An All-Optical Microwave Frequency Divider with Tunable Division Factors Based on DP-DPMZM

Round 1

Reviewer 1 Report

 

Based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The scheme has a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers. Some experimental results are presented. A proof-of-concept experiment was also analyzed. 

 

1、The proposed microwave signal frequency down-converter was based on P2 state oscillation. In Fig. 3, a peak near 1545 nm can be seen after P2 state oscillation. Please state the reason for the peak and whether it will impact the performance of the scheme?

 

2、In the optical spectrum, it is difficult to distinguish the RF1 and RF2 signals. The authors should explain it. What is the optical signal analyzer (OSA) resolution? And please give the types of the used devices.

 

3、It is recommended to give specific values in conclusions.

 

4、The manuscript should be revised for more readbility.

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The manuscript has been revised according to the reviewers’ comments and suggestions. The changes and explanations are represented as follows:

Reviewer 1

Based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The scheme has a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers. Some experimental results are presented. A proof-of-concept experiment was also analyzed.

1、The proposed microwave signal frequency down-converter was based on P2 state oscillation. In Fig. 3, a peak near 1545 nm can be seen after P2 state oscillation. Please state the reason for the peak and whether it will impact the performance of the scheme?

Response: Thanks for the reviewer’s comment. In the P2 state of the DFB laser, there will be multiple frequency components, which are caused by the resonator in the laser and will not affect the system performance.

Please check the third paragraph in page 4 as follows:

“In the P2 state of the DFB laser, there will be multiple frequency components, which are caused by the resonator in the laser and will not affect the system performance.”

 

2、In the optical spectrum, it is difficult to distinguish the RF1 and RF2 signals. The authors should explain it. What is the optical signal analyzer (OSA) resolution? And please give the types of the used devices.

Response: Thanks for the reviewer’s comment. In the P2 state of the DFB laser, there will be multiple frequency components, which are caused by the resonator in the laser and will not affect the system performance. The resolution of the OSA (Yokogawa AQ6730D) is 0.02 nm, which is difficult to distinguish the RF and LO signals in optical spectra.

Please check the third paragraph in page 4 as follows:

“In the P2 state of the DFB laser, there will be multiple frequency components, which are caused by the resonator in the laser and will not affect the system performance. The resolution of the OSA is 0.02 nm, which is difficult to distinguish the RF and LO signals in optical spectra.”

 

3、It is recommended to give specific values in conclusions.

Response: Thanks for the reviewer’s comment. We have added the specific values in conclusions. The power of the 8 GHz frequency component is -38.2 dBm, with the RF signal is 0 dBm, the system has a conversion gain of -38.2 dBm.

Please check the conclusion in page 7 as follows:

“The power of the 8 GHz frequency component is -38.2 dBm, with the RF signal is 0 dBm, the system has a conversion gain of -38.2 dBm.”

 

4、The manuscript should be revised for more readbility.

Response: Thanks for the reviewer’s comment. We have revised the manuscript and changed some clerical errors.

 

Author Response File: Author Response.docx

Reviewer 2 Report

See attachment.

Comments for author File: Comments.doc

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The manuscript has been revised according to the reviewers’ comments and suggestions. The changes and explanations are represented as follows:

Reviewer 2

In this article, based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-15 optical frequency divider is proposed and experimentally demonstrated. However, I could not find anything novel. Exactly saying, there are following problems.

1. After both equations (1) and (2) are introduced, the references should be cited. Then, the creations of Equations (3) and (4) should be supported by a couple of middle stages of derivations.

Response: Thanks for the reviewer’s comment. Both equations (1) and (2) are derived from the principle, and the specific expressions are as follows.

       (1)

      (2)

                    (3)

                     (4)

The middle stage is obvious. For the compactness of the article, the expression is listed directly. Please check the page 3 and 4 as follows:

“       (1)

      (2)

                    (3)

                     (4)

”

2. Analyses and discussions for the experimental results are not enough shown in Figs. 3-5, only analysis for the results shown in Fig. 6 is enough. For instance,

(1) in Fig. 3, spectrum indicate what special the optical output is with the driving microwave frequency, the peak value of the optical output appears at 1545.35nm, is that the designed central wavelength of this device is? what does the vibration of line indicate?

