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The exploration and utilization of marine resources has promoted the rapid development of marine science and technology, and has put forward higher requirements for underwater communication technology. Long distance underwater wireless optical communication (UWOC) requires the selection of light source on the transmitter side. Laser diodes (LDs) have excellent portability and maneuverability, and have been widely used in the UWOC systems. However, their beam quality is not so good and it is difficult to modulate under high power. In recent years, vertical-external-cavity surface-emitting laser (VECSEL) has received much attention due to its high output power and good beam quality. This work is to explore the advantages of using a 490-nm blue VECSEL as a light source in UWOC, and to improve the performance of the UWOC system by the soft-decision pulse-position modulation (PPM). First, the optical power attenuation coefficient of the channel is obtained, and the measured c is about 0.0591 m–1 in a 96-m-long tap channel. Subsequently, soft-decision and hard-decision are simulated and experimentally verified. Both simulations and measurements show that the bit error rate (BER) can be significantly reduced with soft-decision. Afterwards, we improve the system by using the soft-decision algorithm and investigate the communication performance of 64 PPMs at different bandwidths by adjusting the PPM signal rate. Finally, 50 MHz is chosen as a signal rate in the experiment. Then a UWOC system is demonstrated in this work. The transmitter side consists of a 490-nm VECSEL light source with an acousto-optic modulator (AOM). The pseudo-random binary sequence (PRBS) is loaded into the arbitrary waveform generator (AWG) for digital-to-analog conversion after PPM modulation, and the analog signal is sent to the driver of the AOM for acousto-optic modulation of the incident beam. The laser is focused before entering the AOM and then collimated after having exited to reduce its divergence. The modulated laser beam passes through a distance of 96 m in the tank by using multiple mirrors on both sides of the tank. Then, the beam is focused by a lens to the avalanche photodiode (APD) for photoelectric conversion in the end, and the signal is processed by a mixed signal oscilloscope (MSO) after data acquisition. A soft-decision algorithm is introduced to further optimize the performance of the PPM modulation. When the optical signal passes through a relatively long distance of 96 m, the measured BER is as low as 1.9 × 10–5. This indicates that the soft-decision PPM-based 490 nm blue VECSEL UWOC system performs very well.
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Keywords:
- vertical external-cavity surface-emitting lasers /
- pulse-position modulation /
- soft decision algorithms /
- underwater wireless optical communications
[1] Heidemann J, Stojanovic M, Zorzi M 2012 Philos. Trans. R. Soc. London, Ser. A 370 158
[2] Tian P, Liu X, Yi S, Huang Y, Zhang S, Zhou X, Hu L, Zheng L, Liu R 2017 Opt. Express 25 1193
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图 2 蓝光VECSEL的长距离UWOC系统示意图 (a) VECSELS实物图; (b) 光路反射镜; (c) 水箱; (d) 接收装置
Figure 2. Schematic diagram of the long-range UWOC system with blue VECSEL: (a) Physical diagram of VECSEL; (b) optical path reflector; (c) water tank; (d) receiver device.
图 3 VECSEL光源直腔结构图
Figure 3. Structure of straight cavity of VECSEL.
图 4 VECSEL的基频光与倍频光光谱图
Figure 4. Spectrogram of fundamental frequency light and frequency-doubled light of VECSEL.
图 5 VECSEL的$M^2$因子测量图及功率曲线
Figure 5. $M^2$ factor measurement plot and power curve of VECSEL.
图 6 (a) 硬判决原理图; (b) 软判决原理图
Figure 6. (a) Hard judgment schematic; (b) soft judgment schematic.
图 7 曲线拟合96 m处功率衰减系数
Figure 7. Curve fitting power attenuation coefficient at 96 m.
图 8 不同调制阶数的误码率仿真
Figure 8. BER simulation of different modulation orders.
图 9 硬判决与软判决误码率仿真
Figure 9. BER simulation of hard and soft decision.
图 10 基于64 PPM的硬判决与软判决实验误码率比较
Figure 10. BER plot of 64 PPM based hard and soft judgment experiments.
图 11 64 PPM在不同带宽频率下的误码率与接收光功率的关系
Figure 11. BER of 64 PPM at different bandwidth frequencies.
