RF Frequency Selective Switch by Multiple PMIM Conversions
Round 1
Reviewer 1 Report
Comments:
In this paper, the authors report a RF frequency selective switch with broadband and high frequency spectral resolution based on multiple phase modulation to intensity modulation conversions. The structure scheme of the reconfigurable photonic processor is impressive, and the manuscript is well organized. The referee recommends it to be published in Applied Sciences after some following minor revisions are completed:
1. There are some grammar problems in the manuscript, and the manuscript should be carefully copyedited, such as Line 169 on Page 4 and Line 239 on Page 6.
2. It can be seen from Figure 4(b) that the amplitude frequency response follows the RF frequency linearly. Please explain this phenomenon in detail.
3. The authors may like to consider adding the comparison of their technique with other similar microwave photonic processors in the literature (e.g., tables) to show the novelty of their work.
4. It would be better to cite some representative works that have been published recently.
Author Response
Manuscript ID: applsci-2091042
Title: RF frequency selective switch by multiple PMIM conversions
Dear editor and reviewer,
Thank you for the valuable comments concerning our manuscript. The comments are very helpful for improving our manuscript. All the comments are studied and responded carefully, which are also addressed in the submission.
Best regards,
Sincerely,
Wenhui Hao, Yi Peng, Shaohua Wang, Xia Liu
China Academy of Electronics and Information Technology, Beijing 100041, China
Recommendations for the Author(s)
In this paper, the authors report a RF frequency selective switch with broadband and high frequency spectral resolution based on multiple phase modulation to intensity modulation conversions. The structure scheme of the reconfigurable photonic processor is impressive, and the manuscript is well organized. The referee recommends it to be published in Applied Sciences after some following minor revisions are completed:
Reply: We thank the reviewer for the professional comments concerning our manuscript.
1.There are some grammar problems in the manuscript, and the manuscript should be carefully copyedited, such as Line 169 on Page 4 and Line 239 on Page 6.
Reply: We thank the reviewer for the valuable suggestion and the revised paper has been carefully checked for English grammar.
2.It can be seen from Figure 4(b) that the amplitude frequency response follows the RF frequency linearly. Please explain this phenomenon in detail.
Reply: The linearly increased amplitude frequency response is controlled by the amplitude of each single channel, which is used to verify the precise operation of the amplitude frequency characteristics of the proposed scheme. There are 21 individual channels with a frequency interval of 50 MHz from 9.5 GHz to 10.5 GHz. The amplitude response of these channels is set to linear increase with a discrete step of 0.6 dB. The corresponding response is shown in Fig.4 (b), which follows the RF frequency approximately linearly. The amplitude difference of 21 individual channels is also mapped to the final output.
[See page 7, lines 277-284]
With the help of the excellent performance of optical WSS, we can also perform more precise operations on the amplitude frequency characteristics of each RF channel instead of simply selecting on and off. There are 21 individual channels with a frequency interval of 50 MHz from 9.5 GHz to 10.5 GHz. The amplitude response of these channels is set to linear increase with a discrete step of 0.6 dB. Figure 4(b) shows the amplitude frequency response (expressed in dB) from 9.5 to 10.5 GHz, which follows the RF frequency approximately linearly. Moreover, the amplitude difference of 21 individual channels is also mapped to the final output.
3.The authors may like to consider adding the comparison of their technique with other similar microwave photonic processors in the literature (e.g., tables) to show the novelty of their work.
Reply: We thank the reviewer for the helpful comments concerning our manuscript. As the reviewer said, there are lots of impressive microwave photonic filters that have been reported, which are targeted at single-input and single-output. However, few studies focus on the multiple-input and multiple-output (MIMO) microwave photonic processors. In the area of microwave photonic MIMO, the typical solution is a photonic field programmable gate array (FPGA) based on a finite impulse response (FIR) structure. The optical FPGA may suffer from two limitations: 1）the fluctuation of the external environment will cause obvious interference to synthesis; 2) The resolution of optical FPGA is usually worse than 1 GHz, which is limited by the large loss of long optical waveguide on a chip.
[See page 2, lines 51-52]
Photonic field programmable gate array (FPGA) is a new method to realize full function reconfigurable microwave photonic filter [7-14].
