Beamforming and channelization implemented in microwave photonics

Abstract

This application relates to beamforming and channelization implemented in microwave photonics, and discloses a receiver and transmitter suitable for space, air, or ground RF communication systems, and for systems in which one or more signals of various types and properties exist in any given beam of a communication point beam, such as on a high-throughput satellite. The transmitter may include: an optical frequency comb configured to generate a plurality of equally spaced optical wavelengths; an electro-optic modulator that receives the plurality of equally spaced optical wavelengths and data signals and generates a modulated optical beam; an optical circulator that receives the modulated optical beam; an optical switch that switches the modulated optical beam to the output port of an optical switch terminated in one or more fiber Bragg gratings; a wavelength division multiplexer that receives a single wavelength of the time-delayed modulated optical beam from the optical circulator; and a plurality of antenna elements.

Description

Technical Field

[0001] This disclosure relates to systems and methods for beamforming and channelization for microwave photonics implementation. Background Technology

[0002] In conventional radio frequency (RF) design, phased array antenna beamforming relies on electronically controlled phase shifters to align individual array elements. Both RF components and phase shifting components create bandwidth and dynamic range limitations. Increasing bandwidth introduces RF beam disturbances such as beam skew. Digital beamforming after initial downconversion to intermediate frequency requires a high sampling rate analog-to-digital converter (ADC), but this is a trade-off in ADC resolution. This limits the modulation order and ultimately reduces the available data rate. Current systems for satellite, air, and terrestrial communications are seeking to increase capacity through bandwidth-efficient modulation schemes (e.g., Digital Video Broadcasting Satellite II (DVBS-II)), which achieve waveforms greater than 128 quadrature amplitude modulation (QAM) and wider bandwidth channels in the millimeter-wave (mmW or MMW) band. This expansion of bandwidth and modulation order presents challenges for both the front-end RF and digital sampling components. The same issues exist in transmission when all electronic channelization and beamforming are used. Summary of the Invention

[0003] The following is a simplified summary of the invention to provide a basic understanding of some aspects of one or more embodiments of this teaching. This summary is not a broad overview, nor is it intended to identify the key points or essential elements of this teaching, nor to depict the scope of this disclosure. Rather, its primary purpose is merely to present one or more concepts in a simplified form as a prelude to the detailed embodiments that follow.

[0004] According to an example of this disclosure, a receiver is disclosed. The receiver includes: a phased array antenna having P receiving elements configured such that each of the P receiving elements modulates one of P optical modulators; a first optical frequency comb configured to generate a plurality of equally spaced optical wavelengths; and a first 1×P wavelength division multiplexer (WDM1) configured to receive the plurality of equally spaced optical wavelengths and further configured to divide the plurality of equally spaced optical wavelengths into individual optical wavelengths, such that each of the individual optical wavelengths is output as a separate carrier signal to each of the P optical modulators, such that the total incoming radio frequency (RF) beamfield incident on each of the P receiving elements... The system modulates individual optical wavelengths in each optical modulator; a second wavelength division multiplexer (WDM2) is configured to receive each output from each optical modulator in the optical modulator, such that all modulated wavelengths are combined together to form a single output to form a combined signal; and an N-input × M-output optical switch is configured to receive the combined signal from the WDM2 at at least one input port and is further configured to switch the combined signal to an output port terminated in a fiber Bragg grating (FBG), each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber.

[0005] In some examples, in the receiver, the first optical frequency comb is configured such that the spacing between adjacent frequencies is more than twice the maximum RF frequency that the phased array receiving element is expected to receive.

[0006] In some examples, in the receiver, the first wavelength division multiplexer (WDM1) has an inter-channel spacing equal to the adjacent frequency spacing of the first optical frequency comb.

[0007] In some examples, in the receiver, the second wavelength division multiplexer (WDM2) has an inter-channel spacing equal to the adjacent frequency spacing of the first frequency comb.

[0008] In some examples, the second wavelength division multiplexer (WDM2) in the receiver is configured to have a bandpass of more than twice the maximum RF frequency that the phased array elements are expected to receive.

[0009] In some examples, the number of channels in WDM1 and WDM2 in the receiver is at least the number of phased array receiving elements.

[0010] In some examples, the optical paths (including each optical modulator) between WDM1 and WDM2 in the receiver are equal within a 1 mm difference.

[0011] In some examples, the receiver also includes an optical amplifier and a wavelength-independent beam splitter with N output ports, wherein the optical amplifier and the wavelength-independent beam splitter are inserted between WDM2 and the optical switch, such that WDM2 outputs to the optical amplifier, the optical amplifier outputs to the wavelength-independent beam splitter, and the wavelength-independent beam splitter outputs to each input port of the optical switch.

[0012] In some examples, in the receiver, the FBG at the output of the optical switch introduces a time delay between different wavelengths, which represents the actual time delay of the RF beamfield wavefront arriving from different directions illuminating the phased array receiver element.

[0013] In some examples, the number of N inputs for the optical switch in the receiver corresponds to the number of RF beams that can be simultaneously acquired on the phased array receiver element.

[0014] In some examples, in the receiver, the number of M outputs from the optical switch corresponds to the number of different RF beam directions that can be resolved.

[0015] In some examples, in the receiver, an optical switch enables the selection of the output port using an FBG, which introduces a specific real time delay between wavelengths representing the selected RF beam direction.

[0016] In some examples, the receiver also includes an optical circulator inserted between the WDM2 and the FBG.

