Theoretical Development of Polymer-Based Integrated Lossy-Mode Resonance Sensor for Photonic Integrated Circuits

Round 1

Reviewer 1 Report

The paper provides theoretical development of polymer-based integrated lossy mode resonance sensor for photonic integrated circuits. The highest sensor sensitivity about 1400 nm/RIU was achieved with 40 nm of TiO2. I think there are several points, discussed below, that require further clarity before the paper would be ready for publication.

1. What is the pattern size of TiO2? Does the size of the TiO2 affect the final result?

2. How to fabricate TiO2 patterns, by photolithography or other methods? Will this process affect the SU8 waveguide? How to coat the side of the waveguide with TiO2? The authors should give a detailed protocol for the fabrication of TiO2 thin films.

3. What was the mesh cells size taken?

4. Are the parameters in Table 2 the results of the authors' measurements? If not, please add references.

5. The conclusion section needs to clearly give the corresponding size of waveguide and TiO2 film in the case of 1400nm/RIU

6. In my opinion, the authors should classify their results in the discussion even more in comparison to other configurations and/or materials.

Author Response

Dear reviewer,

Please see the attachment.

Regards,

Edvins Letko

Author Response File: Author Response.docx

Reviewer 2 Report

The Authors propose an innovative sensor based on lossy mode resonance sensor. The reported results have been achieved by using FEM simulations. A major revision of the manuscript is suggested according to the following comments:

-          The Authors have experimentally characterized the materials used for the simulations. However, the fabrication of the proposed structure would be the logical pursuance. The Authors should justify their choice.

-          The simulation approach should be clarified, in terms of dimension (2D or 3D). Moreover, the resolution in wavelength for all simulations should be improved, to also investigate the shape of the resonance (Fano or Lorentzian).

-          The term 4 in the equation 3 collides with the standard theory of the propagating field.

-          In order to rate the potentials of the proposed device, the critical wavelength should be physically discussed and the Authors should provide a graph to understand how the waveguide features affect the critical wavelength (also in C band).

-          The resonances shows a different extinction ratio. The Authors should justify this behaviour and the y-axes of the transmission spectra should be expressed in terms of ER.

-          The extinction ratio is very important also for sensing capabilities. Besides it, the Q-factor is the key value that affect the sensitivity. The Authors should report the devices reported in literature with very high Q factor (e.g. Rigorous model for the design of ultra-high Q-factor resonant cavities. In 2016 18th International Conference on Transparent Optical Networks (ICTON) (pp. 1-4). IEEE., 2016; Integrated waveguide coupled Si 3 N 4 resonators in the ultrahigh-Q regime. Optica, 1(3), 153-157., 2014; Ultralow 0.034 dB/m loss wafer-scale integrated photonics realizing 720 million Q and 380 μW threshold Brillouin lasing. Optics letters, 47(7), 1855-1858, 2022), discussing the potential of the proposed device with respect the aforementioned devices.

-          Please check the references in the manuscript (e.g. pag. 5).

Author Response

Dear reviewer,

Please see the attachment.

Regards,

Edvins Leto

Author Response File: Author Response.docx

Reviewer 3 Report

In this paper, authors presented  LMR effect in SU-8 waveguide with locally coated TiO2  as a cladding layer. they showed that this simulated devices can be work as a sensor.  The highest sensitivity of the developed sensor was 1400 nm/RIU, which is higher 182 than that indicated in the literature for a similar coating. This sensitivity was achieved 183 at 40 nm TiO2.

to my view, this is a good work and can be interesting work and idea for the readers. the only thing, I am missing here, the fabrication part, if in the near future, they can present the experimental results and compare it with achieved results, it would increase the quality of the work and more interesting.

However, I can support this work because the idea is interesting. based on this idea, these people also applied to increase coupling from WGs to cavity. I am highly recommend you to cite this pure experimental work too 

https://opg.optica.org/ol/abstract.cfm?uri=ol-40-16-3826

here you can also see more interesting work from these people and would be great to talk about this work and compared with your sensitivity and your sensor performance.

https://opg.optica.org/ol/abstract.cfm?uri=ol-42-3-486

overall, after this revision, I am happy to support this work for publication.

can support this work because the idea is interesting. based on this idea, these people also applied to increase coupling from WGs to cavity. I am highly recommend you to cite this pure experimental work too.

I am looking forward to seeing your revised version. 

Author Response

Dear reviewer.

Please see the attachment.

Regards,

Edvins Letko

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have made revisions as requested and the paper is ready for publication.

Reviewer 2 Report

The Authors have modified the manuscript according to the Reviewer suggestion. Therefore, I recommend the publication.

Minor flaws:

Please improve the quality of Fig. 6 as the Marker Size.