This paper reviews very high-speed optical signal processing technology based on the instantaneous characteristic of optical nonlinearities. Focus is placed on 100-Gbit/s optical time-division multiplexing (TDM) transmission systems. The key technologies including ultrashort optical pulse generation, all-optical multiplexing/demultiplexing and optical timing extraction techniques are alse described together with their major issues and future prospects.

With the foreseen growth of communication capacity, further capacity and flexibility enhancements are required for future transport networks. Photonic switching is expected to be a key technology to solve the potential bottleneck, which could be found in transport network nodes. This paper first explains the "Optical Fiber Freeway" concept, as an example of future transport networks. Following this, the possible optical transport network structure using photonic switching technologies, for realizing the Optical Fiber Freeway concept, is explained. An Optical CrossConnect (OXC) and optical Add/Drop Multiplexer (ADM) are key components. Examples of recent development of photonic switching systems toward these targets are also reviewed. An OXC using photonic Space-Division (SD) switching technology has been proposed and demonstrated. This type of OXC will realize flexible reconfiguration and optical hitless switching, and it can meet the introduction of Wavelength Division Multiplexing (WDM) technique. Line failure restoration operation at 2.4Gb/s has been successfully demonstrated. An optical packet network with a slotted ring/bus structure using a wavelength address technique has been proposed as a packet/cell based optical ADM. The experimental system employs a practical media access control system as well as a fast-wavelength switched transmitter suppressing thermally induced wavelength drift. Cell communication at 622Mb/s has been demonstrated with the experimental system. These results show that hardware technologies have been developed steadily. With a future study on an all optical network management scheme, a high capacity and flexible optical network would be realized.

Cross-phase modulation (XPM) induced by residual intensity modulation in coherent optical frequency-shift-keying (FSK) frequency division multiplexing (FDM) transmission systems that use dispersion-shifted fibers is evaluated theoretically and experimentally in terms of spectral profile deformation. The bit-error rate is measured in a 2.5-Gbit/s 4-channel 40-km dispersion-shifted fiber transmission experiment, and we confirm experimentally and theoretically that the power penalty in the presence of residual intensity modulation of over 4 mWp-p exceeds 1dB. Experimental results show that the penalty due to XPM is large even when the power of the newly generated lights caused by four-wave mixing is 20-dB less than that of signals. This confirms that residual intensity modulation must be reduced in continuous-phase (CP)-FSK-FDM systems even though they are designed to avoid generating four-wave mixing.

We report here a pulsed lightwave frequency synthesizer system that is composed of a pulsed lightwave sweep frequency generator and a tracking generator. The key advance in the sweep generator is the use of a dynamically gain controlled EDFA. The combination of feedback and feed forward dynamic gain control effectively compensates EDFA gain fluctuation and equalizes fiber loop loss so that the initial pulse wave form and amplitude is retained in the loop at large circuit numbers. Over 1000 pulsed lightwave frequencies are synthesized in 250MHz steps by the sweep generator. Almost flat response (0.55dB variation) is realized up to 240GHz. The power spectrum decreases by 67% (1.7dB down) at 250GHz. The peak level of the pulses output from the loop is about -4dBm. Tracking generator and total synthesizer system performance are evaluated by (a) beat frequency between the tracking generator and the master lightwave source, (b) beat frequency between two tracking generators, and (c) a frequency chain between the master lightwave source and another HCN stabilized lightwave source via the synthesizer system. A continuous lightwave frequency locked to a frequency selected from the pulsed sweep frequency signal is demonstrated at over 200GHz to have an instability of 5MHz. Absolute accuracy of the lightwave frequency emitted from the synthesizer system is about 10MHz. Therefore, the relative accuracy of the lightwave frequency is as high as 510^-8.

This paper proposes a photonic frequency-division-multiplexing (FDM) highway switch architecture consisting of 22 multi-frequency-channel switches (MFSs) using multiple ring resonators. An experimental MFS fabricated using a planar-lightwave-circuit (PLC) technology is demonstrated.

Various approaches on optical network systems using wavelength-division multiplexing (WDM) technique have been proposed. It is difficult to make a scale of WDM network larger since a number of the optical wavelength which can be used is limited. In order to make easily larger scale of network, multi-hop WDM network have been proposed. We have studied 2-hop network: RookNet which has simple routing algorithm and high network throughput. Nodes in RookNet are divided into row groups and column groups and are placed in a mesh form. Packets are transferred between nodes over 1-hop or 2-hops. The 2-hop transfer means that a source node sends packets to a destination node via a relay node. When 2-hop traffic increases, relay processing time in a relay node is increasing. This is the reason that network throughput becomes low. To solve this problem is very important. In this paper, we show RookNet rearrangement algorithm which replaces location of node within group so as to decrease the 2-hop traffic and to maintain high network throughput. Proposed rearrangement algorithm can achieve improvement of 10 percent in terms of throughput. We also propose RookNet configuration which discriminates optical wavelength and subcarrier effectively in order to decrease the relay processing time.

