The Application Of Graded-index Lens In The Coupling System For Optical Fiber Communication

Graded-index(GRIN)lens is widely used in the coupling system between LD and optical fiber for it's small cubage,plane surface,high efficiency. Furthermore, GRIN lens can be manufactured and modulated easily.Based on the introduction of the characteristics of LD, the transmition laws of Gaussian beam and the property of the coupling between lens and optical fiber, the laws of Gaussian beam transmit through a GRIN lens are studied. Also, the method of selecting the optimal parameter of the coupling system is discussed.First of all, the characteristics of Gaussian beam transmit through heterogeneous medium are studied by ABCD law and the definition of complex parameter of Gaussian beam. Based on this conclusion, it can be gained that the formulas of Gaussian beam transmit through a GRIN lens. The width and position of the waist of Gaussian beam are deduced from the formula. Based on the formula, the changes of the waist of Gaussian beam can be studied by a program. When one of the parameters (like the original place of the waist of Gaussian beam,the parameter of GRIN,the width of GRIN lens) is modified, the result is displayed by some pictures.Subsequently, the model of coupling system is established by two GRIN lens to study the method of selecting the optimal parameter of the coupling system ,for example the size of the GRIN lens and the space between the two GRIN lens. At the premise of high efficiency, the two parameters should be small. In another words, the coupling system should be very compact. In this paper, the formulas of the optimal coupling are deduced by self-focalizing law. Based on these formulas, the approximate value of optimal parameter is gained by a program.