Photonics

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3 pages, 168 KiB

Open AccessEditorial

Special Issue “Photonics for Emerging Applications in Communication and Sensing”

by Guo-Wei Lu, Zhenzhou Cheng and Ting-Hui Xiao

Photonics 2023, 10(7), 738; https://doi.org/10.3390/photonics10070738 - 28 Jun 2023

Viewed by 2773

Abstract

Photonics has emerged as a crucial enabler for various emerging applications in communication and sensing, revolutionizing industries such as data centers, autonomous driving, 5G wireless networks, cloud computing, the IoT, and virtual reality [...] Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

Research

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14 pages, 2713 KiB

Open AccessArticle

Self-Attention Mechanism-Based Multi-Channel QoT Estimation in Optical Networks

by Yuhang Zhou, Xiaoli Huo, Zhiqun Gu, Jiawei Zhang, Yi Ding, Rentao Gu and Yuefeng Ji

Photonics 2023, 10(1), 63; https://doi.org/10.3390/photonics10010063 - 6 Jan 2023

Cited by 1 | Viewed by 1992

Abstract

It is essential to estimate the quality of transmission (QoT) of lightpaths before their establishment for efficient planning and operation of optical networks. Due to the nonlinear effect of fibers, the deployed lightpaths influence the QoT of each other; thus, multi-channel QoT estimation [...] Read more.

It is essential to estimate the quality of transmission (QoT) of lightpaths before their establishment for efficient planning and operation of optical networks. Due to the nonlinear effect of fibers, the deployed lightpaths influence the QoT of each other; thus, multi-channel QoT estimation is necessary, which provides complete QoT information for network optimization. Moreover, the different interfering channels have different effects on the channel under test. However, the existing artificial-neural-network-based multi-channel QoT estimators (ANN-QoT-E) neglect the different effects of the interfering channels in their input layer, which affects their estimation accuracy severely. In this paper, we propose a self-attention mechanism-based multi-channel QoT estimator (SA-QoT-E) to improve the estimation accuracy of the ANN-QoT-E. In the SA-QoT-E, the input features are designed as a sequence of feature vectors of channels that route the same path, and the self-attention mechanism dynamically assigns weights to the feature vectors of interfering channels according to their effects on the channel under test. Moreover, a hyperparameter search method is used to optimize the SA-QoT-E. The simulation results show that, compared with the ANN-QoT-E, our proposed SA-QoT-E achieves higher estimation accuracy, and can be directly applied to the network wavelength expansion scenarios without retraining. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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14 pages, 4807 KiB

Open AccessArticle

Low-Complexity and Highly-Robust Chromatic Dispersion Estimation for Faster-than-Nyquist Coherent Optical Systems

by Tao Yang, Yu Jiang, Yongben Wang, Jialin You, Liqian Wang and Xue Chen

Photonics 2022, 9(9), 657; https://doi.org/10.3390/photonics9090657 - 15 Sep 2022

Cited by 2 | Viewed by 1767

Abstract

Faster-than-Nyquist (FTN) coherent optical transmission technology is considered to be an outstanding solution to achieve higher spectral efficiency (SE), larger capacity, and greater achievable transmission by using advanced modulation formats in concert with highly efficient digital signal processing (DSP) to estimate and compensate [...] Read more.

Faster-than-Nyquist (FTN) coherent optical transmission technology is considered to be an outstanding solution to achieve higher spectral efficiency (SE), larger capacity, and greater achievable transmission by using advanced modulation formats in concert with highly efficient digital signal processing (DSP) to estimate and compensate various impairments. However, severe inter-symbol interference (ISI) caused by tight FTN pulse shaping will lead to intractable chromatic dispersion (CD) estimation problems, as existing conventional methods are completely ineffective or exhibit unaffordable computational complexity (CC). In this paper, we propose a low-complexity and highly robust scheme that could realize accurate and reliable CD estimation (CDE) based on a designed training sequence (TS) in the first stage and an optimized fractional Fourier transform (FrFT) in the second stage. The training sequence with the designed structure helps us to estimate CD roughly but reliably, and it further facilitates the FrFT in the second stage to achieve accurate CDE within a narrowed searching range; it thereby results in very low CC. Comprehensive simulation results of triple-carrier 64-GBaud FTN dual-polarization 16-ary quadrature amplitude modulation (DP-16QAM) systems demonstrate that, with only overall 3% computational complexity compared with conventional blind CDE methods, the proposed scheme exhibits a CDE accuracy better than 65 ps/nm even under an acceleration factor as low as 0.85. In addition, 60-GBaud FTN DP quadrature phase shift keying (DP-QPSK)/16QAM transmission experiments are carried out, and the results show that the CDE error is less than 70 ps/nm. The advantages of the proposed scheme make it a preferable candidate for CDE in practical FTN coherent optical systems. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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11 pages, 4683 KiB

