Electromagnetic field detector

Abstract

This invention provides an electromagnetic field detector, a system including the electromagnetic field detector, and a method of operating the electromagnetic field detector. The electromagnetic field detector includes: a first optical signal interface configured to receive a first optical signal from one or more remote light sources; an electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated according to the first optical signal, the electromagnetic field transmitter including: a photocurrent generator configured to generate a photocurrent according to the first optical signal; an antenna interface configured to provide the photocurrent to an antenna to transmit the local oscillator electromagnetic field; a second optical signal interface configured to receive a probe optical signal and a coupled optical signal from one or more remote light sources; and a transmission medium. The medium is configured to be excited by a probe optical signal and further excited by a coupling optical signal, wherein the probe optical signal has a probe frequency set to excite electrons in the transmission medium to a first excited state, and the coupling optical signal has a coupling frequency set to excite electrons in the transmission medium to a predetermined Rydberg state to induce an electromagnetically induced transparent (EIT) effect, wherein the transmission medium is further configured to receive a local oscillator electromagnetic field and a phase-modulated electromagnetic field from a remote transmitter, such that the combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change in the probe optical signal, and the phase state of the phase-modulated electromagnetic field can be detected according to the change.

Description

Technical Field

[0001] This invention relates to an electromagnetic field detector, a system including an electromagnetic field detector, and a method for operating the electromagnetic field detector. Background Technology

[0002] Rydberg atoms are atoms with one or more electrons excited to very high principal quantum numbers (e.g., >10). These Rydberg atoms possess a variety of useful properties, such as very large dipole moments and long decay periods.

[0003] Rydberg atoms can be used to detect electromagnetic fields. Rydberg atom-based electromagnetic field detectors are based on the electromagnetically induced transparency (EIT) effect. When electrons in an atomic medium are raised to a Rydberg state using a probe laser and a coupling laser, the EIT effect may occur. In this state, the atomic medium becomes transparent to the probe laser. The electromagnetic field incident on the atomic medium can then cause further transitions of electrons from the Rydberg state to another Rydberg state. The electrons can then descend from this other Rydberg state to the ground state, making the atomic medium less transparent to the probe laser. Therefore, this change in transparency can be used to detect the electromagnetic field as a change in the probe laser intensity, thus creating an AMRF receiver based on Rydberg atoms. A more detailed explanation of this effect can be found in the article “A Multiple-Band Rydberg-Atom Based Receiver / Antenna: AM / FM Stereo Reception”, Holloway et al., National Institute of Standards and Technology.

[0004] Furthermore, Rydberg atom-based FM RF receivers operate in a similar manner. That is, when the RF electric field changes (or "detunes") from its resonant RF transition frequency, the EIT signal (on a graph of the EIT signal versus probe laser detuning) splits into two asymmetric peaks. The separation of the two peaks increases with RF detuning. By locking the probe laser and coupling laser to specific frequencies, the optical detector output is directly correlated with the FM RF electric field. A more detailed explanation of this effect can also be found in the articles "A Multiple-Band Rydberg-Atom Based Receiver / Antenna: AM / FM StereoReception", Holloway et al., National Institute of Standards and Technology, and "Using frequency detuning to improve the sensitivity of electric field measurements via electromagnetically induced transparency and Autler-Townessplitting in Rydberg atoms", Appl. Phys. Lett. 108, 174101 (2016), Matt T. Simons.

[0005] Rydberg RF receivers can also be used to detect phase-modulated RF fields, such as those using binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and quadrature amplitude modulation (QAM) signals (used in many wireless and cellular communication protocols). In these modulation schemes, data is transmitted by modulating the phase of a carrier wave. To detect the phase of the carrier wave, a reference RF field resonating with the transition to a Rydberg state is applied to an atomic medium, which acts as a local oscillator. The difference frequency, or "intermediate frequency," is detected, and the phase of the intermediate frequency signal directly corresponds to the relative phase between the local oscillator and the incident RF electric field. A more detailed explanation of this effect can be found in the articles “ARydberg Atom-Based Mixer: Measuring the Phase of a Radio Frequency Wave”, Appl. Phys. Lett. 114, 114101 (2019), Holloway et al. and “Detecting and Receiving Phase-Modulated Signals With a Rydberg Atom-Based Receiver”, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 18, NO. 9, SEPTEMBER 2019, Holloway et al. Summary of the Invention

[0006] According to a first aspect of the present invention, an electromagnetic field detector is provided, the electromagnetic field detector comprising: a first optical signal interface configured to receive a first optical signal from one or more remote light sources; an electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated according to the first optical signal, the electromagnetic field transmitter comprising: a photocurrent generator configured to generate a photocurrent according to the first optical signal; and an antenna interface configured to provide the photocurrent to an antenna to transmit the local oscillator electromagnetic field; and a second optical signal interface configured to receive a probe optical signal and a coupling optical signal from the one or more remote light sources; The transmission medium is configured to be excited by the probe optical signal and further excited by the coupling optical signal, wherein the probe optical signal has a probe frequency set to excite electrons in the transmission medium to a first excited state, and the coupling optical signal has a coupling frequency set to excite electrons in the transmission medium to a predetermined Rydberg state to induce an electromagnetically induced transparent (EIT) effect, wherein the transmission medium is further configured to receive the local oscillator electromagnetic field and a phase-modulated electromagnetic field from a remote transmitter, such that the combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change in the probe optical signal, and the phase state of the phase-modulated electromagnetic field can be detected according to the change.