[0017] In some examples, in the receiver, the output of the optical circulator represents all wavelengths of the signal from individual phased array elements that form a specific beam direction due to the real time delay imposed between the different wavelengths.

[0018] In some examples, the output of the optical circulator is routed to the signal channelization and processing elements in the receiver.

[0019] In some examples, the receiver provides simultaneous parallel acquisition processing of N RF beam directions.

[0020] According to an example of this disclosure, a transmitter is disclosed. The transmitter includes: an optical frequency comb configured to generate a plurality of equidistant optical wavelengths; an electro-optic modulator (EOM) configured to receive the plurality of equidistant optical wavelengths and a data signal, and generate a modulated optical beam modulated with the data signal; an optical circulator configured to receive the modulated optical beam at an input port; an N-input × M-output optical switch configured to receive the modulated optical beam from a first output port of the optical circulator, and further configured to switch the modulated optical beam to an output port of the optical switch, the output port of which is terminated in one or more fiber Bragg gratings (FBGs), each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber; a 1 × P wavelength division multiplexer (WDM1) configured to receive a single wavelength of the time-delayed modulated optical beam from a second output port of the optical circulator; and a plurality of antenna elements, each of which is configured to receive and transmit a single wavelength of the modulated optical beam.

[0021] In some examples, in the transmitter, each of the multiple antenna elements includes a photodiode and a power amplifier.

[0022] In some examples, the EOM in the transmitter is a Mach-Zehnder modulator. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the teachings and, together with the specification, serve to explain the principles of this disclosure.

[0024] Figure 1 A receiver according to an example of this disclosure is shown.

[0025] Figure 2 A system for channelization with two coherent frequency combs is shown as an example according to this disclosure.

[0026] Figure 3 A receiving method according to an example of this disclosure is shown.

[0027] Figure 4 A method for signal channelization according to an example of this disclosure is shown.

[0028] Figure 5 A method for beam scanning and signal acquisition used in a search mode scenario according to an example of this disclosure is shown.

[0029] Figure 6 A transmitter according to an example of this disclosure is shown.

[0030] It should be noted that some details in the accompanying drawings have been simplified and are drawn to facilitate understanding of the present teachings, rather than to maintain strict structural accuracy, details and proportions. Detailed Description

[0031] Reference will now be made in detail to the exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever convenient, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0032] In general, a receiver and a transmitter are disclosed that are suitable for space, airborne or ground RF communication systems and mitigate common performance parameter constraints (such as bandwidth and dynamic range) associated with conventional RF designs. The disclosed method is applicable to systems where one or more signals of multiple types and natures are present in any given beam of communication spot beams, such as on a high-throughput satellite.

[0033] The receiver includes a first optical frequency comb configured to generate a plurality of equally spaced optical wavelengths. The receiver further includes a first 1×P wavelength division multiplexer (WDM1) configured to receive the plurality of equally spaced optical wavelengths, and further configured to split the plurality of equally spaced optical wavelengths into individual optical wavelengths, such that each of the individual optical wavelengths is output as a separate carrier signal to each of the P optical modulators, so that the total incoming radio frequency (RF) beam field incident on each of the P receiving elements modulates the separate optical wavelength in each optical modulator. The receiver further includes a second wavelength division multiplexer (WDM2) configured to receive each output from each of the optical modulators, such that all modulated wavelengths are combined together into a single output to form a combined signal. The receiver still further includes an N-input port × M-output port optical switch configured to receive the combined signal from WDM2 at at least one input port, and further configured to switch the combined signal to output ports terminated in a respective fiber Bragg grating (FBG), each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each optical fiber. For example, a typical arrayed waveguide grating (AWG) for telecommunications has 32 or 40 ports. In some cases, an AWG can have up to 128 ports. However, the performance of high-port-count devices tends to begin to degrade. For typical commercial off-the-shelf switches, N=96 and M=96 are available. N and M can be different combinations, and for custom components, the number of ports can be increased with N<M, allowing a greater number of beam directions.

[0034] The transmitter includes an optical frequency comb configured to generate multiple equidistant optical wavelengths. It also includes an electro-optic modulator (EOM) configured to receive the multiple equidistant optical wavelengths and a data signal, and to generate a modulated optical beam modulated by the data signal. The transmitter further includes an optical circulator configured to receive the modulated optical beam at an input port. The transmitter also includes an N-input × M-output optical switch configured to receive the modulated optical beam from a first output port of the optical circulator and further configured to switch the modulated optical beam to the output port of the optical switch, the output port of which is terminated in one or more fiber Bragg gratings (FBGs), each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber. Finally, the transmitter includes a 1 × P wavelength division multiplexer (WDM1) configured to receive a single wavelength of the time-delayed modulated optical beam from a second output port of the optical circulator. The transmitter also includes multiple antenna elements, each of which is configured to receive and transmit a single wavelength of the modulated optical beam.

