Types Of Single-mode Fibers Research Articles

Assessment on the Achievable Throughput of Multi-Band ITU-T G.652.D Fiber Transmission Systems

Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by $\sim\!11\times$ the available bandwidth of C-band line systems and by $\sim\!5\times$ C+L-band line systems’. MBT offers a high potential for cost-efficient throughput upgrades of optical networks, even in absence of available dark-fibers, as it utilizes more efficiently the existing infrastructures. This represents the main advantage compared to approaches such as multi-mode/-core fibers or spatial division multiplexing. Furthermore, the industrial trend is clear: the first commercial C $+$ L-band systems are entering the market and research has moved toward the neighboring S-band. This article discusses the potential and challenges of MBT covering the ITU-T optical bands O $\rightarrow$ L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and non-linear fiber propagation effects. Non-linear fiber propagation is taken into account by computing the generated non-linear interference by using the generalized Gaussian-noise (GGN) model, which takes into account the interaction of non-linear fiber propagation with stimulated Raman scattering (SRS), and in general considers wavelength-dependent fiber parameters. For linear effects, we hypothesize typical components’ figures and discussion on components’ limitations, such as transceivers,’ amplifiers’ and filters’ are not part of this work. We focus on assessing the transmission throughput that is realistic to achieve by using feasible multi-band components without specific optimizations and implementation discussion. So, results are meant to address the potential throughput scaling by turning-on excess fiber transmission bands. As transmission fiber, we focus exclusively on the ITU-T G.652.D, since it is the most widely deployed fiber type worldwide and the mostly suitable to multi-band transmission, thanks to its ultra-wide low-loss single-mode high-dispersion spectral region. Similar analyses could be carried out for other single-mode fiber types. We estimate a total single-fiber throughput of 450 Tb/s over a distance of 50 km and 220 Tb/s over regional distances of 600 km: $\sim\!10\times$ and 8× more than C-band transmission respectively and $\sim\!2.5\times$ more than full C+L.

High-Temperature Sensitivity in Stimulated Brillouin Scattering of 1060 nm Single-Mode Fibers.

With the rapid advancement of Yb-doped fiber lasers (YDFL) whose output wavelength is near 1060 nm, passive fibers to carry the high optical power at the spectral range are also gaining significant importance. Stimulated Brillouin scattering (SBS) in the passive fibers connecting components in the lasers, especially, can set a fundamental limit in the power handling of YDFL systems. We experimentally analyzed SBS characteristics of passive single mode fibers (SMF) at a wavelength of 1060 nm. For two types of SMFs (Corning HI1060 and HI1060Flex), the Brillouin frequency (νΒ), its linewidth (ΔνΒ), and their variations with respect to the input laser power and the surrounding temperature were experimentally measured, along with the SBS threshold power (Pth). The optical heterodyne detection method was used to identify temperature-dependent SBS characteristics of fibers, and we found SMFs at λ = 1060 nm showed a temperature sensitivity in SBS frequency shift more than 40% higher than in conventional SMFs operating in C-band. Detailed procedures to measure the SBS properties are explained, and a new potential of 1060 nm SMF as a distributed temperature sensor is also discussed.

Inscription of Bragg gratings in nanostructured graded index single-mode fibers.

We report on efficient inscription of fiber Bragg gratings (FBGs) in a new type of single mode fiber with nanostructured core and with an effective parabolic graded index profile, using the standard phase mask method and a 248 nm pulsed laser. A nanostructured core allows to obtain high concentration of GeO2 in subwavelength glass rods and simultaneously to maintain low average germanium dopant level of silica similarly to standard single mode fibers. We showed that in a nanostructured core fiber, a factor of 3 better efficiency in gratings inscription was achieved, although the fiber has 20% lower average concentration of GeO2 with respect to SMF-28. In the nanostructured fiber we obtained a significant improvement in temperature sensitivity, while the strain sensitivity of FBG in nGRIN optical fiber is the same as in case of standard single-mode fiber (SMF-28). We have measured the strain sensitivity of 0.72 × 10-6 1/με (1.11 pm/με@1.53μm), and the temperature sensitivity is about 30% higher than for FBG in SMF-28 and equals to 10.2 × 10-6 1/K (15.6 pm/K@1.53μm).

Detecting cm-scale hot spot over 24-km-long single-mode fiber by using differential pulse pair BOTDA based on double-peak spectrum.

