High time response distance measurement method and device based on photo-generated microwave chirped pulse

Abstract

The invention discloses a high-time-response distance measurement method and device based on photo-generated microwave chirped pulses, and the method comprises the steps: S1, inputting femtosecond pulse laser, and dividing the femtosecond pulse laser into two independent light path split beams through an optical coupler; respectively accessing dispersion optical fibers with different dispersion amounts into the two independent light path split beams to obtain two new light path split beams; s2, the two new optical paths are split and coupled through an optical coupler to be converted into linear frequency modulation microwave signals; s3, taking the linear frequency modulation microwave signal as a microwave source, and converting the linear frequency modulation microwave signal into a transmitting signal and a reference signal; and S4, sending the emission signal to a to-be-measured object, receiving an echo signal of the to-be-measured object, performing frequency mixing according to the echo signal and the reference signal to obtain a beat frequency signal, performing Fourier transform to obtain the frequency of the beat frequency signal, and further obtaining absolute distance information. The device is used for measuring the distance of the to-be-measured object. The device has the advantages of simple structure, sub-microsecond-level time resolution and micron-level measurement precision.

Description

Technical Field

[0001] The present invention relates to the field of microwave ranging technology, and in particular to a high time response ranging method and device based on photogenerated microwave chirped pulses. Background Art

[0002] Microwave-based non-contact high-time-resolution ranging technology has attracted great attention in the past decade due to its 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 primarily include single-frequency microwave interferometry, pulsed ultra-wideband microwave radar, and frequency-modulated continuous wave (FMCW) radar. Single-frequency continuous wave (SFCW) radar uses a continuous microwave as a carrier wave to interfere with and demodulate the target's echo signal in the time domain with the transmitted signal, calculating the target's displacement by calculating the phase change. While this technology can achieve micron-level measurement accuracy, its temporal resolution is limited to microseconds and is only suitable for relative distance measurements within the centimeter range. Ultra-wideband radar calculates absolute distance information by measuring the flight time of the same pulsed ultra-wideband microwave signal. While it can achieve absolute distance measurement with nanosecond-level response within tens of meters, its measurement accuracy is limited to the centimeter to millimeter range, which is insufficient for precision machining. Frequency-modulated continuous wave (FMCW) radar uses a microwave with a time-varying frequency as a carrier wave to mix the target's echo signal with the transmitted signal and measure the frequency and phase of the difference frequency signal in the time domain to obtain absolute distance information. Within the measurement range from the X-band to the R-band, this technology currently achieves absolute distance measurement accuracy in the micron or submicron range. However, it requires a high-frequency, high-bandwidth, and highly linear swept microwave source, along with complex error correction algorithms, resulting in a complex and costly system. Furthermore, the response time of an electronically swept microwave source is limited by the sweep rate, typically ranging from hundreds of microseconds to milliseconds. This cannot meet the high-resolution requirements of certain transient processes. To date, wide-range, fast-response microwave absolute distance measurement technology remains a pressing frontier in this field. Summary of the Invention

[0004] The purpose of the present 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 micron-level measurement accuracy.

[0005] To achieve the above-mentioned object, the present invention provides a high time response ranging method based on optically generated microwave chirped pulses, which is used to calculate the absolute distance information R of the object to be measured; the method comprises: step S1, inputting a femtosecond pulse laser and dividing it into two independent optical path beams through an optical coupler; respectively connecting a dispersion optical fiber with different dispersion amounts to the two independent optical path beams to obtain two new optical path beams; step S2, coupling the two new optical path beams through an optical coupler and converting them into linear frequency modulated microwave signals; step S3, using the linear frequency modulated microwave signal as a microwave source and converting it into a transmission signal and a reference signal; step S4, sending the transmission signal to the object to be measured and receiving its echo signal, mixing the echo signal with the reference signal to obtain a beat frequency signal, and then performing Fourier transform to obtain the frequency of the beat frequency signal. , and then get the absolute distance information .

[0006] Preferably, in step S1, the pulse width of the femtosecond pulse laser is and 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 splittings respectively.

[0007] Preferably, in step S1, the pulse expressions of the two new light paths are for:

[0008] , i=1, 2;

[0009] Where t is the time offset of the average delay of the two optical path splitting; For femtosecond pulse laser, it is the Fourier transform of the optical signal after passing through the optical coupler; is the corresponding constant of optical path splitting; is the center frequency of the optical pulse relative to the optical path splitting Angular frequency deviation; is the Fourier transform operator; is the imaginary unit; exp is the exponential function.

