We report Ultraviolet (UV)-induced visible light luminescence in artificial-lattice thin films of ion-doped silica glass (silica superstructure thin films). The film was composed of periodic nanometer layers of germanium-doped silica (Ge:SiO2), titanium-doped silica (Ti:SiO2), and tin-doped silica (Sn:SiO2). The thickness of each layer was between 10 and 30 nm. Despite the small thickness of the film (few microns), a relatively bright luminescence of white light was observed, along with cathode-ray luminescence in the superstructure film. In addition, irradiation of the superstructure film with UV light led to light amplification by stimulated emission at 405 nm. The experimental results suggest the potential application of silica superstructure thin films as optical amplifiers.

We have proposed a tunable laser with silica-waveguide ring resonators. In this tunable laser, a semiconductor optical amplifier was passively aligned and mounted onto a silica-waveguide substrate. The ring resonators can be tuned by controlling their temperatures using the thermo optic heaters formed on them, and there are no mechanically moving parts. Thus, they are sufficiently stable and reliable for practical use. Our tunable laser exhibits a high fiber-output power of more than 15 dBm and a wide tunable range of 60 nm (L-band, 50 GHz spacing, 147 channels). Moreover, a tunable laser with a much wider tunable range of 96 nm using 100-GHz-FSR ring resonators is also reported.

Integration of light sources on a Si chip is one of milestone to establish new paradigm of LSI systems, so-called "silicon photonics." In recent years remarkable progress has been made in the Si wire waveguide technologies for optical interconnection on a Si chip. In this paper, several Er embedded materials based on silicon are surveyed from the standpoint of application to the light emission and amplification devices for silicon photonics. We have concentrated to investigate an erbium silicate (Er2SiO5) as a light source medium for silicon photonics. To mention the particular features, this material has a layered structure with 0.86-nm period and a large amount of Er (25at%) as its constituent. The single crystalline nature gives several remarkable properties for the application to silicon photonics. We also discuss our recent studies of Er2SiO5 and a possibility of the shorter waveguide amplifier.

We focus on the development of new silicate phosphors for a white LED. In the europium doped silicate system, four LED phosphor candidates-- Li2SrSiO4:Eu2+, Ba9Sc2Si6O24:Eu2+ , Ca3Si2O7:Eu2+ and Ba2MgSi2O7:Eu2+ were found. Luminescent properties under near UV and visible excitation were investigated for the new Eu2+ doped LED silicate phosphors. These new phosphors have a relatively strong absorption band in a long wavelength region.

We propose and demonstrate a new stacked packaging structure using silica-based planar lightwave circuits (PLCs) with integrated micro-mirrors. This structure enables us to integrate active devices on PLCs with certain flexibility as regards optical coupling design and device selection. To achieve this, we developed an integrated micro-mirror with an accurate reflection angle and shielding structures to prevent crosstalk, and successfully demonstrated an 8-channel photodiode array module with excellent characteristics consisting of a high responsivity of > 0.85 A/W and a low crosstalk of < -65 dB.

Thermal stability of stacked high-κ dielectrics, especially ZrO2, HfO2 and ZrSiO4 /SiO2 layered structures, on silicon has been investigated in terms of ultrahigh vacuum (UHV), 1 Torr N2 and helium (He) gas annealing with controlled oxygen partial pressure (PO2) at 920. Comparison of 2 nm and 20 nm ZrO2 films under UHV annealing revealed that the trigger of silicidation is the contact of ZrO2, SiO and Si accompanying disappearance of interfacial SiO2 layer due to SiO desorption. In the contact position, a small amount of SiO gas can easily change ZrO2 to ZrSi2. This reaction model is also applicable to the silicidation of HfO2 and ZrSiO4, at not only stacked high-κ film/Si substrate interface, but also at gate poly-Si/high-κ film interface. Moreover, comparison of UHV, N2 and He annealing with controlled PO2 revealed that the optimal PO2 ranges in He at which the thermal stability of layered structure can be achieved are wider than those in UHV and N2. This result suggests that He gas physically may obstruct SiO creation due to the quenching of atomic vibration at degradation-prone sites in the SiO2 /Si interface, thus reducing probability of bond breaking process, which is the first step of silicidation.

The mesoporous materials from the self-assembled organic-inorganic compound materials have great possibilities for a variety of applications. However, to make use of these kinds of materials effectively, they must be controlled. In this paper, we are succeeded in powder state pore size control and in significantly fabrication film state for device application use.

Self-ordered mesoporous silicate films from organic-inorganic compound materials are successfully fabricated into the surface photo voltage (SPV) type gas sensor device as a gas adsorption insulator layer. These kinds of gas sensors device exhibit NO gas sensing property dependent on their mesoporous film structure. We are succeeded in indication about a possibility of mesoporous silicate film for the SPV type gas sensor application.

