Research

12 pages, 2362 KiB

Open AccessArticle

Laser Remote Sensing of Seismic Wave with Sub-Millimeter Scale Amplitude Based on Doppler Characteristics Extracted from Wavefront Sensor

by Quan Luo, Hongsheng Luo, Guihan Wu, Xiang Ji, Jinshan Su and Wei Jiang

Photonics 2024, 11(3), 204; https://doi.org/10.3390/photonics11030204 - 24 Feb 2024

Viewed by 623

Abstract

Laser remote sensing of earthquake waves has the potential to be used in many applications. This article shows a Doppler model for laser remote sensing of seismic waves based on a wavefront sensor. The longitudinal vibration wave is analyzed using remote sensing, guided [...] Read more.

Laser remote sensing of earthquake waves has the potential to be used in many applications. This article shows a Doppler model for laser remote sensing of seismic waves based on a wavefront sensor. The longitudinal vibration wave is analyzed using remote sensing, guided by theoretical principles. To determine the magnitude of ground vibration, we employ the method of wavefront phase change analysis, utilizing a continuous laser emitting light with a wavelength of 635 nm to illuminate the ground target. The ground vibration amplitude within the range of 0.12–1.18 mm was examined, confirming the reasonableness of the Doppler model. Simultaneously, the experimental findings indicate that the system exhibits a certain enhancement in detection accuracy compared to the conventional laser remote sensing detection technique. This approach can detect vibration signals at a sub-millimeter scale level, with an accuracy of 1% to 2%. The approach can fulfill the requirements for detecting seismic waves with low frequencies. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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13 pages, 1964 KiB

Open AccessArticle

Performance Evaluation of Maximum Ratio Combining Diversity Technology and Traditional System Based on Comprehensive Noise Analysis in Underwater Wireless Optical Communication

by Weidong Zhang, Lulu Wang, Xiaying Wu, Li Fei, Han Peng, Ke Wen and Yanli Zhao

Photonics 2023, 10(12), 1388; https://doi.org/10.3390/photonics10121388 - 18 Dec 2023

Viewed by 761

Abstract

The maximum ratio combining (MRC) diversity technology has shown outstanding performance in overcoming the adverse effects of underwater wireless optical communication (UWOC) systems. However, its actual performance gain will be affected by the detection area and noise, which requires an in-depth analysis. In [...] Read more.

The maximum ratio combining (MRC) diversity technology has shown outstanding performance in overcoming the adverse effects of underwater wireless optical communication (UWOC) systems. However, its actual performance gain will be affected by the detection area and noise, which requires an in-depth analysis. In this paper, on the basis of fully considering the noises in the UWOC system, the performance of the MRC diversity technology is fairly and comprehensively studied by comparing it with two single-input–single-output (SISO) systems using a small aperture detection (SAD) scheme or a large-aperture detection (LAD) scheme through a Monte Carlo simulation and a formula analysis. The results show that the traditional belief that the MRC diversity scheme has consistently outperformed SISO systems may be misleading. When the thermal noise is dominant and the background noise is small, the LAD scheme performs better than the MRC diversity scheme with the same detection area. And in other cases, the MRC diversity scheme with the same detection area is always superior to the SISO systems. The conclusions obtained in this paper have a guiding significance for the practical application of UWOC. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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17 pages, 6018 KiB

Open AccessArticle

Dynamic Secure Key Distribution Based on Dispersion Equalization and Cellular Automata for Optical Transmission

by Jiabin Cui, Wei Kong, Zhaoyang Liu and Yuefeng Ji

Photonics 2023, 10(12), 1308; https://doi.org/10.3390/photonics10121308 - 27 Nov 2023

Viewed by 1151

Abstract

This paper proposes a dynamic secure key distribution scheme based on dispersion equalization and cellular automata (CAs). The scheme effectively eliminates the key inconsistency problem caused by imperfect channel reciprocity, and dynamic key sequences can be conveniently generated with large key space in [...] Read more.

This paper proposes a dynamic secure key distribution scheme based on dispersion equalization and cellular automata (CAs). The scheme effectively eliminates the key inconsistency problem caused by imperfect channel reciprocity, and dynamic key sequences can be conveniently generated with large key space in long-haul optical transmission. In the process of communication, the legitimate parties obtain the secure core parameter from the frequency domain equalizer algorithm, and a final key sequence is generated through CA iterations on the basis of the core parameter. The randomness and reciprocity characteristics of the channel ensure the security and uniqueness of the core parameter and final key sequence. With 10G Baud 16 quadrature amplitude modulation over 400 km standard single-mode fiber transmission, the proposed scheme is verified with a free key error rate and an unlimited key generation rate. The security robustness of this scheme was theoretically analyzed and verified by sweeping the eavesdropper’s tapping position and improving CA operation processing. The proposed key distribution scheme is compatible with the existing transmission system for different signal modulation formats. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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10 pages, 4178 KiB

