Long-distance radio over fiber transmission system and method based on atomic antenna

Abstract

The invention belongs to the technical field of wireless communication, and relates to a long-distance radio-over-fiber transmission system and method based on an atomic antenna, and the system comprises a transmitting end, a receiving end, and a central station. Wherein the receiving end comprises a Rydberg atom excitation module and a difference frequency light conversion module, the Rydberg atom excitation module excites a cesium atom system to a Rydberg state by using detection light and coupling light, and the Rydberg atom excitation module responds to a radio frequency signal radiated by the transmitting end; and the difference frequency light conversion module receives the transmission detection light which passes through the Rydberg state of the cesium atom system, converts the transmission detection light into an optical signal conforming to an optical communication C wave band standard, and transmits the optical signal to a central station. The RoF communication device is simple in structure, does not need down-conversion at a receiving end, and can realize remote RoF communication.

Description

Technical Field

[0001] This application belongs to the field of wireless communication technology, and particularly relates to a long-distance radio-over-fiber transmission system and method based on an atomic antenna. Background Art

[0002] In the field of radio-over-fiber (RoF) communication, traditional RoF technology solutions modulate radio frequency (RF) signals onto an optical carrier (commonly used wavelength 1530 - 1565 nm, C band) through intensity or phase modulators, and after fiber transmission, at the receiving end of the central station, through optoelectronic conversion and down-conversion. Traditional RoF technology has the significant advantage of low transmission loss. In standard single-mode fiber, the transmission loss is only about 0.2 dB / km, which makes it perform excellently in short-distance and medium-distance communication scenarios. However, this technology requires the configuration of key devices such as electro-optic modulators and local oscillators ( Figure 1 in a), resulting in a complex system architecture, increasing the cost and maintenance difficulty of the system.

[0003] In recent years, with the development of quantum technology, a new antenna system based on Rydberg atoms has brought new breakthroughs to RoF technology. This technology utilizes the ultrasensitive response of the Rydberg state energy levels of alkali metal atoms such as cesium atoms to the RF field to achieve the conversion of RF signals to probe light. By detecting the change in the transmittance of the probe light, the information carried by the RF signal can be directly detected and down-converted to recover, thus omitting the electro-optic modulator and local oscillator down-conversion module in the traditional RoF system, greatly simplifying the system architecture, and showing great application potential ( Figure 1 in b).

[0004] Although the new antenna system based on Rydberg atoms has brought many advantages to RoF technology, existing quantum-enhanced RoF systems still face a series of key technical bottlenecks in practical applications.

[0005] Firstly, excessively high transmission loss is one of the key factors restricting its development. The wavelength of the probe light usually adopts 852 nm, which is located in the first transmission window of the optical fiber. Compared with the transmission loss of about 0.2 dB / km of the C band in standard single-mode fiber, the transmission loss of the 852 nm wavelength is as high as about 2.5 dB / km, and the effective transmission distance is limited to the order of dozens of kilometers, making it difficult to meet the requirements of long-distance communication at the metropolitan area network level.

[0006] Secondly, the limited quantum efficiency also affects the performance of existing quantum-enhanced RoF systems. Due to the short wavelength of the probe light, when transmitting in the optical fiber, the nonlinear effects (such as stimulated Brillouin scattering) caused by the short-wavelength probe light are more significant. These nonlinear effects limit the improvement space of the optical power launched into the fiber, and thus affect the signal-to-noise ratio and transmission distance of the system.

[0007] Therefore, how to solve the problem of limited transmission distance faced by existing quantum-enhanced RoF systems has become the key to promoting the further development and practical application of this technology. Summary of the Invention

[0008] Aiming at the technical problems of limited transmission distance and wavelength compatibility in the prior art, the present application aims to provide a long-distance radio-over-fiber transmission system and method based on an atomic antenna. The technical solution of the present application is based on a novel antenna system of Rydberg atoms. By using the nonlinear optical effect, the 852 nm probe light carrying RF information is converted into the 1560 nm band and transmitted through an optical fiber, which is suitable for long-distance communication and has the advantages of anti-electromagnetic interference and low transmission loss.

