Progress in low-loss and high-bandwidth plastic optical fibers

BASIC CONCEPT AND CLASSIFICATION OF OPTICAL FIBERS

The principle of light propagation through POFs is the same as that for GOFs. POFs are basically composed of two coaxial layers: the core and the cladding. The core is the inner part of the fiber that guides light, whereas the cladding completely surrounds the core. The refractive index of the core is slightly higher than that of the cladding. Hence, when the incident angle of the light input to the core is greater than the critical angle, the input is confined to the core region because of total internal reflection at the interface between the different dielectric materials comprising each layer. Although this simple concept is a useful approximation of light guidance in many kinds of fibers, it does not provide a full explanation. Light is really an electromagnetic wave with a frequency in the optical range. An optical fiber guides the waves in distinct patterns called modes, which describe the distribution of light energy across the waveguide. Commonly used optical fibers can be separated into two classes based on their modal properties: single-mode and multimode fibers. Single-mode fibers are step-index (SI) fibers, whereas multimode fibers can be divided into SI and graded-index (GI) fibers. SI and GI refer to patterns of variation in the refractive index with the radial distance from the fiber axis. Figure 1 schematically shows these three types of fibers: (a) the single-mode fiber, (b) the SI multimode fiber, and (c) the GI multimode fiber.

Currently, most GOFs are fabricated with single-mode structures and are commonly used in long-distance applications such as core and metropolitan networks. With respect to coupling loss, the small core of single-mode fibers is a serious disadvantage; the smaller the core diameter, the harder it is to couple light into the fiber. Hence, GI multimode-type fibers were also extensively studied12-15 and deployed in some telecommunication applications up until the mid-1980s. However, as single-mode GOFs were far superior in both attenuation and bandwidth, they gradually shifted to short-length applications such as storage area networks. Coupling light into a single-mode fiber inevitably requires considerably tighter tolerances than doing so into the larger cores of a multimode fiber. However, such tighter tolerances were achieved; nowadays, the single-mode GOF has become the standard choice for virtually all kinds of telecommunications that involve high bitrates or span distances longer than a couple of kilometers

On the other hand, POFs have attracted attention as optimal candidates for short-distance networks such as intrabuilding networks.9 Optical fibers must be able to connect various devices in the individual rooms of a building; hence, they must be flexible, easy to bend, and connected at several points. Predictably, the single-mode GOF is unsuited for this application given its brittleness and small core. In contrast, POFs can be enlarged to ∼1 mm in diameter without losing flexibility or ease of fiber alignment.

THE ADVENT OF POFs AND ANALYSIS OF ATTENUATION

Currently, most GOFs are fabricated with single-mode structures and are commonly used in long-distance applications such as core and metropolitan networks. With respect to coupling loss, the small core of single-mode fibers is a serious disadvantage; the smaller the core diameter, the harder it is to couple light into the fiber. Hence, GI multimode-type fibers were also extensively studied12-15 and deployed in some telecommunication applications up until the mid-1980s. However, as single-mode GOFs were far superior in both attenuation and bandwidth, they gradually shifted to short-length applications such as storage area networks. Coupling light into a single-mode fiber inevitably requires considerably tighter tolerances than doing so into the larger cores of a multimode fiber. However, such tighter tolerances were achieved; nowadays, the single-mode GOF has become the standard choice for virtually all kinds of telecommunications that involve high bitrates or span distances longer than a couple of kilometers.

Our company is a high-tech enterprise specializing in the research, development, production and sales of a series of optical fibre application products such as plastic optical fibre, plastic optical fibre cable, optical fibre audio, optical fibre patch cord, optical fibre lighting, optical fibre transmission, optical fibre control and so on. Welcome to inquire!