Fiber Optics and Optical Communications|71 Article(s)
Ultra-low loss Rayleigh scattering enhancement via light recycling in fiber cladding
Pengtao Luo, Fengyi Chen, Ruohui Wang, and Xueguang Qiao
Rayleigh backscattering enhancement (RSE) of optical fibers is an effective means to improve the performance of distributed optical fiber sensing. Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE. However, in-core modulation loses more transmission light, thus limiting the sensing distance. In this work, a cladding-type RSE (cl-RSE) structure is proposed, where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core. The refractive-index modulation structure redistributes the light in the cladding, and the backward scattered light is recovered, which enhances the Rayleigh backscattered signal with almost no effect on the core light. Experimentally, it was demonstrated that in an effectual cl-RSE structure, the insertion loss was reduced to 0.00001 dB per scatterer, corresponding to the lowest value for a point scatterer to date. The cl-RSE structure accomplished measurements up to 800°C. In particular, the temperature measurement fluctuation of the cl-RSE fiber portion is only 0.00273°C after annealing. These results show that the cl-RSE structure has effective scattering enhancement, ultra-low loss, and excellent high-temperature characteristics, and has great potential for application in Rayleigh scattering-enhanced distributed fiber sensing.
Photonics Research
  • Publication Date: Aug. 01, 2024
  • Vol. 12, Issue 8, 1813 (2024)
Low-modal-crosstalk doped-fiber amplifiers in few-mode-fiber-based systems
Shuailuo Huang, Lei Shen, Gang Qiao, Yuanpeng Ding, Yuyang Gao, Jian Cui, Baolong Zhu, Siyuan Liu, Mingqing Zuo, Jinglong Zhu, Lei Zhang, Jie Luo, Yongqi He, Zhangyuan Chen, and Juhao Li
Independent light propagation through one or multiple modes is commonly considered as a basic demand for mode manipulation in few-mode fiber (FMF)- or multimode fiber (MMF)-based optical systems such as transmission links, optical fiber lasers, or distributed optical fiber sensors. However, the insertion of doped-fiber amplifiers always kills the entire effort by inducing significant modal crosstalk. In this paper, we propose the design of doped-fiber amplifiers in FMF-based systems adopting identical multiple-ring-core (MRC) index profiles for both passive and doped fibers to achieve low modal crosstalk. We develop the direct-glass-transition (DGT) modified chemical vapor deposition (MCVD) processing for precise fabrication of few-mode erbium-doped fibers (FM-EDFs) with MRC profiles of both refractive index and erbium-ion doping distribution. Then, a few-mode erbium-doped-fiber amplifier (FM-EDFA) with a maximum gain of 26.08 dB and differential modal gain (DMG) of 2.3 dB is realized based on fabricated FM-EDF matched with a transmission FMF supporting four linearly polarized (LP) modes. With the insertion of the FM-EDFA, 60 + 60 km simultaneous LP01/LP11/LP21/LP02 transmission without inter-modal multiple-input multiple-output digital signal processing (MIMO-DSP) is successfully demonstrated. The proposed design of low-modal-crosstalk doped-fiber amplifiers provides, to our knowledge, new insights into mode manipulation methods in various applications.
Photonics Research
  • Publication Date: Aug. 01, 2024
  • Vol. 12, Issue 8, 1768 (2024)
High power cladding-pumped low quantum defect Raman fiber amplifier
Yang Zhang, Jiangming Xu, Junrui Liang, Sicheng Li, Jun Ye, Xiaoya Ma, Tianfu Yao, Zhiyong Pan, Jinyong Leng, and Pu Zhou
Heat generated by the quantum defect (QD) in optically pumped lasers can result in detrimental effects such as mode instability, frequency noise, and even catastrophic damage. Previously, we demonstrated that boson-peak-based Raman fiber lasers have great potential in low QD laser generation. But their power scalability and heat load characteristics have yet to be investigated. Here, we demonstrate a boson-peak-based Raman fiber amplifier (RFA) with 815 W output power and a QD of 1.3%. The low heat generation characteristics of this low QD RFA are demonstrated. Both experimental and simulation results show that at this power level, the heat load of the low QD RFA is significantly lower than that of the conventional RFA with a QD of 4.8%. Thanks to its low heat generation characteristics, the proposed phosphosilicate-fiber-based low QD RFA provides an effective solution for the intractable thermal issue in optically pumped lasers, which is of significance in reducing the laser’s noise, improving the laser’s stability and safety, and solving the challenge of heat removing.
Photonics Research
  • Publication Date: May. 01, 2024
  • Vol. 12, Issue 5, 995 (2024)
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.
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.
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.
