A Study of High-Efficiency Laser Headlight Design Using Gradient-Index Lens and Liquid Lens

Round 1

Reviewer 1 Report

• Novelty needs to be discussed in the introduction with further use of references.
• Please ensure figure 1 is an original drawing.
• In some instances, the authors use the term chapters, whilst it should be written as “paper”.
• The authors refer to Illuminance, it is not the right terminology for referring to brightness of the laser light source. It should rather be radiance density, as illuminance is rather referred to a light source that is not coherent. In this case the authors have deployed a LASER. A coherent, monochromatic, and a specific wavelength, light source which is rather referred to as radiance and more specifically radiance density. So illuminecence should be radiance density and calculations should be used based on radiance density formulation. Lux and illuminance is dated terminology for candle power measurements and quantifying light sources that were not made by light amplification by stimulated emission of radiation.
• What is not clear, is why use a Gaussian beam and then perform the modification to bring it to a lower quality beam? It would make sense to just use (select) a lower quality beam in the first place.
• Authors should put dedicated section for research methodologies and state the methods used as well as the type of components deployed etc.. It is there but doe not look dedicated for a research paper.

 

Author Response

Please see the attached. 

Author Response File: Author Response.docx

Reviewer 2 Report

1. In lines 42-45 the authors referring to references 8 and 9 in the references list of the paper, mention about the BMW design of laser light modules but reference 9 is related to another automotive company.
2. The authors provide with references from the literature to support their arguments but on several occasions it is not clear how a particular reference they refer to is connected with the corresponding argument. For instance, in lines 96, 97 the authors mention that heat dissipation is a crucial technical consideration in diode laser and they quote references 13-16 in the references list as appropriate to support this argument but it is not clear how these references are related to the heat dissipation in diode lasers. The same below in lines 101-103: the authors mention reference 17 as an example of a laser source heat dissipation system but it is not clear how this reference is related to a laser source hear dissipation system.
3. In line 108 the authors mention that one of the purposes of the ROD lens is to "focus parallel beams to form a straight beam" but how could parallel beams form a straight beam once they are focused? Also in line 109 it is not clear what the authors call a "stable" laser beam.
4. In lines 114, 115 the authors quote reference 18 in the references list in order to support their argument that the use of a GRIN lens can reduce the number of lenses required to achieve the effect of light diffusion but reference 18 has to do with the impact of the type of phosphor material on the variation of the luminescent spot size with respect to the incident laser spot size. Unless a GRIN lens uses some kind of phosphor material the connection between the reference and their argument is not strong enough.
5. In the paragraph between lines 179 and 191 it is not clear how the authors' conclusions are extracted and supported by the light ray analysis design of Fig. 7 and parts a, b, c, and d of the figure. For instance in lines 182, 183 the authors claim that part a of the figure shows that laser transmission through the optical system significantly improved the laser polarization but it is not clear how this conclusion is extracted from the design of Fig. 7. The same for the conclusions extracted based on the other parts of the figure, b, c, and d. The authors claim that Fig. 7c indicates the results of homogenization of laser diffusion and the elimination of polarization but it is not clear how the figure shows such a thing.
6. The description between lines 202-210 of the computer algorithm which was used for the adjustment of the values of the liquid lens curvature and optical axis to be compatible with the regulation standards does not follow what it is depicted in the block diagram of Fig. 8. On the diagram a few other tasks are shown which are not described properly or their description is omitted in the corresponding text. The block diagram should be improved as well as its corresponding description in the text.
7. The experimental data reported on Table 9(b) show a relatively high value of illuminance at 5L and 5R as compared with the ECE R-112 regulations (Table 1). The authors should comment on that.
8. It is mentioned in lines 253, 254 that the optical fiber can also adjust the polarization of laser light to achieve precise light pattern control but no simulation or experimental data are included to support this argument.

Author Response

Please see the file attached. 

Author Response File: Author Response.docx

Reviewer 3 Report

This study presents a new integrated optical design for an automotive headlight system, using a Rod lens, a Gradient-index Lens and a Freeform Lens to expand the laser beam. Compared with the current 24-W LED headlight technology, the energy saved by the innovative optical design can increase the efficiency, saving 33% more energy, and the maximum luminance, 18% higher than the standard value.