In distributed Brillouin optical fiber sensor when the length of the perturbation to be detected is much smaller than the spatial resolution that is defined by the pulse width, the measured Brillouin gain spectrum (BGS) experiences two or multiple peaks. In this work, we propose and demonstrate a technique using differential pulse pair Brillouin optical time-domain analysis (DPP-BOTDA) based on double-peak BGS to enhance small-scale events detection capability, where two types of single mode fiber (main fiber and secondary fiber) with 116 MHz Brillouin frequency shift (BFS) difference have been used. We have realized detection of a 5-cm hot spot at the far end of 24-km single mode fiber by employing a 50-cm spatial resolution DPP-BOTDA with only 1GS/s sampling rate (corresponding to 10 cm/point). The BFS at the far end of 24-km sensing fiber has been measured with 0.54 MHz standard deviation which corresponds to a 0.5°C temperature accuracy. This technique is simple and cost effective because it is implemented using the similar experimental setup of the standard BOTDA, however, it should be noted that the consecutive small-scale events have to be separated by a minimum length corresponding to the spatial resolution defined by the pulse width difference.

Endlessly single-mode photonic crystal fiber as a high resolution probe.

We sample ultra-broadband light, focused onto a diffraction-limited spot, to an endlessly single-mode photonic crystal fiber (ESM) and detect both the field amplitude and phase using a SEA TADPOLE interferometer. We resolve spatial features up to 2.5 times finer than the fiber mode size while sampling the periodic features of the bipolar oscillating field in the transverse section. The resolution enhancement is expected also in other types of single-mode fibers in intensity measurements and leads to an inexpensive method for characterizing the point-spread function of such optical fields, e.g., diffraction-limited spots from microscope objectives. In addition, we demonstrate the guidance of a high-NA light field in the fine structure of an ESM fiber mode. The results are especially valuable for devices where a fiber tip acts as an input slit and defines the spatial resolution, e.g., fiber-based interferometers, spectrometers, and sensors.

Distributed Strain and Temperature Discrimination Using Two Types of Fiber in OFDR

We present a simple and effective method to achieve a distributed strain and temperature discrimination using two types of fiber by a Rayleigh backscattering spectra (RBS) shifts in optical frequency domain reflectometry. We paired two types of single mode fiber (SMF) side by side as the sensing fibers. One is the reduced-cladding (RC) SMF, and the other is the standard SMF. Since the RC SMF and the standard SMF have different sensitivity responses to strain and temperature variation, we can measure strain and temperature variation simultaneously by monitoring RBS shifts. We demonstrate that the measure errors are 0.31 °C in temperature and 7.97 μϵ in strain with a measurement range of 50 m and a spatial resolution of 18 cm.

Single-Channel Bandpass Filters Formed by a Metal-Doped Fiber and Long-Period Gratings

We demonstrated all-fiber single-channel bandpass filters formed by a high-attenuation metal-doped fiber as a core mode blocker spliced between two long-period fiber gratings (LPFGs). The LPFGs were written in dissimilar fibers, and their grating periods were adjusted so as to match the resonance wavelengths of only one pair of the same order cladding modes and also avoid matching those of other cladding modes. Three types of single-mode fibers with a relative index difference of about 2% $\sim 2.5$ %, 0.8%, and 0.46% were used for fabricating LPFGs. The insertion loss in passband and the full-width at half-maximum bandwidth of fabricated single-channel bandpass filters were 6.6 dB and 4.7 nm, 6.9 dB and 6.4 nm, and 7.7 dB and 7.1 nm.

High Radiation Sensitivity of Chiral Long Period Gratings

The radiation sensitivity of chiral long period gratings was investigated for the first time. After a Co-60 gamma dose of 100 kGy they show radiation-induced changes of their transmission dip wavelength of up to 10 nm, which is 100 to 1000 times higher than the radiation-induced wavelength shift of different fiber Bragg grating types. They can therefore be used as radiation sensors down to doses of 10 Gy or even below, but not for accurate dose measurements since the size of the wavelength shift after a certain dose still depends on the radiation dose rate. Chiral gratings made of eight single mode fiber types with differences of their radiation-induced attenuation of several orders of magnitude were investigated in order to look for a correlation between dip wavelength shift and fiber attenuation. However, the dip wavelength curves do not show exactly the same order as the fiber attenuation curves. A theory that can exactly predict all properties of the chiral gratings might enable us to specify from our results an optimized fiber for the production of gratings that can also be used for radiation dosimetry.

Influence of Humidity on the Measurement of Brillouin Frequency Shift

Distributed sensing based on the Brillouin frequency shift is a useful technique to measure temperature along an optical fiber. However, the measurement can be influenced by the humidity on the fiber and its history. Experimental results using three different types of single-mode fibers with 1 km length, at 25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C and 30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deg</sup> C are reported. Depending of the type of fiber, a displacement on Brillouin frequency from 0.4 up to 2.8 MHz due to changes of humidity is obtained.

