A Handheld Microwave Electric Field Measurement System

Abstract

The present invention discloses a handheld microwave electric field measurement system, which can realize mobile precision measurement of microwave electric field. The system includes: a first laser, a handheld measurement probe, a second laser, a dichroic mirror, a photodetector, a high-speed oscilloscope, a high-frequency source and a standard gain horn antenna, wherein the handheld measurement probe includes: a first optical fiber collimator, an alkali metal atom gas chamber, a first right-angle reflection prism, a second right-angle reflection prism and a second optical fiber collimator. The advantages of the present invention are: the present invention realizes a portable microwave electric field measurement probe based on Rydberg atoms, realizes a quantum sensor using non-metallic materials, and completes the precision measurement of weak microwave electric fields. The mobile measurement is realized by connecting the measurement probe of the optical fiber, which gets rid of the limitation of the traditional experimental platform, is applicable to various complex environments, provides ideas for the development of quantum sensors based on Rydberg atoms, and has great application value.

Description

Technical Field

[0001] The invention relates to the field of microwave electric field measurement, and in particular to a handheld microwave electric field measurement system. Background Art

[0002] Accurate measurement of microwave electric fields is of great significance for communications, radar, and medical treatment. At present, dipole antennas are commonly used for microwave electric field detection. However, due to its shortcomings such as thermal noise and detection frequency band limited by antenna size, quantum sensors based on Rydberg atoms have been proposed. Quantum sensors based on Rydberg atoms can achieve broadband measurements from DC to terahertz frequencies, and the measurement results can be traced back to basic physical constants. They have been widely used in subwavelength imaging of microwave electric fields [Applied Physics Letters, 104(24): 244102(2014)], terahertz measurement of atomic sensors [Physical Review A, 100(6): 063427(2019)], and communications based on atomic microwave electric field sensing [Applied Physics Express 12(12): 126002.1-4(2019)].

[0003] Microwave electric field detection based on Rydberg atoms has many advantages, but most of the current experiments are based on traditional optical path design, and the portability of the experimental system is not considered. The traditional optical path based on the optical platform has a large spatial volume and complex adjustment, and cannot achieve portable measurement. It is difficult to realize the practical application of quantum sensors based on Rydberg atoms, and the metal of the experimental platform will also affect the actual spatial distribution of the microwave electric field. Therefore, how to design a portable and precise system for measuring microwave electric fields has become an urgent problem to be solved. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a handheld microwave electric field measurement system, which can be used to measure the microwave electric field intensity in space. The measurement principle is based on the electromagnetic induced transparency (EIT) phenomenon and the Autler-Townes splitting phenomenon. In the present invention, a step-type energy level structure is used to realize the EIT phenomenon. When an external microwave electric field is applied to electromagnetic induced transparency, the Autler-Townes splitting phenomenon [Physical Review A100, 703–722 (1955)] can be observed. The splitting frequency difference is proportional to the external microwave electric field intensity, thereby realizing the measurement of the external microwave electric field intensity.

[0005] The specific technical scheme for achieving the purpose of the present invention is as follows:

[0006] A handheld microwave electric field measurement system comprises a first laser, a handheld measurement probe, a dichroic mirror, a second laser, a photodetector, a high-speed oscilloscope, a standard gain horn antenna and a high-frequency signal source;

[0007] The first laser is an external cavity semiconductor laser, which generates a detection light with a central wavelength of 780nm and couples into the handheld measurement probe;

[0008] The second laser is an external cavity semiconductor laser, which generates pump light with a central wavelength of 480nm, and is coupled into the handheld measurement probe through a dichroic mirror;

[0009] The handheld measurement probe is a non-metallic device. The detection light generated by the first laser and the pump light generated by the second laser are coupled respectively through a single-mode polarization-maintaining optical fiber. The two beams of light propagate in opposite directions inside the probe, and the Autler-Townes splitting phenomenon is used to detect the external microwave electric field.

