| In recent years, researchers have been paid attention to the widely application of comb-like spectrum. Because some spectrum can not meet the requirements of time and frequency domain characteristics, such as time domain regularity, signal-to-noise ratio and stability of frequency and temporal. So not all of the spectrum can be effectively applied in some fields. Only a little energy that corresponds to red-shift soliton can be effectively utilized, when spectrum is generated by short pump. The stability of time-frequency domain is reduced due to the effect of noise, when spectrum is generated by long pulse pump. High power density spectrum is generated by continuous-wave radiation pump, however, the stability of time-frequency domain is more susceptible to noise. Not only higher power density spectrum is obtained, but also disadvantage of the above three pumps is overcome by continuous-wave after amplitude modulation. In this paper, time and frequency domain characteristics of comb-like spectrum generated by amplitude-modulated continuous-wave radiation, is studied in theory and main results are obtained as follow.Firstly, generation of comb-like by amplitude-modulated continuous-wave radiation and the effect of peak power, pulse width and pumping efficiency by fiber coefficients and modulation parameters are numerical simulation studied with noise-free. The results as following:(1) Short pulse sequences are generated by modulated CW, whose energy is provided by comb-like frequency and power density spectrum of their pedestal is lower. Constant phase across the pulses, which means Fourier-transform-limited pulse with chirp-free.(2) The variation of pulse peak power with pulse width is opposite when fiber parameters and modulation parameters are varied. We also introduce normalized modulation frequency that is the ratio of modulation frequency and the cut-off frequency of modulation instability as pump efficiency criterion, the variation of pump efficiency with the normalized modulation frequency is consistent. The maximum pump efficiency can reach85%.Secondly, the effect of time-frequency stability of comb-like spectrum and output SNR by modulation parameters is numerically studied with noise. The results as following:(1) Energy is effectively transferred to modulation frequency by modulated CW. So noise amplification is suppressed and the stability of time-frequency domain is improved.(2) Time-domain structure is very disordered and the spectrum cannot be effectively utilized when output SNR is down to10dB, therefore the region of modulation parameters that meets the requirements of output SNR is obtained. |
PDF Full Text Request