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.

Using a full-vector finite element method (FEM) with curvilinear hybrid edge/nodal elements, a single-mode nature of index-guiding photonic crystal fibers, also called holey fibers (HFs), is accurately analyzed as a function of wavelength. The cladding effective index, which is very important design parameter for realizing a single-mode HF and is defined as the effective index of the infinite photonic crystal cladding if the core is absent, is also determined using the FEM. In traditional fiber theory, a normalized frequency, V, is often used to determine the number of guided modes in step-index fibers. In order to adapt the concept of V-parameter to HFs, the effective core radius, a_eff, is determined using the actual numerical aperture given by the FEM. Furthermore, the group velocity dispersion of single-mode HFs is calculated as a function of their geometrical parameters, and the modal birefringence of HFs is numerically investigated.

The effectiveness and possible applications of all-optical wavelength conversion using optical fibers are described. Several types of ultra-broad and ultra-fast wavelength conversion using highly-nonlinear fiber are shown. Over 70 nm conversion band by four-wave mixing, 500-fs pulse trains conversion by cross-phase-modulation-based nonlinear optical loop mirror and time-based optical add-drop multiplexing for 160 Gbit/s signal using wavelength conversion by supercontinuum are successfully demonstrated.

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.

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.

In order to construct optical access networks economically for fiber to the home (FTTH), it is important to reduce the cost of optical fiber cable installation. Optical fiber and cable costs have been reduced over the past ten years, however there have been few reports describing installation cost reduction. In this paper, we describe the design of high-density optical fiber cable that reduces the required installation time. To achieve this we have reduced the optical fiber cable weight and the friction coefficient of the cable sheath. We reduced the cable weight by using polyethylene foam and a non-metallic tensile strength member made of a new material, PBO. These two approaches reduce the cable weight by a total of about 30%. We also added a lubricant to the polyethylene sheath of this cable and this reduced the pulling force required for the additional cable by 30%-50%.

Low cost optical subscriber systems and effective operation are indispensable to the construction and maintenance of greatly expanded optical fiber networks. An optical fiber line monitoring system is essential for reducing maintenance costs and improving service reliability in optical access networks. To promote cost-effective optical fiber line operation, we propose an extended automatic optical fiber operations support system (AURORA) with a remotely installed fiber selector. We suggest a configuration for extended AURORA and design the dynamic range of the system. We confirmed that testing could be carried out on an extended optical network section of 10 km in length by using extended AURORA when the optical trunk line was less than 15 km. We also discuss the effect on the maintenance cost of optical fiber cables in access networks. We calculated the annual maintenance cost for periodic tests in actual operation areas, and confirmed that this cost could be reduced by 30% compared with that for a conventional system.

We have developed an easily-assembled optical coupling device that consists of two multifiber array connectors and a single-mode planar waveguide chip whose ends are passively positioned in novel plastic plug components compatible with the multi-fiber array connectors. The assembled 18 splitter devices are connected and disconnected easily and exhibit excellent levels of optical performance.

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.

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.

In modern high-capacity wavelength division multiplexing (WDM) transmission systems, there is increasing demand for large transmission capacity. To achieve this purpose, an L-band (1565-1625 nm) erbium-doped fiber amplifier (EDFA) is very effective method because the conventional silica-based EDF can be used. In EDFAs that used in WDM transmission systems, the gain flatness of EDFA is very important. A passive gain equalizer flattens the gain profile of EDFA. But the gain flatness in L-band deteriorates due to dynamic gain-tilt (DGT) and temperature gain-tilt (TGT) when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we propose an active gain-slope compensation technique for the L-band EDFA using a thulium-doped fiber (TDF). The EDFA actively gain-slope compensated by the TDF compensator keeps the gain profile constant for the wide input power range of more than 8 dB, a wide temperature range of 65 without gain-tilt in a wavelength band between 1575 nm and 1610 nm. Furthermore, the EDFA keeps a low noise figure of less than 7.5 dB.