[0010] The dichroic mirror is placed before the second laser, reflects the pump light generated by the second laser into the handheld measurement probe, and separates the detection light from the handheld measurement probe from the pump light;

[0011] The photoelectric detector is placed after the dichroic mirror and is used to detect the detection light separated by the dichroic mirror and convert the optical signal into an electrical signal;

[0012] The high-speed oscilloscope is connected to the photodetector and is used to obtain the frequency difference of the double peaks in the Autler-Townes splitting and calculate the intensity of the external microwave electric field;

[0013] The standard gain horn antenna is connected to a high-frequency signal source and is used to generate an external linearly polarized microwave electric field to act on the handheld measurement probe;

[0014] The handheld measuring probe comprises: a first optical fiber collimator, an alkali metal atom gas chamber, a first right-angle reflecting prism, a second right-angle reflecting prism and a second optical fiber collimator;

[0015] The first optical fiber collimator and the second optical fiber collimator have the same structure, both are non-metallic structures, and the two are parallel and placed together on one side of the alkali metal atom gas chamber, and are used to couple and collimate the detection light and pump light generated by the first laser and the second laser, and the second optical fiber collimator couples the detection light emitted from the first optical fiber collimator;

[0016] The alkali metal atom gas chamber is a cylindrical atom gas chamber, and the alkali metal atoms in the gas chamber provide atomic media for the measurement system;

[0017] The first right-angle reflecting prism and the second right-angle reflecting prism are placed together on the other side of the alkali metal atom gas chamber, and are broadband coated and used to reflect the detection light and the pump light;

[0018] The first optical fiber collimator comprises: a single-mode polarization-maintaining optical fiber, a glass ferrule, a glass sleeve, and a gradient refractive index lens;

[0019] One end of the single-mode polarization-maintaining optical fiber is an FC-APC connector for coupling spatial light, and the other end is a glass ferrule. The end face of the glass ferrule has an 8° face angle, which reflects the incident light by deviating from the normal direction to maximize the return loss.

[0020] The glass sleeve is a cylindrical hollow sleeve, the inner diameter of which is the same as the outer diameter of the glass insert and the gradient refractive index lens, and is used to fix the glass insert and the gradient refractive index lens;

[0021] The end face of one side of the gradient refractive index lens is a plane, and the end face of the other side has an 8° face angle that matches the 8° face angle of the glass ferrule, and is used to collimate the detection light and pump light emitted from the single-mode polarization-maintaining optical fiber.

[0022] The calculation formula of the external microwave electric field strength is: in is the reduced Planck constant, Δf is the frequency difference between the two peaks of Autler-Townes splitting, and μ is the Rydberg level transition dipole moment of external microwave coupling.

[0023] Compared with the traditional optical path, the advantages of the present invention are:

[0024] 1. The handheld measuring probe of the present invention is designed with non-metallic materials, which does not affect the actual spatial distribution of the microwave electric field to be measured and improves the measurement accuracy;

[0025] 2. The present invention can manufacture everything from laser to measuring probe by itself, with low manufacturing cost and convenient use, thus improving the practicality of the measuring system;

[0026] 3. The present invention uses optical fiber to transmit light, realizes the movable measurement of microwave electric field, and is a convenient atomic sensor with high application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the present invention;

[0028] Figure 2 It is a schematic diagram of the structure of the optical fiber collimator in the handheld measuring probe of the present invention;

[0029] Figure 3 A schematic diagram of the relationship between the high-frequency signal source output power and the Autler-Townes splitting measured in an embodiment of the present invention;

[0030] Figure 4 A schematic diagram of the relationship between the high-frequency signal source output power and the detected microwave electric field strength measured in an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention realizes a handheld microwave electric field measurement system, which will be explained below in the form of a specific embodiment combined with the accompanying drawings. The described implementation is only a partial implementation of the present invention, and the present invention can also be verified by other different specific examples. The details in this specification can also be modified based on different application scenarios without departing from the spirit of the present invention.

