| 摘要 |
An optical filter is provided having first and second graded index (GRIN) le nsespreferably disposed in a coaxial relationship so tha t they have a common optical axis. Each of the GRIN lenses has an end face providing a port at predetermined lo cation. The ports are disposed on opposite sides of the optical axis and each of the por ts is substantially equidistant from the optical axis, so as to be oppositely offs et from the optical axis by a same amount. The filter also includes an optical interfere nce filter disposed between other end faces of the first and second graded index lenses . Byproviding at least four spaced ports, equidistant fr om the optical axis, such that two ports form a first couplet on opposite sides of the axis from each other and such that two other ports form a second couplet on opposite sides of the axis from each other, w herein one of the ports of one couplet is optically coupled with one of the ports from the other couplet, an add and drop circuit may be realized. The notion of multi-use of an optic al filter applies not only to an add and drop circuit, but also other WDM devices whic h use several optical filters of a same type.
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