Simulation of mm-wave signal generation using phase modulation in ROF system

Abstract

The generation of optical millimeter waves via the improved phase modulator in a RoF system and the transmission character of the signal are theoretically investigated. A new phase modulating scheme is proposed, in which the sidebands are separated by wave length demultiplexer and one of them doesn't feed digital signals, thereby the phase wake-off is restrained.The broadband wireless telecommunication is becoming the main research aspect of the future telecommunication. ROF (radio over fiber) telecommunication technique combines optical fiber with the high frequency radio, thus the broadband wireless communications in 40-60 GHz access can be realized. The generation of millimeter-wave is the key technique of ROF system. Recently, lots of researches have been done in this aspect including direct modulation [1] of the laser, external modulation [2] and optical heterodyne modulation [3][4][5] . Phase modulation [6] is one kind of external modulation techniques. In such a system, there will be no need of bias voltage, complicated control circuits and the float current brought by the use of bias voltage, therefore, the phase modulation system can provide better robustness and simplified structure than traditional external intensity modulation method. In this paper a new phase modulation scheme is proposed based on the theoretical analysis and simulation.The principle of phase modulation is shown in Fig.1.We use the sinusoidal signal without attenuation to describe the signal source and optical light source applied to As shown in formula (1), the power of optical carrier will spread to first-order, second-order, third-order and other higher-order optical sidebands. The amplitude of each sideband is controlled by the parameter of bessel function. After the even harmonics conversion, the output of the phase modulator is described by formula (2),where C is a constant related to A c and the responsivity of the photodetector. After the subcarrier suppression by the FBG filter, the output signal of the filter can be described by formula (3),(1) the modulator. The output wavefront of the phase modulator can be described by formula (1) n m c n c out n t n J A t E 2 ) ( cos ) ( ) ( ) cos( ) ( 0 t J c .(3)

用于1.55 μm波段超连续谱产生的高非线性色散平坦光子晶体光纤

“…6(b), the amplitude noise (%) of SC generated in PCF is calculated to be within 2%, which means the amplitude noise is perfectly controlled during the propagation. For the four different input power values mentioned above, the order of magnitude is comparable to the measured value of PCF in the experiment [34] .…”