Wideband acousto-optic modulator/isolator in integrated photonics
An acousto-optic device employing strong interband coupling in a multi-mode, spiral-shaped optomechanical waveguide is disclosed. The acousto-optic device includes multiple interdigitated transducers to produce phonons, which are directed to the optomechanical waveguide at an angle. By confining the produced phonons to the optomechanical waveguide, using phonon confining elements and/or a suspended structure, the interband coupling is increased. Through the use of spatial mode multiplexers at either end of the optomechanical waveguide to block or pass different spatial optical modes, one can create an acousto-optic modulator or an optical isolator.
1 . An acousto-optic device comprising:
a spiral-shaped optomechanical waveguide including one or more loops, the spiral-shaped optomechanical waveguide adapted to support first and second spatial optical modes; and
one or more interdigitated transducers (IDTs) mechanically coupled to the spiral-shaped optomechanical waveguide, the one or more IDTs adapted to generate phonons and to direct the phonons in a phonon-launch direction toward the spiral-shaped optomechanical waveguide, the phonons adapted to cause interband coupling between the first and second spatial optical modes for light in each of the one or more loops in the spiral-shaped optomechanical waveguide, the phonon-launch direction of each of the one or more IDTs being non-perpendicular to the spiral-shaped optomechanical waveguide, an IDT-loop product, corresponding to a product of a quantity of the one or more IDTs and a quantity of the one or more loops, being greater than or equal to two.
2 . The acousto-optic device of claim 1 , wherein the spiral-shaped optomechanical waveguide includes one of an ovoid spiral shape, a circular spiral shape, or a polygonal spiral shape.
3 . The acousto-optic device of claim 1 , wherein the spiral-shaped optomechanical waveguide doubles back on itself.
4 . The acousto-optic device of claim 1 , wherein the spiral-shaped optomechanical waveguide includes one of silicon, silicon nitride, lithium niobate, or tantalum oxide.
5 . The acousto-optic device of claim 1 , wherein:
a first subset of the one or more IDTs being located adjacent one another and adjacent a first side of the spiral-shaped optomechanical waveguide; and
a second subset of the one or more IDTs being located adjacent one another and adjacent a second side of the spiral-shaped optomechanical waveguide, the second side of the spiral-shaped optomechanical waveguide opposite the first side of the spiral-shaped optomechanical waveguide.
6 . The acousto-optic device of claim 1 , wherein each of the one or more IDTs includes a piezoelectric IDT.
7 . The acousto-optic device of claim 6 , wherein each piezoelectric IDT includes one of AlN, ScAlN, BAlN, or LiNbO 3 .
8 . The acousto-optic device of claim 1 , further comprising one or more phonon confining elements located adjacent to the spiral-shaped optomechanical waveguide, each of the one or more phonon confining elements adapted to confine phonons from the one or more IDTs to the spiral-shaped optomechanical waveguide.
9 . The acousto-optic device of claim 8 , wherein each of the one or more phonon confining elements includes a phononic crystal or a slot.
10 . The acousto-optic device of claim 1 , further comprising a suspended structure, at least a portion of the spiral-shaped optomechanical waveguide being located on the suspended structure.
11 . The acousto-optic device of claim 10 , wherein at least a portion of each of the one or more IDTs is located on the suspended structure.
12 . The acousto-optic device of claim 1 ,
wherein the acousto-optic device is an acousto-optic modulator;
the acousto-optic device further comprising a first spatial mode multiplexer optically coupled to a first end of the spiral-shaped optomechanical waveguide, the first spatial mode multiplexer adapted to:
receive light from the spiral-shaped optomechanical waveguide, and
output a portion of the light having one of the first or second spatial optical modes.
13 . The acousto-optic device of claim 12 ,
the acousto-optic device further comprising a second spatial mode multiplexer optically coupled to a second end of the spiral-shaped optomechanical waveguide, the second spatial mode multiplexer adapted to:
receive input light, and
output to the spiral-shaped optomechanical waveguide a portion of the input light having one of the first or second spatial optical modes.
