Tunable radio frequency and microwave photonic filters
RF and microwave devices and techniques are disclosed for processing RF and microwave signals by using ( 1 ) photonic or optical components and ( 2 ) RF and microwave components. In some implementations, a part of the processing is performed in the RF and microwave domain such as applying a microwave or RF input signal to control an optical modulator ,and another part of the processing is performed in the optical domain such as optical filtering of the modulated optical beam to select desired microwave or RF spectral components. The frequency of a selected spectral component can be tuned by either tuning the frequency of the optical beam that is modulated by the optical modulator or a filter that is used to filter modulated optical beam.
1. A device, comprising:
an input port to receive an input microwave or RF signal;
a laser to produce a continuous-wave laser beam;
a first optical path to receive a first portion of the laser beam;
a second optical path to receive a second portion of the laser beam, the second optical path comprising:
an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and
a tunable optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component, the tunable optical filter comprising two optical resonators that are optically coupled to produce a filter function of at least a second order;
a tuning control unit to tune at least one of the two optical resonators to chance a frequency of the at least one selected spectral component; and
an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component,
wherein the two optical resonators are whispering gallery mode resonators and are tunable via an electro-optic effect, the tunable optical filter further comprising a third electro-optic whispering gallery mode resonator optically coupled to one of the two tunable optical resonators and tuned by the tuning control unit to effectuate a third order filter function in the tunable optical filter.
2. A device, comprising:
an input port to receive an input microwave or RF signal;
a laser to produce a continuous-wave laser beam;
a first optical path to receive a first portion of the laser beam;
a second optical path to receive a second portion of the laser beam, the second optical path comprising:
an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and
a tunable optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component, the tunable optical filter comprising two optical resonators that collectively produce a filter function of at least a second order;
a tuning control unit to tune at least one of the two optical resonators to chance a frequency of the at least one selected spectral component; and
an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component,
wherein the tunable optical filter further comprises:
a first optical waveguide optically coupled to the first and second optical resonators and to receive the modulated optical beam from the optical modulator, and
a second, separate optical waveguide optically coupled to the first and second optical resonators to output the filtered modulated optical beam to the optical detector, wherein the first and second optical resonators are not directly optically coupled to each other and are optically coupled with each other via optical coupling to the first and second waveguides.
3. The device as in claim 2 , wherein the frequency of the laser is at between resonance frequencies of the two optical resonators and the filtered modulated optical beam has a linewidth less than a linewidth of each of the two optical resonators.
4. A device, comprising:
an input port to receive an input microwave or RF signal;
a laser to produce a continuous-wave laser beam;
a first optical path to receive a first portion of the laser beam;
a second optical path to receive a second portion of the laser beam, the second optical path comprising:
an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and
a tunable optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component, the tunable optical filter comprising two optical resonators that are optically coupled to each other;
a tuning control unit to tune at least one of the two optical resonators to chance a frequency of the at least one selected spectral component; and
an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component,
wherein the tunable optical filter further comprises:
a first optical waveguide optically coupled to the first and second optical resonators and to receive the modulated optical beam from the optical modulator and to output the filtered modulated optical beam to the optical detector, and
a second, separate optical waveguide optically coupled to the first and second optical resonators, wherein the first and second optical resonators are directly optically coupled to each other in addition to optical coupling with each other via optical coupling to the first and second waveguides, effectuating a filter function of at least a second order.
5. The device as in claim 4 , wherein the frequency of the laser is between resonance frequencies of the two optical resonators and the filtered modulated optical beam has a third-order filter function.
6. A device, comprising:
an input port to receive an input microwave or RF signal;
a laser to produce a continuous-wave laser beam;
a first optical path to receive a first portion of the laser beam;
a second optical path to receive a second portion of the laser beam, the second optical path comprising:
an optical modulator to modulate the second portion in response to the input signal to produce a modulated optical beam that carries the input signal, and
a tunable optical filter to filter the modulated optical beam to select at least one spectral component in the input signal while rejecting other spectral components and to output a filtered modulated optical beam that carries the at least one selected spectral component, the tunable optical filter comprising two optical resonators that are optically coupled to produce a filter function of at least a second order;
a tuning control unit to tune at least one of the two optical resonators to chance a frequency of the at least one selected spectral component; and
an optical detector to combine the first portion from the first optical path and the filtered modulated optical beam from the second optical path and to produce a filtered output signal comprising the at least one selected spectral component,
wherein the two optical resonators are first and second optical resonators, respectively, and the tunable optical filter further comprises third and fourth optical resonators,
wherein the first optical resonator receives the modulated optical beam from the optical modulator and the fourth optical resonator outputs the filtered modulated optical beam to the optical detector,
wherein the first, second, third and fourth optical resonators are optically coupled to one another in a configuration that,
the first optical resonator is optically coupled to the second and third optical resonators,
the second optical resonator is further optically coupled to the fourth optical resonator,
the third optical resonator is further optically coupled to the fourth optical resonator, and
the second and third optical resonators are not directly coupled to each other and are indirectly coupled via the first and fourth optical resonators.
7. The device as in claim 6 , farther comprising:
a first optical coupler optically coupled to the first optical resonator to direct the modulated optical beam to the first optical resonator; and
a second optical coupler optically coupled to the fourth optical resonator to couple light in the fourth optical resonator out as the filtered modulated optical beam.