Open AccessArticle

Probabilistically-Shaped DMT for IM-DD Systems with Low-Complexity Fast WHT-Based PDSP

by Yi Liu, Haimiao Long, Ming Chen, Yun Cheng and Taoyun Zhou

Photonics 2022, 9(9), 655; https://doi.org/10.3390/photonics9090655 - 15 Sep 2022

Cited by 1 | Viewed by 1813

Abstract

Transmission capacity and receiver sensitivity of an intensity-modulation direct detection (IM-DD) optical discrete multi-tone (DMT) system can be improved by using the probabilistically shaping (PS) technique. However, different probabilistic distributions will be required owing to the unbalanced signal-to-noise ratio (SNR) among data-carrying subcarriers [...] Read more.

Transmission capacity and receiver sensitivity of an intensity-modulation direct detection (IM-DD) optical discrete multi-tone (DMT) system can be improved by using the probabilistically shaping (PS) technique. However, different probabilistic distributions will be required owing to the unbalanced signal-to-noise ratio (SNR) among data-carrying subcarriers (SCs) induced by the imperfect frequency response of optical/electrical devices, which can increase the implementation complexity of the PS-DMT transceiver. In this work, different signal pre-processing schemes including pre-equalization, Walsh–Hadamard transform (WHT)-based full data-carrying SCs precoding (FDSP) and fast WHT-based partial data-carrying SCs precoding (PDSP) are investigated for SNR equalization in a short-reach PS-DMT transmission system. After transmission over 50 km single-mode fiber, the experimental results indicated that three pre-processed signals have almost the same generalized mutual information (GMI) performance and receiver sensitivity improvements. The proposed fast WHT-based PDSP scheme may be a good option for the implementation of the PS-DMT transmission systems with a large SC SNR fluctuation regarding computational complexity. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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16 pages, 2766 KiB

Open AccessArticle

Optical Labels Enabled Optical Performance Monitoring in WDM Systems

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

Photonics 2022, 9(9), 647; https://doi.org/10.3390/photonics9090647 - 9 Sep 2022

Cited by 5 | Viewed by 2142

Abstract

Optical performance monitoring (OPM), particularly the optical power and optical signal-to-noise ratio (OSNR) of each wavelength channel, are of great importance and significance and need to be implemented to ensure stable and efficient operation/maintenance of wavelength division multiplexing (WDM) networks. However, the critical [...] Read more.

Optical performance monitoring (OPM), particularly the optical power and optical signal-to-noise ratio (OSNR) of each wavelength channel, are of great importance and significance and need to be implemented to ensure stable and efficient operation/maintenance of wavelength division multiplexing (WDM) networks. However, the critical monitoring module of existing solutions generally are too expensive, operationally inconvenient and/or functionally limited to apply over WDM systems with numerous nodes. In this paper, a low-cost and high-efficiency OPM scheme based on differential phase shift keying (DPSK)-modulated digital optical labels is proposed and demonstrated. Each pilot tone is modulated by digital surveillance information and treated as an identity indicator and performance predictor that ties up to each wavelength channel and thereby can monitor the performance of all wavelength channels simultaneously by only one low-bandwidth photoelectric detector (PD) and by designed digital signal processing (DSP) algorithms. Simulation results showed that the maximum errors of channel power monitoring and OSNR estimation were both less than 1 dB after 20-span WDM transmission. In addition, offline experiments were also carried out and further verified the feasibility of our OPM scheme. This confirms that the optical label based OPM has lower cost and higher efficiency and thereby is of great potential for mass deployment in practical WDM systems. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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13 pages, 1935 KiB

Open AccessArticle

Parallel Distribution Matcher Base on CCDM for Probabilistic Amplitude Shaping in Coherent Optical Fiber Communication

by Yao Zhang, Hongxiang Wang, Yuefeng Ji and Yu Zhang

Photonics 2022, 9(9), 604; https://doi.org/10.3390/photonics9090604 - 25 Aug 2022

Cited by 2 | Viewed by 2336

Abstract

As a typical high-order modulation format optimization technology, constellation probability shaping enhances generalized mutual information (GMI) by optimizing the probability distribution of each constellation point of the signal. It can improve the transmission capacity of the same order M Quadrature Amplitude Modulation (QAM) [...] Read more.

