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Fiber Optics and Optical Communications|64 Article(s)
Harnessing the power of complex light propagation in multimode fibers for spatially resolved sensing
Darcy L. Smith, Linh V. Nguyen, Mohammad I. Reja, Erik P. Schartner, Heike Ebendorff-Heidepriem, David J. Ottaway, and Stephen C. Warren-Smith
The propagation of coherent light in multimode optical fibers results in a speckled output that is both complex and sensitive to environmental effects. These properties can be a powerful tool for sensing, as small perturbations lead to significant changes in the output of the fiber. However, the mechanism to encode spatially resolved sensing information into the speckle pattern and the ability to extract this information are thus far unclear. In this paper, we demonstrate that spatially dependent mode coupling is crucial to achieving spatially resolved measurements. We leverage machine learning to quantitatively extract the spatially resolved sensing information from three fiber types with dramatically different characteristics and demonstrate that the fiber with the highest degree of spatially dependent mode coupling provides the greatest accuracy. The propagation of coherent light in multimode optical fibers results in a speckled output that is both complex and sensitive to environmental effects. These properties can be a powerful tool for sensing, as small perturbations lead to significant changes in the output of the fiber. However, the mechanism to encode spatially resolved sensing information into the speckle pattern and the ability to extract this information are thus far unclear. In this paper, we demonstrate that spatially dependent mode coupling is crucial to achieving spatially resolved measurements. We leverage machine learning to quantitatively extract the spatially resolved sensing information from three fiber types with dramatically different characteristics and demonstrate that the fiber with the highest degree of spatially dependent mode coupling provides the greatest accuracy.
Photonics Research
- Publication Date: Feb. 08, 2024
- Vol. 12, Issue 3, 411 (2024)
Four-dimensional direct detection receiver enabling Jones-space field recovery with phase and polarization diversity
Qi Wu, Yixiao Zhu, Xueyang Li, Hexun Jiang, Chen Cheng, Mengfan Fu, Yikun Zhang, Qunbi Zhuge, Zhaohui Li, and Weisheng Hu
Data centers, the engines of the global Internet, rely on powerful high-speed optical interconnects. In optical fiber communication, classic direct detection captures only the intensity of the optical field, while the coherent detection counterpart utilizes both phase and polarization diversities at the expense of requiring a narrow-linewidth and high-stability local oscillator (LO). Herein, we propose and demonstrate a four-dimensional Jones-space optical field recovery (4-D JSFR) scheme without an LO. The polarization-diverse full-field receiver structure captures information encoded in the intensity and phase of both polarizations, which can be subsequently extracted digitally. To our knowledge, our proposed receiver achieves the highest electrical spectral efficiency among existing direct detection systems and potentially provides similar electrical spectral efficiency as standard intradyne coherent detection systems. The fully recovered optical field extends the transmission distance beyond the limitations imposed by fiber chromatic dispersion. Moreover, the LO-free advantage makes 4-D JSFR suitable for photonic integration, offering a spectrally efficient and cost-effective solution for massively parallel data center interconnects. Our results may contribute to the ongoing developments in the theory of optical field recovery and the potential design considerations for future high-speed optical transceivers. Data centers, the engines of the global Internet, rely on powerful high-speed optical interconnects. In optical fiber communication, classic direct detection captures only the intensity of the optical field, while the coherent detection counterpart utilizes both phase and polarization diversities at the expense of requiring a narrow-linewidth and high-stability local oscillator (LO). Herein, we propose and demonstrate a four-dimensional Jones-space optical field recovery (4-D JSFR) scheme without an LO. The polarization-diverse full-field receiver structure captures information encoded in the intensity and phase of both polarizations, which can be subsequently extracted digitally. To our knowledge, our proposed receiver achieves the highest electrical spectral efficiency among existing direct detection systems and potentially provides similar electrical spectral efficiency as standard intradyne coherent detection systems. The fully recovered optical field extends the transmission distance beyond the limitations imposed by fiber chromatic dispersion. Moreover, the LO-free advantage makes 4-D JSFR suitable for photonic integration, offering a spectrally efficient and cost-effective solution for massively parallel data center interconnects. Our results may contribute to the ongoing developments in the theory of optical field recovery and the potential design considerations for future high-speed optical transceivers.
