Beyond 100 m Range Mini-LED-Based Visible Light Communication System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a high-performance visible light communication (VLC) system based on mini-LEDs, addressing the challenge of inefficient light collimation due to mini-LEDs' wide emission angle.

Through optimizing a specially designed optical structure, reflective cup， the system achieves approximately 86% light collection efficiency at a 10-meter simulation distance. Experimental results demonstrate error free communication at 190 Mbps over 100 meters and 210 Mbps over 90 meters. With a minimum bit error rate (BER) of 6.67×10ି଺ at the optimal operating point and a -3dB bandwidth of 96.5 MHz, the system significantly outperforms existing short-range mini-LED VLC systems.

Its advantages of high efficiency, low cost, and simple structure provide an excellent solution for long-distance communication scenarios such as underwater wireless optical communication (UWOC), showcasing superior performance in extending communication range and data transmission capabilities. However, the manuscript has some questions, as detailed in the following.

1. Theoretical designs often assume ideal conditions, but practical factors like material properties and fabrication precision can significantly impact performance. The reflective cup’s curve is derived as y=±√2𝑥 ൅ 1. How were real-world factors like material reflectivity (e.g., surface roughness, coating losses) incorporated into the theoretical model.

2. Although the paper mentions the applicability of UWOC and highlights its implications for underwater environments, the experiments were carried out in air. How was the performance of the reflective cup modeled considering seawater's absorption and scattering.

3. The current setup uses a single mini-LED. Would integrating multiple mini-LEDs into an array with optimized reflective cups improve collective collimation efficiency and power output for even longer distances or higher data rates?

Comments for author File: Comments.pdf

Author Response

Comment 1: Theoretical designs often assume ideal conditions, but practical factors like material properties and fabrication precision can significantly impact performance. The reflective cup’s curve is derived as y=±√2x+1 . How were real-world factors like material reflectivity (e.g., surface roughness, coating losses) incorporated into the theoretical model.

Response 1:

Thank you very much for raising this crucial point. Your inquiry about the incorporation of real-world factors into the theoretical model is highly relevant and insightful, as it precisely addresses the key challenge of bridging the gap between theory and practice.

The reflective cup's curve y=±√2x+1  was indeed derived based on the ideal assumption of perfect specular reflection. However, during the model-building process, we were well-aware of the necessity to account for practical factors.

For material reflectivity, we adopted a two-pronged approach of computational simulations and experimental validation. In both the TracePro simulations and the actual fabrication process, we utilized aluminum with a high-reflectivity coating, which has a measured reflectivity of 95% in the 450–550 nm range. To incorporate the effect of surface roughness, we modeled it as a Lambertian scatter with 5% diffuse reflection in our simulations.

The results showed that, compared to the ideal conditions, the efficiency loss due to these real-world factors was only 2%, which is negligible from an engineering perspective. This indicates that, while we carefully considered these practical factors in the model, their impact on the overall performance of the reflective cup, particularly on collimation efficiency and divergence angle, is minimal and well within the acceptable tolerance range.

Comment 2: Although the paper mentions the applicability of UWOC and highlights its implications for underwater environments, the experiments were carried out in air. How was the performance of the reflective cup modeled considering seawater's absorption and scattering.

Response 2:

We greatly appreciate your insightful comments. Although the current experiments were conducted in air, we have incorporated the absorption and scattering coefficients of seawater in the 450–550 nm band into our simulation framework to evaluate the transmission performance of the reflective cup's collimated beam in seawater.

In terms of system design, we have implemented multiple strategies to address underwater transmission challenges. The reflective cup generates a beam with a divergence angle of approximately 25°, significantly reducing the impact of scattering. We have selected a 450 nm mini-LED, which lies within the optimal transmission window of seawater, minimizing absorption losses.

This study serves as proof-of-concept. In future work, we will conduct underwater tests in a tank with controlled turbidity levels to validate the bit error rate and optical link margin predicted by our simulation models. Thank you for your feedback, which we will incorporate to enhance the manuscript.