(2) In Fig. 4, the EPA of device, the context explains that a peak appears at 8GHz frequency indicates the highest conversion efficiency. However, it should also analyze how far the frequency of 8GHz from the designed central wavelength. In addition, the full width at half maximum (FWHM) depends on what elements of device system. In Fig. 5, the EPA covers from 8 GHz to 12 GHz present five peaks, the authors only explain the functionality of frequency divider that is not enough for readers to understand the core idea of the article.

Response: Thanks for the reviewer’s comment. The wavelength of the free running DFB laser is 1545.35 nm. The frequency components in Fig. 3 are the original ML carrier and sidebands and P2 station. The P2 station frequency components are in the middle of the RF modulation sidebands and have different amplitudes. The frequency components close to the DFB laser frequency have higher amplitudes than those away from the DFB laser frequency.

Please check the third paragraph in page 4 as follows:

“The wavelength of the free running DFB laser is 1545.35 nm. The frequency components in Fig. 3 are the original ML carrier and sidebands and P2 station. The P2 station frequency components are in the middle of the RF modulation sidebands and have different amplitudes. The frequency components close to the DFB laser frequency have higher amplitudes than those away from the DFB laser frequency.”

The wavelength of the free running DFB laser is 1545.35 nm. The RF₁ and RF₂ signals are 5 GHz and 11 GHz, respectively. The beams out of the SL are beating by the photodetector (PD). The Δf/2 is 3 GHz, then the 8 GHz frequency component is obtained. Since the RF signals peak frequency emitted by the two electrical signal generators are different between 5 GHz and 11 GHz, which causes the target signal peak frequency is not 8 GHz.

Please check the fifth paragraph in page 5 as follows:

“Since the RF signals peak frequency emitted by the two electrical signal generators are different between 5 GHz and 11 GHz, which causes the target signal peak frequency is not 8 GHz.”

The full width at half maximum (FWHM) depends on elements of device system, such as the RF signals generated from the electrical signal generators.

Please check the fifth paragraph in page 5 as follows:

“The full width at half maximum (FWHM) depends on elements of device system, such as the RF signals generated from the electrical signal generators.”

First, we adjust the RF2 signal to 11 GHz. By changing the RF1 signal to 5 GHz and 7 GHz respectively, we can generate 8 GHz and 9 GHz f_target signals. Then the RF1 signals are set to 5 GHz, 6 GHz and 7 GHz respectively, and the corresponding RF2 signals are set to 15 GHz, 14 GHz and 13 GHz respectively, and the f_target values are all 10 GHz. At last, we adjusted RF1 signal to 7 GHz and RF2 signal to 15 GHz,17 GHz, so that f_target can generate 11 GHz and 12GHz signals. The frequency component at 8 GHz to 12 GHz can be seen, this verifies the adjustable division factor frequency divider operation.

Please check the second paragraph in page 5 as follows:

“First, we adjust the RF2 signal to 11 GHz. By changing the RF1 signal to 5 GHz and 7 GHz respectively, we can generate 8 GHz and 9 GHz f_target signals. Then the RF1 signals are set to 5 GHz, 6 GHz and 7 GHz respectively, and the corresponding RF2 signals are set to 15 GHz, 14 GHz and 13 GHz respectively, and the f_target values are all 10 GHz. At last, we adjusted RF1 signal to 7 GHz and RF2 signal to 15 GHz,17 GHz, so that f_target can generate 11 GHz and 12GHz signals. The frequency component at 8 GHz to 12 GHz can be seen, this verifies the adjustable division factor frequency divider operation.”

 

3. It is not easy to find the impressive innovative points across the article. For example, all the theoretical models were ever published previously, and the experimental method/scheme was also reported before.

Response: Thanks for the reviewer’s comment. Based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved.

As you said, the frequency divider is interesting and useful for application of optical communication, radio astronomy, clock comparison and signal processing. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers. Experiment results also demonstrate that the frequency division factors can be adjusted.

Please check the abstract in page 1 as follows:

“The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted.”