[0009] In order to achieve the technical objectives of the present application, the following technical solutions are adopted: A long-distance radio-over-fiber transmission system based on an atomic antenna, the long-distance radio-over-fiber transmission system includes a transmitting end, a receiving end, and a central station; The transmitting end is used to load a baseband signal onto a carrier to generate a radio frequency signal, and transmit the radio frequency signal to the area where the receiving end is located in a spatial radiation manner; The receiving end includes a Rydberg atom excitation module and a difference-frequency optical conversion module. The Rydberg atom excitation module uses probe light and coupling light to excite a cesium atom system to the Rydberg state, and the Rydberg atom excitation module responds to the radio frequency signal; the difference-frequency optical conversion module receives the transmitted probe light that has passed through the Rydberg state of the cesium atom system and converts the transmitted probe light into an optical signal that conforms to the optical communication C-band standard; The central station receives the C-band optical signal and demodulates and restores the baseband information.

[0010] In one embodiment, the transmitting end includes a signal generator, an analog signal source, and a horn antenna. The analog signal source generates a carrier, the signal generator is connected to the analog signal source, the analog signal source loads the baseband signal generated by the signal generator onto the carrier to generate a radio frequency signal, and the horn antenna is connected to the output end of the analog signal source to directionally transmit the radio frequency signal to the area where the receiving end is located.

[0011] In one embodiment, the Rydberg atom excitation module includes a first laser, a second laser, and a cesium atom gas cell. The first laser generates probe light and injects it into the cesium atom gas cell, the second laser generates coupling light and injects it into the cesium atom gas cell, and the light beams of the probe light and the coupling light coincide with each other in the cesium atom gas cell.

[0012] In one embodiment, the wavelength of the probing light is 852 nm, and the wavelength of the coupling light is 509 nm.

[0013] In one embodiment, the difference-frequency optical conversion module includes a temperature controller and a periodically poled lithium niobate (PPLN) frequency conversion crystal. The periodically poled lithium niobate frequency conversion crystal receives the transmitted probing light and introduces a pump light for difference-frequency conversion to generate an optical signal conforming to the C-band standard. The temperature controller is used to adjust the temperature of the periodically poled lithium niobate frequency conversion crystal to achieve phase matching between the transmitted probing light and the pump light.

[0014] In one embodiment, the wavelength of the introduced pump light is 1878 nm.

[0015] In one embodiment, the central station includes a photodetector and an oscilloscope. The photodetector receives the optical signal conforming to the C-band standard and converts it into an electrical signal, and the oscilloscope receives the electrical signal to demodulate the baseband information.

[0016] In another aspect of the present application, a long-distance optically carried radio frequency transmission method based on an atomic antenna is provided, including the following steps: Using the probing light to excite the cesium atomic system from the ground state to an intermediate excited state, and using the coupling light to excite the cesium atomic system from the intermediate excited state to the Rydberg state; Applying a radio frequency modulation signal loaded with a baseband signal to the Rydberg state of the cesium atomic system to make the transmittance of the probing light vary with the intensity of the radio frequency field; Performing difference-frequency conversion on the transmitted probing light passing through the Rydberg state of the cesium atomic system to generate an optical signal conforming to the optical communication C-band standard; Receiving the optical signal to demodulate the baseband information.

[0017] In one embodiment, a probing light with a wavelength of 852 nm is used to excite the cesium atomic system from the ground state 6S 1 / 2 to the intermediate excited state 6P 3 / 2 , and a coupling light with a wavelength of 509 nm is used to excite the cesium atomic system from the intermediate excited state 6P 3 / 2 to the Rydberg state 63S 1 / 2 .

