A high time response ranging method and device based on light-generated microwave chirp pulse

Abstract

A kind of high time response ranging method and device based on light generation microwave chirp pulse, the method includes: step S1, input femtosecond pulse laser, it is divided into two independent optical path beams by optical coupler;Different dispersion amount of dispersion optical fiber is respectively connected in two independent optical path beams, and two new optical path beams are obtained;Step S2, two new optical path beams are coupled by optical coupler, and are converted into linear frequency modulation microwave signal;Step S3, linear frequency modulation microwave signal is used as microwave source, and is converted into transmitting signal and reference signal;Step S4, transmitting signal is sent to the object to be measured, and its echo signal is received, according to echo signal and reference signal, beat frequency signal is obtained by mixing, then Fourier transform is carried out to obtain the frequency of beat frequency signal, and then the absolute distance information is obtainedThe device is used to measure the distance of the target to be measured.It has the advantages of simple structure, sub-microsecond time resolution and micron level measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of microwave ranging technology, and in particular to a high-time-response ranging method and apparatus based on photogenerated microwave chirped pulses. Background Technology

[0002] Microwave-based non-contact high temporal resolution ranging technology has attracted much attention in the past decade due to its advantages such as high accuracy, strong anti-interference ability, and applicability to complex environments. It has been widely used in various fields such as aircraft navigation, structural monitoring, water level monitoring, explosive combustion, and plasma internal detection.

[0003] Currently, microwave ranging technologies mainly include single-frequency microwave interferometric ranging, pulsed ultra-wideband microwave radar, and frequency-modulated continuous wave radar. Single-frequency continuous wave radar uses continuous microwaves as a carrier wave, interfering with and demodulating the target echo signal with the transmitted signal in the time domain, and obtaining the target displacement by calculating the phase change. Although this technology can achieve measurement accuracy at the micrometer level, its time resolution is only at the microsecond level, and it is only suitable for relative distance measurement within a centimeter range. Ultra-wideband radar calculates absolute distance information by measuring the flight time of the same pulsed ultra-wideband microwave signal. Although it can achieve absolute distance measurement with a nanosecond time response within a range of tens of meters, its measurement accuracy is in the centimeter to millimeter range, which cannot meet the requirements of precision machining. Frequency-modulated continuous wave radar uses microwaves with a frequency that varies with time as a carrier wave, mixing the target echo signal with the transmitted signal, and measuring the frequency and phase of the difference frequency signal in the time domain to obtain absolute distance information. Within the X-band to R-band measurement range, this technology can currently achieve absolute distance measurement accuracy at the micrometer or sub-micrometer level. However, it requires a high-frequency, high-bandwidth, and high-linearity swept microwave source, as well as complex error correction algorithms, resulting in a complex system structure and high cost. Furthermore, the response time of an electronically swept microwave source is limited by the scan rate, typically ranging from hundreds of microseconds to milliseconds, which cannot meet the high time-resolution testing requirements of certain transient processes. To date, wide-range, fast-response microwave absolute distance measurement technology remains one of the most pressing frontiers in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a high-time-response ranging method and device based on photogenerated microwave chirped pulses, which has the advantages of simple structure, sub-microsecond time resolution, and micrometer-level measurement accuracy.

[0005] To achieve the above objectives, this invention provides a high-time-response ranging method based on photogenerated microwave chirped pulses for calculating the absolute distance information R of an object under test. The method includes: Step S1, inputting a femtosecond pulse laser and splitting it into two independent optical beams using an optical coupler; connecting dispersive optical fibers with different dispersion levels to the two independent optical beams to obtain two new optical beams; Step S2, coupling the two new optical beams using an optical coupler to convert them into a linear frequency modulated (LFM) microwave signal; Step S3, using the LFM microwave signal as a microwave source, converting it into a transmit signal and a reference signal; Step S4, sending the transmit signal to the object under test and receiving its echo signal; mixing the echo signal with the reference signal to obtain a beat frequency signal, and then performing a Fourier transform to obtain the frequency of the beat frequency signal. This allows us to obtain the absolute distance information. .

