Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides

Research output: Working paperProfessional

Abstract

We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si 3 N 4 waveguides with a standard core cross section of 4.4× 0.03 μ m 2 size, buried 8 μ m deep in a SiO 2 cladding we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10 −3 was obtained for TE polarized light, using an IDT period of 30 - 35 μ m, a film thickness of 2.5 - 3.5 μ m, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to 1.2x10 −3 , with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 μ m. The relative index change is about 300-times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200-times higher. Exploiting the maximum relative index change of 1.2× 10 −3 in a low-loss balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 μ m (half-wave voltage length product = 0.24 Vcm).
Original languageEnglish
PublisherarXiv.org
Number of pages19
Publication statusPublished - 2018

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acousto-optics
silicon nitrides
waveguides
modulation
acoustics
transducers
resonant frequencies
refractivity
strain distribution
wave generation
shift
electric potential
actuation
optical waveguides
frequency modulation
polarized light
wave equations
proximity
modulators
film thickness

Cite this

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title = "Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides",
abstract = "We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si 3 N 4 waveguides with a standard core cross section of 4.4× 0.03 μ m 2 size, buried 8 μ m deep in a SiO 2 cladding we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10 −3 was obtained for TE polarized light, using an IDT period of 30 - 35 μ m, a film thickness of 2.5 - 3.5 μ m, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to 1.2x10 −3 , with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 μ m. The relative index change is about 300-times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200-times higher. Exploiting the maximum relative index change of 1.2× 10 −3 in a low-loss balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 μ m (half-wave voltage length product = 0.24 Vcm).",
author = "{van der Slot}, P.J.M. and {Garcia Porcel}, M.A. and Boller, {Klaus J.}",
year = "2018",
language = "English",
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type = "WorkingPaper",
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}

Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides. / van der Slot, P.J.M.; Garcia Porcel, M.A.; Boller, Klaus J.

arXiv.org, 2018.

Research output: Working paperProfessional

TY - UNPB

T1 - Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides

AU - van der Slot, P.J.M.

AU - Garcia Porcel, M.A.

AU - Boller, Klaus J.

PY - 2018

Y1 - 2018

N2 - We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si 3 N 4 waveguides with a standard core cross section of 4.4× 0.03 μ m 2 size, buried 8 μ m deep in a SiO 2 cladding we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10 −3 was obtained for TE polarized light, using an IDT period of 30 - 35 μ m, a film thickness of 2.5 - 3.5 μ m, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to 1.2x10 −3 , with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 μ m. The relative index change is about 300-times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200-times higher. Exploiting the maximum relative index change of 1.2× 10 −3 in a low-loss balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 μ m (half-wave voltage length product = 0.24 Vcm).

AB - We theoretically investigate the use of Rayleigh surface acoustic waves (SAWs) for refractive index modulation in optical waveguides consisting of amorphous dielectrics. Considering low-loss Si 3 N 4 waveguides with a standard core cross section of 4.4× 0.03 μ m 2 size, buried 8 μ m deep in a SiO 2 cladding we compare surface acoustic wave generation in various different geometries via a piezo-active, lead zirconate titanate film placed on top of the surface and driven via an interdigitized transducer (IDT). Using numerical solutions of the acoustic and optical wave equations, we determine the strain distribution of the SAW under resonant excitation. From the overlap of the acoustic strain field with the optical mode field we calculate and maximize the attainable amplitude of index modulation in the waveguide. For the example of a near-infrared wavelength of 840 nm, a maximum shift in relative effective refractive index of 0.7x10 −3 was obtained for TE polarized light, using an IDT period of 30 - 35 μ m, a film thickness of 2.5 - 3.5 μ m, and an IDT voltage of 10 V. For these parameters, the resonant frequency is in the range 70 - 85 MHz. The maximum shift increases to 1.2x10 −3 , with a corresponding resonant frequency of 87 MHz, when the height of the cladding above the core is reduced to 3 μ m. The relative index change is about 300-times higher than in previous work based on non-resonant proximity piezo-actuation, and the modulation frequency is about 200-times higher. Exploiting the maximum relative index change of 1.2× 10 −3 in a low-loss balanced Mach-Zehnder modulator should allow full-contrast modulation in devices as short as 120 μ m (half-wave voltage length product = 0.24 Vcm).

UR - https://arxiv.org/abs/1710.03055

M3 - Working paper

BT - Surface acoustic waves for acousto-optic modulation in buried silicon nitride waveguides

PB - arXiv.org

ER -