Process variation-tolerant cascaded tapered optical ring resonators
Embodiments herein describe a method for selectively filtering different wavelengths of optical signals received from an optical channel using cascaded ring resonators, each of the cascaded ring resonators having a first ring and a second ring. The first ring has a varying waveguide width along its length configured to form a first waveguide width portion and a second waveguide width portion, the first waveguide width portion having a greater width than the second waveguide width portion. The second ring has a varying waveguide width along its length configured to form a third waveguide width portion and a fourth waveguide width portion, the fourth waveguide width portion having a greater width than the third waveguide width portion. The method further connects receivers to respective cascaded ring resonators, each of the receivers having a photodetector configured to differentiate between the optical signals.
1 . A cascaded ring resonator comprising:
a first ring having a varying waveguide width along its length configured to form a first waveguide width portion and a second waveguide width portion, the first waveguide width portion having a greater width than the second waveguide width portion; and
a second ring having a varying waveguide width along its length configured to form a third waveguide width portion and a fourth waveguide width portion, the fourth waveguide width portion having a greater width than the third waveguide width portion,
wherein the second waveguide width portion of the first ring and the third waveguide width portion of the second ring are positioned to face one another to form a first coupling region in which both first and second rings have narrowed waveguide widths.
2 . The cascaded ring resonator of claim 1 , wherein the first waveguide width portion of the first ring is coupled to a first linear waveguide to form a second coupling region.
3 . The cascaded ring resonator of claim 1 , wherein the first coupling region comprises a tapered transition between wide and narrow portions of the first and second rings.
4 . The cascaded ring resonator of claim 3 , wherein the fourth waveguide width portion of the second ring is coupled to a second linear waveguide to form a third coupling region.
5 . The cascaded ring resonator of claim 1 , wherein the first coupling region supports a single propagating mode.
6 . The cascaded ring resonator of claim 1 , wherein the first coupling region suppresses higher order modes such that less coupling occurs between a fundamental frequency of the first ring and higher order modes of the second ring, or vice versa.
7 . The cascaded ring resonator of claim 1 , wherein the first waveguide width portion of the first ring and the fourth waveguide width portion of the second ring are each configured to support more than one optical mode outside the first coupling region.
8 . The cascaded ring resonator of claim 1 , wherein the second waveguide width portion of the first ring and the third waveguide width portion of the second ring are axially aligned along the first coupling region.
9 . The cascaded ring resonator of claim 1 , wherein the cascaded ring resonator is used in a wavelength division multiplexing (WMD) optical system for wavelength selection.
10 . A wavelength division multiplexing (WMD) optical system comprising:
cascaded ring resonators configured to selectively filter different wavelengths of optical signals received from an optical channel, each of the cascaded ring resonators including:
a first ring having a varying waveguide width along its length configured to form a first waveguide width portion and a second waveguide width portion, the first waveguide width portion having a greater width than the second waveguide width portion; and
a second ring having a varying waveguide width along its length configured to form a third waveguide width portion and a fourth waveguide width portion, the fourth waveguide width portion having a greater width than the third waveguide width portion;
wherein the second waveguide width portion of the first ring and the third waveguide width portion of the second ring are positioned to face one another to form a first coupling region in which both first and second rings have narrowed waveguide widths; and
receivers configured to be connected to respective cascaded ring resonators, each of the receivers having a photodetector configured to differentiate between the optical signals.
11 . The WMD optical system of claim 10 , wherein the first waveguide width portion of the first ring is coupled to a first linear waveguide to form a second coupling region.
12 . The WMD optical system of claim 10 , wherein first coupling region comprises a tapered transition between wide and narrow portions of the first and second rings.
13 . The WMD optical system of claim 12 , wherein the fourth waveguide width portion of the second ring is coupled to a second linear waveguide to form a third coupling region.
14 . The WMD optical system of claim 10 , wherein the first coupling region supports a single propagating mode.
15 . The WMD optical system of claim 10 , wherein the first coupling region suppresses higher order modes such that less coupling occurs between a fundamental frequency of the first ring and higher order modes of the second ring, or vice versa.
16 . The WMD optical system of claim 10 , wherein the first waveguide width portion of the first ring and the fourth waveguide width portion of the second ring are each configured to support more than one optical mode outside the first coupling region.
17 . The WMD optical system of claim 10 , wherein the second waveguide width portion of the first ring and the third waveguide width portion of the second ring are axially aligned along the first coupling region.
18 . A method comprising:
selectively filtering different wavelengths of optical signals received from an optical channel using cascaded ring resonators, each of the cascaded ring resonators including:
a first ring having a varying waveguide width along its length configured to form a first waveguide width portion and a second waveguide width portion, the first waveguide width portion having a greater width than the second waveguide width portion; and
a second ring having a varying waveguide width along its length configured to form a third waveguide width portion and a fourth waveguide width portion, the fourth waveguide width portion having a greater width than the third waveguide width portion;
wherein the second waveguide width portion of the first ring and the third waveguide width portion of the second ring are positioned to face one another to form a first coupling region in which both first and second rings have narrowed waveguide widths; and
connecting receivers to respective cascaded ring resonators, each of the receivers having a photodetector configured to differentiate between the optical signals.
19 . The method of claim 18 ,
wherein the first waveguide width portion of the first ring is coupled to a first linear waveguide to form a second coupling region.
20 . The method of claim 18 ,
wherein the first coupling region supports a single propagating mode; and
wherein the first coupling region suppresses higher order modes such that less coupling occurs between a fundamental frequency of the first ring and higher order modes of the second ring, or vice versa.