We applied a Brillouin-OTDR, which is a distributed optical fiber strain sensor, to two actual concrete piles. The piles were made for use as highway foundations by on-site-pouring at construction sites and underwent load testing to ensure that their characteristics satisfied the required levels. Compressive strain caused by the load exerted on the piles was measured to an accuracy of 0.01% and a spatial resolution of 1 m. This measurement was obtained by embedding a strain-sensing optical fiber in the piles during construction. The results showed that there was good agreement between the measured strain and both the theoretical values and the values obtained with a conventional strain gauge based on electric resistance. Furthermore, the obtained strain distribution reflected the effects of friction between the pile surface and the ground. These results demonstrate the effectiveness of the Brillouin-OTDR for this kind of testing and also as a means of obtaining detailed data on the strain in concrete piles.

We have developed a distributed optical fiber strain sensor for detecting the collapse of river embankments. The sensor uses a Brillouin optical time domain reflectometer (BOTDR) and consists of an optical fiber cable and pieces of nonwoven cloth. Pieces of cloth are fixed to the cable at 1.5-meter intervals and it is then embedded in a U-shaped configuration in a river embankment. The pieces of cloth are displaced when there is movement of the soil in which they are embedded. If one of two adjacent pieces of cloth remains stationary while the other moves, the optical fiber between the two pieces is stretched. The collapse of an embankment can be detected by using a BOTDR to monitor any such stretching in the 1.5-m lengths of fiber. The developed sensor operates at a sensitivity of 0.025%/kgf, which is equivalent to 0.067%/mm, and is thus capable of detecting soil movements of a few mm in river embankments. The sensor is also able to provide effective advance warning of the collapse of a river embankment resulting from water penetration. We subjected the sensor system to field tests that demonstrated the effectiveness of its construction and its long-term stability. The developed sensor system is an effective tool for use in river management systems of the very near future.

An electric filed sensor using Mach-Zehnder interferometers has been designed to operate more than 10 GHz. The velocity of optical wave on the waveguide is investigated to determine the electrode length, and the characteristics of frequency response are analyzed using the moment method to determine the sensor element length. The electrode length of 1 mm and the element length of 8 mm are settled by these investigations. An isotropic electric field sensor is constructed using three sensors. The minimum detectable electric field strength is 22 mV/m at frequency bandwidth of 100 Hz. This is about 100 times for the conventional electric field sensor using the similar element. The sensitivity deviation is within 3 dB when temperature changes from 0 degree to 40 degree. The deviation of directivity can be tuned within 1 dB to calibrate the sensitivity of the each element. The sensitivity degradation is within 6 dB up to 5 GHz and within 10 dB up to 10 GHz. This is almost agree with the calculated results. The sensor can measure almost the same waveform as the applied electric field pulse whose width is 6 ns and rise time is less than 2.5 ns.

The economic success of monolithic optoelectronic and photonic ICs (OEICs, PICs) on InP depends strongly on their cost and performance. Taking into account these requirements as well as today's advanced hybrid integration approaches, the current status of monolithic InP integration technology is reviewed in examples, especially on components suitable for future telecommunication systems.

Various types of wavelength-selectable light sources (WSLs) and wavelength-tunable laser diodes (LDs) have been developed, and the one based on an array of distributed feedback (DFB) laser diodes (LDs) has the advantage of tuning that is both simple and stable tuning. It requires only the selection of a DFB-LD and a temperature control. We report on monolithically integrated WSLs with a DFB-LD array, multimode interference (MMI) coupler, semiconductor optical amplifier (SOA), and electro-absorption (EA) modulator. To make them compact, we introduced microarray structures and to ensure that they were easy to fabricate, we used selective area growth. For the WSL with an integrated EA modulator, we developed a center-temperature-shift method that optimizes the detuning wavelength between the lasing wavelength and the absorption edge wavelength of the EA-modulator. Using this method, we obtained a uniform extinction ratio and were able to demonstrate error-free 2.5-Gb/s transmission over a 600-km fiber span. A CW-WSL without an EA-modulator should provide enough output power to compensate the loss caused by the external modulators, but the high-power operation of a CW-WSL is sensitive to optical feedback from the front facet. We therefore used an angled facet in our WSLs and eliminated a mode hop problem. More than 20 mW of fiber-coupled power was obtained over 23 ITU-T channels on a 50-GHz grid.

