Reflectometry Study of the Pyroelectric Effect on Proton-Exchange Channel Waveguides in Lithium Niobate

Round 1

Reviewer 1 Report

The paper is studying the pyroelectric effect on the qualities of optical wave guides formed in a lithium niobate crystal by proton exchange. The authors demonstrate that in the range of 1530–1570 nm, all wavelengths are suppressed equally.  By the optical reflectometry method in the frequency domain authors show that during the suppression of channeling  radiation, the reflection in the channel waveguide increases along almost its entire length, except for short segments near the ends of the chip.

The presentation is clear, with detailed explanations and suggesting structural representation. The subject presents a high interest, so I believe that it fulfill the criteria to be accepted for publication in this form.

Author Response

Thank You very much for your revision!

We have found some English mistakes in manuscript text. 

We will correct them.

 

Best regards to You

Reviewer 2 Report

The authors present a reflectometry study of the pyroelectric effect in a lithium niobate crystal WG by proton exchange.
The paper is weakly presented in the form of a report not a paper! The advantage of an obsolete LN waveguide type to state-of-the-art available LN waveguides are not explained. e.g.:
Wang, C. et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature 562, 101–104 (2018). https://doi.org/10.1038/s41586-018-0551-y
Why should this type of LN WGs be still addressed for IOMs?! This is mainly due to the lack of in-depth literature review and proper number of references.
There are not enough justification and explanation for Figures. For instance see Fig. 4. What are the reasoning for the peaks and valleys?
The paper suffers from weak discussion and in the current format is not acceptable.
The comparison of the results to that of the literature is a MUST. This is not a modulator but a Y branch, unless discussed. There is no applied voltage within the manuscript!
How much is the waveguide loss in room temp?
Fig. 8: Delta_L is not 55 mm.
The measured length of the IOM as the distance between the peaks (35 mm) is NOT consistent with its physical length (38 mm)?
An English Review is a MUST, See lines: 48-49, 113, ...

Author Response

Dear Reviewer, thank you for your comments, it help us make manuscript better.

Please see our answers and updated version of manuscript.

 

 

• The paper is weakly presented in the form of a report not a paper! 

 

The paper consists of an experimental part as well as discussion of the results. This structure is typical for scientific experimental papers.

 

• The advantage of an obsolete LN waveguide type to state-of-the-art available LN waveguides are not explained. e.g.:

Wang, C. et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature 562, 101–104 (2018). https://doi.org/10.1038/s41586-018-0551-y

Why should this type of LN WGs be still addressed for IOMs?! This is mainly due to the lack of in-depth literature review and proper number of references.

 

Thank you for your comment. We agree with you that with no voltage applied this IOM is just a Y-branch. To avoid the misunderstanding, we have added the explanation of why we use the term modulator: IOM'S design and future application allow us to name it this way.

 

• There are not enough justification and explanation for Figures. For instance see Fig. 4. What are the reasoning for the peaks and valleys?

 

Fig. 4 shows two transmitted radiation spectra for the modulator at different temperatures. The initial spectrum corresponds to the spectrum of the used radiation source (ASE). Such a spectrum is typical for Erbium-doped ASE sources.  

 

• The paper suffers from weak discussion and in the current format is not acceptable.

 

The paper is experimental primarily. This is the first reflectometric study of this type IOM to our best knowledge. Indeed, the several results have no explanation. For this purpose, additional experiments are planned. At the same time, the qualitative description of observed temperature behaviour is proposed. We hope that these results will promote new studies of well-known IOM in the context of real operating conditions.

 

• The comparison of the results to that of the literature is a MUST. 

 

The review of the other IOMs is expanded. The corresponding references are added. However, no works were found devoted to similar effect. The present work is an extension of previously published study. The corresponding comment is presented in the introduction.  

 

• This is not a modulator but a Y branch, unless discussed. There is no applied voltage within the manuscript!

 

The studied object is a serial IOM, but not an ordinary Y branch. The application of voltage lets you modulate input signals. Indeed, there is no applied voltage within the text. However the studied effect is very important for practical application (gyroscopy, for example), where modulation is required.      

 

• How much is the waveguide loss in room temp?

 

Waveguide losses at room temperature is measured as 1dB/cm. The corresponding information is added to the text.

 

• Fig. 8: Delta_L is not 55 mm.

The measured length of the IOM as the distance between the peaks (35 mm) is NOT consistent with its physical length (38 mm)?

 

Thank the reviewer for finding the mistake. The real physical length of the modulator is 35 mm instead of 38 mm as indicated earlier. The corresponding correction is performed.  

 

• An English Review is a MUST, See lines: 48-49, 113, …

 

The careful English review of the text is performed.

 

Reviewer 3 Report

It would be useful, if possible, to make some comments on the reproducibility of the experimental results: were they obtained in a single or multiple experiments or how many experiments have been performed for collecting these data?