[0035] The transmitter and receiver disclosed herein offer numerous improvements over conventional devices. First, the use of an optical frequency comb (also known as a fiber optic comb) allows the total RF field incident on the antenna phased array to be modulated onto the optical frequency comb, where each wavelength carries the field on a phased array element. By introducing a time delay (corresponding to a phase shift between different RF elements) through optical dispersion, reconstruction of one of the incident light beams can be achieved independently of the frequency of the incident RF field. By combining the reconstructed beam with another optical frequency comb, down-channelization to smaller bandwidths is allowed. Combining an N×M switch with a fiber Bragg grating allows for the formation of a fast, reconfigurable RF beamformer based on real time delay. The transmitter and receiver are electronically switchable, allowing for rapid beam scanning in search or track applications. The N×M switch and FBG can be implemented using several tunable FBGs. This allows for very fine beam pointing control once the initial search has positioned the beam. The N×M switch can be used in tracking mode, where the channel is sequentially switched to different beam pointing angles as the satellite passes over the Earth, but only routed to different dispersion FBGs. N×M switching and FGB beamforming are independent of RF signal frequency and bandwidth. Once the OFC frequency spacing is correctly selected to allow sufficient space for modulation sidebands, the RF carrier frequency and total RF bandwidth have no effect on beamforming.

[0036] Figure 1A receiver 100 according to an example of this disclosure is shown. The receiver 100 includes a plurality of antenna phased array receiving elements 105 configured to receive incident RF 110 from different angles. Each of the plurality of phased array receiving elements 105 includes a receiver low noise amplifier (LNA) 115 and an optical modulator 120.

[0037] Receiver 100 also includes a first optical frequency comb (OFC1) 125, which is configured to generate a plurality of equally spaced optical wavelengths. In some examples, the first OFC1 125 is configured such that the spacing between adjacent frequencies is more than twice the maximum RF frequency that the phased array receiving element is expected to receive. Other suitable frequency spacings may be used.

[0038] Receiver 100 also includes a first 1×P wavelength division multiplexer (WDM1) 130, configured to receive a plurality of equally spaced optical wavelengths. The first WDM1 130 is further configured to divide the plurality of equally spaced optical wavelengths into individual optical wavelengths, such that each of the individual optical wavelengths is output as a separate carrier signal to each of P optical modulators, such that the total incoming radio frequency (RF) beamfield incident on each of the P receiving elements modulates the individual optical wavelength in each optical modulator. In some examples, the first WDM1 130 has an inter-channel spacing equal to the adjacent frequency spacing of the first optical frequency comb. Other suitable inter-channel spacings may be used.

[0039] Receiver 100 also includes a second wavelength division multiplexer (WDM2) 135, which is configured to receive each output from each optical modulator in the optical modulator, such that all modulated wavelengths are combined together to form a single output to form a combined signal. In some examples, the second WDM2 135 has an inter-channel spacing equal to the adjacent frequency spacing of the first frequency comb. Other suitable inter-channel spacings can be used. In some examples, the second WDM2 135 is configured to have a bandpass of more than twice the maximum RF frequency expected to be received by the phased array elements. Other suitable bandpass parameters can be used. In some examples, the number of channels in WDM1 130 and WDM2 135 is at least the number of phased array receiving elements. Other suitable numbers of channels can be used. In some examples, the optical paths (including each optical modulator) between WDM1 130 and WDM2 135 are equal within a 1 mm difference. Other suitable optical path lengths can be used.

[0040] Receiver 100 also includes a first optical amplifier 140 that receives the output of WDM2 135 and provides input to a first wavelength-independent beam splitter 145. The first optical amplifier 140 and the first wavelength-independent beam splitter 145 are interposed between WDM2 135 and optical switch 160, such that the output of WDM2 135 is sent to the first optical amplifier 140, which in turn sends an output to the first wavelength-independent beam splitter 145, which in turn sends an output to each input port of optical switch 160. Optical switch 160 can be a microelectromechanical system (MEMS) based or a piezoelectric-based non-blocking optical cross-connect switch. Optical switch 160 connects any input to any output and is independent of signal baud rate / RF modulation, and has a typical signal loss of less than 1 dB.

[0041] The output is provided to a first optical circulator 150 and a second optical circulator 155. The first optical circulator 150 is interposed between the WDM2 135 and the FBG 165. In some examples, the second optical circulator 155 may be a P-th circulator, where P equals the number of channels in the WDM2 135. In some examples, the output of the first optical circulator 150 and / or the second optical circulator 155 carries all wavelengths representing signals from individual phased array elements that form a specific beam direction due to the real time delay imposed between the different wavelengths.

[0042] Receiver 100 further includes an N-input × M-output optical switch 160 configured to receive a combined signal from the WDM2 135 at at least one input port. The optical switch 160 is further configured to switch the combined signal to an output port terminated in a fiber Bragg grating (FBG) 165 or another suitable fiber-based wavelength-dispersion element material, each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber. FBG 165 is a structured (periodic or chirped) variation of the refractive index in the fiber. These refractive index perturbations cause wavelength dispersion or simply form a wavelength-selective mirror. For example, FBG 165 includes a linear chirped variation along the length of the fiber, which serves as a narrowband wavelength-selective mirror. The spacing between different FBGs introduces a time delay between different wavelengths. In some examples, the FBG at the output of the optical switch introduces a time delay between different wavelengths that represents the actual time delay of the RF beamfield wavefront arriving from different directions illuminating the phased array receiver element. In some examples, the number of N inputs to optical switch 160 corresponds to the number of RF beams that can be simultaneously acquired on the phased array receiver element. In some examples, the number of M outputs from optical switch 160 corresponds to the number of different RF beam directions that can be resolved. In some examples, optical switch 160 enables the selection of output ports using an FBG, which introduces a specific real time delay between wavelengths representing the selected RF beam direction.

