This paper investigates the prospects and challenges of hierarchical optical path networks. The merits and issues of introducing higher order optical paths are elucidated. State of the art of the key enabling technologies are demonstrated including hierarchical optical cross-connect switch architectures, hierarchical optical path network design algorithms, a newly developed waveband filter, and waveband conversion technologies.

Link-level and node-level blocking in photonic networks has been intensively investigated for several decades and the C/D/C approach to OXCs/ROADMs is often emphasized. However, this understanding will have to change in the future large traffic environment. We herein elucidate that exploiting node-level blocking can yield cost-effective large-capacity wavelength routing networks in the near future. We analyze the impact of link-level and node-level blocking in terms of traffic demand and assess the fiber utilization and the amount of hardware needed to develop OXCs/ROADMs, where the necessary number of link fibers and that of WSSs are used as metrics. We clarify that the careful introduction of node-level blocking is the more effective direction in creating future cost effective networks; compared to C/D/C OXCs/ROADMs, it offers a more than 70% reduction in the number of WSSs while the fiber increment is less than ~2%.

A 1.5 V 8 mW BiCMOS video A/D converter has been developed by using a BiCMOS pumping comparator. Combining Bipolar high-speed and good-matching characteristics with CMOS switched capacitor techniques, this A/D converter is suitable for use in battery-operated multimedia terminals.

In this paper, we propose a projection based design of near perfect reconstruction QMF banks. An advantage of this method is that additional design specifications are easily implemented by defining new convex sets. To apply convex projection technique, the main difficulty is how to approximate the design specifications by some closed convex sets. In this paper, introducing a notion of Magnitude Product Space where a pair of magnitude responses of analysis filters is expressed as a point, we approximate design requirements of QMF banks by multiple closed convex sets in this space. The proposed method iteratively applies a convex projection technique, Hybrid Steepest Descent Method, to find a point corresponding to the optimal analysis filters at each stage, where the closed convex sets are dynamically improved. Design examples show that the proposed design method leads to significant improvement over conventional design methods.

HRTFs (head-related transfer functions) are available for sound field reproduction with spatial fidelity, since HRTFs involve the acoustic cues such as interaural time difference, interaural intensity difference and spectral cues that are used for the perception of the location of a sound image. Generally, FIR filters are used in the simulation of HRTFs. However, this method is not useful for a simply system, since the orders of the FIR filters are high. In this paper, we propose a method using IIR filter for simply realization of sound image localization. The HRTFs of a dummy-head were approximated by the following filters: (A) fourth to seventh-order IIR filters and (B) third-order IIR filters. In total, the HRTFs of 24 different directions on the horizontal plane were used as the target characteristics. Sound localization experiments for the direction and the elevation angle of a sound image were carried out for 3 subjects in a soundproof chamber. The binaural signal sounds using the HRTFs simulated by FIR filters and approximated by IIR filters (A) and (B) were reproduced via two loudspeakers, and sound image localization on the horizontal plane was realized. As the result of the experiments, the sound image localization using the HRTFs approximated by IIR filters (A) is the same accuracy as the case of using the FIR filters. This result shows that it is possible to create sound fields with binaural reproduction more simply.

In this paper, we present a novel iterative MPEG super-resolution method based on an embedded constraint version of Adaptive projected subgradient method [Yamada & Ogura 2003]. We propose an efficient operator that approximates convex projection onto a set characterizing framewise quantization, whereas a conventional method can only handle a convex projection defined for each DCT coefficient of a frame. By using the operator, the proposed method generates a sequence that efficiently approaches to a solution of super-resolution problem defined in terms of quantization error of MPEG compression.

This paper presents a fast and large-scale optical circuit-switch architecture for intra-datacenter applications that uses a combination of space switches and wavelength-routing switches are utilized. A 1,440 × 1,440 optical switch is designed with a fast-tunable laser, 8×8 delivery-and-coupling switch, and a 180×180 wavelength-routing switch. We test the bit-error-ratio characteristics of all ports of the wavelength-routing switch using 180-wavelength 10-Gbps signals in the full C-band. The worst switching time, 498 microseconds, is confirmed and all bit-error ratios are acceptable.

We propose an efficient network design algorithm that realizes shared protection. The algorithm iteratively improves the degree of wavelength resource usage and fiber utilization. To achieve this, we newly define two metrics to evaluate the degree of wavelength resource usage of a pair of working/backup paths and the fiber utilization efficiency. The proposed method iteratively redesigns groups of paths that are selected in the order determined by the metrics. A numerical analysis verifies that the proposed algorithm can substantially reduce the required wavelength resources and hence fiber cost. It is also verified that the computational complexity of the proposed algorithm is small enough to terminate within practicable time.

Adaptive and flexible network control technology is considered essential for efficient network resource utilization. Moreover, such technology is becoming a key to cost-effectively meet diverse service requirements and accommodate heavier traffic with limited network resources; demands that conventional static operation cannot satisfy. To address this issue, we previously studied dynamic network control technology for large-capacity network services including on-demand broad bandwidth provisioning services and layer-one VPN. Our previous study introduced a simple weighting function for achieving fairness in terms of path length and proposed two dynamic Make Before Break Routing algorithms for reducing blocking probability. These algorithms enhance network utilization by rerouting existing paths to alternative routes while completely avoiding disruption for highly reliable services. However, the impact of this avoidance of service disruption on blocking probability has not been clarified. In this paper, we propose modified versions of the algorithms that enhance network utilization while slightly increasing disruption by rerouting, which enable us to elucidate the effectiveness of hitless rerouting. We also provide extensive evaluations including a comparison of original and modified algorithms. Numerical examples demonstrate that they achieve not only a high degree of fairness but also low service blocking probability. Hitless rerouting is achieved with a small increase in blocking probability.