Comment 3: The current setup uses a single mini-LED. Would integrating multiple mini-LEDs into an array with optimized reflective cups improve collective collimation efficiency and power output for even longer distances or higher data rates?

Response 3:

Thank you for raising this practically significant question. Your insight touches on an important aspect of scalability, which is essential for the real-world deployment of VLC or UWOC systems.

We deliberately employed a single mini-LED in this study to isolate and evaluate the performance contribution of the reflective cup without introducing the additional complexity of multi-source alignment or interference. This approach enabled us to clearly demonstrate the effectiveness of the collimation strategy and its impact on long-distance transmission.

We fully agree that scaling up the system through a mini-LED array is both feasible and advantageous. The benefits of such an array configuration include higher optical power density, increased data throughput and so on. Therefore, your suggestion has reinforced the importance of presenting this scalability discussion more prominently.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This work proposes a 100-m VLC system using mini-LEDs. Several questions need to be addressed:
1. Why use mini-LEDs? It is claimed that mini-LEDs are a good choice for UWOC. However, this work focuses on an indoor scenario, not an underwater one. If the conclusion is intended to have reference value for UWOC, experiments or simulations should be conducted under UWOC conditions.
2. Please list existing works on mini-LED-based VLC systems in a table, including key parameters, and provide a comparison to highlight the advantages of this work.
3. Why is the reflective cup specifically designed for mini-LEDs? Has the similar reflective cup design been applied to VLC systems using conventional LEDs to extend the communication distance?
4. In the simulation, how is the "efficiency of approximately 86%" defined and calculated?
5. Are there any comparative experiments demonstrating that the reflective cup design is superior to traditional lens-based designs in terms of cost, size, and optical efficiency? In what scenarios is the reflective cup preferable or inferior?
6. Has the design of the reflective cup been optimized? If so, please provide a comparison of system performance (e.g., SNR) before and after optimization.

Author Response

Comment 1: Why use mini-LEDs? It is claimed that mini-LEDs are a good choice for UWOC. However, this work focuses on an indoor scenario, not an underwater one. If the conclusion is intended to have reference value for UWOC, experiments or simulations should be conducted under UWOC conditions.

Response 1:

Thank you for this insightful comment. Your observation regarding the relevance of our conclusions to UWOC scenarios is highly valuable. Indeed, the current study was conducted in an indoor free-space environment. However, the choice of mini-LEDs is based on their intrinsic advantages that are particularly beneficial for UWOC systems.

Mini-LEDs exhibit significantly higher modulation bandwidths compared to conventional LEDs, which is crucial for achieving high-speed data transmission. In UWOC environments where optical signal attenuation is substantial, the ability to modulate at high frequencies directly contributes to maintaining data integrity over longer distances. This characteristic makes mini-LEDs a strong candidate for future UWOC applications.

Furthermore, although our work does not directly simulate UWOC conditions, we emphasize in the introduction and conclusion that the reflective cup design and its demonstrated benefits—such as high optical efficiency, low cost, and simple structure—provide a valuable reference for the design of UWOC systems. These features are particularly suited to address the challenge of limited communication range in underwater scenarios.

Our results offer a foundational approach and feasible engineering solution that can be adapted and validated in future UWOC-specific environments.

Comment 2: Please list existing works on mini-LED-based VLC systems in a table, including key parameters, and provide a comparison to highlight the advantages of this work.

Response 2:

We appreciate this constructive suggestion. Comparing our work with existing literature is indeed crucial to positioning our contribution within the current research landscape.

In the revised manuscript, we have added two recent references, and listed a comparative table summarizing representative mini-LED-based VLC/UWOC systems. Key performance parameters such as communication distance, data rate, light source configuration, modulation scheme and channel are included. The comparison reveals that most prior works achieved high data rates but over relatively short distances (typically 1–2 m underwater or a few meters in air)…

In contrast, our work achieves error-free communication at a data rate of 190 Mbps over 100 m—a distance not previously reported in mini-LED-based systems. This demonstrates a significant advancement in communication range while maintaining a competitive data rate, thereby highlighting the practical potential of our system design in scenarios demanding long-range and stable data transmission.