Although the research of an innovative and cheaper lighting system may be an interesting topic for this journal, the paper is generally very short, lacking many descriptions and information, which are useful and should be present. In fact, the article focuses on many aspects related to optical systems, which have however been taken for granted, minimizing the contribution of information about the development of the experimental set-up and the choices completed.

More in detail, the abstract is well written, the conclusions are short but clear. While the introduction is really poor and should be improved a lot; there is no analysis of the state of the art regarding the development of innovative lighting systems; no comparison with the papers of other authors was made; it is not explained on which basis the use of a diode laser source occurs, instead of another. The structure of the entire paper does not convince me, as there is a lot of confusion in its development and presentation. In the experimental section there is confusion between the system design, the simulations and tests completed. It follows that even the experimental results are not clear; it is not clear if only simulations were carried out or if the system was actually built and tested. The absence of a lot of information and motivations, regarding the choices of tools, components, experimental factors and levels, further complicates the understanding of the experimental part. At the same time the characterization methods have been poorly and quickly described, they must certainly be implemented. The comparison with the current 24-W LED system is not clear, as well as the choice to carry out the simulations with a total power of only 6.4 W, instead of the 16 W of the system. The paper presents only a few citations. Some self-citations are not motivated; many citations have been grouped together, without clarifying the contribution of each of the works referred to.

Below are detailed all the points to which the authors should carefully address:

1. At line 22, the keywords are few and of little significance for the development and results of the paper. The authors should improve them.
2. At line 26-27, the authors wrote: “has higher illumination efficiency than halogen and xenon headlights, and its energy efficiency is also no less than that of an LED headlight”. These statements need to be confirmed by at least one reference.
3. At line 28-30, the authors wrote: “Since its successful development in a laboratory in 1960, laser has been considered an extremely important scientific achievement; however, it is rarely used in lighting applications”. These statements need to be better detailed and confirmed by one or more references.
4. At line 33-35, the authors wrote: “The advantage of using a laser application in headlights is that the laser diode is only one-tenth the size of a conventional halogen lamp. In addition, the laser diode height has been reduced from 35 cm to 3 cm, which saves space and reduces power consumption”. These statements need to be better detailed and confirmed by one or more references.
5. At line 41, there are multiple citations, even 7 together [1-7]. The citations have to be divided, to be placed well in the text, explaining in detail the contribution of each in the context of the topic being discussed..
6. About the introduction section, this is too short, it needs to be improved. It is not explained why the use of a diode laser source compared to the others, no comparison is made with the state of the art of literature regarding the development of lighting systems, with or without laser sources; no comparison with the contributions of other authors is present. In the context of the use of diode lasers, there is no mention of their application filed, both conventional and innovative, based on the latest literature.
7. At line 67-69, the authors wrote: “The laser was transmitted from the laser diode to the headlight system via optical fibers that have the ability to transmit light over long distances and can eliminate the phenomenon of partially polarized light through total reflection”. These statements need to be confirmed by at least one reference.
8. In general the presentation of chapter 2 is not clear at all. It is not clear on the basis of what the choices of the various components took place, whether this system was only designed or even actually built. The description of the elements of figure 2 is very poor, therefore completely insufficient, very few features are provided, without any support regarding the choices. It is difficult to understand the innovative contribution of the paper, in the absence of so much information, explanations and fundamental parameters. The text of this chapter should be improved and also a lot to allow an effective understanding of what has been achieved in the paper.
9. About line 92, too little information is provided regarding the laser source. Which parameters influenced the choice? Which laser was chosen? On which grounds?
10. At line 97, there are multiple citations, even 4 together [13-16]. The citations have to be divided, to be placed well in the text, explaining in detail the contribution of each in the context of the topic being discussed.
11. About line 98, too little information is provided regarding optical fiber. Which parameters influenced the choice? Which fiber was chosen? On which grounds?
12. At line 103-104, the authors wrote: “This study uses Ø 1-mm single-mode fiber as the optical transmission component”. On the basis of which reasons was this value chosen and not another?
13. About line 105, too little information is provided regarding the optical device (ROD). Which parameters influenced the choice? Why did they choose that geometry? On which grounds?
14. At line 106-107, the authors wrote: “It comprises a highly reflective mirror, and its function is to integrate a light source and produce a uniform light beam with a specific shape”. What would the specific shape be? Why is it necessary to produce just that shape?
15. About line 116, too little information is provided regarding the liquid lens. Which parameters influenced the choice? Which was chosen in the end? On which grounds?
16. At line 132, it is not clear where the equation of the lens under consideration comes from. An explanation should be given, even in the text, so that the reader could better understand.
17. About figure 3, at line 137, the image should be significantly improved, also providing its dimensions, not specified, and its other characteristics.
18. About figures 7a-7b-7c-7d, at lines 195-198, it is not clear how and with which instrument they were acquired, captured, also setting which parameters. This information must also be specified in the text, providing details on the characterization parameters set.
19. About lines 200-201, the authors wrote: “The freeform lens was made of Kopp Sharp CutRed 2424 glass”. It is not clear at all on the basis of what this choice took place. It is important information for understanding the work. The text must be implemented about this choice.
20. At line 203, the authors speak in first person. It is certainly more appropriate to use the 3rd. I suggest correcting it at all points in the text.
21. About line 213, the authors speak about an experiment, but it is not clear what they are referring to, that is to say something practical or merely theoretical. This is also valid elsewhere in the text. There was no clarity regarding the development of the experimental part. It must be corrected and well specified.
22. The choice of a 6.4 W laser power, at line 214, was not at all motivated in the text.
23. About figures 9 and 10, there are no indications regarding the SW used for the simulations in question ... therefore it is not clear how these graphs were calculated, setting which parameters.
24. About line 234, the authors speak about "simulation results", but it is not clear what they refer to. Was the whole set-up simulated or built or were only the tests simulated? This passage is not at all clear, as is the whole experimental part.
25. In the commens on the results no reference is made to any comparison with any literature work. Is it possible that no other author has already tried to improve the actual optical lighting systems? No results are reported in the literature?
26. At line 271, the authors wrote that the system has a maximum power of 16W, but they did not explain why all the simulations/tests have been completed with a much lower power (6.4W). This information should be implemented also in the text.
27. 23 references are really few. I suggest the authors to increase them, also revising the introduction, which is really poor, and the comments on the results. The increase in references would be a consequence of this improvements.
28. The self-citations [13] and [20] need to be well motivated within the paper. They do not seem so relevant to what is reported in the written part.