Photonics Research
- Publication Date: Feb. 08, 2024
- Vol. 12, Issue 3, 399 (2024)
10 Gb/s classical secure key distribution based on temporal steganography and private chaotic phase scrambling
Zhensen Gao, Zhitao Deng, Lihong Zhang, Xulin Gao, Yuehua An, Anbang Wang, Songnian Fu, Zhaohui Li, Yuncai Wang, and Yuwen Qin
Secure distribution of high-speed digital encryption/decryption keys over a classical fiber channel is strongly pursued for realizing perfect secrecy communication systems. However, it is still challenging to achieve a secret key rate in the order of tens of gigabits per second to be comparable with the bit rate of commercial fiber-optic systems. In this paper, we propose and experimentally demonstrate a novel solution for high-speed secure key distribution based on temporal steganography and private chaotic phase scrambling in the classical physical layer. The encryption key is temporally concealed into the background noise in the time domain and randomly phase scrambled bit-by-bit by a private chaotic signal, which provides two layers of enhanced security to guarantee the privacy of key distribution while providing a high secret key rate. We experimentally achieved a record classical secret key rate of 10 Gb/s with a bit error rate lower than the hard-decision forward error correction (HD-FEC) over a 40 km standard single mode fiber. The proposed solution holds great promise for achieving high-speed key distribution in the classical fiber channel by combining steganographic transmission and chaotic scrambling. Secure distribution of high-speed digital encryption/decryption keys over a classical fiber channel is strongly pursued for realizing perfect secrecy communication systems. However, it is still challenging to achieve a secret key rate in the order of tens of gigabits per second to be comparable with the bit rate of commercial fiber-optic systems. In this paper, we propose and experimentally demonstrate a novel solution for high-speed secure key distribution based on temporal steganography and private chaotic phase scrambling in the classical physical layer. The encryption key is temporally concealed into the background noise in the time domain and randomly phase scrambled bit-by-bit by a private chaotic signal, which provides two layers of enhanced security to guarantee the privacy of key distribution while providing a high secret key rate. We experimentally achieved a record classical secret key rate of 10 Gb/s with a bit error rate lower than the hard-decision forward error correction (HD-FEC) over a 40 km standard single mode fiber. The proposed solution holds great promise for achieving high-speed key distribution in the classical fiber channel by combining steganographic transmission and chaotic scrambling.
Photonics Research
- Publication Date: Feb. 01, 2024
- Vol. 12, Issue 2, 321 (2024)
Impact of doping profiles on the formation of laser-active centers in bismuth-doped GeO2–SiO2 glass fibers
Sergey Alyshev, Alexander Vakhrushev, Aleksandr Khegai, Elena Firstova, Konstantin Riumkin, Mikhail Melkumov, Lyudmila Iskhakova, Andrey Umnikov, and Sergei Firstov
Multi-wavelength-band transmission technology based on the exploitation of the extended spectral region is considered as a potential approach to increase the transmission capacity in the deployed fiber-optic communication infrastructure. The development of optical amplifiers operating in the O-, E-, S-, and U-telecom bands is an extremely important challenge for the successful implementation of this technology. Bismuth-doped fibers are of increasing interest as gain materials, which can be used to provide broadband amplification in the mentioned telecom bands. This is due to the ability of Bi ions incorporated into glass network to form bismuth active centers (BACs) with specific optical properties, which are primarily determined by the glass modifiers. In this work, the impact of the doping profiles of both Ge atoms as glass modifiers and Bi ions on the BACs formation is studied using a series of bismuth-doped fibers fabricated by the modified chemical vapor deposition (MCVD) technique. The Bi-to-BACs conversion efficiency in various spatial regions of the studied samples is presented. It is turned out that for high-Bi concentration regions, the conversion efficiency is very low (less than 10%). In addition, the relationship of the conversion efficiency to the distribution of Bi ions and/or Ge atoms is discussed. Finally, a continuous-wave laser at 1.46 μm with a record slope efficiency of 80% is demonstrated using a Bi-doped fiber with confined doping profile, where the Bi-to-BACs conversion efficiency is 35%. This paper provides new information which might help to facilitate understanding of the features of Bi-doped fibers and their potentially achievable characteristics. Multi-wavelength-band transmission technology based on the exploitation of the extended spectral region is considered as a potential approach to increase the transmission capacity in the deployed fiber-optic communication infrastructure. The development of optical amplifiers operating in the O-, E-, S-, and U-telecom bands is an extremely important challenge for the successful implementation of this technology. Bismuth-doped fibers are of increasing interest as gain materials, which can be used to provide broadband amplification in the mentioned telecom bands. This is due to the ability of Bi ions incorporated into glass network to form bismuth active centers (BACs) with specific optical properties, which are primarily determined by the glass modifiers. In this work, the impact of the doping profiles of both Ge atoms as glass modifiers and Bi ions on the BACs formation is studied using a series of bismuth-doped fibers fabricated by the modified chemical vapor deposition (MCVD) technique. The Bi-to-BACs conversion efficiency in various spatial regions of the studied samples is presented. It is turned out that for high-Bi concentration regions, the conversion efficiency is very low (less than 10%). In addition, the relationship of the conversion efficiency to the distribution of Bi ions and/or Ge atoms is discussed. Finally, a continuous-wave laser at 1.46 μm with a record slope efficiency of 80% is demonstrated using a Bi-doped fiber with confined doping profile, where the Bi-to-BACs conversion efficiency is 35%. This paper provides new information which might help to facilitate understanding of the features of Bi-doped fibers and their potentially achievable characteristics.
