| 摘要 |
PURPOSE:To obtain sufficiently large coupling efficiency even if a distance from the surface of the lens of a light emitting diode to the end surface of an optical fiber is made large, by adopting a composite lens system comprising two lenses, and optimizing the design. CONSTITUTION:A first lens 2 of a light emitting diode is a spherical glass lens made of Na2O-CaO-SiO2 which has a refractive index of 1.5 and a diameter of 200mum. A second lens 5 is a glass convex lens made of Na2O-CaO-SiO2 which has a radium of curvature of 0.8mm for both an incident surface and an output surface, a thickness of 1mm and a refractive index of 1.5. The lenses 2 and 5 are fixed with an interval of 0.8mm being provided. Light comes into a graded index type optical fiber, which has a core diameter of 50mum and an angular aperture of 0.2. A ratio between the power of the incident light and the power of total light emitted from the surface of an LED chip 1 is determined. The relation between said ratio and a distance between the output surface of the second lens and the end surface of the optical fiber is determined from an experiment and computer simulation. Then relative coupling efficiency of about 42%, which is equal to the conventional value, is determined at a position, which is separated from the surface of a cap by about 1.5mm. |
