Optical wavelength-division multiplexing and demultiplexing by using a common optical bandpass filter for adding, dropping, or excanging one or more channels

A device, comprising:

• a first lens and a second lens spaced from each other and aligned to define an optical axis, said first lens having a first focal plane on one side of said first lens opposite to a side where said second lens is located and said second lens having a second focal plane on one side of said second lens opposite to a side where said first lens is located;
• an optical bandpass filter located between said first and said second lenses and operable to transmit light at a transmitting wavelength and to reflect light at other wavelengths;
• first and second fiber ports placed in said first focal plane and symmetrically displaced from said optical axis so that a beam from said first fiber port, upon reflection by said optical bandpass filter, is focused onto said second fiber port by said first lens and vice versa;
• third and fourth fiber ports placed in said second focal plane and symmetrically displaced from said optical axis so that a beam from said first fiber port at said transmitting wavelength transmits through said first lens, said second lens, and said optical bandpass filter to reach said fourth fiber port and vice versa and a beam from said third fiber port at said transmitting wavelength transmits through said second lens, said optical bandpass filter, and said first lens to reach said second fiber port and vice versa;
• fifth and sixth fiber ports at said first focal plane and symmetrically displaced from said optical axis so that a beam from said fifth fiber port, upon reflection by said optical bandpass filter, is focused onto said sixth fiber port by said first lens and vice versa;
• and
• seventh and eighth fiber ports at said second focal plane and symmetrically displaced from said optical axis so that a beam from said fifth fiber port, if transmissive to said optical bandpass filter, transmits through said first lens, said optical bandpass filter, and said second lens to reach said eighth fiber port and vice versa, and a beam from said seventh fiber port, if transmissive to said optical bandpass filter, transmits through said second lens, said optical bandpass filter, and said first lens to reach said sixth fiber port and vice versa.

A method, comprising:

• directing an input optical signal with a plurality of WDM channels to a first side of an optical bandpass filter which transmits light at a selected WDM channel wavelength and reflects other channels;
• receiving a transmitted optical signal at said selected WDM channel at a second, opposing side of said optical bandpass filter as a drop channel;
• using a reflection of said input optical signal from said first side of said optical bandpass filter as an output optical signal;
• and
• directing a second optical input signal at said selected WDM channel wavelength as an add channel to said second, opposing side of said optical bandpass filter so that said second optical input signal transmits through said optical bandpass filter and merges with said reflection as a part of said output optical signal.