Low-profile inverter power supplies are increasingly required for backlight systems of liquid crystal displays (LCDs). A great deal of attention has been focused on the application of piezoelectric transformers (PTs) to such power supplies. To miniaturize PT inverters still further, PTs need to have sufficient high voltage-step-up-ratio, which can be achieved by a multilayered PT. First, this paper describes a method for simulating such performance using a distributed constant equivalent circuit model. The results of the simulation for a multilayered PT operated in the third order longitudinal vibration mode show that the resistance of internal electrodes causes the dominant loss factor. Next, a power inverter incorporating the multilayered PT was fabricated. This power inverter can be operated over a wide input DC voltage range from 7-20 V. Regarding a conventional inverter drive circuit, when input DC voltage range was extended, the inverter efficiency remarkably decreased. For the reason, we developed a new inverter circuit, which is equipped with an automatic drive voltage control circuit to maintain the drive voltage to the PT at a constant value. As a result, the fabricated power inverter exhibited more than 90% overall efficiency and 3.5 W output power, which is enough to light up a 12.1-inch color LCD. The maximum luminance efficiency on a light transmission plate of the backlight was as high as 30 cd/m2/W.

A new rewritable medium utilizing a guest-host (G-H) polymer-dispersed liquid-crystal (PDLC) film has been developed in our laboratory. The medium is thermally written and electrically erased. It is portable, like paper, and can store recorded data because of the memory effect of smectic-A liquid crystal (SmA LC), which exhibits bistable states of homeotropic and focal conic alignment. Dichroic dye is added to the SmA LC to form the G-H type. An evaluation of the characteristics revealed that this medium exhibits both high contrast and good reliability.

In this paper, we describe design considerations for inverse dispersion fiber (IDF) whose chromatic dispersion is designed to compensate for that of conventional 1.3 µm zero-dispersion single-mode fiber (SMF). We clarify the appropriate structural parameters for W-type, triple-clad-type and ring-type refractive index profiles to realize a hybrid transmission line composed of SMF and IDF taking into consideration the bending sensitivity and the available wavelength bandwidth that achieves an average chromatic dispersion of below 1 ps/nm/km in the 1.55 µm region. We also show that, when the launched power is less than 0 dBm/ch, a hybrid transmission line composed of SMF and IDF provides better 40 Gbps 8 ch dense wavelength division multiplexing (DWDM) transmission performance than a conventional dispersion compensation scheme with a dispersion compensating fiber (DCF) module.

The possibility of applying a recently proposed emission source location method, which is based on CISPR measurements, to sources with arbitrary directional current components is studied. We propose a new finding algorithm in which the horizontal and the vertical current components are estimated at the same time by taking into account the contribution of horizontal current components when calculating the vertical electric field. As a result of experimental verification by using two spherical dipole antennas as ideal emission sources, estimated values show good agreement with the original ones in the frequency range from 300 MHz to 1 GHz, where the position estimation deviation d was less than 0.15 m, the amplitude estimation deviation j was less than 2.1 dB, and furthermore the angle of current direction could be estimated. Consequently, this method with the presented new algorithm can be applied to find radiated emission sources even when the current components point to arbitrary directions.

We investigate a method to suppress the polarization-dependent loss (PDL) of long-period fiber gratings (LPFGs). We study the origins of the PDL and propose an azimuthally isotropic UV exposure to suppress the UV-induced birefringence and to realize low-PDL LPFGs. By using this technique and a low birefringent fiber together, the PDL of LPFGs can be reduced to a sufficiently low level required in high performance communication systems. Moreover, the validity of our theoretical modeling is confirmed by the experimental results.

For the purpose of applying to 50 GHz channel spacing 10 Gb/s DWDM systems, the dispersion reduced fiber Bragg gratings (FBG) is demonstrated. This new FBG is designed by applying in optimized cosine expansion series to the refractive index profile. The 10 π-phase shifts in the refractive index profile realize both square filtering characteristics and linear phase responses resulting in reducing group delay variation in the reflective bandwidth. The FBG, fabricated according to the new design, is tested and shows more than 30 dB isolation for the adjacent channel and less than 10 psec group delay variation in the reflective bandwidth. This small dispersion leads to vast improvement of 10 Gb/s transmission performance. The power penalty of the new FBG is suppressed to 1/6 of that of conventional FBG. Furthermore, the symmetrical refractive index profile, realized by applying a cosine expansion series, shows that these optical characteristics have no dependence of the light launching direction. From these results, this new design offers an FBG suitable for the ADM used in 10 Gb/s DWDM systems.