Photonics Research
- Publication Date: Feb. 01, 2024
- Vol. 12, Issue 1, 260 (2024)
Accurate mode purity measurement of ring core fibers with large mode numbers from the intensity distribution only
Zekun Shi, Baiwei Mao, Zhi Wang, and Yan-ge Liu
Mode purity measurement is crucial for various applications utilizing few-mode fibers and related devices. In this paper, we propose a simple and accurate method for measuring the mode purity of the output optical field in few-mode ring-core fibers (RCFs). Mode purity can be calculated solely from the outgoing intensity distribution with high precision. This method is theoretically capable of measuring the mode purity of RCFs that support orbital angular momentum modes with an infinite number of azimuthal orders and has strong applicability to various RCF types and image qualities simultaneously. We demonstrate our approach numerically and verify it experimentally in a few-mode RCF supporting four (five) mode groups at 1550 (1310) nm. A polarization test method is proposed to verify its accuracy. We believe that this straightforward and cost-effective characterization method for RCFs and RCF-based devices can promote the development of mode-division multiplexing technology and its applications. Mode purity measurement is crucial for various applications utilizing few-mode fibers and related devices. In this paper, we propose a simple and accurate method for measuring the mode purity of the output optical field in few-mode ring-core fibers (RCFs). Mode purity can be calculated solely from the outgoing intensity distribution with high precision. This method is theoretically capable of measuring the mode purity of RCFs that support orbital angular momentum modes with an infinite number of azimuthal orders and has strong applicability to various RCF types and image qualities simultaneously. We demonstrate our approach numerically and verify it experimentally in a few-mode RCF supporting four (five) mode groups at 1550 (1310) nm. A polarization test method is proposed to verify its accuracy. We believe that this straightforward and cost-effective characterization method for RCFs and RCF-based devices can promote the development of mode-division multiplexing technology and its applications.
Photonics Research
- Publication Date: Aug. 31, 2023
- Vol. 11, Issue 9, 1592 (2023)
300 km ultralong fiber optic DAS system based on optimally designed bidirectional EDFA relays
Cunzheng Fan, Hao Li, Keqing Zhang, Huanhuan Liu, Yixiang Sun, Haoguang Liu, Baoqiang Yan, Zhijun Yan, Deming Liu, Perry Ping Shum, and Qizhen Sun
Optical fiber distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (φ-OTDR) is in great demand in many long-distance application fields, such as railway and pipeline safety monitoring. However, the DAS measurement distance is limited by the transmission loss of optical fiber and ultralow backscattering power. In this paper, a DAS system based on multispan relay amplification is proposed, where the bidirectional erbium-doped fiber amplifier (EDFA) is designed as a relay module to amplify both the probe light and the backscattering light. In the theoretical noise model, the parameters of our system are carefully analyzed and optimized for a longer sensing distance, including the extinction ratio (ER), span number, span length, and gain of erbium-doped fiber amplifiers. The numerical simulation shows that a bidirectional EDFA relay DAS system can detect signals over 2500 km, as long as the span number is set to be more than 100. To verify the effectiveness of the scheme, a six-span coherent-detection-based DAS system with an optimal design was established, where the cascaded acoustic-optic modulators (AOMs) were used for a high ER of 104 dB. The results demonstrate that the signal at the far end of 300.2 km can be detected and recovered, achieving a high signal-to-noise ratio of 59.6 dB and a high strain resolution of 51.8pε/Hz at 50 Hz with a 20 m spatial resolution. This is, to the best of our knowledge, a superior DAS sensing distance with such a high strain resolution. Optical fiber distributed acoustic sensing (DAS) based on phase-sensitive optical time domain reflectometry (φ-OTDR) is in great demand in many long-distance application fields, such as railway and pipeline safety monitoring. However, the DAS measurement distance is limited by the transmission loss of optical fiber and ultralow backscattering power. In this paper, a DAS system based on multispan relay amplification is proposed, where the bidirectional erbium-doped fiber amplifier (EDFA) is designed as a relay module to amplify both the probe light and the backscattering light. In the theoretical noise model, the parameters of our system are carefully analyzed and optimized for a longer sensing distance, including the extinction ratio (ER), span number, span length, and gain of erbium-doped fiber amplifiers. The numerical simulation shows that a bidirectional EDFA relay DAS system can detect signals over 2500 km, as long as the span number is set to be more than 100. To verify the effectiveness of the scheme, a six-span coherent-detection-based DAS system with an optimal design was established, where the cascaded acoustic-optic modulators (AOMs) were used for a high ER of 104 dB. The results demonstrate that the signal at the far end of 300.2 km can be detected and recovered, achieving a high signal-to-noise ratio of 59.6 dB and a high strain resolution of 51.8pε/Hz at 50 Hz with a 20 m spatial resolution. This is, to the best of our knowledge, a superior DAS sensing distance with such a high strain resolution.
