Optical Fiber Technology最新文献

Randomly-coupled unit grouping multi-core fiber (RC-UG-MCF) is a new fiber structure that combines weakly and strongly coupled multi-core fiber technologies. Compared to the weakly-coupled MCF with a large cladding size, the RC-UG-MCF can shrink the cladding size by grouping the cores. On the other hand, the RC-UG-MCF only maintains a few cores in the strongly-coupled condition, which can reduce the multiple-input multiple- output digital signal processing (MIMO-DSP) complexity compared to the coupled MCFs with full MIMO-DSP for all the cores. In this paper, we intro- duce three types of randomly-coupled unit grouping 12-core fiber, which are randomly-coupled 2-core unit grouping MCF (RC-2CUG-MCF), RC-3CUG- MCF and RC-4CUG-MCF. Subsequently, we compare these three RC-UG- MCFs in terms of group delay spread, inter-unit crosstalk (XT), and cladding size. To achieve an inter-unit XT of −40 dB/100 km, RC-3CUG-MCF can provide a solution to maintain MIMO-DSP scale at the level of 6 × 6 with 180-µm cladding radius. However, the RC-2CUG-MCF has worse inter-unit XT, and the RC-4CUG-MCF has larger MIMO complexity. Based on the analysis, there is a trade-off relationship between the MIMO-DSP scale and the fiber cladding size, assuming that the target inter-unit XT is fixed.

This study presents a multi-point sensing system for cable fault detection based on fiber Bragg grating (FBG). The system detects vibration signals caused by cable faults through changes in the reflected power of the FBGs. By integrating time division multiplexing (TDM) technology, the system achieves multi-point fault detection and distinguishes vibration signals from faults at different cable locations. To verify the system’s feasibility, different fault scenarios were simulated. The results show that the system can detect the vibration signals caused by cable joint faults, successfully demodulate the corresponding frequency components, and reconstruct the strain applied to the FBGs. Additionally, to address the impact of front-end FBG on back-end FBG, a power compensation method was developed to improve detection accuracy. The proposed cable fault detection system facilitates online detection of cable joint faults but also reduces system equipment costs, offering a novel approach to cable fault detection.

This paper introduces a miniaturized optical fiber temperature sensor based on Fluorescence Intensity Ratio (FIR) technology for real-time monitoring of graphics processing unit (GPU) temperature. Utilizing a femtosecond micromachining system, miniature rectangular holes are etched on a standard multimode fiber. These holes are then filled with a mixture of Er³⁺/Yb³⁺ co-doped TeO₂-Na₂CO₃-ZnO powder and polydimethylsiloxane (PDMS) through capillary action, forming a sandwich structure. When illuminated by a 980 nm light source, upconversion (UC) fluorescence is generated, and a mathematical model correlating the fluorescence intensity ratio of two adjacent energy levels with temperature is established. The fundamental temperature sensing characteristics of the sensor are tested in a temperature-controlled chamber, with a maximum error of ± 1 K. The sensor is also applied to a GPU with real-time temperature variations, demonstrating a maximum error of 0.9 K and a response time of 1.96 s. The sensor not only possesses the advantages of a simple structure, micro size, and convenient fabrication but also exhibits immunity to electromagnetic interference, rapid response, good stability, and excellent repeatability in real-time monitoring of GPU temperature, showing potential for large-scale application.

Low-velocity impacts can cause microscopic and invisible damage to carbon fiber reinforced polymer (CFRP) structures, potentially compromising their integrity and leading to catastrophic failures. Therefore, obtaining precise information about the impact location is crucial for monitoring the health of CFRP structures. In this paper, an impact localization system for CFRP structures was developed by using fiber Bragg grating (FBG) sensors, and impact signals detected by FBG sensors are demodulated by edge-filtering at high speed. An impact localization method of CFRP structure based on CNN-LSTM-Attention is proposed. The time difference of arrival (TDOA) between signals from different FBG sensors are collected to characterize the impact location, and attention mechanism is introduced into the CNN-LSTM model to augment the significance of TDOA of impact signal detected by proximal FBG sensors. The model is trained using the training set, its parameters are optimized using the validation set and the localization performance of different models are compared by the test set. The proposed impact localization method based on CNN-LSTM-Attention model was verified on a CFRP plate with an experiment area of 400 mm*400 mm. Experimental results prove the effectiveness and satisfactory performance of the proposed method.