Photonics Research
  • Publication Date: Feb. 01, 2024
  • Vol. 12, Issue 2, 321 (2024)
Maximizing transmission capacity in optical communication systems utilizing a microresonator comb laser source with adaptive modulation and bandwidth allocation strategies|Editors' Pick
Jun Hu, Wei Wang, Zhenyu Xie, Chengnian Liu, Fan Li, and Daquan Yang
Traditional optical communication systems employ bulky laser arrays that lack coherence and are prone to severe frequency drift. Dissipative Kerr soliton microcombs offer numerous evenly spaced optical carriers with a high optical signal-to-noise ratio (OSNR) and coherence in chip-scale packages, potentially addressing the limitations of traditional wavelength division multiplexing (WDM) sources. However, soliton microcombs exhibit inhomogeneous OSNR and linewidth distributions across the spectra, leading to variable communication performance under uniform modulation schemes. Here, we demonstrate, for the first time, to our knowledge, the application of adaptive modulation and bandwidth allocation strategies in optical frequency comb (OFC) communication systems to optimize modulation schemes based on OSNR, linewidth, and channel bandwidth, thereby maximizing capacity. Experimental verification demonstrates that the method enhances spectral efficiency from 1.6 to 2.31 bit ⋅ s-1 ⋅ Hz-1, signifying a 44.58% augmentation. Using a single-soliton microcomb as the light source, we achieve a maximum communication capacity of 10.68 Tbps after 40 km of transmission in the C-band, with the maximum single-channel capacity reaching 432 Gbps. The projected combined transmission capacity for the C- and L-bands could surpass 20 Tbps. The proposed strategies demonstrate promising potential of utilizing soliton microcombs as future light sources in next-generation optical communication.
Photonics Research
  • Publication Date: Oct. 31, 2024
  • Vol. 12, Issue 11, 2573 (2024)
Superfine multiresonant fiber grating sensors assisted with silica capillaries
Kaiwei Li, Yongguang Xiao, Fu Liu, Zhiyong Yang, Xiangyu Yan, Zhaohui Li, Tuan Guo, Gaozhi George Xiao, and Jacques Albert
We propose and demonstrate a superfine multiresonant fiber grating sensor characterized by superior spectral resolution and enhanced sensing capabilities. This sensor can be easily constructed by inserting a tilted fiber Bragg grating (TFBG) probe into a silica capillary filled with a refractive index (RI) matching oil. As the fiber cladding, the RI-matching oil, and the capillary all have the same RI, the cladding modes excited by the TFBG can extend into the RI-matching oil and capillary, facilitating surface sensing outside the capillary. Our study shows that the number of cladding modes increases, and the resonance spectrum becomes denser as the outer diameter of the capillary gets larger. As a result, the detection accuracy of RI based on mode cutoff wavelength identification can be improved. Particularly, with a capillary diameter of 1 mm, the heightened spectral density enhances refractometric accuracy by nearly an order of magnitude compared to the intrinsic TFBG. The superfine multiresonant fiber grating sensor proposed here is flexible in configuration and easy to fabricate, providing a new strategy for developing new fiber sensing devices.
Photonics Research
  • Publication Date: Oct. 29, 2024
  • Vol. 12, Issue 11, 2488 (2024)
Two-photon 3D printed fiber-optic Fabry–Perot probe for triaxial contact force detection of guidewire tips
Ruixue Yin, Yuhang Yang, Linsong Hou, Heming Wei, Hongbo Zhang, and Wenjun Zhang
The demand for real-time feedback and miniaturization of sensing elements is a crucial issue in the treating vascular diseases with minimally invasive interventions. Here, Fabry–Perot microcavities fabricated via direct laser writing using a two-photon polymerization technique on fiber tips are proposed, designed, simulated, and experimentally demonstrated as a miniature triaxial force sensor for monitoring real-time interactions between the tip of a guidewire and human blood vessels and tissues during minimally invasive surgeries. The sensor contains four fiber tip-based Fabry–Perot cavities, which can be seamlessly integrated into medical guidewires and achieves three-axis force decoupling through symmetrically arranged flexible structures. The results showed that the proposed sensor achieved a cross-sectional diameter of 890 μm and a high sensitivity of about 85.16 nm/N within a range of 0 to 0.5 N with a resolution of hundreds of micro-Newtons. The proposed triaxial force sensor exhibits high resolution, good biocompatibility, and electromagnetic compatibility, which can be utilized as an efficient monitoring tool integrated into minimally invasive surgical intervention devices for biomedical applications.
Photonics Research
  • Publication Date: Oct. 29, 2024
  • Vol. 12, Issue 11, 2474 (2024)
Realizing submeter spatial resolution for Raman distributed fiber-optic sensing using a chaotic asymmetric paired-pulse correlation-enhanced scheme
Bowen Fan, Jian Li, Zijia Cheng, Xiaohui Xue, and Mingjiang Zhang
The sensing spatial resolution and signal-to-noise ratio (SNR) of Raman distributed optical fiber sensors are limited by the pulse width and weak Raman scattering signals. Notably, the sensing spatial resolution cannot exceed the order of meters at several kilometers sensing distances. To break through this physical bottleneck, a novel, to our knowledge, Raman scattering model based on paired-pulse sensing is constructed. The fundamental origins of the observed limited spatial resolution of conventional schemes are analyzed, and a chaotic asymmetric paired-pulse correlation-enhanced scheme for Raman distributed fiber-optic sensing is proposed and experimentally demonstrated. The proposed scheme uses a chaotic asymmetric paired-pulse as the sensing signal and extracts the light intensity information of each data point of the sensing fiber, which carries the random undulation characteristics of chaotic time series, based on the time-domain differential reconstruction method. This scheme overcomes the pulse width limitation of spatial resolution via correlation and demodulation, enhances the correlation characteristics between the temperature-modulated Raman scattered light field and detection signal, and improves the SNR. Finally, a sensing performance of 10 km, a spatial resolution of 30 cm, and an SNR of 6.67 dB are realized in the experiment. This scheme provides a new research idea for a high-performance Raman distributed optical fiber sensing system.
Photonics Research
  • Publication Date: Oct. 01, 2024
  • Vol. 12, Issue 10, 2365 (2024)
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