs). We present the shortest optical pulses ever generated directly from a laser. The modelocking build-up time (T BU) of 60 µs is, to our knowledge, the shortest reported for a passively modelocked KLM laser to date.

Narrow-beam and low threshold current characteristics have been realized for a 1.3 µm FS-BH (Facet Selective growth Buried Heterostructure) laser diode monolithically integrated with a tapered waveguide lens by a selective area epitaxial growth technique. The beam divergences in the perpendicular and horizontal directions have been reduced down to about 12. By the introduction of the strained quantum well structure and the optimized cavity structure, the threshold current has been kept as low as 6 mA which is comparable to the conventional Fabry-Perot laser diodes. Even at high temperature as high as 85, the threshold current and the operation current (P=10 mW) have been suppressed to as low as 23 mA and 63 mA, respectively. Furthermore error-floor-free characteristics for 622 Mbps-50 km transmission have been confirmed under severe optical feedback condition.

In this paper, we propose a camera calibration method that estimates both intrinsic parameters (perspective and distortion) and extrinsic parameters (rotational and translational). All camera parameters can be determined from one or more images of planar pattern consists of parallelogramatic grid points. As far as the pattern can be visible, the relative relations between camera and patterns are arbitrary. So, we have only to prepare a pattern, and take one or more images changing the relative relation between camera and the pattern, arbitrarily; neither solid object of ground truth nor precise z-stage are required. Moreover, constraint conditions that are imposed on rotational parameters are explicitly satisfied; no intermediate parameter that connected several actual camera parameters are used. Taking account of the conflicting fact that the amount of distortion is small in the neighborhood of the image center, and that small image has poor clues of 3-D information, we adopt iterative procedure. The best parameters are searched changing the size and number of parallelograms selected from grid points. The procedure of the iteration is as follows: The perspective parameters are estimated from the shape of parallelogram by nonlinear optimizations. The rotational parameters are calculated from the shape of parallelogram. The translational parameters are estimated from the size of parallelogram by least squares method. Then, the distortion parameters are estimated using all grid points by least squares method. The computer simulation demonstrates the efficiency of the proposed method. And the results of the implementation using real images are also shown.

A quasi-optical Superconductor-Insulator-Superconductor (SIS) mixer has been designed and tested in the 270-GHz band. The mixer used a substrate-lens-coupled log-periodic antenna and a tuning circuit for RF matching. The antenna is planar and self-complementary, and has a frequency-independent impedance of around 114 Ω over several octaves. The tuning circuit consists of two Nb/AIOx/Nb tunnel junctions separated by inductance for tuning out the junction capacitances and a λ/4 impedance transformer for matching the resistance of the two-junction circuit to the antenna impedance. The IF output from the mixer is brought out in a balanced method at each edge of the antenna, and is coupled to a low noise amplifier through a balun transformer using a 180-degree hybrid coupler for broadband IF matching. Double sideband receiver noise temperatures, determined from experimental Y-factor measurements, are about 150 K across the majority of the desired operating frequency band. The minimum receiver noise temperature of 120 K was measured at 263 GHz, which is as low as that of waveguide receivers. At this frequency, measurement of the noise contribution to the receiver results in input losses of 90 K, mixer noise of 17 K, and multiplied IF noise of 13 K. We found that the major sources of noise in our quasi-optical receiver were the optical losses.

A new electron-beam wafer inspection system has been developed. The system has a resolution of 5 nm or better, and is applicable to quarter-micron devices such as 256 Mbit DRAMs. The most remarkable feature of this system is that a specimen stage is built in the objective lens and allows a working distance (WD) of 0. "WD=0"minimizes the effect of lens aberrations, and maximizes the resolving power. Innovative designs to achieve WD=0 are as follows: (1)A large objective lens of 730-mm width 730-mm depth 620-mm height that serves as a specimen chamber, has been developed. (2)A hollow specimen stage made of non-magnetic materials has been developed.It allows the lower pole piece and magnetic coile of the objective lens inside it. (3)Acoustic motors made of non-magnetic materials are em-ployed for use in vacuum.

