Abstract
OFDM system has recently replaced the traditional OOK (on-of keying) modulation. Due to orthogonal is characteristic of OFDM, so that each carrier can overlap with the other, therefore, we can enabling higher spectral efficiency. And the fundamentals of optical OFDM are using coherent detection and direct detection, respectively. Compared with the coherent detection, the lower-priced and less-complex direct detection would be more suitable to base on experimental architecture. However, Due to square-law nature of the photodiode, the Signal-Signal Beating Interference (SSBI) would be mix with our detected signal and thus severely influence the system performance. To avoiding this problem is inserted a frequency gap with the same width as the detected signal. Nevertheless, the drawback in a direct detection OFDM system is the low spectral efficiency. Hence, there have been some proposals to the gap issue if the gap width could be reduced or even be discarded. So far, it can be mainly two proposals at this subject：(1) Carrier-boosting, in which the optical carrier is filtered out and amplified with an EDFA. (2) Signal processing, in which estimates and removes the SSBI by using a digital iterative equalizer. Therefore, our method is also using optical component to solved this gap issue just like Carrier-boosting, but compared with Carrier-boosting, Beat Interference Cancellation (BIC) system can also reduce the frequency gap with least complexity receive architecture. In this paper, we discuss BIC system with different parameter, ex. Filter order and frequency gap. Furthermore, acquired the better performance we analysis between carrier power and signal power.