Comment 3: Why is the reflective cup specifically designed for mini-LEDs? Has a similar reflective cup design been applied to VLC systems using conventional LEDs to extend the communication distance?

Response 3:

Thank you for this thoughtful question. The design of the reflective cup in our system was specifically tailored to address a key limitation of mini-LEDs: their wide emission angle.

Unlike laser diodes or narrow-beam LEDs, mini-LEDs emit light over a large solid angle, making it difficult for conventional lenses to efficiently collect and collimate this light. Traditional lenses often fail to utilize light emitted at high divergence angles, leading to substantial optical loss and reduced communication efficiency, especially over long distances.

Our reflective cup design overcomes this challenge by redirecting and collimating a broader portion of the emitted light, thus enhancing the usable optical power without the need for complex alignment. While similar reflector structures have been occasionally used with standard LEDs in other optical systems, their application in long-range VLC—particularly in conjunction with mini-LEDs—has not been thoroughly explored or optimized.

This work pioneers a practical, scalable design that simplifies the optical setup while significantly improving the transmission efficiency.

Comment 4: In the simulation, how is the “efficiency of approximately 86%” defined and calculated?

Response 4:

We appreciate your interest in the simulation methodology. In response to your suggestion, we have revised the manuscript. The modifications made to the manuscript have been clearly highlighted to facilitate your review. The efficiency figure cited in our paper refers to the optical collection efficiency of the reflective cup system, calculated under ideal simulation conditions.

Specifically, the total irradiance emitted by the point-source LED model was set to 1 W, and the irradiance received by a planar surface that simulates the light receiving side of a lens with a diameter of 10 cm and positioned 10 m from the LED light source was measured to be approximately 0.86 W. Hence, the efficiency is calculated as:

Efficiency=0.86W÷1W×100% = 86%

This result underscores the highlight utilization enabled by our reflective cup design and validates its role in extending the effective transmission range of the system.

Comment 5: Are there any comparative experiments demonstrating that the reflective cup design is superior to traditional lens-based designs in terms of cost, size, and optical efficiency? In what scenarios is the reflective cup preferable or inferior?

Response 5:

Thank you for raising this important point. While we have not conducted additional experiments directly comparing the reflective cup with traditional lens systems, we provide a theoretical and practical comparison based on existing knowledge and design constraints.

As we know, in short-distance or highly focused applications where space is constrained and beam divergence is minimal, lens-based systems may still offer superior collimation precision.

However, in long-distance communication scenarios or when the distance is adjustable, lenses require precise focal alignment, which becomes increasingly challenging and costly with increasing divergence angle—as is typical with mini-LEDs. Additionally, large lenses that would be needed to capture wide-angle emissions are expensive and bulky.

In contrast, our reflective cup is simple to manufacture, compact in size, and does not require meticulous alignment. It collects and redirects wide-angle light effectively, making it especially advantageous in long-range and low-cost deployment scenarios.

Comment 6: Has the design of the reflective cup been optimized? If so, please provide a comparison of system performance (e.g., SNR) before and after optimization.

Response 6:

Thank you for this valuable question. Yes, the design of the reflective cup underwent optimization in terms of both geometric and reflective parameters.

Specifically, we optimized the shape of the reflection curve using differential equations solved in MATLAB to ensure that most of the light is reflected in a parallel direction. Moreover, we fine-tuned the height-to-diameter (H/D) ratio of the cup, stabilizing it around 2, which provided the best trade-off between optical collimation and physical size.

While we did not conduct a direct before-and-after experimental comparison (e.g., in terms of SNR), our simulation and theoretical analyses confirm that the optimized cup results in improved light directionality and higher irradiance at the receiver. The 86% efficiency achieved in simulation is a direct result of these optimization steps.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have answered the questions well.