[0018] In one embodiment, the transmitted probing light is injected into a periodically poled lithium niobate frequency conversion crystal, and a pump light is introduced for difference-frequency conversion to generate an optical signal conforming to the C-band standard.

[0019] In one embodiment, the wavelength of the pump light is 1878 nm, and the wavelength of the optical signal is 1560 nm.

[0020] The beneficial effects of the present application are as follows: 1) Simplification of the system architecture and reduction of costs This application directly realizes the photon - quantum state conversion of radio frequency (RF) signals through the electromagnetically induced transparency (EIT) effect of Rydberg atoms, omitting the electro - optic modulator, local oscillator, and complex mixing circuits in the traditional radio - over - fiber (RoF) system, which can effectively reduce the device volume, power consumption, and hardware cost.

[0021] 2) Reduction of transmission loss Using the nonlinear optical difference - frequency conversion technology, the 852 - nm probe light carrying RF information is converted into a 1560 - nm C - band optical signal. Combining with the characteristics of the low - loss window of optical fiber, the optical - fiber transmission loss is reduced from 2.5 dB / km in the traditional scheme to 0.25 dB / km. Taking a transmission distance of 100 km as an example, the signal attenuation is reduced from 250 dB to 25 dB, and the theoretical transmission distance can be extended to more than 400 km. Brief description of the drawings

[0022] Figure 1 It is a schematic diagram of a traditional radio - over - fiber communication system; where, a is the system for modulating RF signals by a modulator, and b is the traditional Rydberg - atom antenna system; Figure 2 It is the long - distance radio - over - fiber transmission system of the embodiment of this application; Figure 3 It is the Rydberg - atom energy - level diagram of the long - distance radio - over - fiber transmission system of the embodiment of this application. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of this application will be clearly and completely described in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this application.

[0024] In an embodiment of this application, a long - distance radio - over - fiber transmission system based on an atomic antenna is provided. The radio - over - fiber transmission system includes a transmitting end, a receiving end, and a central station.

[0025] In some embodiments, the transmitting end includes a signal generator, an analog signal source, and a horn antenna. The analog signal source generates a carrier wave. The signal generator is connected to the analog signal source. The analog signal source loads the base - band signal generated by the signal generator onto the carrier wave to generate an RF signal. The horn antenna is connected to the output end of the analog signal source and directionally transmits the RF signal to the area where the receiving end is located.

[0026] The modulation technology used by the analog signal source to load the baseband signal onto the carrier to generate the radio frequency signal can be amplitude modulation (AM) or frequency modulation (FM). Taking amplitude modulation as an example, the amplitude change of the baseband signal controls the amplitude change of the carrier signal, causing the amplitude of the carrier signal to change accordingly with the change of the baseband signal, thereby "carrying" the information of the baseband signal onto the carrier and generating the radio frequency signal. At this time, the generated radio frequency signal contains the information of the baseband signal and has the high-frequency characteristics of the carrier, which is convenient for long-distance transmission in space.

[0027] The output end of the analog signal source is connected to the horn antenna. After the radio frequency signal generated by modulation is output from the analog signal source, it is transmitted to the horn antenna. The horn antenna converts the radio frequency signal into space electromagnetic waves and, according to its radiation direction, directionally emits the electromagnetic waves to the area where the receiving end is located.

[0028] In some embodiments, the frequency of the carrier is selected from 14.53169 GHz, and the baseband signal is amplitude modulated to the 14.53169 GHz carrier through the analog signal source. This frequency resonates with the transition frequency from the third energy level 63S 1 / 2 to the fourth energy level 63P 1 / 2 of the Rydberg atom.

[0029] The receiving end includes a Rydberg atom excitation module and a difference frequency light conversion module. The Rydberg atom excitation module uses the probe light and the coupling light to excite the cesium atom system to the Rydberg state.