Author Response

Please see the file attached.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors provided with satisfactory enough answers to the comments raised and revised their paper accordingly so now the paper is ready to be published.

Author Response

Many thanks for your kind instruction. 

Reviewer 3 Report

The authors in the second version of the work have certainly improved their paper, also providing answers to most of the observations that had been provided them. In the first review of the work, I had in fact pointed out to them a series of shortcomings that made the paper in my opinion weak in terms of introduction, methods and results, mainly due to low scientific solidity and reduced ability to replicate what was produced. I was satisfied with many of the authors' answers, but these were not followed by changes in the paper as requested. Yet they would have clarified much better their paper. Reason for which I have also reported in the second version many of the points of the first, asking to specify what the authors replied to me also in the text. For the rest, the introduction continues to be in my opinion too short and unconvincing; the comparison with the state of the art is too reduced. There are still many shortcomings about experimental parameters and choices, really reduced to the bone, motivating them with the need to reduce the length of the work. It is correct to be concise, but this cannot conflict with the need to ensure good replicability of results and strong scientific solidity. It is preferable that the authors write half a page more than leave many choices in the experimental setting unexplained.

 

Below are detailed all the remaining points to which the authors should carefully address:

1. Question: Although the research of an innovative and cheaper lighting system may be an interesting topic for this journal, the paper is generally very short, lacking many descriptions and information, which are useful and should be present. In fact, the article focuses on many aspects related to optical systems, which have however been taken for granted, minimizing the contribution of information about the development of the experimental set-up and the choices completed.

Answer: Optical design of AFS either with LED or Laser source is so complicated so that it is very difficult to write everything clear in an eight -page papers. We have tried our best to focus on optical design and simulation but I understand that there are various critical points in the future such as opto-mechatronical system, digital signal processing, human vision, over heat problem and etc. Hopefully, I am able to write more engineering reports and patent in the future from different point of views.

