Apparatus for coupling to high-index micro-resonators with tapered optical fibers
Tapered waveguides made of high-index material attached to a tapered optical fiber are provided, enabling access to the optical modes of large, high-index resonators. In some embodiments, an optical fiber having a central axis, a tapered portion, and an untapered portion is provided. The tapered portion is configured to expose an evanescent field. An elongated waveguide is optically coupled to the optical fiber along the tapered portion and parallel to the central axis of the optical fiber. The elongated waveguide has a substantially triangular cross section perpendicular to the central axis of the optical fiber.
1. A device comprising:
an optical fiber, the optical fiber having a central axis, a tapered portion, and an untapered portion, the tapered portion configured to expose an evanescent field; and
an elongated waveguide optically coupled to the optical fiber along the tapered portion and disposed parallel to the central axis of the optical fiber, the elongated waveguide having a substantially triangular cross section in a plane perpendicular to the central axis of the optical fiber.
2. The device of claim 1 , the elongated waveguide having two substantially pointed opposing ends, the ends disposed on the optical fiber.
3. The device of claim 2 , the elongated waveguide having a maximal width at a midpoint.
4. The device of claim 3 , wherein the maximal width is about 1 μm.
5. The device of claim 2 , wherein an effective refractive index of the elongated waveguide is less than an effective refractive index of the optical fiber at each of the opposing ends of the elongated waveguide.
6. The device of claim 5 , wherein the effective refractive index of the elongated waveguide is greater than the effective refractive index of the optical fiber at a midpoint of the elongated waveguide.
7. The device of claim 1 , the substantially triangular cross section being isosceles.
8. The device of claim 7 , the substantially triangular cross section having two angles of about 30°.
9. The device of claim 1 , wherein the substantially triangular cross-section is oriented such that an edge is tangent to the optical fiber.
10. The device of claim 1 , the optical fiber comprising silica.
11. The device of claim 1 , the tapered portion having a minimal diameter of about 1 μm.
12. The device of claim 1 , the elongated waveguide comprising diamond, quartz, or silicon.
13. The device of claim 1 , wherein the elongated waveguide is coupled to the optical fiber by van der Waals forces.
14. The device of claim 1 , further comprising:
a resonator optically coupled to the elongated waveguide.
15. The device of claim 1 , wherein the elongated waveguide has a length parallel to the central axis of the optical fiber of about 40 μm.