Ultra-low Loss Fiber Research Articles

Ultra-Low Loss Fiber Deployment in Elastic Optical Networks With Fixed and Variable Topologies

Ultra-Low Loss Fiber Deployment in Elastic Optical Networks With Fixed and Variable Topologies

The effect of frozen-in stress on fiber attenuation and a preparation method for ultra-low loss fiber

As the data-rate of the optical fiber communication system evolves to 400 Gb/s or even 1 Tb/s, higher requirements are put forward for transmission rate and repeater distance. To meet the requirements, further decreasing the optical fiber attenuation coefficient is one of the effective methods. In this paper, we did research on the relationship between the distribution of elements and frozen-in stress in the core layer and the cladding. Subsequently, their effect on optical fiber attenuation is also investigated. The results show that the co-doping of germanium, fluorine, and chlorine in the core layer can improve the stress matching between the core layer and the optical cladding. In addition, based on our research, the outer cladding with a high softening point can restrain the stress mismatch between the core layer and the optical cladding. Furthermore, the thickness of the second cladding will also affect the stress mismatch. Eventually, ultra-low loss fibers with the optimal attenuation of 0.156 dB/km at 1550 nm were prepared successfully by analyzing the stress distribution inside the optical fiber and adjusting the doping amount of germanium, fluorine, chlorine and other elements in the core layer, optical cladding, and outer cladding to maintain that the core layer and the optical cladding share the same stress.

Integration of Self-Adaptive Physical-Layer Key Distribution and Encryption in Optical Coherent Communication

We propose and experimentally demonstrate a compatible physical-layer secure optical communication (PLSOC) system that integrates self-adaptive physical-layer key distribution (PLKD) and encryption (PLE) in optical coherent communication. Based on bit error rate difference of QAM signals mapped by asymmetric basis state Y-00 protocol, the secret key can be secretly exchanged over public fiber links without the pre-shared keys. Moreover, we perform a parameter self-adaptive strategy for practical and dynamic PLKD. The security of the key is evaluated in the case of a fiber-tapping attack. A secure hash algorithm, SHA3-512, is used to perform privacy amplification to obtain the virtually secure key. An error-free PLKD rate reaches 39.3 Kbits/s over 300km ultra-low loss fiber. We experimentally enable the integration of the proposed PLKD scheme and quantum noise stream cipher (QNSC) with a single wavelength, same system. Q factor penalty of the integration system compared to the QNSC system is 3.7dB (optical back-to-back) and 4.8dB (300km) respectively. By exploiting a common hardware platform, with the same wavelength, the proposed PLSOC system addresses the problem that PLKD and PLE are separately performed through independent optical fiber links or wavelengths. Since only digital signal processing is used, the scheme does not require extra hardware.

Ultralong Single‐Ended Random Fiber Laser and Sensor

AbstractRandom fiber laser (RFL) utilizing stimulated Raman scattering and distributed random Rayleigh backscattering in fiber as optical gain and feedback mechanisms, respectively, has been developed rapidly in the past decade. Here, it is found, for the first time, that the combination of a high‐order pump and new transmission fiberthat has lower transmission loss, Rayleigh backscattering coefficient, and Raman gain coefficient than standard single‐mode fibercan break the length limits of both random fiber lasing and sensing. With a higher‐order pump and ultralow loss fiber (ULLF), the position of maximum intracavity lasing power can be shifted toward the far end of the fiber span resulting in more remote pump power for the erbium‐doped fiber (EDF) inserted in the fiber span, which plays a dominant role of cavity length extension in RFL. A 200 km ultralong single‐ended RFL and sensor are experimentally demonstrated, which are the longest single‐ended RFL and sensor with functional remote reflectors reported to date. It is believed that the proposed combination of high‐order random lasing and ULLF with EDF can become a general method to extend the working distance of various fiber sensing systems for safety monitoring of ultralong infrastructures, such as power transmission lines and oil/gas pipelines.

