Optimized Dual-Stokes Raman Laser for 1.1 µm Emission and Temperature Sensing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents an optimized dual-Stokes Raman fiber laser system operating at 1.1 µm wavelength, demonstrating dual-wavelength emission (1119/1177 nm) through FBG-integrated cascaded heterogeneous fiber architecture. While the concept of combining laser generation with distributed temperature sensing shows technological promise, the current submission requires substantial revisions to meet Photonics' publication standards. Below are specific recommendations for improvement:

 

1. The introduction should be strengthened by incorporating recent advancements in fiber-optic temperature sensors, particularly those employing Raman scattering mechanisms. A comparative table contrasting the proposed system with existing technologies would help highlight the novelty in sensitivity enhancement and innovation.
2. On page 2, line 91, the unit of area should be superscript, please check the full text for similar errors.
3. In the second section of this paper, we propose incorporating specific parameters related to FBG welding processes, particularly the inter-FBG spacing. The subsequent experimental procedure details a localized heating method targeting individual FBGs. A critical technical consideration arises: does this localized thermal stimulation induce measurable crosstalk interference in adjacent FBG sensors?
4. For fiber laser-based sensors, what are their advantages? Do they have high sensitivity or high resolution? In the references of Journal of lightwave technology, 43(3):1429-1436, 2025; IEEE Sensors Journal, 23(15):16944-16952, 2023; Sensors and Actuators: A. Physical, 387, 116481(2025), they showed the benefit of fiber laser. The authors can add a discussion.
5. The authors need to discuss this and ref these
6. In Figure 2, it is suggested to add labels for wavelength fluctuation and maximum power.
7. Figure 5 necessitates methodological improvements regarding temperature calibration: either (a) optimizing the temperature fitting through linear regression analysis, or (b) establishing the sensitivity quantification approach corresponding to the existing fitting methodology.
8. For the images with different trends in Figure 6, it is recommended to select different legends or different colors to distinguish them.
9. Please explain why the output spectral lines in Figure 7B) are not smooth.

Author Response

Cover letter response Photonics-3603391

 

Dear reviewers and Editor,

 

We thank you for your effort and time spent on our manuscript. We appreciate all of your comments and have carefully considered them. Please see our detailed responses. We also want to mention that a discussion section was included.

 

Reviewer #1:

The manuscript presents an optimized dual-Stokes Raman fiber laser system operating at 1.1 µm wavelength, demonstrating dual-wavelength emission (1119/1177 nm) through FBG-integrated cascaded heterogeneous fiber architecture. While the concept of combining laser generation with distributed temperature sensing shows technological promise, the current submission requires substantial revisions to meet Photonics' publication standards. Below are specific recommendations for improvement:

1. Response: Thank you for your concern. We agree with the reviewer on the importance of incorporating recent advances in RFLs and strengthening the introduction. Accordingly, we have updated the introduction with relevant background information and added a discussion section that includes a comparative table to highlight this work's main contributions and results. The following information has been incorporated:   One practical application that receives particular attention in fiber-optic Raman systems is long-distance distributed temperature monitoring [2, 3]. In this context, temperature monitoring can be performed along an 85 km-long fiber with an accuracy of 8 °C by increasing the probe light power, thereby enhancing the intensity of the an-ti-Stokes Raman signal [2]. Currently, several research groups have made significant efforts to improve fiber-optic Raman systems by proposing algorithms that increase the SNR without compromising signal information [4], optimizing the frequency for Raman scattering power measurements [5], and post-processing the Raman signal to improve temperature precision [6].

   The introduction should be strengthened by incorporating recent advancements in fiber-optic temperature sensors, particularly those employing Raman scattering mechanisms. A comparative table contrasting the proposed system with existing technologies would help highlight the novelty in sensitivity enhancement and innovation.

