Systems and methods for coupling light into a multi-mode resonator
A photonic system includes a passive optical cavity and an optical waveguide. The passive optical cavity has a preferred radial mode for light propagation within the passive optical cavity. The preferred radial mode has a unique light propagation constant within the passive optical cavity. The optical waveguide is configured to extend past the passive optical cavity such that at least some light propagating through the optical waveguide will evanescently couple into the passive optical cavity. The passive optical cavity and the optical waveguide are collectively configured such that a light propagation constant of the optical waveguide substantially matches the unique light propagation constant of the preferred radial mode within the passive optical cavity.
1 . A photonic system, comprising:
an optical cavity having a preferred radial mode for light propagation within the optical cavity, wherein the preferred radial mode has a unique light propagation constant within the optical cavity; and
an optical waveguide configured to approach the optical cavity within an evanescent optical coupling distance at a first location along a circumferential half the optical cavity and at a second location along said circumferential half of the optical cavity, wherein the optical waveguide is not within the evanescent optical coupling distance of the optical cavity between the first location and the second location, the optical waveguide having a light propagation constant that substantially matches the unique light propagation constant of the preferred radial mode within the optical cavity, such that at least some light propagating through the optical waveguide will optically couple into the preferred radial mode of the optical cavity at each of the first location and the second location along said circumferential half of the optical cavity, wherein a distance along said circumferential half of the optical cavity between the first location and the second location is less than one-quarter of a total circumferential distance around the optical cavity.
2 . The photonic system as recited in claim 1 , wherein said circumferential half of the optical cavity is a first circumferential half of the optical cavity, wherein the optical waveguide is configured such that light propagating through the optical waveguide does not substantially optically couple into the optical cavity along a second circumferential half of the optical cavity.
3 . The photonic system as recited in claim 1 , wherein the optical waveguide is configured to turn from a first direction to a second direction to enable approach of the optical cavity within the evanescent optical coupling distance at each of the first location and the second location along said circumferential half of the optical cavity.
4 . The photonic system as recited in claim 1 , wherein an angle between the first direction and the second direction is greater than ninety degrees.
5 . The photonic system as recited in claim 1 , wherein a first light coupling region between the optical waveguide and the optical cavity is formed at the first location, wherein a second light coupling region between the optical waveguide and the optical cavity is formed at the second location, wherein the first light coupling region is configured to allow a portion of the light propagating through the optical waveguide to optically couple into the optical cavity over the first light coupling region, such that a remaining portion of light propagating through the optical waveguide is allowed to continue propagating on through the optical waveguide toward the second light coupling region.
6 . The photonic system as recited in claim 5 , wherein the second light coupling region is configured to cause optical coupling of substantially all of the remaining portion of light propagating through the optical waveguide into the optical cavity over the second light coupling region.
7 . The photonic system as recited in claim 5 , wherein the optical waveguide has a first width within the first optical coupling region and a second width within the second optical coupling region, wherein the first width and the second width of the optical waveguide are measured in a transverse direction relative to a light propagation direction through the optical waveguide.
8 . The photonic system as recited in claim 7 , wherein the first width and the second width of the optical waveguide are substantially equal.
9 . The photonic system as recited in claim 7 , wherein the first width and the second width of the optical waveguide are different.
10 . The photonic system as recited in claim 1 , wherein the optical cavity has an outer wall defined by an outer radius, an inner wall defined by an inner radius, and a radial width measured as the outer radius minus the inner radius, wherein the radial width of the optical cavity is within a range extending from about 500 nanometers to about 3 micrometers.
11 . The photonic system as recited in claim 1 , wherein the preferred radial mode for light propagation within the optical cavity is a fundamental mode.
12 . The photonic system as recited in claim 1 , wherein the preferred radial mode for light propagation within the optical cavity is a lowest order mode having a radius of maximum energy density closest to an the outer wall of the optical cavity relative to others of the multiple radial modes.
13 . The photonic system as recited in claim 7 , wherein the optical cavity has an outer wall defined by an outer radius, an inner wall defined by an inner radius, and a radial width measured as the outer radius minus the inner radius, wherein the radial width of the optical cavity is greater than or equal to two times the first width of the optical waveguide, and wherein the radial width of the optical cavity is greater than or equal to two times the second width of the optical waveguide.
14 . The photonic system as recited in claim 13 , wherein each of the first width of the optical waveguide and the second width of the optical waveguide is within a range extending from about 250 nanometers to about 650 nanometers.
15 . The photonic system as recited in claim 1 , further comprising:
a cladding material disposed around and between the optical cavity and the optical waveguide, the cladding material having an optical refractive index different than each of an optical refractive index of the optical cavity and an optical refractive index of the optical waveguide.
16 . The photonic system as recited in claim 15 , wherein the cladding material is disposed between the first location and the second location along said circumferential half of the optical cavity.
17 . The photonic system as recited in claim 15 , wherein the optical cavity has an outer wall defined by an outer radius, an inner wall defined by an inner radius, and a radial width measured as the outer radius minus the inner radius, wherein the radial width of the optical cavity is greater than
λ
/
n
c
o
r
e
2
-
n
clad
2
,
wherein λ is a free-space wavelength of light corresponding to the preferred radial mode within the optical cavity, n core is the optical refractive index of the optical cavity, and n clad is the optical refractive index of the cladding material.