[0030] In some embodiments, the Rydberg atom excitation module includes a first laser, a second laser, and a cesium atom gas cell. The first laser generates the probe light and injects it into the cesium atom gas cell, and the second laser generates the coupling light and injects it into the cesium atom gas cell. The light beams of the probe light and the coupling light overlap with each other in the cesium atom gas cell.

[0031] In some embodiments, the first laser is controlled to lock the frequency of the probe light. When the coupling light is scanned, the transmission spectrum of the probe light shows a higher transmittance at the resonance frequency of the coupling light and has a transmission peak. At this time, the frequency of the coupling light is locked at the spectral peak, that is, at the frequency zero detuning.

[0032] In some embodiments, the first laser generates 852 nm probe light, and the second laser generates 509 nm coupling light. The 852 nm probe light and the 509 nm coupling light are respectively injected from opposite ends inside the cesium atom gas cell, and the 852 nm probe light and the 509 nm coupling light are injected overlappingly. The 852 nm probe light excites the cesium atom from the ground state 6S 1 / 2 to the intermediate excited state 6P 3 / 2 , and the coupling light excites the atomic intermediate excited state 6P 3 / 2 to the Rydberg state 63S 1 / 2 .

[0033] Transmittance of the 852 nm probe light through the cesium atomic cell T is: (1) In the formula, and are the input and output optical powers of the probe light. Obtained from the Lambert-Beer law (2) where is the wavelength of the probe light, L is the length of the cesium atomic cell, is the wave number vector of the probe light, is the imaginary part of the polarizability of the atomic cell.

[0034] When the probe light, coupling light, and carrier frequency are all resonant with the corresponding energy levels, expands to: (3) In the formula, N is the atomic density in the cesium atomic cell, and are the vacuum permittivity and the reduced Planck constant respectively, and are the transition dipole moments of the probe light and the RF signal corresponding to the energy levels, and are the Rabi frequencies of the RF signal and the coupling light corresponding to the energy levels respectively. , is the spontaneous decay rate of the ground state, is the energy level 's spontaneous decay rate.

[0035] (4) where and are the intensities of the RF signal and the coupling light, is the transition dipole moment of the coupling light corresponding to the energy level.

[0036] Baseband signal The expression of the RF signal RF formed by amplitude modulating onto the local oscillator carrier signal LO is: (5) where and are the amplitude and frequency of the local oscillator carrier signal respectively, t represents the time parameter, and the field strength of RF is specifically: (6) Filter out the DC component , and the intensity of the RF signal is the field strength amplitude of the baseband signal.

[0037] Therefore, according to Equation (2), the relationship between the probe light transmittance and the field strength of the RF signal is obtained: the probe light transmittance (optical power) at the EIT peak is nonlinearly negatively correlated with the field strength of the RF signal, that is, the intensity of the baseband signal.

[0038] The difference-frequency optical conversion module receives the transmitted probe light that has passed through the Rydberg state of the cesium atom system, and converts the transmitted probe light into an optical signal that conforms to the optical communication C-band standard.

[0039] In some embodiments, the difference-frequency optical conversion module includes a temperature controller and a periodically poled lithium niobate (PPLN) frequency conversion crystal. The periodically poled lithium niobate frequency conversion crystal receives the transmitted probe light and introduces a pump light for difference-frequency conversion to generate an optical signal that conforms to the C-band standard. Specifically, the pump light and the probe light interact in the crystal, and the energy is transferred from the high-frequency pump light to the low-frequency difference-frequency light to achieve wavelength conversion. It can be understood that the pump light is derived from a pump light source, such as a solid-state laser.

[0040] The temperature controller is used to adjust the temperature of the periodically poled lithium niobate frequency conversion crystal to achieve phase matching between the transmitted probe light and the pump light. Specifically, the efficiency of the nonlinear optical effect highly depends on the phase matching among the pump light, the probe light, and the difference-frequency light. If there is a phase mismatch, the conversion efficiency will periodically decrease with the crystal length. The refractive index of the PPLN frequency conversion crystal is sensitive to temperature. By adjusting the crystal temperature, its refractive index can be changed, thereby compensating for the phase mismatch caused by dispersion. The temperature controller can precisely control the crystal temperature to ensure that the three beams of light maintain phase matching in the crystal and maximize the conversion efficiency.