Recent technical advances in WDM (Wavelength Division Multiplexing) technologies suggest that their practical application is imminent. By adopting WDM technologies in the transport network, a bandwidth abundant B-ISDN could be realized cost-effectively. This requires the introduction of WDM technologies, especially into the path layer. This paper explores optical path cross-connect (OPXC) nodes that offer very high levels of expandability because existing traffic demands, which are rather limited, must be efficiently supported while permitting easy step-wise expansion in capacity. This paper highlights modularity with regard to incoming/outgoing links. The OPXC architecture that offers the highest modularity is elaborated, and its transmission characteristics, optical loss and switching power consumption are evaluated. This paper also examines OPXC architecture considering the interface needed to connect electrical path cross-connects. The proposed OPXC architectures provide flexibility and minimum investment to encourage the early introduction of B-ISDN and also supports incremental network growth to match traffic demand. The design of OPXC parameters in terms of transmission performance is shown to ensure the applicability of the proposed OPXC architecture to long-haul optical fiber transmission networks. This is made possible with the low optical component losses offered by the OPXC. The proposed OPXC architectures will, therefore, be applied not only to regional networks, but also to global area networks. Thus they will play a key role in realizing the optical path infrastructure for the future bandwidth abundant B-ISDN.

This paper discusses an all-optical tank circuit that uses the comb-shaped gain spectrum generated by a Brillouin amplifier. The theory of timing clock extraction is shown for two cases: with two gains and with three gains. In both cases, the waveform of the extracted timing clock is simulated. According to the simulation, unlike an ordinary tank circuit, the amplitude of the extracted clock is not constant even though the quality factor (Q) is infinite. The extracted clock is clearly influenced by the pattern of the original data stream if the Brillouin gain is finite. The ratio of the maximum extracted clock amplitude to the minimum extracted amplitude is calculated as a function of Brillouin gain. The detuning of the pump light frequency is also discussed. It induces not only changes in the Brillouin gain, but also phase shift in the amplified light. The relation between the frequency drift of the pump lights and the jitter of the extracted timing clock is shown, in both cases: two pump lights are used and three pump lights are used. It is numerically shown that when the all pump lights have the same frequency drift, i.e., their frequency separation is constant, the phase of the extracted clock is not influenced by the frequency drift of the pump lights. The operation principle is demonstrated at 5Gbit/s, 2.5Gbit/s, and 2Gbit/s using two pumping techniques. The parameters of quality factor and the suppression ratio in the baseband domain are measured. Q and the suppression ratio are found to be 160 and 28dB, respectively.

The intermodulation distortion (IMD) due to laser diode (LD) nonlinearity of an asynchronous direct-sequence code division multiple access (DS/CDMA) system in optical transmission is analyzed. A third-order polynomial without memory is used to present LD nonlinearity. In DS/CDMA systems, only one harmonic of the third-order inter-modulation term falls on the signal frequency band and influences the system performance. The average distortion is derived with only the information of autocorrelation functions. The results are useful for CDMA system design and performance analysis. With LD nonlinearity it is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio (SNR). The analytical method is applicable to other general nonlinearities in CDMA systems.

When communication network planning-design is performed, especially in a short-term case, it is important to utilize existing facilities in the construction of the new network. In this paper, link capacity assignment problem (CA problem) for packet-switched networks is investigated with the consideration of the existing network. To deal with this, per-unit cost of existing link capacity is thought to be less than that of newly installed capacity and a link cost function is modeled by a non-linear, non-differentiable one which is composed of two portions of capacity cost. After formulating the CA problem, two optimum algorithms derived from Lagrange multiplier method are presented and a modified algorithm is used for solving the CA problem in order to reduce the computation time. Some numerical results show that according to the values of link traffic flows, there will be links whose capacities must be set equally to the existing values. Moreover, when link cost difference is introduced in the CA problem, the number of links that the capacities of which have to be changed from existing values is less than that of linear cost function case, i.e., the case without consideration of the cost difference in link capacity.

This paper studies routing methods for the complete broadcast multipoint-to-multipoint communication. For a Z-node (Z-site) of the participants of the connection, each site transmits one signal and receives Z-1 signals. The routing method based on connecting each participant by multiple directed point-to-point circuits uses wasteful bandwidth that the source-to-destination data may be duplicated needlessly. We propose routing methods that the connection approach is based on setting multicast tree routes that each participant (site) has one own multicast tree connecting to the other participants under two constraints: the delay-bounded constraint of source-destination path and the available constrained bandwidth for the service of links. For this routing approach, we propose both heuristic algorithm finding approximate solution and search enumeration based algorithm finding optimal solution, and compare the approximate solution with the optimal solution. This approach can lower costs for the subscribers and conserves bandwidth resources for the network providers.