We describe hybrid integration technologies that employ silica-based planar lightwave circuit (PLC) platforms, and report several high-performance optical components based on these technologies. First, we describe the requirements for optical integrated circuits. Then, we discuss the technologies used in hybrid integration, namely optical coupling between a semiconductor optical device and a silica waveguide, electrical signal transmission to the semiconductor optical device, and high quality optical signal processing. In addition, we describe optical integrated circuits developed for short- and long-haul networks. We realized these high-performance integrated components by combining appropriate hybrid integration technologies.

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.

We have reviewed recent progress on arrayed waveguide gratings for DWDM applications. AWGs can be used to realize not only mux/demux filters with various channel spacings, but also highly integrated optical components.

Long-period fiber gratings (LPGs) using a high-silica core fiber are presented. A high-silica core fiber has a residual stress in the core, and the grating structure is formed by stress releasing of the core using a focused CO2 laser beam. The dependence of the transmission spectrum on temperature and tensile strength is measured, and low dependence compared with conventional LPGs is observed. These unique characteristics are caused by the difference of temperature and tensile strength changes of the effective indices for the fundamental propagation mode and the cladding mode in the high-silica core fiber.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

Planar lightwave circuits (PLCs) provide various important devices for optical wavelength division multiplexing (WDM) systems, subscriber networks and etc. This paper reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating multiplexers, optical add/drop multiplexers, programmable dispersion equalizers and hybrid optoelectronics integration technologies.

The temperature dependence of central wavelength of optical filters is a serious problem for the dense WDM systems. This dependence is owing to the temperature dependence of optical path-length of the waveguide. In this study, we realized a temperature independent silica-based optical filter at 1. 55 µm wavelength using an athermal waveguide, in which optical pathlength is independent of temperature. First, we designed a silica-based athermal waveguide, and next we designed and fabricated a ring resonator using the athermal waveguide. As a result, we successfully decreased the temperature dependence of central wavelength to less than 4 10 -4 nm/K, which is 3% and 0. 3% of corresponding values of conventional silica-based and semiconductor waveguide filters, respectively.

We propose low Rayleigh scattering Na2O-MgO-SiO2 (NMS) glass as a candidate material for low-loss optical fibers. This glass exhibits Rayleigh scattering which is only 0.4 times that of silica glass, and a theoretical evaluation suggests that it is dominated by density fluctuation. An investigation of the optical properties of NMS glass reveals that a minimum loss of 0.06 dB/km is expected at a wavelength of 1.6 µm and that the zero-material dispersion wavelength is found in the 1.5 µm band. To establish the waveguide structure, we evaluated the feasibility of using F-doped NMS (NMS-F) glass as a cladding layer for an NMS core and found that it is suitable because it exhibits low relative scattering (e.g. 0.7) and is versatile in terms of viscosity matching. We also describe an attempt to draw optical fibers using the double crucible technique.

We describe the design, fabrication, and characteristics of FDM/WDM coupler deposited by TEOS-O3 based APCVD method on silicon substrates. Due to drastically reduced birefringence by APCVD process, completely polarization independent narrow band (100 GHz) Mach-Zehnder type FDM coupler was obtained. We also fabricated 1.3/1.55 µm directional coupler type WDM coupler with very low insertion loss.

This paper proposes a photonic integrated beam forming and steering network (BFN) that uses switched true-time-delay (TTD) silica-based waveguide circuits for phased array antennas. The TTD-BFN has thermooptic switches and variable time delay lines. This TTD-BFN controls four array elements, and can form and steer a beam. An RF test was carried out in the 2.5 GHz microwave frequency range. The experimental results show a peak-to-peak phase error of 6.0 degrees and peak-to-peak amplitude error of 2.0 dB. Array factors obtained from the measured results agree well with the designed ones. This silica-based beam former will be a key element in phased array antennas.

A strictly nonblocking 88 matrix switch was designed and fabricated using silica-based planar lightwave circuits (PLC) on a silicon substrate. The average insertion loss was 11 dB in the TE mode and 11.3 dB in the TM mode. The average switch element extinction ratio was 16.7 dB in the TE mode and 17.7 dB in the TM mode. The accumulated crosstalk was estimated to be 7.4 dB in the TE mode and 7.6 dB in the TM mode. The driving power of the phase shifter required for switching was about 0.5 W and the polarization dependence of the switching power was 4%. The switching response time was 1.3 msec. The wavelength range with a switch extinction ratio of over 15 dB was 1.31 µm30 nm.