14 . The acousto-optic device of claim 1 ,
wherein the acousto-optic device is an optical isolator;
the acousto-optic device further comprising a first spatial mode multiplexer optically coupled to a first end of the spiral-shaped optomechanical waveguide, the first spatial mode multiplexer adapted to:
receive first input light,
output to the spiral-shaped optomechanical waveguide a portion of the first input light having one of the first or second spatial optical modes, the portion of the first input light passing through the spiral-shaped optomechanical waveguide becoming first processed light,
receive second processed light from the spiral-shaped optomechanical waveguide, and
block the second processed light; and
a second spatial mode multiplexer optically coupled to a second end of the spiral-shaped optomechanical waveguide, the second end of the spiral-shaped optomechanical waveguide opposite the first end of the spiral-shaped optomechanical waveguide, the second spatial mode multiplexer adapted to:
receive first processed light from the spiral-shaped optomechanical waveguide,
output a portion of the first processed light having the one of the first or second spatial optical modes,
receive second input light, and
output to the spiral-shaped optomechanical waveguide a portion of the second input light having the one of the first or second spatial optical modes, the portion of the second input light passing through the spiral-shaped optomechanical waveguide becoming second processed light.
15 . The acousto-optic device of claim 1 , wherein the acousto-optic device is fabricated using CMOS-compatible processes.
16 . An optical isolator comprising:
a first spatial mode multiplexer;
a first nonreciprocal spatial mode beamsplitter including at least one first interdigitated transducer (IDT) and a first optomechanical waveguide, the at least one first IDT mechanically coupled to the first optomechanical waveguide, and the first optomechanical waveguide optically coupled to the first spatial mode multiplexer;
a dispersion balanced delay line optically coupled to the first nonreciprocal spatial mode beamsplitter, the dispersion balanced delay line adapted to minimize dispersion between light in first and second spatial optical modes;
a second nonreciprocal spatial mode beamsplitter including at least one second IDT and a second optomechanical waveguide, the at least one second IDT mechanically coupled to the second optomechanical waveguide, and the second optomechanical waveguide optically coupled to the dispersion balanced delay line; and
a second spatial mode multiplexer optically coupled to the second nonreciprocal spatial mode beamsplitter;
wherein each of the at least one first and second IDTs is adapted to generate phonons and to direct the phonons in a corresponding phonon-launch direction toward a corresponding one of the first and second optomechanical waveguides, the phonons adapted to cause interband coupling between the first and second spatial optical modes for light in a corresponding one of the first and second optomechanical waveguides, the corresponding phonon-launch direction of each of the at least one first and second IDTs being non-perpendicular to a corresponding one of the first and second optomechanical waveguides.
17 . The optical isolator of claim 16 , wherein the dispersion balanced delay line includes a dispersion engineered waveguide structure, the dispersion engineered waveguide structure adapted to control a dispersion of the first and second spatial optical modes.
18 . The optical isolator of claim 16 , wherein the dispersion balanced delay line includes:
a third spatial mode multiplexer optically coupled to the first nonreciprocal spatial mode beamsplitter;
the dispersion balanced delay line including first and second single-mode delay lines, the first and second single-mode delay lines optically coupled to the third mode multiplexer; and
a fourth spatial mode multiplexer optically coupled to the first and second single-mode delay lines and to the second nonreciprocal spatial mode beamsplitter;
wherein lengths of each of the first and second single-mode delay lines are adapted to equalize a group delay across the optical isolator.
19 . The optical isolator of claim 16 , wherein each of the first and second nonreciprocal spatial mode beamsplitters further includes:
one or more corresponding phonon confining elements located adjacent to a corresponding one of the first and second optomechanical waveguides, each of the one or more phonon confining elements adapted to confine phonons from a corresponding one of the at least one first and second IDTs to a corresponding one of the first and second optomechanical waveguides, each of the one or more phonon confining elements including a phononic crystal or a slot; and
a suspended structure, at least a portion of a corresponding one of the first and second optomechanical waveguides being located on a corresponding suspended structure.
20 . The optical isolator of claim 16 , wherein each of the at least one first and second IDTs includes a piezoelectric IDT, each piezoelectric IDT including one of AlN, ScAlN, BAlN, or LiNbO 3 .