364 km ultra-long Raman fiber laser based on high-order pumping and ultra-low-loss fiber

Raman fiber laser (RFL) based on distributed Raman gain along optical fiber is an ideal platform for realizing ultra-long-cavity laser, which is of great interest in fundamental laser science and multidisciplinary fundamental studies such as complex systems exhibiting turbulence-like characteristics. RFL based on standard single-mode fiber sets the record of the longest laser cavity reaching 270 km with a clearly resolvable mode structure. Here, we explore the effect of pumping scheme and key fiber parameters to further extend the ultimate length of RFL. We theoretically analyze and experimentally demonstrate that by adopting higher-order pumping and ultra-low-loss fiber (ULLF) with low transmission loss and low Rayleigh backscattering coefficient, the laser cavity length of RFL with resolvable mode structure can be significantly increased. As a result, a 364 km-long bi-directional pumped 6th-order ultra-long Raman fiber laser (URFL) based on ULLF is demonstrated with resolvable longitudinal mode, an extension of 35 % over the prior 270 km record. This work paves a way to lengthen cavity length of URFL and provides a new platform for fundamental laser physics study and the ultra-long fiber laser applications in communication and sensing.

Experimental Mode-Pairing Measurement-Device-Independent Quantum Key Distribution without Global Phase Locking.

In the past two decades, quantum key distribution networks based on telecom fibers have been implemented on metropolitan and intercity scales. One of the bottlenecks lies in the exponential decay of the key rate with respect to the transmission distance. Recently proposed schemes mainly focus on achieving longer distances by creating a long-arm single-photon interferometer over two communication parties. Despite their advantageous performance over long communication distances, the requirement of phase locking between two remote lasers is technically challenging. By adopting the recently proposed mode-pairing idea, we realize high-performance quantum key distribution without global phase locking. Using two independent off-the-shelf lasers, we show a quadratic key-rate improvement over the conventional measurement-device-independent schemes in the regime of metropolitan and intercity distances. For longer distances, we also boost the key rate performance by 3 orders of magnitude via 304km commercial fiber and 407km ultralow-loss fiber. We expect this ready-to-implement high-performance scheme to be widely used in future intercity quantum communication networks.

High-speed multi-channel long-haul coherent optical transmission system

In this work, high-speed transmission over the long-haul optical channel using orthogonal frequency division multiplexing (OFDM) was investigated. Furthermore, we recommend mixing polarization division multiplexing (PDM) with coherent OFDM (CO-OFDM) and quadrature amplitude modulation (16-QAM) to improve spectral efficiency (SE) while transmitting over a wavelength division multiplexing (WDM) system. An 800 Gb/s WDM PDM-CO-OFDM-16QAM transmission system with various channel spacing of 100 GHz, 50 GHz, and 25 GHz is examined utilizing the OptiSystem (2021) version 18.0 software package over ten spans of 60 km standard single-mode fiber (SSMF). Different channel spacing WDM systems have been compared in terms of performance and SE. The results reveal that the WDM system with 100 GHz channel spacing has a longer transmission range and needs minimal optical signal to noise ratio (OSNR) at the reception. The 25 GHz channel spacing WDM system exceeds the others in terms of SE. Further, the effect of ultra-low loss and large effective area fiber in lowering span loss and nonlinear effects for 25 GHz channel spacing WDM system is investigated. The findings show that the system performance with the new fiber outperforms the SSMF. The acceptable bit error rate (BER) for this study is 0.033 (20% concatenated forward error correction (FEC) threshold).

Chlorine incorporation into SiO2 beyond the chemical equilibrium

The long-haul subsea applications have driven recent development to focus on incorporation of chlorine replacing germania as index adapting component in ultralow loss fibers. We present a method to dope silica glass with a chlorine level above the one expected from thermodynamical equilibrium consideration. Gaseous SiCl4 was used as dopant for the treatment of porous green body prepared by the powder sinter technique (REPUSIL). To be able to optimize the chlorination process steps, the exhaust species of the individual steps had been analyzed using an online process monitoring of exhaust gases via IR spectroscopy. Finally, we could realize a chlorine level of 1.2 wt% Cl with an initial pressure of SiCl4 of 0.1 bar while the calculation of thermodynamic chemical equilibrium predicted only a maximum level of less than 1.0 wt% Cl in SiO2 under those optimized conditions.