As a typical high-order modulation format optimization technology, constellation probability shaping enhances generalized mutual information (GMI) by optimizing the probability distribution of each constellation point of the signal. It can improve the transmission capacity of the same order M Quadrature Amplitude Modulation (QAM) signal under the condition of limited average transmission power, and further narrow the gap with the Shannon limit capacity. The distribution matcher is a key part of constellation probability shaping since it not only ensures the one-to-one mapping of input and output sequences but also realizes the function of probability shaping. The constant composition distribution matcher (CCDM) structure is a widely utilized distribution matcher in the current probability shaping technology. Based on CCDM, a parallel distribution matcher scheme is proposed in this paper. It has a lower rate loss than CCDM for short output lengths (n is less than 100). Block lengths can be reduced by up to 30% with the same rate loss. When the GMI is the same as for the probability shaping (PS) 64QAM signal using CCDM, the OSNR required by the PS-64QAM signal using this scheme can be enhanced by 0.12dB, the block length can be reduced by 40%, and the transmission distance in a standard single-mode fiber can be slightly extended. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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12 pages, 2791 KiB

Open AccessArticle

Numerical Study on a Bound State in the Continuum Assisted Plasmonic Refractive Index Sensor

by Shulin Tang, Chang Chang, Peiji Zhou and Yi Zou

Photonics 2022, 9(4), 224; https://doi.org/10.3390/photonics9040224 - 28 Mar 2022

Cited by 9 | Viewed by 2674

Abstract

Plasmonic sensors have attracted intensive attention due to their high sensitivity. However, due to intrinsic metallic loss, plasmonic sensors usually have a large full width at half maximum (FWHM) that limits the wavelength resolution. In this paper, we numerically investigate and propose a [...] Read more.

Plasmonic sensors have attracted intensive attention due to their high sensitivity. However, due to intrinsic metallic loss, plasmonic sensors usually have a large full width at half maximum (FWHM) that limits the wavelength resolution. In this paper, we numerically investigate and propose a dielectric grating-assisted plasmonic device, leveraging the bound states in the continuum (BIC) effect to suppress the FWHM of the resonance. We initiate quasi-SP-BIC modes at 1559 nm and 1905 nm wavelengths by slightly tilting the incident angle at 2° to break the symmetry, featuring a narrow linewidth of 1.8 nm and 0.18 nm at these two wavelengths, respectively. Refractive index sensing has also been investigated, showing high sensitivity of 938 nm/RIU and figure of merit (FOM) of 521/RIU at 1559 nm and even higher sensitivity of 1264 nm/RIU and FOM of 7022/RIU at 1905 nm. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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12 pages, 2854 KiB

Open AccessFeature PaperArticle

Wavelength-Tunable Optical Two-Tone Signals Generated Using Single Mach-Zehnder Optical Modulator in Single Polarization-Mode Sagnac Interferometer

by Akito Chiba and Yosuke Akamatsu

Photonics 2022, 9(3), 194; https://doi.org/10.3390/photonics9030194 - 17 Mar 2022

Cited by 1 | Viewed by 2547

Abstract

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this [...] Read more.

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this scheme in conjunction with the optimized parameters, more than 20 dB of suppression of undesired optical sidebands have been successfully achieved over a 40 nm wavelength range. This scheme allows us to generate optical two-tone signals at the desired wavelength. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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11 pages, 5143 KiB

Open AccessArticle

Broadband Generation of Polarization-Immune Cloaking via a Hybrid Phase-Change Metasurface

by Ximin Tian, Junwei Xu, Ting-Hui Xiao, Pei Ding, Kun Xu, Yinxiao Du and Zhi-Yuan Li

Photonics 2022, 9(3), 156; https://doi.org/10.3390/photonics9030156 - 4 Mar 2022

Cited by 9 | Viewed by 2425

Abstract

Metasurface-enabled cloaking offers an alternative platform to render scatterers of arbitrary shapes indiscernible. However, specific propagation phases generated by the constituent elements for cloaking are usually valid for a single or few states of polarization (SOP), imposing serious restrictions on their applications in [...] Read more.