[0043] Receiver 100 also includes a second optical frequency comb (OFC2) 170. OFC1 125 generates optical wavelengths spaced between 25 GHz and 200 GHz, and OFC2 170 generates optical wavelengths spaced between 25 GHz and 200 GHz with a small offset within the range of 25 MHz to 200 MHz. The output of OFC2 170 is provided to a second optical amplifier 175, and then to a second wavelength-independent beam splitter 185. The outputs of the optical circulator 135 and the second wavelength-independent beam splitter 185 are then routed to signal channelization and processing elements 190 and a digital signal processor (DSP) 195 for processing. DSP 195 allows for electronic amplitude balancing between signals acquired by a single RF antenna. As described above, true beamforming involves aligning the phase with the true time delay and equalizing the amplitude to compensate for possible system losses in the receiver. This can be done electronically because it is easy to digitally change the signal magnitude. Receiver 100 allows simultaneous parallel acquisition and processing of N RF beam directions.

[0044] Figure 2An example of a channelization system 200 with two coherent frequency combs according to this disclosure is shown. Two coherent optical combs with a relative frequency offset Δ are used for downconversion and channelization of the acquired RF bandwidth. The offset is selectable and can range from 100 kHz to 1 GHz. Figure 2 In the example shown, the offset is fixed at 25 MHz. In this example, the first frequency comb 210 and the second frequency comb 215 can have 200 lines spaced at 25 GHz and 24.75 GHz respectively, occupying a gain spectrum of approximately 40 nm. Frequency combs composed of silicon dioxide and silicon-based frequency combs have been shown to have a gain spectrum greater than 100 nm. RF signals (data) are multicast on the 25 GHz frequency comb using MZI. The second frequency comb 215 at 24.75 GHz is used as an optical local oscillator (LO). Due to the frequency difference between the first frequency comb 210 and the second frequency comb 215, the LO slices the spectrum of the RF signal, and each slice is converted into I and Q streams by a coherent detector.

[0045] like Figure 2 As shown, the output of the master laser 205 is split and provided to a first tunable optical frequency comb (TOC1) 210 and a second tunable optical frequency comb (TOC2) 215. The spectrum 220 from TOC1 shows multiple equally spaced optical frequencies. An electro-optic modulator 225, such as a Mach-Zehnder modulator (MZM), receives data 230 and the output from TOC1 210, and modulates the data 230 to produce a modulated spectrum 235. The output of the electro-optic modulator 225 is provided to a first arrayed waveguide grating (AWG1) 240, and the output of TOC2 215, which serves as an optical local oscillator 245, is provided to a second arrayed waveguide grating (AWG2) 250. A coherent receiver 255 receives the outputs of AWG1 240 and AWG2 250.

[0046] Figure 3A method of receiving 300 according to an example of this disclosure is illustrated. The method of receiving 300 includes establishing an instantaneous RF bandwidth (IB) requirement for the RF receiver at 305. The method of receiving 300 also includes selecting a first optical frequency comb (OFC1) at 310 with an adjacent frequency spacing greater than 2 × IB. The number of comb frequencies is twice the number of phased array elements of the receiver. To improve system gain, the output power of OFC1 can be maximized. The method of receiving 300 also includes selecting a second optical frequency comb (OFC2) at 315 with an adjacent frequency of OFC1 + Δ, where Δ is equal to the first channel bandwidth provided to the in-phase (I) and quadrature (Q) components of the DSP. For example, a typical range of Δ is between 10 MHz and 1 GHz. The method of receiving 300 also includes injecting light from OFC1 into a wavelength division multiplexing (WDM1) element at 320, the WDM1 element having an inter-channel spacing that perfectly matches the frequency spacing of OFC1. Each fiber output of WDM1 carries a single wavelength from OFC1, which is guided to an electro-optic modulator that takes an RF signal from the phased array element as its data input. The modulator can be directly connected to an antenna element or at the output of a low-noise amplifier (LNA). Once all optical wavelengths have been modulated with the incoming RF field in each modulator, the receiving method continues at 300°, and at 325°, the light is propagated individually in the fiber to a second WDM2 element, which combines them into a single fiber. The individual fiber paths between WDM1 and WDM2 are identical within less than 1 mm to minimize phase error in the subsequent RF beamforming stage. The combined optical wavelength contains the total RF field incident on the phased array from all directions. The signal is optically amplified, providing a uniform RF gain across the entire RF field. The receiving method continues at 300°, and at 330°, to separate the individual RF beams incident on the phased array, a wavelength-independent beam splitter divides the amplified optical signal into N distinct copies. Each output coupled into the optical fiber has the same signal copy as the WDM2 output and is supplied to the N input ports of the optical non-blocking switch. The lengths of the optical paths between the splitter and the switch are identical to those less than 1 mm.

[0047] Optical switch 160 has N inputs and M outputs, where N is less than or equal to M. Optical switch 160 is electronically controlled, and each input can be directed to any output. Each output of optical switch 160 is connected to FBG 165, which is designed with different dispersion properties, causing different wavelengths to be back-reflected from different points along the optical fiber. All wavelengths input to the switch are ultimately back-reflected sequentially, and different time delays are imposed between them according to the dispersion properties of the FBG. This process constitutes the real time delay associated with the RF signal and is independent of the properties of the incident RF field. The process of introducing a time delay between different wavelengths allows an RF field of one beam direction to be illuminated in each optical path after switching.