[Also see page 2, lines 54-67]
Firstly, the optical FPGA needs coherent synthesis, and the fluctuation of the external environment will cause obvious interference to the synthesis, so the filter needs very precise control. Secondly, according to the theory of FIR structure, the resolution of a signal processor or filter is inversely proportional to the longest time interval among many taps, that is to say, the maximum delay difference required for a processing resolution of 1 GHz is about 1 ns. This delay corresponds to a waveguide with a length of ten centimeters. A waveguide of this length will face a large loss or optical phase jitter, but this resolution is too wide for RF communications. If one wants to achieve a resolution below 100 MHz, the corresponding optical waveguide length must also be increased ten times. Finally, the future microwave photonic filter must have the ability of multiple-input and multiple-output (MIMO) processing, that is, it can process multiple radio frequency signals in parallel at the same time. At present, many related demonstrations are aimed at single input and output, especially various uncoherent structures.
4.It would be better to cite some representative works that have been published recently.
Reply: We thank the reviewer for the professional suggestions. The main target technology is optical FPGA, which is a promising candidate in the realization of MIMO processor. The recently published papers of typical realization of optical FPGA have been cited in this manuscript.
[Also see page 9, lines 361-370]
- W. Zhang, J. Yao, “Photonic integrated field-programmable disk array signal processor,” Nat. Commun. 11:406 (2020).
- D. P. López, A. M. Gutierrez, E. Sánchez, P. DasMahapatra, and J. Capmany, “Integrated photonic tunable basic units using dual-drive directional couplers,” Opt. Express. 27(26), 38071-38086 (2019).
- L. Zhuang, C. G. H. Roeloffzen, M. Hoekman, K. J. Boller and A. J. Lowery, “Programmable photonic signal processor chip for radiofrequency applications,” Optica, 2(10), 854-859 (2015).
- D. Pérez, I. Gasulla and J. Capmany, “Field-programmable photonic arrays,” Opt. Express. 26(21), 27265-27278 (2018).
- H. Jiang, L. Yan and D. Marpaung, “Chip-based arbitrary radio-frequency photonic filter with algorithm-driven reconfigu-rable resolution,” Opt. Lett. 43(3), 415-418 (2018).
- D. Pérez, I. Gasulla, L. Crudgington, D. J. Thomson, A. Z. Khokhar, K. Li, W. Cao, G. Z. Mashanovich, J. Capmany, “Multi-purpose silicon photonics signal processor core,” Nat. Commun. 8:636, (2017).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The Authors propose a RF frequency selective switch based on multiple phase modulation to intensity modulation conversion. The reported results have been achieved with experiments. Here, my comments:
- The Authors should discuss more about the technologies of optical switch technologies (see, i.e., MEMS optical switches. IEEE Communications magazine, 39(11), 158-163, 2001, Design of a large bandwidth 2× 2 interferometric switching cell based on a sub-wavelength grating. Journal of Optics, 23(8), 085801, 2021, Waveguided optical switch in InGaAs/InP using free-carrier plasma dispersion. Electronics Letters, 6(20), 228-229, 1984.) and how its performance affects the overall one.
- More details should be provided about the experimental setup, as the ring resonator. The Authors should discuss about the material, radius, Q-factor and ER and how its performance affects the overall one. Moreover, the source of the optical frequency comb should be described.
- Fig. 3-5 show large ripple within the bandwidth. The Authors should physically justify it and propose approaches to suppress it.
Author Response
Manuscript ID: applsci-2091042
Title: RF frequency selective switch by multiple PMIM conversions
Dear editor and reviewer,
Thank you for the valuable comments concerning our manuscript. The comments are very helpful for improving our manuscript. All the comments are studied and responded carefully, which are also addressed in the submission.
Best regards,
Sincerely,
Wenhui Hao, Yi Peng, Shaohua Wang, Xia Liu
China Academy of Electronics and Information Technology, Beijing 100041, China
Recommendations for the Author(s)
The Authors propose a RF frequency selective switch based on multiple phase modulation to intensity modulation conversion. The reported results have been achieved with experiments. Here, my comments:
Reply: We thank the reviewer for the professional comments concerning our manuscript.
