Ultra-low Loss Optical Fiber Research Articles

Twin-Field Quantum Key Distribution with Local Frequency Reference.

Twin-field quantum key distribution (TFQKD) overcomes the linear rate-loss limit, which promises a boost of secure key rate over long distance. However, the complexity of eliminating the frequency differences between the independent laser sources hinders its practical application. We analyzed and determined the frequency stability requirements for implementing TFQKD using frequency-stabilized lasers. Based on this analysis, we proposed and demonstrated a simple and practical approach that utilizes the saturated absorption spectroscopy of acetylene as an absolute reference, eliminating the need for fast frequency locking to achieve TFQKD. Adopting the 4-intensity sending-or-not-sending TFQKD protocol, we experimentally demonstrated the TFQKD over 502, 301, and 201km ultralow-loss optical fiber, respectively. We expect this high-performance scheme will find widespread usage in future intercity and free-space quantum communication networks.

Radiation Monitoring with Radiosensitive Pure-Silica Core Ultra-Low Loss Optical Fiber

Radiation Monitoring with Radiosensitive Pure-Silica Core Ultra-Low Loss Optical Fiber

Preliminary Study on Mechanism and Feasibility of Manufacturing Ultra-Low Loss Optical Fiber in Space

Preliminary Study on Mechanism and Feasibility of Manufacturing Ultra-Low Loss Optical Fiber in Space

Photobleaching Effect on the Radiation‐Induced Attenuation of an Ultralow Loss Optical Fiber at Telecommunication Wavelengths

An unexpected high sensitivity to radiation has recently been discovered in a new generation of ultralow loss pure‐silica core optical fiber, the Corning Vascade EX1000. It is investigated how the injected power level of the probing signal at 1310 and 1550 nm affects the radiation‐induced attenuation (RIA) during and after steady‐state X‐ray exposure up to a total ionizing dose (TID) of 250 kGy (SiO2) at room temperature. The experiments confirm this fiber's high sensitivity to radiations, mainly due to the generation of metastable defects absorbing in the infrared domain. RIA kinetics are characterized by a non‐monotonic behavior, reaching a maximum of the radiation‐induced losses at 3.3 kGy (SiO2). Through successive radiation tests, the RIA dependence on the signal power level at the dose corresponding to the maximum of the RIA is studied, finding out that, for the two investigated wavelengths, the RIA follows a power law dependence in the 100 nW–1 mW injected power range, whose exponent seems independent on the dose rate (between 1 and 6 Gy s−1). The results highlight a clear photobleaching phenomenon, with the RIA associated to these metastable defects strongly reduced at higher injected powers of mW levels.

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.

How fluorine minimizes density fluctuations of silica glass: Molecular dynamics study with machine-learning assisted force-matching potential

Transparent silica glass is an indispensable material for today's information technology society as an ultra-low loss optical fiber. Recently, further low-loss optical fibers are demanded due to rapidly expanding information. A small amount of fluorine doping is known to reduce the Rayleigh scattering further by reducing the density fluctuations of silica glass, even though the fluorine is an impurity for the pristine silica glass. This study devoted to answer the riddle of F-doping and an accurate force-matching potential optimized by machine-learning enables us to understand how fluorine remedies the disorders in silica glass. It was found that fluorine mainly replaces an oxygen in tetrahedral SiO4 unit, but also forms five-fold Si, such as SiO4F and SiO3F2 units. The former disrupts silica network, while the latter attenuates the network rigidity by loosening the five Si-O(F) bonds. Since the two local effects of fluorine spreads through the glass network, F-doping prompts silica glass to relax further even at temperature lower than the glass transition (fictive) temperature. Consequently, fluorine minimizes the density fluctuation (thus, Rayleigh scattering) of silica glass at around 1 wt%, although fluorine itself is an impurity for silica glass.

Long-Distance Continuous-Variable Quantum Key Distribution over 202.81km of Fiber.