It is not possible for Universities to build up an experimental prototype of AFS automotive lighting system because it costs more than 100K US dollars for few samples. Apologize for that but we don’t have sufficient funds to do that experimental work.

Reviewer: I accept the author's answer, but this last point (reported in the last 3 rows) must be better explained not only to the reviewer but also in the paper, underlining that it is a simulation of the system, not actually implemented for reasons about costs related to experimentation. If the paper will be half a page longer, that's not a problem. What is important is to clarify these aspects well.

 

2. Question: More in detail, the abstract is well written, the conclusions are short but clear. While the introduction is really poor and should be improved a lot; there is no analysis of the state of the art regarding the development of innovative lighting systems; no comparison with the papers of other authors was made.

Answer: With regard to development of AFS, there have been so many different models from various automotive companies since 2000’s. Some projects were in success, some were still under improvements but most cases failed. Many papers have been announced in conference and patent but the critical problem is that their information is not very clear. We are not able to check if it is a successful sample or not due to commercial confidential purposes. I knew some famous successful sample such as BMW i8, Audi, Porsche’s PDLS and etc. However, there is no way to find exact information from those great automotive great companies. Compared to German company, it is much difficult to get information from automotive companies in Japan.

Compared to academic papers in science or materials, it is hard to find exact data and information from commercial market. We do apologize for that.

Reviewer: I accept the author's answer, but this last point must be better explained not only to the reviewer but also in the paper, underlining the absence of academic contribution in this field and therefore the difficulty of comparing what was designed and simulated with paper written by other authors and with the projects that the major car companies are studying, due to industrial secrecy.

 

3. Question: The absence of a lot of information and motivations, regarding the choices of tools, components, experimental factors and levels, further complicates the understanding of the experimental part.

Answer: motivations line25-line 41; Tools: line164-168; components: Line 62-63 experimental factors: Please see Fig2; Level: from the point view of optical design, we employ LightTool to optimized all the system with variance of curvature, index, space, abbe number and others. There is initial value and target like Fig8, slightly different from level in Chemistry.

Reviewer: I accept the reviewer's response but this information about the parameters optimization must be better clarified within the text. Otherwise it is difficult in my opinion to guarantee a good replicability of the results, in the absence of parameter values.

 

4. Question: At the same time the characterization methods have been poorly and quickly described, they must certainly be implemented.

Answer: Characterization methods: (Methodology) Line 164 to 210. Due to limitation of words in paper, this is no room for more words, I am afraid. Or please advise which critical issue I shall explain then I would like to add more.

Personally, I think that my description for all the experimental methodology is clear.

Reviewer: all the parameters of the 3D finite element modeling of the innovative lighting system were not provided, except for the number of sources (16) and the power (1W). Furthermore, the whole simulation was carried out with LightTool, as it was explained to me, even the figures were obtained by processing that program. But no parameters were provided, such as spatial or optical resolution for example.

 

5. Question: The comparison with the current 24-W LED system is not clear, as well as the choice to carry out the simulations with a total power of only 6.4 W, instead of the 16 W of the system.

Answer: Laser source is employed in this research due to its compactness, high efficiency and lower potentials of heat effects. In addition, it is easier to make color temperature to be controlled precisely.

All eight laser diodes perform 16W ideally. However, in this simulation, only four laser diodes are working in high beam mode, which is 6.4W only. Please see Line 216-218 

24W LED is a current commercial products available in the market. We did compare its performance test chart with our proposed design. Unfortunately, we are not able to find the optical design and other details of this 24W LED headlighting system so that we have no idea about its light efficiency and others.

What we conclude is that our proposed optical design has better performance compared to samples in current market but we are not able to compare both from the point view of optical design, light efficiency, optimization method and others.

Reviewer: I don't understand why 4 out of 8 lasers in "high beam" mode can deliver 6.4W and not 8W for example. Maybe for the author it is obvious, for a reader not. As well as the motivation behind the choice of this value is difficult to understand. Has it been optimized? If so, based on which considerations? Why was chosen that power and not another? Instead, I accept the author's answer on the choice of the 24-W LED system, but this point needs to be better clarified in the text.