[0048] Figure 4 A method of signal channelization 400 according to an example of this disclosure is illustrated. The method of signal channelization 400 includes time delaying a wavelength in one optical fiber at 405 to align the information carried by the RF with the phase-front of a specific beam incident on a phased array. Channelization provides a smaller bandwidth for processing and decoding. Channelization utilizes the fact that each optical fiber carries multiple wavelengths, each with a copy of the RF field. Each fiber output from the circulator is coupled to a WDM3, which separates the different wavelengths into individual fibers. The method of signal channelization 400 continues at 410, where a second OFC2 with a frequency offset relative to OFC1 is provided as a local oscillator to channel the signal. OFC2 is also coupled to a WDM4 to separate the individual wavelengths into separate fibers. An optical coherent receiver array equal to the number of wavelengths in OFC1 and OFC2 is used for channeling the incoming data. Method 400 continues, at 415, an optical fiber from WDM3 (e.g., AWG1 240) and WDM4 (e.g., AWG2 250) is provided to each optical coherent receiver for use as both data and local oscillator signals to extract in-phase (I) and quadrature (Q) signal components. This generates N pairs of I and Q signal streams, which are fed for subsequent DSP analysis. Receiver 100 has N beamforming paths, and each beamforming path outputs in a coherent receiver array. Therefore, receiver 100 generates a total of N×N pairs of I and Q signals, representing N RF beams incident on a phased array having a sub-channel bandwidth equal to IBN.

[0049] Figure 5A method for beam scanning and signal acquisition 500 used in a search mode scenario according to an example of this disclosure is illustrated. The method for beam scanning and signal acquisition 500 can be implemented using a beamformer with optical switches and an FBG arranged with ML fixed-dispersion FBGs and L tunable-dispersion FBGs. The method for beam scanning and signal acquisition 500 includes performing a first coarse signal scan search at 505 by simultaneously acquiring signals using ML channels. Once a signal is identified, the method for beam scanning and signal acquisition 500 continues at 510, selecting a real-time delay for the channel with the maximum signal strength and encoding one of the tunable FBGs. The method for beam scanning and signal acquisition 500 continues at 515, tuning the dispersion of the tunable FBG to maximize the detected RF signal. The maximum signal corresponds to optimal alignment with the incoming RF beam. In some examples, a feedback-locked loop can be utilized to improve the stability of signal acquisition. The method for beam scanning and signal acquisition 500 can be repeated for multiple beams and can be tracked. Once the beam leaves the range of the tunable FBG, it can be transmitted to a different tunable FBG.

[0050] Figure 6 An example of a transmitter 600 according to this disclosure is shown. The transmitter 600 includes a transmitter optical frequency comb (OFC) 605 configured to generate a plurality of equally spaced optical wavelengths, as shown in the transmitter spectrum 610.

[0051] Transmitter 600 also includes an electro-optic modulator (EOM) 615 configured to receive a plurality of equidistant optical wavelengths from OFC 605 and receive a data signal 620, and generate a modulated optical beam 625 modulated with the data signal 620. In some examples, EOM 615 is a Mach-Zehnder modulator. Other suitable EOMs may also be used. Transmitter 600 also includes an optical circulator 630 configured to receive the modulated optical beam 625 at an input port.

[0052] The transmitter 600 also includes an N-input × M-output optical switch 635, configured to receive a modulated optical beam 625 from a first output port of the optical circulator 630. The optical switch 635 is further configured to switch the modulated optical beam 625 to the output port of the optical switch, which is terminated in one or more fiber Bragg gratings (FBGs) 640, each FBG having different wavelength dispersion properties, thereby introducing different time delays between different wavelengths in each fiber.

[0053] The transmitter 600 also includes a 1×P wavelength division multiplexer (WDM1) 645, which is configured to receive a single wavelength of a time-delayed modulated optical beam 625 from the second output port of the optical circulator 630.

[0054] The transmitter 600 also includes a plurality of antenna elements 650. Each of the plurality of antenna elements 650 is configured to receive and transmit a single wavelength of a time-delayed modulated optical beam. Each of the plurality of antenna elements 650 includes a photodiode 655 and a power amplifier 660.

[0055] In summary, the receiver 100 and transmitter 600 described above allow for the reception, transmission, and electro-optical processing of multiple beams simultaneously entering the phased array antenna, which eliminates or reduces beam skew. The receiver 100 provides a separate optical carrier for the first OFC1 125, with each wavelength separated and used as an optical modulator at each phased array element, where the RF delay phased array input modulates each optical modulator. The receiver 100 also provides an N×N cross-connected optical switch 160, which switches the recombined (but delayed) optical carriers into different FBGs, each FBG being tuned to reflect the real time delay back into the optical switch 160. The receiver 100 provides a second OFC2 170, which is coherent but offset from the first OFC1 251 to mix with it and demodulate the real time-delayed signal, thereby producing a demodulated signal for the signal channelization and processing element 190. The DSP 195 can examine each real time-delayed signal and determine which signal comes from which direction and which signal is the optimal demodulated signal.

[0056] Receiver 100 and transmitter 600 provide true time-domain beamforming, allowing processing of signals with bandwidths up to one-tenth of a GHz. Using coherent, ultra-low phase noise optical frequency combs, such as OFC1 125, OFC2 170, and OFC 605, allows for parallel spectrum slicing and decomposition of multiple GHz to sub-channels ranging from 10 MHz to 100 MHz, and in applications with RF frequencies from 1 GHz to 100 GHz, the upper limit is set by currently used electro-optic modulators. For example, receiver 100 allows reception of the full Ka-band from 26 GHz to 40 GHz, allowing simultaneous scaling in beam count and bandwidth without suffering beam skew, eliminating or reducing the requirements of high ENOB (effective number of bits) high-bandwidth analog-to-digital converters.