 

 

 

 

 

 

 

 

 

 

 

4. Discussion Raman fiber lasers (RFLs) are exciting because they enable flexible wavelength switching by appropriately choosing the Raman gain medium, pump source, and re-flective cavity elements.  Then, several configurations have been proposed and demonstrated. For instance, specific wavelength bands that are challenging to access with traditional rare-earth-doped fibers can be achieved by seeding a tunable random Raman fiber laser and high-power pigtailed pump diodes [26]. Other prior alternatives employ a high-power Ytterbium fiber laser as a seed element to excite SRS[27]. The above-mentioned works show that the reflective devices involved play an important role and can be adjusted according to the RFL demands. However, choosing a suitable high-power pump source makes it possible to propose RFL with minimal elements in-volved, which can be more suitable for practical applications [28].  Recently, some groups have explored different all-fiber optic filters to control RFL laser output. Here, Yuxi Ma et al., introduce a few-mode all-fiber filter to achieve multiwavelength generation in dif-ferent NIR bands from 1.1um to 1.5 µm[29]. Meanwhile, it was demonstrated that by a suitable design of Long-Period fiber grating, it is possible to control the emission in a 5kW Raman fiber laser[30]. In this work, we propose to include the minimal elements required in Raman fiber lasers and employ a high-power pump source at 1064 nm. Using 4 km of metro-core fiber as a Raman gain medium and incorporating a short segment 980-HP, it is possible to obtain a Raman laser emission centered at 1177.13 nm. Moreover, incorporating two FBGs makes it possible to obtain dual-laser wavelength emissions that are challenging to achieve using Ytterbium-doped fiber laser systems. Furthermore, by using these re-flective devices (FBGs), it is possible to explore the sensing capabilities of the RFL, which makes it possible to be a competitive alternative and explore further sensing applications for strain [31], volatile organic compounds detection [32], and high-sensitive temperature monitoring [33]. In these applications, and considering the laser line, it is possible to achieve high-resolution fiber laser sensors. In addition, the proposed technique in this work is a competitive temperature sensor alternative in terms of sensitivity. The capabilities of the proposed RFL in this work are compared in Table 1. Table 1. Comparative review of the latest developments in temperature sensors based on Raman scattering mechanisms. Sensing Head Sensitivity/Temperature Range Wavelength Operation (um) Ref/year FBG 13.38 pm/°C/ 22–500 1.5 [34]/2005 FBG 9.7 pm/°C 25–70 1.5 [35]/2016 All-Fiber Interferometer 10 pm/°C 30–80 1.5 [36]/2024 LPFG 8.61pm/°C 35–60 1.5 [37]/2024 FBG 11.9 pm/°C 20–150 1.5 [38]/2024 FBG 15.07 pm/°C 35–160 1.1 This Work

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. On page 2, line 91, the unit of area should be superscript, please check the full text for similar errors.

Response: We sorry for this inconvenience, the manuscript was fully reviewed, and all the superscripts were reviewed. Please see new submitted version.

 

 

 

1. In the second section of this paper, we propose incorporating specific parameters related to FBG welding processes, particularly the inter-FBG spacing. The subsequent experimental procedure details a localized heating method targeting individual FBGs. A critical technical consideration arises: does this localized thermal stimulation induce measurable crosstalk interference in adjacent FBG sensors?

Response: We agree with the reviewer that this critical information must be included.  The FBGs are separated by 1.0 m and are arranged to allow thermal changes to one or both FBGs. The following statement was included:   with a separation of 1 meter between the FBGs

 

 

 

 

 

 

1. For fiber laser-based sensors, what are their advantages? Do they have high sensitivity or high resolution? In the references of Journal of lightwave technology, 43(3):1429-1436, 2025; IEEE Sensors Journal, 23(15):16944-16952, 2023; Sensors and Actuators: A. Physical, 387, 116481(2025), they showed the benefit of fiber laser. The authors can add a discussion.

Response: Thank you for your concern. In the discussion section, we include the references and highlight the advantages of fiber laser sensors.

