Broadband Microwave Photonic Channelizer with 18 Channels Based on Acousto-Optic Frequency Shifter
Round 1
Reviewer 1 Report
Comments for author File: 
Comments.pdf
Author Response
Point 1: The authors say that The novelty is that our scheme greatly reduces the demand for the number of comb lines when realizing the reception of 3n sub-channels, since our scheme only needs to generate n-line OFCs while other schemes need to generate 3n- Although the number of comb lines required for optical frequency combs is reduced, two additional frequency shifters (AOFs) are required. As far as I know, the cost, adjustment, power consumption, etc. of the AOFs may not simpler than a multi-lines OFC generator. Therefore, I wonder if your improvements can effectively reduce the system complexity? Please give a clarify on it.
Response1: The multi-line OFC used in channelized RF receiver is often realized by electro-optic modulation and micro-ring resonator (MRR). As we all know that electro-optic OFC schemes usually require multiple electro-optic modulators and RF power amplifiers, which will suffer high cost, high power consumption and system complexity and. Also, the system stability and spectrum purity will also be challenged by the modulator bias drift. The disadvantages of the Kerr OFC schemes contain temperature-induced instability and the difficulty in frequency adjustment. In addition, due to the generation of useless optical sidebands, it will cause more serious channel crosstalk if the sidebands are not completely suppressed.
|
Method |
Electro-optic modulation |
Micro-ring resonator |
AOFS |
|
Cost |
High |
Low |
Moderate |
|
Frequency Adjustment |
Good |
Low |
Low |
|
Power consumption |
High |
Low |
High |
|
Conversion efficiency |
Low |
Low |
High |
|
Spectrum purity |
Low |
Low |
High |
|
System stability |
Low |
Low |
High |
|
system complexity |
High |
Low |
Moderate |
The AOF used in our scheme has a fixed frequency shift of 500 MHz and an insertion loss of 6 dB. Its cost in acousto-optic modulator may be a little higher than the electro-optic modulator, but its cost in low-frequency driver is obviously lower than that of wideband RF driver for the electro-optic modulator. It is really true as reviewer said that the frequency tunability range of the AOFS is related small (usually less than 10% of its operating frequency). However, for an RF receiver with fixed frequency allocation, it may be not much required to change the frequency shift value of the AOFS. Its system is no more complexity than the electro-optic modulation system. Except for the above problems, the AOFS exhibits obvious advantages in conversion efficiency, spectrum purity and system stability. So, it seems to be a competitive solution.
Point 2: The proposed system architecture and language description are similar to that reported in [22]. So I think there is still room for optimization of the paper structure.
Response2: The reference [22] is our previous research. The previous scheme is to change a single LO signal into three LO signals by frequency up- and down- shift of the LO signal to, so only 6 sub-channels reception can be achieved without using any OFC. In the current scheme, the novelty is that a frequency shift module and two OFC generation modules are added. The local OFC is used to replace the single LO signal. When equation (7) is satisfied, the frequency of a n-line OFC is shifted up and down by using two AOFSs. So it can realize the reception of 3n sub-channels, which greatly increases the sub-channels, while other schemes based on OFC can only realize the reception of n sub-channels. In order to simplify the experiment, only 3-line OFC is used in this manuscript. Therefore, to realize the reception of the same number of sub-channels, our scheme is simpler in structure and has lower implementation difficulty than others scheme based on OFC.
Point 3: A lot of detailed information is provided, but at the Eq. 7, the authors say that “The following frequency configuration in the scheme must be satisfied”. It will be very helpful if the authors can explain in detail. Moreover, it is necessary to add some discussions or references about the working principle of the IRM.
Response3: Thank you for your suggestion and we have added a detailed explanation of Eq. 7 in the manuscript. Taking our scheme as an example, the broadband RF signal with a bandwidth of 18B is regarded as three RF signals with a bandwidth of 6B and continuous spectrum, which are labeled RF1, RF2 and RF3 respectively. is satisfied so that the center frequency of the 3 lines OFC is exactly aligned with the center frequency of the RF2 signal. means the frequency of the other two lines are aligned with the center frequency of the RF1 and RF3, so as to achieve the dual output of image suppression. The working principle of the IRM is described in detail in our previous research Ref [22].
Point 4: Resolution of all the Figures may be improved, otherwise some marks will not be distinguishable.
Response4: Thank you very much for the suggestion you give us and we have improved the figures in the revised manuscript.
Point 5: Some errors need to be fixed, including but not limited to the following examples:
(1) Line 131: can captured can capture
(2) Line 140 have language error
(3)First abbreviations need to give the full name.
Response5: I am very sorry for the careless mistakes, and thank you for your reminder. We have revised accordingly in the paper.
Point 6: Fig. 1(a) should be improved. The Line connection in this picture is some what confusing.
Response6: Thank you very much for the suggestion you give us and we have revised accordingly in the paper.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors proposed a scheme to shift the frequency of the OFC by using AOFS. where they sued 3-line OFC is used in the experiment. The proposed design allows a large number of sub-channels with minimal channel crosstalk.
Overall, the experimental performance of the proposed system is interesting and worth publishing. However, the following should be addressed before the manuscript can be accepted:
1- The quality of the figures is very poor and hard to follow.
2- There are many abbreviations used in the manuscript without definitions. Please define. The overall English language can also be improved.
3-What is the tuning accuracy and range of the subbands? More discussion is needed on frequency stability and jitter.
4- How do the laser's residual intensity modulation and line width impact the overall system performance?
