Ken Tanizawa

Ultrahigh-Definition Video Transmission and Extremely Green Optical Networks for Future

The Internet traffic is essentially increasing because the contents are more associated with video, a higher definition video, rather than just text or picture. In fact, next-generation television (TV) standards are being explored toward the so-called 8-k definition, or ultrahigh-definition TV (UHDTV) that requires a bandwidth more than 70 Gb/s for real-time transmission. In the long run, chunks of such video data will eventually prevail over the network, and this trend would ensure a persistent traffic growth for the next decades to come. However, we will point out that the present IP-based technology cannot scale to the increasing traffic for the future mostly due to energy-consumption limits and will become a grave bottleneck for the sustainable growth of the traffic. We will then argue that the only promising solution for this would be the utilization of optical circuit switching, potentially having a few digits better energy efficiency than the present IP-router-based network. As specific implications, we are proposing the concept of the dynamic optical-path network (DOPN). We discuss how to scale the DOPN to the WAN, and show that an extremely green optical network for video-related services is possible at a clean-slate level. Then, we argue that DOPN will be first applied to LANs for broadcasting stations where a technology for scalable network interface cards are essential to accommodate the real-time UHDTV transmissions. Finally, we will briefly introduce our recent demonstration of UHDTV video transmissions using the optical time-division multiplexing based on integratable ultrafast optical devices only.

Controlling Optical Signals Through Parametric Processes

Parametric processes are capable of preserving the phase information of optical signals while their frequencies are converted. This feature, in conjunction with other basic features such as instantaneous and wideband operation, low noise, and high reliability, creates various unique functionalities in optical domain, invaluable for realizing future dynamic all optical networks that are scalable in capacity without energy crunch. This paper will review the fundamentals and proof of concept of the parametric devices that authors have been proposing as important building blocks for the future networks. The devices to be reviewed are parametric wavelength converters, parametric tunable dispersion compensators, parametric delay dispersion tuners, and wavelength-tunable optical parametric regenerators.

Efficient generation of holographic movies with frame interpolation using a coherent neural network

Computer-generated hologram (CGH) is recently expanding its application fields. However, the calculation cost is very high, in particular, in the generation of CGH streams for three-dimensional movies. This paper proposes a small-calculation-cost method to generate CGH streams based on a coherent neural network (CNN) that deals with complex-amplitude information with generalization ability in the carrier-frequency domain. After carrier-frequency-dependent learning, we can generate a CGH stream, by sweeping a virtual carrier frequency in the CNN, with neural interpolation thanks to the frequency-domain generalization. Experiments demonstrate a successful stream generation with 1/6 the conventional calculation time.

Adaptive control of tunable dispersion compensator that minimizes time-domain waveform error by steepest descent method

We propose a novel technique to compensate dispersion adaptively. First, an error is calculated from the waveform of output signal in the time domain. Then a tunable dispersion compensator is controlled toward minimizing the error value by means of steepest-descent method. Transmission experiments and simulations show that the proposed technique can compensate the dispersion quickly for a wide dispersion range

Dynamic Optical Path Switching in 172-Gb/s OTDM Transmissions of Ultra-High Definition Video Signals Using Fast Channel-Identifiable Clock Recovery and Integratable Devices

We demonstrate dynamic optical path switching in 172-Gb/s OTDM transmissions of real ultra-high definition (UHD) video signals. To allow integration, the 172-Gb/s OTDM transmission system was composed of semiconductor devices, which are newly developed CMOS-based transceivers, quantum-dot SOAs and monolithic all-optical gates based on inter-sub-band transitions in a quantum well waveguide. In order to realize dynamically switchable OTDM (DS-OTDM), we developed a novel clock distribution scheme using an optical null header (ONH). The ONH, which was inserted between the OTDM signal pulses with a repetition rate equal to the clock frequency, enabled to achieve channel identification and fast yet robust clock recovery. An uncompressed UHD video signal, which required a bandwidth of 72 Gb/s for the real-time transmission, was transmitted using two channels of the 172-Gb/s DS-OTDM signal. The two channels were de-multiplexed at the same time immediately after the optical path switching. Through optical path switching, two UHD video signals were dynamically switched within a switching time of 15 μ m and displayed on a screen successively.

Performance Analysis of Steepest Descent-Based Feedback Control of Tunable-Dispersion Compensator for Adaptive Dispersion Compensation in All-Optical Dynamic-Routing Networks

In this paper, we report the performance-analysis results of our proposed high-speed and low-cost feedback-control method of a tunable-dispersion compensator (TDC) for adaptive dispersion compensation in all-optical dynamic-routing networks. In this method, we monitor the received waveform in the time domain and control a TDC repeatedly to reshape the waveform by means of the steepest descent method. Transmission experiments and simulations show that the proposed method can compensate for the dispersion quickly over a wide dispersion range. The compensation range is from -6000 to 6000 ps/nm in 10-Gb/s transmission. The compensation time is 1-2 s for dispersions within 1000 ps/nm. This method is applicable to the adaptive dispersion compensation in all-optical dynamic-routing networks

High-quality frame interpolation in computer generated holographic movies using coherent neural networks with a hybrid learning method.

Computer generated holograms (CGHs) are widely used in optical tweezers, which will be employed in various research fields. We previously proposed an efficient generation method of CGH movies based on frame interpolation using coherent neural networks (CNNs) to reduce the high calculation cost of three-dimensional CGHs. At the same time, however, we also found that the quality observed in the interpolated CGH images needed to be improved even further so that the method could be accepted for general use. We report a successful error reduction in interpolated images by developing a new learning method of CNNs. We reduce the error by combining locally connected correlation learning and steepest descent learning in a sequential manner.

In-Line Polarization-Insensitive Parametric Tunable Dispersion Compensator for WDM Signals

We develop frequency-preserving parametric tunable dispersion compensator (P-TDC) with polarization diversity for simultaneous dispersion compensation of wavelength division multiplexing channels. The in-line polarization-insensitive P-TDC is composed of cascaded parametric tunable frequency converters based on degenerate four-wave mixing process in polarization-maintaining highly nonlinear fibers with a low dispersion slope. Dispersion-managed error-free transmission of four channels of 43 Gb/s nonreturn-to-zero ON-OFF keying signal is successfully demonstrated over 126 km dispersion-shifted fiber with the in-line polarization-insensitive P-TDC.

Field Demonstration of Parametric Tunable Dispersion Compensator Employing Polarization Diversity Scheme

We report long-term polarization-insensitive operation of a parametric tunable dispersion compensator (P-TDC) in 43-Gb/s NRZ-OOK transmission over 105-km field-installed fiber. The P-TDC employs polarization diversity loop using polarization-maintaining highly nonlinear fiber with a low dispersion slope. Stable dispersion-managed transmission for more than 8 hours is achieved under the polarization-fluctuating conditions in the field-installed fiber.

Fast Tracking Algorithm for Adaptive Compensation of High-Speed PMD Variation Caused by SOP Change in Milliseconds

We propose a tracking algorithm based on the steepest descent method for adaptive polarization-mode-dispersion (PMD) compensation. Transmission simulations at 160 Gb/s are conducted under the condition that the PMD fluctuates with a sequential random state of polarization change at a rate of 0.13 rad per 4 ms on average. The results show that our algorithm can successfully compensate PMD variations at speeds where a conventional hill-climbing-based tracking algorithm cannot maintain effective PMD compensation.