 

6. Question: About the introduction section, this is too short, it needs to be improved. It is not explained why the use of a diode laser source compared to the others, no comparison is made with the state of the art of literature regarding the development of lighting systems, with or without laser sources; no comparison with the contributions of other authors is present. In the context of the use of diode lasers, there is no mention of their application filed, both conventional and innovative, based on the latest literature.

Answer: I found that this proposed optical design is very rare after careful check of many published conference papers. Nothing similar to be found so far so that we are going to apply for US patent in few weeks.

We did find some papers with regard to optical design of AFS automotive lighting system although their design is not similar to us. However, no sufficient information was provided even optical software, optimization method and exact data in papers so that it is very difficult to have them compared with my proposed systems.

Optical design of Automotive lighting system is very popular in Automotive manufactures but all data are confidential. That is the reason why I am not able to do comprehensive comparison with other designs.

Reviewer: I accept the author's answer, but the text must be implemented, explaining all the concepts reported to me. In fact, I believe that the authors should explain the reason of the use of a diode source and not another, as well as they should cite the papers of other authors who have studied the problem of lighting systems. It is not necessary to compare the results of the paper with theirs, but at least mentioning them and giving some brief information about the state of the art of scientific research, even if only academic, in this area is absolutely necessary.

 

7. Question: In general, the presentation of chapter 2 is not clear at all. It is not clear on the basis of what the choices of the various components took place, whether this system was only designed or even actually built. The description of the elements of figure 2 is very poor, therefore completely insufficient, very few features are provided, without any support regarding the choices. It is difficult to understand the innovative contribution of the paper, in the absence of so much information, explanations and fundamental parameters. The text of this chapter should be improved and also a lot to allow an effective understanding of what has been achieved in the paper.

Answer: I understand that it is not easy to fully understand what kind of methodology with regard to chapter two if reader’s background is nothing to do with optical design and engineering. As a professor who works for optical design and engineering for more than twenty years, I believe that it is not difficult for optical engineers or optical designer to realize the concept proposed in this paper because they got used to employ these components for most optical engineering project. I have been lead featured editors of Applied Optics, IEEE and others so that I believe that chapter two is not too bad.

The page of this paper is only eight to nine pages so that it is not possible to describe every component in details or it might be estimated to be a more than twenty to thirty-page paper, which will be not accepted by most Journals. Apologize for that.

Reviewer: I accept the author's response but I still believe that some more data could be provided to ensure the replicability of what was developed and to allow the reader to better understand the reason behind experimental choices. There is hardly any design data in the whole paper. I understand that the authors want to patent the system, but saying that the explanation of the system is clear and simple is far from reality. And it is also true for those who understand engineering, such as myself.

 

8. Question: About line 92, too little information is provided regarding the laser source. Which parameters influenced the choice? Which laser was chosen? On which grounds?

Answer: This laser source was set by LightTool as a light source sample for optimization. There were many different laser models employed in LightTool. LightTool might create those Laser source from current market or after -market samples, which depends on which years they created the files. Apologize for that LightTool never reveal the exact serial number and manufactures of their samples in LightTool or those laser companies might feel unhappy should their model is not in the general light source files of LightTool.

It is not possible for user to find a current market laser source then simply put it into LightTool for optimization. It is not possible because there is no light distribution files available from manufactures. LightTool or other software companies have to measure the laser and its light characteristics by professional spectrophotometer, which is not available in most Universities. Many thanks for your understanding.

It seems to be a 3W white laser diode made by a company in States. I am not 100% confirmed so that I am not able to say what it exactly is in this paper.  

Reviewer: the authors should better clarify this point in the text, even if briefly. At least saying on which basis the choice of the source took place. It really seems to me the minimum contribution necessary in a scientific work.

 

9. Question: About line 98, too little information is provided regarding optical fiber. Which parameters influenced the choice? Which fiber was chosen? On which grounds?

At line 103-104, the authors wrote: “This study uses Ø 1-mm single-mode fiber as the optical transmission component”. On the basis of which reasons was this value chosen and not another?