Photonics Research
- Publication Date: May. 18, 2023
- Vol. 11, Issue 6, 968 (2023)
Chaos synchronization of semiconductor lasers over 1040-km fiber relay transmission with hybrid amplification
Longsheng Wang, Junli Wang, Yushan Wu, Yuehui Sun, Songsui Li, Lianshan Yan, Yuncai Wang, and Anbang Wang
Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution. Optical chaos communication and key distribution have been extensively demonstrated with high-speed advantage but only within the metropolitan-area network range of which the transmission distance is restricted to around 300 km. For secure-transmission requirement of the backbone fiber link, the critical threshold is to realize long-reach chaos synchronization. Here, we propose and demonstrate a scheme of long-reach chaos synchronization using fiber relay transmission with hybrid amplification of an erbium-doped fiber amplifier (EDFA) and a distributed fiber Raman amplifier (DFRA). Experiments and simulations show that the hybrid amplification extends the chaos-fidelity transmission distance thanks to that the low-noise DFRA suppresses the amplified spontaneous emission noise and self-phase modulation. Optimizations of the hybrid-relay conditions are studied, including launching power, gain ratio of DFRA to EDFA, single-span fiber length, and number of fiber span. A 1040-km chaos synchronization with a synchronization coefficient beyond 0.90 is experimentally achieved, which underlies the backbone network-oriented optical chaos communication and key distribution.
Photonics Research
- Publication Date: May. 16, 2023
- Vol. 11, Issue 6, 953 (2023)
Interband cascade technology for energy-efficient mid-infrared free-space communication
Pierre Didier, Hedwig Knötig, Olivier Spitz, Laurent Cerutti, Anna Lardschneider, Elie Awwad, Daniel Diaz-Thomas, A. N. Baranov, Robert Weih, Johannes Koeth, Benedikt Schwarz, and Frédéric Grillot
Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network. Mid-infrared wavelengths offer numerous advantages for building such a system, spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions. We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18 µm. The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application. Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice. The bandwidth of the system is evaluated to be around 1.5 GHz. It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme. The quality of the transmission is enhanced by conventional pre- and post-processing in order to be compatible with standard error-code correction. Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network. Mid-infrared wavelengths offer numerous advantages for building such a system, spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions. We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18 µm. The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application. Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice. The bandwidth of the system is evaluated to be around 1.5 GHz. It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme. The quality of the transmission is enhanced by conventional pre- and post-processing in order to be compatible with standard error-code correction.