[0007] The first optical signal interface may also be configured to receive a second optical signal from the one or more remote light sources, and the photocurrent generator may be configured to generate the photocurrent by mixing the first optical signal and the second optical signal.

[0008] The local oscillator electromagnetic field and the phase-modulated electromagnetic field can be synchronized.

[0009] The first optical signal may have a wavelength in one of the O-band, E-band, S-band, C-band, L-band, and U / XL-band.

[0010] The second optical signal may have a wavelength in one of the O-band, E-band, S-band, C-band, L-band, and U / XL-band.

[0011] The electromagnetic field of the local oscillator can be bipolarized.

[0012] The electromagnetic field detector may further include: a first module, the first module including the first optical signal interface and the electromagnetic field transmitter; and a second module, the second module including the second optical signal interface and the transmission medium.

[0013] The first module and the second module can be implemented in a single housing or in their respective housings.

[0014] The second module may be one of a plurality of second modules, each of which may include: a corresponding second optical signal interface configured to receive the probe optical signal and the coupling optical signal from the one or more remote light sources, and a corresponding transmission medium configured to be excited by the probe optical signal and further excited by the coupling optical signal, wherein the probe optical signal has a probe frequency configured to excite electrons in the transmission medium to a first excited state, and the coupling optical signal has a coupling frequency configured to excite electrons in the corresponding transmission medium to a predetermined Rydberg state to induce an electromagnetically induced transparent (EIT) effect, wherein the corresponding transmission medium may also be configured to receive a phase-modulated electromagnetic field from the remote transmitter and a local oscillator electromagnetic field from the electromagnetic field transmitter of the first module, such that the combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change in the probe signal, and the phase state of the phase-modulated electromagnetic field can be detected according to the change.

[0015] The first module may be one of a plurality of first modules, each first module may include: a corresponding first optical signal interface configured to receive the first optical signal from the one or more remote light sources, and a corresponding electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated according to the first optical signal, wherein each of the plurality of first modules may be associated with a second module of the plurality of second modules, such that the local oscillator electromagnetic field transmitted by the corresponding electromagnetic field transmitter of the first module may be received at the transmission medium of the associated second module.

[0016] According to a second aspect of the present invention, a system is provided, the system comprising: an electromagnetic field detector according to a first aspect of the present invention; and one or more light sources, the one or more light sources being located away from the electromagnetic field detector, configured to generate the first optical signal, the probe optical signal, and the coupling optical signal, and to transmit the first optical signal, the probe optical signal, and the coupling optical signal to the electromagnetic field detector.

[0017] The system may be part of a telecommunications network, wherein the one or more light sources may be configured to receive a synchronization signal distributed by the network, and the one or more light sources may be configured to synchronize the first optical signal based on the synchronization signal.

[0018] The phase-modulated electromagnetic field can be synchronized with the synchronization signal distributed by the network.

[0019] The system may also include a master clock and a transmitter configured to transmit a synchronization signal derived from the master clock to the remote transceiver, wherein the first optical signal can be synchronized to the synchronization signal.

[0020] The system may also include an optical communication network, wherein the first optical signal, the probe optical signal, and the coupling optical signal can be transmitted to the electromagnetic field detector via the optical communication network.

[0021] According to a third aspect of the invention, a method for operating an electromagnetic field detector having a transmission medium is provided, the method comprising the steps of: receiving a first optical signal from one or more remote light sources; generating a photocurrent based on the first optical signal; transmitting a local oscillator electromagnetic field generated based on the first optical signal by providing the photocurrent to an antenna; receiving a probe optical signal and a coupling optical signal from the one or more remote light sources, wherein the transmission medium is excited by the probe optical signal having a probe frequency configured to excite electrons in the transmission medium to a first excited state, and wherein the transmission medium is further excited by a coupling optical signal having a coupling frequency configured to excite electrons in the transmission medium to a predetermined Rydberg state to induce an electromagnetically induced transparent (EIT) effect; and receiving at the transmission medium the transmitted local oscillator electromagnetic field and a phase-modulated electromagnetic field from a remote transmitter, such that the combination of the phase-modulated electromagnetic field and the transmitted local oscillator electromagnetic field causes a change in the probe optical signal, according to which the phase state of the phase-modulated electromagnetic field can be detected.

[0022] The method may further include the step of receiving a second optical signal from one or more light sources, wherein the step of generating the local oscillator electromagnetic field may further include mixing the first optical signal and the second optical signal to generate the photocurrent.

[0023] The electromagnetic field detector may be an element of an electromagnetic field detector array, each element of the electromagnetic field detector array having a transmission medium, wherein the transmission medium of each element of the electromagnetic field detector array is excited by the probe optical signal and further excited by the coupling optical signal to induce an EIT effect in the transmission medium of each element of the electromagnetic field detector array, wherein the method may further include the following steps: receiving a transmitted local oscillator electromagnetic field and a phase-modulated electromagnetic field from the remote transmitter at the transmission medium of each element of the electromagnetic field detector array, such that the combination of the phase-modulated electromagnetic field and the transmitted local oscillator electromagnetic field causes a change in the probe optical signal, and the phase state of the phase-modulated electromagnetic field can be detected according to the change. Attached Figure Description

[0024] To better understand the present invention, embodiments thereof will now be described by way of example only with reference to the accompanying drawings, wherein:

[0025] Figure 1 This is a schematic diagram illustrating an RF detector based on Rydberg atoms;

[0026] Figure 2 This is a schematic diagram illustrating an RF detector array based on Rydberg atoms; and

[0027] Figure 3 This is an example operation. Figure 1 Rydberg atom-based RF detectors or Figure 2 A flowchart of a method for using a Rydberg atom-based RF detector array. Detailed Implementation

[0028] Figure 1 A wireless telecommunications network 100 is illustrated. Wireless telecommunications network 100 is a cellular telecommunications network operating according to the fifth-generation (5G) protocol defined by the 3rd Generation Partnership Project (3GPP). Wireless telecommunications network 100 includes a Rydberg atom-based radio frequency (RF) receiver 110, an optical device housing 120, and a signal transmitter 130.