Low-loss single-mode fiber with nearly zero chromatic dispersion

We present a new type of single-mode fiber containing 11 radial layers surrounding the core of the fiber and having the same refractive index. The proposed fiber has low propagation losses with nearly zero residual chromatic dispersion for the spectral range of optical communication, and thus it may be a good candidate for transmission of information.

Intensity based erbium distribution for erbium doped fiber amplifiers

A method to calculate an optimum Erbium distribution to enhance the gain efficiency in EDFA is proposed. This method calculates Erbium distribution based on optical pump envelop, pump power and optical properties of Erbium ion. The intensity-based Erbium distribution is obtained for single-mode fiber and dispersion-shifted fiber types EDFA for pump power from 10 to 40 mW. All of the profiles have a Gaussian-like shape. For single-mode fiber type EDFA, high gain enhancement is obtained in a relatively short optimal length of fiber. Optimal length of EDFA, using intensity-based Erbium distribution, is increased by a factor of 1.5–3 with respect to the one using stepwise. This optimal length increasing factor is considerably smaller than that of the EDFA, using the one-fourth confinement Erbium profile.

Characterization of stimulated Brillouin scattering spectra by use of optical single-sideband modulation.

We introduce an enhanced method for the characterization of stimulated Brillouin scattering (SBS) spectra in single-mode fiber that is based on optical single-sideband modulation. This novel technique is shown to provide high-resolution characterization of SBS even under saturation operation in a simple and stable setup in which the spectrum is translated from the optical to the electrical domain, sweeping the frequency of an electrical signal generator. Experimental results are used to demonstrate the performance of the system in measuring the detailed structure of acoustic modes in three types of single-mode fiber.

Chromatic dispersion distribution measurement along a single-mode optical fiber

A nondestructive measurement technique, which uses a four-wavelength bidirectional optical time domain reflectometer (OTDR) to measure the chromatic dispersion distribution along a single-mode fiber, is compared with the destructive interferometric technique. The experimental results obtained by this technique are in good agreement with those obtained by the interferometric technique. In addition, a measurement procedure is proposed for a transmission line composed of different types of single-mode fiber. These results show that this technique is extremely useful for the design of wavelength division multiplexer (WDM) and finite difference multiplexer (FDM) optical communication systems.

Group effective indices of different types of optical fibers measured around 1550 nm

The effective group indices of different single mode fiber types (standard, dispersion shifted or dispersion compensated, polarization maintaining, pure silica core, erbium doped) have been measured in the wavelength range 1.500–1.580 μm; their values range from 1.4635 to 1.4778 at 1.54 μm. These values have been determined by a resonant-cavity method, which provides an accuracy to the fourth decimal place.

Production of preforms for single-mode optical fibers

Production was started of two types of performs with different structures and index profiles. One type of prefo~ns for single-mode (SM) optical fibers at % = 1.3 ~m had the following structure: cladding doped with P and F, a difference An 0 = (1o5-2)o10 -3 between the refractive indices of the cladding and pure SiO 2, and a core doped with Ge, P, and G; in this case An = 0.0040-0.0055~ The other type of SM fiber performs had the following structure: cladding doped with P and Y, refractive-index difference An 0 = (I-2)o10 -4 , i.e., compensated; Ge-doped core; in this case An = 0.0045-0.0055~

Mode coupling effects of the cutoff wavelength characteristics of dispersion-shifted and dispersion-unshifted single-mode fibers

The authors present theoretical background and experimental results to clarify the nature of the hump in the cutoff region of different types of single-mode fibers and discuss its implications. A theoretical model in terms of the coupling between the whispering-gallery mode formed near the silica-cladding/primary-coating boundary and the first higher-order core mode is presented to explain the presence of the hump. An experimental verification of this theoretical model is presented for these fibers. In addition, the curvature sensitivity of the hump is studied for these three fiber types. The results of the study show that for both dispersion-shifted and matched-cladding, dispersion-unshifted fibers, the hump is curvature sensitive and occurs at intermediate (28 and 15 cm) bend diameters. At large (40 cm) and small (10 cm) bend diameters, the hump was not observed in the cutoff region of these two fiber types. However, in the case of the depressed-cladding fiber, the hump was found to be curvature insensitive and occurred at all bend diameters (40, 28, 15, and 10 cm) used in this study.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>