Depressed Cladding Single-mode Fibers Research Articles

Stability of Grating-Based Optical Fiber Sensors at High Temperature

We present a comparison of four different grating-based optical fiber high-temperature sensors. Three of the sensors are commercially available, and include a heat treated, twisted (chiral) pure-silica microstructured optical fiber, a femtosecond laser written Bragg grating in a depressed cladding single mode fiber, and a regenerated fiber Bragg grating. We compare these to an in-house fabricated femtosecond laser ablation grating in a pure-silica microstructured optical fiber. We have tested the sensors in increments of 100 °C up to 1100 °C for the duration of at least 24 hours each. All four sensors were shown to be operational up to 900 °C, however, the two sensors based on pure-silica microstructured fiber displayed higher stability in the reflected sensor wavelength, compared to the other sensors at the temperatures of 700 °C and higher. We further investigated the high-temperature stability of silica suspended-core fibers with femtosecond laser inscribed ablation gratings, which show improved stability up to 1050 °C, following thermal annealing. This investigation can be used as a guide for selecting fiber types, packaging, and grating types for high-temperature sensing applications.

Optical time-domain reflectometry (OTDR) of diameter modulations in single mode fibers

The influence of several types of diameter variations on the attenuation and on the optical time-domain reflectometry (OTDR) traces of specially prepared depressed cladding SM (single-mode) fibers is experimentally investigated. Depressed-cladding SM fibers have been prepared by the low-pressure plasma-induced chemical vapor deposition (PCVD) process. The core consists of GeO/sub 2/-doped SiO/sub 2/ and the cladding region of fluorine-doped silica. During drawing, the diameter of the fiber is controlled within +or-0.3 mu m for slow perturbations by adjusting the drawing speed (Anritsu M501A). Variations of the core diameter have been accomplished by changing the set point of the fiber diameter control. Core diameter changes give rise to steps or deviations in slope of the OTDR power trace of about 0.3 dB/ mu m. No indication of additional attenuation due to axial fiber parameter variations has been found up to core diameter changes of 12 mu m/m, despite severe distortions of the OTDR traces. >

Stress-optic effects, birefringence, and reduction of birefringence by annealing in fiber Fabry-Perot interferometers

The effects of inherent fiber birefringence, packaging stresses, and stress tuning on the behavior of a fiber Fabry-Perot interferometer are examined. A polarization doublet due to birefringence is observed. For birefringence of 1 ps/km, the doublet spacing is 40 MHz, at 1.5- mu m wavelength, independent of the FFP finesse or free spectral range, and is due mainly to the inherent fiber birefringence. It was found that annealing depressed-cladding single-mode fiber reduced the fiber birefringence, for example, from 40-80 MHz to 15-25 MHz. Where the bandpass of the FFP is greater than the birefringence doublet, this device should be polarization insensitive for most applications. >

Single-Mode Fiber: From Research and Development to Manufacturing

Single-mode lightwave has completely replaced multimode as the technology of choice for long-haul, metropolitan interoffice, and subscriber loop systems. This article discusses the design principles and performance of four kinds of single-mode fibers developed by AT&T Bell Laboratories. AT&T Technologies has shipped over a thousand megameters of a fiber (in cable form) optimized for 1310-nm systems. This fiber is known as a depressed-cladding single-mode fiber, because of its refractive-index profile. It was designed to provide low intrinsic loss, high bandwidth, low splice loss, and a high resistance to macrobending- and microbending-induced losses. Three other fibers that offer new possibilities to system designers are: dispersion-shifted fiber that is optimized for 1550-nm systems; dispersion-flattened fiber that has high bandwidth over a wide wavelength range; and polarization-maintaining fiber that can be used with phase-sensitive receivers.

Interferometric determination of dispersion variations in single-mode fibers

Interferometry is used to study the variation of the zero dispersion wavelength (λ 0 ) and the absolute group index (N g ) along the lengths of depressed cladding single-mode fibers. All of the results are for 34-cm samples of AT&T fibers drawn on production facilities. For two 7.5-km fibers sampled approximately every 1 km, \bar{\lambda_{0}} = 1299.6 \pm 2.7 and 1300.5 ± 2.9 nm. For five additional 0.8-km fibers, the average of the end-to-end differences of λ 0 is 2.0 nm. These results indicate the feasibility of inferring λ 0 for long lengths of these fibers from measurements made on a 34-cm length. At 1.30 μm, \bar{N_{g}} and σ are 1.4659 and 0.0003, respectively (60 fibers from 28 preforms). The corresponding values at 1.55 μm are 1.4666 and 0.0003 (46 fibers from 19 preforms). These results place a lower limit of 0.02 percent on the accuracy of pulse delay measurements of unstressed lengths of AT&T production fibers.

Fabrication of matched cladding and depressed cladding single mode optical fibers

Abstract Modified chemical vapor deposition method was used to fabricate single mode optical fibers. Both matched and depressed cladding single mode fibers were designed and fabricated. Loss as low as 0.3 dB/km has been obtained at wavelength 1.55 μm.

Review of the Depressed Cladding Single-Mode Fiber Design and Performance for the SL Undersea System Application

High-capacity undersea cable systems based on optical transmission over single-mode lightguides offer tremendous economic advantage over coaxial cable technology due to their combined high-bit-rate long repeater spacing potential. However, very stringent requirements for the lightguide transmission medium properties must be met in order to realize the performance goals of such systems. This paper will review the depressed index cladding single-mode fiber design and its resultant performance. The ability to simultaneously realize excellent optical, mechanical, and dimensional properties in lightguides of this type fabricated using the Modified Chemical Vapor Deposition (MCVD) process has resulted in their use in the AT&T SL system to be used in TAT8.

Review of the depressed cladding single-mode fiber design and performance for the SL undersea system application

High-capacity undersea cable systems based on optical transmission over single-mode lightguides offer tremendous economic advantage over coaxial cable technology due to their combined high-bit-rate long repeater spacing potential. However, very stringent requirements for the lightguide transmission medium properties must be met in order to realize the performance goals of Such systems. This paper will review the depressed index cladding single-mode fiber design and its resultant performance. The ability to simultaneously realize excellent optical, mechanical, and dimensional properties in lightguides of this type fabricated using the Modified Chemical Vapor Deposition (MCVD) process has resulted in their use in the AT&T SL system to be used in TAT8.

Length dependence of the effective cutoff wavelength in single-mode fibers

The effective cutoff wavelength of a depressed cladding single-mode fiber in either a cabled or a loose state depends upon the length of the fiber. This dependence can be accurately represented by a linear function of the logarithm of the fiber length for lengths between 1 m and 1 km. Cutoff will shift 55-66 nm per decade length for slightly and moderately depressed cladding designs, respectively. Neglecting all sources of differential mode attenuation except leaky-mode loss, the computed behavior of cutoff as a function of fiber length agrees reasonably well with the observed behavior for a moderately depressed cladding design. On the other hand, agreement is poor for a slightly depressed cladding design. A knowledge of the length dependence of cutoff is essential for establishing a production requirement for cutoff based upon the needs of the system.