[0029] The optical device housing 120 includes a first light source 121, a second light source 123, a third light source 125, a fourth light source 127, and a photodetector 129. The first light source 121 is a laser transmitter configured to generate a first optical signal. The second light source 123 is also a laser transmitter configured to generate a second optical signal. Certain characteristics of these first and second optical signals, such as their wavelengths and corresponding frequencies, are configurable. In this example, the wavelengths of the first and second optical signals are 1550.01438 nm and 1549.98562 nm, respectively, corresponding to a frequency interval of 3.58894 GHz. As described below, the frequency to be detected by the Rydberg atom-based RF receiver 110 is 3.58891 GHz. Therefore, the difference between the frequency detected by the Rydberg atom-based RF receiver 110 and the frequency interval of the first and second optical signals is 30 kHz.

[0030] The third light source 125 and the fourth light source 127 are also laser transmitters and are configured to generate a third optical signal (hereinafter referred to as the "probe" signal) and a fourth optical signal (hereinafter referred to as the "coupled" signal), respectively. The frequencies of the probe signal and the coupled signal can be configured by the third light source 125 and the fourth light source 127. The probe signal and the coupled signal are discussed in more detail below.

[0031] The optical device housing 120 includes a phase noise reduction module (not shown) configured to reduce the phase difference between a first optical signal and a second optical signal. This is achieved by locking the first and second light sources to an optical cavity or frequency comb to achieve a stable light source.

[0032] A first light source 121, a second light source 123, a third light source 125, and a fourth light source 127 transmit a first signal, a second detection signal, and a coupling signal to corresponding first optical fibers 151, second optical fibers 153, third optical fibers 155, and fourth optical fibers 157 (collectively referred to as the plurality of optical fibers 150). The plurality of optical fibers 150 connect an optical device housing 120 to a Rydberg atom-based RF receiver 110. The optical device housing 120 and the Rydberg atom-based RF receiver 110 are positioned far apart from each other. The wavelengths of the first and second optical signals are within the “C-band” of optical communication, such that they experience relatively low attenuation when they communicate over the distance between the optical device housing 120 and the Rydberg atom-based RF receiver 110 using conventional optical fibers such as single-mode fibers. Furthermore, the difference between the wavelength of the first optical signal and the wavelength corresponding to the minimum attenuation in the C-band (+0.01438 nm) is equal to and opposite to the difference between the wavelength of the second optical signal and the wavelength corresponding to the minimum attenuation in the C-band (-0.01438 nm). This ensures that the first and second optical signals have equal attenuation.

[0033] The third optical fiber 155 and the fourth optical fiber 157, which carry the probe signal and the coupling signal respectively, are specialized optical fibers (such as hollow optical fibers) designed for low attenuation at the frequencies of the probe signal and the coupling signal.

[0034] Multiple optical fibers 150 can be connected to an optical network interface to transmit a first signal, a second signal, a probe signal, and a coupling signal to a Rydberg atom-based RF receiver 110.

[0035] The photodetector 129 is configured to receive the detection signal after it has passed through the Rydberg atom-based RF receiver 110, as described below.

[0036] The signal transmitter 130 may be a user equipment (UE) such as a mobile phone or an Internet of Things (IoT) transmitter, configured to transmit a phase-modulated wireless signal at 3.58891 GHz using a 16-QAM modulation scheme. The signal transmitter 130 is also configured to synchronize with network-distributed synchronization signals, such as the primary synchronization signal and secondary synchronization signals (PSS, SSS) of a cellular telecommunications network. These synchronization signals may be broadcast by base stations (not shown) of the cellular telecommunications network.

[0037] The Rydberg atom-based RF receiver 110 is configured to detect the phase of various wireless phase-modulated signals transmitted by the signal transmitter 130, and thus demodulate and encode the data into a plurality of these phase-modulated signals. The Rydberg atom-based RF receiver 110 includes one or more fiber optic interfaces for receiving a plurality of optical fibers 150 from the optical device housing 120. The Rydberg atom-based RF receiver 110 also includes a transmission medium 115, such as a glass cell filled with atomic vapor of rubidium-85 atoms. A probe signal from the third optical fiber 155 travels through the transmission medium 115 and excites electrons in the rubidium-85 atoms. The probe signal is then transmitted from the transmission medium 115 by the third optical fiber 155 to a photodetector 129 in the optical device housing 120. A coupled signal travels through the transmission medium 115 (propagating in the reverse direction and overlapping with the probe signal), and is then... Figure 1The probe signal (represented by the dashed line in the image) also excites electrons in rubidium-85 atoms. The frequency of the probe signal is set to correlate with the transition of electrons in rubidium-85 atoms from the ground state to a first excited state, and the frequency of the coupling signal is set to correlate with the transition of electrons in rubidium-85 atoms from the first excited state to a predetermined Rydberg state. The predetermined Rydberg state is selected based on the specific frequencies of the probe and coupling signals, such that a wireless, phase-modulated signal (from the signal transmitter 130) incident on the transmission medium 115 at a specific frequency excites electrons from the predetermined Rydberg state to another Rydberg state, resulting in a detectable change in the probe signal. In this example, the signal transmitter 130 transmits a wireless signal near 3.58891 GHz, with a probe frequency of 780.2463 nm and a coupling frequency of 479.4370 nm, causing electrons to be excited to the 84th Rydberg state.