 

 

 

1. Response: We agree with the reviewer and the references were included and discussed.

   The authors need to discuss this and ref these

 

 

1. In Figure 2, it is suggested to add labels for wavelength fluctuation and maximum power.

Response: Thank you, the labels were included. Please see the new version.

 

 

1. Figure 5 necessitates methodological improvements regarding temperature calibration: either (a) optimizing the temperature fitting through linear regression analysis, or (b) establishing the sensitivity quantification approach corresponding to the existing fitting methodology.

Response: We agree with the reviewer, and the discussion and fitting values support data were included.     Figure 5. Shows the Bragg wavelength shift curve when the TCS provides temperature to the FBG-1177-nm from 26°C to 160°C and then back to 26°C, forming a hysteresis curve, we performed the experiment several times and the results were consistent.

 

 

 

 

 

 

 

 

 

 

 

1. For the images with different trends in Figure 6, it is recommended to select different legends or different colors to distinguish them.

Response: We agree with the reviewer; the color was included in Figure 6 to distinguish between the thermal process.

 

 

 

1. Response:  Thank you for your comment. The spectral line shape is generated when both FBGs are in the refractory furnace.  The following information was included:   The shape of the first Stokes profile at 1119 nm is affected by the bending indicated when both fibers are located over the refractory furnace. This bending adds to the Bragg wavelength phase, resulting in a reflection band with small ripples.

   Please explain why the output spectral lines in Figure 7B) are not smooth.

 

 

 

 

Once again, we thank the editor and reviewer very much for their valuable comments and suggestions.

Sincerely,

THE AUTHORS.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Bragg grating Raman fiber lasers have attracted much attention due to their advantages and a wide range of possible applications. In this regard, research in this area is relevant.

There are a number of questions and comments on the presented work:

-the authors can consider some related articles:

A G Kuznetsov et al., Quantum Electron. 39, 1078 (2009)

A.G. Kuznetsov et al., Quantum Electron. 47, 967 (2017)

-the experimental methodology section does not say anything about the characteristics of the power meter and optical spectrum analyzer;

-in lines 91 and 92, it is necessary to correct the superscripts;

-what does the intensity maximum near 1186 nm in Fig. 3 correspond to?

-what is the magnitude of the thermal expansion of the Bragg grating during heating?

- does the thermal expansion of the Bragg grating cause damage to the fiber?

- I suggest that the curve corresponding to the cooling process in Fig. 6 be made in a different shade; what is the reason for the absence of a point at 20 degrees Celsius in this figure for cooling?

Author Response

Cover letter response Photonics-3603391

 

Dear reviewers and Editor,

 

We thank you for your effort and time spent on our manuscript. We appreciate all of your comments and have carefully considered them. Please see our detailed responses. We also want to mention that a discussion section was included.

 

Reviewer #2:

Bragg grating Raman fiber lasers have attracted much attention due to their advantages and a wide range of possible applications. In this regard, research in this area is relevant.

There are a number of questions and comments on the presented work:

-the authors can consider some related articles: A G Kuznetsov et al., Quantum Electron. 39, 1078 (2009); A.G. Kuznetsov et al., Quantum Electron. 47, 967 (2017)

Response: Thank you for your concern. We agree with the reviewer on the importance of incorporating the mentioned references. Accordingly, we have updated the introduction.

 

-the experimental methodology section does not say anything about the characteristics of the power meter and optical spectrum analyzer;

 

Response: We apologize for the inconvenience; the missing information has now been included in the new version.

 

The laser output is analyzed with an optical spectrum analyzer (OSA, Yokogawa model AQ6370C), and a power meter (PM, model FieldBest from 10 mW to 50 W) monitored the total output.

 

 

 

-in lines 91 and 92, it is necessary to correct the superscripts;

Response: We sorry for this inconvenience, the manuscript was fully reviewed, and all the superscripts were reviewed. Please see new submitted version.