[0057] The advantages of the disclosed receiver and transmitter are at least in part based on improvements to coherent optical frequency combs, which provide ultra-stable low-phase-noise microwave sources, time metrology, RF beamforming, signal sampling and up / down conversion, frequency channeling, and parallel signal processing. Since photon frequencies are several orders of magnitude higher than typical RF bands, they provide terahertz bandwidth, which can now be channelized and sliced ​​with the help of optical frequency combs to match hundreds of RF frequency sub-bands, thus allowing parallel processing and channelization. Test case signals were analyzed in the V-band from 45 GHz to 50 GHz. A microwave photonic implementation of the disclosed receiver and transmitter modules was implemented, characterized by beamforming, downconversion, and channeling of the entire 5 GHz bandwidth into selectable sub-channels down to 1 GHz. RF beam reconstruction is then shown using tens or hundreds of coherent optical / frequency combs, with simultaneous readout of antenna elements, and the real time delay, a characterization of the beam direction, is set using predefined dispersive elements. The disclosed features can be applied to multiple beams simultaneously and are independent of data, modulation format, or RF frequency because the actual time delay is implemented in the optical domain. The signal is optically down-converted from RF to baseband and channelized to a bandwidth of several hundred megahertz, generating I and Q streams in the electrical domain. The disclosed features utilize an electronic digital signal processing core wrapped with a photonic layer for handling high frequencies and beamforming.

[0058] Furthermore, the present invention includes embodiments according to the following provisions: Clause 1. A receiver comprising: A phased array antenna having P receiving elements, wherein each of the P receiving elements is configured to modulate one of the P optical modulators; The first optical frequency comb is configured to generate multiple equally spaced optical wavelengths; A first 1×P wavelength division multiplexer (WDM1) is configured to receive a plurality of equally spaced optical wavelengths and is further configured to divide the plurality of equally spaced optical wavelengths into individual optical wavelengths, such that each of the individual optical wavelengths is output as a separate carrier signal to each of P optical modulators such that the total incoming radio frequency (RF) beamfield incident on each of P receiving elements modulates the individual optical wavelength in each optical modulator. The second wavelength division multiplexer (WDM2) is configured to receive each output from each optical modulator in the optical modulator, such that all modulated wavelengths are combined together to form a single output to form a combined signal; and An N-input × M-output optical switch is configured to receive a combined signal from a WDM2 at at least one input port and is further configured to switch the combined signal to an output port terminated in a fiber Bragg grating (FBG), each FBG having different wavelength dispersion properties, thereby introducing different time delays between different wavelengths in each fiber.

[0059] Clause 2. The receiver according to Clause 1, wherein the first optical frequency comb is configured such that the spacing between adjacent frequencies is more than twice the maximum RF frequency that the phased array receiving element is expected to receive.

[0060] Clause 3. The receiver according to Clause 1 or Clause 2, wherein the first wavelength division multiplexer (WDM1) has an inter-channel spacing equal to the adjacent frequency spacing of the first optical frequency comb.

[0061] Clause 4. A receiver according to any one of Clauses 1-3, wherein the second wavelength division multiplexer (WDM2) has an inter-channel spacing equal to the adjacent frequency spacing of the first frequency comb.

[0062] Clause 5. A receiver as described in any one of Clauses 1-4, wherein the second wavelength division multiplexer (WDM2) is configured to have a bandpass of more than twice the maximum RF frequency that the phased array elements are intended to receive.

[0063] Clause 6. A receiver according to any one of Clauses 1-5, wherein the number of channels in WDM1 and WDM2 is at least the number of phased array receiver units.

[0064] Clause 7. A receiver according to any one of Clauses 1-6, wherein the optical paths (including each optical modulator) between WDM1 and WDM2 are equal within a 1 mm difference.

[0065] Clause 8. The receiver described under any one of Clauses 1-7 also includes: Optical amplifiers; and A wavelength-independent beam splitter with N output ports. The optical amplifier and the wavelength-independent beam splitter are inserted between WDM2 and the optical switch, so that the output of WDM2 goes to the optical amplifier, the optical amplifier then goes to the wavelength-independent beam splitter, and the wavelength-independent beam splitter then goes to each input port of the optical switch.

[0066] Clause 9. A receiver according to any one of Clauses 1-8, wherein the FBG at the output of the optical switch introduces a time delay between different wavelengths, which represents the actual time delay of the RF beamfield wavefronts arriving from different directions illuminating the phased array receiver elements.

[0067] Clause 10. A receiver according to any one of Clauses 1-9, wherein the number of N inputs for the optical switch corresponds to the number of RF beams that can be simultaneously acquired on the phased array receiver element.

[0068] Clause 11. A receiver according to any one of Clauses 1-10, wherein the number of M outputs from the optical switch corresponds to the number of different RF beam directions that can be resolved.

[0069] Clause 12. A receiver according to any one of Clauses 1-11, wherein an optical switch enables selection of an output port using an FBG, the FBG introducing a specific real time delay between wavelengths representing the selected RF beam direction.

[0070] Clause 13. The receiver described in any one of Clauses 1-12 further includes an optical circulator inserted between the WDM2 and the FBG.