Spectral efficiency and performance improvement of coherent optical transmission system

This paper presents an orthogonal frequency division multiplexing (OFDM) for a long-haul optical transmission system with high-rate transferability to alleviate dispersion effects. In addition, we suggest combining polarization division multiplexing (PDM) with coherent OFDM (CO-OFDM) to increase spectral efficiency (SE). Based on OptiSystem (2021) version 18.0" software package, a 100 Gbps single-channel PDM-CO-OFDM transmission system is investigated using different modulation formats; bipolar phase keying (BPSK), quadrature phase shift keying (QPSK), Eight-Phase-Shift Keying modulators (8-PSK), and quadrature amplitude modulation (16-QAM). A 60 km span of standard single-mode fiber (SSMF) cable is employed in this investigation. The system's performance and spectral efficiency have been evaluated by comparing against the different modulation schemes. The outcomes that were got show that the BPSK modulation scheme has the longest transmission distance and requires a lesser level of optical signal to noise ratio (OSNR) at the receiver side. Concerning spectral efficiency, 16-QAM outperforms the others. Farther, the impact of employing ultra-low loss and large effective area fiber in reducing loss and nonlinear effects in the optical channel for 16-QAM modulation formats is examined. The result found that the system with advanced fiber has superior performance than the SSMF. The bit error rate (BER) of 0.033 (20% concatenated forward error correction (FEC) threshold) is used as a baseline.

9 Tb/s Transmission Using 29 mW Optical Pump Power Per EDFA With 1.24 Tb/s/W Optical Power Efficiency Over 15,050 km

We transmit 143x32.6 GBd 8D-QPSK signal over 15,050 km with EDFAs consuming 29 mW of 980 nm-pump power. We experimentally achieve record optical power efficiency from 6.5 to 1.24 Tb/s/W with the corresponding optimum spectral efficiency from 2.4 to 2.0 b/s/Hz for transmission distances ranging from 6,020 to 15,050 km respectively. These results are enabled by: precisely tuned information spectral efficiency and EDFA output power based on our power efficiency model to maximize optical power efficiency; the use of coded modulation format with <1.6 dB gap to Shannon limit and variable overhead FEC; the use of ultra-low loss fiber; more power efficient gain equalization with a single gain flattening filter per two EDFAs; and low back-to-back implementation penalty. We also confirmed the validity of our power efficiency model comparing the designed and measured OSNR evolution, achieved optical power efficiency and the corresponding spectral efficiency.

Modeling the splice loss of ultra-low loss fiber and single-mode optical fiber in high altitude area

The application of Ultra-low loss (ULL) fiber in high altitude areas is gradually expanding, and the junctions between ULL fiber and single mode optical fiber (SMF) will continue to increase. More factors affect the fusion of SMF and ULL fibers in high altitude areas, and the harsh environments add a further complication to the fusion. Accordingly, a model of splice loss for fusion SMF and ULL fibers affected by altitude is proposed in this work. The model takes the splice losses caused by thermally diffused expanded core (TEC), lateral misalignment, and angular misalignment into account, as well as the effect of atmospheric pressure on TEC and angular misalignment, and the fusion experiments of SMF and ULL fibers are carried out at different altitudes. The results illustrate that the model established in this work shows a good agreement with the data of experiments, and the model can play a guidance role for splicing SMF and ULL fibers at high altitudes in the future.

16 QAM Quantum Noise Stream Cipher Coherent Transmission Over 300 km Without Intermediate Amplifier

This letter first reports a digital coherent quantum noise stream cipher (QNSC) experiment over 300km fiber without intermediate amplifiers. With the help of Raman fiber amplifiers, ultra-low loss fiber, and the optimized fuzzy C-means clustering algorithm, the results show the system can carry 10.2 Tbit/ s·km data, which is significantly improved in the single polarization and single wavelength digital coherent context without intermediate amplifiers. We further analyze the transmission and security performances under the 16 quadrature amplitude modulation (QAM) scenario in detail. The number of masked signals of 16 QAM/QNSC is 3843.2.

The effect of fusion current on thermally diffused expanded core of splicing ultra-low loss fiber and traditional single-mode fiber

Ultra-low loss (ULL) optical fiber is already being used at high altitude in optical communication due to the stable performance in long haul links. Whereas, traditional single-mode optical fiber (SMF) is still used in most general areas since the high price of ULL fiber. Accordingly, there will be an increasing number of junctions between SMF and ULL fibers. The main contents of this work are to study the influence of fusion current on the splice loss caused by thermally diffused expanded core (TEC) of splicing SMF and ULL fibers, and the variations on the diffusion of core dopants and fusion time are also taken into account. Furthermore, the analysis was verified by experiment and simulation. The results illustrate that the changes in fusion current will cause varying degrees of changes in the core and lead to different splice losses due to diffusion, which plays a guidance role in the current calibration of fusion splicer in the future when splicing SMF and ULL fibers. The significance of this work is to reduce the splice loss of SMF and ULL fibers. If the method is applied in a modern fusion splicer, the splice loss of SMF and ULL fibers will be deduced further.

