This paper reports on time-space conversion-based differential processing of optical signals using a high-resolution arrayed-waveguide grating (AWG) and a spatial filter at a wavelength of 1.55 µm. We clarify the advantages of the AWG device and show where it is applicable. In order to reduce loss at the spatial filter, we propose a new phase-only filter that functions as a differential filter. The difference between the exact differential filter and the proposed phase-only filter is calculated theoretically. We confirm experimentally that the optical pulse can be differentiated by the proposed filter. For application of differential processing, we also proposed a phase modulation to amplitude modulation (PM-AM) conversion and demonstrated the PM-AM conversion at 10 Gbit/s signals using a PSK-non-return-to-zero (NRZ) format.

Precise plastic V-grooved alignment parts for connecting single-mode optical fiber arrays to multi-port optical devices were successfully molded with a thermosetting resin by using a highly productive injection molding technique. The molded parts are two types of V-grooved blocks that are compatible with the size of optical devices having eight or twelve optical ports. Their dimensional accuracy must be better than 1 µm over the whole length of the V-grooves for efficient optical coupling. This strict requirement was satisfied using precisely processed molding tools with a specially chosen resin under optimum molding conditions. The feasibility of the optical alignment parts was assured by an evaluation of their loss characteristics and reliability in coupling single-mode fibers to 18 power splitters, where the average optical loss was 0.2 dB and the change in loss was less than 0.2 dB under a temperature cycling test and also under a damp heat test. These results show that plastic molded parts can be used for precise coupling of single-mode optical devices, and will lead to a breakthrough in innovation in the field of optical packaging.

Recent status of the polymer optical fiber (POF) for high speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time 20 years ago at Keio University, and several methodologies to fabricate GI POF have been currently proposed worldwide. In this paper, we both theoretically and experimentally verify that the most transparent GI POF can be obtained by the polymer-dopant system. The relation between the refractive index profile and the dispersion characteristics of the GI POF was quantitatively clarified. The refractive index profile of the GI POF obtained by the interfacial-gel polymerization process was controlled to enable to transmit the order of gigabit per second bit rate. Furthermore, the accurate approximation of the refractive index profile and consideration of mode dependent attenuation enabled to precisely predict the dispersion characteristics of the GI POF.

Precise plastic V-grooved alignment parts for connecting single-mode optical fiber arrays to multi-port optical devices were successfully molded with a thermosetting resin by using a highly productive injection molding technique. The molded parts are two types of V-grooved blocks that are compatible with the size of optical devices having eight or twelve optical ports. Their dimensional accuracy must be better than 1 µm over the whole length of the V-grooves for efficient optical coupling. This strict requirement was satisfied using precisely processed molding tools with a specially chosen resin under optimum molding conditions. The feasibility of the optical alignment parts was assured by an evaluation of their loss characteristics and reliability in coupling single-mode fibers to 18 power splitters, where the average optical loss was 0.2 dB and the change in loss was less than 0.2 dB under a temperature cycling test and also under a damp heat test. These results show that plastic molded parts can be used for precise coupling of single-mode optical devices, and will lead to a breakthrough in innovation in the field of optical packaging.

This paper reports on time-space conversion-based differential processing of optical signals using a high-resolution arrayed-waveguide grating (AWG) and a spatial filter at a wavelength of 1.55 µm. We clarify the advantages of the AWG device and show where it is applicable. In order to reduce loss at the spatial filter, we propose a new phase-only filter that functions as a differential filter. The difference between the exact differential filter and the proposed phase-only filter is calculated theoretically. We confirm experimentally that the optical pulse can be differentiated by the proposed filter. For application of differential processing, we also proposed a phase modulation to amplitude modulation (PM-AM) conversion and demonstrated the PM-AM conversion at 10 Gbit/s signals using a PSK-non-return-to-zero (NRZ) format.

Recent status of the polymer optical fiber (POF) for high speed data communication and telecommunication is reviewed. The GI POF was proposed for the first time 20 years ago at Keio University, and several methodologies to fabricate GI POF have been currently proposed worldwide. In this paper, we both theoretically and experimentally verify that the most transparent GI POF can be obtained by the polymer-dopant system. The relation between the refractive index profile and the dispersion characteristics of the GI POF was quantitatively clarified. The refractive index profile of the GI POF obtained by the interfacial-gel polymerization process was controlled to enable to transmit the order of gigabit per second bit rate. Furthermore, the accurate approximation of the refractive index profile and consideration of mode dependent attenuation enabled to precisely predict the dispersion characteristics of the GI POF.