This paper describes design optimization and performances of hybrid optical transmission lines consisting of effective-area-enlarged pure silica core fiber and dispersion compensating fiber. As a result of the design optimization, considering low nonlinearity and good bending characteristic, the developed fibers exhibit a span average loss of 0.208 dB/km, a span average dispersion slope of 0.02 ps/nm2/km and low nonlinearity with an equivalent effective area of 60 µm2. Further optimization of the relationship among the nonlinearity, the dispersion slope and the bending characteristic enables perfectly dispersion-flattened hybrid optical transmission lines exhibiting a low transmission loss of 0.211 dB/km, low nonlinearity with an equivalent effective area of 60 µm2 and small dispersion deviation of 0.03 ps/nm/km in a wavelength band wider than 40 nm.

This paper presents a historical review of fiber technologies from the 1970s till now, focused on design, transmission characteristics, and reliability assurance of silica optical fibers. Discussion is made by dividing the period into two phases; the first phase closing nearly at the end of the 1980s and the second one starting at the same time. As for the first phase, we present designs of graded-index multimode fiber and single-mode fiber, and development of dispersion shifted fiber. Mechanical reliability assurance and loss increase phenomena due to hydrogen are also described. Development of an optical fiber amplifier triggered the start of the second phase. Due to the introduction of WDM transmission systems as well as demand on high bit-rate transmission, fiber dispersion and nonlinearity have become indispensable factors to be taken into consideration for system design and performance evaluation. We discuss novel non-zero dispersion shifted fibers and dispersion compensating fibers, developed to meet the requirements for long distance and high bit-rate WDM transmission systems. Finally, discussions are made on the future research and development items, which are necessary to realize anticipating photonic networks.

A numerical technique based on Haar wavelets is used for solving transient problems of transmission lines. The approach of our method is to convert the original coupled partial differential equations, the transmission line equations or the telegrapher equations, to a system of ordinary matrix differential equations via Haar wavelets. Then, transient problems of transmission lines can be solved by matrix operations. Numerical examples of homogeneous and dispersive lines, along with both linear and nonlinear loads are verified. In addition, non-sinusoidal signals such as the unit step function and the rectangular pulse for digital applications are included to demonstrate the use of this efficient, easy-to-handle, stable, and versatile method.

This contribution discusses which information can be derived from estimated directions of arrival (DOAs) and directions of departure (DODs) from a multiple-input multiple-output (MIMO) radio system, and establishes two new parameters describing the multipath spread at both link ends. We find that the multipath component separation, MCS, combines delay, (double-) angular and Doppler dispersion, as appropriate. MCS provides a system-independent radio characterization of propagation environments and aids in selecting optimum positions for smart-antenna deployment. Evaluation of double-directional measurements (antenna arrays at both link ends) in indoor environments show the usefulness and the limits of the multipath component separation concept.

The initial phase alternation of RZ pulses having duty cycle beyond 50% in dispersion-managed-link is found to help stabilize DM solitons transmissions. The stable soliton propagation of such wide RZ pulses should ease the difficulties designing soliton-based DWDM systems due to less spectral occupancy/channel. For the proof of concept, 40 Gbit/s WDM transmissions are numerically investigated and the initial phase alternation improved the transmission distance by the factor of 2 in the soliton-soliton interaction limited regime. The advantage of this concept has also been verified by conducting 40 Gbit/s single and 8 channels WDM transmission experiments using OTDM techniques with initial phase alternation.

A novel optical transmission line consisted of fibers characterized by positive and negative medial dispersion of NZ-DSF and SMF was designed and fabricated. Both P-MDF and N-MDF have achieved the medial dispersion and low non-linearity simultaneously. Total characteristics were confirmed to be suitable for the future high-bit-rate transmission.

We demonstrated variable dispersion compensation using the Virtually Imaged Phased Array (VIPA) for a 40-Gbit/s dense-WDM transmission system. The large tunable range from -800 to +800 ps/nm in the entire C-band wavelength range and the high tunable resolution of 1 ps/nm was achieved by using a 3-dimensional mirror equipped with a stepping motor that we developed. We adopted the dispersion monitor of 40-GHz intensity extracted from the received 40-Gbit/s baseband signals, and verified that this dispersion monitoring method is applicable to nonlinear transmission by detecting the monitor peak. Using the VIPA variable dispersion compensator and the dispersion monitor, we demonstrated 1.28-Tbit/s (40-Gbit/s 32 ch) automatic dispersion compensation. As a result, we confirmed that only two VIPAs and one fixed dispersion compensating fiber (DCF) are needed to make our method applicable to the entire C-band for dense WDM 40-Gbit/s systems having a large transmission range of 80 km.

