Pure Silica Core Fiber Research Articles

Dopant, coating, and grating effects in silica optical fibers under extreme neutron irradiation

Radiation effects on fiber Bragg gratings (FBGs) have been studied but data gaps related to the effects of displacement damage resulting from high fast neutron fluence remain. In this work, Type-I and Type-II FBGs inscribed in optical fibers with various core dopants (Ge and F) and fiber coatings (acrylate, polyimide) were monitored in situ during 75 days of neutron irradiation to a peak fast (>0.1 MeV) neutron fluence of 3×1021 nfast/cm2. The reflected intensity of the Type-I FBGs inscribed in a Ge-doped core fiber decreased by >30 dB within 7 h of irradiation (1019 nfast/cm2), whereas Type-II FBGs inscribed in a pure silica core fiber eventually approached >40 dB attenuation after accumulating a fast neutron fluence on the order of 1020 nfast/cm2. Type-II FBGs inscribed in F-doped core fiber improved stability: the attenuation approached an equilibrium value in the range of 10 to 20 dB.

Real-Time 59.2 Tb/s Unrepeated Transmission Over 201.6 km Using Ultra-Wideband SOA as High-Power Booster

Ultrawide-bandwidth (UWB) optical amplification covering C+L bands over 102 nm is implemented by using a seamless semiconductor optical amplifier (SOA) as a high-power booster with a maximum output power of 24.4 dBm as well as a hybrid scheme of pre-amplification, which combines backward distributed Raman pumping with SOA. In order to provide understanding of the transmission performance of SOA, we perform a thorough SOA characterization. By applying different total input powers, we have measured the output spectrum shape and power. In addition, the dependence of the gain on the driving current is also shown. The SOA noise figure is also analyzed for the case of a single channel input. Using the characterized SOA and employing real-time transponders, supporting two different modulation formats: 400 Gb/s PDM-16QAM and 200 Gb/s PDM-QPSK, a total real-time throughput of 59.2 Tb/s has been achieved over an unrepeated transmission span of 201.6 km-long pure silica core fiber (PSCF). Three different configurations of the output power of SOA booster are compared, which demonstrates an improvement of 17% in total throughput when increasing the SOA output power from 21 dBm to 24.4dBm. Our results show the advantages and benefits of high-power SOA boosters for UWB amplification.

Demonstration and Characterization of High-Throughput 200.5 Tbit/s S+C+L Transmission over 2x100 PSCF Spans

Recent advances in multi-band amplification support ultra-wideband (UWB) systems as a suitable solution to cope with the increasing fiber communications traffic demand. The combination of UWB with spectral-efficient modulation formats can significantly increase in the total throughput of wavelength division multiplexed (WDM) transmission systems. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this work, we demonstrate a 240×70 Gbaud PCS-256QAM WDM transmission using an optical bandwidth of 150 nm across the S, C and L bands. We combine doped-fiber amplifiers, semiconductor optical amplifiers (SOA) and backward distributed Raman amplification to achieve 200.5 Tbit/s of total generalized mutual information (GMI) throughput over two 100 km pure-silica-core fibers (PSCFs). We also present the digital twin of this experiment, providing the impact of wavelength-dependent impairments on the system performance. Our results demonstrate the feasibility of high-throughput multi-span UWB transmission.

Simultaneous measurement of strain and temperature based on pure-silica-core fiber and no-core fiber

We propose and demonstrate an all-fiber sensor for simultaneous measurement of strain and temperature that is based on a no-core fiber (NCF) and pure-silica-core fiber (PSCF). Two segments of NCF used as a beam splitter and combiner were embedded on the two ends of the PSCF, which constitutes a Mach–Zehnder interferometer (MZI) susceptible to the strain and temperature. With the change of strain and temperature, the dip wavelengths of transmission spectrum shifted, and simultaneous measurement of strain and temperature was realized by means of a sensitivity coefficient matrix. The experimental results showed that the sensitivity of strain was −0.6 and − 0.9 pm / με in the range from 0 to 1000 με, and the sensitivity of temperature ranging from 20°C to 80°C was 16.9 pm/°C and 11.7 pm/°C, respectively. Furthermore, the fiber sensor processed the advantages of easy-fabrication, compactness, low cost, and all-fiber configuration, and it has potential applications in blade load and damage monitoring in the field of wind power generation.