[0038] The Rydberg atom-based RF receiver 110 also includes a dual-polarized patch antenna 117 and a photovoltaic photodiode 119 (such as an indium gallium arsenide (InGaAs) photodiode). The photovoltaic photodiode 119 receives a first optical signal and a second optical signal from a first optical fiber 151 and a second optical fiber 153, which in this example are phase-correlated continuous waves spaced 3.58894 GHz apart. The photovoltaic photodiode 119 utilizes optical heterodyne technology to act as an optical mixer to obtain a photocurrent from the input first and second optical signals. In other words, the photovoltaic photodiode 119 can operate in photovoltaic mode to generate a voltage from the first and second optical signals without any power supply. The frequency of the photocurrent is equal to the frequency difference between the first and second optical signals (i.e., 3.58894 GHz). This photocurrent drives the patch antenna array to generate a local oscillator RF signal with the same frequency (i.e., 3.58894 GHz) as the photocurrent and a flat dual-polarized radiation pattern.

[0039] A dual-polarized patch antenna 117 is configured to transmit a local oscillator RF field through a transmission medium 115. Both the local oscillator signal and the wirelessly phase-modulated signal transmitted by the signal transmitter 130 have frequencies corresponding to a transition from a predetermined Rydberg state to another Rydberg state. In this example, the frequency of the wirelessly phase-modulated signal resonates with this transition, while the frequency of the local oscillator signal is slightly non-resonant with it. The superposition of the local oscillator signal and the wirelessly phase-modulated signal at the transmission medium 115 modifies the detection signal, allowing the phase and amplitude of the wirelessly phase-modulated signal to be detected at a photodetector 129. This detection technique has been discussed in several papers, such as “A Rydberg Atom-Based Mixer: Measuring the Phase of a Radio Frequency Wave”, Matthew T. Simons et al., and “Detecting and Receiving Phase Modulated Signals with a Rydberg Atom-Based Mixer”, Christopher L. Holloway et al. In short, the combination of the probe signal and the coupling signal in transmission medium 115 excites electrons to a predetermined Rydberg state, thus producing the EIT effect. As the wireless phase-modulated signal further excites these electrons to another Rydberg state, a phenomenon known as Otler-Townes (AT) splitting occurs in transmission medium 115. The interference between the local oscillator signal and the wireless phase-modulated signal at transmission medium 115 can then be detected by its effect on the EIT / AT splitting. That is, the probe signal is modulated by the interference between the local oscillator signal and the wireless phase-modulated signal. If one of these signals is detuned to the other, the modulation depth of the EIT signal in the probe signal (i.e., the difference between the probe signal when the wireless phase-modulated signal is incident on transmission medium 115 and when the wireless phase-modulated signal is not incident on transmission medium 115) is modulated in time by a beat (also called the “intermediate frequency”), which varies in time by the frequency difference between the local oscillator signal and the wireless phase-modulated signal. The phase difference between the local oscillator signal and the wireless phase-modulated signal can then be measured as the phase of that beat.

[0040] The theory behind this detection technology will now be briefly outlined.

[0041] The total electric field E experienced by the atomic medium transport medium 115 atomsIt is the sum of the electric field E1 of the local oscillator signal and the electric field E2 of the wireless phase-modulated signal from the signal transmitter 130:

[0042] E atroms =E1+E2 (1)

[0043] The electric field strength of a local oscillator signal and the electric field strength of a wireless phase-modulated signal can be defined as follows:

[0044] E1 = E LO cos(ω LO t+φ LO (2)

[0045] E2 = E SIG cos(ω SIG t+φ SIG (3)

[0046] in:

[0047] ·E LO and E SIG These represent the maximum electric field strengths of the local oscillator signal and the phase-modulated wireless signal, respectively.

[0048] ·ω LO and ω SIG These represent the angular frequencies of the local oscillator signal and the phase-modulated wireless signal, respectively.

[0049] ·t represents time, and

[0050] ·φ LO and φ SIG These represent the phases of the local oscillator signal and the phase-modulated wireless signal, respectively.

[0051] Because the difference between the frequency of the local oscillator signal and the frequency of the phase-modulated wireless signal is much smaller than the average of these frequencies (i.e., (ω) LO +ω SIG Therefore, the total electric field can be expressed as: ) / 2).

[0052]

[0053] in:

[0054] Δω is the difference between the angular frequency of the local oscillator signal and the angular frequency of the phase-modulated wireless signal (i.e., ω). LO -ω SIG ),and

[0055] Δφ is the difference between the phase of the local oscillator signal and the phase of the wireless phase-modulated signal (i.e., φ). LO -φSIG ).

