Tetsuro Inui

Highly efficient tunable fiber Bragg grating filters using multilayer piezoelectric transducers

Abstract We realized a wavelength tunable optical filter based on a fiber Bragg grating using multilayer piezoelectric transducers (MLP). The Bragg wavelength of the filter can be easily tuned in proportion to an applied low DC voltage. The tuning range efficiency was as high as 0.2 nm/V. We realized a 10 nm Bragg wavelength shift by applying as low as 50 V to the MLP. The MLP was also used in a higher order dispersion equalizer which consists of a pair of nonlinearly chirped gratings. A zero dispersion wavelength shift of 7 nm was successfully realized for the equalizer.

The design of dispersion equalizers using chirped fiber Bragg gratings

Dispersion equalizers designed to compensate for the arbitrary dispersion characteristics of optical fibers can be synthesized by cascading chirped fiber Bragg gratings and optical circulators. We have derived a synthesis rule for the equalizers and applied it to the fabrication of a third-order dispersion equalizer operating at the zero dispersion wavelength.

40-Gb/s RZ transmission over transoceanic distance in a dispersion managed standard fiber using a new inline synchronous modulation method

We propose a modified soliton control method for a strongly dispersion managed line, which employs a highly nonlinear fiber in addition to conventional inline synchronous modulation. This method enables us to transmit a 10-Gb/s return-to-zero signal over 20000 km using a dispersion managed line composed of a standard (nondispersion shifted) fiber and dispersion compensation. Optimizing the length of the highly nonlinear fiber greatly increases the power margin of the transmitted optical power.

Group delay ripple reduction and reflectivity increase in a chirped fiber Bragg grating by multiple-overwriting of a phase mask with an electron-beam

The phase errors in electron-beam-written step-chirped masks can be reduced by using a method based on the continuous movement approach and overwriting a pattern at the same place on the substrate several times. The group delay ripple of chirped fiber Bragg gratings fabricated by a four-times-overwritten phase mask is comparable with that of gratings obtained using a holographically written chirped phase mask.

40-Gb/s RZ transmission over a transoceanic distance in a dispersion managed standard fiber using a modified inline synchronous modulation method

This paper analyzes in detail numerically a 40-Gb/s return-to-zero (RZ) transmission system over a transoceanic distance in a strongly dispersion managed line composed of standard single-mode fiber (SMF) and dispersion compensation fiber (DCF). We derived a periodically steady-state pulse (a DM soliton) in a DM line. Since the pulse width of a steady-state pulse is too broad for a 40 Gb/s system, the conventional in-line synchronous modulation technique cannot greatly improve the transmission quality. However, we found that the modified inline synchronous modulation technique, which is reported as the black-box optical regenerator, can effectively extend the transmission distance even in such a strongly DM line. We discuss the mechanism of the modified synchronous modulation technique with respect to a steady-state pulse in a transmission line, and show that a 40-Gb/s RZ signal can be transmitted over 20 000 km.

A wavelength-tunable dispersion equalizer using a nonlinearly chirped fiber Bragg grating pair mounted on multilayer piezoelectric transducers

We realized a wavelength-tunable dispersion equalizer using a pair of nonlinearly chirped fiber Bragg gratings mounted on multilayer piezoelectric transducers. The operation region can be continuously tuned up to 7 nm by applying 50 V. This device enables us to equalize the second- and third-order dispersion of dispersion-shifted fibers with different zero dispersion wavelengths over 6 mn. This performance shows that our equalizer can be employed for adaptive equalization.

Multiperiod IP-over-elastic network reconfiguration with adaptive bandwidth resizing and modulation

Elastic optical networks (EONs) represent a promising network architecture that accommodates a wide variety of traffic demands in the optical layer. Thanks to the functionality of bandwidth flexibility of elastic optical paths, we can now accommodate IP traffic directly into the optical layer by configuring, for example, the modulation format and subcarrier counts to client demands (optical path demands). At the same time, to accommodate temporally and geographically changing IP traffic demands efficiently in optical networks, cooperation between the IP and optical layers is essential. This paper proposes a multilayer network reconfiguration algorithm that supports periodically changing IP traffic patterns. We incorporate two schemes, which make IP over EONs more flexible, into the heuristic iterative multilayer network reconfiguration algorithm (IMNR). The first scheme involves bandwidth resizing achieved through subcarrier expansion and reduction, and the second employs energy-efficient adaptive modulation according to the data rate and distance of the client demands. We evaluated the impact of the following on energy efficiency: the IMNR algorithm, the proposed adaptive bandwidth resizing and modulation schemes, and some multicarrier-based transponder architectures including bandwidth-variable transponder (BVT) and sliceable BVT (SBVT). The evaluation results show that the IMNR algorithm with the proposed schemes significantly reduces the energy consumption compared with traditional network planning schemes and equipment.

Monitoring of orthogonal polarization power ratio due to PDL using intensity tones in polarization multiplexed signals

We demonstrate a technique for monitoring orthogonal polarization power ratio (OPPR) occurring in WDM polarization-multiplexed signals due to PDL. We employ low-frequency intensity tones to estimate the effect of PDL and level of OSNR.

Demonstration of Single-Mode Multicore Fiber Transport Network With Crosstalk-Aware In-Service Optical Path Control

Multicore fiber (MCF) transmission is considered as one of the promising technologies for breaking the capacity limit of traditional single mode fibers. Managing the crosstalk (XT) and configuring optical paths adaptively based on the XT as well as achieving longer distance and larger capacity transmission are important, because intercore XT could be the main limiting factor for MCF transmission. In a real MCF network, the intercore XT in a particular core is likely to change continuously as the optical paths in the adjacent cores are dynamically assigned to match the dynamic nature of the data traffic. If we configure the optical paths while ignoring the intercore XT value, the Q-factors may become excessive. Therefore, monitoring the intercore XT value continuously and configuring optical path parameters adaptively and flexibly are essential. To address these challenges, we develop an MCF transport network testbed and demonstrate an XT-aware traffic engineering scenario. With the help of a software-defined network controller, the modulation format and optical path route are adaptively changed based on the monitored XT values by using programmable devices such as a real-time transponder and a reconfigurable optical add–drop multiplexer.

Subcarrier restoration for survivable multi-flow transponders in elastic optical networks

We discuss survivability considerations for multi-carrier-based elastic optical networks, focusing on the multi-carrier transponder (MCT). We explain the necessity of subcarrier restoration that can recover multi-carrier connections using backup sub-channels. An initial evaluation shows our restoration scheme improves transponder reliability.