Author Response File: Author Response.docx

Reviewer 3 Report

The authors report on an optical frequency divider with a DP-DPMZM and a DFB laser. The DFB laser is operated under the injection of an optical two-tone generated by using the DP-DPMZM with two RF signals (RF1 and RF2). Oscillation of the DFB laser with a frequency of (RF1+RF2)/2 is converted into an electrical signal which corresponds to operation of a frequency divider. The authors claim that use of the DP-DPMZM for obtaining a tunable frequency division factor has novelty. The paper should be revised so as to clarify importance of the authors’ work.

 

1. The frequency-divided signal is expected to has phase correlation, otherwise use of another electrical signal generator is much simpler. Please clarify this point.

 

2. The importance of the DP-DPMZM is unclear. An optical two-tone can be generated by using an MZM. The proposed configuration in Fig. 1 seems to be useful to control the optical injection condition for the DFB laser. However, the paper does not include discussion about the optical injection condition and its effect on the optical frequency divider.

 

3. In Table 1, how many significant digits are there? The peak frequency is not 8.0 GHz in Fig. 4. Is there conversion accuracy?

 

4. Please add discussion about the difference among three states in Fig. 6.

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The manuscript has been revised according to the reviewers’ comments and suggestions. The changes and explanations are represented as follows:

Reviewer 3

The authors report on an optical frequency divider with a DP-DPMZM and a DFB laser. The DFB laser is operated under the injection of an optical two-tone generated by using the DP-DPMZM with two RF signals (RF1 and RF2). Oscillation of the DFB laser with a frequency of (RF1+RF2)/2 is converted into an electrical signal which corresponds to operation of a frequency divider. The authors claim that use of the DP-DPMZM for obtaining a tunable frequency division factor has novelty. The paper should be revised so as to clarify importance of the authors’ work.

1. The frequency-divided signal is expected to has phase correlation, otherwise use of another electrical signal generator is much simpler. Please clarify this point.

Response: Thanks for the reviewer’s comment. The frequency-divided signal is a device that is a subharmonic of the input signal, which is widely used in microwave photonic radar and optical communication. In practical applications, we need to process the received high-frequency signals, so we cannot directly use electrical signal generator to generate signals.

Please check the first paragraph in page 1 as follows:

“In practical applications, we need to process the received high-frequency signals, so we cannot directly use electrical signal generator to generate signals.”

2. The importance of the DP-DPMZM is unclear. An optical two-tone can be generated by using an MZM. The proposed configuration in Fig. 1 seems to be useful to control the optical injection condition for the DFB laser. However, the paper does not include discussion about the optical injection condition and its effect on the optical frequency divider.

Response: Thanks for the reviewer’s comment. The MZM can generate optical two-tone signal, which is fed into DFB laser. However, these signals cannot realize tunable division factors in frequency divider. The DP-DPMZM can adjust the frequency division factor by changing RF1 and RF2 signals respectively to realize carrier-suppressed single sideband.

Please check the third paragraph in page 2 as follows:

“The DP-DPMZM can adjust the frequency division factor by changing RF1 and RF2 signals respectively to realize carrier-suppressed single sideband.”

3. In Table 1, how many significant digits are there? The peak frequency is not 8.0 GHz in Fig. 4. Is there conversion accuracy?

Response: Thanks for the reviewer’s comment. Different values in Table 1 indicate that the microwave photonic frequency divider has tunable division factors, and can realize the same target signal under different RF input signals. Since the RF signals peak frequency emitted by the two electrical signal generators are different between 5 GHz and 11 GHz, which causes the target signal peak frequency is not 8 GHz.

Please check the first paragraph in page 5 as follows:

“Since the RF signals peak frequency emitted by the two electrical signal generators are different between 5 GHz and 11 GHz, which causes the target signal peak frequency is not 8 GHz.”

4. Please add discussion about the difference among three states in Fig. 6.

Response: Thanks for the reviewer’s comment. As shown in Fig. 6, with the RF1 and RF2 signals change, we keep the f_target as 10 GHz. The RF1 signal is 5 GHz, 6 GHz, 7 GHz, respectively. The RF2 signal is 15 GHz, 14 GHz, 13 GHz, respectively. The frequency divider corresponding to the change of different RF1 and RF2 signals has different frequency division factors, and the final target frequency signal is 10 GHz. The corresponding power of the state noise and frequency peak value under different frequency division factors is different.