Photonics Research
- Publication Date: Mar. 27, 2023
- Vol. 11, Issue 4, 582 (2023)
Machine learning-based analysis of multiple simultaneous disturbances applied on a transmission-reflection analysis based distributed sensor using a nanoparticle-doped fiber
Letícia Avellar, Anselmo Frizera, Helder Rocha, Mariana Silveira, Camilo Díaz, Wilfried Blanc, Carlos Marques, and Arnaldo Leal-Junior
Photonic technology combined with artificial intelligence plays a key role in the development of the latest smart system trends, integrating cutting-edge technology with machine learning models. This paper proposes a transmission-reflection analysis based system using dielectric nanoparticle-doped fiber combined with artificial intelligence to address one of the major problems in the distributed sensing approach: reducing the cost while maintaining high spatial resolution to close the gap between distributed sensors and the general public. Machine learning-based models are designed to classify the perturbed positions when the same force is used and force regression when different forces are applied on each position. The results show an accuracy of 99.43% in the position classification of multiple disturbances and an rms error of 1.53 N in the force regression, which represents 5% of the force range. In addition, a smart environment using the current system is proposed, which presented 100% accuracy in identifying the positions of different persons in the environment. This smart environment enables remote home care of patients with high reliability, intelligent decision-making, and a predictive capability. Photonic technology combined with artificial intelligence plays a key role in the development of the latest smart system trends, integrating cutting-edge technology with machine learning models. This paper proposes a transmission-reflection analysis based system using dielectric nanoparticle-doped fiber combined with artificial intelligence to address one of the major problems in the distributed sensing approach: reducing the cost while maintaining high spatial resolution to close the gap between distributed sensors and the general public. Machine learning-based models are designed to classify the perturbed positions when the same force is used and force regression when different forces are applied on each position. The results show an accuracy of 99.43% in the position classification of multiple disturbances and an rms error of 1.53 N in the force regression, which represents 5% of the force range. In addition, a smart environment using the current system is proposed, which presented 100% accuracy in identifying the positions of different persons in the environment. This smart environment enables remote home care of patients with high reliability, intelligent decision-making, and a predictive capability.
Photonics Research
- Publication Date: Feb. 09, 2023
- Vol. 11, Issue 3, 364 (2023)
Simultaneously enhancing capacity and security in free-space optical chaotic communication utilizing orbital angular momentum
Yiqun Zhang, Mingfeng Xu, Mingbo Pu, Mengjie Zhou, Jiazheng Ding, Shuangcheng Chen, Kun Qiu, Ning Jiang, and Xiangang Luo
Optical chaotic signals emitted from an external-cavity feedback or injected laser diode enable small-signal information concealment in a noise-like carrier for secure optical communications. Due to the chaotic bandwidth limitation resulting from intrinsic relaxation oscillation frequency of lasers, multiplexing of optical chaotic signal, such as wavelength division multiplexing in fiber, is a typical candidate for high-capacity secure applications. However, to our best knowledge, the utilization of the spatial dimension of optical chaos for free-space secure communication has not yet been reported. Here, we experimentally demonstrate a free-space all-optical chaotic communication system that simultaneously enhances transmission capacity and security by orbital angular momentum (OAM) multiplexing. Optical chaotic signals with two different OAM modes totally carrying 20 Gbps on–off keying signals are secretly transmitted over a 2 m free-space link, where the channel crosstalk of OAM modes is less than -20 dB, with the mode spacing no less than 3. The receiver can extract valid information only when capturing approximately 92.5% of the OAM beam and correctly demodulating the corresponding mode. Bit error rate below the 7% hard-decision forward error correction threshold of 3.8×10-3 can be achieved for the intended recipient. Moreover, a simulated weak turbulence is introduced to comprehensively analyze the influence on the system performance, including channel crosstalk, chaotic synchronization, and transmission performance. Our work may inspire structured light application in optical chaos and pave a new way for developing future high-capacity free-space chaotic secure communication systems. Optical chaotic signals emitted from an external-cavity feedback or injected laser diode enable small-signal information concealment in a noise-like carrier for secure optical communications. Due to the chaotic bandwidth limitation resulting from intrinsic relaxation oscillation frequency of lasers, multiplexing of optical chaotic signal, such as wavelength division multiplexing in fiber, is a typical candidate for high-capacity secure applications. However, to our best knowledge, the utilization of the spatial dimension of optical chaos for free-space secure communication has not yet been reported. Here, we experimentally demonstrate a free-space all-optical chaotic communication system that simultaneously enhances transmission capacity and security by orbital angular momentum (OAM) multiplexing. Optical chaotic signals with two different OAM modes totally carrying 20 Gbps on–off keying signals are secretly transmitted over a 2 m free-space link, where the channel crosstalk of OAM modes is less than -20 dB, with the mode spacing no less than 3. The receiver can extract valid information only when capturing approximately 92.5% of the OAM beam and correctly demodulating the corresponding mode. Bit error rate below the 7% hard-decision forward error correction threshold of 3.8×10-3 can be achieved for the intended recipient. Moreover, a simulated weak turbulence is introduced to comprehensively analyze the influence on the system performance, including channel crosstalk, chaotic synchronization, and transmission performance. Our work may inspire structured light application in optical chaos and pave a new way for developing future high-capacity free-space chaotic secure communication systems.
Photonics Research
- Publication Date: Nov. 30, 2023
- Vol. 11, Issue 12, 2185 (2023)
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