[0006] Preferably, in step S1, the pulse width of the femtosecond pulsed laser is... The dispersion coefficient of dispersive fiber Conditions should be met , i=1, 2; where i = 1 and i=2 correspond to two independent optical path beam splits respectively.

[0007] Preferably, in step S1, the pulse expression for the two new optical path beam splitting... for:

[0008] i = 1, 2;

[0009] Where t is the time offset of the average delay between the two optical paths; For femtosecond pulsed lasers, the Fourier transform of the optical signal after passing through the optical coupler is performed. This is the corresponding constant for beam splitting in the optical path; The center frequency of the optical pulse relative to the optical path beam splitting Angular frequency deviation; For Fourier transform operators; is the imaginary unit; exp is the exponential function.

[0010] Preferably, in step S1, and absolute angular frequency Represented as:

[0011] i = 1, 2;

[0012] t = n × T, n = 2, 3, 4, 5;

[0013] Where T is the pulse period.

[0014] Preferably, in step S2, the linear frequency modulated microwave signal is:

[0015]

[0016] in, ; It is the responsivity of photoelectric detection; The light field intensity when i=1; The light field intensity when i=2; For conjugate operators; It is a constant; The amplitude of the light field intensity when i=1; It is a constant; The amplitude of the light field intensity when i=2; For phase.

[0017] Preferably, in step S2, the instantaneous frequency of the linear frequency modulated microwave signal... for:

[0018]

[0019] When t=0, the center frequency is:

[0020]

[0021] Pulse duration of the generated linear frequency modulated microwave pulse and bandwidth for:

[0022]

[0023]

[0024] in, The center wavelength of the femtosecond pulsed laser. This refers to the wavelength width of a femtosecond pulsed laser. It is the speed of light.

[0025] Preferably, in step S4, the absolute distance information for:

[0026]

[0027]

[0028] .

[0029] Preferably, the device is used in any of the aforementioned high-time-response ranging methods based on optically generated microwave chirped pulses. The device is used to measure the target and includes: a femtosecond laser that generates femtosecond pulsed laser light, with an internal optical coupler that splits the femtosecond pulsed laser light into two optical branches; a first dispersion-compensating fiber and a second dispersion-compensating fiber, respectively connected to the optical coupler of the femtosecond laser, introducing different chirps into the two optical branches; a photodetector with an internal optical coupler, the photodetector's optical coupler being connected to the first dispersion-compensating fiber and the second dispersion-compensating fiber, converting the optical signal into a linearly frequency-modulated microwave signal; and a power divider connected to the photodetector, where the linearly frequency-modulated microwave pulse is used as... A microwave source and a power divider divide the microwave signal into a transmit signal and a reference signal; a microwave circulator, comprising a first port, a second port, and a third port, which are interconnected; the first port is connected to the power divider and is used to receive the transmit signal; an antenna, connected to the second port, receives the transmit signal and transmits it to the target under test, and receives the echo signal from the target under test; a mixer, connected to the third port and the power divider respectively, receives the echo signal and the reference signal, and mixes them; an oscilloscope, connected to the mixer, acquires the mixed signal to obtain the beat frequency signal; and a computer, connected to the oscilloscope, performs a Fourier transform on the generated beat frequency signal to obtain the frequency value, and then calculates the absolute distance information.

[0030] Preferably, the femtosecond laser optical coupler is 50:50; the photodetector optical coupler is 50:50.

[0031] In summary, compared with the prior art, the high time response ranging method and device based on photogenerated microwave chirped pulses provided by the present invention have the following beneficial effects:

[0032] First, the advantage of the high time response ranging method and device based on photogenerated microwave chirped pulses proposed in this invention is that the single measurement time is only 40 nanoseconds, thereby realizing ultrafast microwave absolute distance measurement with nanosecond time resolution and micrometer-level accuracy.

