Junya Kurumida

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.

A Theoretical and Experimental Study on Modulation-Format-Independent Wavelength Conversion

Modern optical networks are adopting advanced modulation formats. Future dynamic optical networks will benefit from all-optical wavelength conversion and signal regeneration techniques in support of multiple modulation formats. This paper presents a concept for a modulation-format-independent wavelength conversion technique based on an optical hybrid and an in-phase/quadrature (IQ) wavelength converter. This technique has the potential for wavelength conversion and signal regeneration of multiple modulation formats. This paper also discusses the signal distortions and noises in the semiconductor optical amplifier based IQ wavelength converter. A proof-of-principle experiment shows the wavelength conversion results of multiple modulation formats. Further, this paper presents the signal regeneration of a return-to-zero quadrature-phase-shifted-keying signal through simulation.

Nonlinear Optical Signal Processing in Optical Packet Switching Systems

This paper discusses nonlinear optical signal processing employed in optical packet switching systems. Nonlinear optical signal processing provides optical label (header) recognition, optical switching, wavelength conversion, and time buffering with typically higher capacity, lower latency, and lower power consumption than electronic counterparts. In order to provide diverse signal processing functions, large-scale integration of nonlinear optical signal processing devices is essential. We discuss possible future directions in optical packet switching involving nonlinear optical signal processing of optical packets with advanced data and label modulation formats.

Wide range operation of regenerative optical parametric wavelength converter using ASE-degraded 43-Gb/s RZ-DPSK signals

For sustainable growth of the Internet, wavelength-tunable optical regeneration is the key to scaling up high energy-efficiency dynamic optical path networks while keeping the flexibility of the network. Wavelength-tunable optical parametric regenerator (T-OPR) based on the gain saturation effect of parametric amplification in a highly nonlinear fiber is promising for noise reduction in phase-shift keying signals. In this paper, we experimentally evaluated the T-OPR performance for ASE-degraded 43-Gb/s RZ-DPSK signals over a 20-nm input wavelength range between 1527 nm and 1547 nm. As a result, we achieved improved power penalty performance for the regenerated idler with a proper pump power range.

Microsecond switching of parametric tunable dispersion compensator

A record-fast, 2 μs switching operation of an optical tunable dispersion compensator is demonstrated with a parametric tunable dispersion compensation scheme. We alternately switch two optical paths having different net dispersions with a microsecond guard interval of the compensator response and achieve successful transmissions of 43 Gbit/s non-return-to-zero on-off-keying optical signals. The error-free guard time for the switching of the two optical paths is 125 μs, limited mostly by the clock synchronization of the bit-error detector. The power penalty due to the switching of the compensator is less than 0.5 dB.

First demonstration of ultra-low-energy hierarchical multi-granular optical path network dynamically controlled through NSI-CS for video related applications

We developed ODU-XC, CDC-ROADM, and silicon photonics switch, and built an eight-node network capable of 90Tbps based on NSI-CS standard protocol. Its energy consumption was orders of magnitude lower than that achievable with IP routers.

40 Gb/s 8×8 low-latency optical switch for data centers

This paper reports on a 40 Gb/s 8×8 optical switch for data centers. Experiments demonstrate error-free operation with 118.2 ns switching latency in contention-less architecture. Simulations show 150 ns latency for consolidated architectures.

Wavelength-tunable optical parametric regenerator.

We designed a wavelength-tunable optical parametric regenerator, where functions of reamplification, reshaping, and wavelength conversion are incorporated into a highly nonlinear fiber component. The uniform power transfer functions and negative penalties over a 20nm input wavelength range are experimentally demonstrated.

Energy consumption and traffic scaling of dynamic optical path networks

Dynamic path switching in lower layers such as optical or sub-wavelength layer-1 path connections is essential for future networks to provide end-to-end, bandwidth-guaranteed, large-capacity services without energy crunch. While this is almost generally agreed, the number of ports in optical switches tends to be limited by technological difficulties, severely restraining the scale of the network. However, video-related services, that occupies most of the traffic nowadays, could significantly alleviate such restraints if we utilized the nature of video usage. In most cases, video-related services are virtually provided through prior reservation scheme in which a relatively high call-blocking probabilities or long latency for a connection can be tolerated. This situation allows us to accommodate a relatively high number of subscribers with a limited number of switch ports. This paper shows that a network using optical switches with a technologically feasible number of ports, multi-granular paths, and a hierarchical network topology can be of a national scale accommodating several tens of millions of subscribers. The purpose of detailing a plausible network topology is to show that such a network offers a benefit of energy efficiency approximately three orders of magnitude compared with that extrapolated from recent router-based networks. We then discuss important technical aspects of such dynamic optical path networks including our several research activities. We emphasize the importance of vertically integrated research activities from application to device layers to develop the dynamic optical path networks.