Impact of cladding elements on the loss performance of hollow-core anti-resonant fibers.

Understanding the impact of the cladding tube structure on the overall guiding performance is crucial for designing a single-mode, wide-band, and ultra low-loss nested hollow-core anti-resonant fiber (HC-ARF). Here we thoroughly investigate on how the propagation loss is affected by the nested elements when their geometry is realistic (i.e., non-ideal). Interestingly, it was found that the size, rather than the shape, of the nested elements has a dominant role in the final loss performance of the regular nested HC-ARFs. We identify a unique 'V-shape' pattern for suppression of higher-order modes loss by optimizing free design parameters of the HC-ARF. We find that a 5-tube nested HC-ARF has wider transmission window and better single-mode operation than a 6-tube HC-ARF. We show that the propagation loss can be significantly improved by using anisotropic nested anti-resonant tubes elongated in the radial direction. Our simulations indicate that with this novel fiber design, a propagation loss as low as 0.11 dB/km at 1.55 μm can be achieved. Our results provide design insight toward fully exploiting a single-mode, wide-band, and ultra low-loss HC-ARF. In addition, the extraordinary optical properties of the proposed fiber can be beneficial for several applications such as future optical communication system, high energy light transport, extreme non-nonlinear optics and beyond.

Comparative Analysis of Highly Sensitive PCF for Chemical Sensing in THz Regime

Nowadays photonic crystal fiber (PCF) is used for sensing purposes in different fields. In this work, we have proposed a PCF based chemical (Benzene and Ethanol) sensor. Finite Element Method (FEM) based software COMSOL 5.3a is used to investigate the numerical characteristics for the proposed structure. From the numerical analysis, we obtained high sensitivity with low losses for an optimum core diameter of 210 µm. Our proposed PCF works on a broad range of core diameters and THz frequency spectra. The fabrication of this model is very simple due to its simplistic design structure. Full Text: PDF ReferencesMd.F.H. Arif, Md.J.H. Biddut, "A new structure of photonic crystal fiber with high sensitivity, high nonlinearity, high birefringence and low confinement loss for liquid analyte sensing applications", Sensing Bio-Sensing Res. 12, 8 (2017). CrossRef P. Kumar, Md.H. Bikash, K. Ahmed, S. Sen, "A Novel Hexahedron Photonic Crystal Fiber in Terahertz Propagation: Design and Analysis", Photonics 6(1), 32 (2019). CrossRef S. Asaduzzaman, K. Ahmed, T. Bhuiyan, T. Farah, "Hybrid photonic crystal fiber in chemical sensing", SpringerPlus 5, 748 (2016). CrossRef Md.S. Islam, J. Sultana, J. Atai, D. Abbott, S. Rana, M.R. Islam, "Ultra low-loss hybrid core porous fiber for broadband applications", App. Opt. 56(4), 1232 (2017). CrossRef S. Atakaramians, S. Afshar, H. Ebendorff-Heidepriem, M. Nagel, B.M. Fischer, D. Abbott, T.M. Monro, "THz porous fibers: design, fabrication and experimental characterization", Opt. Expr. 17(16), 14053 (2009). CrossRef

Analysis of achievable distances of BB84 and KMB09 QKD protocols

Quantum key distribution (QKD) is a proven secured way to transmit shared secret keys using quantum particles. Any adversarial attempt to intercept and eavesdrop secret key results in generating errors alerting the legitimate users. Since QKD is constrained by quantum mechanics principles, the practical transmission of the key at a greater distance is an issue. In this paper, we discover and analyze the key factors associated with transmission media, hardware components and protocol implementation of the QKD system that causes hindrance in distance range. Practical implementation of BB84 and KMB09 protocols is discussed to determine the achievable distance given current technology. We find that by using ultra low loss fiber, short-pulse laser and superconducting nanowire single photon detector the maximum achievable distance for both of the quantum protocols is 250[Formula: see text]km.

