Shuko Kobayashi

All-Optical Asynchronous Detection for a Compact Integrable Incoherent Optical CDMA System

In this paper, we investigate all-optical truly asynchronous detection without global clocking in an incoherent optical code-division multiple-access (CDMA) system. The implemented system is designed with an integrable optical source consisting of an electro-absorption modulator for pulse carving, compact coders consisting of fiber Bragg grating arrays for encoding and decoding, and receiver consisting of an all-optical thresholder for data and clock recovery. We compare three detection schemes: (1) synchronous detection with data from a photodetector and clock from an external source; (2) asynchronous detection with data and clock from the all-optically thresholded signal received by a clock and data recovery (CDR) unit; and (3) asynchronous detection with data from a photodetector and clock extracted from the all-optically thresholded signal using CDR. Error-free transmission is obtained for detection schemes (1) and (3). A combination of all-optical thresholding and CDR technology is demonstrated in an optical CDMA system for the first time.

Demonstration of 10 Gbit/s-Based Time-Spreading and Wavelength-Hopping Optical-Code-Division-Multiplexing Using Fiber-Bragg-Grating En/Decoder

We studied 10Gbit/s-based time-spreading and wavelength-hopping (TS-WH) optical code division multiplexing (OCDM) using fiber Bragg gratings (FBGs). To apply it to such the high bit rate system more than ten gigabit, two techniques are adopted. One is encoding with the maximum spreading time of 400 ps, which is four times as data bit duration, to encode without shortening chip duration. Another is encoder design. The apodized refractive index profile to the unit-gratings composing the encoder is designed to encode the pulses with 10-20ps width at 10Gbit/s rate. Using these techniques, 2 × 10Gbit/s OCDM is demonstrated successfully. In this scheme, transmission distance is limited due to dispersion effect because the signal has wide bandwidth to assign a wavelength-hopping pattern. We use no additional devices to compensate the dispersion, in order to construct simple and cost-effective system. Novel FBG encoder is designed to incorporate both encoding and compensating of group delay among chip pulses within one device. We confirm the extension of transmission distance in the TS-WH OCDM from the demonstration over 40 km-long single mode fiber.

Design of Hybrid WDM/OCDM Add/Drop Filters and Its Experimental Demonstration for Passive Routing in Metropolitan and Access Integrated Network

We have proposed a newly metropolitan and access integrated network to provide services to long-reach depopulated households due to geographical difficulty, with smooth and energy-saving upgrade of the system. The feasibility of the system based on hybrid wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) is investigated from the viewpoints of add-drop multiplexing (ADM) operation and WDM/OCDM crosstalk. The ADM operation is verified when the adding, dropping, and transmitting signals are simultaneously operated, by examining the structure of multiplexer. The range of the input signal power to the multiplexer is derived. The crosstalk impact of WDM and OCDM is reduced by apodizing the filter device. By using the apodized devices, 16 × 1.25 Gb/s OCDM is successfully demonstrated at a wavelength band of 3.2 nm in C-band. From the results, the feasibility of 160-channel hybrid multiplexing in a proposed network is estimated.

Field trial of time-spreading and wavelength-hopping OCDM transmission using FBG en/decoders.

In this paper, field trial on optical code division multiplexing through the commercial-used fiber line is presented. We fabricated fiber Bragg grating en/decoders with time-spreading and wavelength-hopping scheme, considering environmental fluctuation of transmission fiber. 200 km-long transmission of 2-channel x 10 Gb/s signals was achieved on the field photonic network test bed of JGN II. Error free transmission was demonstrated in real field deployed single-mode transmission fiber.

Inter-Band Crosstalk Reduction Using Sinc Apodization of Super-Structured Fiber Bragg Gratings for Hybrid WDM/OCDM Add/Drop Filters

Here, we propose a newly developed hybrid system of wavelength-division multiplexing (WDM) and optical code-division multiplexing (OCDM) with phase-shifted coherent time-spreading for the future metro-access integrated network. In order to suppress the inter-band crosstalk from the WDM interfering channels, the sinc-apodizing technique is proposed for the super-structured fiber Bragg gratings (SSFBGs) as the add/drop filters. The suppression of crosstalk is demonstrated by two-channel WDM and OCDM experiments, compared with conventional SSFBGs with uniform index profile. The proposed method suppresses the crosstalk and shows the feasibility of the 160 (10 WDM 16 OCDM)-channel system.

Phase-coding OCDM using fiber-Bragg-grating with enlarged signal pulse width

We evaluate correlation characteristics for phase-coding scheme utilizing fiber-Bragg-gratings as encoder/decoder. From the results, we confirmed that channel discrimination is sufficiently capable with the enlarged pulse width 4 times longer than chip duration.

Demonstration of 80-km-Long SMF Transmission on Time-Spread Wavelength-Hopping-Type OCDM With Dispersion Compensators

We demonstrate the novel dispersion compensation for time-spread/wavelength-hop (TS-WH) optical code-division multiplexing (OCDM). The single-mode-fiber transmission, up to 80 km long, on TS-WH OCDM was achieved by a combination of the dispersion-compensated decoder and the multichannel-type dispersion-slope compensator.