Ultraviolet and visible light integrated acousto-optic modulators
An acousto-optic modulator that includes a waveguide on an acoustic actuator is disclosed. The waveguide carries an optical signal having a UV or visible wavelength. When the acoustic actuator is activated, the optical signal in the waveguide is bathed in intense acoustic waves. By using a waveguide having the appropriate dimensions to strongly confine both the optical signal and the acoustic waves, strong optomechanical coupling may be achieved between the optical and acoustic modes, resulting in an efficient modulator. By employing either intra-modal or inter-modal conversion, the modulator may be used to implement a variety of dual- or single-sideband functions, including an isolator, a phase modulator, a single-sideband frequency shifter, or a high-extinction shutter.
1. An acousto-optic (AO) modulator comprising:
a substrate including a surface layer formed of a first material;
an acoustic actuator on the substrate, the acoustic actuator adapted to receive an actuator signal and to produce a corresponding acoustic signal upon receipt of the actuator signal, the substrate adapted to reduce an acoustic radiation loss from the acoustic actuator, the acoustic actuator including a second material; and
a waveguide on a surface of the acoustic actuator opposite the substrate, the acoustic actuator and the waveguide being co-linear, the waveguide adapted to guide an optical signal, and to confine an energy of the optical signal, wherein the acoustic actuator and the waveguide are adapted to confine an energy of the acoustic signal such that efficient optomechanical coupling occurs between the optical signal and the acoustic signal and the optical signal and the acoustic signal are co-linear, the waveguide including:
a waveguide core formed of a third material different than the second material, the third material adapted to transmit at least one of visible or ultraviolet wavelengths; and
a cladding surrounding the waveguide core, the cladding formed of a fourth material different than the first material.
2. The AO modulator of claim 1 , wherein the first material includes one of silicon or sapphire.
3. The AO modulator of claim 1 , wherein the acoustic actuator includes:
an active layer;
a first electrode on a surface of the active layer; and
a second electrode, the second electrode on a same or opposite surface of the active layer as the first electrode.
4. The AO modulator of claim 1 , wherein the second material includes one of aluminum nitride, scandium aluminum nitride, or quartz.
5. The AO modulator of claim 3 , wherein the first electrode and the second electrode each includes one of aluminum, an aluminum alloy, a silicide, or gold.
6. The AO modulator of claim 3 , wherein at least one of the first electrode or the second electrode is patterned to form a directional acoustic transducer as part of the acoustic actuator, the directional acoustic transducer adapted to generate the acoustic signal.
7. The AO modulator of claim 6 , wherein the directional acoustic transducer is one of a unidirectional acoustic transducer or a bidirectional acoustic transducer.
8. The AO modulator of claim 6 , wherein the directional acoustic transducer is one of a single-phase unidirectional transducer or a chirped acoustic transducer.
9. The AO modulator of claim 1 , wherein the third material includes one of silicon nitride, alumina, tantalum pentoxide, gallium phosphide, or titanium oxide.
10. The AO modulator of claim 1 , wherein the fourth material includes silica.
11. The AO modulator of claim 1 , wherein an optomechanical coupling coefficient |g| is greater than or equal to approximately
50
rad
s
*
m
.
12. The AO modulator of claim 1 , further comprising at least one of a pedestal, a tether, or a nano-pillar, the at least one of the pedestal, the tether, or the nano-pillar structurally connecting the acoustic actuator to the substrate, the at least one of the pedestal, the tether, or the nano-pillar adapted to reduce the acoustic radiation loss from the acoustic actuator to the substrate.
13. The AO modulator of claim 1 , wherein the AO modulator implements one of an isolator function, a phase modulator function, a single-sideband frequency shifter function, or a high-extinction shutter function.
14. The AO modulator of claim 1 , wherein the AO modulator implements an isolator function, the AO modulator further comprising:
a first mode multiplexer, the first mode multiplexer optically coupled to a first end of the waveguide, the first mode multiplexer including:
a passing port, the passing port adapted to receive a forward input optical signal in a fundamental optical mode, the first mode multiplexer adapted to optically couple the forward input optical signal to the waveguide; and
a blocking port, the blocking port adapted to receive a reverse output optical signal in a higher order optical mode from the waveguide, the first mode multiplexer adapted to isolate the reverse output optical signal from the passing port; and
a second mode multiplexer, the second mode multiplexer optically coupled to a second end of the waveguide opposite the first end of the waveguide, the second mode multiplexer including a second port, the second multiplexer adapted to receive a forward output optical signal in a higher order optical mode from the waveguide and to transmit the forward output optical signal to the second port, the second mode multiplexer further adapted to receive a reverse input optical signal in a higher order optical mode from the second port and to optically couple the reverse input optical signal to the waveguide.
15. The AO modulator of claim 1 , wherein the AO modulator implements a phase modulator function, the acoustic signal being a phononic standing wave.
16. The AO modulator of claim 1 , wherein the AO modulator implements a single-sideband frequency shifter function, the AO modulator further comprising:
a first mode multiplexer, the first mode multiplexer optically coupled to a first end of the waveguide, the first mode multiplexer including a first port, the first port adapted to receive a forward input optical signal in a fundamental optical mode, the first mode multiplexer adapted to optically couple the forward input optical signal to the waveguide; and
a second mode multiplexer, the second mode multiplexer optically coupled to a second end of the waveguide opposite the first end of the waveguide, the second mode multiplexer including a second port, the second mode multiplexer adapted to receive a forward output optical signal in a higher order optical mode from the waveguide and to transmit the forward output optical signal to the second port.
17. The AO modulator of claim 1 , wherein the AO modulator implements a high-extinction shutter function, the AO modulator further comprising:
a mode multiplexer, the mode multiplexer optically coupled to a first end of the waveguide, the first mode multiplexer including a second port, the mode multiplexer adapted to receive an input optical signal in a higher order optical mode from the second port and to optically couple the input optical signal to the waveguide; and
a mode filter, the mode filter optically coupled to a second end of the waveguide opposite the first end of the waveguide, the mode filter including a port, the mode filter adapted to receive an output optical signal from the waveguide and to transmit the output optical signal from the port when the output optical signal is in a fundamental optical mode, the mode filter further adapted to block the output optical signal when the output optical signal is in the higher order optical mode.