[0033] Secondly, the high time response ranging device based on photogenerated microwave chirped pulses proposed in this invention has a simple structure and is easy to operate. It can effectively reduce the requirements of microwave ranging technology on the performance of experimental equipment and the application environment, which will promote the practical application of non-contact absolute distance measurement based on microwave band in scientific research, production and other fields. Attached Figure Description

[0034] Figure 1 This invention proposes a high-time-response ranging device based on photogenerated microwave chirped pulses.

[0035] Figure 2 This is a flowchart of a high-time-response ranging method based on photogenerated microwave chirped pulses proposed in this invention.

[0036] Figure 3 This is the Fourier transform waveform of the beat frequency signal obtained in the experiment.

[0037] Figure 4 The measurement results are from 50 measurements performed on the target.

[0038] Figure label:

[0039] 101-Femtosecond laser, 102-First dispersion compensation fiber, 103-Second dispersion compensation fiber, 104-Photodetector, 105-Power divider, 106-Microwave circulator, 107-Antenna, 108-Mixer, 109-Oscilloscope, 110-Computer, 111-Target under test, 1-First port, 2-Second port, 3-Third port. Detailed Implementation

[0040] The following will be combined with the appendix in the embodiments of the present invention. Figure 1 ~Appendix Figure 4 The technical solutions, structural features, objectives and effects achieved in the embodiments of the present invention will be described in detail.

[0041] It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions. They are only used to facilitate and clarify the purpose of illustrating the embodiments of the present invention, and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationship, or adjustments to the size should still fall within the scope of the technical content disclosed in the present invention, provided that they do not affect the effects and objectives that the present invention can produce.

[0042] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only the expressly listed elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0043] This invention proposes a high-time-response ranging method and device based on photogenerated microwave chirped pulses. "Photogenerated microwave chirped pulses" are microwave pulses generated by optical methods and have frequency-varying characteristics over time. This invention combines the efficient conversion technology of "photogenerated microwaves" with the frequency modulation characteristics of "chirped pulses" and has important applications in radar, communication, spectroscopy and other fields.

[0044] "Optically generated microwaves" refers to the technology of converting optical signals into microwave signals through optical means (such as optical mixing and photoelectric conversion). High-frequency, high-purity microwaves can be generated by frequency difference or modulation of optical signals, breaking through the bottleneck of traditional electronic methods in high frequency and broadband.

[0045] A "chirped pulse" refers to a signal whose instantaneous frequency changes over time. For example, the frequency of a linearly chirped pulse increases linearly with time ("upper chirp") or decreases linearly with time ("lower chirp"); while a nonlinear chirp exhibits a nonlinear frequency change with time (such as a quadratic curve). The chirping characteristic gives it unique advantages in the "time-frequency" two-dimensional domain (such as achieving high-resolution measurements through frequency scanning).

[0046] A high-time-response ranging method based on photogenerated microwave chirped pulses is used to calculate the absolute distance information R of an object to be measured; the method includes:

[0047] Step S1: Input a femtosecond pulse laser and split it into two independent optical paths using an optical coupler; connect dispersive optical fibers with different dispersion levels to the two independent optical path beams to obtain two new optical path beams.

[0048] In step S1, different chirps are naturally formed when dispersive optical fibers with different dispersion levels are introduced, that is, the difference in chirps is due to the difference in dispersion.

[0049] Step S2: The two new optical paths are split and coupled through an optical coupler to convert them into linear frequency modulated microwave signals;

[0050] Step S3: The linear frequency modulated microwave signal is used as a microwave source and converted into a transmitted signal and a reference signal;

[0051] Step S4: Send the transmitted signal to the object under test and receive its echo signal. Mix the echo signal with the reference signal to obtain the beat frequency signal, and then perform a Fourier transform to obtain the frequency of the beat frequency signal. This allows us to obtain the absolute distance information. .

[0052] Specifically, in step S1, the pulse width of the femtosecond pulsed laser... The dispersion coefficient of dispersive fiber Conditions should be met , i=1, 2; where i = 1 and i=2 correspond to two independent optical path beam splits respectively.