Please check the abstract in page 1 as follows:

“As shown in Fig. 6, with the RF₁ and RF₂ signals change, we keep the f_target as 10 GHz. The RF1 signal is 5 GHz, 6 GHz, 7 GHz, respectively. The RF₂ signal is 15 GHz, 14 GHz, 13 GHz, respectively. The frequency divider corresponding to the change of different RF₁ and RF₂ signals has different frequency division factors, and the final target frequency signal is 10 GHz. The corresponding power of the state noise and frequency peak value under different frequency division factors is different.”

Author Response File: Author Response.docx

Reviewer 4 Report

This paper proposed a tunable division factors all-optical microwave divider. Based on the dual-beam injection effect, the DFB laser is oscillating in P2 177 state, With the help of DP-DPMZM, two CS-SSB sidebands are generated to inject in the 178 DFB by driving two RF signals in two orthogonally DPMZM branches. Then the optical 179 frequency component is produced. It seems to be interesting and useful for application of optical communication, while the scheme and principle seems to lack novelty compared to the previous study. I do not recommend it published in Photonics and I think this paper is suitable for published in some engineering journal.

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The manuscript has been revised according to the reviewers’ comments and suggestions. The changes and explanations are represented as follows:

Reviewer 4

This paper proposed a tunable division factors all-optical microwave divider. Based on the dual-beam injection effect, the DFB laser is oscillating in P2 177 state, With the help of DP-DPMZM, two CS-SSB sidebands are generated to inject in the 178 DFB by driving two RF signals in two orthogonally DPMZM branches. Then the optical 179 frequency component is produced. It seems to be interesting and useful for application of optical communication, while the scheme and principle seems to lack novelty compared to the previous study. I do not recommend it published in Photonics and I think this paper is suitable for published in some engineering journal.

Response: Thanks for the reviewer’s comment. Based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved.

As you said, the frequency divider is interesting and useful for application of optical communication, radio astronomy, clock comparison and signal processing. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers. Experiment results also demonstrate that the frequency division factors can be adjusted.

Please check the abstract in page 1 as follows:

“The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted.”

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Please see the reviewer report in attachment.

 

Comments for author File: Comments.pdf

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The manuscript has been revised according to the reviewers’ comments and suggestions. The changes and explanations are represented as follows:

Reviewer 2

In this article, the authors want to use the In- and Quadrature-Phase (I-Q) modulation format of two MZM structures with dual-polarization dual-parallel optical carriers to divide the driving microwave frequency. Further, by applying the special optical circular scheme to improve the performance of the I-Q modulation system. Albeit several schemes of the dual-polarization dual-parallel MZM (DP-DPMZM) optical I-Q modulation have been investigated and even adopted in the modern telecommunications systems, the innovation of the system in this article lies in simple and practical regime of sideband suppression. In this innovative system, with a circular, only one slave laser (SL) signal is employed to improve the tunable frequency division effect of the DP-DPMZM to the input master laser (ML) signal. So, this work is of significance in modern microwave photonics and its applications in modern optical communications. In this article, however, there are drawbacks in the following aspects.

1. In the section of INTRODUCTION, the basic reasons supporting this work are not enough and some reason-resulting relations are not very clear. For instance,

(1) the starting two sentences: “Frequency dividers are of great importance in radio astronomy, clock comparison 28 and signal processing [1, 2]. It can be widely used in generating millimeter waves or frequency synchronization.” These two sentences can not clearly express a causality. Probably, behind [1, 2], it would be better that the dot is changed to be comma, and the word ‘It’ is changed to be ‘because’ or ‘as’.

Response: Thanks for the reviewer’s comment. We have revised the reason-resulting relations between the sentences in the revised manuscript.

Please check the INTRODUCTION in page 1 as follows:

“Frequency dividers are of great importance in radio astronomy, clock comparison and signal processing [1, 2], because it can be widely used in generating millimeter waves or frequency synchronization.”

(2) Similarly, the revised sentence, “In practical applications, we need to process the received high-30 frequency signals, so we cannot directly use electrical signal generator to generate signals.”, seams lack the causality, too.