Radioluminescence Response of Ce-, Cu-, and Gd-Doped Silica Glasses for Dosimetry of Pulsed Electron Beams.

Radiation-induced emission of doped sol-gel silica glass samples was investigated under a pulsed 20-MeV electron beam. The studied samples were drawn rods doped with cerium, copper, or gadolinium ions, which were connected to multimode pure-silica core fibers to transport the induced luminescence from the irradiation area to a signal readout system. The luminescence pulses in the samples induced by the electron bunches were studied as a function of deposited dose per electron bunch. All the investigated samples were found to have a linear response in terms of luminescence as a function of electron bunch sizes between Gy/bunch and Gy/bunch. The presented results show that these types of doped silica rods can be used for monitoring a pulsed electron beam, as well as to evaluate the dose deposited by the individual electron bunches. The electron accelerator used in the experiment was a medical type used for radiation therapy treatments, and these silica rod samples show high potential for dosimetry in radiotherapy contexts.

Measurement of fiber parameters of pure silica core fibers based on the OTDR technique.

We propose a simple technique based on optical time domain reflectometry (OTDR) for measuring the cutoff wavelength and core radius distributions in a pure silica core fiber for the first time. The proposed technique can simultaneously measure several important fiber parameters such as the mode field diameter, relative-index difference, effective area, and chromatic dispersion, including the cutoff wavelength and core radius. We experimentally demonstrate that our proposed technique can successfully evaluate these fiber parameter distributions and can be applied for the measurements of few-mode and multi-core fibers with pure silica cores using multi-channel OTDR and mode couplers.

Independent and mixed transmission of 166.5 Gb/s PM‐8QAM and 222 Gb/s PM‐16QAM Nyquist‐wavelength division multiplexed superchannel for long‐haul metro network

SummaryThis paper investigates the Nyquist‐wavelength division multiplexed (Nyquist‐WDM) terabit superchannel by employing independent and mixed line rate (MLR) transmission of different polarization‐multiplexed quadrature amplitude modulation (PM‐QAM) subcarriers. Here, terabit superchannel transmission including forward error correction overhead is successfully achieved by employing either 7 × 166.5 Gb/s PM‐8QAM or 5 × 222 Gb/s PM‐16QAM or both 2 × 166.5 Gb/s PM‐8QAM and 3 × 222 Gb/s PM‐16QAM simultaneous transmission. Considering linear filtering penalties and nonlinear propagation effects, the proposed superchannel is transmitted over standard single‐mode fiber (SSMF) and pure silica core fiber (PSCF) along with erbium‐doped fiber amplifier (EDFA) at 19.8‐ and 15.12‐dB span loss for SSMF and PSCF, respectively. The performance of both terabit superchannels is analyzed in terms of maximum reach, good spectral efficiency, highest transmission capacity, and optimum launch power with variation in channel spacing from 50‐GHz fixed ITU‐T grid to 29 GHz, at an acceptable bit error rate (BER). To achieve BER 4 × 10−3, MLR‐based 166.5 Gb/s PM‐8QAM and 222 Gb/s PM‐16QAM suffer a penalty of 5.5‐ and 9.2‐dB OSNR over Nyquist‐only 7 × 166.5 Gb/s PM‐8QAM and 5 × 222 Gb/s PM‐16QAM transmission at the advent of a flexible multi‐flow transponder. It is observed that at 33.33‐GHz Nyquist spacing over PSCF, 5 × 222 Gb/s PM‐16QAM and 7 × 166.5 Gb/s PM‐8QAM superchannels deliver a reach up to 1800 and 2970 km, while MLR approach results in extreme reach of 2250 and 3600 km over PSCF as per MLR PM‐16QAM and PM‐8QAM subcarriers, respectively. Hence, an appreciable spectral efficiency–distance product (SEDP) is achieved due to PSCF at Nyquist spacing of 33.33 GHz with 5.25 bit/s/Hz spectral efficiency. A good link power budget is also calculated for the proposed MLR‐based Nyquist‐WDM superchannel. MLR‐based PM‐16QAM and PM‐8QAM subcarriers deliver excellent SEDP of 11,812 and 18,900 bit/s/Hz·km, respectively, which is, to the best of author's knowledge, better on comparing with the other existing literature for single‐core channel explorations.

