Optical add/drop multiplexer

1. 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.

2. The optical add/drop multiplexer of claim 1 , wherein the drop signal separator comprises a first waveguide and a second waveguide, wherein a first input end of the first waveguide and a first output end of the second waveguide are on a first plane, wherein a second output end of the first waveguide and a second input end of the second waveguide are on a second plane, wherein a third width of the first waveguide at the first input end is equal to a fourth width of the second waveguide at the first output end, wherein a fifth width of the first waveguide linearly increases from the first input end to the second output end, wherein a sixth width of the second waveguide linearly decreases from the first output end to the second input end, wherein the second output end is coupled to the first upper layer waveguide and the first lower layer waveguide, wherein the first input end is the main input end, and wherein the first output end is the drop end.

3. The optical add/drop multiplexer of claim 2 , wherein a seventh width of a third input end of the first upper layer waveguide is equal to an eighth width of the second output end, and wherein a ninth width of the first upper layer waveguide is equal to the second width.

4. The optical add/drop multiplexer of claim 3 , wherein a tenth width of a fourth input end of the first lower layer waveguide is equal to the eighth width, wherein an eleventh width of a third output end of the first lower layer waveguide is greater than the first width, and wherein a twelfth width of the first lower layer waveguide linearly increases from the fourth input end to the third output end.

5. The optical add/drop multiplexer of claim 2 , wherein the first waveguide has a first length.

6. The optical add/drop multiplexer of claim 5 , wherein the second waveguide has a second length.

7. The optical add/drop multiplexer of claim 6 , wherein the first length is equal to the second length.

8. The optical add/drop multiplexer of claim 2 , wherein the first waveguide is a strip-shaped waveguide.

9. The optical add/drop multiplexer of claim 2 , wherein modal refractive indexes of the first waveguide and the second waveguide are not equal.

10. The optical add/drop multiplexer of claim 1 , wherein a thickness of the first upper layer waveguide is greater than a thickness of the first lower layer waveguide.

11. The optical add/drop multiplexer of claim 1 , wherein a third width of a first input end of the second upper layer waveguide is equal to the second width, and wherein a fourth width of a first output end of the second upper layer waveguide is equal to the second width.

12. The optical add/drop multiplexer of claim 11 , wherein a fifth width of a second input end of the second lower layer waveguide is equal to a sixth width of a second output end of the first lower layer waveguide, wherein a seventh width of a third output end of the second lower layer waveguide is equal to the sixth width, and wherein an eighth width of the second lower layer waveguide is constant.

13. The optical add/drop multiplexer of claim 1 , wherein a thickness of the second upper layer waveguide is greater than a thickness of the second lower layer waveguide.

14. The optical add/drop multiplexer of claim 1 , wherein a third width of a first input end of the third upper layer waveguide is equal to the second width, and wherein a fourth width of the third upper layer waveguide linearly decreases from the first input end to a first output end of the third upper layer waveguide.

15. The optical add/drop multiplexer of claim 14 , wherein a fifth width of a second input end of the third lower layer waveguide is equal to a sixth width of a second output end of the second lower layer waveguide, wherein a seventh width of a third output end of the third lower layer waveguide is equal to an eighth width of the first output end, and wherein a ninth width of the third lower layer waveguide linearly decreases from the second input end to the third output end.

16. The optical add/drop multiplexer of claim 1 , wherein a thickness of the third upper layer waveguide is greater than a thickness of the third lower layer waveguide.

17. The optical add/drop multiplexer of claim 1 , wherein the first upper layer waveguide, the second upper layer waveguide, and the third upper layer waveguide have a same thickness.

18. The optical add/drop multiplexer of claim 1 , wherein the first mode is a 0-order mode, and wherein the second mode is a 1-order mode.

19. The optical add/drop multiplexer of claim 1 , wherein the first lower layer waveguide, the second lower layer waveguide, and the third lower layer waveguide have a same thickness.

20. The optical add/drop multiplexer of claim 1 , wherein the first mode is a 1-order mode, and wherein the second mode is a 0-order mode.