Fundamentals of Plastic Optical Fibers

3Transmission Capacity

The bandwidth of a fiber determines the maximum transmission data rate or maximum transmission distance. Most common POF (plastic optical fiber) transmission systems adopt on–off keying by direct modulation of the optical source (laser or light-emitting diode). If an input pulse waveform can be detected without distortion at the other end of the fiber, the maximum link length is limited by the fiber attenuation. However, in addition to the optical power attenuation, the output pulse is generally broader in time than the input pulse. This pulse broadening limits the transmission capacity, namely, the bandwidth of the fiber. The bandwidth is determined by the impulse response as follows [1]: Optical fibers are usually considered quasi-linear systems; thus, the output pulse is described by

3.1

The output pulse p_out(t) from the fiber can be calculated in the time domain through the convolution (denoted by *) of the input pulse p_in(t) and the impulse response function h(t) of the fiber. Fourier transformation of Equation 3.1 provides a simple expression as the product in the frequency domain:

3.2

where H(f) is the power transfer function of the fiber at the baseband frequency f. The power transfer function defines the bandwidth of the optical fiber as the lowest ...