1.The Authors should discuss more about the technologies of optical switch technologies (see, i.e., MEMS optical switches. IEEE Communications magazine, 39(11), 158-163, 2001, Design of a large bandwidth 2x 2 interferometric switching cell based on a sub-wavelength grating. Journal of Optics, 23(8), 085801, 2021, Waveguided optical switch in lnGaAs/lnP using free-carrier plasma dispersion. Electronics Letters, 6(20), 228-229, 1984.) and how its performance affects the overall one.
Reply: We thank reviewer’s professional suggestion. Actually, the optical wavelength selective switch (WSS) employed in our system is a commercial product (Finisar, 10WSAA20FLI). The resolution of WSS is 12.5 GHz with frequency range of 4.8 THz. Here is the access to the introduction of this product link. The design and fabrication of optical switch is beyond our filed of expertise, we are sorry for not being able to provide a more detailed analysis. In our experiment, the FSR of optical frequency comb (OFC) is around 50 GHz and the WSS is able to realize precise operation of spectrum under this resolution. The ripple within the bandwidth mainly caused by the Lorenz-shape transmission peak of ring resonator.
[See page 9, lines 312-321]
The resolution of the optical WSS is 12.5 GHz and the insertion loss is about 5 dB. The optical WSS employed in our system is a commercial product (Finisar, 10WSAA20FLI), which is used to control the amplitude of each channel.
2.More details should be provided about the experimental setup, as the ring resonator. The Authors should discuss about the material, radius, Q-factor and ER and how its performance affects the overall one. Moreover, the source of the optical frequency comb should be described.
Reply: The ring resonator employed in this system is a commercial product of Micro-Optics, where its FSR and 3-dB bandwidth of transmission peak are 50.05 GHz and 50 MHz, respectively. The optical frequency comb (OFC) module consists of two phase modulators and one intensity modulator, which is a typical method to generation flat combs based on electronic-optical modulation. For more detail of the OFC generator based on cascaded modulators can refer to “Opt. Lett. 33, 1822 (2008)”. Finally, 21 comb lines are generated in our setup with flatness better than 3 dB. Moreover, the WSS is used to further flatten the comb lines. The reviewer is correct that the ripples are caused by synthesis of Lorenz-shape channels during the phase-modulation to intensity-modulation (PMIM) conversion. The ripples of amplitude response during the synthesis of Lorenz-shape channels have been demonstrated in previous literature. The ripples can be eliminated by cascaded notch filter, which is already verified and demonstrated in “J. Lightwave. Technol. 36(19), 4557-4564, (2018)”. Its experiment shows that the ripples are well compensated by employing two cascaded ring resonator during the PMIM conversion.
[See page 5, lines 219-222]
The loss of the periodic notch filter is about 6 dB, the bandwidth of 3 dB is about 50 MHz, and the FSR is about 50.05 GHz. The ring resonator employed in this system is a commercial product provided by Micro-Optics.
[Also see page 5, lines 237-240]
The optical frequency comb is generated by cascaded modulators, which consists of two phase modulators and one intensity modulator. Finally, 21 comb lines are generated in our setup with flatness better than 3 dB. Moreover, the WSS is used to further flatten the comb lines.
[Also see page 9, lines 317-322]
This is because the notch optical filter uses a single resonant cavity device, so its frequency response is only Lorentz type with a poor rectangular coefficient. This has been discussed in many existing reports, and therefore there are some solutions [30, 31]. We think that the more promising scheme is to make full use of the advantages of photonic integration and use multiple resonators to combine and approximate a notch frequency response with better rectangular coefficient [32].
3.Fig. 3-5 show large ripple within the bandwidth. The Authors should physically justify it and propose approaches to suppress it.
Reply: Thanks for the valuable suggestion. The notch optical filter uses a single resonant cavity device, so its frequency response is only Lorentz type with poor rectangular coefficient. This has been discussed in many existing reports, and therefore there are some solutions. The literature “J. Lightwave. Technol. 36(19), 4557-4564, (2018)” experimentally demonstrated that the ripples can be eliminated by combining multiple resonators and the frequency response can be realized with better rectangular coefficient. As long as the combined optical resonators have the same FSR, the combined frequency response can also appear periodically in the optical spectrum, which can be used in our multiple PMIM conversions.