In this work, we have developed signal quality monitoring approaches in 100/400 Gbit/s short-reach transmission systems, with the application of four advanced modulation formats. In 100G and 400G transmission systems, it is shown that accuracies of 100 % have been achieved in the modulation format identification (MFI), with the use of random forest (RF) and multitask learning-based artificial neural network (MTL-ANN) for the four modulation formats mentioned. Meanwhile, average mean-square errors (MSEs) of the monitored optical signal-to-noise ratio (OSNRs) are less than 0.1 dB. Random forest uses up to 29 adders and 190 comparators, reducing its complexity by two orders of magnitude compared to MTL-ANN.

In this paper, we propose a scheme for enhancing the physical layer security and transmission performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The scheme for OFDM data first after 3-dimensional (3D) Brownian motion rotational permutation, and then according to the time zone and band number (TZBN) scrambling to achieve the effect of further data perturbation, which through the SHA-256 algorithm and 6-dimensional (6D) hyperchaotic processing to obtain the chaotic keys to enhance the security. After simulation experiment of 16QAM CO-OFDM security system transmitting over 80 km standard single-mode fiber (SSMF) at the symbol rate of 30 Gbaud, it is shown that the encryption scheme can guarantee that the authorized user receives valid data and the eavesdropper obtains the information with the BER of about 0.5. The key space of the scheme is about $2.88\times {10}^{194}$, which can effectively resist attacks such as violent attacks and chosen plaintext attacks. And the peak-to-average power ratio (PAPR) can be reduced by about 1.09 dB while the encryption process.

We propose a modified multi-symbol output (MSO) neural network (NN)-based equalization scheme. In this scheme, the multi-label realization is optimized to support high-order 64-QAM MSO, and the performance is enhanced by adding residual connections, which split linear and nonlinear equalization in one model. The proposed scheme is utilized in a 70-m D-band photonics-aided millimeter wave (MMW) transmission system. We successfully realized 12-Gbaud 64-QAM transmission with Q-factor satisfying SD-FEC.

A novel active fiber cavity ringdown (FCRD) gas sensing system using autocorrelation denoising technology was proposed for the first time. Using this scheme, external parameters can be monitored by measuring the ringdown time from the autocorrelation ringdown curve. Compared with the conventional active FCRD scheme, our proposed method not only can significantly improve the stability of the sensing system, but also the detection limit can be greatly improved. A FCRD-based gas concentration sensing system using autocorrelation denoising technology was simulated as a proof-of-concept demonstration. The simulation results demonstrate that the proposed gas sensing system with a sensitivity of 0.402 (μs⁻¹/%) was achieved. Especially, high stability of 0.50% was obtained, which is the ∼10 times better stability compared to the stability of the conventional active FCRD sensing system under the same condition. Due to the high stability, meanwhile the more than 10-fold enhancement of the detection limit was also achieved. We believe that the proposed sensing system has great potential applications for various industry and agriculture in which high stability meanwhile keeping ultralow detection limit is usually needed.

A high-dimensional multi-mode index modulation orthogonal frequency division multiplexing (HD-MMIM-OFDM) based on geometric shaping is proposed and demonstrated in cost-effective and power efficient intensity modulation direct detection (IM/DD) systems. Four geometrically shaped three-dimensional (3D-GS) constellation schemes are compared and evaluated in terms of minimum Euclidean distance (MED) and constellation figure of merit (CFM). We select the 3D constellation C3 with the optimal performance as the basis and construct three HD constellation schemes by stacking low-dimensional constellations, namely 4D, 5D, and 6D. To further improve the spectral efficiency (SE) of the system, a multi-mode index modulation (MMIM) based on OFDM is proposed and validated at different fiber lengths. The result shows that compared with traditional 2D-OFDM, the receiver sensitivity of 4D-MMIM-OFDM under the same SE increases by 0.46 dB, and the pseudo-Gray coding scheme further improves the receiver sensitivity by 0.16 dB. When the fiber length increases from 50 km to 80 km, the receiver sensitivity of 6D-MMIM-OFDM increases by 0.97 dB compared to 4D-MMIM-OFDM. It has been demonstrated that as the dimension of the constellation increases, the designed scheme exhibits enhanced tolerance to nonlinearity.

We report a fiber amplifier crafted with commercially available Erbium/Ytterbium codoped fiber, concurrently amplifying 1 μm and 1.5 μm laser signals by utilizing the bottleneck effect of energy transfer from Yb to Er irons. The amplifier achieved a single-frequency balanced laser output of 17.5 W at 1550 nm and 18.1 W at 1064 nm after the optimization of pump wavelength and signal power ratio, and showcasing an overall optical-to-optical efficiency of 50.9 %. The technology holds promise for compact mid-infrared laser devices based on difference frequency generation and may find applications in space laser communication and related fields.