 

 

-what does the intensity maximum near 1186 nm in Fig. 3 correspond to?

Response: Thank you for this interesting comment. This emission bands correspond to the frequency shift peaks at 13.2 THz and 15 THz in the Raman gain spectrum of silica when pumped at 1064 nm. The following information was included:

 

The maximum intensity at 1179.44 and near 1186 nm correspond, respectively, to the frequency shift peaks at 13.2 THz and 15 THz of the Raman gain spectrum for silica molecules when pumped at 1 μm [21].

 

-what is the magnitude of the thermal expansion of the Bragg grating during heating?

- does the thermal expansion of the Bragg grating cause damage to the fiber?

Response: We would like to attend these points by including the following information:

It is important to recall that the wavelength shift is related to the thermal expansion coefficient (0.55 × 10⁻⁶ /°C) and the thermo-optic coefficient (8.6 × 10⁻⁶ /°C) of silica optical fiber [8]. In addition, these fibers can withstand significant thermal variations without damage [13].

 

 

 

 

- I suggest that the curve corresponding to the cooling process in Fig. 6 be made in a different shade; what is the reason for the absence of a point at 20 degrees Celsius in this figure for cooling?

 

Response: We appreciate your observation. Figure 6 has been updated—please refer to the revised version. It is important to note that room temperature should not fall below 20 °C or should remain stable near this value. Therefore, the thermal range considered in this work reflects this condition.

 

 

 

 

 

 

Once again, we thank the editor and reviewer very much for their valuable comments and suggestions.

Sincerely,

THE AUTHORS.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have generally addressed the reviewers' concerns in their revision, and the manuscript's organization and presentation have shown notable improvement. However, several minor editorial issues still require attention prior to final publication. The authors are advised to carefully address the following specific points:

1. On page 1, line 40, there are punctuation marks before and after reference [7].
2. On page 8, there is a missing space before reference [27] in line 248.
3. On page 9, the 1.1 micrometer unit in line 252 is not in the standard form.

Author Response

Cover letter response Photonics-3603391R2

Dear reviewers and Editor,

We thank you for your effort and time spent on our manuscript. We appreciate all of your comments and have carefully considered them. Please see our detailed responses. We also want to mention that a discussion section was included.

Reviewer #1:

The authors have generally addressed the reviewers' concerns in their revision, and the manuscript's organization and presentation have shown notable improvement. However, several minor editorial issues still require attention prior to final publication. The authors are advised to carefully address the following specific points:

1. On page 1, line 40, there are punctuation marks before and after reference [7].
2. On page 8, there is a missing space before reference [27] in line 248.
3. On page 9, the 1.1 micrometer unit in line 252 is not in the standard form.

Response: We apologize for these typographical errors. The manuscript has been thoroughly reviewed, and in the revised version, we have carefully addressed all the points raised by the reviewer.

Once again, we thank the editor and reviewer very much for their valuable comments and suggestions.

Sincerely,

THE AUTHORS.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Looking at Table 1, one can conclude that the results of the peer-reviewed article are slightly inferior to work 34 from the References.

Author Response

Cover letter response Photonics-3603391R2

Dear reviewers and Editor,

We thank you for your effort and time spent on our manuscript. We appreciate all of your comments and have carefully considered them. Please see our detailed responses. We also want to mention that a discussion section was included.

Reviewer #2:

Looking at Table 1, one can conclude that the results of the peer-reviewed article are slightly inferior to work 34 from the References.

Response: We sincerely thank the reviewer for their time and thoughtful feedback on our manuscript. We agree that the proposed technique's performance can be further improved, which represents a valuable direction for future research. Additionally, Table 1 has been carefully reviewed, and several typographical errors have been corrected.

Once again, we thank the editor and reviewer very much for their valuable comments and suggestions.

Sincerely,

THE AUTHORS.

 

Author Response File: Author Response.pdf