Aiming at the problem of low classification accuracy of surface defects of lithium battery pole pieces by traditional classification methods, an image classification algorithm for surface defects of lithium battery pole piece based on deep learning is proposed in this paper. Firstly, Wavelet Threshold and Histogram Equalization are used to preprocess the detect image to weaken influence of noise in non-defect regions and enhance defect features. Secondly, a VGG-InceptionV2 network with better performance is proposed by adding InceptionV2 structure to the improved VGG network structure. Then the original data set is expanded by rotating, flipping and contrast adjustment, and the optimal value of the model hyperparameters is determined by experiments. Finally, the model in this paper is compared with VGG16 and GoogLeNet to realize the recognition of defect types. The results show that the accuracy rate of the model in this paper for the surface pole piece defects of lithium batteries is 98.75%, and the model parameters is only 1.7M, which has certain significance for the classification of lithium battery surface pole piece defects in industry.

Silica-LiNbO3 (LN) hybrid modulators have a hybrid configuration of versatile passive silica-based planar lightwave circuits (PLCs) and simple LN phase modulators arrays. By combining the advantages the two components, these hybrid modulators offer large-scale, highly-functionality modulators with low losses for advanced modulation formats. However, the reliability evaluation necessary to implement them in real transmissions has not been reported yet. In terms of reliability characteristics, there are issues originating from the difference in thermal expansion coefficients between silica PLC and LN. To resolve these issues, we propose design guidelines for hybrid modulators to mitigate the degradation induced by the thermal expansion difference. We fabricated several tens of silica-LN dual polarization quadrature phase shift keying (DP-QPSK) modulators based on the design guidelines and evaluated their reliability. The experiment results show that the modules have no degradation after a reliability test based on GR-468, which confirms the validity of the design guidelines for highly reliable silica-LN hybrid modulators. We can apply the guidelines for hybrid modules that realize heterogeneous device integration using materials with different coefficients of thermal expansion.

Recent advances in phase-sensitive amplifiers (PSAs) using periodically poled LiNbO3 are reviewed. Their principles of operation and distinct features are described. Applications in optical communication are studied in terms of the inline operation and amplification of a sophisticated modulation format. Challenges for the future are also discussed.

In all-optical switches using the cascade of second harmonic generation and difference frequency mixing in periodically poled lithium niobate (PPLN) waveguide devices, walk-off between the fundamental and second harmonic pulses causes crosstalk between neighboring symbols, and limits the switching performance. In this paper, we numerically study retiming characteristics of all-optical switches that employ the PPLN waveguide devices with consideration for the effects of the crosstalk and for the input timing of the data and clock pulses. We find that the time offset between the data and clock pulses can control the timing jitter of the switched output; an appropriate offset can reduce the jitter while improving the switching efficiency.

We present recent progress of high-speed Mach-Zehnder modulator technologies for advanced modulation formats. Multi-level quadrature amplitude modulation signal can be synthesized by using parallel Mach-Zehnder modulators. We can generate complicated multi-level optical signals from binary data streams, where binary modulated signals are vectorially summed in optical circuits. Frequency response of each Mach-Zehnder interferometer is also very important to achieve high-speed signals. We can enhance the bandwidth of the response, with thin substrate. 87 Gbaud modulation was demonstrated with a dual-parallel Mach-Zehnder modulator.

A new LiTaO3 electro-optic polarization modulator utilizing traveling-wave electrodes and a double periodic poling structure is proposed. Utilizing the double periodic poling structure, both quasi-phase matching between TE and TM guided-modes, and quasi-velocity matching between a lightwave and a modulation microwave are obtainable at modulation frequencies over 10 GHz.

A fuzzy logic control battery equalizing controller (FLC-BEC) is adopted to control the cell voltage balancing process for a series connected Li-ion battery string. The proposed individual cell equalizer (ICE) is based on the bidirectional Cuk converter operated in the discontinuous capacitor voltage mode (DCVM) to reduce the switching loss and improve equalization efficiency. The ICE with the proposed FLC-BEC can reduce the equalizing time, maintain safe operations during the charge/discharge state and increase the battery string capacity.

