Takeshi Ozeki

Wavelength-band generation and transmission of 3.24-Tbit/s (81-channel WDM×40-Gbit/s) carrier-suppressed return-to-zero format by use of a single supercontinuum source for frequency standardization

A wavelength band of 40-Gbit/s–based 81-channel dense-wavelength–division multiplexing of a carrier-suppressed (CS) return-to-zero (RZ), i.e., CS-RZ format is simultaneously generated by use of a single supercontinuum (SC) source pumped by an optically multiplexed 40-Gbit/s CS-RZ signal. Because the SC is generated while coherent characteristics are maintained, CS multiplexing in each wavelength-division multiplexing (WDM) channel is multiplied. Furthermore, because a single mode-locked laser-diode (MLLD) pulse is an originated signal source, the WDM channel spacing is strongly locked by the microwave mode-locking frequency. As a result, the proposed technique would be favorably applicable to cost-effective multichannel frequency standardization when the center wavelength of the MLLD is locked to an ITU grid. Transmission of 3.24-Tbit/s (81-channel×40-Gbit/s) DWDM in the CS-RZ format with a 66-nm continuous signal band in the C and the L wavelengths is experimentally demonstrated by use of tellurite-based erubium-doped fiber amplifiers.

Polarization-mode dispersion measurement by an optical time-domain reflectometer with polarimetry assuming backscattering by randomly oriented nonspherical particles.

In previous work on polarization-mode dispersion (PMD) measurement with an optical time-domain reflectometer with polarimetry (p-OTDR), scatterers were assumed to be a cloud of small spherical particles in a fiber. We have found that the p-OTDR waveforms were fitted well by modified Mueller matrices, assuming scattering by a cloud of nonspherical particles. We realized a PMD measurement based on the p-OTDR Jones matrix eigenanalysis (JME) method. The measured PMD was consistent with that of JME standard measurement with transmission-type polarimetry.

Buffer Management for Shared Feedback Buffer-Type Optical Packet Switches

We design a buffer management scheme for shared feedback buffer-type optical packet switches. The buffer is of the fiber-delay-line type and handles variable-length optical packets. The buffer limits the number of feedbacks of a packet to avoid degradation of the physical characteristic. We try to reduce packet loss probability in the packet switch by adopting new buffer management methods in which void spaces at output ports are reduced, packets are aligned in the buffer to avoid contention at output ports, and buffer utilization is increased. Through simulation, we find that the proposed methods provide better packet loss probability and delay performance than existing methods. We show that the improvement is obtained when we use buffer structures in which a variety of delay lengths are installed. The proposed methods are also better when wavelength conversions are allowed and when unbalanced traffic enters.

PMD Distribution Measurement by an OTDR With Polarimetry Considering Depolarization of Backscattered Waves

In previous studies of polarization-mode-dispersion (PMD) distribution measurement by an optical time-domain reflectometer with polarimetry (p-OTDR), scatterers were assumed to be clouds of nonspherical particles in a fiber. However, the pulsewidth dependence of the degree of polarization (DOP) could not be explained by the assumption of nonspherical backscattering alone. In this paper, it is reported that the p-OTDR waveforms were fitted well by modified Mueller matrices under the assumptions of scattering by cloud of spherical particles and a reduction in the DOP due to the interference of the backscattered waves with the phase fluctuation. A PMD distribution measurement is demonstrated based on the p-OTDR Jones matrix eigenvalue method with the assumption of slowly varying PMD along the fiber length, and the regeneration of the PMD distribution of test fibers fabricated by splicing constituent fibers with known PMDs was successful. Surprisingly, the regenerated PMD distribution along the fiber length shows a linear accumulation of constituent fiber PMD in the short range of 6 km. The reverse-direction measurements show a reasonable regeneration of what is assumed to be a linear accumulation along the fiber length, which strongly suggests that the PMD distribution along the fiber shows a linear accumulation rather than a root-length accumulation in relatively short fibers with smaller PMD

Simultaneously generated 3.24 Tbit/s (81 WDM /spl times/ 40 Gbit/s) carrier suppressed RZ transmission using a single supercontinuum source

A 3.24 Tbit/s (81 WDM /spl times/ 40 Gbit/s) carrier suppressed RZ (CS-RZ) format is simultaneously generated using a single supercontinuum source pumped by optically multiplexed 40 Gbit/s CS-RZ and is transmitted over an 80 km link.

Birefringence distribution along fiber length

We demonstrate the Birefringent Optical Circuit Synthesis (BOGS) capable of estimating modal coupling and phase-shift distributions along a fiber length. By measuring the Stokes parameters dependence on optical frequency, we can derive the unitary matrix elements as z-polynomials to synthesize the birefringent lattice optical circuit. The distribution of mode-coupling angle along the fiber length obtained from BOGS is compared with the POTDR waveform to find their correlation.

Wideband tunable wavelength conversion of 10-Gbit/s return-to-zero signals by optical time gating of a highly chirped rectangular supercontinuum light source

We propose a novel technique for wideband tunable wavelength conversion of return-to-zero signals by optical time gating of a supercontinuum (SC) light source. A SC pulse generated by nonlinear propagation in a normal-dispersion fiber has a rectangular shape with highly linear upchirping. By control of the optical time-gating position, the center wavelength of time-gated SC pulse can be precisely tuned. Error-free 10-Gbit/s wavelength conversion with a tuning range of 27.1 nm is experimentally demonstrated.

Evolutional family networks generated by group-entry growth mechanism with preferential attachment and their features

The group-entry growth mechanism with preferential attachment generates a new class of scale free networks, of which exact asymptotic connectivity distribution and generation function are derived. They evolve from aristocratic networks to egalitarian networks with asymptotic power law exponent of γ=2+M depending on the size M and topology of the constituent groups. The asymptotic connectivity distribution fits very well with numerical simulation even in the region of smaller degrees. Then it is demonstrated small size networks can be analysed to find their growth mechanism parameters using asymptotic connectivity distribution templates in region of smaller degrees, where it is easy to satisfy a statistical level of significance. This approach is believed to develop new search of scale free networks in real worlds. As an example of evolutional family network in the real world, Tokyo Metropolitan Railway Network is analysed.

Fiber dispersion cancellation by all-optical quantum signal processing based on quantum correlations

A quantum dispersion canceller is proposed that uses all-optical quantum signal processing based on strong quantum correlations in the signal and idler waves amplified by an optical parametric amplifier at the receiver end. It cancels the even-order dispersion and can regenerate an optical data packet without any ambiguity.

Nonlinear inter-channel cross talk of linear optical amplifier (LOA) in DWDM applications

We investigated the third order nonlinear effect of linear optical amplifier (LOA) under the condition of amplification of 8ch* 10 Gb/s WDM signals. We observed the remarkable inter-channel cross talk caused by FWM in the saturated region.