Integration of spot-size converters (SSCs) with semiconductor optical amplifiers (SOAs) that improves chip-fiber optical coupling is inevitable for realizing high performance SOA modules. In this paper SSCs that can be easily integrated with SOAs and have little influence on the polarization sensitivity have been studied. We found that polarization insensitive active width-tapered SSCs can be realized by an optimum waveguide design of tensile-strained bulk structures. The SOA module exhibited large fiber-to-fiber gain (> 19 dB), small polarization sensitivity (< 0.4 dB), high fiber-coupled saturation output power (> +11.7 dBm) and record low module noise figure (< 6.3 dB) for the signal wavelength range of 1530-1560 nm.

We demonstrate a single high-order transverse mode surface emitting laser (VCSEL) with narrow trenches formed on a top surface. The design and the fabrication of a single high-order mode 850 nm GaAs VCSEL with micromachined surface relief are presented. Stable single-mode operation with a side-mode suppression ratio of over 40 dB was obtained in an entire measured current range. We obtained the maximum single mode power of over 3.5 mW and a record low series resistance of below 50 Ω. In addition, a single-lobe far field pattern is demonstrated even under high-order transverse mode operation by loading phase-shift on the top surface. A coupling efficiency with optical fibers is dramatically improved.

Optical disk systems have been used in a wide range of applications and the performance of these systems has been improving rapidly. The optical integration is one of the important technologies of the progress of the optical pickup head in the system. It can make the optical pickup head miniature, light sized, ease to assemble, cost reduced and reliable during long time operation. In this paper, at first, merits and features of the optical integration for optical disk systems are briefly reviewed. Then, our activities on the development of the various hybrid-integrated optical devices, "Laser Couplers" are reported. Especially, the most recent results on the "Two-wavelength-beam Laser Coupler," are described in detail. It has two-wavelength laser emission/detection functions and easily realizes an ultimate solution of the optical pickup head for the DVD/CD system, now being used in "PlayStaion2. " To simplify the structure and the fabrication of this device, a new monolithic-integrated two-wavelength laser diode, called a visible and infrared laser diode, has been developed, which can be easily fabricated using only two steps of metal organic chemical vapor deposition. The structures and characteristics of this device are reported. Lastly, other recent technologies of the optical integration, including monolithically integration, near field optics and so on, are reviewed.

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.

The Lorentzian-shape filter response of a microring resonator filter is not suitable to the practical use in WDM systems, because of the lack of pass band flatness, high cross talk, and the large wing in the stop band. Therefore, the tailoring of filter response shape is required to improve the performance. In this paper, the authors designed and demonstrated the box-like filter response of microring resonator filter by using the supermodes of stacked double microring resonators. The thicknesses of microrings and the separation between them were optimally designed to give the maximally flat response. A fine fabrication process was developed to achieve the deep and very smooth side wall. The shape factor, which is defined by the ratio of -1 dB bandwidth to -10 dB bandwidth, was successfully improved by three factors from 0.17 of Lorentzian shape to 0.51.

We studied various types of 2D and 3D Si-based photonic crystal structures that are promising for future photonic integrated circuit application. With regard to 2D SOI photonic crystal slabs, we confirmed the formation of a wide photonic bandgap at optical communication wavelengths, and used structural tuning to realize efficient single-mode line-defect waveguides operating within the bandgap. As regards 3D photonic crystals, we used a combination of lithography and the autocloning deposition method to realize complicated 3D structures. We used this strategy to fabricate 3D full-gap photonic crystals and 3D/2D hybrid photonic crystals.

We theoretically and experimentally demonstrate low loss branches in a Si photonic wire waveguide. Approximate calculation by the two-dimensional finite-difference time-domain (2-D FDTD) method and detailed design by the 3-D FDTD method indicate that low excess loss less than 0.2 dB is expected for a µm-size bend-waveguide-type branch at a wavelength of 1.55 µm. This branch is fabricated in a silicon-on-insulator substrate and the loss is evaluated to be 0.3 dB. This value is small enough to construct a very compact branching circuit.

All-optical switching operating at 1.55 µm band in fabricated GaInAsP directional couplers loaded with grating are reported experimentally. These switching operations were realized in spatially separated output ports. The devices are suitable for optical integrated circuits and would operate as all-optical routing switches in practical power level by use of optical Kerr effect and Bragg grating. Using the optical bistability in the device, latching operation for output signal can be realized in spatially separated output ports and the outputs from each port are complementary. Two all-optical gate operations, which are optical inverting operation and optically controlled switching in spatially separated output ports, are also demonstrated, where the signal and control lights have different wavelength.