| Optical feedback degrades signal-to-noise ratio and consequently results in high bit-error rate in fiber communication. The light would cause back scattering and feedback problems if it enters the source. Fiber optic isolators are passive optical devices that allow light to be transmitted in only one direction. They are most often used to prevent any light from reflecting back down the fiber. Ultra-speed and large-capacity optical fiber trunk systems are expanding as a result of the development of optical fiber amplifiers, and the demand for optical isolators is increasing. Demand is also expected to increase, as LAN and other subscriber optical fiber networks expand. It is therefore required that isolators and other optical components be further improved to achieve higher performance, smaller size, and lower price. At present a vital part of optical component production depends on human skill and know-how, so we need to develop new technologies for the production of isolators or other new type optical components to meet the challenge. In the thesis, at first the application of fiber optical isolator in the optical communication is introduced. Its working in EDFA (Erbium Doped Fiber Amplifier) and optimizing the EDFA are analyzed. The development of passive components in China is mentioned. Secondly the light tracks in wedge-type dual-stage polarization independent optical isolator are studied and the locations of light transported in and out isolator core as well as the relationship between the angle-alignment of back going lights and the wedge angle are described. Then the development of the parts of optical isolator, such as collimator, wedge, Faraday rotator and magnetic ring, is presented and the coupling losses between collimators are compared. Finally the laboratory work on isolator and isolator array is demonstrated. Some theoretical analysis and measuring job on IL, ISO, PDL and PER are made, especially the PMD test method, a hot subject, is presented. |
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