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Description
Orthogonal Frequency Division Multiplexing (OFDM) is a widespread
technology in broadband communication (wired and wireless) because of its ability to cope with
strong channel distortions (interference, frequency fading, multipath propagation). OFDM
takes advantage of the Fast Fourier Transform (FFT) to achieve a high spectral efficiency
and perform simple channel equalization.
For these reasons, optical OFDM has been identified as an attractive solution for optical
long-haul transmission, as it offers a reduced signal bandwidth and enables simple digital
equalization of chromatic dispersion.
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Typical Results
The simulation setup is displayed in
.
It is similar to the one reported in [1]: single-side band optical OFDM is used to transmit a 10-Gb/s
signal over 1000 km of SSMF without the need for inline dispersion compensation. The OFDM signal
consists of 64 subcarriers, each being encoded with Quadrature Amplitude Modulation (QAM). Optical
to electrical conversion is realized with a single photodiode. The detected signal is then passed
to an electrical OFDM receiver that performs downconversion, electrical filtering, analog to digital
conversion (ADC) and demodulation (cyclic-prefix removal and inverse FFT). The phase of each
subcarrier can be equalized separately to compensate for chromatic dispersion. The received
constellation diagram with and without equalization are displayed in
(ASE noise from inline EDFAs is switched off).
One drawback of this technique is its high OSNR requirement. Indeed, most of the power is located
in the optical carrier (necessary for direct detection). This limits the achievable signal-to-noise
ratio of the individual subcarriers. The impact of optical noise on system performance is
illustrated in
,
where the spectrum and constellation diagram of the received signal are displayed for the case that
ASE noise from inline EDFAs is switched on.
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Further Information
Keywords: Orthogonal Frequency Division Multiplexing (OFDM), Chromatic Dispersion, Digital Equalization
Similar demonstrations are available in VPItransmissionMaker Optical Systems and on the VPIphotonics Forum.
[1] A. J. Lowery, J. Armstrong, OPTICS EXPRESS, Vol. 14, No. 6 (2006).