Quantum key distribution provides secure keys resistant to code-breaking quantum computers. The continuous-variable version of quantum key distribution offers the advantages of higher secret key rates in metropolitan areas, as well as the use of standard telecom components that can operate at room temperature. However, the transmission distance of these systems (compared with discrete-variable systems) are currently limited and considered unsuitable for long-distance distribution. Herein, we report the experimental results of long distance continuous-variable quantum key distribution over 202.81km of ultralow-loss optical fiber by suitably controlling the excess noise and employing highly efficient reconciliation procedures. This record-breaking implementation of the continuous-variable quantum key distribution doubles the previous distance record and shows the road for long-distance and large-scale secure quantum key distribution using room-temperature standard telecom components.

Observation of four Fermi-Pasta-Ulam-Tsingou recurrences in an ultra-low-loss optical fiber.

We report the experimental observation of more than four Fermi-Pasta-Ulam-Tsingou recurrences in an optical fiber thanks to an ultra-low loss optical fiber and to an active loss compensation system. We observe both regular (in-phase) and symmetry-broken (phase-shifted) recurrences, triggered by the input phase. Experimental results are confirmed by numerical simulations.

Nonlinearities tolerant modulation format enabled Tb/s superchannel transmission over 420 km of unrepeated Raman amplified link

Abstract In this work we investigate different nonlinearities compensation and mitigation techniques for an unrepeated Raman-amplified link over 420 km of ultra-low loss (ULL) optical fiber. For such long links (over 400 km) fiber nonlinearities become very significant as high forward pump power is needed to ensure sufficient optical-signal-to-noise-ratio (OSNR) to acquire a bit-error-rate (BER) not exceeding the forward-error-correction (FEC) threshold. Such nonlinearities will significantly limit the performance. Through numerical simulations, we show successful net 200 Gb/s single carrier and 1 Tb/s superchannel transmission using PM-QPSK and symbol-rate-optimization (SRO). First we implement single carrier 200 G transmission either using 28 Gbaud PM-16QAM or 56 Gbaud PM-QPSK. Nonlinearities are compensated by either using digital-back-propagation (DBP) or phase-conjugated twin waves (PCTWs). We compare the performance of DBP and PCTWs based single carrier 28 Gbaud PM-16QAM, at the same transmission distance and capacity, with single carrier PM-QPSK and find that PM-QPSK does not require any nonlinearity compensation to give better performance than 28 Gbaud PM-16QAM. Following this result, we show a successful unrepeated transmission of net 1 Tb/s PM-QPSK Nyquist-spaced superchannel with an intra-superchannel net spectral efficiency (SE) of ∼3.6 b/s/Hz, over 420 km of Raman amplified ULL fiber without using any nonlinearity compensation. To improve the performance of this superchannel we implement nonlinearity mitigation scheme based on SRO. We investigate 5 × 56 Gbaud, 10 × 28 Gbaud, 20 × 14 Gbaud and 40 × 7 Gbaud PM-QPSK channels and found that the best performance is shown by 20 × 14 Gbaud superchannel. For PM-16QAM, successful transmission is only possible either using DBP or PCTWs based transmission link. DBP has a very high computational complexity whereas PCTWs halves the overall link spectral efficiency. Even then both schemes do not outperform PM-QPSK for the same transmission distance and capacity. So for practical realization the nonlinearity robust modulation format PM-QPSK using SRO has been identified as the most promising approach for superchannel implementation of unrepeated Raman amplified links.

Unrepeatered Nyquist PDM-16QAM transmission over 364 km using Raman amplification and multi-channel digital back-propagation.