Transmission of 61 C-Band Channels Over Record Distance of Hollow-Core-Fiber With L-Band Interferers

We report on two recirculating loop transmission experiments over a hollow-core fiber of the Nested-Antiresonant Nodeless type (NANF). We transmitted 61 channels in C-band at 32 GBaud, with either PM-QPSK or PM-16QAM modulation. In addition, 61 L-band interferers co-propagated in the NANF at all times, though they were not recirculated in the loop, to check for the presence of possible crosstalk effects between C and L-band in the NANF. The loop comprised the longest NANF transmission line yet constructed (7.72 km), as well as 55 km of pure-silica-core fiber (PSCF) needed to provide enough signal buffering and EDFA stabilization for the loop. The launch power into the PSCF was low enough to avoid generation of any significant non-linear noise. Using PM-QPSK, we achieved a record 618 km transmission in NANF (80 recirculations), at an overall average GMI of 3.44 bits/symb. Using PM-16QAM, we achieved a record 201 km transmission, at an overall average GMI of 7 bits/symb. We saw no adverse effect from the presence of L-band interferers in the NANF. If progress in the reduction of NANF loss and inter-modal interference continues at the rate of the last few years, these hollow-core fibers might become a promising alternative in the quest for next-generation higher-throughput fibers, given their theoretical potential of achieving low loss and ultra-low non-linearity over ultra-wide bandwidths, ideally bringing about a many-fold increase in throughput per fiber.

Extreme Radiation Sensitivity of Ultra-Low Loss Pure-Silica-Core Optical Fibers at Low Dose Levels and Infrared Wavelengths.

We report here the response of a commercial ultra-low loss (ULL) single-mode (SM) pure silica core (PSC) fiber, the Vascade EX1000 fiber from Corning, associated with 0.16 dB/km losses at 1.55 µm to 40 keV X-rays at room temperature. Today, among all fiber types, the PSC or F-doped ones have been demonstrated to be the most tolerant to the radiation induced attenuation (RIA) phenomenon and are usually used to design radiation-hardened data links or fiber-based point or distributed sensors. The here investigated ULL-PSC showed, instead, surprisingly high RIA levels of ~3000 dB/km at 1310 nm and ~2000 dB/km at 1550 nm at a limited dose of 2 kGy(SiO2), exceeding the RIA measured in the P-doped SM fibers used for dosimetry for doses of ~500 Gy. Moreover, its RIA increased as a function of the dose with a saturation tendency at larger doses and quickly recovered after irradiation. Our study on the silica structure suggests that the very specific manufacturing process of the ULL-PSC fibers applied to reduce their intrinsic attenuation makes them highly vulnerable to radiations even at low doses. From the application point of view, this fiber cannot be used for data transfer or sensing in harsh environments, except as a very efficient radiation detector or beam monitor.