The effectiveness of Aeff enlarged positive dispersion fiber (EE-PDF) and hybrid amplification configuration with erbium-doped fiber amplifier (EDFA) and fiber Raman amplifier for reducing the fiber nonlinearity and improving the transmission performance in long distance 40 Gbit/s-based WDM transmission was investigated. We have confirmed that the use of EE-PDF in modified dispersion map for 40 Gbit/s transmission is quite effective to increase the transmissible distance and have successfully demonstrated 16 40 Gbit/s WDM transmission over 2000 km with proper dispersion management. We have also confirmed that the use of distributed Raman amplification is quite effective to extend the repeater spacing. By adding the optimum Raman amplification, almost the same transmission performance was obtained with a doubled repeater spacing in long distance 40 Gbit/s-based WDM transmission.

In this paper, we propose an activity-based estimation scheme to determine the received signal power disparity, that enhances the BER performance of the SIC scheme in a DS/CDMA system considering a practical voice activity factor, and compare BER performance with those of other schemes with or without estimation. Numerical analysis results show that the SIC scheme with the proposed activity-based estimation improves the BER performance compared with that without considering voice activity, and it approaches to that of the ideal estimation as the total number of concurrent users increases. In addition, the higher becomes the maximum attainable SNR, the better becomes the BER performance of the proposed activity-based estimation scheme.

We achieved a dispersion tolerance of 25-ps/nm at 80-Gbit/s using novel carrier-suppressed return-to-zero (CS-RZ) coding realized by duty ratio and optical multiplexing phase control. We also show that the dispersion tolerance strongly depends on the relative optical phase difference between adjacent time slots, and demonstrate 80-Gbit/s 60-km DSF transmission without dispersion compensation by using a newly-fabricated stable 80-Gbit/s OTDM transmitter.

In leased line services used by ISPs (Internet Service Providers) the bandwidth is fixed, but the traffic changes dynamically. Therefore, there is a necessity for ISPs to accommodate extra capacity to meet peak usage demands; many resources are not used in off-peak hours. To address this, we propose an auction method for the dynamic allocation of bandwidth to ISPs sharing backbone networks. By this method, backbone networks can be used effectively as each ISP is able to secure bandwidth according to its own policy. The Internet users can also be expected to receive good services, as it enables them to obtain information about all ISPs, such as the access fee and QoS (quality of service) provided, and to select congenial ISPs from among all ISPs according to this information. In this study, we compare a dynamic bandwidth allocation service with a leased line service (fixed allocation of bandwidth to ISPs) by using the users' utility to estimate the effectiveness of the proposed method.

Two planar asymmetric coupled waveguides were fabricated by using different materials (InGaAsP and TiO2/Si) and tested as dispersion compensators (or pulse compressors). Compression of a more-than-10-ps chirped pulse is experimentally demonstrated by using an InGaAsP planar asymmetric coupled waveguide whose group velocity dispersion (GVD) is enhanced by structural optimization and is spectrally tuned to an input pulse as precisely as possible. A large polarization dependence of the pulse compression was also observed and indicates that the observed pulse compression results from dispersion compensation due to the GVD associated with supermodes. A new planar, asymmetric coupled waveguide with a large difference in refractive indices of the two waveguides was fabricated by using a combination of dielectric (TiO2) and semiconductor (Si) materials in order to obtain better GVD characteristics than semiconductor (for example, InGaAsP) asymmetric coupled waveguides. A preliminary experiment on pulse compression using the TiO2/Si planar asymmetric coupled waveguide was conducted. A 2.8-ps blue chirped pulse was compressed down to about 1 ps by a 1-mm-long waveguide (compression ratio: 0.375, which is better than those of the previous InGaAsP planar asymmetric coupled waveguides). This compression ratio agrees well with a theoretical result obtained by a numerical model based on a supermode's GVD.

We review recent progresses in our studies on the fiber-optic soliton compression and related subjects with special emphasis on dispersion-flattened fibers (DFFs). As for the ultimately short pulse generation, it has been demonstrated to compress 5 ps laser diode pulses down to 20 fs with a 15.1 m-long single-stage step-like dispersion profiled fiber employed. The compression was brought about through a series of the higher order soliton processes in conjunction with a single and ordinary erbium-doped fiber preamplifier, and DFFs contained at its end played a major role. We have performed intensive investigations on the DFF compression mechanisms in the 100-20 fs range. A fairly reliable model was developed for the higher order soliton propagation along a DFF in the temporal range from 100 down to 30 fs by taking into consideration the higher order nonlinear and dispersion effects as well as incident pulse shape dependence. Through the simulation, parametric spectrum generation originating from the modulation instability gain was pointed out at frequencies apart from the pump wave frequency, which agrees with the experimental observation. Its possible application is also discussed.

In this letter, we describe the conditions for measuring the nonlinear refractive index n2 when using the self-phase modulation-based cw dual-frequency method. We clarify the appropriate measurement conditions for dispersion-shifted and conventional single-mode fibers both numerically and experimentally. We also show experimentally that the evaluated n2 values for conventional single-mode fiber depend on the signal wavelength separation.