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We have achieved the longest three mode-multiplexed full C-band transmission yet attained over 3060 km. In wideband mode-multiplexed transmission over weakly-coupled fewmode fibers (FMFs), the width of signal impulse responses is dependent on wavelength, and also exhibits a linear growth with increased transmission distance because of the presence...
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... Consequently, the traditional optical fiber transmission system based on single-mode fibers (SMF) is approaching the crunch of its transmission capacity. Mode division multiplexing (MDM) technology, based on the few-mode fiber (FMF), has emerged as an effective solution to boost the transmission capacity of optical fiber [1][2][3]. A key enabler for practical MDM transmission is the mode division multiplexers/ de-multiplexers that can achieve both mode selective conversion and multiplexing. ...
Photonic lanterns (PL) fabricated by the fiber bundle fusion tapering technique offer a low-loss and highly efficient interconnection module between single-mode fiber (SMF) and few-mode fiber (FMF). However, due to the lower fusion temperature, the fluorine-doped silica at the PL cladding is prone to intruding into the core region, resulting in the core deformation of the PL. In the current submission, we present a comprehensive study of the impact of capillary material intrusion (CMI) on the PL performance. Theoretical analysis reveals that CMI leads to a petal-shaped core at the few-mode end of the PL. As for the 3-mode PL, the asymmetry induced by the petal-shaped core breaks the degeneracy between mode groups, leading to the enhancement of the PL mode selectivity (MS) by 2∼3 dB. In addition, CMI brings a distortion of the mode field, leading to a performance penalty when the PL is coupled with the traditional FMF, particularly for higher-order modes. As the number of mode groups increases, the reduction of asymmetry induced by the mode field mismatch effect becomes more dominant. As for the 6-mode PL, CMI causes an MS reduction of 3∼5 dB. Higher-order modes of both the 3-mode and 6-mode PLs experience an insertion loss (IL) deterioration of 0.45 dB and 0.64 dB, respectively. Meanwhile, the mode conversion efficiency (MCE) decreases by 10% and 14%, in comparison with the scenario without the CMI. Furthermore, CMI strengthens the wavelength dependence of PL, leading to the compression of the operation wavelength range. As the number of modes increases, the CMI effect gradually diminishes as the petal-shaped core becomes more circular. Those findings provide valuable insights for the design and fabrication of PL, with the potential to enhance the PL performance for ultra-wideband mode division multiplexing transmission.
... As typical proof-of-concept examples, two different cyclic three-mode converters are designed and experimentally demonstrated. Numerous studies have shown cyclic mode permutation (CMP) to be an effective path to decrease the impact of differential mode delay (DMD) and mode-dependent loss (MDL) [29][30][31][32][33] in mode-division-multiplexing (MDM) systems. In contrast to the use of ring core 34,35 and nanopore-assisted core 36 for suppressing DMD and MDL, CMP is not affected by high doping difficulty and fabrication tolerance. ...
The recent advancements in nano-optics have created a strong demand for ultra-compact, miniaturized photonic devices. However, the mainstream inverse design algorithms face challenges in achieving compact size, efficient performance, and superior process manufacturability simultaneously. The present study proposes an exceptionally efficient segmented hierarchical variable step-size binary search-based digital inverse design method, aiming to transcend these limitations. The concept of “pixel splitting” is introduced for the first time in this paradigm. By layering the optimization process in several segments, the size of each pixel also changes dynamically, achieving both high efficiency and superior performance. The chosen examples of cyclic mode converters serve as typical complex proof-of-concept structures. The simulation results demonstrate that this method not only maintains excellent manufacturability but also enhances design efficiency over three times and exhibits superior performance. The experimental demonstration of two types of cyclic mode converters (CMCs), with dimensions of 3.84 × 9.6 μm² and 3.84 × 12 μm², respectively, based on this model, showcases their significantly smaller footprints compared to previously reported devices. The characterizations of these two CMCs demonstrate minimal insertion losses (<2.86 and <3.26 dB) and minimal crosstalk (<−11.89 and <−9.24 dB) across bandwidths of 50 nm. The data transmission of 3 × 60 Gbps on-off-keying signals and 3 × 80 Gbps four-level pulse amplitude signals are also demonstrated successfully. The proposed variable step-size binary search offers a novel approach for efficiently designing compact digital nano-photonic devices, addressing limitations such as slow convergence, sensitivity to initial patterns, and susceptibility to local optima. In addition, ultra-compact CMCs provide an effective solution for reducing link damage in mode division multiplexing transmission systems.
... Wavelength division multiplexing (WDM) and space division multiplexing (SDM) based on few-mode fiber (FMF) and multi-core fiber (MCF) have been vigorously developed to increase the transmission capacity of optical communication networks [1][2][3][4][5]. However, the mode crosstalk generated in the mode division multiplexing (MDM) system causes the correlation between different mode signals, which seriously damages the transmission performance. ...