[0041] In some embodiments, the 852 nm transmitted probe light and the 1878 nm pump light are input into the PPLN frequency conversion crystal for difference-frequency conversion into a 1560 nm optical signal.

[0042] To achieve difference-frequency conversion, two conditions need to be met: ① Energy conservation, that is Remain unchanged before and after: (7) ② Momentum conservation: Or (8) Among them, ( i = 1, 2, 3) are the wavelengths and wave vectors of the 852 nm probe light, the 1878 nm pump light, and the 1560 nm optical signal respectively, is the refractive index. The law of conservation of momentum determines the phase-matching condition in the nonlinear process. The core of phase matching is to adjust the refractive index such that . In the embodiment, a periodically poled lithium niobate (PPLN) crystal is selected as the frequency conversion medium. Its refractive index is sensitive to temperature changes. Therefore, the refractive index of light is changed by adjusting the crystal temperature to achieve phase matching. The power change before and after difference frequency conversion can be expressed as: (9) where ( i = 1, 2, 3) are the powers of the 852 nm probe light, 1878 nm pump light, and 1560 nm optical signal respectively, L is the length of the frequency conversion crystal. is the conversion efficiency. In the case where the transmission loss can be ignored, is approximately: (10) where is the conversion parameter for a specific device, with the unit of W -1 cm -2 .

[0043] It can be seen from Equation (9) that under the condition of a fixed pump light power, the power of the 1560 nm optical signal output by difference frequency conversion is positively correlated with the power of the input 852 nm probe light, and thus is negatively correlated with the electric field strength of the RF signal.

[0044] The central station receives the C-band optical signal to demodulate and restore the baseband information. The central station receives the C-band optical signal. The response of the Rydberg atoms to the radio frequency field causes the transmittance of the 852 nm probe light to change in real time with the intensity of the radio frequency signal. This change is converted into the intensity change of the 1560 nm optical signal. The 1560 nm optical signal is transmitted to the central station through a low-loss optical fiber, converted into an electrical signal by a photodetector, and the electrical signal is collected and processed to restore the baseband information, completing the long-distance radio over fiber communication reception.

[0045] In some embodiments, the central station includes a photodetector and an oscilloscope. The photodetector receives the optical signal in the C-band standard and converts it into an electrical signal. The oscilloscope receives the electrical signal and demodulates the baseband information. Among them, the photodetector, such as a PIN photodiode or an avalanche photodiode APD, receives the 1560 nm optical signal and converts it into an electrical signal. After being collected by the oscilloscope and signal processed, the baseband information is restored, completing the long-distance radio over fiber communication reception.

[0046] In some embodiments, the long-distance optical-radio frequency transmission system further includes an optical path splitting device, which includes a first dichroic mirror and a second dichroic mirror. The first dichroic mirror is used to adjust the optical path of the probe light injected into the cesium atomic gas cell, reflect the probe light and transmit the coupling light. The second dichroic mirror is used to adjust the optical path of the coupling light injected into the cesium atomic gas cell, reflect the coupling light and transmit the probe light. At the same time, the probe light is injected into the periodically poled lithium niobate frequency conversion crystal.

[0047] In some embodiments, the first dichroic mirror is arranged between the first laser and the cesium atomic gas cell. The probe light generated by the first laser is refracted and its optical path is regulated by the first dichroic mirror and then injected into the left end of the cesium atomic gas cell; the first dichroic mirror is arranged between the second laser and the cesium atomic gas cell. The coupling light generated by the second laser is refracted and its optical path is regulated by the second dichroic mirror and then injected into the right end of the cesium atomic gas cell. At the same time, the transmitted probe light passing through the cesium atomic gas cell is injected into the periodically poled lithium niobate frequency conversion crystal after passing through the second dichroic mirror.

