IP: OCDM Experiment Sends 1.52 Tbits/s over 80km

[David Farber <dave () farber net>]

The Communications Research Laboratory of Japan and Osaka University 
achieved a transfer rate of 1.52 Tbits/s in an experiment of optical code 
division multiplexing (OCDM) technology. The Laboratory has positioned OCDM 
as a basic technology to achieve even higher speed for wavelength division 
multiplexing (WDM).

In the experiment, four channels, each handling a 20 Gbits/s optical 
signal, are multiplexed into the same wavelength. These 19 optical signal 
waves are transferred via WDM to achieve a throughput of 1.52 Tbits/s over 
a distance of 80km. The frequency utilization efficiency is about 0.4 
bits/s/Hz, or about the same as Tbit-class WDM transfer experiments. 
Numerical simulation confirmed that code division multiplexing can handle 
up to 8 channels. The Communications Research Laboratory comments that 
frequency efficiency can be boosted higher than in WDM, which uses 
vestigial sideband or similar modulation.

OCDM transfer uses encoders and decoders, each consisting of planar optical 
waveguides integrating splitters, optical phase-shifters, delay devices and 
synthesizer. The optical pulses are injected into the encoder and divided 
into eight optical signals with time shifts. The divided pulse string is 
modulated using binary phase shift keying (BPSK), with encoding and 
decoding implemented through the orthogonality of the modulated channel 
pulse strings.

(August 2001 Issue, Nikkei Electronics Asia)



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