[0053] Furthermore, due to the frequency-time mapping effect caused by dispersive fiber, the pulses of the two optical paths are broadened in the time domain.

[0054] Therefore, in step S1, the pulse expression for the two new optical path beam splitting... for:

[0055] i = 1, 2;

[0056] Where t is the time offset of the average delay between the two optical paths; For femtosecond pulsed lasers, the Fourier transform of the optical signal after passing through the optical coupler is performed. This is the corresponding constant for beam splitting in the optical path; The center frequency of the optical pulse relative to the optical path beam splitting Angular frequency deviation; For Fourier transform operators; The imaginary unit is exp; exp is an exponential function; thus, we obtain and .

[0057] Will and Replace with absolute angular frequency This indicates that you have obtained:

[0058] i = 1, 2;

[0059] t = n × T, n = 2, 3, 4, 5;

[0060] Therefore, by adjusting the time delay of the two independent optical path beam splitting to an integer multiple of the pulse period T of the two independent optical path beam splitting, it means that the optical pulses of the two independent optical path beam splitting can arrive at the optical coupler in step S2 at the same time and interfere.

[0061] Specifically, in step S2, the linear frequency modulated microwave signal is:

[0062]

[0063] in, ; It is the responsivity of photoelectric detection; The light field intensity when i=1; The light field intensity when i=2; For conjugate operators; It is a constant; The amplitude of the light field intensity when i=1; It is a constant; The amplitude of the light field intensity when i=2; For phase.

[0064] Based on the differential relationship between the phase factor and frequency, the instantaneous frequency of the linear frequency modulated microwave signal is... for:

[0065]

[0066] When t=0, the center frequency can be written as:

[0067]

[0068] Pulse duration of the generated linear frequency modulated microwave pulse and bandwidth It can be approximated as:

[0069]

[0070]

[0071] in, The center wavelength of the femtosecond pulsed laser. This refers to the wavelength width of a femtosecond pulsed laser. It is the speed of light.

[0072] Specifically, in step S3, the generated linearly chirped microwave pulse is used as a microwave source and transmitted through an antenna, converting it into a transmitted signal and a reference signal. The principle here is that the reference signal and the transmitted signal will have a time delay. ( (), where R represents the absolute distance to the target object, and c represents the speed of light. Therefore, subsequent time delays can be used to... , to obtain the absolute distance information R of the target object.

[0073] Specifically, in step S4, when the target object is relatively stationary, the received echo signal and the transmitted reference signal are mixed to obtain a beat frequency signal, and then a Fourier transform is performed to obtain the frequency of the beat frequency signal. This allows us to obtain the absolute distance information. .

[0074] In a preferred embodiment, according to the similar triangle theorem, the absolute distance information Represented as:

[0075]

[0076]

[0077] .

[0078] In addition, such as Figure 1 As shown, the present invention also proposes a high time response ranging device based on photogenerated microwave chirped pulses; wherein, the solid line represents optical signal transmission, the long dashed line represents microwave signal transmission, and the short dashed line represents data transmission.

[0079] The device is used to measure the target 111 to be measured, and the device includes:

[0080] The femtosecond laser 101 generates femtosecond pulsed lasers and has a 50:50 optical coupler (not shown in the figure) inside it. The optical coupler splits the femtosecond pulsed lasers into two optical paths. Of course, the aforementioned optical coupler can also be set outside the femtosecond laser 101. There is no limitation here. Those skilled in the art can set it according to the actual situation.

[0081] The first dispersion compensation fiber 102 and the second dispersion compensation fiber 103 are respectively connected to the optical coupler of the femtosecond laser 101, and different chirps are introduced into the two optical path branches through the wavelength-time mapping effect; that is, the paths corresponding to i=1 and i=2.