[0048] In another embodiment of the present application, a long-distance optical-radio frequency transmission method based on an atomic antenna is provided, including the following steps: S1: Using the probe light to excite the cesium atom system from the ground state to an intermediate excited state, and using the coupling light to excite the cesium atom system from the intermediate excited state to the Rydberg state.

[0049] In some embodiments, a probe light with a wavelength of 852 nm is used to excite the cesium atom system from the ground state 6S 1 / 2 to the intermediate excited state 6P 3 / 2 , and a coupling light with a wavelength of 509 nm is used to excite the cesium atom system from the intermediate excited state 6P 3 / 2 to the Rydberg state 63S 1 / 2 . The 852-nm probe light and the 509-nm coupling light are transmitted in opposite directions in the cylindrical cesium atomic gas cell. The frequency of the 852-nm laser is locked to control the frequency of the probe light. When the coupling light is scanned, the transmission spectrum of the probe light shows a higher transmittance at the resonance frequency of the coupling light, resulting in a transmission peak. At this time, the frequency of the coupling light is locked at the spectral peak, i.e., the frequency zero detuning.

[0050] S2: Applying the radio frequency modulation signal loaded with the baseband signal to the Rydberg state of the cesium atom system, so that the transmittance of the probe light changes with the intensity of the radio frequency field.

[0051] In some embodiments, the baseband information is amplitude-modulated onto the carrier by an analog signal source. The carrier is related to the third energy level 63S 1 / 2 and the fourth energy level 63P 1 / 2Resonance, with a carrier frequency of 14.53169 GHz. Based on the quantum characteristics of the Rydberg state cesium atom system, the radio frequency signal is correlated with the change in the transmittance of the probe light, and the baseband information loaded on the radio frequency signal is indirectly demodulated by measuring the transmittance of the probe light.

[0052] S3: Perform difference frequency conversion on the transmitted probe light passing through the Rydberg state of the cesium atom system to generate an optical signal that meets the optical communication C-band standard.

[0053] In some embodiments, the wavelength of the pump light is 1878 nm, and the wavelength of the optical signal is 1560 nm. To achieve difference frequency conversion to generate a 1560 nm optical signal, the 852 nm transmitted probe light carrying information and the 1878 nm pump light are injected into the PPLN frequency conversion crystal through an optical fiber, and temperature phase matching is performed on the PPLN frequency conversion crystal. The temperature is adjusted to maximize the conversion efficiency, and the crystal outputs an optical signal with a wavelength of 1560 nm. The change in the transmittance of the probe light is converted into a change in the power of the 1560 nm optical signal.

[0054] S4: Receive the optical signal and demodulate the baseband information.

[0055] In some embodiments, the 1560 nm optical signal is transmitted to the central station through a low-loss optical fiber, converted into an electrical signal by a photodetector, and finally collected and signal processed by an oscilloscope to achieve long-distance radio over fiber communication reception.

[0056] Exemplary embodiment In this embodiment, refer to Figure 2 As shown, the long-distance radio over fiber transmission system includes an 852 nm laser, a 509 nm laser, an 1878 nm laser, a 1560 nm single-mode optical fiber, a periodically poled lithium niobate (PPLN) frequency conversion crystal, a temperature controller, a cesium atomic gas cell, a photodetector (PD), an analog signal source, a horn antenna, an oscilloscope, and a first dichroic mirror and a second dichroic mirror.

