Photonic image rejection RF mixer, a phased-array radio frequency receiver implementing the same and related methods of operation
A photonic image rejection radio frequency (RF) mixer and a receiver implementing the same may suppress undesired mirror image signals having frequencies at a spectral location that is mirror-symmetric, with respect to a local oscillator (LO), to that of a signal of interest. An upconverted optical beam corresponding to a captured RF beam is extracted by an optical processor. The upconverted optical beam is mixed with the LO to obtain a desired composite optical signal and an undesired composite optical signal, each providing a corresponding beat frequency optical signal at the same frequency. The desired and undesired composite optical signals are captured by multiple optical pickups with relative phase shifts in their beat frequency optical signals which are converted into corresponding electrical signals and combined to suppress the undesired signal.
1 . A receiver comprising:
an antenna array comprising a plurality of antennas configured to capture a first RF beam;
a plurality of channels each configured to communicatively couple a corresponding antenna of the antenna array to an interference space, each channel comprising:
an electro-optic modulator to modulate an RF electrical signal provided by the corresponding antenna with an optical carrier signal to generate a corresponding modulated optical signal including the optical carrier signal and two sidebands that constitute a first upconverted optical signal and a second upconverted optical signal, respectively, and
a first optical waveguide configured to convey the first upconverted optical signal to the interference space;
the interference space, configured to receive the upconverted optical signals provided by the plurality of channels at a channel edge of the interference space to allow the upconverted optical signals to interfere with each other and form a first optical beam corresponding to the first RF beam at a beamspace edge of the interference space;
a plurality of sensors arranged at the beamspace edge to capture an interference pattern at the beamspace edge including the first optical beam, the plurality of sensors including a first sensor comprising an image rejection mixer,
wherein the image rejection mixer comprises a Fourier transform space (FTS), a first optical beam source to receive the first optical beam and transmit the same into the FTS, a local oscillator (LO) source to transmit the local oscillator into the FTS, and first and second pickups each configured to capture a corresponding combined signal of the first optical beam and the LO forming a beat frequency signal, wherein the beat frequency signal of the combined signals captured by the first and second pickups are formed at quadrature phase increments with respect to each other.
2 . The receiver of claim 1 , wherein the image rejection mixer comprises third and fourth pickups each configured to capture a corresponding combined signal of the first optical beam and the LO forming a beat frequency signal, wherein the beat frequency signal of the combined signals captured by the first, second, third and fourth pickups are formed at quadrature phase increments with respect to each other.
3 . The receiver of claim 2 , further comprising:
a first set of balanced photodiodes configured to receive the combined signals from the first and second pickups to generate a first intermediate frequency (IF) electrical signal;
a second set of balanced photodiodes configured to receive the combined signals from the third and fourth pickups to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
4 . The receiver of claim 2 , wherein the first, second, third and fourth pickups are located at a downstream side of the Fourier transform space (FTS) and are spaced apart from one another along an output surface of the Fourier transform space (FTS), and wherein the first optical beam source and the local oscillator (LO) source are located at an upstream side of the Fourier transform space (FTS) and are spaced apart from one another along an input surface of the Fourier transform space (FTS).
5 . The receiver of claim 1 , further comprising:
a first photodiode configured to receive the combined signal from the first pickup to generate a first intermediate frequency (IF) electrical signal;
a second photodiode configured to receive the combined signal from the second pickup to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
6 . The receiver of claim 1 ,
wherein the Fourier transform space (FTS) is defined between an input surface and an output surface,
wherein the first optical beam and the LO are input into the Fourier transform space (FTS) respectively at first and second locations at the input surface,
wherein the first and second pickups are respectively arranged at third and fourth locations at the output surface,
wherein a first optical path length between the first and third locations is different than a second optical path length between the first and fourth locations.
7 . The receiver of claim 6 ,
wherein a third optical path length between the second location and the third location is different than a fourth optical path length between the second location and the fourth location.
8 . The receiver of claim 1 ,
wherein the Fourier transform space (FTS) is defined between an input surface and an output surface,
wherein the first optical beam and the LO are input into the Fourier transform space (FTS) respectively at first and second locations at the input surface,
wherein the first and second pickups are respectively arranged at third and fourth locations at the output surface,
wherein a spacing d in between the first location and the second location is equal to a spacing d out between the third location and the fourth location.
9 . The receiver of claim 1 , wherein the image rejection mixer comprises a star coupler that forms the Fourier transform space (FTS), the star coupler comprising a first input port configured to receive the first optical beam, a second input port configured to receive the LO, and wherein the first and second pickups are each configured to capture the corresponding combined signals of the first optical beam and the LO from the Fourier transform space (FTS).
10 . The receiver of claim 9 , wherein each of the plurality of sensors include a corresponding image rejection mixer that each comprise a corresponding star coupler configured to receive a corresponding optical beam captured by the sensor.
