Frequency Comb Generation Based on Brillouin Random Lasing Oscillation and Four-Wave Mixing Assisted with Nonlinear Optical Loop Mirror
, Zengguang Qin 2,3, Zhaojun Liu 2,3 and Yanping Xu 1,2,*
Round 1
Reviewer 1 Report
1. Please explain why HNLF is selected as the gain medium for Brillouin scattering? In this experiment, in addition to using HNLF, what other methods can achieve more order Stokes light excitation?
2. In this experiment, the splitting ratio of OC2 is 50:50. Does this affect the order and flatness of output Stokes light? Because for ordinary single-ring fiber lasers, the output splitting ratio is very important.
3. The transmission spectrum of NOLM formed by Sagnac ring shows periodicity with the change of wavelength, and the waveform is similar to that in Figure 2 (a), which shows that Sagnac ring is sensitive to wavelength. However, the curve of transmittance changing with wavelength is not given in this paper, which is necessary for optical frequency comb and supercontinuum spectrum to have a wide wavelength range output. The periodic transmissivity of Sagnac ring may lead to the difference of transmissivity between two Stokes light with several orders of interval, which will eventually reduce the number of output optical frequency comb teeth and affect the flatness of optical frequency comb. Please describe in detail how you designed NOLM? In addition, please give the reason why the OC3 spectral ratio is 7:3 ?
4. Brillouin scattering effect has natural linewidth compression effect. Please explain why the linewidth of high-order Stokes light such as 5, 6 and 7 in Figure 6 is wider than that of low-order Stokes light ?
5. 5. How to further obtain Stokes light with more wavelengths or narrower linewidth in this experimental configuration?
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The author experimentally demonstrate a frequency comb generator based on the dual-cavity Brillouin random oscillator including a main-cavity and a sub-cavity. The four-wave mixing (FWM) effect in the HNLF is effectively excited under phase-matching conditions, which not only increases the number of stokes lines but also boosts the power of the anti-Stokes lines to make them resonate in the main-cavity.
The paper is well organized and the topic is interesting. The work can be considered to be published in case several questions are clarified.
1. In Figure 1, could the author provide the detailed propagation direction of the pump light, Stokes and anti-Stokes signals in the experimental setup scheme?
2. In Figure 5, could the author give physical explanation of the difference between forward and backward propagating frequency combs?
3. In Figures 12 and 13, are there any rogue waves generation? Could the author provide physical mechanism of the distribution deviation from Gaussian to L-shaped distribution when the Stokes and anti-Stokes order increases?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
In this paper, the authors propose and experimentally investigate a dual-cavity FCG based on Brillouin random lasing oscillation. Under the phase-matching condition, the four-wave mixing effect in the highly nonlinear fiber is effectively excited, which not only increases the number of Stokes lines but also boosts the power of the anti-Stokes lines to make them resonate in the main cavity. In addition, the authors applied a nonlinear optical loop mirror (NOLM) to achieve smaller power deviations.
Some parts need to be revised:
1. Please add notes to Figure 3 to help readers distinguish which part is the Stokes line/anti-Stokes line.
2. Please check that the numbers on line 298 correspond to the numbers shown in Figure 7.
3. There are two full stops in line 385. Please revise it and check the full text.
4. Please check the paragraph formatting at the bottom of Figure 11.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have well responded to my coments and clearly improved the manuscript.