[0032] like Figure 1 As shown, the first laser 1 is a littrow type external cavity semiconductor laser with a central wavelength of 780nm, and the laser diode model used is Sharp GH0781RA2C, the laser output power is 50mW, and 30μW of light is coupled into the handheld measurement probe 2 as the detection light. The outgoing light of the detection light is collimated by the first fiber collimator 21, and the detection light passes through the alkali metal atom gas chamber 22, and is reflected by the first right-angle reflection prism 23 and the second right-angle reflection prism 24 in turn, and then coupled into the second fiber collimator 25, passes through the dichroic mirror 3, and then the light intensity signal is detected by the photodetector 5, and the electrical signal is collected and stored by the high-speed oscilloscope 6.

[0033] Since the optical fiber in the system needs to transmit the detection light (780nm) and the pump light (480nm), a broadband coated single-mode polarization-maintaining optical fiber 211 is selected, and the wavelength range of the anti-reflection coating is 400nm-800nm. In the present invention, the alkali metal atom gas chamber 22 is a cylinder with a bottom diameter of 2.5cm and a height of 3cm. The gas chamber is filled with rubidium atoms to provide an atomic medium for the measurement system. The first right-angle reflection prism 23 and the second right-angle reflection prism 24 are isosceles right-angle triangular prisms of 1cm×1cm×1cm, and the outer surface of the inclined surface is coated with a broadband high-reflection film.

[0034] The second laser 4 is a littrow type external cavity semiconductor laser with a central wavelength of 480nm, and the laser diode model used is NICHIA NDA4216, the laser output power is 100mW, and part of the emitted light passes through the dichroic mirror 3 and is coupled into the handheld measurement probe 2 as pump light, and the coupled light power is 30mW. After the pump light is collimated by the second fiber collimator 25, it propagates in the alkali metal atom gas chamber 22 in the same axis as the detection light, so as to offset the Doppler broadening of the room temperature atoms.

[0035] The first optical fiber collimator 21 and the second optical fiber collimator 25 have the same structure and are entirely non-metallic. Taking the first optical fiber collimator 21 as an example, its structural schematic diagram is shown in FIG. Figure 2As shown. One end of the single-mode polarization-maintaining fiber 211 in the fiber collimator is an FC-APC connector to couple the probe light and the pump light, and the other end is a glass ferrule 212 with a diameter of 1.8 mm and a length of 5.6 mm. The end face of the ferrule has an 8° face angle, which can reflect the incident light by deviating from the normal direction to maximize the return loss. The probe light and pump light in the optical fiber are collimated by a gradient refractive index lens 214 with a diameter of 1.8 mm and a length of 4.3 mm. The gradient refractive index lens 214 in the present invention also uses broadband coating, one end face of which is a plane, and the other end face has an 8° face angle to match the 8° face angle of the glass ferrule 212 of the single-mode polarization-maintaining fiber. In order to facilitate adjustment, the pitch of the gradient refractive index lens 214 is selected to be 0.23. For the probe light, the working distance of the gradient refractive index lens 214 is 0.2 mm, and for the pump light, the working distance of the gradient refractive index lens 214 is 0.5 mm. The glass ferrule 212 and the gradient refractive index lens 214 of the single-mode polarization-maintaining optical fiber are fixed by a glass sleeve 213 with an outer diameter of 2.8 mm and an inner diameter of 1.8 mm, and are reinforced by curing glue after the system adjustment is completed.

[0036] During the production process of the handheld measuring probe 2, three types of glue were selected for fixation, namely: Dymax OP-67-LS, LOCTITE STYCAST 2850FT and Norland NOA 68, wherein Dymax OP-67-LS is a UV-curing glue used to quickly fix the position of each optical component; LOCTITE STYCAST 2850FT is an epoxy resin glue with a low thermal expansion coefficient, which has the characteristics of long curing time and high hardness, and is used to fix the first right-angle reflection prism 23 and the second right-angle reflection prism 24 to ensure that the coupling efficiency between the optical fibers remains unchanged, and is used to reinforce the position of each component; Norland NOA 68 is a UV-curing glue with a short solidification time, which is liquid when not solidified, and is suitable for bonding between irregular devices. In the present invention, it is mainly used for fixing the gradient refractive index lens 214, the glass sleeve 213 and the glass ferrule 212 of the optical fiber.

