1. Field of the Invention
The present invention relates to tunable optical filters used in telecommunications applications such as Dense Wavelength Division Multiplexing (DWDM), and more particularly to a multi-layered thin film tunable optical filter.
2. Description of the Related Art
Generally, an optical filter comprises a multi-layered thin film, and utilizes interference of incident light in a multi-layered structure to selectively pass or transmit a particular wavelength range of the incident light. The conventional thin film optical filter has a multi-layered structure of non-metallic materials having different refractive indexes, the layers being formed on a glass substrate by vacuum evaporation. Each layer has a given thickness and a different refractive index to form a filter having a specific filtering characteristic for a given wavelength.
DWDM is an essential technology needed to meet the growing demand for increased communications system capacity. Current DWDM technology requires at least one filter for one DWDM channel. Each channel includes one filter, one multi-fiber collimator and one single-fiber collimator. Therefore, the more channels there are, the more filters are required. Thus conventional DWDM systems are very expensive and bulky. In addition, mechanical and optical reliability is limited due to there being a great many three-port devices in the system.
A tunable optical filter can be provided to resolve the abovementioned problems. The tunable optical filter can selectively add or drop particular wavelength channels from a multi-wavelength network.