[0056] Rubidium-85 atomic demodulation high-frequency field ω in transmission medium 115 LO This makes the received probe signal T, which is a function of time,... probe It is given by the following formula:

[0057]

[0058] The received probe signal therefore has a sinusoidal form, with its frequency being the difference (Δω) between the frequency of the local oscillator signal and the frequency of the wireless signal, and its phase being the difference (Δφ) between the phase of the local oscillator signal and the phase of the wireless signal. Therefore, by measuring the relative phase shift of the received probe signal over time, the phase state of the phase-modulated wireless signal can be determined. Furthermore, the amplitude of the probe signal is a function of both the electric field strength of the local oscillator signal and the electric field strength of the phase-modulated wireless signal, allowing the amplitude of the phase-modulated wireless signal to be determined based on the amplitude of the received probe signal. More specifically, for a modulation scheme that uses multiple amplitudes (in addition to phase) to identify symbols, different amplitudes among the multiple amplitudes transmitted by the signal transmitter 130 result in different amplitudes in the received probe signal.

[0059] The response of photodetector 129 to wireless phase-modulated signals and E LO and E SIG Both are scaled proportionally, so the stronger local oscillator signal compensates for the weaker phase-modulated wireless signal (but any noise power in the local oscillator signal must be kept lower than the power of the phase-modulated wireless signal).

[0060] Advantageously, the Rydberg atom-based RF receiver 110 generates a local oscillator signal for detecting phase-modulated RF signals without any active electronics. In conventional Rydberg atom-based RF receivers configured to detect phase-modulated signals, the local oscillator signal is generated by an antenna driven by a local signal generator. The local signal generator is an active electronics device, making conventional Rydberg atom-based RF receivers require a power supply. In contrast, the Rydberg atom-based RF receiver described herein generates the local oscillator signal by driving the antenna with a photocurrent derived from an optical signal from an external, remote light source. Therefore, no power supply is required when generating the local oscillator signal, enabling the use of the Rydberg atom-based RF receiver for phase-modulated signals in an electrically passive deployment.

[0061] The local oscillator signal and the wireless phase-modulated signal are phase-synchronized. As described above, the signal transmitter 130 is configured to synchronize with a network-distributed synchronization signal broadcast by a base station of the cellular telecommunications network. The optical device housing 120 includes a cellular telecommunications receiver configured to receive the same network-distributed synchronization signal. The first and second optical signals are subsequently synchronized to these synchronization signals and thus with the wireless phase-modulated signal transmitted by the signal transmitter 130.

[0062] Figure 2 A wireless telecommunications network 200 is illustrated. The wireless telecommunications network 200 includes a Rydberg atom-based RF receiver array 210, an optical device housing 220, and a signal transmitter 230. The Rydberg atom-based RF receiver array 210 includes multiple elements 210a, 210b, 210c, and 210d, each element including one or more fiber optic interfaces, transmission media 215a, 215b, 215c, and 215d, dual-polarized patch antennas 217a, 217b, 217c, and 217d, and photovoltaic photodiodes 219a, 219b, 219c, and 219d.

[0063] like Figure 2 As shown, the optical device housing 220 includes a light source for generating a first optical signal, a second optical signal, a detection signal, and a coupling signal (as described above). Figure 1 These signals are transmitted to the first optical fiber 251, the second optical fiber 253, the third optical fiber 255, and the fourth optical fiber 257 (collectively referred to as the plurality of optical fibers 250).

[0064] Multiple optical fibers 250 transmit these optical signals to various elements of a Rydberg atom-based RF receiver array 210. Each element of the Rydberg atom-based RF receiver array 210 receives corresponding portions of the first and second optical signals. This is achieved by splitting a portion of the power of the first optical signal from the first optical fiber 251 to the corresponding fiber optic interface of each element of the Rydberg atom-based RF receiver array 210, and similarly splitting a portion of the power of the second optical signal from the second optical fiber 253 to the corresponding fiber optic interface of each element of the Rydberg atom-based RF receiver array 210. These first and second optical signals can then be utilized by various photovoltaic photodiodes 219a, 219b, 219c, and 219d to generate photocurrents (as described above regarding...). Figure 1 As described, the photocurrent is then used to generate local oscillator signals by the respective dual-polarized patch antennas 217a, 217b, 217c, 217d, which are then sent to the respective transmission media 215a, 215b, 215c, 215d.

[0065] The power of the first and second optical signals generated at the optical device housing 220 is configured to ensure that equal and sufficient optical power is received at each element of the Rydberg atom-based RF receiver array 210 to generate equally strong local oscillator signals at each transmission medium.

[0066] Furthermore, each element of the Rydberg atom-based RF receiver array 210 receives a probe signal from the third fiber 255 and a coupling signal from the fourth fiber 257. These signals are transmitted serially to each element of the Rydberg atom-based RF receiver array 210, such that the probe signal passes through the first element, then the second element, then the third element, then the fourth element of the Rydberg atom-based RF receiver array 210, and the coupling signal passes through the fourth element, then the third element, then the second element, then the first element of the Rydberg atom-based RF receiver array 210, propagating in reverse through the respective transmission media and overlapping with the probe signal. The probe signal and the coupling signal are thus (as described above regarding...) Figure 1 (As described) to excite the electrons of each of the transmission media 215a, 215b, 215c, 215d to a predetermined Rydberg state.

[0067] The power of the detection signal and the coupling signal generated at the optical device housing 220 is configured to ensure that equal and sufficient optical power is received at each element of the Rydberg atom-based RF receiver array 210 to raise sufficient electrons in each of the transmission media 215a, 215b, 215c, 215d to a predetermined Rydberg state for detecting the wireless phase-modulated signal from the signal transmitter 230.

