Optical duplexer for bidirectional optical information transmission

An optical duplexer for bidirectional optical information transmission, having a wavelength-selective optical coupler having first, second, third and fourth ports, the first port being provided for input of a first optical wavelength and the second port being provided for input of a second optical wavelength, said coupler being fashioned such that an optical wave of the first optical wavelength input through the first port is conducted partially to the second port and partially to the third port, such that an optical wave of the second optical wavelength input through the second port is at least partially conducted to the fourth port, such that each of said second and third ports have a reflection coefficient that respectively produces a first reflected optical wave of the first optical wavelength returning to the coupler from the second port and supplied to the coupler on a first path and a second reflected optical wave of the first optical wavelength returning to the coupler from the third port and supplied to the coupler on a second path, and such that the first and second reflected optical waves of the first optical wavelength returning to the coupler on the first and second paths, respectively, are brought to interference in the coupler and the combined first and second reflected optical waves of the first optical wavelength are at least partially supplied to the fourth port, comprising:

• the first and second paths having a predetermined difference in optical path length produced by a permanent difference in refractive index between the first and second paths such that a resulting phase difference between the first and second reflected optical waves of the first optical wavelength has a value that reduces near-end crosstalk of the coupler to a predetermined level.

An optical duplexer for bidirectional optical information transmission, comprising:

• a wavelength-selective optical coupler having first, second, third and fourth ports, a first optical wavelength being input on only said first port and a second optical wavelength being input on only said second port, said first optical wavelength being different than said second optical wavelength, said first optical wavelength being output on only said second port and said second optical wavelength being output on only said fourth port, said first and second optical wavelengths being input to said first and second ports, respectively, independent of one another;
• said coupler structured such that an optical wave of the first optical wavelength input through the first port is conducted partially to the second port and partially to the third port, an optical wave of the second optical wavelength input through the second port being at least partially conducted to the fourth port, each of said second and third ports having a reflection coefficient that respectively produces a first reflected optical wave of the first optical wavelength returning to the coupler from the second port and supplied to the coupler on a first path and a second reflected optical wave of the first optical wavelength returning to the coupler from the third port and supplied to the coupler on a second path, the first and second reflected optical waves of the first optical wavelength returning to the coupler on the first and second paths being brought to interference in the coupler and the combined first and second reflected optical waves of the first optical wavelength being at least partially supplied to the fourth port;
• and means for controlling the phase of one of the first and second reflected optical waves of the first optical wavelength returning to the coupler on the respective path of the first and second paths to a predetermined value in a predetermined value range such that a resulting phase difference between the first and second reflected optical waves of the first optical wavelength has a value that reduces near-end crosstalk of the coupler to a predetermined level.