Answer: same answer such as the choice of laser diode. The fiber employed is the standard setting in LightTool for single mode fiber. We are not able to find a commercial optical fiber then have it set inside LightTool software for optimization due to being lack of many information.

1mm diameter of fiber is feasible choice for laser light source setting in LightTool as our choice. Anyway, this diameter of fiber is not sensible to optimization result so that it is not a parameter for optimization.

Reviewer: the authors should integrate information about the fiber used and the need to optimize the diameter of the fiber in the text.

 

10. Question: About line 105, too little information is provided regarding the optical device (ROD). Which parameters influenced the choice? Why did they choose that geometry? On which grounds?

Answer: ROD is a commonly seen optical component for laser or LED projector due to light distribution. In this paper, ROD is employed due to flat distribution of light intensity. The depth length and width, height might be parameters of optimization according the system of optical design. Much larger diameter will run the risks of spaces and smaller size will eliminate the energy efficiency.

Reviewer: I accept the author's answer, but something must also be added within the text of what has been reported to me in the previous rows.

 

11. Question: About figure 3, at line 137, the image should be significantly improved, also providing its dimensions, not specified, and its other characteristics.

Answer: Has been updated in Line 141, Fig3. This freeform is simply a sample, not the freeform employed in proposed optical design in this paper. The 3D drawing of freeform of optical design proposed in this paper is subject to limited drawing capabilities of LightTool for academic. I believe that LightTool for commercial edition will have great performance; unfortunately, we are not able to afford to that edition.

Reviewer: these explanations should also be added briefly within the text. It is not enough to tell them to the reviewer, since they are also interesting to the reader.

 

12. Question: About figures 7a-7b-7c-7d, at lines 195-198, it is not clear how and with which instrument they were acquired, captured, also setting which parameters. This information must also be specified in the text, providing details on the characterization parameters set.

Answer: that is the output performance of LightTool after long time optimization. Please be kind enough to check Line 182 to Line 194. It is a decent optimization work via LightTool based on ray-tracing analysis.

Reviewer: the answer is convincing, but the authors should better specify what is reported in the answer also within the text.

 

13. Question: About lines 200-201, the authors wrote: “The freeform lens was made of Kopp Sharp CutRed 2424 glass”. It is not clear at all on the basis of what this choice took place. It is important information for understanding the work. The text must be implemented about this choice.

Answer: Freeform must be made either by five-axis processing machine or glass mold processing. As far as I am concerned, this kind of freeform must be made via glass mold processing. Due to effect of complicated annealing process during freeform manufacture, only very few optical glass in the current market is feasible for this project. CutRed 2424 glass is always strongly recommended for this kind of project. 

Reviewer: I accept the explanation, but it must also be reported briefly within the text; it is very useful for the reader's understanding.

 

14. Question: About line 234, the authors speak about "simulation results", but it is not clear what they refer to. Was the whole set-up simulated or built or were only the tests simulated? This passage is not at all clear, as is the whole experimental part.

Answer: This proposed optical design has been set up, calculated as simple ray tracking method, then key-in into LightTool for significant optimization. If the result is not good, repeat the work then restart again for next set up and optimization. Simulation result is selected from LightTool’s best results.

It is not possible for University to build up a protype due to expensive tool expense.

Reviewer: I understand the authors' answer and motivations; the same clarity, however, should be present within the text; the absence of many explanations and clarifications creates the possibility of misinterpretations of what has been studied in an experimental setting in this paper. The authors should implement the text regarding this point.

 

15. Question: 23 references are really few. I suggest the authors to increase them, also revising the introduction, which is really poor, and the comments on the results. The increase in references would be a consequence of this improvements.

Answer: has revised the reference. Honestly, paper related to AFS automotive lighting system is very few compared to scientist papers. Some papers are either not clear or far from the proposed optical design in this paper. Apologize for that.

Reviewer: it does not seem to me that the effort to improve the bibliography was sufficient, quite the opposite. I therefore invite the authors to implement at least the introduction about the state of the art of scientific works in this area, if they fail with the results paragraph (for the reasons they explained to me). By citing the latest works in this field, the bibliography will certainly improve as well, since it is still lacking, compared to the standards of a scientific paper.

 

16. Question: The self-citations [13] and [20] need to be well motivated within the paper. They do not seem so relevant to what is reported in the written part.