[0068] In this configuration, each transmission medium 215a, 215b, 215c, and 215d can receive a combination of a wireless phase-modulated signal and a local oscillator signal, causing a change in the detection signal. Based on this detection signal, the phase state of the wireless phase-modulated signal can be detected (again, as mentioned above regarding...). Figure 1 As described. As the probe signal passes sequentially through the various elements of the Rydberg atom-based RF receiver array 210, the changes in the probe signal indicate the wireless detection of the phase-modulated signal at any element of the Rydberg atom-based RF receiver array 210.

[0069] Therefore, the Rydberg atom-based RF receiver array 210 enables electrically passive detection of phase-modulated signals at multiple locations, with the added advantage of sharing a relatively expensive light source.

[0070] Figure 3 This is an example Figure 1 Rydberg atom-based RF receiver 110 or Figure 2A flowchart of the operation of the Rydberg atom-based RF receiver array 210 is provided. In step S101, the Rydberg atom-based RF receiver (or array) receives a first optical signal from one or more remote light sources. In step S103, the Rydberg atom-based RF receiver (or array) generates a photocurrent based on the first optical signal. In step S105, the Rydberg atom-based RF receiver (or array) transmits a local oscillator electromagnetic field generated based on the first optical signal by providing the photocurrent to an antenna. In step S107, the Rydberg atom-based RF receiver (or array) receives a probe optical signal and a coupling optical signal from one or more remote light sources, wherein the transmission medium is excited by the probe optical signal having a probe frequency set to excite electrons in the transmission medium to a first excited state, and wherein the transmission medium is further excited by a coupling optical signal having a coupling frequency set to excite electrons in the transmission medium to a predetermined Rydberg state to induce an electromagnetically induced transparent (EIT) effect. In step S109, the Rydberg atom-based RF receiver (or array) receives the transmitted local oscillator electromagnetic field and the phase-modulated electromagnetic field from the remote transmitter at the transmission medium, such that the combination of the phase-modulated electromagnetic field and the transmitted local oscillator electromagnetic field causes a change in the probe optical signal, and the phase state of the phase-modulated electromagnetic field can be detected based on this change.

[0071] As described above, a dual-polarized patch antenna was used to generate the local oscillator field. Those skilled in the art will understand that this is not mandatory, and other antenna designs (such as dipole antennas) can be used alternatively. However, the dual-polarized patch antenna is preferred because it generates a local oscillator signal with two orthogonal polarizations and a radiation pattern close to that of a plane wave—ensuring mixing of the local oscillator signal and the wireless phase-modulated signal from the signal generator, independent of the polarization of that wireless phase-modulated signal. In contrast, a dipole antenna design generates a local oscillator signal with a single polarization aligned with the axis of the dipole antenna, which can be orthogonal to the polarization of the wireless phase-modulated signal—resulting in reduced mixing.

[0072] As described above, the phase of the local oscillator signal and the wireless phase-modulated signal are synchronized by the optical housing and the signal transmitters by synchronizing these signals with a synchronization signal distributed over a public network. However, this is not mandatory, and other synchronization methods can be used. For example, the system can implement Precision Timing Protocol (PTP) technology, where the optical housing also includes a local master clock (e.g., an atomic clock) and provides synchronization signals to one or more signal transmitters within the optical housing via the PTP protocol.

[0073] Furthermore, when using both the first and second optical signals simultaneously, a wavelength of approximately 1550 nm is not required for these signals. In other words, these optical signals can have wavelengths within any optical fiber transmission band, such as the O band (1260 to 1360 nm), E band (1360 to 1460 nm), S band (1460 to 1530 nm), C band (1530 to 1565 nm), L band (1565 to 1625 nm), or U / XL band (1625 to 1675 nm).

[0074] Those skilled in the art will also understand that Rydberg atom-based RF receivers (or arrays) can be used to detect electromagnetic signals of different frequencies. That is, for a specific target frequency to be detected, the system can be configured such that an EIT signal is generated on the probe signal by an incident electromagnetic signal at that target frequency, for example by selecting a suitable atomic medium (e.g., rubidium, cesium, or strontium) having a Rydberg state corresponding to the target frequency and selecting frequencies corresponding to that Rydberg state for the probe and coupling signals. Furthermore, it is not necessary for the EIT signal to be generated after a trapezoidal configuration of electronic transitions. That is, any configuration (e.g., lambda, vee) can be used. A glass-filled cavity as the transmission medium is also not necessary, as an optical cavity of optical fiber can be used alternatively. The optical housing using one or more lasers to generate the probe and coupling signals is also not necessary. That is, any other optical transmitter or coherent optical transmitter (e.g., a light-emitting diode) can be used alternatively.

[0075] As described above, a drive current for the antenna used to transmit a local oscillator signal is generated by mixing a first optical signal and a second optical signal using optical heterodyne technology, thereby generating a photocurrent at the target frequency of the local oscillator signal. This is advantageous because the first and second optical signals can have corresponding wavelengths within the low-attenuation band of conventional optical fibers (e.g., as described above). Figure 1 and Figure 2The wavelength is approximately 1550 nm, but the frequency is equal to the target frequency of the local oscillator signal. However, this is not necessary. That is, a single optical signal with a frequency equal to the target frequency of the local oscillator signal can be received at a Rydberg atom-based RF receiver (or an element of a Rydberg atom-based RF receiver array) and used to generate a local oscillator signal at that frequency. This may require dedicated optical fiber, such as hollow fiber, to transmit the single optical signal from the remote optical device housing to the Rydberg atom-based RF receiver (or an element of a Rydberg atom-based RF receiver array) to limit the attenuation loss of the single optical signal. Alternatively, the single optical signal can be intensity modulated at the target frequency, and then the signal can be used by the Rydberg atom-based RF receiver (or an element of the array) to generate a local oscillator signal. However, these techniques are more prone to noise compared to optical heterodyne techniques that use the first and second optical signals.

