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.

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.

Thermally-diffused expanded core (TEC) techniques brought the fibers with the mode fields expanded by thermal diffusion of core dopants. The techniques are effective to the reduction of splice or connection losses between the different kind of fibers, and are applied to the integrations of thin film optical devices in fiber networks, the fabrications of chirped fiber gratings, and so on. In the practical use of TEC techniques, the fibers are heated high temperature of about 1650 because of a short peried of time in processing by microburners. The mode field diameter expansion (MFDE) ratio, which is defined as the ratio of the mode field diameter in the fiber section having the core expanded and that unexpanded, is desired to be more than 2.0 from the viewpoint of loss reduction in industrial uses of the TEC techniques. When the TEC techniques are applied to polarization-maintaining optical fibers (PM fibers), such as PANDA fibers, both core dopants and stress applying part (SAP) dopants diffuse simultaneously. So the MFDE ratio is less than two without mode field deformation in conventional PANDA fibers which are practically used as PM fibers. In this paper a PANDA fiber design suitable for the TEC techniques is newly proposed. The fiber has 1.28 µm cutoff wavelength and the mode field diameter is about 11 µm before core expansion at 1.3µm wavelength.

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 demonstrate highly quick response and long distance distributed oil sensors using a newly developed eccentric core fiber (ECF). This distributed oil sensor,based on an interaction between measurand oil and evanescent-wave from the ECF, has achieved as short as 4 minutes response time by using an improved coating material and a sensing length over 17 km at a signal wavelength of 1310 nm. The observed sensitivity characteristics coincide with the calculations of the evanescent power outside the cladding and it is shown that the sensitivity can be well estimated from the amount of the outer cladding component of the evanescent power.

MPO optical backplane connectors using multi-fiber push-on plugs (MPO plugs) have been developed. MPO optical backplane connector is a connector connecting a printed board to a backplane using MPO plug. MPO plug is held in the housing with self-retentive mechanism. To get same optical performances as standard MPO connector, precision in dimension and mechanism for appropriate connecting-disconnecting sequence are necessary. We have developed a new backplane housing and printed board housing based on previously reported MU connector. The optical performance is similar to that of MPO connectors.

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 novel technique is proposed to fabricate a chirped fiber Bragg grating utilizing thermal diffusion of core dopant. The chirped grating is written with a uniform period by using UV exposure technique in the fiber whose effective index of the guided mode varies along its length. Thermal diffusion of the core dopant it employed to realize this change of the effective index. Through the thermal diffusion process, the effective index of the fiber decreases from its initial value. When the grating is written in the diffused core region, its reflection wavelength becomes shorter than that in the non-diffused region. The continuous change of effective index is required for making a chirped grating. The fiber is heated by a non-uniform heat source. When the uniform grating is written in this region, the reflection wavelength smoothly changes along the fiber length although the grating period is constant. By optimizing the fiber parameters to realize a highly chirped grating, we have obtained a typical one whose bandwidth is 14.1 nm at half maximum and maximum rejection in transmission is 29 dB. Additionally, the proposed method has an advantage to control the chirp profile with high mechanical reliability.

In ATM networks, a usage parameter control (UPC) strategy must regulate incoming traffic according to the characteristics of the sources declared at call set-up. Among various UPC schemes, Leaky Bucket is a conventionally method having been discussed extensively. This paper examines the characteristics of the multiplexer with a sufficient buffer in which cell arrivals are policed by Enhanced Leaky-Bucket (ELB) before entering the system. In addition to the factor of mean rate, peak rate and cell delay variation (CDV) are also considered for each ELB. We find out the worst output pattern from the ELB and derive the upper bound on average waiting time as a function of the ELB parameters.

A highly reliable network which can restore itself from network failures is one important concept for the future high capacity broadband network. In such self-healing network, flooding based failure-restoration algorithm is used to locate new routes and then to reroute failure traffic to that routes automatically when network failures such as link or node failures occur. Since the speed of this algorithm is degraded by the large amount of restoration messages produced by the process, such large volume messages should be reduced. In this paper, the scheme will be proposed, which reduces the large volume messages and efficiently selects alternative routes. In this scheme, the Message Wall will be used to filter useless restoration messages at the tandem nodes and Multi-Message Selecting method will be used to rapidly select a group of link-disjointed alternative routes from the feasible ones in each Flooding Wave sequence. The simulation results show that restoration messages are dramatically reduced and adequate alternative routes can be quickly found out.

It is known that in a nonblocking packet switch with input queueing, head-of-line (HOL) blocking affects significantly the maximum throughput of the packet switch. To alleviate the HOL blocking effect, a window policy has been proposed in that each input queue can scan up to a fixed number of packets (called the window size) to select for transmission on the outputs. However, the performance of the window policy has never been precisely characterized. In this paper, we use a closed queueing network model to characterize the performance of the packet switch with window policy. We obtain explicit closed-form formulae for the maximum throughput of the packet switch as a function of the window size. Both balanced and imbalanced traffic patterns are discussed. The formulae can easily determine the effectiveness of the window policy.