Response: Thanks for the reviewer’s comment. We have revised the reason-resulting relations and grammar between the sentences in the revised manuscript.

Please check the INTRODUCTION in page 1 as follows:

“In practical applications, instead of directly using electrical signal generator to generate low-frequency signals, we need to process the received high-frequency signals to obtain low-frequency signals.”

(3) Followed sentence “Traditionally, frequency dividers include digital or analog types.”, the necessary references should be cited.

Response: Thanks for the reviewer’s comment. We have added references to this sentence in the revised manuscript.

Please check the INTRODUCTION in page 1 as follows:

“Traditionally, frequency dividers include digital or analog types [3].”

Please check the REFERENCES in page 8 as follows:

“3.  Bomford, M. Selection of frequency dividers for microwave PLL applications, Microwave Journal, 1990, 33, 159-165.”

 

2. In the section of INTRODUCTION, the sentence “Frequency dividers are of great importance in radio astronomy, clock comparison 28 and signal processing” is very broad and impacting for a reader to under this work, so authors should be able to illustrate some examples to support it. However, in the context, authors direct turn to the description of another topic.

Response: Thanks for the reviewer’s comment. In order to reflect the application and importance of microwave photonics frequency dividers, we have added specific examples of its application. For example, in radar systems, it is necessary to mix the received high-frequency echo signal with the local oscillator signal to realize frequency down conversion at the receiver, so that low speed electrical devices can be used for signal post-processing.

Please check the INTRODUCTION in page 1 as follows:

“In radar systems, it is necessary to mix the received high-frequency echo signal with the local oscillator (LO) signal to realize frequency down conversion, so that low speed elec-trical devices can be used for signal post-processing.”

 

3. In the first paragraph of INTRODUCTION section, authors of this article only mentioned some typical researchers investigated/reported what types of traditional electrical microwave frequency dividers, but on the one hand the illustrations, I believe, are not enough, on the other hand authors have never mentioned what are the technical problems in performance and what common faced problems in applications. So, in the followed paragraph, it seams make readers feel too abrupt changing topic for the authors to discuss the advantages of all-optical frequency dividers.

Similar shortages can also be found across the entire section of INTRODUCTION.

Response: Thanks for the reviewer’s comment. We summarized the technical problems in performance and common problems of the frequency divider with traditional structure, in contrast to several typical structures of the frequency dividers, for example, dynamic logic frequency divider, current logic frequency divider, and Miller frequency divider, the electrical injection locking frequency divider, they have high operating band and low power consumption, and serves as the first stage of high-frequency dividing. However, all these structures have limited bandwidth because of the bandwidth restrictions of electric filters. In previous designs, the optimization between the high operating band and wide locking range exists conflicts.

Please check the INTRODUCTION in page 1 as follows:

“In contrast to several typical structures of the frequency dividers, they have high operating band and low power consumption, and serves as the first stage of high-frequency dividing. However, all these structures have limited bandwidth because of the bandwidth restrictions of electric filters. In previous designs, the optimization between the high operating band and wide locking range exists conflicts.”

 

4. In principle of the optical modulation system, the frequency division process of the I-Q modulation format of the Mach-Zehnder modulator (MZM) construction, so the questions for defining the interference output signals of an I-Q unit at the two ports and further based on the two parallel optical carriers with two cross polarizations, the final frequency division process is implemented. But, for some different constructions of interference between two I-Q systems, the optical signal-to-noise ratio (OSNR) effects are generally different, while it is one of the important performance specifications. For this reason, the researchers generally employed different approaches to improve the OSNR. In the optical modulation scheme the operations of the PSC, the EDFA, and the optical circular can cause the OSNR phenomena, thus by comparing the theoretical and experimental results, expect authors to discuss some phenomena of OSNR results.

Response: Thanks for the reviewer’s comment. The optical signal-to-noise ratio (OSNR) is related to the P2 state of optical injection and the input optical power. The optical frequency components contain ML carrier and sidebands. By adjusting them in the middle of the RF modulation sidebands, they have different amplitudes. The optical signal near the SL frequency has higher optical power and better OSNR. The P2 station of the laser will also affect the OSNR, this is reflected in the influence of laser cavity length on P2 resonance.