[0076] By locking the first and second light sources to an optical cavity or frequency comb, the phase noise of the first and second optical signals is reduced. However, this is not necessary, and other methods can be used to reduce phase noise. For example, an electro-optic modulator or an acousto-optic modulator can be used to correlate the phases of the first and second light sources. In another example, the phases of the first and second light sources can be locked by frequency offset locking, for example, by mixing the first and second optical signals and measuring the heterodyne signal between them.

[0077] Furthermore, it is not necessary for the light source to be contained within a single optical device housing. That is, the light source can be distributed. Similarly, it is not necessary for the Rydberg atom-based RF receiver (or array elements) to be implemented in a single unit. That is, the photovoltaic photodiode and antenna can be implemented in the first module of the Rydberg atom-based RF receiver (or array elements), and the transmission medium can be implemented in the second module. These first and second modules can be separate, provided that the local oscillator signal transmitted by the antenna of the first module has sufficient strength at the transmission medium of the second module.

[0078] exist Figure 2In the Rydberg atom-based RF receiver array, each element includes a photovoltaic photodiode and an antenna for generating a local oscillator signal and transmitting it to the transmission medium of that element. However, in the alternative configuration described above, where the photovoltaic photodiode and antenna are disposed in a first module and the transmission medium can be disposed in a second module, each first module can be configured to generate a local oscillator signal and transmit it to the transmission medium of multiple second modules in the array. That is, a one-to-one mapping from first module to second module is not necessary, and a one-to-many mapping from first module to second module can be alternatively implemented. This may be suitable when multiple second modules are very close together, allowing the local oscillator signal to be transmitted with sufficient strength from a single first module at the transmission medium of each second module. This has the added advantage of reducing the number of photovoltaic photodiodes and antennas in the array.

[0079] Figure 1 Rydberg atom-based RF receiver and Figure 2 The array is configured to detect wireless signals modulated using a 16-QAM modulation scheme. However, those skilled in the art will understand that other phase modulation schemes, such as binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), or higher-order QAM, can be used alternatively.

[0080] exist Figure 1 Rydberg atom-based RF receiver and Figure 2 In the array, the frequency difference between the local oscillator signal and the wireless phase-modulated signal is 30 kHz. However, this specific frequency difference is not necessary. The response time of the rubidium-85 atoms in the transmission medium 115 to the wireless phase-modulated signal is limited by the spontaneous lifetime of the first excited state, ranging from 1 MHz to 10 MHz. Therefore, ideally, the frequency difference between the local oscillator signal and the wireless phase-modulated signal should be less than 10 MHz. Otherwise, the atomic response to the wireless phase-modulated signal will be reduced, and the Rydberg atom-based RF receiver may not be able to accurately detect the correct relative phase. Furthermore, it is also not necessary that the atomic transitions between the local oscillator signal and the predetermined Rydberg state and another Rydberg state are in resonance, nor that the atomic transitions between the wireless phase-modulated signal and the predetermined Rydberg state and another Rydberg state are in resonance. Alternatively, the local oscillator signal can resonate with the atomic transition between a predetermined Rydberg state and another Rydberg state, and the wireless phase-modulated signal can be non-resonant with the atomic transition between the predetermined Rydberg state and another Rydberg state. Both the local oscillator signal and the wireless phase-modulated signal can be non-resonant with the atomic transition between the predetermined Rydberg state and another Rydberg state.

[0081] Furthermore, it is not necessary for the Rydberg atom-based RF receiver (or array) to act as a receiver (i.e., demodulate data from multiple phase states of a series of wireless phase-modulated signals). That is, the device can be operated simply to detect the phase states of one or more wireless phase-modulated signals. In other words, Figure 1 The device can be a Rydberg atom-based RF detector, and Figure 2 The device could be an RF detector array based on Rydberg atoms.

[0082] Those skilled in the art will understand that any combination of elements is possible within the scope of the claimed invention.

Claims

1. An electromagnetic field detector, comprising: a first optical signal interface configured to receive a first optical signal from one or more remote optical sources; an electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated from the first optical signal, the electromagnetic field transmitter comprising: a photocurrent generator configured to generate a photocurrent from the first optical signal; and an antenna interface configured to provide the photocurrent to an antenna to transmit the local oscillator electromagnetic field; a second optical signal interface configured to receive a probe optical signal and a coupling optical signal from the one or more remote optical sources; and a transmission medium configured to be excited by the probe optical signal and further excited by the coupling optical signal, wherein the probe optical signal has a probe frequency arranged to excite an electron of the transmission medium to a first excited state and the coupling optical signal has a coupling frequency arranged to excite the electron of the transmission medium to a predetermined Rydberg state to cause an effect of electromagnetic induced transparency (EIT), wherein the transmission medium is further configured to receive the local oscillator electromagnetic field and a phase-modulated electromagnetic field from a remote transmitter, such that a combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change in the probe optical signal from which a phase state of the phase-modulated electromagnetic field can be detected.

2. The electromagnetic field detector of claim 1, wherein, the first optical signal interface is further configured to receive a second optical signal from the one or more remote optical sources, and the photocurrent generator is configured to generate the photocurrent by mixing the first optical signal and the second optical signal.