The proton-exchanged waveguide formed on MgO-doped lithium niobate crystals is resistant to the optical damage or the photorefractive effect. Therefore, this waveguide is believed to be a promising device for optical information and processing. However, the optical damage can also be an important problem for this waveguide in the communication wavelength since the high-power optical source is used. In this report, a brief general review on the optical properties and its practical application of the lithium niobate crystal as the optical waveguide are given. Then the experimental research work aimed to clarify the properties and its mechanism of the electrooptic effect and the optical damage or photorefractivity of the lithium niobate optical waveguide is described. In this work, the optical damage in this proton-exchanged waveguide is measured quantitatively at various optical wavelengths including blue and red light by using the holographic grating method and the infrared communication wavelength (1550 nm) by using the prism coupler method. The optical damage is significant not only in blue wavelength but also in the red, and even at 1550 nm with high power (100 mW) laser diode for communication. So the optical damage cannot be negligible also in the communication wavelengths. The effect of annealing temperature is also discussed. At the relatively high temperatures, the optical damages are founde to be annealed out. The effect of the applied electric field to the optical damage is experimentally discussed and its enhancement is observed to the applied d.c. and a.c. fields. In conclusion, the optical properties as the electrooptic constant and the optical damage are experimentally measured and the many fundamental data are obtained to realize the useful and practical optical devices.

A lithium niobate (LiNbO3)/silicon (Si) hybrid structure has been developed by the surface-activated bonding of LiNbO3 chips with gold (Au) thin film to Si substrates with patterned Au film. After organic contaminants on the Au surfaces were removed using argon radio-frequency plasma, Au-to-Au bonding was carried out in ambient air. Strong bonding at significantly low temperatures below 100 without generating cracks has been demonstrated.

A systematic approach to the analysis and design of a bi-directional Cuk converter for the cell voltage balancing control of a series-connected lithium-ion battery string is presented in this paper. The proposed individual cell equalizers (ICE) are designed to operate at discontinuous-capacitor-voltage mode (DCVM) to achieve the zero-voltage switching (ZVS) for reducing the switching loss of the bi-directional DC/DC converters. Simulation and experimental results show that the proposed battery equalization scheme can not only enhance the bi-directional battery equalization performance, but also can reduce the switching loss during the equalization period. Two designed examples are demonstrated, the switch power losses are significantly reduced by 52.8% from the MOSFETs and the equalization efficiency can be improved by 68-86.9% using the proposed DCVM ZVS battery equalizer under the specified cell equalization process. The charged/discharged capacity of the lithium-ion battery string is increased by using the proposed ICEs equipped in the battery string.

We fabricate a 763-nm laser module based on second-harmonic generation using a direct-bonded quasi-phase-matched LiNbO3 ridge waveguide. We obtained a 0.84-mW output of 763 nm light using a 1526-nm distributed-feedback laser diode. We also demonstrate O2 gas detection using the module output.

A rack-mounted DC power-supply system utilizing Li-ion batteries, which have higher energy density than conventional VRLA batteries, was developed. The system was designed to have the management functions of Li-ion batteries, such as overcharge protection, over-discharge protection, and cell-voltage equalization, by taking operational requirements into consideration. The volume and weight of the entire system were decreased to one-fourth and three-fifths, respectively, of the volume and weight of a conventional system, making the proposed system ideal as a high-energy-density backup power supply. The functions, system configuration, and characteristics of this rack-mounted DC power supply system utilizing Li-ion batteries are described.

This paper describes the characteristics of lithium-ion cells developed for stationary use, as in the case of stand-by sources in power systems. The effect of a cell-voltage-equalizing circuit developed for batteries of cells is also demonstrated. The tested lithium-ion cells were suitable to be charged by the constant-current, constant-voltage (CCCV) method and could be charged efficiently over a wide range of temperatures. They also showed good discharge performance with little dependence on the discharge current and temperature. Total capacity reduction of over 60% can be expected in batteries of lithium-ion cells. The cell-voltage-equalizing circuit was shown to be useful and necessary for batteries of lithium-ion cells in order to suppress deviations in the cell voltage and capacity loss.

The recent progress in the field of Ti:Er:LiNbO3 waveguide lasers with emission wavelengths in the range 1530 nm < λ < 1603 nm is reviewed. After a short discussion of the relevant fabrication methods concepts and properties of different types of lasers with grating resonator, acoustooptically tunable Fabry Perot type lasers and new ring laser structures are presented.

This paper presents a proposal for a novel integrated tunable coupler device called programmable coupler ladder, based on Titanium diffused lithium niobate waveguide and Y-junction reflector. Unlike the traditional serial to parallel converter, the coupler ladder sorts the output bits in the time axis using a built-in delay waveguide. With a proper control signal it can perform signal processing at the bit level. It also can generate coherent multi-channel outputs with theoretically arbitrary amplitude and phase from continuous input light source. Its application in optical microwave beam forming is briefly described. The key component, built-in delay line based on Y-junction reflector, has been experimentally verified via a loop resonator structure. 1 dB loss is found for each Y-junction reflector, which enables a practical coupler ladder. The loop itself is also an important device for optical signal processing.

