Practical design of a high-efficiency relief-type waveguide hologram is demonstrated for the future integration of holograms in optical IC. The hologram is recorded in light-sensitive layer on a thin film waveguide. After the exposure and the subsequent etching, one can obtain a waveguide hologram of relief type. It is shown analytically that, when the parameters are optimized, the relief type provides a high efficiency and an aperture size suitable for storing pictorial informations. Waveguide holograms were fabricated by chemical etching technique in amorphous As2S3 (recording medium)/sputtered glass film (wave-guiding layer) structure. From the intensity distribution of the diffracted light in the hologram plane, the total diffraction efficiency (the sum of the efficiencies in the air side and in the substrate side) was estimated to be 92%. This result compares favourably with the theoretical prediction, and the efficiency of 92% is remarkably higher value than that of a hologram of coventional type storing a pictorial information. Very little deterioration of the image quality owing to the etching was observed. The applicability of the method to the design of a waveguide hologram to be reconstructed by ir light was also confirmed. The high efficiency would make the waveguide hologram of this type promising also as an advancement of holographic circult couplers.

This letter presents experimental results of an efficient TE-TM mode converter using a Z-propagation LiNbO3 waveguide. A three-section electrode structure with 10 mm length allows us to control mode coupling and phase matching independently by two different applied voltages. The drive voltage is only 5.2 V with the mode conversion efficiency of 98% when the phase matching condition is satisfied by the voltage tuning. This mode converter is also free from optical damage because of the use of Z-propagation LiNbO3.

This paper presents an analysis of a multi-hole directional coupler attached to an overmoded circular waveguide. The directional coupler is analized as a boundary value problem, and is solved numerically by a virtual cavity method. The approximate analysis of a small hole coupling coefficient is verified by this analysis. Numerical results indicate that the mutual coupling between holes is not negligible for calculating the directivity of the directional coupler.

Integrated detection optics for magnetooptical (MO) disk pickup are proposed. The pickup consists of a waveguids device, external lenses, a beam splitter and a laser diode. The detection optics is constructed by integrating a trifocal focusing grating coupler and five photodiode elements in a glass-film waveguide on a Si substrate. The design considerations and fabrication are described, and experimental results are reported. The wavelength bandwidth of the devices are discussed in relation to the wavelength instability of laser diode. Although the obtained performances are not sufficient for practical application, the elementary functions, i.e., MO signal readout, focusing error detection and stabilization by multimode LD, were successfully demonstrated in the simulation experiments.

The light emitted from the exit end of an optical fiber can be used as the reference wave in recording a hologram and/or the illuminating wave in reconstructing it. The fundamental problems associated with such an application have been investigated. First, the radiation characteristics of a step-index fiber was analyzed and a simple scalar description, suitable for the holography application, of the far radiation field was derived. It was found that the wavefront of the radiation field is identical with that of a spherical wave radiating from the center of the fiber end. The rough estimation for the size of the far field pattern was given and the orthogonality property of the radiation field was proved. Then the wavefront reconstructing characteristics of the hologram were discussed. The resolution capability of the system was determined by using the point spread function. A reduction coefficient concept has been introduced to describe the effects of the reference and illuminating wavefronts on the diffraction efficiency. It was deduced that recording with a spherical reference wave and illuminating with light derived from a fiber result in negligible reduction of the efficiency. The feasibility of the method was proved experimentally and some theoretical predictions were also confirmed.

This paper proposes that a combination of pre-chirping and dispersion compensation is effective in suppressing the waveform distortion due to the self-phase modulation and the group-velocity dispersion in 10 Gb/s repeaterless transmission using 1.3-µm zero-dispersion single-mode fibers (SMF) operating at a wavelength of 1.55µm. The following results were obtained through simulation. 1) Setting the α-parameter of a LiNbO3 optical modulator negative (α1.0) gives a large tolerance of the launched power Pin. 2) For 90-km SMF transmission, the maximum Pin is obtained when the dispersion compensation ratio β is from 50% to 70%. 3) For the allowable β as a function of the transmission distance when a dispersion compensator is located in the receiver (post-compensation scheme), the lower limit of β is determined by the constant residual dispersion value, which agrees well with the dispersion tolerance without dispersion compensation. Our 90-km SMF transmission experiments using a LiNbO3 optical modulator and a dispersion compensating fiber (DCF) confirmed the simulation results regarding the optimum value of β and the large tolerance of the fiber launched power. Based on the above investigations, we achieved a 10-Gb/s repeaterless 140-km SMF transmission with α1.0 and post-compensation.

Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FDE block cannot be ignored. The ISI reduction performance of FDE degrades since the cyclicity of the channel matrix is lost. To solve this problem, a method of dividing the received data block into multiple subblocks has been proposed, where pseudo cyclic prefix (CP) processing is introduced to realize periodicity in each subblock. In this method, the performance is degraded by the inherently-inaccurate pseudo CP. In this paper, we study the application of frequency-domain turbo equalization (FDTE) to subblock processing for improving the accuracy of pseudo CP. The simulation results show that FDTE with subblock processing yields remarkable performance improvements.

Massive multiple-input multiple-output (MIMO) technology is one of the key enablers in the fifth generation mobile communications (5G), in order to accommodate growing traffic demands and to utilize higher super high frequency (SHF) and extremely high frequency (EHF) bands. In the paper, we propose a novel transmit precoding named “nonlinear block multi-diagonalization (NL-BMD) precoding” for multiuser MIMO (MU-MIMO) downlink toward 5G. Our NL-BMD precoding strategy is composed of two essential techniques: block multi-diagonalization (BMD) and adjacent inter-user interference pre-cancellation (IUI-PC). First, as an extension of the conventional block diagonalization (BD) method, the linear BMD precoder for the desired user is computed to incorporate a predetermined number of interfering users, in order to ensure extra degrees of freedom at the transmit array even after null steering. Additionally, adjacent IUI-PC, as a nonlinear operation, is introduced to manage the residual interference partially allowed in BMD computation, with effectively-reduced numerical complexity. It is revealed through computer simulations that the proposed NL-BMD precoding yields up to 67% performance improvement in average sum-rate spectral efficiency and enables large-capacity transmission regardless of the user distribution, compared with the conventional BD precoding.

In time-varying fading environments, the performance of multiple-input multiple-output (MIMO) systems applying an eigenbeam-space division multiplexing (E-SDM) technique may be degraded due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed some channel prediction methods. Simulation results based on computer-generated channel data showed that better performance can be obtained when using the prediction methods in Rayleigh fading environments assuming the Jakes model with rich scatterers. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS case, scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antennas at both the transmitter and the receiver cannot be ignored as it affects the system performance in actual implementation. We conducted MIMO channel measurement campaigns at a 5.2 GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. The results show that robust bit-error rate performance is obtained when using the channel prediction methods and that the methods can be used in both Rayleigh and Rician fading environments, and do not need to know the maximum Doppler frequency.

MIMO systems using a space division multiplexing (SDM) technique in which each transmit antenna sends an independent signal substream have been studied as one of the successful applications to increase data rates in wireless communications. The throughput of a MIMO channel can be maximized by using an eigenbeam-SDM (E-SDM) technique, and this paper investigates the practical performance of 22 and 44 MIMO E-SDM based on indoor measurements. The channel capacity and bit error rate obtained in various uniform linear array configurations are evaluated and are compared with the corresponding values for conventional SDM. Analysis results show that the bit error rate performance of E-SDM is better than that of SDM and that E-SDM gives better performance in line-of-sight (LOS) conditions than in non-LOS ones. They also show that the performance of E-SDM in LOS conditions depends very much on the array configuration.

For simulating i.i.d. time-varying MIMO channels using multiple Jakes' rings, it is desirable to generate channels having stable statistics with fewer scatterers. The statistical property of the conventional Jakes' model may depend on the initial phase set assigned to scattering points. In this letter, we present simple and effective conditions on arrangement of scattering points to achieve stable fading properties. The results show that the proposed arrangement provides higher statistical stability in generating time-varying channels.

The MIMO system can meet the growing demand for higher capacity in wireless communication fields. So far, the authors have reported that, based on channel measurements, uncoded performance of narrowband MIMO spatial multiplexing in indoor line-of-sight (LOS) environments generally outperforms that in non-LOS (NLOS) ones under the same transmit power condition. In space-frequency coded MIMO-OFDM spatial multiplexing, however, we cannot expect high space-frequency diversity gain in LOS environments because of high fading correlations and low frequency selectivity of channels so that the performance may degrade unlike uncoded cases. In this letter, we present the practical performance of coded MIMO-OFDM spatial multiplexing based on indoor channel measurements. The results show that an LOS environment tends to provide lower space-frequency diversity effect whereas the MIMO-OFDM spatial multiplexing performance is still better in the environment compared with an NLOS environment.