As a rule, all abbreviations have to be explained even they are well-known or the meaning seems obvious (e.g. data acquisition system (DAQ), device under test (DUT), optical spectral analyzer (OSA), etc.). Most convenient for the reader is to have this in the captures of figures with block diagrams (Figs. 2 and 7) instead of in the text.

Some technical corrections are needed; they are highlighted and pointed out in the pop-up notes in the manuscript attached.

The study is a logical addition to the previous studies of the team on the subject and is a base for future experiments. Taking into account the need of experimental data acquisition on any possible factors affecting the stability of IOM’s performance, and the fact that the article is well-written and appropriately illustrated, I would like to recommend the submitted manuscript for publication after the minor technical corrections are made.

List of technical revisions:

5 – Shevtsov

11 – quality (or properties ) instead of qualities

14 – the instead of a

33 – reproduced instead of recreated

36 – decrease (Dn)

40 – of instead of for

45 – in changing waveguide optical properties (instead of: in waveguide optical properties changing)

46 – no comma after [4]

47 – was instead of is

48 – was instead of is

49 – what is instead of what

50 – is has to be deleted

53 – capabilities instead of qualities

54 – To study the backscattered signal we also used the distributed method based on …..

75 – Channels were created instead of Channel waveguides were created

89 – high-/low-temperature chamber instead of heat and cold chamber

100 – broadband spontaneous radiation source (instead of: radiation source of spontaneous radiation)

101 – wavelength instead of illumination

113 – of the – to be removed

129 – at different temperatures (instead of: at different wavelengths)

133 – does the channeling occur (instead of: the channeling occurs)

134 – does it have (instead of has)

135 – by using instead of using

144 – on instead of from

Figure 8: DL=35 mm (instead of DL=55 mm)

157 – the area between B and C (instead of: areas B and C)

162 – on instead of of

Figure 10: Temperature, ^oC

178 – is because instead of is since

182 – (at about 100 min) instead of (near the time of 100 minutes); thereafter instead of after

183 – (at about 110 min) instead of (near the time of110 minutes)

186 – pyroelectric effect instead of pyroeffect

192 -  pyroelectric  effect instead of pyro effect

197 -  pyroelectric effect instead of pyro effect

205 – in intensity instead of its intensity

206 - pyroelectric effect instead of pyro effect

223 – input and output – (instead of: both the input and the output)

244 – 13.4×10^-6 instead of 13.4-10^-6

247 - extraordinary instead of uncommon

270 – indices instead of index

272 – of instead of with

Comments for author File: Comments.pdf

Author Response

Thank you very much for attentive review!

 

We will add information about samples/experiments statistic, correct pictures with experiments schemes and also correst english mistakes.

All of corrections will come in new version of manuscript.

Best regards,

Dr. Roman Ponomarev

Reviewer 4 Report

The authors performed a thorough optical study in a broad temperature range. The presented results are very well explained.
Based on the quality of the presented research, I am recommending the acceptance after minor revision.
Comments:
Authors should extend the introduction and point out what is new in their study from previously published research. Is the presented work an extension of a previously published study (reference 4), or is it utterly novel from an experimental and theoretical perspective?
The novelty of this work should be highlighted.

Author Response

Dear reviewer, thank You for your review!

The present work is an extension of previously published study. The corresponding comment is presented in introduction:  

“...The study [4] shows that heating of the lithium niobate (LN) integrated-optical circuit, pre-cooled to low temperatures, can lead to a significant increase in optical losses in the channel or even complete cessation of radiation channeling…. In the study [4], we measured only the optical signal power at the IOM output, and it is not precisely determined which point of the integrated-optical circuit the signal channeling is terminated in, whether this area is extended or point-wise, how does the restoration of the channel waveguide properties occur, what the spectral sensitivity of the effect under study is. The present work aims to answer these questions and investigate in more detail the processes occurring inside the waveguide during a change in the crystal temperature…”

 

Sincerely, 

Roman Ponomarev, Yuri Konstantinov, Ivan Lobach, Maxim Belokrylov, Denis Shevtsov

Round 2

Reviewer 2 Report

The study still suffers from the lack of in-depth literature review and proper number of references.
Why should the LOSSY proton exchange type (1 dB/m) be used for IOMs while LOW-LOSS titanium in-diffused waveguides are available (0.05 dB/cm)?
See for instance:
1- Hu H, Ricken R, Sohler W. Low-loss ridge waveguides on lithium niobate fabricated by local diffusion doping with titanium. Applied Physics B. 2010;98:677-679. DOI: 10.1007/s00340-010-3908-y

Therefore, although there are experimental results, the paper in general is misleading for the reader for the possible APPLICATION.
It can be re-written and submitted to another MDPI Journal.
An English Review is a MUST, See new lines: 57 & ...