Transmission of a net 467-Gb/s PDM-16QAM Nyquist-spaced superchannel is reported with an intra-superchannel net spectral efficiency (SE) of 6.6 (b/s)/Hz, over 364-km SMF-28 ULL ultra-low loss optical fiber, enabled by bi-directional second-order Raman amplification and digital nonlinearity compensation. Multi-channel digital back-propagation (MC-DBP) was applied to compensate for nonlinear interference; an improvement of 2 dB in Q(2) factor was achieved when 70-GHz DBP bandwidth was applied, allowing an increase in span length of 37 km.

Ultra-long-haul 112 Gb/s PM-QPSK transmission systems using longer spans and Raman amplification

Ultra-long-haul transmission at distances greater than 10,000 km is investigated for 112 Gb/s PM-QPSK signals using span lengths of 75 km and 100 km and all-Raman amplification. Two different ultra-low loss and large effective area optical fibers are studied. We demonstrate a reach length of 10,200 km for a 40 channel system using a fiber with effective area 112 μm(2) with 100 km spans, and a reach length of 13,288 km for a system with 75 km spans using a fiber with effective area of 134 μm(2).

低損失光ファイバの実現を目指して

低損失光ファイバの実現を目指して

Sol-gel-derived silica preforms for optical fibers

Sol-gel fabrication of high-silica glass preforms for ultralow-loss optical fibers is reviewed, mainly on the basis of the works of the author. Inherent difficulties in the sol-gel process such as bubble formation during fiber drawing, incorporation of dopants, and formation of a refractive index profile were investigated. Bubbling occurred when the pore-closing temperature of dry gels was lower than a suitable value. Increasing the particle size in a sol solution was remarkably useful in suppressing reboil from dehydrated silica glasses. Using gel-derived fluorine-doped silica glass tubes, a refractive index profile was formed by the out-diffusion technique. Gel-derived optical fibers of 0.43 dB/km optical loss have been successfully fabricated.

Recent progress in halide and chalcogenide glasses

Halide and chalcogenide glasses which are superior to oxide glasses in transmitting light in the mid IR, allow optical operations in the 3–5 and 8–12 μm atmospheric optical windows. The specific family of fluoride glasses has been specially developed in order to achieve ultralow loss optical fibers and waveguiding in the 0.3 to 5 μm region. The extension of the IR transmission domain has been achieved with chalcogenide glasses and these traditional materials will be compared to a new class of IR glasses, the tellurium halides, TeX glasses, which transmit up to 20 μm and have high transparency in the 8–12 μm region.

Progress in Halide Glass Fibers

ABSTRACTFluoride glasses are being considered for use in long distance, mid-infrared transmitting optical fibers. The multi-phonon edge of these fibers is shifted to longer wavelengths compared to silica fibers. The intrinsic loss is therefore lower (< 0.01 dB/km) and occurs at about 2.5 microns. Applications for these fibers include ultra-low loss communication links, radiation resistant links, remoting of IR focal plane arrays and IR power delivery. In addition, this ultra low loss optical fiber may be used for fiber guided missiles with capability for distances longer than 500 km. Most of the interest however, has been focused on development of ultra long (thousands of kilometers), repeaterless communication links. Such repeaterless links may decrease system cost and cable weight, while increasing overall reliability and ease of repair compared to silicate optical fibers.

Interaction of Pb-Cd-Al-Li fluoride glass with water

Fluoride glasses based on high atomic weight metals are being actively investigated for use as ultralow-loss mid-IR optical fiber. In addition to stability, formability and strength, resistance to degradation by water is an important selection criterion. CLAP glass, based on PbF2 and CdF2 has been suggested as a more resistant alternative to fluorozirconate glasses, which are based on ZrF4 and BaF2. For this study, high optical quality CLAP glass has been prepared, exposed to distilled water at room temperature and closely observed. Visible effects of reaction were observed as line etching in a gridlike network and dulling of the surface within 1–1/2 min. Transmissivity was severely impaired within one hr and excrescence had developed at a number of locations by the end of the 18-hr test. The character of alteration appears to depend upon whether the surface is pristine (original) or nascent (formed by fracture). The pristine surface formed a coherent layer containing pores and sporadic, nondescript cellular outgrowths, whereas the nascent surface developed a network of fissures which nucleated and sustained growth of an abundance of crystalline, hexagonal platelet clusters. These results indicate that attack by water is most disruptive on surfaces such as those created in cleaving an optical fiber for splicing. Hermeticity, particularly at connectors, must be assured in order to prevent degradation of fiber and function in glasses of this type.