[0071] Clause 14. A receiver according to any one of Clauses 1-13, wherein the output of the optical circulator carries all wavelengths representing signals from individual phased array elements that form a particular beam direction due to the real time delay imposed between different wavelengths.

[0072] Clause 15. A receiver according to any one of Clauses 1-14, wherein the output of the optical circulator is routed to a signal channelization and processing element.

[0073] Clause 16. A receiver according to any one of Clauses 1-15, wherein N RF beam directions are acquired and processed simultaneously in parallel.

[0074] Clause 17. A receiver according to any one of Clauses 1-16, wherein digital signal processing is used to amplitude balance the RF beam formed by the real time delay.

[0075] Clause 18: A transmitter comprising: An optical frequency comb, which is configured to generate multiple equally spaced optical wavelengths; An electro-optic modulator (EOM) is configured to receive multiple equally spaced optical wavelengths and data signals, and generate a modulated optical beam modulated by the data signals. An optical circulator configured to receive a modulated optical beam at its input port; An N-input port × M-output port optical switch is configured to receive a modulated optical beam from the first output port of an optical circulator and is further configured to switch the modulated optical beam to the output port of the optical switch, the output port of which is terminated in one or more fiber Bragg gratings (FBGs), each FBG having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber. A 1×P wavelength division multiplexer (WDM1) is configured to receive a single wavelength of a time-delayed modulated optical beam from the second output port of an optical circulator; and Multiple antenna elements, each of which is configured to receive and transmit a single wavelength of a modulated optical beam.

[0076] Clause 19. The transmitter as described in Clause 18, wherein each of the plurality of antenna elements includes a photodiode and a power amplifier.

[0077] Clause 20. A transmitter as described in Clause 18 or Clause 19, wherein the EOM is a Mach-Zehnder modulator.

[0078] While the teachings have been described with reference to examples of their implementation, those skilled in the art will be able to make various modifications to the described implementations without departing from their true spirit and scope. The terminology and descriptions used herein are set forth by way of illustration only and are not intended to be limiting. In particular, although processes have been described by example, the stages of a process may be performed in a different order or simultaneously than illustrated. Furthermore, where the terms “comprising,” “including,” “having,” “containing,” “with,” or variations thereof are used in the detailed description, these terms are intended to be included in a manner similar to the term “comprising.” As used herein, the terms “one or more” and “at least one” relating to a list of items (such as, for example, A and B) mean A alone, B alone, or A and B. Furthermore, unless otherwise specified, the term “set” should be interpreted as “one or more.” Additionally, the terms “coupled” or “linked” mean an indirect or direct connection. Thus, if a first device is coupled to a second device, the connection can be a direct connection or an indirect connection via other devices, components, and connections.

[0079] Those skilled in the art will be able to make various modifications to the described examples without departing from the true spirit and scope. The terminology and descriptions used herein are set forth by way of illustration only and are not intended to be limiting. In particular, although the method has been described by example, the steps of the method may be performed in a different order or simultaneously than illustrated. Those skilled in the art will recognize that these and other variations are possible within the spirit and scope defined in the appended claims and their equivalents.

[0080] The foregoing description and related examples of this disclosure are for illustrative purposes only. It is not exhaustive and does not limit this disclosure to its exact form. Those skilled in the art will understand from the foregoing description that modifications and variations can be made in accordance with the above teachings, or modifications and variations can be obtained from practicing this disclosure. For example, the described steps need not be performed in the same order or at the same intervals. Similarly, various steps may be omitted, repeated, or combined as needed to achieve the same or similar objectives. Likewise, the described system need not include all the parts described in the examples, and may also include other parts not described in the examples. Therefore, the invention is not limited to the foregoing examples, but is defined by the appended claims in the full scope of their equivalents.

[0081] Although the numerical ranges and parameter settings used to illustrate the broad scope of this teaching are approximations, the numerical values ​​described in the specific examples are reported as precisely as possible. However, any numerical value inherently contains a certain degree of error, which is necessarily caused by the standard deviation found in its corresponding test measurement. Furthermore, all ranges disclosed herein should be understood to encompass any and all subranges included therein. For example, the range “less than 10” can include any and all subranges with a minimum value of 0 and a maximum value of 10 (inclusive), that is, any and all subranges with a minimum value equal to or greater than zero and a maximum value equal to or less than 10, such as 1 to 5. In some cases, the numerical values ​​of the parameters may be negative. In such cases, example values ​​for the range expressed as “less than 10” can be assumed to be negative, such as -1, -2, -3, -10, -20, -30, etc.

[0082] While this teaching has been described with respect to one or more embodiments, changes and / or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it should be understood that although the process is described as a series of actions or events, this teaching is not limited to the order of these actions or events. Some actions may occur in a different order and / or simultaneously with other actions or events not described herein. Furthermore, not all process phases are necessary to implement the method according to one or more aspects or embodiments of this teaching. It should be understood that structural components and / or processing phases may be added, or existing structural components and / or processing phases may be removed or modified. Furthermore, one or more actions described herein may be performed in one or more separate actions and / or phases. Additionally, where the terms “comprising,” “including,” “having,” “containing,” “with,” or variations thereof are used in the detailed description and claims, these terms are intended to be included in a manner similar to the term “comprising.” The term “at least one” is used to indicate that one or more of the listed items may be selected. As used herein, the term “one or more” with respect to a list of items (such as, for example, A and B) means A alone, B alone, or A and B. The term "about / approximately" indicates that the listed values ​​may vary to some extent, as long as the change does not result in a process or structure inconsistent with the illustrated implementation. Finally, "exemplary" indicates that the description is used as an example and not to imply that it is ideal. Other embodiments of this teaching will be clearly seen by those skilled in the art in light of the specification and practice disclosed herein. It is intended that the specification and examples be considered exemplary only, and that the true scope and spirit of this teaching are indicated by the appended claims.