Author Response
Reviewer 2
Point 1: The quality of the figures is very poor and hard to follow.
Response 1: Thank you very much for the suggestion you give us and we have improved the figures in the revised manuscript.
Point 2: There are many abbreviations used in the manuscript without definitions. Please define. The overall English language can also be improved.
Response 2: Thank you very much for the suggestion. We have checked the text again and tried our best to improve the language use.
Point 3: What is the tuning accuracy and range of the subbands? More discussion is needed on frequency stability and jitter.
Response 3: We are very sorry for our unclear statement and we have revised accordingly in the paper. In fact, the bandwidth of subchannels is equal to the frequency shift of the AOFS, which is related small (usually less than 10% of its operating frequency). So it cannot be easily widely adjusted. The AOFs used in our scheme is 500MHz, so the bandwidth of subchannels is set to 500 MHz. If the frequency of the sub-band is required to be adjusted, it’s suggested to replace the type of the AOFS. Compared with electro-optic modulation and Micro-ring resonator, only a specific low-frequency RF signal is used to drive the AOFS without bias drift, so it exhibits high frequency stability without obvious jitter.
Point 4: How do the laser's residual intensity modulation and line width impact the overall system performance?
Response 4: The laser's residual intensity modulation will produce spurious signals during down conversion, and the linewidth mainly leads to the phase noise in the IF signals. However, the residual intensity modulation is related small with about -50 dBc side mode suppression. In addition, the line width of the modulator is as below as several kHz and the fiber loop difference between the RF path and LO path is small. So the system performance will not be obviously impacted by the laser in our experiment.
Author Response File: Author Response.docx
Reviewer 3 Report
The paper presents a new approach for a channelizer. The method is interesting. However there are several points that will need clarification. The authors claim that the design is simpler than other ones, which tend to use more MZM. However, in this design, apart from the MZMs, there are additional elements, multiple RF LO, AOFSs, amplifiers etc. What is the total loss of the system? Optical amplifiers raise the noise floor and affect performance(?) At what diffraction efficiency do the AOFS work and what is the insertion loss? What type of RF drivers are required. Typically, the RF drivers for AO devices tend to be bulky and power hungry.
What is the total power consumption for the channelizer, which includes 2 AOFS, RF amplifiers, Optical amplifiers, RF signal generrators etc?
The figures are of very poor image quality and are hard to follow. Furthermore, the main Fig. Fg. 1, is very confusing and as a reviewer I had very hard time to follow the description and the figure.
The description of the figures and the results is not well presented. The readers will have to go over again and again and it is difficult to make the connection with all the different LO (optical, RF) etc. Results are also not presented clearly and although interesting, the reader is lost through all the descriptions.
Author Response
Reviewer 3
Point 1: The authors claim that the design is simpler than other ones, which tend to use more MZM. However, in this design, apart from the MZMs, there are additional elements, multiple RF LO, AOFSs, amplifiers etc. What is the total loss of the system? Optical amplifiers raise the noise floor and affect performance(?) At what diffraction efficiency do the AOFS work and what is the insertion loss? What type of RF drivers are required. Typically, the RF drivers for AO devices tend to be bulky and power hungry. What is the total power consumption for the channelizer, which includes 2 AOFS, RF amplifiers, Optical amplifiers, RF signal generrators etc?
Response 1: The total loss of the system we proposed is about 40 dB. It is really true as reviewer said that Optical amplifiers raise the noise floor and affect performance such as reduce the SFDR of the system. The insertion loss of the AOFS we used is 6 dB and the diffraction efficiency is 25%. Only one RF driver with an output power of 2 W (33 dBm) is used for the two AOFS, where each AOFS receives about 30-dBm RF power. Luckily, the frequency of the RF driver is only 500 MHz, so its cost and power consumption is lower than the high-frequency RF drivers used in the electro-optic modulation method. The total power consumption of the experiment setup is about 60 W.
Point 2: The figures are of very poor image quality and are hard to follow. Furthermore, the main Fig. 1, is very confusing and as a reviewer I had very hard time to follow the description and the figure.
Response 2: Thank you very much for the suggestion you give us and we have revised accordingly in the paper.
Point 3: The description of the figures and the results is not well presented. The readers will have to go over again and again and it is difficult to make the connection with all the different LO (optical, RF) etc. Results are also not presented clearly and although interesting, the reader is lost through all the descriptions.
Response 3: Thank you very much for the suggestion you gave us. We have checked the text again and tried our best to improve the language use.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Accept after minor revision1. Experimental parameters can be added to a table, so that the author's work is more intuitive and convenient to be understood by readersï¼›
2. Some errors need to be fixed, including but not limited to the following examples:
(1) Line 105: inFigure. 1(c)
(2) Line 116: inFigure. 1(a)
3. There is abbreviation used in the abstract without definition. Please define.
Author Response
Point 1：Experimental parameters can be added to a table, so that the author's work is more intuitive and convenient to be understood by readers.
Response 2: Thank you very much for the suggestion you give us and we have adopted.
Point 2：Some errors need to be fixed, including but not limited to the following examples:
(1) Line 105: inFigure. 1(c)
(2) Line 116: inFigure. 1(a)
Response 2: I am very sorry for the careless mistakes, and thank you for your reminder. We have revised accordingly in the paper.
Point 3：There is abbreviation used in the abstract without definition. Please define.
Response3: Thank you for your suggestion and we have revised accordingly in the paper.
Author Response File: Author Response.docx
Reviewer 2 Report
The authors have addressed my comments, I recommend the manuscript for publication.
Author Response
Thank you very much for your suggestions.