Effects of hydroxyl content in pure silica optical fiber exposed to kGy electron beams

We present a study on the effect of high dose (kGy) electron beams on pure silica core fibers through examining the following phenomena within the fibers: radioluminescence (RL), radiation induced attenuation (RIA), and recovery. The objective is to identify the relevant characteristics of these fibers having favourable radiation response, that can be utilized in the development of dose measurement systems for high dose (kGy) environments. Two types of 20 m long pure silica optical fiber samples have been used, differing in their concentrations of hydroxyl (OH) content. Segments of 3.5 m length from each fiber were wound into coils of radius ~25 cm and exposed to consecutive irradiation doses, in the order of tens of kGy (10 kGy through 70 kGy in individual exposures), leading to a cumulative dose of some 300 kGy. The low-OH fiber showed saturation of response at the shorter wavelengths of the RL spectrum for doses of 30 kGy and above, resulting from presence of Oxygen Defect Centers (ODC). At the longer wavelengths the RL response of the low-OH optical fibers is observed to increase with dose, attributed to various bonding structural defects of silica nanoclusters. The saturation effect at shorter wavelengths is less prominent in the high-OH samples, where a monotonic increase is observed up to ~60 kGy indicating the formation of radiation induced ODC beyond this point. For cumulative dose of ~70 kGy, the highest RIA losses were registered at 550 nm (12.74 dB/m) for low-OH sample, and at 460 nm (4.75 dB/m) for high-OH sample. The high-OH sample showed much faster recovery post-irradiation, making it more suitable for repeated usage. Both the RL and RIA phenomena observed herein show the feasibility of pure silica optical fibers for dose measurement in high dose (kGy) environments up to individual dose of ~70 kGy.

0.55 Tb/s heterogeneous Nyquist-WDM superchannel using different polarization multiplexed subcarriers

This paper depicts the design of 0.55 Tb/s heterogeneous Flexi-rate Nyquist-wavelength division multiplexed (Nyquist-WDM) Superchannel. Here, for the first time, four subcarriers of different modulation formats are accommodated, namely polarization multiplexed-binary phase-shift keying, polarization multiplexed-quadrature phase-shift keying (PM-QPSK), polarization multiplexed-8-quadrature amplitude modulation and PM-16QAM, each with 27.75 Gbaud symbol rate. The system transmission performance with acceptable bit error rate (BER) 4 × 10−3 is analyzed over pure silica core fiber (PSCF) in the presence of hybrid optical amplification, i.e., Raman amplifier along with a counter-propagating pump and Erbium-doped fiber amplifier. The presence of this hybrid optical amplification unit results in a limited optical signal-to-noise ratio requirement and makes the whole system cost-effective. The proposed work delivers excellent spectral efficiency of 4.5 b/s/Hz and highest transmission reach of 5500 km for PM-QPSK subcarrier and 2300 km for PM-16QAM subcarrier in the presence of PSCF. The system performance against intersymbol interference and noise is also analyzed with the aid of eye pattern plot at a minimum and maximum transmission length.

Overview of radiation induced point defects in silica-based optical fibers

Abstract Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emission and the radiation induced refractive index change. Depending on the fiber profile of use, these phenomena differently contribute to the degradation of the fiber performances and then have to be either mitigated for radiation tolerant systems or exploited to design radiation detectors and dosimeters. Considering the strong impact of radiation on key applications such as data transfer or sensing in space, fusion and fission-related facilities or high energy physics facilities, since 1970′s numerous experimental and theoretical studies have been conducted to identify the microscopic origins of these changes. The observed degradation can be explained through the generation by ionization or displacement damages of point defects in the differently doped amorphous glass (SiO2) of the fiber's core and cladding layers. Indeed, the fiber chemical composition (dopants/concentrations) and elaboration processes play an important role. Consequently, identifying the nature, the properties and the generation and bleaching mechanisms of these point defects is mandatory in order to imagine ways to control the fiber radiation behaviors. In this review paper, the responses of the main classes of silica-based optical fibers are presented: radiation tolerant pure-silica core or fluorine doped optical fibers, germanosilicate optical fibers and radiation sensitive phosphosilicate and aluminosilicate optical fibers. Our current knowledge about the nature and optical properties of the point defects related to silica and these main dopants is presented. The efficiency of the known defects to reproduce the transient and steady state radiation induced attenuation between 300 nm and 2 µm wavelength range is discussed. The main parameters, related to the fibers themselves or extrinsic - harsh environments, profile of use - affecting the concentration, growth and decay kinetics of those defects are also reviewed. Finally, the main remaining challenges are discussed, including the increasing needs for accurate and multi-physics modeling tools.