Minimizing the guard time, Tguard, in the TCM-TDMA PDS scheme is essential in maximizing TCM transmission efficiency. As a replacement for the commonly adopted worst-case approach to TCM-TDMA PDS system estimation, this paper proposes a statistical approach. The level distributions of losses and n-th order Fresnel reflections are determined from published measurements. The proposed approach estimates the reflection of the optical access network.

Frequency chirping induced in an electorabsorption (EA) modulator can degrade transmission performance because of the chromatic dispersion of fiber. This letter studies the frequency chirping in an EA modulator from the viewpoint of the influence of the modulation bandwidth. Both simulations and experiments, in which fiber transmission was carried out applying modulation signals of different bandwidths to an EA modulator, show that a large bandwidth causes small degradation in the transmission performance. This result is attributed to the short chirping time that occurs when a large bandwidth signal is applied.

The hybrid electrical/optical multi-chip integration technique for optical modules for optical network system has been developed. Employing the technique, a 44 broadcast-and-select type optical matrix switch module has been realized. The module consists of four sets of silica waveguide 1 : 4 splitters/4 : 1 combiners, four 4-channel arrays of polarization insensitive semiconductor optical amplifiers with spot-size converters as optical gates, printed wiring chips for electrical wiring and single mode fibers for optical signal interface on planar waveguide platform fabricated by atmospheric pressure chemical vapor deposition. All the gates and the wiring chips were mounted precisely onto the platform at once in flip-chip manner by self-align technique using AuSn solder bumps. Coupling loss between the waveguide and the SOA gate was estimated to be 4.5 dB. Averaged fiber-to-fiber signal gain, on-off ratio and polarization dependent loss for each of the signal paths was 7 dB 2 dB, more than 40 dB and 0.5 dB, respectively. High speed 10 Gb/s photonic cell switching as short as 2 nsec has been successfully achieved.

The hybrid electrical/optical multi-chip integration technique for optical modules for optical network system has been developed. Employing the technique, a 44 broadcast-and-select type optical matrix switch module has been realized. The module consists of four sets of silica waveguide 1 : 4 splitters/4 : 1 combiners, four 4-channel arrays of polarization insensitive semiconductor optical amplifiers with spot-size converters as optical gates, printed wiring chips for electrical wiring and single mode fibers for optical signal interface on planar waveguide platform fabricated by atmospheric pressure chemical vapor deposition. All the gates and the wiring chips were mounted precisely onto the platform at once in flip-chip manner by self-align technique using AuSn solder bumps. Coupling loss between the waveguide and the SOA gate was estimated to be 4.5 dB. Averaged fiber-to-fiber signal gain, on-off ratio and polarization dependent loss for each of the signal paths was 7 dB 2 dB, more than 40 dB and 0.5 dB, respectively. High speed 10 Gb/s photonic cell switching as short as 2 nsec has been successfully achieved.

A high-density multi-port optical connector that exploits the flexibility of bare optical fibers has been developed for use as an optical interface of a parallel optical interconnection module. In the BF (Bare-Fiber) connector, 24 multimode-fibers are mated by direct physical contact in micro-glass-capillaries with a 250-µm pitch. The buckling forces of the optical fibers themselves secure the physical contact. Optical fiber buckling is investigated theoretically and experimentally. A new design method to optimize the span length l and the longitudinal displacement ΔL for the buckling is also proposed based on the requirements afor optical characteristics, mechanical reliability, and dimensional tolerances, etc. A prototype BF connector with l 10 mm and ΔL of 50 µm was designed and fabricated for multimode fiber connections. This connector provides high optical performance: an average insertion loss of 0.05 dB and a return loss of over 35 dB at 850 nm. The optical performance remained stable after a durability test with ten connection-repetitions.

In pursuing its vision that digital signals will come to dominate not only voice communications but also various services on an integrated basis in future telecommunications, NTT has successfully completed a major part of telephone network preparations by digitizing all of its networks by the end of 1997. Accompanying digitization, it has also started providing various new services including the initiation of best-effort services through OCN. At the same time, the steady progress in Internet diffusion, the globalization of enterprise networks and inter-company electronic transactions are leading to the full scale usage of IP network communications. Because IP networks are still faced with pressing demand and unresolved issues, NTT believes it is also necessary to structure and provide computer-compatible networks suitable for IP communications by shifting from telephone-focused architecture in order to respond better to these growing needs. This paper overviews the digital network assets including ISDN that NTT has accumulated as a carrier as well as the IP networks such as the Internet that have spread throughout our societies. It also outlines new access services and network offerings based on optical and other technologies and the ATM networks that serve as the infrastructure for highly reliable and economical IP networks, and presents our thinking behind how such networks will be organically combined.