The optical ATM transport networks are the key technology for B-ISDN which integrates wide variety of communication services. In a photonic ATM switch, electronically operated switching control drastically limits the total throughput. With this bottleneck of the control speed of the switch compared to the cell transmission speed, if the unit of switching operation can be made longer, the system throughput will be improved. This paper proposes the optical backbone network configuration to obtain traffic concentrating effect to construct a large switching unit called a multi-cell. In the backbone network applied the concept of virtual path set (VPS), a multi-cell is constructed by cells from all of ATM switches in a regional network connected with each own's cross connect. The multi-cell format in the case of two different network models is investigated in this paper. The average delay and average idle cells per multi-cell in the multi-cell MUX of an optical cross connect are evaluated by computer simulation as the performance of the multi-cell transfer scheme in the backbone network. Simulation results show that the multi-cell transfer scheme can be operated efficiently with traffic load of more than 0.5. This paper also proposes the configuration of multiplexing and demultiplexing module to assemble and disassemble the multi-cell.

In this paper, two models are proposed for the simulation of MPEG video sources in ATM networks. The projected autoregressive (PAR) model is based on the autoregressive (AR) model compensated by a projection function. The projection function is capable of adjusting the histogram generated by the AR model so that it better fits the histogram obtained from real data. The state transition (ST) model is developed on die basis of recording the variation of frame size in a video sequence. Each state denotes the size of a frame and the number of state depends on the degree of correlation between frames. Our results show that the histogram generated by the ST model is almost identical with that of the real data and the PAR model performs better in capturing the property of autocorrelation of real data. When compared with other models, both of the two models demonstrate an excellent property of fitting the complex histogram curve, which was not achieved by the AR model, and preserving the correlation characteristics. A heuristic search algorithm is also proposed to make our modelling processes more efficient.

In coherent optical space communication systems, the phase noise generated from high power laser diodes and the polarization axis mismatch between transmitter and receiver are the serious problem. In this paper, a novel coherent optical space communication system, called optical polarization azimuth modulation (POLAM)/heterodyne detection system is newly proposed, and its system performance is theoretically investigated. It is clarified that the POLAM system can perfectly remove the laser phase noise, is actually insensitive to the polarization axis mismatch, and can provide the remarkable performance improvement compared to a conventional optical frequency modulation system.

The performance of trellis coded hybrid frequency and phase shift modulation (TC HFPSK) with the expurgated phase code and the asymmetric signal constellation is investigated by using the minimum squared free Euclidean distance d ²_free and the bit error rate (BER). It is found that TC hybrid 2FSK/4PSK with the expurgated phase code shows larger d ²_free than the corresponding TC hybrid 2FSK/4PSK with the complete phase code for varying the angle φ that determines the asymmetric signal constellation. The maximum value of d ²_free of TC hybrid 2FSK/4PSK with the expurgated phase code can be obtained when the signal constellation is symmetric. The performance of BER is analyzed in additive white Gaussian noise (AWGN) and fading channels by using uniform error property and error bound based on transfer function. It is found that the coding gain of TC hybrid 2FSK/4PSK with the expurgated phase code over uncoded hybrid 2FSK/2PSK at BER=10^-4 are 2.71dB and 4.74dB in AWGN and fading channels, respectively. The performance improvements of TC hybrid 2FSK/4PSK with the expurgated phase code over TC 8PSK at BER=10^-4 are 0.68dB and 4.07dB in AWGN and fading channels, respectively.

This paper describes a fully digitized modem designed for variable baud rate transmission systems with the aim of efficiently providing multimedia services over a wireless communication network. The concept of a variable baud rate wireless communication system is discussed focusing on the access scheme and channel allocation from the viewpoint of frequency utilization efficiency. For easy system construction, we propose a fully digitized variable baud rate modem based on multirate digital signal processing, taking into account the need for even performance and easy clock control for all transmission rates. We also discuss the operational principle of modulation, the degradation factor in the A/D converter, and the configuration of the clock recovery circuit. Steady modulation performance can be kept by generating the same frequency system clock for all transmission rates and using the sampling rate conversion technique without selecting the channel filter for each transmission rate. It is proved by the analysis of the degradation factor in the A/D converter that only the bandwidth of the channel filter in demodulator should be changed for the transmission rate. A double loop clock recovery configuration capable of both tank-limit type and baseband estimation type clock recovery is shown to be suitable for this system. The tank-limit clock recovery circuits can be constructed easily by employing a tank circuit array. Finally, we present experimental results for a modem having transmission rates of 1.544Mbps and 6.312Mbps for the digital hierarchy and information speed of video signals such as MPEG-1 and MPEG-2. The measured basic performance of the proposed modem shows it delivers superior performance without the need for precise adjustment when a QPSK modulation scheme is employed.

A new approximation calculation method, named the Recursive Matrix-calculation (RM) method, is proposed. It uses matrix calculation to determine the number of link disjoint paths under a hop link number constraint, i.e. hop limit. The RM method does not overestimate the number of link disjoint paths. When networks are designed by this method, network reliability is perfectly guaranteed. Moreover, the RM method is based on matrix calculation, so CPU time can be reduced by using super-computers equipped with vector processors. Simulation results confirm that the RM method yields rapid approximations that are conservative. Thus the proposed method is very useful for designing reliable multimedia networks.

We study behavior of multi-zone MCA (Multi-Channel Access) mobile communication systems with a finite number of channels in each zone. Three queueing schemes for channel requests named holding scheme, ready-nonready scheme, and optimum scheme are investigated. The delay performance of channel requests is studied through computer simulations.