Metasurface-enabled cloaking offers an alternative platform to render scatterers of arbitrary shapes indiscernible. However, specific propagation phases generated by the constituent elements for cloaking are usually valid for a single or few states of polarization (SOP), imposing serious restrictions on their applications in broadband and spin-states manipulation. Moreover, the functionality of a conventional metasurface cloak is locked once fabricated due to the absence of active elements. Here, we propose a hybrid phase-change metasurface carpet cloak consisting of coupled phase-shift elements setting on novel phase-change material of Ge₂Sb₂Se₄Te₁ (GSST). By elaborately arranging meta-atoms at either 0 or 90 degrees on the external surface of the hidden targets, the wavefront of its scattered lights can be thoroughly rebuilt for arbitrary SOP exactly as if the incidence is reflected by a flat ground, ensuring the targets’ escape from polarization-scanning detections. Furthermore, the robustness of phase dispersion of meta-atoms endows the metasurface cloak wideband indiscernibility ranging from 7.55 to 8.35 µm and tolerated incident angles at least within ±25°. By reversibly switching of the phase states of Ge₂Sb₂Se₄Te₁, the stealth function of our design can be turned on and off. The generality of our approach will provide a straightforward platform for polarization-immune cloaking, and may find potential applications in various fields such as electromagnetic camouflage and illusion and so forth. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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9 pages, 1874 KiB

Open AccessArticle

Control of Surface Plasmon Resonance in Silver Nanocubes by CEP-Locked Laser Pulse

by Ju Liu and Zhiyuan Li

Photonics 2022, 9(2), 53; https://doi.org/10.3390/photonics9020053 - 19 Jan 2022

Cited by 13 | Viewed by 2589

Abstract

Localized surface plasmon resonance (LSPR) of metal nanoparticles has attracted increasing attention in surface-enhanced Raman scattering, chemical and biological sensing applications. In this article, we calculate the optical extinction spectra of a silver nanocube driven by an ultrashort carrier envelope phase (CEP)-locked laser [...] Read more.

Localized surface plasmon resonance (LSPR) of metal nanoparticles has attracted increasing attention in surface-enhanced Raman scattering, chemical and biological sensing applications. In this article, we calculate the optical extinction spectra of a silver nanocube driven by an ultrashort carrier envelope phase (CEP)-locked laser pulse. Five LSPR modes are clearly excited in the optical spectra. We analyze the physical origin of each mode from the charge distribution on different parts of the cubic particle and the dipole and quadrupole excitation features at the LSPR peaks. The charge distribution follows a simple rule that when the charge concentrates from the face to the corners of the cubic particle, the resonant wavelength red-shifts. Then we modulate the LSPR spectra by changing CEP. The results show that CEP has selective plasmon mode excitation functionality and can act as a novel modulation role on LSPR modes. Our work suggests a novel means to regulate LSPR modes and the corresponding optical properties of metal nanoparticles via various freedoms of controlled optical field, which can be useful for optimized applications in chemical and biological sensors, single molecule detection, and so on. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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10 pages, 2161 KiB

Open AccessArticle

Key Distribution Scheme for Optical Fiber Channel Based on SNR Feature Measurement

by Xiangqing Wang, Jie Zhang, Bo Wang, Kongni Zhu, Haokun Song, Ruixia Li and Fenghui Zhang

Photonics 2021, 8(6), 208; https://doi.org/10.3390/photonics8060208 - 9 Jun 2021

Cited by 3 | Viewed by 2676

Abstract

With the increase in the popularity of cloud computing and big data applications, the amount of sensitive data transmitted through optical networks has increased dramatically. Furthermore, optical transmission systems face various security risks at the physical level. We propose a novel key distribution [...] Read more.

With the increase in the popularity of cloud computing and big data applications, the amount of sensitive data transmitted through optical networks has increased dramatically. Furthermore, optical transmission systems face various security risks at the physical level. We propose a novel key distribution scheme based on signal-to-noise ratio (SNR) measurements to extract the fingerprint of the fiber channel and improve the physical level of security. The SNR varies with time because the fiber channel is affected by many physical characteristics, such as dispersion, polarization, scattering, and amplifier noise. The extracted SNR of the optical fiber channel can be used as the basis of key generation. Alice and Bob can obtain channel characteristics by measuring the SNR of the optical fiber channel and generate the consistent key by quantization coding. The security and consistency of the key are guaranteed by the randomness and reciprocity of the channel. The simulation results show that the key generation rate (KGR) can reach 25 kbps, the key consistency rate (KCR) can reach 98% after key post-processing, and the error probability of Eve’s key is ~50%. In the proposed scheme, the equipment used is simple and compatible with existing optic fiber links. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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11 pages, 2357 KiB

Open AccessCommunication

Dispersion Optimization of Silicon Nitride Waveguides for Efficient Four-Wave Mixing

by Yaping Hong, Yixiao Hong, Jianxun Hong and Guo-Wei Lu

Photonics 2021, 8(5), 161; https://doi.org/10.3390/photonics8050161 - 11 May 2021

Cited by 14 | Viewed by 5767

Abstract

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite [...] Read more.