This paper describes recent progress in research on wavelength converters that employ quasi-phase-matched LiNbO3 (QPM-LN) waveguides. The basic structure and operating principle of these devices are presented. The conversion efficiency in difference frequency generation (DFG), second harmonic generation (SHG) and an SHG/DFG cascade scheme are explained. Device fabrication technologies such as periodic poling, and those used for annealed proton-exchanged (APE) waveguides, and direct bonded waveguides are introduced. An APE waveguide is used to demonstrate the wavelength conversion of broadband (> 1 Tbit/s) WDM signals. The low penalty conversion of high-speed (40 Gbit/s) based WDM signals is also reported. Excellent resistance to photorefractive damage in a direct bonded waveguide is presented. This high level of resistance enabled highly efficient wavelength conversion. A new design concept is introduced for a multiple QPM device based on the continuous phase modulation of a periodically poled structure. This multiple QPM device enables the variable wavelength conversion of WDM signals. High-speed wavelength switching between ITU-T grid wavelengths using a finely tuned multiple QPM device is also reported. QPM-LN based wavelength converters have several advantages, including the ability to convert high-speed signals of 1 THz or greater, no signal-to-noise (S/N) ratio degradation, no modulation format dependence, and they are capable of the simultaneous conversion of broadband WDM channels. They will therefore be key devices in future photonic networks.

In the microwave band, Optical Electric Field Sensors (OEFS) provide an attractive method to measure electromagnetic fields precisely. It is difficult however, to develop an OEFS that operates with both wide bandwidth and high sensitivity. In this paper, we propose a Log-Periodic Dipole antenna Array (LPDA)-type OEFS that achieves high sensitivity over a wide bandwidth. The LPDA-type OEFS has a large number of electrodes that are attached to each of the antenna elements. Not only the lengths of the antenna elements but also the lengths of electrodes vary log-periodically. The OEFS responds to microwaves by synchronizing the propagation direction of light with the propagation direction of the microwave. An OEFS constructed of y-cut z-propagation Lithium Niobate (LN) demonstrates good stability against temperature variation. Theoretical analysis with respect to the refractive index variation and optical modulator with the crystal orientation will be provided in this paper. In addition, the characteristics of the proposed LPDA-type OEFS will be shown over wide bandwidth in the microwave band.

We have developed manganese-based lithium secondary battery technology as a part of a 10-year national project in Japan for The Development of Dispersed-Type Battery Energy Storage Technology. The cell chemistry we developed consisted of a modified graphite anode material containing dispersed Ag particles, and a partially substituted LiMn2O4 cathode with Li in the Mn sites. These materials showed a significant improvement in a cell's cycle life performance. The 250 Wh class single cell with the cell chemistry mentioned above showed energy densities of 131 Wh/kg and 295 Wh/dm3. The 2 kWh class module battery including 8 cells connected in series and a battery management system delivered energy densities of 122 Wh/kg and 255 Wh/dm3 that exceeded the final target of 120 Wh/kg and 240 Wh/dm3 for the project. Most of the target items for the battery performance were accomplished and proved. Thus the basis for practical application was developed, however, some areas concerning the further durability under various circumstances and conditions still remain to be accomplished. Continuous development for mass production and cost reduction is also expected for this technology in order to contribute to industry and society.

Using LiTaO3 and LiNbO3 single crystals, we wish to miniaturize a powerful ultrasonic vibrator. We studied the method of measuring mechanical fractures of resonators with good reproducibility and collected data on mechanical fractures of crystals due to high input electric power. Chip resonators with a 4 MHz and 8 MHz shear mode were selected for the test samples. The driving frequency was swept near the resonance frequency, the duration time was short enough to raise the resonant vibrations and the driving voltage increased in one-volt increments. The method is free from unstable temperature increases. Values of the fracture limit for the driving current were measured and transformed to mechanical vibration velocities. These showed a nearly normal distribution. It was a surprise that concavity in the crater was observed at the center of the 16 MHz LiNbO3 resonator due to high input power. It was confirmed that the elastic fracture limit was latently very high for LiNbO3 and LiTaO3 single crystals.

We present three-wave mixing devices useful for signal processing functions in WDM and TDM systems, including wavelength conversion, spectral inversion, and gated mixing. These mixers exhibit extremely wide bandwidth, low noise, high efficiency, and format transparency.