As already noted in the introduction, OMs are currently widely used not only in FOSP but also in various fiber-optic sensors (VOD) of physical quantities and in fiber-optic devices (HEU). The specificity of this application requires the creation of OM with special properties. Among these special optical agents, formed mainly (like telecommunication optical agents) based on highly pure silica glass, are primarily: optical agents preserving the polarization of radiation; active agents; radiation-resistant OM and microstructured OM. Below, we consider the main characteristics of these OMs and the technology for preparing blanks for these OMs, the fibers themselves are pulled from the blanks on a conventional exhaust system.
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OBs preserving the polarization of radiation
The light propagating in single-mode fibers can be represented as the sum of two polarization modes. Each polarization mode propagates parallel to the fiber axis with its own phase and group velocity values. The phase front of the modes is flat, and the normal to the plane of the phase front is parallel to the fiber axis. The spatial distribution of fields in the polarization fiber modes is the same (Gaussian), and they differ in that they are polarized orthogonally, as can be seen from Fig. 6.1. In an ideal OB, these modes should propagate with the same velocities, i.e. must be degenerate.
However, in a real fiber, some defects are possible: the ellipticity of the core, its misalignment with the fiber axis, microbeads, various non-isotropic stresses lying in the plane of the perpendicular axis of the aircraft, inhomogeneities along the fiber length, etc. All these defects lead to different propagation velocities of modes orthogonal in polarization, and the phase velocities of these modes are inversely proportional to their SP. As a result of this, a phase delay R (the difference between the phase incursions of the modes) arises between the polarization modes. The length of the OM, at which the phase delay is 2, is called the runout length. In modern high-quality organic matter, the run-out length ranges from 10 cm to several meters. Therefore, we can talk about the inherent OM birefringence (DLP), which is written as:
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OBs preserving the polarization of radiation
The light propagating in single-mode fibers can be represented as the sum of two polarization modes. Each polarization mode propagates parallel to the fiber axis with its own phase and group velocity values. The phase front of the modes is flat, and the normal to the plane of the phase front is parallel to the fiber axis. The spatial distribution of fields in the polarization fiber modes is the same (Gaussian), and they differ in that they are polarized orthogonally, as can be seen from Fig. 6.1. In an ideal OB, these modes should propagate with the same velocities, i.e. must be degenerate.
However, in a real fiber, some defects are possible: the ellipticity of the core, its misalignment with the fiber axis, microbeads, various non-isotropic stresses lying in the plane of the perpendicular axis of the aircraft, inhomogeneities along the fiber length, etc. All these defects lead to different propagation velocities of modes orthogonal in polarization, and the phase velocities of these modes are inversely proportional to their SP. As a result of this, a phase delay R (the difference between the phase incursions of the modes) arises between the polarization modes. The length of the OM, at which the phase delay is 2, is called the runout length. In modern high-quality organic matter, the run-out length ranges from 10 cm to several meters. Therefore, we can talk about the inherent OM birefringence (DLP), which is written as:
where B - DLP, which is the difference between the PP of two polarization modes (Dn = n slow. - n fast. ), Lb is the beat length at a wavelength l. Thus, in telecommunication OMs, Dn is small in comparison with the difference between the PPs of the core and shell materials; therefore, polarization dispersion in OMs is only spoken at high transmission rates (> 10 Gbit / s). However, it is impossible to transmit polarized, in particular, linearly polarized radiation over telecommunication OBs over considerable distances.
There are two different approaches to the creation of organic matter preserving the polarization of radiation: these are fibers with a small DLP (respectively, a large beating length) and fibers with a large DLP, which is much larger than the DLP characteristic of a conventional AC.
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