| 1. |
- Du, Ji, et al.
(author)
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A Comprehensive Performance Comparison of DFT-S DMT and QAM-DMT in UOWC System in Different Water Environments
- 2021
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In: IEEE Photonics Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1943-0655. ; 13:1
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Journal article (peer-reviewed)abstract
- In this paper, we experimentally demonstrate a 450-nm laser underwater optical wireless transmission system, in which a comprehensive investigation is made to show the significant performance improvement of the discrete Fourier transform spread discrete multi-tone (DFT-S DMT) as compared to the conventional quadrature amplitude modulation discrete multi-tone (QAM-DMT) modulation. DFT-S DMT outperforms QAM-DMT in terms of bit error rate (BER) performance due to low peak-to-average-power ratio (PAPR) and capability of counteracting high frequency fading in a band-limited underwater optical wireless communication (UOWC) system. In order to avoid signal-to-noise-ratio (SNR) degradation at fringe subcarriers, several zeros are padded at the edge of each block before DFT-S operation. The experimental results show the superiority of DFT-S DMT compared with QAM-DMT in different water environments, including turbidities, bubbles, and water flow. Data rates of similar to 16.16 Gbps and similar to 13.96 Gbps at a BER of 3.8 x 10(-3) are achieved by 16-QAM DFT-S DMT and 16-QAM-DMT over a 5-m water channel, respectively, which indicates that capacity enhancement of similar to 2.2 Gbps is obtained by the DFT-S DMT. Meanwhile, over 3-dB receiver sensitivity improvement can always be achieved by the DFT-S DMT at the tested underwater transmission distances. Combined with adaptive bit-power loading, 20.04 Gbps over a 5-m "clear ocean" channel transmission with a single laser diode (LD) is demonstrated. For a 35-m water link, the distance-data rate product reaches 498.4 Gbps*m. To the best of our knowledge, both the data rate and distance-data rate product are the largest among all the results reported for a single visible LD. Aimed at high-speed deep ocean applications, the studies are promising for future UOWC research.
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| 2. |
- Fei, Chao, et al.
(author)
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100-m/3-Gbps underwater wireless optical transmission using a wideband photomultiplier tube (PMT)
- 2022
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In: Optics Express. - : The Optical Society. - 1094-4087. ; 30:2, s. 2326-2337
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Journal article (peer-reviewed)abstract
- In this paper, a wideband photomultiplier tube (PMT)-based underwater wireless optical communication (UWOC) system is proposed and a comprehensive experimental study of the proposed PMT-based UWOC system is conducted, in which the transmission distance, data rate, and attenuation length (AL) is pushed to 100.6 meters, 3 Gbps, and 6.62, respectively. The receiver sensitivity at 100.6-meter underwater transmission is as low as -40 dBm for the 1.5-Gbps on-off keying (00K) modulation signal. To the best of our knowledge, this is the first Gbps-class UWOC experimental demonstration in >100-meter transmission that has ever been reported. To further minimize the complexity of channel equalization, a sparsity-aware equalizer with orthogonal matching pursuit is adopted to reduce the number of the filter coefficients by more than 50% while keeping slight performance penalty. Furthermore, the performance of the proposed PMT-based LIWOC system in different turbidity waters is investigated, which shows the robustness of the proposed scheme. Thanks to the great sensitivity (approaching the quantum limit) and a relatively larger effective area, benefits of misalignment tolerance contributed by the PMT is verified through a proof-of-concept LIWOC experiment.
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| 3. |
- Wu, Shengnan, et al.
(author)
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Optical Fiber Fabry-Perot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method
- 2023
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In: Sensors. - : MDPI AG. - 1424-8220. ; 23:6, s. 3198-
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Journal article (peer-reviewed)abstract
- In this paper, an optical fiber Fabry-Perot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side illuminated by another single mode fiber (SMF). The CF acts as a naturally microfluidic channel, which can be served as a potential microfluidic solution concentration sensor. Moreover, the FP cavity formed by silica wall is insensitive to ambient solution refractive index but sensitive to the temperature. Thus, the HFP sensor can simultaneously measure microfluidic refractive index (RI) and temperature by cross-sensitivity matrix method. Three sensors with different inner air hole diameters were selected to fabricate and characterize the sensing performance. The interference spectra corresponding to each cavity length can be separated from each amplitude peak in the FFT spectra with a proper bandpass filter. Experimental results indicate that the proposed sensor with excellent sensing performance of temperature compensation is low-cost and easy to build, which is suitable for in situ monitoring and high-precision sensing of drug concentration and the optical constants of micro-specimens in the biomedical and biochemical fields.
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