Comparative Investigation of Gamma Radiation Effects on Long Period Gratings and Optical Power in Different Optical Fibers

This work presents a comparative study regarding the effects of gamma radiation on standard and different radiation hardened optical fibers, by means of arc-induced long period gratings (LPGs) written in these fibers. In particular, the resonance wavelength shift (Δλres) of LPG attenuation bands and the attenuation in the fiber transmitted optical power (ΔP) have been comparatively explored during irradiation. Different responses were observed depending on the fiber model. The Ge-doped fiber exhibits significant changes of both resonance wavelength and optical transmission loss, whereas the pure silica core fiber is mostly insensitive to radiation (Δλres and ΔP keep almost close to zero). Surprisingly, the radiation resistant fiber, with doped core, exhibits significant resonance shift even if with trivial power losses. In addition, by combining these results with numerical modeling of LPGs, we were able to estimate the radiation effects on the optical fibers under investigation, in terms of average refractive index change. These results can be useful for the application of such devices in radiation environments, i.e., for the development of both radiation sensitive and radiation hardened sensors.

Spectrally efficient 1.55 Tb/s Nyquist-WDM superchannel with mixed line rate approach using 27.75 Gbaud PM-QPSK and PM-16QAM

This paper investigates the transmission performance of a 1.55-Tb/s Nyquist-wavelength division multiplexing superchannel along with a mixed line rate approach using 4 × 111 Gb / s polarization-multiplexed quadrature phase shift keying (PM-QPSK) and 5 × 222 Gb / s polarization-multiplexed quadrature amplitude modulation (PM-16QAM) formats. The system transmission performance with acceptable bit error rate of 4 × 10 − 3 is analyzed over standard single mode fiber (SSMF), large effective area fiber (LEAF), and pure silica core fiber (PSCF). It is observed that SSMF increases 45% reach over LEAF, whereas PSCF increases 66% to 84% reach over LEAF for 4.5 b/s/Hz spectral efficiency of the system. Also, spectral efficiency × distance product of 24,750 and 10,350 b/s/Hz.km are obtained for PM-QPSK and PM-16QAM, respectively, which is, to the best of our knowledge, better in comparison with the other existing literatures for single core channel investigations.

Long Period Gratings in unconventional fibers for possible use as radiation dosimeter in high-dose applications

In this work, we conducted experimental and theoretical investigations on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique in two different single mode optical fibers, designed to be radiation resistant, with the aim to understand their behavior under irradiation and their radiation hardness as a function of core/cladding dopants. The first fiber is sold by the manufacturer to be used in harsh environments and has doped core and pure-silica cladding, while the second one is radiation-hardened with pure-silica core and F-doped silica cladding. Gamma irradiation was performed at a 60Co source with a 0.2 kGy/h dose rate, until a total absorbed dose close to 30 kGy was reached. During the experiments, the LPGs spectral changes were recorded in real-time, moreover pre- and post- irradiation investigations were done to establish the impact of gamma radiation over fiber refractive index modification and LPGs temperature sensitivity. The LPG in pure-silica core fiber proved its radiation hardness exhibiting changes in resonant wavelength position lower than 0.2 nm, on the contrary the LPG written in doped-core fiber showed high sensitivity to radiation with a wavelength shift of 5.7 nm at the end of the irradiation. The outcomes of this experimentation, along with our previous results on gamma irradiated LPGs, are useful for the design of an all LPG-based temperature compensated radiation dosimeter.