Some aspects of glass science evolution

The development of halide glasses gives rise to several problems. From a basic point of view, the occurrence of glasses in numerous unexpected systems makes the prediction of glass forming ability a matter of reflection. An approach which encompasses kinetical, thermodynamical and structural aspects would be helpful for further investigations. Progress may be expected from computer simulations and calculations. Surface problems appear to be critical in various aspects of fluoride glass technology. They include hydrolysis, phase separation and diffusion processes. Finally, the reduction of the impurity level will be a major problem with respect to the manufacturing of ultra low loss optical fibers. During the next twenty years, numerous new glass forming systems will be investigated. Heavy metal oxide glasses will be synthesized. Increasing contents of nitrogen will be incorporated in glasses. New halide glasses will be discovered, especially in chloride, bromide, and mixed halide systems. Materials will be developed for optical transmission beyond 10 μm. Optical fibres lower than 10 −2 dB/km in attenuation will be achieved. BeF 2 fibres will be used for UV transmission. New sources and detectors will be available in the medium infrared range. Finally, new data and new concepts will provide a better understanding of glass structure, devitrification processes and optical losses.

Absorption measurement of ν_2 + 2ν_3 band of CH_4 at 133 μm using an InGaAsP light emitting diode

The combination band of nu2 + 2nu3 of CH4 at 1.33 microm (7512 cm(-1)) was observed at 0.3-cm(-1) resolution by a simple experimental arrangement using a near-infrared high-radiant InGaAsP light emitting diode (LED) and a Ge detector. Forty-six line centers were measured with accuracies of 0.03 cm(-1). The assignment of these manifolds was made by inspection of the P, Q, and R branches. The experimental result indicates that the nu2 + 2nu3 band can be used for fully optical remote monitoring of methane using InGaAsP optical sources in conjunction with an ultralow-loss optical fiber network.

Optical remote monitoring of CH4 gas using low-loss optical fiber link and InGaAsP light-emitting diode in 1.33-μm region

Purely optical remote monitoring of low-level CH4 gas is realized for the first time by the method employing a 2-km long-distance, low-loss silica optical fiber link and a compact absorption cell in conjunction with a high radiant InGaAsP light-emitting diode (LED) at 1.33 μm. Based on the present experiment, the detection limit of CH4 in air was confirmed to be approximately 2000 ppm, i.e., 4% of the lower explosion limit of CH4. This result supports the conclusion that the fully optical remote sensing system incorporating ultralow loss optical fiber networks and near infrared LEDs or laser diodes can be extensively used for the detection and surveillance of various inflammable and/or explosive gases in industrial and mining complexes as well as in residential areas.

Verres fluores a large bande de transmission optique et a haute resistance chimique

New stable fluoride glasses have been obtained in the ThF 4-AlF 3-YF 3-BaF 2 quaternary system. The vitreous areas are described in the ThF 4-(Al 0.5Y 0.5)F 3-BaF 2 system and in the four basic ternary diagrams. For a standard glass with molar composition 22.5 % ThF 4, 28.75 % AlF 3, 28.75 % YF 3, 20 % BaF 2, the characteristic temperatures are 446° C for T G and 710° C for the fusion. The refractive index n D is 1.489 and the density is 5.1. The optical transmission range lies from 330 nm to 7000 nm. These glasses are fluorine and water resistant. They are potential ultralow-loss optical fiber materials. Glass formation in this system is discussed by reference to the ionic analysis of the vitreous state.