We realize a multicore erbium-doped fiber amplifier (MC-EDFA) with 2dB optical gain improvement (average) by recycling the residual 0.98μm pump light from the MC-EDF output. Eight-channel per core wavelength division multiplexed (WDM) Nyquist PM-16QAM optical signal amplification is demonstrated over a 40-minute period. Furthermore, we demonstrate the proposed MC-EDFA's stability by using it to amplify a Nyquist PM-16QAM signal and evaluating the resulting Q-factor variation. We found that our scheme contributes to reducing the total power consumption of MC-EDFAs in spatial division multiplexing (SDM)/WDM networks by up to 33.5%.

Recently, a great deal of effort has been devoted to the design problem of "constrained least squares M-D FIR filter" because a significant improvement of the squared error is expected by a slight relaxation of the minimax error condition. Unfortunately, no design method has been reported, which has some theoretical guarantee of the convergence to the optimal solution. In this paper, we propose a class of novel design methods of "constrained least squares M-D FIR filter. " The most remarkable feature is that all of the proposed methods have theoretical guarantees of convergences to the unique optimal solution under any consistent set of prescribed maximal error conditions. The proposed methods are based on "convex projection techniques" that computes the metric projection onto the intersection of multiple closed convex sets in real Hilbert space. Moreover, some of the proposed methods can still be applied even for the problem with any inconsistent set of maximal error conditions. These lead to the unique optimal solution over the set of all filters that attain the least sum of squared distances to all constraint sets.

In this paper, the effects of visual information on associated auditory information were investigated when presented simultaneously under dynamic conditions on a wide screen. Experiments of an auditory-visual stimulus presentation using a computer graphics movie of a moving patrol car and its siren sound, which were combined in various locations, were performed in 19 subjects. The experimental results showed the following: the visual stimulus at the beginning of the presentation captured the sound image stronger than that at the end (i.e., beginning effect), the sound image separated from the visual image even when both stimulus locations were exactly at the same place and then when both stimuli moved in opposite directions from each other, the visual stimulus tended to capture the sound image stronger in the peripheral visual field than in the central visual field, and the visual stimulus moving toward the sound source captured the sound image stronger than that moving away from the sound source.

This study compares the performances of waveband protection and wavelength path protection in survivable hierarchical optical path networks. Network costs and the number of switching operations necessary are evaluated for different ratios of protected demand. Numerical results demonstrate that waveband protection can drastically decrease the number of switching operations in the case of failure, while both waveband and wavelength path protection effectively reduce the network resources needed compared to single layer optical path networks.

This paper proposes optical node architectures for the single-layer optical cross-connect (OXC) and hierarchical OXC (HOXC) that utilize dedicated add/drop switches for originating/terminating traffic at a node. For both single-layer OXC and HOXC, three architectures with different restrictions on add/drop capabilities are presented. The performance of the proposed architectures is compared through numerical experiments. The architectures significantly reduce total switch scale and minimize necessary switch size while attaining colorless, directionless and contentionless capabilities.

A novel coarse and fine hybrid granular routing network architecture is proposed. Virtual direct links (VDLs) defined by the coarse granular routing to bridge distant node pairs, and routing via VDL mitigate the spectrum narrowing caused by optical filtering at wavelength-selective switches in ROADM (Reconfigurable Optical Add/Drop Multiplexing) nodes. The impairment mitigation yields denser channel accommodation in the frequency domain, which substantially increases fiber spectral efficiency. The proposed network simultaneously utilizes fine granular optical path level routing so that optical paths can be effectively accommodated in VDLs. The newly developed network design algorithm presented in this paper effectively implements routing and spectrum assignment to paths in addition to optimizing VDL establishment and path accommodation to VDLs. The effectiveness of the proposed architecture is demonstrated through both numerical and experimental evaluations; the number of fibers necessary in a network, and the spectrum bandwidth and hop count product are, respectively, reduced by up to 18% and increased by up to 111%.

We propose a compact matrix-switch-based hierarchical optical cross-connect (HOXC) architecture that effectively handles the colorless waveband add/drop ratio restriction so as to realize switch scale reduction. In order to implement the colorless waveband add/drop function, we develop a wavelength MUX/DMUX that can be commonly used by different wavebands. We prove that the switch scale of the proposed HOXC is much smaller than that of conventional single-layer optical cross-connects (OXCs) and a typical HOXC. Furthermore, we introduce a prototype system based on the proposed architecture that utilizes integrated novel wavelength MUXs/DMUXs. Transmission experiments prove its technical feasibility.

In this paper, we propose a method of linear time-varying filtering of discrete time signals. The objective of this method is to derive a component, of an input signal, whose alias-free generalized discrete time-frequency distribution [Jeong & Williams 1992] concentrates on a specific region of a time-frequency plane. The method is essentially realized by computing an orthogonal projection of an input onto a subspace that is spanned by orthonormal signals, whose distributions concentrate on the region. We show that such orthonormal signals can be derived as eigenvectors of a matrix whose components are explicitly expressed by using the kernel of the distribution and the regions. This result shows that we can design such a filter prior to processing of the input if the specific region is given as a priori. This result is a generalization of [Hlawatsch & Kozek 1994], that is originally derived for the continuous Wigner distributions, to the discrete distributions.