[0037] Each component in the handheld measuring probe 2 is fixed on a separate displacement stage for position adjustment, and the coupling efficiency of the detection light between the first fiber collimator 21 and the second fiber collimator 25 is about 50%. Since the system is designed as a handheld measuring system, it should have high stability. After inspection, the fiber coupling efficiency of the detection light of the handheld measuring probe 2 of the present invention remains unchanged after being placed for two months. After external reinforcement, the overall final length of the handheld measuring probe 2 is about 10 cm and the diameter is 3 cm, which meets the design requirements.

[0038] The performance of the handheld microwave electric field measurement system is verified by measuring the external microwave electric field. The energy level of the rubidium atom used in the present invention is: 5S 1 / 2→5P 3 / 2 (detection light coupling, about 780.24nm), 5P 3 / 2 →50D 5 / 2 (pump light coupling, about 480.12nm), 50D 5 / 2 →51P 3 / 2 (microwave coupling, about 17.04GHz), a standard gain horn antenna 7 is connected through a high-frequency signal source 8 to generate a Rydberg state related to the external microwave electric field coupling. The Autler-Townes splitting phenomenon can be seen by observing the high-frequency oscilloscope 6, and the external microwave electric field strength can be calculated.

[0039] like Figure 3 As shown, the handheld microwave electric field measurement system of the present invention is used to measure the relationship between pump light detuning and detection light transmission at different microwave output powers. Figure 3 (a) is the relationship between pump light detuning and probe light transmission when the microwave source output is turned off. The higher peak in the middle is 5S 1 / 2 →5P 3 / 2 →50D 5 / 2 The EIT peak produced by the transition, and the shorter peak next to it is 5S 1 / 2 →5P 3 / 2 →50D 3 / 2 The EIT peak generated by the transition. The energy level of the external microwave electric field coupling is 50D 5 / 2 →51P 3 / 2 , the frequency is about 17.04GHz, so 5S 1 / 2 →5P 3 / 2 →50D 3 / 2 The EIT peak produced by the transition does not undergo Autler-Townes splitting in this microwave electric field. Figure 3 (b)-(d) are the relationship between pump light detuning and probe light transmission when the microwave source output is -15.55dbm, -11.35dbm and -8dbm respectively. It can be seen that as the microwave source power increases, the Autler-Townes splitting frequency difference also increases. The microwave electric field strength at the handheld measuring probe 2 can be calculated, where is the reduced Planck constant, Δf is the frequency difference between the two peaks of Autler-Townes splitting, and μ is the Rydberg level transition dipole moment of external microwave coupling.

[0040] like Figure 4 As shown, through the above microwave electric field strength calculation formula, the relationship between the output power of the microwave signal source 8 and the microwave electric field strength can be obtained. The points in the figure are experimental measurement data, and the straight line is the fitting curve of the experimental data. Through observation, it basically satisfies the linear relationship and conforms to the relationship between the electric field strength at the target position and the output power of the signal source determined by the standard antenna formula: Where α is a constant factor determined by the experimental system. Figure 4 It can be seen that the handheld measuring probe 2 of the present invention can measure the weakest electric field strength of about 0.7 V / m. Of course, it is also possible to measure weaker microwave electric field strength by extending the measuring time or increasing the gain of the photodetector 5.

[0041] In summary, the present invention realizes a handheld microwave electric field measurement probe system, which can movably measure the microwave electric field intensity in space. The present invention has low production cost and is easy to use. It provides ideas for Rydberg sensing measurement based on rubidium atoms, achieves a major breakthrough from principle verification to practical application, and has a high application prospect.