[0082] The photodetector 104 has a 50:50 optical coupler inside. The optical coupler of the photodetector 104 is connected to the first dispersion compensation fiber 102 and the second dispersion compensation fiber 103 respectively, and converts the optical signal into a linear frequency modulated microwave signal. The aforementioned optical coupler can also be disposed outside the photodetector 104. There is no limitation here. Those skilled in the art can set it according to the actual situation.

[0083] The power divider 105 is connected to the photodetector 104. At this time, the linear frequency modulated microwave pulse is used as a microwave source, and the power divider 105 divides the microwave signal into a transmitted signal and a reference signal.

[0084] The microwave circulator 106 includes a first port 1, a second port 2, and a third port 3, which are interconnected. The first port 1 is connected to the power divider 105 and is used to receive transmitted signals.

[0085] Antenna 107 is connected to the second port 2, receives the transmitted signal and transmits it to the target 111 under test, and receives the echo signal from the target 111 under test;

[0086] Mixer 108 is connected to the third port 3 and the power divider 105 respectively, receives the echo signal and the reference signal, and mixes them.

[0087] The oscilloscope 109 is connected to the mixer 108 to acquire the mixed signal and obtain the beat frequency signal.

[0088] Computer 110, connected to oscilloscope 109, performs Fourier transform on the generated beat frequency signal to obtain frequency value, and then calculates the absolute distance information.

[0089] For a high-time-response ranging device based on photogenerated microwave chirped pulses, with attached... Figure 1 The structure shown is used as an example to illustrate the optimal implementation scheme. The light source used in this experiment is laser light generated by a femtosecond fiber laser, with a repetition rate, output power, and center wavelength of 21.38 MHz, 22.30 mW, and 1550 nm, respectively. The dispersion measures of the two arms are -8391 ps² and -8624 ps², respectively.

[0090] Linear chirped microwave pulses with a bandwidth of 12 GHz and a pulse width of 35 ns were generated using the optical heterodyne beat frequency method.

[0091] The power divider has a bandwidth of 6-18 GHz, the antenna has a bandwidth of 7-13 GHz, the microwave circulator has a bandwidth of 7-12.4 GHz, the mixer has an RF / LO bandwidth of 10-44 GHz, and the IF bandwidth is DC-14 GHz. The target under test is a metal plate, and the test distance is approximately 40 cm. The Fourier transform waveform of the beat frequency signal obtained in the experiment is shown below. Figure 3 As shown.

[0092] The target was measured 50 times, and the measurement results are as follows: Figure 4 As shown, the Type A uncertainty of the device can be calculated to be 149 μm (95% confidence interval). Its absolute distance measurement value is 40.938 ± 0.0149 cm (95.5% confidence interval).

[0093] In summary, this invention, based on the FMCW radar ranging principle, constructs a simple microwave absolute distance measuring device, achieving absolute distance measurement with a time resolution of 50 nanoseconds and an accuracy of 100 micrometers.

[0094] This invention employs a microwave absolute distance measurement device and method with a simple structure, sub-microsecond time resolution, and micrometer-level measurement accuracy. Under non-equilibrium dispersion conditions, femtosecond laser interferometry can obtain nanosecond-level linearly frequency-modulated microwave pulses, and then high time resolution absolute distance measurement is achieved using the principle of frequency-modulated continuous wave (FMCW) radar. The technology described in this patent allows for high time resolution and high precision absolute distance measurement using existing commercially available components.

