Patent ID: 6640024
Filing Date: 2003-10-28
Classification: G02B

Abstract:
An optical signal add-drop wavelength filter for separating optical signals having at least one wavelength &lgr;i(1&lE;i&lE;n) from input optical signals consisting of multiple wavelengths of &lgr;i, . . . , and &lgr;n (n is a positive integer more than 1) or adding optical signals having at least one wavelength &lgr;j to said input optical signals, said wavelength filter comprising:a dual mode optical waveguide and a first optical waveguide in which input of the multiple wavelength optical signals and output of optical signals which experienced wavelength add-drop are performed in a mutually exchanging manner; a mode discriminating directional coupler formed with a first portion of the dual mode optical waveguide and a portion of the first optical waveguide, the mode discriminating directional coupler characterized by energy transfer of at least 50% between a fundamental mode of said first optical waveguide and a higher-order mode of said dual mode optical waveguide and also by enabling the fundamental mode of said dual mode optical waveguide to propagate without change, in said input optical signal range; and a second portion of the dual mode optical waveguide for transmitting optical signals to and from said mode discriminating directional coupler and an arrangement of Bragg gratings, wherein the arrangement of Bragg gratings is written within said second portion of the dual mode optical waveguide, and at least one Bragg grating in the arrangement of Bragg gratings is connected in series and tilted with an angle of more than 0.1 degree with respect to a plane perpendicular to a propagation direction of the optical signals, said at least one Bragg grating serving to perform both mode conversion and reflection of the optical signals propagating within said second dual mode optical waveguide portion at drop wavelength &lgr;i and add wavelength &lgr;j, wherein said first and second portions of the dual mode optical waveguide are provided integrally without any splice, wherein the fundamental mode of said first optical waveguide and the higher-order mode of said dual mode optical waveguide have a same propagation constant, and wherein said mode discriminating directional coupler utilizes coupling of one or more evanescent electric fields.