Akihiko Nishiki

High reflectivity superstructured FBG for coherent optical code generation and recognition

The performance of the phase-shifted superstructured fiber Bragg grating (SSFBG) for optical code (OC) recognition was investigated with different reflectivity as well as input pulse width. The auto-correlation peak (PA) and the ratios of PA to the maximum wing level (P/W) and cross-correlation level (P/C) were used to quantitatively evaluate the OC recognition performance. There is a conflict between obtaining high PA and high P/W and P/C ratios in high reflectivity regime. The approach of applying apodization technique to improve the performance in high reflectivity regime is proposed. The comparative experimental investigations with 127-chip 160-Gchip/s SSFBG are carried out to confirm the effectiveness of the proposed approach. Error-free transmission with multiplexing of two active users has been successfully achieved by the apodized SSFBG at a data rate of 1.25 Gbit/s.

High-performance optical code generation and recognition by use of a 511-chip, 640-Gchip/s phase-shifted superstructured fiber Bragg grating

The generation and recognition of a record-length 511-chip optical code is experimentally demonstrated by use of a superstructured fiber Bragg grating (SSFBG) with a chip rate of 640 Gchips/s. Very high reflectivity (92%) is achieved with high-quality correlation properties. The temperature deviation tolerance is approximately +/- 0.3 degrees C, which is within the packages temperature stability range (+/- 0.1 degrees C). Experimental results show good agreement with the theory. They indicate the SSFBGs potential for processing a long optical code with an ultrahigh chip rate, which could significantly improve the systems performance.

Ten-user truly asynchronous gigabit OCDMA transmission experiment with a 511-chip SSFBG en/decoder

A ten-user truly asynchronous gigabit coherent-optical-code-division-multiple-access (OCDMA) transmission was experimentally demonstrated without using any timing coordination. The enabling technologies are a record-length 511-chip superstructured-fiber-Bragg-grating (SSFBG) en/decoder and a supercontinuum (SC)-based optical-thresholding technique to significantly suppress the signal interference beat noise as well as the multiple-access-interference (MAI) noise.

Experimental demonstration of performance improvement of 127-chip SSFBG en/decoder using apodization technique

We present the experimental result of apodiz 127-chip 160-Gchip/s superstructured fiber Bragg grating (SSFBG) en/decoder with Gold code in bipolar phase-shift key coherent time-spreading optical code-division multiple-access system. Compared with uniform SSFBGs, the apodized SSFBG demonstrates the overall performance improvements, including a high reflectivity and a good peak-to-wing ratio of autocorrelation as well as a good bit-error-rate performance.

10 Gb/s x 2 ch signal unrepeated transmission over 100 km of data rate enhanced time-spread/wavelength-hopping OCDM using 2.5-Gb/s-FBG en/decoder

We developed data rate enhanced time-spread/wavelength-hopping optical code-division multiplexing using 2.5-Gb/s fiber Bragg grating encoder/decoder and achieved 10 Gb/s /spl times/ 2 ch signal unrepeated transmission over 100 km distance. Five-chip multiwavelength prime hop code in the 1550.4-1553.6-nm region with spacing of 0.8 nm was used.

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.

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.

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.