Takayuki Kurosu

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.

Laser cooling and trapping of calcium and strontium

Calcium and strontium atomic beams are cooled and trapped by using the 1S0-1P1 transition in the 400 nm region. The trapping of 8 isotopes, 40Ca, 42Ca, 43Ca, 44Ca, 84Sr, 86Sr, 87Sr and 88Sr, is observed. The decay rate of the trapped atom is found to be of the order of 10 ms and the average atomic velocity less than 1 m/s.

Continuously tunable 22 ns delay for wideband optical signals using a parametric delay-dispersion tuner

We present a concept of parametric delay-dispersion tuner (PDDT) that is capable of the continuous tuning of delay and dispersion for wideband optical signals in a simultaneous and independent manner. We experimentally demonstrate a tunable delay of 22 ns for 2.6 ps return-to-zero optical signals without distortion and error-free transmissions at 43 gigabits per second. We show that PDDT has a bandwidth of ~0.9 THz, resulting in the delay-bandwidth product of ~20,000, and exhibits an excellent performance in terms of stability and reproducibility.

Laser Cooling and Trapping of Alkaline Earth Atoms

Characteristics of laser trapping of Ca and Sr are experimentally studied and discussed. The lifetime of the trap is found to be limited by accumulation of the population in the 3P2 state, not by the decay 1P1→1D2. This result allows us to generate a continuous free-falling flow of ultra-cold ground state atoms which is useful for ultra-high resolution spectroscopy. Effects of an optical pumping laser which recycles the 1D2 population in Sr are investigated.

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.

No guard-band wavelength translation of Nyquist OTDM-WDM signal for spectral defragmentation in an elastic add-drop node.

We demonstrate a seamless spectral defragmentation in an elastic all-optical add-drop node based on wavelength division multiplexing (WDM) channels of Nyquist optical time division multiplexing (OTDM) signal. A 172 Gbaud Nyquist OTDM signal occupying a 215 GHz range is elastically shifted adjacent to its neighboring channel, completely filling a variable spectral gap caused by the dropped channel. The frequency shift is done in a dual-stage polarization-diversity four wave mixing-based converter using polarization-maintaining highly nonlinear fiber. The spectrally defragmented signals are successfully transmitted over a 80 km fiber link with BER<10(-9).

Low Penalty Uniformly Tunable Wavelength Conversion Without Spectral Inversion Over 30 nm Using SBS-Suppressed Low-Dispersion-Slope Highly Nonlinear Fibers

We demonstrate a simple and efficient cascaded operation of parametric wavelength conversion at 43 Gb/s by four-wave mixing for arbitrary input and output wavelengths over 30 nm, using SBS-suppressed low-dispersion-slope highly nonlinear fibers with a power penalty below 0.7 dB.

Transmission and pass-drop operations of mixed baudrate Nyquist OTDM-WDM signals for all-optical elastic network

We propose the use of Nyquist OTDM-WDM signal for highly efficient, fully elastic all-optical networks. With the possibility of generation of ultra-coarse yet flexible granular channels, Nyquist OTDM-WDM can eliminate guard-bands in conventional WDM systems, and hence improves the spectral efficiency in network perspective. In this paper, transmission and pass-drop operations of mixed baudrate Nyquist OTDM-WDM channels from 43 Gbaud to dual-polarization 344 Gbaud are successfully demonstrated over 320 km fiber link with four FlexGrid-compatible WSS nodes. A stable clock recovery is also carried out for different baudrate Nyquist OTDMs by optical null-header insertion technique.

Frequency measurements and hyperfine structure of the R(85)33–0 transition of molecular iodine with a femtosecond optical comb

Absolute frequency measurements of the R(85)33‐0 transition of molecular iodine at the blue end of the tuning range of a frequency-doubled Nd:YAG laser are implemented with a femtosecond optical comb based on a mode-locked Ti:sapphire laser. The hyperfine structure of the R(85)33‐0 transition is observed by use of high-resolution laser spectroscopy and is measured by the femtosecond optical comb. The observed hyperfine transitions are good frequency references for both frequency-doubled Nd:YAG and Nd:YVO4 lasers in the 532-nm region. High-accuracy hyperfine constants are obtained by our fitting the measured hyperfine splittings to a four-term Hamiltonian, which includes the electric quadrupole, spin‐rotation, tensor spin‐spin, and scalar spin‐spin interactions.

Cesium Atomic Fountain with Two-Dimensional Moving Molasses

In this paper we describe a cesium atomic fountain with two-dimensional moving molasses. This method is applicable for multipulse operation of the cesium atomic fountain frequency standard, which will improve the frequency stability and reduce the frequency shift due to spin exchange collisions of atomic fountain frequency standards. Multipulse launching is demonstrated experimentally, and the frequency shift due to the fluorescent light from the loaded atoms is estimated.