[0095] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A high-time-response ranging method based on photogenerated microwave chirped pulses, characterized in that, The method is used to calculate the absolute distance information R of the object to be measured; the method includes: Step S1: Input a femtosecond pulse laser and split it into two independent optical paths using an optical coupler; connect dispersive optical fibers with different dispersion levels to the two independent optical path beams to obtain two new optical path beams. Step S2: The two new optical paths are split and coupled through an optical coupler to convert them into linear frequency modulated microwave signals; Step S3: The linear frequency modulated microwave signal is used as a microwave source and converted into a transmitted signal and a reference signal; Step S4: Send the transmitted signal to the object under test and receive its echo signal. Mix the echo signal with the reference signal to obtain the beat frequency signal, and then perform a Fourier transform to obtain the frequency of the beat frequency signal. This allows us to obtain the absolute distance information. , In step S1, the pulse width of the femtosecond pulsed laser Dispersion coefficient of dispersive fiber Conditions should be met i = 1, i = 2; where i = 1 and i = 2 correspond to two independent optical path beam splitting, respectively. In step S1, the pulse expression for the two new optical path beam splitting for: ，i=1、2； Where t is the time offset of the average delay between the two independent optical paths; For femtosecond pulsed lasers, the Fourier transform of the optical signal after passing through the optical coupler is performed. For independent optical path beam splitting, the corresponding constants are: The center frequency of the optical pulse relative to the independent optical path beam splitting Angular frequency deviation; For Fourier transform operators; The imaginary unit is exp; exp is an exponential function. In step S1, and absolute angular frequency Represented as: ，i=1、2； t = n × T, n = 2, 3, 4, 5; Where T is the pulse period.

2. The high time response ranging method based on photogenerated microwave chirped pulses according to claim 1, characterized in that, In step S2, the linear frequency modulated microwave signal is: in, ; It is the responsivity of photoelectric detection; Let i be the light field intensity when i=1; The light field intensity when i=2; For conjugate operators; It is a constant; The amplitude of the light field intensity when i=1; It is a constant; The amplitude of the light field intensity when i=2; For phase.

3. The high time response ranging method based on photogenerated microwave chirped pulses according to claim 2, characterized in that, In step S2, the instantaneous frequency of the linear frequency modulated microwave signal for: When t=0, the center frequency is: Pulse duration of the generated linear frequency modulated microwave signal and bandwidth for: in, The center wavelength of the femtosecond pulsed laser. This refers to the wavelength width of a femtosecond pulsed laser. It is the speed of light.

4. The high time response ranging method based on photogenerated microwave chirped pulses according to claim 3, characterized in that, In step S4, the absolute distance information for: 。 5. A high-time-response ranging device based on photogenerated microwave chirped pulses, characterized in that, The device is used to implement the high time response ranging method based on photogenerated microwave chirped pulses as described in any one of claims 1 to 4. The device is used to measure the target (111) to be measured. The device includes: A femtosecond laser (101) generates femtosecond pulsed lasers. An optical coupler is installed inside the laser to split the femtosecond pulsed lasers into two independent optical paths. The first dispersion compensation fiber (102) and the second dispersion compensation fiber (103) are respectively connected to the optical coupler of the femtosecond laser (101) to introduce different chirps into the two independent optical paths. The photodetector (104) has an optical coupler inside. The optical coupler of the photodetector (104) is connected to the first dispersion compensation fiber (102) and the second dispersion compensation fiber (103) respectively, and the two new optical paths are split into linear frequency modulated microwave signals. A power divider (105) is connected to a photodetector (104). At this time, the linear frequency modulated microwave signal is used as a microwave source, and the power divider (105) divides the linear frequency modulated microwave signal into a transmission signal and a reference signal. A microwave circulator (106) includes a first port (1), a second port (2), and a third port (3), which are interconnected. The first port (1) is connected to a power divider (105) for receiving transmitted signals. The antenna (107) is connected to the second port (2) to receive the transmitted signal and transmit it to the target (111) under test, and to receive the echo signal of the target (111) under test; The mixer (108) is connected to the third port (3) and the power divider (105) respectively, receives the echo signal and the reference signal, and mixes them; An oscilloscope (109) is connected to a mixer (108) to acquire the mixed signal and obtain the beat frequency signal; A computer (110) is connected to an oscilloscope (109) to perform a Fourier transform on the generated beat frequency signal to obtain the frequency value, and then calculate the absolute distance information.

6. A high-time-response ranging device based on photogenerated microwave chirped pulses according to claim 5, characterized in that, The femtosecond laser (101) has a 50:50 optical coupler; the photodetector (104) has a 50:50 optical coupler.

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