A fiber Bragg grating, which has periodical perturbation of the refractive index in the fiber core, acts as a wavelength selective reflection filter and steep optical spectrum can be realized by forming more than ten thousand of gratings along the fiber core. Owing to capability of making steep optical spectrum, fiber Bragg gratings has been expected to be introduced practical use as multiplexing or demultiplexing filters in dense WDM transmission systems. On the other hand, radiation mode loss, reflection side mode and temperature dependence of Bragg wavelength, should be improved to put the fiber Bragg grating to practical use in dense WDM transmission systems. In this paper, an optimum design and performance of the fiber Bragg grating for dense WDM systems are described. The photosensitive cladding fiber realized less than 0. 2 dB insertion loss at transmitted signal channels and less than 0. 1 dB splicing loss with standard single-mode fibers. An adequate apodization technique in the refractive index distribution suppressed reflection side modes. A temperature compensating package, which gives longitudinal strain with negative temperature dependence to a fiber Bragg grating, minimized temperature dependence of Bragg wavelength less than 0. 001 nm/. Thermal decay of Bragg grating was also investigated and adequate annealing condition was estimated to obtain sufficient stability for practical use in dense WDM transmission.

This paper describes the fiber unit blowing length of an optical fiber distribution system for business buildings which employs pipe cable, fiber units and the fiber unit blowing technique. The relationship between the applied force and the length of a fiber unit blown into a straight pipe is investigated theoretically and experimentally and the fiber unit blowing length is estimated. Moreover, the pipe bending radius which has a small bending resistance force is clarified. Cables, fiber units and unit blowing equipment are manufactured based on the results and their transmission and mechanical characteristics are confirmed to be stable.

An MT connector assembly machine has been designed and developed. The connector assembly time using this machine is about 30% less than with the conventional method. The MT connectors assembled employing this machine have a low connection loss and stable mechanical characteristics.

Random fluctuations of the propagation constants of modes along the fiber axis are taken into consideration and the power coupling coefficient between cores of an image fiber is theoretically derived. For the fiber used for the measurement in the previous paper (A. Komiyama, IEICE, vol.E79-C, no.2, pp.243-248, 1996) it is verified that the coupling coefficient can be described in terms of statistical properties of the propagation constants in the cross-section of the fiber.

High density and small diameter optical fiber cables are required in order to construct "Fiber To The Home (FTTH)" to support multi media services economically. By reducing the cable diameter and weight, it will be possible to install longer lengths of cable and use conduits more effectively. Moreover, the development of low loss multifiber connectors and joint boxes will reduce the joining time. It is expected that the achievement of the above will lead to reductions in installation and joining costs. This paper describes the design and performance of 1000-fiber single slotted core cable. Its diameter is 30 mm compared to 40 mm for currently used multi slotted core cable, and its weight is 0.85 kg/m compared to 1.4 kg/m. The reduced cable outer diameter and weight allow us to increase both the installed length from 1 to 2 km (pre-connectorized) and the maximum fiber count from 1000 to 1600 for multiple installation in a conduit. We also describe low loss 4, and 8 mechanically transferable (MT) connectors, a pulling head and a joint box. The average connection loss of those connectors is reduced from 0.35 to 0.2 dB. The cable joining time was greatly reduced from 9 to 4.5 hours by using 5 stacks of multi fiber connectors and newly developed pulling heads and a joint boxes. Finally, we describe field test results for 1000-fiber pre-connectorized cable. In field tests, this preconnectorized cable is sufficiently stable with present installation methods. These results will lead to reductions in installation and joining costs. The 1000-fiber pre-connectorized single slotted core cable is promising with regard to upgrading the access network towards FTTH.

A brief overview is done to the development of the fiber-optic technology. These recent topics, not the commonly established techniques, are described connecting with the developments of the basic concepts and the expected applications. Some of these newly introduced ideas will become the seeds for the future development of the fiber-optic technology. These seeds include the very deep understanding of the fiber material, new concepts for the fiber characteristics, the brandnew fiber-optic devices and the fiber-optic systems and the applications.

A 3-dimensional beam propagation method is described for the analysis of nonlinear optical fibers, where the finite element and finite difference methods are, respectively, utilized for discretizing the fiber cross section and the propagation direction. For efficient evaluation of wide-angle beam propagation, Pade approximation is applied to the differential operator along the propagation direction. In order to improve accuracy of solutions, isoparametric elements and numerical integration formulae derived by Hammer et al. are introduced. The propagation characteristics of nonlinear optical fibers with linear core and nonlinear cladding are analyzed, and unique features of nonlinear guided-wave propagation, such as spatial soliton emission, are investigated.

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.