[0042] The above embodiments of the present invention further describe the technical features and basic structure of the present invention in detail. It should be understood that the content of the present invention is not limited to the above specific embodiments. Any modification, replacement and improvement made within the spirit of the present invention shall be within the protection scope of the present invention. The subject matter of the present invention is defined by the claims rather than by the specific description of the embodiments.

Claims

1. A handheld microwave electric field measurement system, characterized in that: The device comprises a first laser (1), a handheld measuring probe (2), a dichroic mirror (3), a second laser (4), a photodetector (5), a high-speed oscilloscope (6), a standard gain horn antenna (7) and a high-frequency signal source (8), wherein: The first laser (1) is an external cavity semiconductor laser, which generates detection light with a central wavelength of 780 nm and couples into the handheld measurement probe (2); The second laser (4) is an external cavity semiconductor laser, which generates pump light with a central wavelength of 480 nm and is coupled into the handheld measurement probe (2) via a dichroic mirror (3); The handheld measuring probe (2) is a non-metallic device, and the detection light generated by the first laser (1) and the pump light generated by the second laser (4) are respectively coupled through a single-mode polarization-maintaining optical fiber, and the two beams of light propagate in opposite directions inside the probe, and the Autler-Townes splitting phenomenon is used to realize the detection of the external microwave electric field; The dichroic mirror (3) is placed before the second laser (4), reflects the pump light generated by the second laser (4) into the handheld measurement probe (2), and separates the detection light from the handheld measurement probe (2) from the pump light; The photoelectric detector (5) is placed behind the dichroic mirror (3) and is used to detect the detection light separated by the dichroic mirror (3) and convert the optical signal into an electrical signal; The high-speed oscilloscope (6) is connected to the photodetector (5) and is used to obtain the frequency difference of the double peaks in the Autler-Townes splitting and calculate the intensity of the external microwave electric field; The standard gain horn antenna (7) is connected to a high-frequency signal source (8) and is used to generate an external linearly polarized microwave electric field to act on the handheld measurement probe (2); The handheld measuring probe (2) comprises: a first optical fiber collimator (21), an alkali metal atom gas chamber (22), a first right-angle reflection prism (23), a second right-angle reflection prism (24) and a second optical fiber collimator (25); The first optical fiber collimator (21) and the second optical fiber collimator (25) have the same structure and are both non-metallic structures. The two are parallel and placed together on one side of the alkali metal atom gas chamber (22) and are used to couple and collimate the detection light and pump light generated by the first laser (1) and the second laser (4), and the second optical fiber collimator (25) couples the detection light emitted from the first optical fiber collimator (21); The alkali metal atom gas chamber (22) is a cylindrical atomic gas chamber, and the alkali metal atoms in the gas chamber provide atomic media for the measurement system; The first right-angle reflection prism (23) and the second right-angle reflection prism (24) are placed together on the other side of the alkali metal atom gas chamber (22) and are broadband coated and used for reflecting detection light and pump light.

2. The handheld microwave electric field measurement system according to claim 1, characterized in that: The first optical fiber collimator (21) comprises: a single-mode polarization-maintaining optical fiber (211), a glass ferrule (212), a glass sleeve (213), and a gradient refractive index lens (214), wherein: One end of the single-mode polarization-maintaining optical fiber (211) is an FC-APC connector for coupling spatial light, and the other end is a glass ferrule (212). The end face of the glass ferrule (212) has an 8° face angle, and the face angle reflects the incident light in a direction deviating from the normal line, thereby maximizing the return loss. The glass sleeve (213) is a cylindrical hollow sleeve, the inner diameter of which is the same as the outer diameter of the glass insert (212) and the gradient refractive index lens (214), and is used to fix the glass insert (212) and the gradient refractive index lens (214); One end face of the gradient refractive index lens (214) is a plane, and the other end face has an 8° face angle that matches the 8° face angle of the glass ferrule (212), and is used to collimate the detection light and pump light emitted from the single-mode polarization-maintaining optical fiber (211).

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