... The vertical axis on the left refers to the Max/Min MDL, while the vertical axis on the right refers to the Std-MDL. The results in the latter figure show no substantial differences among the various permutation scenarios, indicating that MP does not affect the accumulation of MDL, in agreement with what was observed in [30]. An interesting feature that emerges from the results of Fig. 6 is that MDL accumulates proportionally to the square root of propagation distance not only in the presence of MP, but also when no MP is implemented. ...
... A possible explanation for this evidence is that MDL accumulates within groups of strongly coupled modes as a result of random and distributed local MDL, compatible with multiple fiber splices, thereby growing proportionally to the square root of propagation distance even in the absence of MP. Independence of the MDL accumulation on the mode permutation scheme has also been reported in [30], where it was argued that this might follows from the fact that MDL is mainly introduced by the single-mode stages connecting two recirculating loops. ...
We explore the efficacy of mode permutation to mitigate the impact of modal dispersion in a 15-mode fiber link for long-haul space-division multiplexed transmission. By introducing strong coupling between all the fiber modes, mode permutation reduces the growth rate of the link's intensity impulse response (IIR) with transmission distance, yielding a reduction in the receiver MIMO-DSP complexity. Using a recirculating fiber-loop configuration, we experimentally compare four permutation schemes and find that they are similarly effective in reducing the increase of the IIR duration from proportional to the square-root of propagation distance. At the reach of 530 km – the largest achievable with the time-domain MIMO window of 71.4 ns available in the experiment in the absence of mode permutation – the IIR duration is seen to reduce from almost 40 ns to less than 15 ns, while the maximum reach achieved with the use of mode permutation increases to 1178 km. We also devise a simple model to simulate propagation in realistic MMF links with independent fiber spans, whose parameters can be conveniently extracted from the data. In achieving good agreement between the simulated and experimental results, the model suggests that the effectiveness of mode permutation in a realistic 15-mode fiber link, composed of independent fiber spans, is only slightly greater than in the experimental recirculating-loop configuration.
... Zhang et al. transmitted 80-WDM-channels 8-OAM-mode 16-GBaud QPSK over 50 km ring-core fiber combined with 4 × 4 MIMO equalizers, and the transmission rate reached 2.56 Tbit/s [17] . In 2020, Shibahara et al. achieved 3060 km three-mode signal transmission in the C-band based on weakly coupled FMF with a transmission rate of 40.2 Tbit/s [18] . Zhang et al. transmitted 5-WDM-channels two-mode 28-GBaud 16QAM over 5 km FMF based on the direct detection (DD) technique with a transmission rate of 1.12 Tbit/s [19] . ...
... Next, the signal is input into a loop system. [14] QPSK/2/100 640 Gbit/s 2018 [15] PDM-64-QAM/3/30 280 Tbit/s 2019 [16] PS-PDM-16QAM/10/48 402.7 Tbit/s 2019 [17] QPSK/8/50 2.56 Tbit/s 2020 [18] 16QAM/3/3060 40.2 Tbit/s 2020 [19] 16QAM/2/5 1.12 Tbit/s 2021 [20] 64QAM/15/23 1.01 Pbit/s 2021 [21] DP-16QAM/2/100 16 Tbit/s Chinese Optics Letters 010602-2 ...
... Few-mode fiber has multiple orthogonal modes, and each mode can be used as an independent channel for information transmission. The information transmission capacity can be increased exponentially using mode-division multiplexing (MDM) technology, which has developed rapidly in recent years [3][4][5][6][7][8][9][10]. ...
By increasing the number of modes of transmission in optical fiber, the mode-division multiplexing (MDM) technology can effectively improve the transmission capacity. The mode add-drop technology is an important part of the MDM system and a key element for realizing flexible networking. In this paper, a mode add-drop technology based on few-mode fiber Bragg grating (FM-FBG) is reported for the first time. The technology utilizes the reflection characteristics of Bragg grating to realize the add-drop function in the MDM system. The grating is written in parallel according to the optical field distribution characteristics of different modes. By changing the writing grating spacing Δa to match the optical field energy distribution of the few-mode fiber, the few-mode fiber grating with high self-coupling reflectivity for the high-order mode is fabricated, and the performance of the add-drop technology is improved. The mode add-drop technology is verified in a 3 x 3 MDM system, which uses quadrature phase shift keying (QPSK) modulation and coherence detection. The experimental results show that the excellent transmission, add, and drop of 3 x 8 Gbit/s QPSK signals in 8 km few-mode fibers are achieved. The realization of this mode add-drop technology only requires Bragg gratings, few-mode fiber circulators, and optical couplers. It has the advantages of high performance, simple structure, low cost, and easy implementation, and it can be widely used in the MDM system.