Please check the fourth paragraph in page 4 as follows:

“The optical signal-to-noise ratio (OSNR) is related to the P2 state of optical injection and the input optical power. The optical frequency components contain ML carrier and sidebands. By adjusting them in the middle of the RF modulation sidebands, they have different amplitudes. The optical signal near the SL frequency has higher optical power and better OSNR. The P2 station of the laser will also affect the OSNR, this is reflected in the influence of laser cavity length on P2 resonance.”

 

5. Once an equation (or theoretical model) of the system principle is introduced, the original powerful source should be cited. So, prior o Eq. (1), a reference must be given.

Response: Thanks for the reviewer’s suggestion. We have added references to the Eq. (1) in the revised manuscript.

Please check the first and second paragraphs in page 3 as follows:

“The optical field at the output of x-DPMZM is given by [11]

”

“Similarly, sub-MZM3 and sub-MZM4 are driven by the RF2 signal in the CS-SSB sta-tion, the optical field at the output of y- DPMZM is given by [11]

”

Please check the REFERENCES in page 8 as follows:

“11. Zhang, S. J., Wang, H., Zou, X. H., Zhang, Y. L., Lu, R. G., and Liu, Y. Calibration-free electrical spectrum analysis for microwave characterization of optical phase modulators using frequency-shifted heterodyning, IEEE Photon. J., 2014, 6, Art. no. 5501008.”

 

6. Some English expressions need to be improved. For example, in the 2nd paragraph of page 2, in the sentence: “it can be designed with high operating frequency due to it does not require any electrical amplifiers”, “due to” is not very appropriate, it will become better to change the “due to” to be “since” or “because”.

Response: Thanks for the reviewer’s suggestion. We have revised the English expressions in the revised manuscript.

Please check the second paragraph in page 2 as follows:

“Theoretically, it can be designed with high-operating frequency since it does not require any electrical amplifiers.”

 

7. In page 3, on line 85 the sentence, “βRF2=πVRF2/Vπ is the modulation index of the sub- 85 MZMs, ϕy is the main DC bias of the y-DPMZM” in which the two definitions are not completely correct, so please re-write this sentence.

Response: Thanks for the reviewer’s comment. We have revised the wrong expression in the article.

Please check the first paragraph in page 3 as follows:

“β_RF1=πV_RF1/V_π is the modulation index corresponding to RF2 loaded on the sub-MZMs,”

“ϕ_x is the phase shift introduced by main DC bias of the the x-DPMZM.”

Please check the second paragraph in page 3 as follows:

“β_RF2=πV_RF2/V_π is the modulation index corresponding to RF2 loaded on the sub-MZMs, ϕ_y is the phase shift introduced by main DC bias of the y-DPMZM.”

 

Reviewer 3 Report

The authors revised the manuscript.

Author Response

We are grateful to the reviewers for their helpful comments and suggestions.

Reviewer 4 Report

The author argue that the innovation of the scheme lies in having a simple structure and only requires optical devices. While, it is not new for me. Actually, it is a basica idea for microwave photonics. 

Author Response

We are grateful to the reviewers for their helpful comments and suggestions. The significance of our system is to realize the all-optical frequency divider with microwave photonic devices, and to realize the microwave photonic frequency divider with adjustable frequency division factor by using the optical injection effect of laser, which is very important in radar. In radar systems, it is necessary to mix the received high-frequency echo signal with the local oscillator (LO) signal to realize frequency down conversion, so that low speed electrical devices can be used for signal post-processing. In practical applications, instead of directly using electrical signal generator to generate low-frequency signals, we need to process the received high-frequency signals to obtain low-frequency signals. In contrast to several typical structures of the frequency dividers, they have high operating band and low power consumption, and serves as the first stage of high-frequency dividing. However, all these structures have limited bandwidth because of the bandwidth restrictions of electric filters. In previous designs, the optimization between the high operating band and wide locking range exists conflicts. Thanks to the advantages of microwave photonics, we realize wide bandwidth divider. Based on dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted. The types of core devices in microwave photons are relatively small, but we use these only existing devices to achieve different functions. The highlight of our work is to use existing devices to achieve higher functions.