tailieunhanh - Microengineering MEMs and Interfacing - Danny Banks Part 12

Tham khảo tài liệu 'microengineering mems and interfacing - danny banks part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 202 Microengineering MEMS and Interfacing A Practical Guide Cladding Core FIGURE An optical fiber waveguide cross section consists of a core of 3-200 pm and cladding that form a fiber of 140-400 pm diameter. The fiber is usually coated with a protective plastic sheath indicated . Fibers are normally provided with additional protective sleeving. To make a connection between two fibers splice the fibers the outer protective sheath has to be stripped off the fibers cleaved cleanly at right angles and the two cores aligned. Even slight misalignment can cause considerable loss of signal and this is one area in which microsystems have been deployed micromanipulation and alignment of optical fibers for splicing. There are two different kinds of fiber single mode and multimode. Singlemode fibers have thin cores usually less than 10 pm in diameter and light can propagate through them via only one direct path Figure . In multimode fibers light can propagate by many paths Figure and Figure the difference between the two fiber types is that multimode propagation tends to lead to less signal attenuation diminution with distance but more signal broadening because different parts arrive at the end of the fiber at slightly different times which results in lower data rates. This can also be a problem if particular properties of the signal polarization for instance are important. There are a further two classifications to be made for fibers depending on the profile of the refractive index change between the core and cladding. This can be either a step change or a graded change. Figure and Figure show how this affects propagation in multimode fibers. Optical fibers convey signals with optimal efficiency in the infrared region at wavelengths of about 850 nm 1300 nm and 1550 nm. Fabrication of Optical Fibers The fabrication of glass optical fibers is instructive because the small dimensions observed are achieved without micromachining. The basic .