Fused-fiber multi-window wavelength filter using unbalanced Michelson Interferometer

A method of forming a fused-fiber multi-window wavelength filter (MWF), comprising:

• fusing a first and a second optic filter in an interior portion of the first and second optic fibers to form a fused coupled region;
• cleaving a first end of the first optic fiber to form a first portion having a length l1;
• cleaving a first end of the second optic fiber to form a second portion having a length l2;
• and
• forming a reflective surface on the first ends of the first and second optic fiber, wherein the first and second portions have different optical path elements, wherein the forming comprises attaching a reflective substrate to the first ends of the first and second optic filter.

A method of forming a fused-fiber multi-window wavelength filter (MWF), comprising:

• fusing a first and a second optic filter in an interior portion of the first and second optic fibers to form a fused coupled region;
• cleaving a first end of the first optic fiber to form a first portion having a length l1;
• cleaving a first end of the second optic fiber to form a second portion having a length l2;
• forming a reflective surface on the first ends of the first and second optic fiber, wherein the first and second portions have different optical path elements;
• and
• inserting a composite substrate between the first and second portions, wherein the composite substrate applies different tension to the first and second portions as temperature changes.

A method of forming a fused-fiber multi-window wavelength filter (MWF), comprising:

• fusing a first and a second optic filter in an interior portion of the first and second optic fibers to form a fused coupled region;
• cleaving a first end of the first optic fiber to form a first portion having a length l1;
• cleaving a first end of the second optic fiber to form a second portion having a length l2;
• forming a reflective surface on the first ends of the first and second optic fiber, wherein the first and second portions have different optical path elements;
• and
• securing a substrate on the first portion, wherein the substrate expands or contracts with temperature to increase or decrease tension in the first portion.

A bandpass filter, comprising:

• a first multi-window filter (MWF), comprising:
• a first fiber portion for inputting a light source;
• a second fiber portion for outputting a light signal;
• a third fiber portion having a length l1, a refractive index n1, and a first reflective end;
• a fourth fiber portion having a length l2, a refractive index n2, and a second reflective end, wherein the third and fourth fiber portions have different optical path lengths;
• and
• a fused region coupling the first, second, third, and fourth fiber portions;
• and
• a second MWF, comprising:
• a first fiber portion coupled to the second portion of the first MWF;
• a second fiber portion for outputting a second light signal;
• a third fiber portion having a length l3, a refractive index n3, and a first reflective end:
• a fourth fiber portion having a length l4, a refractive index n4, and a second reflective end, wherein the third and fourth fiber portions have different optical path lengths.

A multi-window wavelength division multiplexer (MWDM), comprising:

• a first multi-window wavelength filter (MWF) having an input fiber, an output fiber, first and second reflecting fibers, and a fused region coupling the input, output, and first and second reflecting fibers, wherein the first and second reflecting fibers have an optical path length difference;
• a second MWF having an input fiber, an output fiber, first and second reflecting fibers, and a fused region coupling the input, output, and first and second reflecting fibers, wherein the first and second reflecting fibers of the second MWF have the same path length difference as the first and second reflecting fibers of the first MWF, and wherein the output of the second MWF is complementary to the output of the first MWF;
• and
• a coupler having an input fiber, a first output fiber coupled to the input fiber of the first MWF and a second output fiber coupled to the input fiber of the second MWF.

A high isolation multi-window wavelength division multiplexer (MWDM), comprising:

• a first multi-window wavelength filter (MWF) having an input fiber, an output fiber, first and second reflecting fibers, and a fused region coupling the input, output, and first and second reflecting fibers, wherein the first and second reflecting fibers have an optical path length difference;
• a second MWF having an input fiber, an output fiber, first and second reflecting fibers, and a fused region coupling the input, output, and first and second reflecting fibers, wherein the first and second reflecting fibers of the second MWF have the same path length difference as the first and second reflecting fibers of the first MWF;
• and
• an MWDM having an input fiber and two output fibers and a channel separation capability of Δλ, each of the two output fibers coupled to the input fiber of the first and second MWFs, wherein the first and second MWFs have the same channel separation capability Δλ as the MWDM.

A dense wavelength division multiplexer (DWDM), comprising:

• a first multi-window WDM (MWDM), comprising:
• a first fiber portion for inputting a light source;
• a second fiber portion for outputting a light signal;
• a third fiber portion having a length l1, a refractive index n1, and a first reflective end;
• a fourth fiber portion having a length l2, a refractive index n2, and a second reflective end, wherein the third and fourth fiber portions have different optical path lengths;
• and
• a fused region coupling the first, second, third, and fourth fiber portions;
• a second MWDM having an input fiber and two output fibers;
• and
• a third MWDM having an input fiber and two output fibers, wherein two of the three MWDMs are coupled to the third of the three MWDMs to form a cascaded stage of MWDMs.