Claims

1. A receiver (100) comprising: A phased array antenna having P receiving elements (105) configured such that each of the P receiving elements (105) modulates one of the P optical modulators (120); A first optical frequency comb (125) is configured to generate multiple optical wavelengths that are equidistantly spaced from 25 GHz to 200 GHz; First optical amplifier (140); The first wavelength-independent beam splitter (145) has N output ports. A second optical frequency comb (170) is configured to generate optical wavelengths ranging from 25 GHz to 200 GHz and spaced apart from the wavelength range generated by the first optical frequency comb (125) by 25 MHz to 200 MHz. The output of the second optical frequency comb (170) is provided to a second optical amplifier (175) and then to a second wavelength-independent beam splitter (185). Signal channelization and processing elements (190); The first 1×P wavelength division multiplexer, namely WDM (130), is configured to receive the plurality of equally spaced optical wavelengths and is further configured to divide the plurality of equally spaced optical wavelengths into individual optical wavelengths, such that each of the individual optical wavelengths is output as a separate carrier signal to each of the P optical modulators (120), such that the total incoming radio frequency beam field, namely RF beam field, incident on each of the P receiving elements (105) modulates the individual optical wavelength in each optical modulator (120); The second wavelength division multiplexer (135) is configured to receive each output from each of the optical modulators (120) such that all modulated wavelengths are combined together to form a single output to form a combined signal. as well as An N-input × M-output optical switch (160) is configured to receive the combined signal from the second wavelength division multiplexer (135) at at least one input port and is further configured to switch the combined signal to an output port terminated in a fiber Bragg grating (FBG) (165), each FBG (165) having different wavelength dispersion properties, such that different time delays are introduced between different wavelengths in each fiber, wherein a first optical amplifier (140) and a first wavelength-independent beam splitter (145) are interposed between the second wavelength division multiplexer (135) and the optical switch (160), such that the second wavelength division multiplexer (135) outputs to the first optical amplifier (140), the first optical amplifier (140) then outputs to the first wavelength-independent beam splitter (145), and the first wavelength-independent beam splitter (145) then outputs to each input port of the optical switch (160); A first optical circulator (150) is inserted between the second wavelength division multiplexer (135) and the FBG (165). The output of the first optical circulator (150) carries all wavelengths representing signals from a single phased array element that forms a specific beam direction due to the real time delay applied between different wavelengths. Furthermore, the output of the first optical circulator (150) and the output of the second wavelength-independent beam splitter (185) are routed to the signal channelization and processing element (190) and the digital signal processor (195) for processing.

2. The receiver (100) according to claim 1, wherein the first optical frequency comb (125) is configured such that the spacing between adjacent frequencies is more than twice the maximum RF frequency that the receiving element (105) is expected to receive.

3. The receiver (100) according to claim 1, wherein the first 1×P wavelength division multiplexer (130) has an inter-channel spacing equal to the adjacent frequency spacing of the first optical frequency comb (125).

4. The receiver (100) according to claim 1, wherein the second wavelength division multiplexer (135) has an inter-channel spacing equal to the adjacent frequency spacing of the first optical frequency comb (125).

5. The receiver (100) according to claim 1, wherein the second wavelength division multiplexer (135) is configured to have a bandpass of more than twice the maximum RF frequency that the receiving element (105) is expected to receive.

6. The receiver (100) according to claim 1, wherein the number of channels in the first 1×P wavelength division multiplexer (130) and the second wavelength division multiplexer (135) is at least the number of the receiving elements (105).

7. The receiver (100) according to claim 1, wherein the optical paths including each optical modulator (120) between the first 1×P wavelength division multiplexer (130) and the second wavelength division multiplexer (135) are equal within a 1 mm difference.

8. The receiver (100) according to any one of claims 1-7, wherein the optical switch (160) has a signal loss of less than 1 dB.

9. The receiver (100) of claim 1, wherein the FBG (165) at the output of the optical switch (160) is configured to introduce a time delay between the different wavelengths, the time delay representing the actual time delay of the RF beamfield wavefront arriving from different directions illuminating the receiving element (105).

10. The receiver (100) according to claim 1, wherein the number of N inputs for the optical switch (160) corresponds to the number of RF beams that can be simultaneously acquired on the receiving element (105).

11. The receiver (100) according to claim 1, wherein the number of M outputs from the optical switch (160) corresponds to the number of different RF beam directions that can be resolved.

12. The receiver (100) of claim 1, wherein the optical switch (160) is configured to enable selection of an output port using the FBG (165), the FBG (165) introducing a specific real time delay between wavelengths representing the selected RF beam direction.

13. The receiver (100) according to claim 1, wherein N RF beam directions are acquired and processed simultaneously in parallel.

14. The receiver (100) according to claim 1, wherein the optical switch (160) is a microelectromechanical system (MEMS) based or a piezoelectric non-blocking optical cross-connect switch.

15. The receiver (100) of claim 1, wherein digital signal processing is used to perform amplitude balancing on the RF beam formed by the real time delay.

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