Answer: as described above, both papers were developed under the basis of our team’s continuous efforts since 2008. There were some relative papers announced since 2010; similar optical design and methodology.

Reviewer: now I better understand the self-citation [13], while I still don't understand the role of the self-citation [20] within this paper. The explanation about the research team's efforts is not convincing. How does this paper relate to the paper [20], at the point where the self-citation was inserted? Since the question seems to me to be clear, I await a convincing answer.

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 3

Reviewer 3 Report

The authors in the third version have significantly improved their paper, providing much more information on the idea behind the work, on the research project, on the objectives of the same, on the experimental methods followed, on the parameters of the simulation and on the optimization procedures of the same. The introduction has finally been improved, linking this paper better to the state of the art of scientific and industrial research. As a consequence, also the bibliography has been implemented, now more complete and updated.

 

Before accepting the paper, I point out to the authors some remaining points to fix and to which they should carefully respond:

1. Question: The comparison with the current 24-W LED system is not clear, as well as the choice to carry out the simulations with a total power of only 6.4 W, instead of the 16 W of the system.

Answer: Laser source is employed in this research due to its compactness, high efficiency and lower potentials of heat effects. In addition, it is easier to make color temperature to be controlled precisely.

All eight laser diodes perform 16W ideally. However, in this simulation, only four laser diodes are working in high beam mode, which is 6.4W only. Please see Line 216-218.

24W LED is a current commercial products available in the market. We did compare its performance test chart with our proposed design. Unfortunately, we are not able to find the optical design and other details of this 24W LED headlighting system so that we have no idea about its light efficiency and others.

What we conclude is that our proposed optical design has better performance compared to samples in current market but we are not able to compare both from the point view of optical design, light efficiency, optimization method and others.

Reviewer: I don't understand why 4 out of 8 lasers in "high beam" mode can deliver 6.4W and not 8W for example. Maybe for the author it is obvious, for a reader not. As well as the motivation behind the choice of this value is difficult to understand. Has it been optimized? If so, based on which considerations? Why was chosen that power and not another? Instead, I accept the author's answer on the choice of the 24-W LED system, but this point needs to be better clarified in the text.

Round 2 answer: With regard to Laser 8W input/ 6.4W output, apologize for misunderstanding. Please check figure 6 (Line 219) with revised description. Laser diodes 2345678ef is designed and optimized for low beam; abcdefgh is designed and optimized for high beam. Total ideal output either low beam or high beam is 8W. However, light loss due to non-perfection of system light efficiency so that finally there is estimated to be 6.4W available. Please check revised line (274-275).

Reviewer Round 3: I accept the authors' answer but 9 active (instead of 8) diode laser sources for the low beam seem to me too many. Are you sure that both 2 and 8 laser are active? I advise the authors to check this data and, if necessary, also to modify the text.

 

2. Question: In general, the presentation of chapter 2 is not clear at all. It is not clear on the basis of what the choices of the various components took place, whether this system was only designed or even actually built. The description of the elements of figure 2 is very poor, therefore completely insufficient, very few features are provided, without any support regarding the choices. It is difficult to understand the innovative contribution of the paper, in the absence of so much information, explanations and fundamental parameters. The text of this chapter should be improved and also a lot to allow an effective understanding of what has been achieved in the paper.

Answer: I understand that it is not easy to fully understand what kind of methodology with regard to chapter two if reader’s background is nothing to do with optical design and engineering. As a professor who works for optical design and engineering for more than twenty years, I believe that it is not difficult for optical engineers or optical designer to realize the concept proposed in this paper because they got used to employ these components for most optical engineering project. I have been lead featured editors of Applied Optics, IEEE and others so that I believe that chapter two is not too bad.

The page of this paper is only eight to nine pages so that it is not possible to describe every component in details or it might be estimated to be a more than twenty to thirty-page paper, which will be not accepted by most Journals. Apologize for that.

Reviewer: I accept the author's response but I still believe that some more data could be provided to ensure the replicability of what was developed and to allow the reader to better understand the reason behind experimental choices. There is hardly any design data in the whole paper. I understand that the authors want to patent the system, but saying that the explanation of the system is clear and simple is far from reality. And it is also true for those who understand engineering, such as myself.

