Optical add/drop multiplexer

An optical add/drop multiplexer, comprising:

• a drop signal separator comprising a main input end and a drop end;
• and
• a drop signal reflector coupled to the drop signal separator and comprising:
• a main output end;
• a first transmission mode converter comprising:
• a first lower layer waveguide coupled to the drop signal separator;
• and
• a first upper layer waveguide located above the first lower layer waveguide and coupled to the drop signal separator;
• a fiber Bragg grating waveguide comprising:
• a second lower layer waveguide coupled to the first lower layer waveguide;
• and
• a second upper layer waveguide located above the second lower layer waveguide and coupled to the first upper layer waveguide, wherein a width of the second upper layer waveguide varies with a first width alternating with a second width to form a fiber Bragg grating, and wherein the first width is greater than the second width;
• and
• a second transmission mode converter comprising:
• a third lower layer waveguide coupled to the second lower layer waveguide;
• and
• a third upper layer waveguide located above the third lower layer waveguide, wherein a first end of the third upper layer waveguide is coupled to the second upper layer waveguide, and wherein a second end of the third upper layer waveguide is coupled to the main output end,
• wherein the main input is configured to:
• receive first optical signals that are in a first mode;
• and
• transfer the first optical signals to the drop signal reflector in a single-layer waveguide transmission mode,
• wherein the first transmission mode converter is configured to:
• receive the first optical signals from the drop signal separator;
• and
• convert the first optical signals in the single-layer waveguide transmission mode into a double-layer waveguide transmission mode,
• wherein the fiber Bragg grating waveguide is configured to:
• receive the first optical signals from the first transmission mode converter;
• reflect, to the first transmission mode converter, a first optical signal of the first optical signals as a second optical signal in a second mode and comprising a predetermined wavelength;
• and
• send, to the second transmission mode converter, a third optical signal of the first optical signals except the first optical signal,
• wherein the second transmission mode converter is configured to:
• convert a transmission mode of the third optical signal into the single-layer waveguide transmission mode;
• and
• output the third optical signal using the main output end,
• wherein the first transmission mode converter is further configured to:
• convert the second optical signal into the single-layer waveguide transmission mode;
• and
• output the second optical signal to the drop signal separator, and
• wherein the drop signal separator is further configured to output the second optical signal using the drop end.