An optical scheme to improve the quality of an RF signal is proposed. The 6 dB linewidth is reduced to sub hertz and the
low frequency noise below 1 KHz is reduced about 10 dB. The scheme utilizes a Brillouin-semiconductor optical
amplifier (SOA) ring laser fitted with an RF intensity modulator and an APD detector. The experimental results show
cavity modes with FSR of 30.57 KHz due to Brillouin fiber length of 6.6 km and 6 dB bandwidth of 780 mHz typical of
Brillouin lasers. The gain of the SOA balances out most of the losses in the ring mainly that due to the RF modulator.
The modulated optical signal beats at the APD. The optical loop acts as a cavity filter to the RF signal. A jitter in the
cavity resonances due to temperature variations is completely eliminated from the output beat signal. There is a 10 dB
increase in the phase noise at the FSR frequency and its harmonics. The setup is tested with signals generated by
different sources and to frequencies up to 10 GHz, the limit of the APD. Sources with RF linewidth less than the optical
FSR produces one output mode with sub-hertz line width. For larger line width signals more than one RF frequency is
produced, separated by the FSR, each showing the Brillouin linewidth.
Fiber-Optic code division multiple access communication systems (FO-CDMA) have been given an intensifying interest in the last decade. This is due to several advantages may be offered by this technology, where it offers a promising solution for efficient truly asynchronous multiple access network as well as it has the ability to support variable bit rate and bursty traffic. FO-CDMA system permits an extra high optical signal processing speed compared to electronic signal processing, and there is no need to use wavelength sensitive components which are required in WDMA networks. FO-CDMA may be performed in time domain "t" or in wavelength domain "λ"(spectral amplitude encoding), this strategy is called one dimensional (1-D)
optical coding. One of the most serious problems for CDMA is the multiple access interference (MAI), where it produces an asymptotic floor to the error probability, and limits the number of simultaneous users. Developing of FO-CDMA system to increase the number of users as well as to improve the system performance may be done through developing the system structure, choice of the appropriate detection scheme and the proper signature codes, developing the encoders and decoders hardware, use of adequate error correcting codes, incorporating optical amplifiers, use of multidimensional FO-CDMA
techniques, and use of MAI cancellation and dispersion compensation techniques. This paper highlights the main directions of system development. The main technological challenges that have to be overcome before a wide spread of this technology have been also investigated. Finally, potential applications of this technology have been discussed.