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[1] Heidemann J, Stojanovic M, Zorzi M 2012 Philos. Trans. R. Soc. London, Ser. A 370 158
[2] Tian P, Liu X, Yi S, Huang Y, Zhang S, Zhou X, Hu L, Zheng L, Liu R 2017 Opt. Express 25 1193
Google Scholar
[3] Kaushal H, Kaddoum G 2016 IEEE Access 4 1518
Google Scholar
[4] Saeed N, Celik A, Al-Naffouri T Y, Alouini M S 2019 Ad Hoc Networks 94 101935
Google Scholar
[5] Mobley C D, Gentili B, Gordon H R, Jin Z, Kattawar G W, Morel A, Reinersman P, Stamnes K, Stavn R H 1993 Appl. Opt. 32 7484
Google Scholar
[6] Bricaud A, Babin M, Morel A, Claustre H 1995 J. Geophys. Res. Oceans 100 13321
Google Scholar
[7] 李军, 罗江华, 元秀华 2021 光学学报 41 0706005
Google Scholar
Li J, Luo J H, Yuan X H 2021 Acta Opt. Sin. 41 0706005
Google Scholar
[8] 王宝鹏, 余锦, 王云哲, 孟晶晶, 貊泽强, 王金舵, 代守军, 何建国, 王晓东 2020 激光与光电子学进展 57 230604
Google Scholar
Wang B P, Yu J, Wang Y Z, Meng J J, Mo Ze Qiang, Wang J D, Dai S J, He J G, Wang X D 2020 Laser Optoelectron. P. 57 230604
Google Scholar
[9] Wu Z Y, Liu X Y, Wang J S, Wang J 2018 Opt. Lett. 43 4570
Google Scholar
[10] Ghassemlooy Z, Popoola W, Rajbhandari S 2019 Optical Wireless Communications: System and Channel Modelling with Matlab® (Boca Raton: CRC Press
[11] Fei C, Wang Y, Du J, Chen R, Lv N, Zhang G, Tian J, Hong X, He S 2022 Opt. Express 30 2326
Google Scholar
[12] Qi Z, Wang L, Liu P, Bai M, Yu G, Wang Y 2023 Opt. Express 31 9330
Google Scholar
[13] Wang J, Lu C, Li S, Xu Z 2019 Opt. Express 27 12171
Google Scholar
[14] 黄安, 殷洪玺, 季秀阳, 梁彦军, 文浩, 王建英, 沈众卫 2024 光学学报 44 0606002
Google Scholar
Huang A, Yin H X, Ji X Y, Liang Y J, Wen H, Wang J Y, Shen Z W 2024 Acta Opt. Sin. 44 0606002
Google Scholar
[15] Shen J, Wang J, Yu C, Chen X, Wu J, Zhao M, Qu F, Xu Z, Han J, Xu J 2019 Opt. Commun. 438 78
Google Scholar
[16] Yan Q R, Wang M, Dai W H, Wang Y H 2021 Opt. Commun. 495 127024
Google Scholar
[17] Han X T, Li P, Li G Y, Chang C, Jia S W, Xie Z, Liao P X, Nie W C, Xie X P 2023 Photonics 10 451
Google Scholar
[18] Bossert M, Schulz R, Bitzer S 2022 IEEE Trans. Inf. Theory 68 7107
Google Scholar
[19] Zhang C, Zhang Y, Tong Z, Zou H, Zhang H, Zhang Z, Lin G, Xu J 2022 Opt. Express 30 38663
Google Scholar
[20] Hu S, Mi L, Zhou T, Chen W 2018 Opt. Express 26 21685
Google Scholar
[21] Guina M, Rantamäki A, Härkönen A 2017 J. Phys. D: Appl. Phys. 50 383001
[22] Rahimi-Iman A 2016 J. Opt. 18 093003
Google Scholar
[23] Rudin B, Rutz A, Hoffmann M, Maas D J, Bellancourt A R, Gini E, Südmeyer T, Keller U 2008 Opt. Lett. 33 2719
Google Scholar
[24] Heinen B, Wang T L, Sparenberg M, Weber A, Kunert B, Hader J, Koch S W, Moloney J V, Koch M, Stolz W 2012 Electron. Lett. 48 11
Google Scholar
[25] Yan R, Zhu R, Wu Y, Wang T, Jiang L, Lu H, Song Y, Zhang P 2023 Appl. Phys. Lett. 123 011106
Google Scholar
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