... Short-distance transmission using MMFs guiding up to 55 modes has been demonstrated [7]- [17], with 55 mode transmission limited to 25.9 km with a data rate of 1.53 Pb/s [6]. Long-distance transmission, on the other hand, used to be mostly limited to 3 or 6-mode transmission [8], [18]- [24], as can be seen in Fig. 1. Notable is also the first 10-mode transmission over 1300 km from [25] presented at the same time as our original work [26], but this is not included in Fig. 1 as the total throughput was not measured. ...
In recent years, space-division multiplexing (SDM) has been proposed and investigated as a technique to increase the per-fiber capacity in order to cope with the ever-increasing demand for capacity in optical transmission networks. Considering the various SDM architectures proposed, multi-mode fibers potentially allow for the highest spatial channel density, but current demonstrations have been limited to mostly short-distance high-mode count or long-distance low-mode count transmission. In this work, we transmit 15 modes × 184 wavelength channels × 24.5 GBd PDM-16-QAM signals, spanning the full C-band, over 1001 km of 15-mode multi-mode fiber. The resulting net data rate of 273.6 Tb/s is the highest reported data rate in long-distance multi-mode fiber transmission and results in a record capacity-distance product of 273.9 Pb/s · km for multi-mode transmission. This was achieved by using mode multiplexers with low mode-dependent loss (MDL) and insertion loss, as well as a 15-mode fiber optimized for a low differential mode delay (DMD) transmission regime.
... Without a doubt the optical fiber plays a dominant role in the explosive boost of the channel capacity in telecommunication infrastructures, thanks to the solid research of the classical telecom community. [43][44][45][46] A singlemode fiber (SMF) is the most mature and widely deployed fiber, which is capable of transporting photons encoded in polarization, 47,48 path, 22,49,50 frequency, 51 and time-bin. [52][53][54] To take full advantage of the photonic platform, the spatial modes as quantum information carriers are of great importance and interest. ...
The field of quantum communication is thriving as a complement to conventional telecommunication with its distinctive feature of absolute security. As the core technology for delivering quantum information, substantial advances in quantum communication have already been demonstrated on various platforms, including photonic systems. Among all of them, the orbital angular momentum (OAM) of photons with its infinite Hilbert space has attracted much attention and has been widely employed in both classical and quantum regimes. In particular, many types of fiber have been designed and fabricated to allow transmitting OAM of photons. Here, we review recent progress in transmitting OAM quantum states through different types of fiber, including few-mode fibers, multi-mode fibers, ring-core fibers, and single-mode fibers. We also discuss the challenges and prospects of quantum OAM in fibers.
... A novel cyclic mode permutation (CMP) technique [10] has been proposed recently for 3500 km DMD-unmanaged 6-mode-multiplexed transmission. A threefold recirculating loop system is constructed to transmit signals carried by spatial mode. ...
In this paper, a novel cyclic mode converter (CMC) is proposed and fabricated to implement cyclic mode permutation (CMP) on-chip for differential mode delay and mode-dependent loss elimination in the mode division multiplexing (MDM) transmission system. Cascaded by three optimally designed mode converters that do not affect the non-target modes, the proposed CMC can realize the conversion of any input mode among the TE0/TE1/TM0/TM1 modes. The three-dimensional finite-difference time-domain (3D-FDTD) simulation results show that the insertion loss of our device is less than 0.59 dB, and the crosstalk of each mode is lower than −15 dB under the range of 1500–1600 nm. The flat spectral response of this CMC is maintained even in the presence of fabrication errors up to±10 nm, showing great robustness. The experimental results also prove that at the center wavelength of 1550 nm the measured insertion loss of each mode is below 2.22 dB, and the crosstalk of each mode is lower than −15 dB. The proposed CMC provides a new idea for effectively reducing link damage in the MDM transmission system.
... Mode-division multiplexed (MDM) transmission based on fewmode fibers (FMFs) has attracted significant attention recently as a promising approach to boost optical fiber capacity beyond the theoretical nonlinear capacity limit [1][2][3][4]. However, MDM systems are complex, as they require matched few-mode amplifiers, mode (de)multiplexers, and highly complex digital signal processing (DSP). ...
In this Letter, we show numerically and experimentally that multipath interference can be reduced significantly by distributed Raman amplification (DRA) in quasi-single-mode transmission using few-mode fibers, owing to the extra differential mode attenuation induced between the fundamental mode and higher-order modes. The experimental results show that the required number of equalization taps can be reduced by 1.6 times. Moreover, by carefully optimizing the intensity overlap between the LP01 and LP11 modes through structural adjustment of the two-mode fiber, a 3.5-times reduction in the required number of taps can be obtained.