This paper proposes an adaptive coding rate and process gain control technique with channel activation function to realize a CDMA based radio subsystem for multi-media communication services that include two types of media, i.e., fixed size data such as the computer data and still image, and constant bit rate data such as voice and video. The proposed system achieves high throughput data transmission for the fixed size data by controlling the process gain and coding rate according to the variation of the channel. Moreover, to adopt the constant bit rate data, the proposed system also employs a channel activation technique. Computer simulation confirms that the proposed system is very effective for multi-media communication services.

The multiple registration schemes (MRSs) proposed here are classified into 3 cases by combining five registration schemes which are power up registration scheme (PURS), power down registration scheme (PDRS), zone based registration scheme (ZBRS), distance based registration scheme (DBRS), and implicit registration scheme (IRS) as follows: the first is MRS1 which covers PURS, PDRS, and ZBRS; the second is MRS2 which covers PURS, PDRS, and DBRS; the third is MRS3 which covers PURS, PDRS, IRS, and DBRS. The three proposed schemes are compared each other by analyzing their combined signaling traffic of paging and registration with considering various parameters of a mobile station behavior (unencumbered call duration, power up and down rate, velocity, etc.). Also, we derive allowable location areas from which the optimal location area is obtained. Numerical results show that MRS3 yields better performance than ZBRS, DBRS, MRS1, and MRS2 in most cases of a mobile station behavior, and it has an advantage of distributing the load of signaling traffic into every cell, which is important in personal communication system.

In this paper, we propose a handoff scheme with two-level priority for the reservation of handoff request calls in mobile cellular radio systems. We assume two types of mobile subscribers with different distributions of moving speed, that is, users with low average moving speed (e.g., pedestrians) and high average moving speed (e.g., people in moving cars). A fixed number of channels in each cell are reserved exclusively for handoff request calls. Out of these number of channels, some are reserved exclusively for the high speed handoff request calls. The remaining channels are shared by both the originating and handoff request calls. In the proposed scheme, both kinds of handoff request calls make their own queues. The system is modeled by a three-dimensional Markov chain. We apply the Successive Over-Relaxation (SOR) method to obtain the equilibrium state probabilities. Blocking probabilities of calls, forced termination probabilities and average queue length of handoff calls of each type are evaluated. We can make the forced termination probabilities of handoff request calls smaller than the blocking probability of originating calls. Moreover, we can make the forced termination probability of high speed handoff request calls smaller than that of the low speed ones. Necessary queue size for the two kinds of handoff request calls are also estimated.

A new numerical technique, termed the method of matrix-order reduction (MMOR), is developed for handling electromagnetic problems in this paper, in which the matrix equation resulted from a method-of-moments analysis is converted either to an eigenvalue equation or to another matrix equation with the matrix order in both cases being much reduced, and also, the accuracy of solution obtained by solving either of above equations is improved by means of a newly proposed generalized Jacobian iteration. As a result, this technique enjoys the advantages of less computational expenses and a relatively good solution accuracy as well. To testify this new technique, a number of wire antennas are examined and the calculated results are compared with those obtained by using the method of moments.

This paper presents the beam forming characteristics of an optical waveguide-type phased array antenna. Four linearly arranged array antenna was monolithically fabricated on one LiNbO₃ substrate containing variable power dividers (VPDs) and optical phase shifters (OPSs). The amplitude and the phase of each antenna element was controlled by applying DC voltage on each VPD and OPS. Open ends of Ti-indiffused waveguides were used as antenna elements. This antenna was designed to operate at 1.3 µm wavelength band. Experimental results confirm the good beam forming capability of optical phased array antennas.

New network survivability measures are developed and compared with conventional ones. The advantages of using multiple survivability measures, including the new ones, are discussed. The measures are illustrated and interpreted through several numerical examples. We also show how survivability can be included as a constraint in network optimization models.

We propose an improved orthogonal frequency division multiplexing (OFDM) signal detector which uses the minimum mean-square error (MMSE) noise feedback equalization (NFE). The input bit stream is trellis-coded to form OFDM signal blocks and the maximal ratio combining (MRC) is adopted at the receiver in order to improve the performance of the detector. As a result, we obtain significantly improved detection performance compared with the conventional OFDM receivers as follows. Using the proposed MMSE-NFE in the receiver, we can obtain the performance gain of about 1.5 dB to 2 dB in symbol energy to noise power spectral density (E_s/N_o) for Doppler frequencies of f_d=20 and 100 Hz, respectively, over the receiver with the MMSE linear equalization (LE) alone at symbol error rate (SER) of about 10^-3. With MRC and trellis coding, the performance gain of about 11 dB in E_s/N_o for f_d=20 and 100 Hz at SER of about 10^-3 is obtained.