[0057] The 852 nm laser generates probe light that is refracted by the first dichroic mirror and injected from the left end of the cesium atomic gas cell. The 509 nm laser generates coupling light that is refracted by the second dichroic mirror and injected from the right end of the cesium atomic gas cell. The injected probe light and coupling light overlap with each other. Refer to Figure 3 As shown, the 852 nm probe light excites cesium atoms from the ground state 6S 1 / 2 to the intermediate excited state 6P 3 / 2 , and the coupling light excites the atomic intermediate excited state 6P 3 / 2 to the Rydberg state 63S 1 / 2, the radio frequency signal is radiated into the cesium atomic gas cell. The 852 nm probe light is transmitted through the cesium atomic gas cell and the transmitted 852 nm probe light is output from the right end. After being transmitted by the second dichroic mirror, the transmitted 852 nm probe light is input into the PPLN frequency conversion crystal, and a 1878 nm laser is used to generate 1878 nm pump light and input it into the PPLN frequency conversion crystal to convert the transmitted 852 nm probe light into a 1560 nm optical signal, which is transmitted over a long distance through an optical fiber and converted into an electrical signal by a photodetector. The oscilloscope collects this electrical signal for signal processing.

[0058] The specific implementation process of this system is as follows: A beam of 852 nm probe light and a beam of 509 nm coupling light are transmitted in opposite directions in a cylindrical cesium atomic gas cell. The spot diameters of the probe light and the coupling light are about 300 μm, and the light intensities are 240 μW and 60 mW respectively. The probe light excites the atoms from the ground state 6S 1 / 2 to the excited state 6P 3 / 2 , and the coupling light excites the atomic state to the first Rydberg state 63S 1 / 2 . The frequency of the 852 nm laser is controlled to lock the frequency of the probe light. When the coupling light is scanned, the spectrum of the probe light shows a higher transmittance at the resonance of the coupling light frequency and has a transmission peak. At this time, the coupling light frequency is locked at the spectral peak, that is, at the frequency zero detuning.

[0059] The carrier frequency is selected as 14.53169 GHz, which resonates with the energy levels 63S 1 / 2 , 63P 1 / 2 . The baseband signal is amplitude-modulated to the carrier by an analog signal source, and the power is set to -5 dBm. The modulated radio frequency RF is radiated to the atomic gas cell through a horn antenna.

[0060] The 852 nm probe light and the 1878 nm pump light are input into the PPLN frequency conversion crystal for difference frequency, and the pump light power is set to 400 mW. The temperature is adjusted for phase matching to maximize the conversion efficiency, that is, to maximize the power of the output 1560 nm optical signal. The output 1560 nm light is connected to a single-mode optical fiber, and the other end is connected to a photodetector.

[0061] The photodetector is connected to the oscilloscope, and data is collected and signal processing is performed. The transmittance of the 852 nm probe light shows a significant non-linear negative correlation with the radio frequency signal field strength (i.e., the amplitude of the baseband information). At the same time, the power change of the 1560 nm pump light has a positive correlation with the probe light power. Through this coupling effect, the real-time change of the pump light transmittance accurately reflects the original baseband information, thus realizing direct optical domain demodulation and avoiding the necessary local oscillator down-conversion link in the traditional system.

[0062] The radio-over-fiber communication system based on atomic antennas for long-distance transmission in this application has a simple structure and is easy to implement. It not only avoids the cable transmission loss in the electrical domain, but also eliminates the electro-optical modulation in the traditional RoF system and the down-conversion at the receiving end, enabling long-distance RoF communication.

[0063] In summary, the above-described embodiments are only examples of the present invention and are not solely used to limit the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, several equivalent deformations and substitutions can be made based on the disclosed content of the present invention. The frequency and number of carriers, modulation methods, quantum states of atoms, etc. can all be changed. These equivalent deformations, substitutions, and adjustments of the frequency range should also be regarded as within the protection scope of the present invention.