In this study we present a new Laser Doppler Velocimeter (LDV) with an optical fiber to measure the velocity of blood flow accurately. After the validity of the present method was evaluated by the fundamental experiments, the blood flow profiles in canine femoral arteries were measured in anesthetized mongrel dogs. It was shown that our LDV is a valid and useful velocimeter to measure the phasic blood flow velocity in the artery.

DH lasers are believed to be one of the most suitable light sources for optical fiber transmission. However, the light output of DH lasers has usually such detrimental effects as a relaxation oscillation and a spectral broadening during pulse response. For high bit rate and long-distance fiber transmission, lasers need to have a high performance pulse responce and a narrow spectral width. We examined the dynamic characteristics of GaAs/GaAlAs DH lasers, which had an internally striped planar (ISP) structure using sulfur diffusion, by changing the stripe width. By narrowing the stripe width to the range of 5 to 7 µm of ISP lasers with an undoped active region and the cavity length of about 150 µm, significant improvement was achieved in frequency response, pulse response and spectral behavior as well. The frequency response was flat up to 2 GHz without a resonant-like peak. The relaxation oscillation was suppressed up to 10-mW light output. The spectral width at 400-Mb/s modulation was controlled within 20 without degradation of extinction ratio. Threshold currents were in the range of 55 to 70 mA. The light output increased linearly up to 10 mW without a kink. The external differential quantum efficiency was about 60 %. These lasers are operating stably after more than 1,000 hours at 70 under 3-mW light output. A narrow stripe-geometry ISP laser has a promising feature in that it can be used in high bit rate and long-distance fiber transmission.

This paper presents a method of estimation for the temporal resolution of a catheter type blood velocimeter and applied it to a laser Doppler blood velocimeter (LDV) with an optical fiber. After the evaluation of temporal resolution practical measurements were made in model flow tubings and in the coronary of mongrel dog.

Al doped zinc oxide (AZO) films were deposited using a radio frequency (rf) magnetron sputtering apparatus with a mesh grid electrode. Improvement of crystalline uniformity was achieved by the use of an appropriate negative grid bias to effectively suppress the bombardment of high-energy charged particles onto the film surface. The uniformity of the film's electronic properties, such as resistivity, carrier concentration and Hall mobility, was also improved using the sputtering method. Hydrogen plasma annealing was investigated to further decrease the resistivity of the ZnO films and the carrier concentration was increased by 1-21020 cm-3 without decrease in the Hall mobility.

In a frequency-selective multiple-input multiple-output (MIMO) channel, the optimum transmission is achieved by beamforming with eigenvectors obtained at each discrete frequency point, i.e., an extension of eigenbeam-space division multiplexing (E-SDM). However, the calculation load of eigenvalue decomposition at the transmitter increases in proportion to the number of frequency points. In addition, frequency-independent eigenvectors increase the delay spread of the effective channel observed at the receiver. In this paper, we propose a pseudo eigenvector scheme for the purpose of mitigating the calculation load and maintaining frequency continuity (or decreasing the delay spread). First, we demonstrate that pseudo eigenvectors reduce the delay spread of the effective channels with low computational complexity. Next, the practical performance of the pseudo E-SDM (PE-SDM) transmission is evaluated. The simulation results show that PE-SDM provides almost the same or better performance compared with E-SDM when the receiver employs a time-windowing-based channel estimation available in the low delay spread cases.

A diversity strategy is efficient to reduce the fluctuation of communication quality caused by fading. In order to further maintain the communication quality and improve the communication capacity, this paper proposes a two-dimensional diversity approach by serially-concatenating spectral precoding and power normalized-differential space time block coding (PN-DSTBC). Spectral precoding is able to take benefit from a frequency diversity effect without loss in spectral efficiency. In addition, PN-DSTBC is robust against serious phase noise in an extremely high frequency (EHF) band by exploiting a spatial diversity effect. However, there is a problem that a naive concatenation degrades the performance due to the imbalance of equivalent noise variances over transmit frequencies. Thus, we examine an equalized PN-DSTBC decoder as a modified approach to uniform equivalent noise variances over frequencies. The performance evaluation using computer simulations shows that the proposed modified approach yields the performance improvement at any modulation schemes and at any number of transmit frequencies. Furthermore, in the case of 64QAM and two transmit frequencies, the performance gain of the modified approach is 4dB larger than that of PN-DSTBC only at uncoded BER=10-4.

This letter presents an approximate analysis for coupling coefficients of a multi-slotted directional coupler to diagnose propagating modes in an output waveguide of a gyrotron. The coupling coefficients are calculated approximately and verified by a rigorous analysis.