Silicon nitride waveguides have emerged as an excellent platform for photonic applications, including nonlinear optical signal processing, owing to their relatively high Kerr nonlinearity, negligible two photon absorption, and wide transparent bandwidth. In this paper, we propose an effective approach using 3D finite element method to optimize the dispersion characteristics of silicon nitride waveguides for four-wave mixing (FWM) applications. Numerical studies show that a flat and low dispersion profile can be achieved in a silicon nitride waveguide with the optimized dimensions. Near-zero dispersion of 1.16 ps/km/nm and 0.97 ps/km/nm at a wavelength of 1550 nm are obtained for plasma-enhanced chemical vapor deposition (PECVD) and low-pressure chemical vapor deposition (LPCVD) silicon nitride waveguides, respectively. The fabricated micro-ring resonator with the optimized dimensions exhibits near-zero dispersion of −0.04 to −0.1 ps/m/nm over a wavelength range of 130 nm which agrees with the numerical simulation results. FWM results show that near-zero phase mismatch and high conversion efficiencies larger than −12 dB using a low pump power of 0.5 W in a 13-cm long silicon nitride waveguide are achieved. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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14 pages, 4146 KiB

Open AccessArticle

An Optical Analog-to-Digital Converter with Enhanced ENOB Based on MMI-Based Phase-Shift Quantization

by Yue Liu, Jifang Qiu, Chang Liu, Yan He, Ran Tao and Jian Wu

Photonics 2021, 8(2), 52; https://doi.org/10.3390/photonics8020052 - 14 Feb 2021

Cited by 7 | Viewed by 3436

Abstract

An optical analog-to-digital converter (OADC) scheme with enhanced bit resolution by using a multimode interference (MMI) coupler as optical quantization is proposed. The mathematical simulation model was established to verify the feasibility and to investigate the robustness of the scheme. Simulation results show [...] Read more.

An optical analog-to-digital converter (OADC) scheme with enhanced bit resolution by using a multimode interference (MMI) coupler as optical quantization is proposed. The mathematical simulation model was established to verify the feasibility and to investigate the robustness of the scheme. Simulation results show that 20 quantization levels (corresponding to 4.32 of effective number of bits (ENOB)) are realized by using only 6 channels, which indicates that the scheme requires much fewer quantization channels or modulators to realize the same amount of ENOB. The scheme is robust and potential for integration. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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11 pages, 3673 KiB

Open AccessCommunication

Programmable High-Resolution Spectral Processor in C-band Enabled by Low-Cost Compact Light Paths

by Zichen Liu, Chao Li, Jin Tao and Shaohua Yu

Photonics 2020, 7(4), 127; https://doi.org/10.3390/photonics7040127 - 7 Dec 2020

Cited by 1 | Viewed by 2629

Abstract

The flexible photonics spectral processor (PSP) is an indispensable element for elastic optical transmission networks that adopt wavelength division multiplexing (WDM) technology. The resolution and system cost are two vital metrics when developing a PSP. In this paper, a high-resolution 1 × 6 [...] Read more.

The flexible photonics spectral processor (PSP) is an indispensable element for elastic optical transmission networks that adopt wavelength division multiplexing (WDM) technology. The resolution and system cost are two vital metrics when developing a PSP. In this paper, a high-resolution 1 × 6 programmable PSP is investigated and experimentally demonstrated by using low-cost compact spatial light paths, which is enabled by a 2 K (1080p) liquid crystal on silicon (LCoS) and two cascaded transmission gratings with a 1000 line/mm resolution. For each wavelength channel, the filtering bandwidth and power attenuation can be manipulated independently. The total insertion loss (IL) for six ports is in the range of 5.9~9.4 dB over the full C-band. The achieved 3-dB bandwidths are able to adjust from 6.2 GHz to 5 THz. Furthermore, multiple system experiments utilizing the proposed PSP, such as flexible spectral shaping and optical frequency comb generation, are carried out to validate the feasibility for the WDM systems. Full article

(This article belongs to the Special Issue Photonics for Emerging Applications in Communication and Sensing)

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