Femtosecond FBG Written through the Coating for Sensing Applications.

Type I fiber Bragg gratings (FBG) written through the coating of various off-the-shelf silica fibers with a femtosecond laser and the phase-mask technique are reported. Inscription through most of the common coating compositions (acrylate, silicone and polyimide) is reported as well as writing through the polyimide coating of various fiber cladding diameters, down to 50 µm. The long term annealing behavior of type I gratings written in a pure silica core fiber is also reported as well as a comparison of the mechanical resistance of type I and II FBG. The high mechanical resistance of the resulting type I FBG is shown to be useful for the fabrication of various distributed FBG arrays written using a single period phase-mask. The strain sensing response of such distributed arrays is also presented.

Thermally Stable Type II FBGs Written Through Polyimide Coatings of Silica-Based Optical Fiber

Type II-IR fiber Bragg gratings (FBGs) were written directly through the protective polyimide coatings of off-the-shelf pure silica core and standard telecom Ge-doped silica core single mode fibers using ultrafast IR radiation and the phase mask FBG writing method. Using a short focal length acylindrical lens and nonlinear photoluminescent imaging, type II grating structures could be created when Fourier transform limited pulses were chirped to 500 fs. The resulting gratings in the Ge-doped fibers were thermally stable up to 1000 °C and could be used directly as fabricated without annealing to stabilize the structure.

Comparison of Probabilistically Shaped 64QAM With Lower Cardinality Uniform Constellations in Long-Haul Optical Systems

In this paper, we compare the performance of probabilistically shaped 64QAM with uniform 16QAM and 32QAM modulation formats at the same net data rate in long-haul coherent optical communications systems. Experimental results at 16 GBaud are shown, with offline postprocessing of the data performed using either an ideal or a realistic carrier phase estimation (CPE) scheme. We show that the choice of the CPE algorithm at the receiver is crucial, since, as predicted by current models, most of the additional nonlinear noise introduced by the shaping is nonlinear phase noise (NLPN). Thanks to the use of probabilistic shaping (PS), maximum reach gains ranging from 15.5% and 34% are obtained over pure silica-core fiber, where the NLPN can be efficiently compensated for by standard CPE algorithms, while over nonzero dispersion-shifted fiber, the gain of PS is drastically reduced, due to residual short-correlated NLPN.

Gamma radiation-induced blue shift of resonance peaks of Bragg gratings in pure silica fibres

We report the first observation of a significant gamma radiation-induced blue shift of the reflection/transmission peak of fibre Bragg gratings inscribed into pure-silica core fibres via multiphoton absorption of femtosecond pulses. At a total dose of , the shift is . The observed effect is attributable to the ionising radiation-induced decrease in the density of the silica glass when the rate of colour centre formation is slow. We present results of experimental measurements that provide the key parameters of the dynamics of the gratings for remote dosimetry and temperature sensing.

All-optical and digital non-linear compensation algorithms in flex-coherent grouped and un-grouped contiguous spectrum based networks

We have evaluated that in-line non-linear compensation schemes decrease the complexity of digital backward propagation and enhance the transmission performance of 40/112/224 Gbit/s mixed line rate network. Multiple bit rates, i.e. 40/112/224 Gbit/s and modulation formats (i.e. DP-QPSK and DP-16QAM) are transmitted over 1280 km of Large \(\hbox {A}_{eff}\) Pure-Silica core fiber. Both grouped and un-grouped spectral allocation schemes are investigated. Optical add-drop multiplexers are used to drop the required wavelength for signal processing in the transmission link. Moreover, hybrid mid-link spectral inversion and in-line non-linear compensation methods are also analyzed. This gives us enhanced system performance and DBP step-size of 400 km in WDM 224 Gbit/s DP-16QAM system, significantly reducing the complexity of digital backward propagation.