Efficient Multi-Stage Deployment of Ultra-Low Loss Fibers in Elastic Optical Networks

Ultra-low loss (ULL) fibers allow high-quality signal transmission and are expected to become important candidates for new deployment of fiber links in an optical network. In our previous study, we investigated strategies for selecting network links to be deployed with ULL fibers in a single stage, subject to an annual operational budget. As a step further, this study considers such deployment in multiple stages, which corresponds to a scheduling problem of ULL fiber deployment. To this end, we cannot simply adopt a repetition of our previous single-stage deployment approach since it cannot tell which set of links are to be deployed with ULL fibers in each stage. Rather, we need to jointly consider the set and the order of links to be deployed in each stage so as to get a maximum overall gain in terms of time-weighted frequency slot (FS) usage. Also, the time taken for deploying each fiber link and the interval between neighboring deployment stages should be considered. To achieve a global optimization, we develop a mixed integer linear programming (MILP) model and look at three scheduling strategies which are physical length (PL), shortest route traversed (SRT), and maximum deployment gain (MDG) based strategies. We evaluate the performance of these strategies through simulations and find that the proposed MDG strategy performs best in terms of the total time-weighted FS usage. Results also show that there is an optimal number of deployment stages which provides maximum gain of spectrum usage while requiring few network re-optimizations.

Implementation of quantum key distribution surpassing the linear rate-transmittance bound

Quantum key distribution (QKD offers a long-term solution to establish information-theoretically secure keys between two distant users. In practice, with a careful characterization of quantum sources and the decoy-state method, measure-device-independent quantum key distribution (MDI-QKD) provides secure key distribution. While short-distance fibre-based QKD has already been available for real-life implementation, the bottleneck of practical QKD lies on the limited transmission distance. Due to photon losses in transmission, it was believed that the key generation rate is bounded by a linear function of the channel transmittance, $O(\eta)$, without a quantum repeater, which puts an upper bound on the maximal secure transmission distance. Interestingly, a new phase-encoding MDI-QKD scheme, named twin-field QKD, has been suggested to beat the linear bound, while another variant, named phase-matching quantum key distribution (PM-QKD), has been proven to have a quadratic key-rate improvement, $O(\sqrt{\eta})$. In reality, however, the intrinsic optical mode mismatch of independent lasers, accompanied by phase fluctuation and drift, impedes the successful experimental implementation of the new schemes. Here, we solve this problem with the assistance of the laser injection technique and the phase post-compensation method. In the experiment, the key rate surpasses the linear key-rate bound via 302 km and 402 km commercial-fibre channels, achieving a key rate over 4 orders of magnitude higher than the existing results in literature. Furthermore, with a 502 km ultralow-loss fibre, our system yields a secret key rate of 0.118 bps. We expect this new type of QKD schemes to become a new standard for future QKD.

Ultra low loss and dispersion flattened microstructure fiber for terahertz applications

In this paper, a rectangular core hexagonal lattice porous core photonic crystal fiber (PC-PCF) is reported for effectively guiding the terahertz light signal. Finite element method with circular perfectly matched layer boundary condition is employed to find out the propagation characteristics of this proposed porous core fiber. Extensive simulation results of that microstructure fiber over wide frequency range shows that very low effective material loss of 0.035 cm-1, large effective area of 1.79×10-7 m2 and high core power fraction of 36% can be obtained simultaneously. In addition, for same designing condition nearly zero flattened dispersion of 0.46 ± 0.07 ps/THz/cm can be achieved over 600 GHz frequency band in terahertz range. Furthermore, other important parameters like single mode operation, confinement loss and bending loss are also investigated rigorously for the proposed fiber. The excellent results of this optical waveguide will pave the way to implement it in various real life terahertz applications.

200 Gb/s per Channel Unrepeatered Transmission Over 520 km Terrestrial Fibers

This letter demonstrates unrepeatered real-time transmission of 200 Gb/s (5 bit per symbol modulation format, 56.8 GBaud) signal over terrestrial 520 km single-span fiber link. This was achieved using ultra low-loss fibers with large effective area, ROPAs with dedicated fibers, and distributed Raman amplifiers with co- and counter-propagating pumps.