[See page 9, lines 314-323]
In the experiment, we also find that the frequency response of RF filter is poor in the out of band suppression. This is because the notch optical filter uses a single resonant cavity device, so its frequency response is only Lorentz type with poor rectangular coefficient. This has been discussed in many existing reports, and therefore there are some solutions [30, 31]. We think that the more promising scheme is to make full use of the advantages of photonic integration and use multiple resonators to combine and approximate a notch frequency response with better rectangular coefficient [32]. As long as the combined optical resonators have the same FSR, the combined frequency response can also appear periodically in the optical spectrum, which can be used in our multiple PMIM conversions.
Thanks again for the valuable comments and helpful suggestions.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The Authors address all the Reviewer comments except the Comment #1, where an overview of the switch technologies is requested. After addressing this comment, the manuscript could be accepted.
Author Response
Manuscript ID: applsci-2091042
Title: RF frequency selective switch by multiple PMIM conversions
Dear editor and reviewers,
Thank you for the valuable comments concerning our manuscript. The comment #1 from Reviewer 2 is carefully reconsidered and discussed in this revised manuscript.
Best regards,
Sincerely,
Wenhui Hao, Yi Peng, Shaohua Wang, Xia Liu
China Academy of Electronics and Information Technology, Beijing 100041, China
Reviewer: 2
- The Authors should discuss more about the technologies of optical switch technologies (see, i.e., MEMS optical switches. IEEE Communications magazine, 39(11), 158-163, 2001, Design of a large bandwidth 2x 2 interferometric switching cell based on a sub-wavelength grating. Journal of Optics, 23(8), 085801, 2021, Waveguided optical switch in lnGaAs/lnP using free-carrier plasma dispersion. Electronics Letters, 6(20), 228-229, 1984.) and how its performance affects the overall one.
Reply: We thank reviewer’s professional suggestion. As the reviewer said, considerable effort has been directed to the optical switch technologies. An lnGaAs/lnP waveguide four-port switch by using free-carrier plasma-dispersion is demonstrated, where the switching speed may be greatly improved. MEMS’s inherent advantages such as small size and scalability are also adopted into optical switch. Recently, an interferometric switching cell with bandwidth larger than 150 nm is experimentally demonstrated. In our proposal, the optical wavelength selective switch (WSS) is used to change the output ports of different spectral components, where the switching speed of our system totally depends on WSS. Each channel will occupy 50 GHz on optical domain, while the operation bandwidth of WSS can reach ~ 100 nm. From this perspective, the scalability of our system is hardly limited by WSS.
Reviewer 2#1:
[See page 4, lines 161--171]
Considerable effort has been directed to the optical switch technologies in recent years [1–3]. An lnGaAs/lnP waveguide four-port switch by using free-carrier plasma-dispersion is demonstrated, where the switching speed may be greatly improved [1]. MEMS’s inherent advantages such as small size and scalability are also adopted into optical switch [2]. Recently, an interferometric switching cell with bandwidth larger than 150 nm is experimentally demonstrated [3]. In our proposal, the optical wavelength selective switch (WSS) is used to change the output ports of different spectral components, where the switching speed of our system totally depends on WSS. Higher switching speed is also demanded in future MIMO processing. Each channel will occupy 50 GHz on optical domain, while the operation bandwidth of WSS can reach ~ 100 nm. From this perspective, the scalability of our system is hardly limited by WSS.
[See page 5, lines 232-235]
The resolution of the optical WSS is 12.5 GHz and the insertion loss is about 5 dB. The optical WSS employed in our system is a commercial product (Finisar, 10WSAA20FLI), which is used to control the amplitude of each channel.
[Also see page 9, lines 398-402]
- O. Mikami and H. Nakagome, "Waveguided optical switch in InGaAs/InP using free-carrier plasma dispersion," Electronics Letters 6, 228–229 (1984).
- Tze-Wei Yeow, K. L. E. Law, and A. Goldenberg, "MEMS optical switches," IEEE Commun. Mag. 39, 158–163 (2001).
- G. Brunetti, G. Marocco, A. D. Benedetto, A. Giorgio, M. N. Armenise, and C. Ciminelli, "Design of a large bandwidth 2 × 2 interferometric switching cell based on a sub-wavelength grating," J. Opt. 23, 085801 (2021).
Author Response File: Author Response.pdf