Open AccessCommunication

Look-Up-Table-Based Direct-Detection-Faster-Than-Nyquist-Algorithm-Enabled IM/DD Transmission with Severe Bandwidth Limitation

by Xiaoying Zhang, Jiahao Huo, Shaonan Liu, Wei Huangfu and Keping Long

Photonics 2023, 10(11), 1222; https://doi.org/10.3390/photonics10111222 - 31 Oct 2023

Viewed by 735

Abstract

The emergence of new applications is driving a dramatic growth in the capacity of data center interconnects. Intensity modulation and direct detection (IM/DD) has the characteristics of low cost, low power consumption and a small footprint. Industry and academia have conducted much research [...] Read more.

The emergence of new applications is driving a dramatic growth in the capacity of data center interconnects. Intensity modulation and direct detection (IM/DD) has the characteristics of low cost, low power consumption and a small footprint. Industry and academia have conducted much research on IM/DD systems as a cost-effective solution. However, optical/electronic bandwidth and fiber dispersion are the restricting factors for the improvement of transmission capacity. Pattern-dependent distortion is an important aspect that affects system performance. In this paper, we propose a look-up table (LUT)-based direct-detection-faster-than-Nyquist (DDFTN) algorithm to compensate for pattern-dependent distortion. The performances of feedforward-equalization (FFE) only, the original DDFTN, least-squares (LS)-based DDFTN, and LUT-based DDFTN algorithms in IM/DD-based 112/140 Gbit/s four-level pulse-amplitude modulation (PAM-4) signal transmission were evaluated. The experimental results indicate that LUT-based DDFTN performs better with low computational complexity. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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15 pages, 4646 KiB

Open AccessArticle

Optimization Method for Center Frequency Accuracy of High-Channel-Count Arrayed Waveguide Grating in Dense Wavelength Division Multiplexing Systems

by Xin Tang, Yu Zheng, Jianzhe Liu and Ji-an Duan

Photonics 2023, 10(11), 1178; https://doi.org/10.3390/photonics10111178 - 24 Oct 2023

Cited by 1 | Viewed by 916

Abstract

The arrayed waveguide grating (AWG) is an essential component in dense wavelength division multiplexing (DWDM) systems. With advancements in optical communication technology, the number of AWG output channels has rapidly increased. However, achieving high center frequency accuracy (CFA) for these channels has become [...] Read more.

The arrayed waveguide grating (AWG) is an essential component in dense wavelength division multiplexing (DWDM) systems. With advancements in optical communication technology, the number of AWG output channels has rapidly increased. However, achieving high center frequency accuracy (CFA) for these channels has become a significant challenge. This paper presents a design and optimization approach for a high-channel-count AWG based on the silica platform and the finite difference beam propagation method (FD-BPM). The causes of center frequency deviation are analyzed, and an optimization method is proposed to adjust the constraint relationship and geometric position of the output waveguides in order to improve CFA. Simulation results demonstrate the excellent optical performance of the designed AWG, achieving a CFA of up to 0.04 times the output channel frequency spacing. The insertion loss, insertion loss uniformity, and adjacent output channel crosstalk are simulated as 1.51 dB, 0.38 dB, and 23.81 dB, respectively. The optimized CFA could compensate for center frequency deviations caused by manufacturing errors and temperature fluctuations. The findings of this research hold potential for extending the optimization to other material platforms and contributing to the development of DWDM systems in the field of optical communication. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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14 pages, 3244 KiB

Open AccessArticle

Frequency-Shift Monitoring of Optical Filter Based on Optical Labels over FTN-WDM Transmission Systems

by Kaixuan Li, Tao Yang, Xue Wang, Sheping Shi, Liqian Wang and Xue Chen

Photonics 2023, 10(10), 1166; https://doi.org/10.3390/photonics10101166 - 18 Oct 2023

Viewed by 897

Abstract

Optical network monitoring and soft failure identification such as optical filter shifting and filter tightening are increasingly significant for the complex and dynamic optical networks of the future. Center frequency shift of optical filtering devices in optical networks has a serious impact on [...] Read more.

Optical network monitoring and soft failure identification such as optical filter shifting and filter tightening are increasingly significant for the complex and dynamic optical networks of the future. Center frequency shift of optical filtering devices in optical networks has a serious impact on the performance of multi-span transmission, especially in high spectrum efficiency faster-than-Nyquist (FTN) transmission systems with various optical switching and add/drop nodes. Existing monitoring schemes generally have the problems of high cost, high complexity, and inability to realize multi-channel online monitoring, which makes it difficult for them to be applied in a wavelength division multiplexing (WDM) system with numerous nodes. In this paper, a monitoring scheme of frequency shift of optical filtering devices based on optical label (OL) is proposed and demonstrated. The signal spectrum of each channel is intentionally divided into many sub-bands with corresponding optical labels loading. The characteristics of spectrum power changing caused by frequency shift can be reflected on labels power changing of each sub-band, which are used to monitor and estimate the value of frequency shift via DSP algorithm. Simulation results show that the monitoring errors of frequency shift can be kept reasonably below 0.5 GHz after 10-span WDM transmission in FTN polarization multiplexing m-ary quadrature amplitude modulation (PM-mQAM) systems. In addition, 250 km fiber transmission experiments are also carried out, and similar results are obtained, which further verify the feasibility of our proposed scheme. The characteristics of low cost, high reliability, and efficiency make it a better candidate for practical application in future FTN-WDM networks. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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15 pages, 4860 KiB