3. The electromagnetic field detector according to claim 1 or 2, wherein the local oscillator electromagnetic field and the phase-modulated electromagnetic field are synchronized.

4. The electromagnetic field detector of claim 1 or 2, wherein, the first optical signal has a wavelength in one of an O band, an E band, an S band, a C band, an L band, and a U / XL band.

5. The electromagnetic field detector of claim 2, wherein, the second optical signal has a wavelength in one of an O band, an E band, an S band, a C band, an L band, and a U / XL band.

6. The electromagnetic field detector of claim 1 or 2, wherein, the local oscillator electromagnetic field is dual-polarized.

7. The electromagnetic field detector of claim 1 or 2, further comprising: a first module comprising the first optical signal interface and the electromagnetic field transmitter; and a second module comprising the second optical signal interface and the transmission medium. the first module and the second module are implemented in a single housing or in respective housings.

8. The electromagnetic field detector of claim 7, wherein, the second module is one of a plurality of second modules, each second module comprising:

9. The electromagnetic field detector of claim 7, wherein, a respective second optical signal interface configured to receive the probe optical signal and the coupling optical signal from the one or more remote optical sources, and a respective transmission medium configured to be excited by the probe optical signal and further excited by the coupling optical signal. a respective transmission medium configured to be excited by the probe light signal and further excited by the coupling light signal, wherein the probe light signal has a probe frequency arranged to excite an electron of the transmission medium to a first excited state and the coupling light signal has a coupling frequency arranged to excite an electron of the respective transmission medium to a predetermined Rydberg state to cause an effect of Electromagnetic Induction Transparency, EIT, wherein the respective transmission medium is further configured to receive a phase-modulated electromagnetic field from the remote transmitter and the local oscillator electromagnetic field from the electromagnetic field transmitter of the first module, such that a combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change of the probe light signal, according to which a phase state of the phase-modulated electromagnetic field can be detected.

10. The electromagnetic field detector of claim 9, wherein, the first module is one of a plurality of first modules, each first module comprising: a respective first light signal interface configured to receive the first light signal from the one or more remote light sources, and a respective electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated from the first light signal, wherein each first module of the plurality of first modules is associated with a second module of the plurality of second modules, such that the local oscillator electromagnetic field transmitted by the respective electromagnetic field transmitter of that first module is received at the transmission medium of the associated second module.

11. An electromagnetic field detection system, the electromagnetic field detection system comprising: an electromagnetic field detector according to any one of claims 1 to 10; one or more light sources remote from the electromagnetic field detector configured to generate and transmit the first light signal, the probe light signal and the coupling light signal to the electromagnetic field detector.

12. The electromagnetic field detection system of claim 11, being part of a telecommunication network, wherein, The one or more light sources are configured to receive a network distributed synchronization signal and the one or more light sources are configured to synchronize the first light signal based on the synchronization signal.

13. The electromagnetic field detection system of claim 12, wherein, The phase-modulated electromagnetic field is synchronized with the network distributed synchronization signal.

14. The electromagnetic field detection system of claim 11, further comprising a master clock and a transmitter configured to transmit a synchronization signal derived from the master clock to the remote transmitter, wherein, The first light signal is synchronized to the synchronization signal.

15. The electromagnetic field detection system of any one of claims 11 to 14, further comprising an optical communication network, wherein, The first light signal, the probe light signal and the coupling light signal are transmitted to the electromagnetic field detector via the optical communication network.

16. A method of operating an electromagnetic field detector having a transmission medium, the method comprising the steps of: receiving a first light signal from one or more remote light sources; generating a photocurrent from the first light signal; transmitting a local oscillator electromagnetic field generated from the first light signal by providing the photocurrent to an antenna; receiving a probe light signal and a coupling light signal from the one or more remote light sources, wherein the transmission medium is excited by the probe light signal having a probe frequency arranged to excite the electrons of the transmission medium to a first excited state, and wherein the transmission medium is further excited by the coupling light signal having a coupling frequency arranged to excite the electrons of the transmission medium to a predetermined Rydberg state to cause an Electromagnetic Induced Transparency, EIT, effect; and receiving at the transmission medium the transmitted local oscillator electromagnetic field and the phase modulated electromagnetic field from the remote transmitter such that the combination of the phase modulated electromagnetic field and the transmitted local oscillator electromagnetic field causes a change in the probe light signal from which a phase state of the phase modulated electromagnetic field can be detected.

17. The method of claim 16, further comprising the steps of: receiving a second light signal from the one or more remote light sources, wherein the step of generating the local oscillator electromagnetic field further comprises mixing the first light signal and the second light signal to generate the photocurrent.

18. The method of claim 16 or 17, wherein, the electromagnetic field detector is an element of an array of electromagnetic field detectors, each element of the array of electromagnetic field detectors having a transmission medium, wherein the transmission medium of each element of the array of electromagnetic field detectors is excited by the probe light signal and further excited by the coupling light signal to cause an EIT effect in the transmission medium of each element of the array of electromagnetic field detectors, wherein the method further comprises the steps of: receiving at the transmission medium of each element of the array of electromagnetic field detectors the transmitted local oscillator electromagnetic field and the phase modulated electromagnetic field from the remote transmitter such that the combination of the phase modulated electromagnetic field and the transmitted local oscillator electromagnetic field causes a change in the probe light signal from which a phase state of the phase modulated electromagnetic field can be detected.

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