Tilt margins for disk and lens for a magneto-optical (MO) head were studied for designing a disk system for use with objective lenses having numerical apertures (NA) of 0.55, 0.60, and 0.65. The tilt margins were examined to determine the aberration characteristics of objective lenses and bit error rate (BER) by recording and reproducing signal. In preparing the optical head for testing disk and lens tilt margins, the aberrations were measured by image processing from the CCD area sensor for the spot image of the focused beam, and BER dependencies on the tilting of lens and disk were obtained at the velocity of the outer diameter of the MO disk at the bit rate of 80-Mbps (1, 7 code modulation) recording. According to the aberration and BER characteristics, the limitation for effective wavefront aberration would be 0.05λ rms, the tilt margins corresponded to BER limitation at the level of 3*10-5. The disk margins for NA=0.55, 0.6, and 0.65 were 0.4, 0.2, and 0.1 degrees. The lens tilt margins for NA=0.55, 0.6, and 0.65 were 0.2, 0.1, and 0.05 degrees.

A 3-dimensional specific thickness profile was fabricated on a thin glass diaphragm lens to reduce aberration at short focal distances for greater dynamic focusing. The deformation of the diaphragm was calculated by stress analysis utilizing the Finite Element Method (FEM). Geometric non linearity is considered in the FEM analysis. The glass diaphragm is 10 mm in diameter and the average thickness is 11 µm. To obtain both a curved shape and an optical surface on the glass diaphragm, the 3-dimensional precision grinding technique was utilized. The processed shape matches the designed one with less than 0.3 µm deviation, and the average surface roughness is 0.005 µm. Optical characteristics of the dynamic focusing lens having a specific thickness profile, were measured by Modulation Transfer Function (MTF) measurement equipment. At a focal distance of 250 mm, the specific thickness diaphragm lens resolution is 10 cycles/mm, whereas, the uniform thickness diaphragm is 4 cycles/mm. Even at other focal distances, the specific thickness diaphragm shows superior optical characteristics in comparison with those of the uniform thickness diaphragm. The 3-dimensional profile diaphragm resolution is 2.5 times finer at a focal distance of 250 mm, thus, being capable of displacement control for variable optic devices. This was achieved by employing semiconductor processing methods in conjunction with precision grinding techniques which are necessary for fabricating micro structures.

Measuring mechanical characteristics of optical disks is significant not only for designing drives but also for assuring disk interchangeability. This paper shows that the lens-movement detection method has the greatest overall potential and thus fits to a practical system for measuring mechanical characteristics. A system based on this method was constructed by developing simple and accurate capacitive sensors that can be built into an optical head to detect lens movement. The system configuration includes a precision turntable and a high-duarability reference disk to fully extract the potential. Test results show that this measuring system has adequate measuring range, accuracy, and stability. Some applications of this system are described in this paper. They show that the system is useful for evaluating and improving optical disk mechanical characteristics.

Monopulse technique is widely used for tracking radars. For tracking at a low elevation angle, a narrow beam is required in the elevation plane to reduce multipath signals such as gound reflections. In this case, an elliptical aperture is desired. We have developed an antenna with a high tracking accuracy and a high aperture efficiency which is composed of a monopulse feed and an elliptical aperture. In this paper we discuss a design of the feed through lens array with an elliptical aperture and a new monopulse feed. Evaluation test results of a production model proved validity of our design and showed good performance.

This paper discusses how to achieve eye contact in teleconferences attended by two or three conferees through a "Private Display Method." This method, which allows several images to be simultaneously displayed on a single screen, makes it possible to achieve eye contact. Each conferee can see a unique image, which is captured by a camera, which effectively acts as a substitute for the conferee in a counterparts room. The unique image is selected by a duoble-lenticular lens from images from two or three projectors. The effectiveness of the private display method has been demonstrated by ray-tracing simulation and by using a 50 double-lenticular screen. A prototype teleconferencing system for two persons was constructed with the 50 double-lenticular screen, a semi transparent silver coated mirror, two projectors and two cameras. Eye-contact with all counterparts can be achieved with the prototype teleconference system. The private display method is a promising way of achieving eye contact in teleconferences attended by two or three conferees.