Claims

1. A long-distance optically carried radio frequency transmission system based on an atomic antenna, characterized in that It includes a transmitting end, a receiving end and a central station; The transmitting end is used to load a baseband signal onto a carrier to generate a radio frequency signal, and transmit the radio frequency signal to the area where the receiving end is located in a spatial radiation manner; The receiving end includes a Rydberg atom excitation module and a difference frequency optical conversion module. The Rydberg atom excitation module uses a probe light and a coupling light to excite a cesium atom system to the Rydberg state, and the Rydberg atom excitation module responds to the radio frequency signal; The difference frequency optical conversion module receives the transmitted probe light that has passed through the Rydberg state of the cesium atom system, and converts the transmitted probe light into an optical signal that conforms to the optical communication C-band standard; The central station receives the C-band optical signal and demodulates and restores the baseband information.

2. The long-distance optical radio frequency transmission system according to claim 1, wherein The transmitting end includes a signal generator, an analog signal source and a horn antenna. The analog signal source generates a carrier. The signal generator is connected to the analog signal source. The analog signal source loads the baseband signal generated by the signal generator onto the carrier to generate a radio frequency signal. The horn antenna is connected to the output end of the analog signal source and directionally transmits the radio frequency signal to the area where the receiving end is located.

3. The long-distance optical-radio frequency transmission system according to claim 1, characterized in that The Rydberg atom excitation module includes a first laser, a second laser and a cesium atom gas cell. The first laser generates a probe light and injects it into the cesium atom gas cell. The second laser generates a coupling light and injects it into the cesium atom gas cell. The light beams of the probe light and the coupling light coincide with each other in the cesium atom gas cell.

4. The long-distance optical radio frequency transmission system according to claim 1, characterized in that The wavelength of the probe light is 852 nm, and the wavelength of the coupling light is 509 nm.

5. The long-distance optical-radio frequency transmission system according to claim 1, wherein The difference frequency optical conversion module includes a temperature controller and a periodically poled lithium niobate frequency conversion crystal. The periodically poled lithium niobate frequency conversion crystal receives the transmitted probe light and introduces a pump light to convert and generate an optical signal that conforms to the C-band standard of optical communication. The temperature controller is used to adjust the temperature of the periodically poled lithium niobate frequency conversion crystal to achieve the phase matching between the transmitted probe light and the pump light.

6. The long-distance optical-radio frequency transmission system according to claim 5, wherein The wavelength of the introduced pump light is 1878 nm.

7. The long-distance optical radio frequency transmission system according to claim 1, wherein The central station includes a photodetector and an oscilloscope. The photodetector receives the optical signal of the C-band standard and converts it into an electrical signal. The oscilloscope receives the electrical signal and demodulates the baseband information.

8. A method for long-distance optical-radio frequency transmission based on an atomic antenna, characterized in that It includes the following steps: Use the probe light to excite the cesium atom system from the ground state to an intermediate excited state, and use the coupling light to excite the cesium atom system from the intermediate excited state to the Rydberg state; Apply the radio frequency modulation signal loaded with the baseband signal to the Rydberg state of the cesium atom system, so that the transmittance of the probe light changes with the intensity of the radio frequency field; Perform difference frequency conversion on the transmitted probe light that has passed through the Rydberg state of the cesium atom system to generate an optical signal that conforms to the optical communication C-band standard; Receive the optical signal and demodulate the baseband information.

9. The long-distance optical-radio frequency transmission method according to claim 8, wherein, Using a probe light with a wavelength of 852 nm to excite the cesium atom system from the ground state 6S 1 / 2 to an intermediate excited state 6P 3 / 2 , and using a coupling light with a wavelength of 509 nm to excite the cesium atom system from the intermediate excited state 6P 3 / 2 to a Rydberg state 63S 1 / 2 .

10. The long-distance optical-radio frequency transmission method according to claim 8, wherein Inject the transmitted probe light into a periodically poled lithium niobate frequency conversion crystal, and introduce a pump light for difference frequency conversion to generate an optical signal that conforms to the C-band standard; The wavelength of the pump light is 1878 nm, and the wavelength of the optical signal is 1560 nm.

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