11 . The receiver of claim 9 , further comprising:
a first set of balanced photodiodes configured to receive the combined signals from the first and second pickups to generate a first intermediate frequency (IF) electrical signal;
a second set of balanced photodiodes configured to receive the combined signals from third and fourth pickups of the star coupler to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
12 . The receiver of claim 9 , further comprising:
a first photodiode configured to receive the combined signal from the first pickup to generate a first intermediate frequency (IF) electrical signal;
a second photodiode configured to receive the combined signal from the second pickup to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
13 . A receiver comprising:
a plurality of channels that are each coupled to an interference space, each channel comprising:
an electro-optic modulator to modulate an RF electrical signal with an optical carrier signal to generate a corresponding modulated optical signal including the optical carrier signal and two sidebands that constitute a first upconverted optical signal and a second upconverted optical signal, respectively,
a first optical waveguide configured to convey the first upconverted optical signal to the interference space;
the interference space configured to receive the upconverted optical signals at a channel edge of the interference space to allow the upconverted optical signals to interfere with each other and form one or more optical beams at a beamspace edge of the interference space;
a plurality of sensors, including a first sensor, arranged at the beamspace edge to capture an interference pattern at the beamspace edge including the one or more optical beams, the plurality of sensors each comprising a sensor having an image rejection mixer, each image rejection mixer comprising a star coupler forming a Fourier transform space (FTS), the star coupler comprising:
a first input port configured to receive a corresponding optical beam of the interference pattern;
a second input port configured to receive a local oscillator (LO) from a local oscillator (LO) source; and
first and second pickups each configured to capture a corresponding combined signal of the received optical beam and the LO forming a beat frequency signal, wherein the beat frequency signals of the combined signals captured by the first and second pickups are formed at quadrature phase increments with respect to each other.
14 . The receiver of claim 13 , wherein, with respect to the first sensor:
the Fourier transform space (FTS) is defined between an input surface and an output surface, the corresponding optical beam and the LO are input into the Fourier transform space (FTS) respectively at first and second locations at the input surface, the first and second pickups are respectively arranged at third and fourth locations at the output surface, a first optical path length between the first and third locations is different than a second optical path length between the first and fourth locations.
15 . The receiver of claim 14 , wherein, with respect to the first sensor, a third optical path length between the second location and the third location is different than a fourth optical path length between the second location and the fourth location.
16 . The receiver of claim 13 , wherein, with respect to the first sensor:
the Fourier transform space (FTS) is defined between an input surface and an output surface,
the corresponding optical beam and the LO are input into the Fourier transform space (FTS) respectively at first and second locations at the input surface,
the first and second pickups are respectively arranged at third and fourth locations at the output surface, and
a spacing d in between the first location and the second location is equal to a spacing d out between the third location and the fourth location.
17 . The receiver of claim 13 , wherein each of the sensors further comprise:
a first set of balanced photodiodes configured to receive the combined signals from the first and second pickups to generate a first intermediate frequency (IF) electrical signal;
a second set of balanced photodiodes configured to receive the combined signals from third and fourth pickups of the star coupler to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
18 . The receiver of claim 13 , wherein, with respect to each sensor, the pickup array comprises third and fourth pickups each configured to capture a corresponding combined signal of the received optical beam and the LO forming a beat frequency signal, wherein the beat frequency signals of the combined signals captured by the first, second, third and fourth pickups are formed at quadrature phase increments with respect to each other.
19 . The receiver of claim 18 , wherein each sensor further comprises:
a first set of balanced photodiodes configured to receive the combined signals from the first and second pickups to generate a first intermediate frequency (IF) electrical signal;
a second set of balanced photodiodes configured to receive the combined signals from the third and fourth pickups to generate a second IF electrical signal; and
a 90 degree hybrid coupler to receive the first IF electrical signal at a 0 degree input port and to receive the second IF electrical signal at a 90 degree input port, and to combine the first IF electrical signal with a phase shifted second IF electrical signal to generate an output IF electrical signal.
20 . A method of performing an image rejection on received radio frequency (RF) beams, the method comprising:
capturing a first RF beam with an antenna array comprising a plurality of antennas, each of the antennas generating a corresponding RF electrical signal;
modulating each RF electrical signal with an optical carrier signal to generate a corresponding modulated optical signal including the optical carrier signal and two sidebands that constitute a first upconverted optical signal and a second upconverted optical signal, respectively;
forming a first optical beam corresponding to the first RF beam at an output edge of an interference space including receiving at an input edge of the interference space at least the first upconverted optical signals;
capturing the first optical beam at the output of the interference space;
delivering the first optical beam and a local oscillator (LO) to a Fourier transform space (FTS);
capturing by first and second pickups first and second composite optical signals, respectively, wherein the first and second composite optical signals each comprise a combination of the first optical beam and the LO that form a corresponding beat frequency signal, wherein the beat frequency signal of the first composite optical signal and the beat frequency signal of the second composite optical signal are formed at quadrature phase increments with respect to each other.