Round 2 Answer: Many thanks for your kind instruction. Introduction has been revised and more information and description has been added. Please check Line 34-88.

Reviewer Round 3: the authors have implemented this point sufficiently, even if I would have expected even greater efforts in improving the description of the elements of the system of fig. 2.

 

3. Question: About line 98, too little information is provided regarding optical fiber. Which parameters influenced the choice? Which fiber was chosen? On which grounds?

At line 103-104, the authors wrote: “This study uses Ø 1-mm single-mode fiber as the optical transmission component”. On the basis of which reasons was this value chosen and not another?

Answer: same answer such as the choice of laser diode. The fiber employed is the standard setting in LightTool for single mode fiber. We are not able to find a commercial optical fiber then have it set inside LightTool software for optimization due to being lack of many information.

1mm diameter of fiber is feasible choice for laser light source setting in LightTool as our choice. Anyway, this diameter of fiber is not sensible to optimization result so that it is not a parameter for optimization.

Reviewer: the authors should integrate information about the fiber used and the need to optimize the diameter of the fiber in the text.

Round 2 Answer: Please check Line 249-251 added, Fig 7a and Fig 7b. Firstly, we find the right laser diode and its LightTools file from LightTools database. Secondly, we find some fiber files from LightTools database. They are files with all fixed data so that it is not able to be optimized.

If laser diode is determined like Fig 7a, fiber will be selected in order to achieve best performance according to light efficiency basically like Fig 7b.

Generally speaking, it is just a procedure of match of optical components each other’s. There is nothing to do with optimization. Has added the description under Fig 7b as line 249-251.

Reviewer Round 3: the information given in the previous answer is clear and important in understanding the research completed. However, it does not seem to me to have been reported in the text, if not very partially. The authors should therefore add more information about this point to improve the presentation and the clarity of the paper.

 

4. Question: The self-citations [13] and [20] need to be well motivated within the paper. They do not seem so relevant to what is reported in the written part.

Answer: as described above, both papers were developed under the basis of our team’s continuous efforts since 2008. There were some relative papers announced since 2010; similar optical design and methodology.

Reviewer: now I better understand the self-citation [13], while I still don't understand the role of the self-citation [20] within this paper. The explanation about the research team's efforts is not convincing. How does this paper relate to the paper [20], at the point where the self-citation was inserted? Since the question seems to me to be clear, I await a convincing answer.

Round 2 answer: Reference 20 is not my paper so that it is not self-cited. It is from another team in Taichung, Taiwan who works for automotive lighting system as well. That team has their own design for laser automotive lighting system so that I cite their newly-published paper. Please be kind enough to check their paper following:

3. Design, simulation, and fabrication of laser headlight module (LHM)

3.1 Design of laser headlight module (LHM)

Figure 2 shows a schematic diagram of laser headlight module (LHM). This LHM consisted of a blue laser, an aspherical lens, a glass phosphor-converter layer, an Al substrate, and adichroic filter. OSRAM blue lasers with wavelength of 453 nm were used in this work. A blue laser with electrical power of 5 W produced an optical power of 1.2 W and then converted to a white light of 370 lm. The glass-based phosphor was fabricated by lowtemperature of 750°C and then mounted on an Al thermal dissipation substrate………..

The reason I cite their paper is only because I know their design and concept although this paper focus on glass phosphor.

Reviewer Round 3: I accept the authors' response and the presence of this citation in the paper, but I do not understand its positioning in the text, which continues to seem wrong to me. This citation should provide additional information with respect to tab. 1, or "high beam test specifications", but has nothing to do with it. So why was this citation placed there? How does it relate to "test specifications"? I would move it to a part of the paper that is more inherent to the quotation in question.

 

5. Question: I recommend the authors to reorder the references in the text and in the bibliography, depending on the order of insertion in the paper, that is from the abstract to the conclusions.

6. Question: I recommend authors to check again the overall formatting of the text after the changes made in the previous revision stages.

7. Question: the captions of fig. 6-7b-7c-7d-9 are to be better arranged.

 

Author Response

Please see the attachment

Author Response File: Author Response.docx