OPTICAL WAVELENGTH FILTER

摘要

PURPOSE:To stabilize a fiber system by providing low refractive index parts having the refractive index lower than the refractive index of a clad so as to face each other with the core in the clad in-between and stretching part of the fiber in the longitudinal direction thereof. CONSTITUTION:A filter consists of the fiber 21 having the low refractive index, a stretching region 22, the core 23, the clad 24 and the low refractive index parts 25 installed to face each other with the core 23 in the clad 24 in-between. Part of the fiber 21 having the low refractive index parts 25 is heated and stretched to form the stretching region 22. The core diameter decreases as well with a decrease in the outside diameter of the clad in the region 22 and the electric field of light spreads to the clad 24. Then mode coupling arises between the electric field spreading in equal directions around the core 23 and the electric field around the region sandwiched by the parts 22 and the outside of the clad 24 and the transfer of light power arises. As a result, the wavelength of a small loss and the wavelength of a large loss exist periodically and function as a filter.