As the demand for high transmission data rates rise, there becomes an increasing research interest in orthogonal frequency division multiplexing (OFDM) modulation formats. OFDM is a multi-carrier transmission technique which divides the available spectrum into several carriers, each one modulated by a lower data rate stream. Compared to conventional serial modulation schemes, optical OFDM [1] has the following advantages:
It reduces the symbol rate which makes optical OFDM robust against chromatic dispersion (CD) and polarization mode dispersion (PMD).
It transfers the complexity of transmitters and receivers from analog to digital domain. The implementations of inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) in the transceiver make electronic dispersion compensation (EDC) possible.
The subcarrier frequencies are selected so that signals are mathematically orthogonal over one OFDM symbol period. The spectra of individual subcarriers are partially overlapped, resulting in high optical spectral efficiency.
I am attaching a link. This will also be of some good help.
http://www.ict-accordance.eu/knowledge_base/Optical_OFDM_Design_-_Direct_and_Coherent_Detection
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