基于谐波拟合产生周期性三角形光脉冲串的实验研究

实验研究了一种基于谐波拟合产生周期性三角形光脉冲串的方法,方案首先利用马赫曾德调制器的载波抑制调制,获得具有周期性起伏的连续光强度信号,然后利用光纤色散所致的射频功率衰落效应,对光强度表达式中四次谐波分量进行抑制,调节调制深度后,光强度表达式将向理想三角形傅里叶展开式的前三项进行逼近,最后以谐波拟合的方式获得重复频率为射频调制频率二倍的周期性三角形光脉冲串.结合实验,在9.862 GHz和7.678 GHz射频调制频率下,获得了脉冲重复频率19.724 Gb/s(脉冲全宽约50.7 ps)和15.356Gb/s(脉冲全宽约65.1 ps)的稳定三角形光脉冲串输出,改变色散量并反向调节调制频率,可进一步改变脉冲的重复频率,所获得的实验结果与理论预期基本符合.

Experimental demonstration on triangular-shaped pulse train generation based on harmonic fitting

We demonstrate an approach for triangular-shaped pulse train generation experimentally based on harmonic fitting. The operation principle is that a Mach-Zehnder modulator is firstly employed to suppress modulation of the optical carrier. Thus a periodically variable lightwave can be obtained at the output. Then the signal is coupled into a section of dispersive fiber. Due to the dispersion-induced power fading, the undesired 4^th order harmonics in the optical intensity can be fully removed. By adjusting modulation index to an optimum value (m=2.305), the generated harmonics of the optical intensity can be made corresponding to the Fourier components of typical periodic triangular pulses. Finally, the triangular-shaped pulse train at a repetition rate two times of the driving frequency can be obtained. In the experiments, 19.724 Gb/s and 15.356 Gb/s triangular-shaped pulse trains are generated by using 9.862 GHz and 7.678 GHz driving signals respectively. Besides, the repetition rate can be switched to another value by using a different fiber dispersion (β ₂L). It is found that the experimental data agree well with theoretical results.
Keywords： optical communications microwave photonic crystal triangular-shaped pulse train