Open AccessEditor’s ChoiceArticle

Gyrotropic Crystals as a Basis for Creation of Helical Polychromatic Singular Beams

by Yuriy Egorov and Alexander Rubass

Photonics 2023, 10(9), 1044; https://doi.org/10.3390/photonics10091044 - 14 Sep 2023

Viewed by 880

Abstract

In this work, studies are carried out in the field of optical singular beams that have passed through gyrotropic crystals. We have experimentally shown that singular beams with a helical intensity distribution are formed when passing through a system of two gyrotropic crystals [...] Read more.

In this work, studies are carried out in the field of optical singular beams that have passed through gyrotropic crystals. We have experimentally shown that singular beams with a helical intensity distribution are formed when passing through a system of two gyrotropic crystals with opposite values of the gyration coefficient. It is shown that the system is capable of generating optical vortices with a double topological charge in one of the components of circular polarization when light propagates through two gyrotropic crystals. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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12 pages, 3069 KiB

Open AccessArticle

Kalman Filter Based Pseudo-Code Ranging and Carrier Phase Measurement for Fiber Optical Time Transfer Method

by Hongyan Sun, Hang Gong and Jing Peng

Photonics 2023, 10(9), 981; https://doi.org/10.3390/photonics10090981 - 28 Aug 2023

Viewed by 742

Abstract

In the optical fiber time transfer system, fiber optic time transfer is limited by the pulse signal time delay measurement precision, and cannot benefit from a higher precision of the carrier phase information. Its transfer precision compared to the frequency transfer exists in [...] Read more.

In the optical fiber time transfer system, fiber optic time transfer is limited by the pulse signal time delay measurement precision, and cannot benefit from a higher precision of the carrier phase information. Its transfer precision compared to the frequency transfer exists in a larger gap transfer. This paper proposes a time delay measurement method based on carrier phase and pseudo-code ranging for optical time transfer. The time signal is modulated with pseudo-random code and carrier at the transmitter, and the time delay is measured at the receiver by the methods of pseudo-code ranging and carrier phase measurement. The time transfer is achieved by eliminating the transmission link delay through a two-way method. The first-order difference value of the carrier phase measurement and the pseudo-code ranging measurement are used as the observation quantities, and they are fused through a Kalman filtering method to finally obtain the high-precision time difference measurement. We validate the theory on the common-clock experimental platform over a 50 km fiber link, The time transfer stabilities of the systems are

5.2254 \times 10^{- 14}

/s and

2.146 \times 10^{- 16}

/

10^{4}

s (modified Allan deviation),

3.0169 \times 10^{- 14}

/s and

1.2392 \times 10^{- 12}

/

10^{4}

s (time deviation). The standard deviation of the time transfer system after fusion can reach 2.4255 ps. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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14 pages, 4656 KiB

Open AccessArticle

Fine Structure of Optical Vortices in Linearly Polarized Laguerre–Gaussian Beams in Oblique Beams Propagating a Uniaxial Crystal

by Yuriy Egorov and Alexander Rubass

Photonics 2023, 10(6), 684; https://doi.org/10.3390/photonics10060684 - 13 Jun 2023

Cited by 1 | Viewed by 861

Abstract

Traditional ideas about linearly polarized paraxial beam propagation along the optical axis of a uniaxial crystal suggest that at the crystal exit face, after propagation through the polarizer, the beam will form an intensity distribution in the form of a conoscopic pattern. Any [...] Read more.

Traditional ideas about linearly polarized paraxial beam propagation along the optical axis of a uniaxial crystal suggest that at the crystal exit face, after propagation through the polarizer, the beam will form an intensity distribution in the form of a conoscopic pattern. Any violation of axial propagation was considered as a perturbation of the conoscopic pattern and was not taken into account. Nevertheless, this process opens up a wide variety of transformations of polarization singularities caused by weak perturbations. In this article, the behavior of linearly polarized low-order Laguerre–Gauss beams in a uniaxial crystal is considered. The existence of a fine structure of radiation on the output face of a uniaxial crystal and the dependence of this fine structure on the parameters of the crystal and the beam are shown. Full article

(This article belongs to the Special Issue Optical Communication, Sensing and Network)

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