[0010] Preferably, in step S1, and The absolute angular frequency Expressed 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, ; is the responsivity of photodetection; is the light field intensity when i=1; is the light field intensity when i=2; is the conjugate operator; is a constant; is the light field intensity amplitude when i=1; is a constant; is the light field intensity amplitude 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, is the central wavelength of the femtosecond pulse laser, is the wavelength width of the femtosecond pulse laser, The speed of light.

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

[0026]

[0027]

[0028] .

[0029] Preferably, the device is used for any of the above-mentioned high time response ranging methods based on optically generated microwave chirped pulses, the device is used to measure the target to be measured, and the device includes: a femtosecond laser, which generates a femtosecond pulse laser, an optical coupler is arranged inside the laser, and the optical coupler divides the femtosecond pulse laser into two optical path branches; a first dispersion compensating optical fiber and a second dispersion compensating optical fiber are respectively connected to the optical coupler of the femtosecond laser to introduce different chirps into the two optical path branches; a photodetector, which has an optical coupler arranged inside the laser, and the optical coupler of the photodetector is respectively connected to the first dispersion compensating optical fiber and the second dispersion compensating optical fiber to convert the optical signal into a linear frequency modulated microwave signal; a power divider is connected to the photodetector, and the linear frequency modulated microwave pulse is used as A microwave source, a power divider divides the microwave signal into a transmission signal and a reference signal; a microwave circulator, the microwave circulator includes a first port, a second port and a third port, and the first port, the second port and the third port are interconnected; the first port is connected to the power divider and is used to receive the transmission signal; the antenna is connected to the second port, receives the transmission signal and transmits it to the target to be measured, and receives the echo signal of the target to be measured; the mixer is respectively connected to the third port and the power divider, receives the echo signal and the reference signal, and mixes them; the oscilloscope is connected to the mixer, collects the mixed signal, and obtains a beat frequency signal; the computer is connected to the oscilloscope, performs Fourier transform on the generated beat frequency signal to obtain a 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 has 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 the present invention is that the single measurement time is only 40 nanoseconds, thereby realizing ultrafast microwave absolute distance measurement with nanosecond time resolution and micron-level accuracy.

[0033] Second, the high-time-response ranging device based on photogenerated microwave chirped pulses proposed in the present 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. This will promote the practical application of non-contact absolute distance measurement based on microwave segments in scientific research, production and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0035] Figure 2 This is a flow chart of a high time response ranging method based on optically generated microwave chirped pulses proposed by the present invention.

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

[0037] Figure 4 The following are the measurement results of 50 measurements on the target.

[0038] Reference numerals:

[0039] 101 - femtosecond laser, 102 - first dispersion-compensating fiber, 103 - second dispersion-compensating fiber, 104 - photodetector, 105 - power divider, 106 - microwave circulator, 107 - antenna, 108 - mixer, 109 - oscilloscope, 110 - computer, 111 - target to be measured, 1 - first port, 2 - second port, 3 - third port. DETAILED DESCRIPTION

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

[0041] It should be noted that the drawings are in a very simplified form and use non-precise proportions. They are only used to conveniently and clearly assist in explaining the embodiments of the present invention, and are not used to limit the conditions for the implementation of the present invention. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

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

[0043] The present 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 the characteristic of frequency varying with time. They combine the efficient conversion technology of "photogenerated microwaves" with the frequency modulation characteristics of "chirped pulses" and have important applications in radar, communications, spectroscopy and other fields.

[0044] "Photogenerated microwaves" refers to the technology of converting optical signals into microwave signals through optical means (such as optical mixing and photoelectric conversion). By frequency-modulating or modulating optical signals, high-frequency, high-purity microwaves can be generated, breaking through the high-frequency and broadband bottlenecks of traditional electronic methods.

[0045] A chirped pulse is a signal whose instantaneous frequency varies with time. For example, a linearly chirped pulse has a frequency that increases linearly ("up-chirp") or decreases ("down-chirp") with time; a nonlinear chirp has a frequency that varies nonlinearly with time (e.g., a quadratic curve). This chirping property offers unique advantages in the two-dimensional "time-frequency" domain (e.g., high-resolution measurements through frequency sweeps).

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

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

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

[0049] Step S2, splitting the two new optical paths and coupling them through an optical coupler to convert them into linear frequency modulated microwave signals;

[0050] Step S3, using the linear frequency modulated microwave signal as a microwave source to convert it into a transmission signal and a reference signal;

[0051] Step S4: Send the transmission signal to the object to be measured, and receive its echo signal, mix the echo signal with the reference signal to obtain a beat signal, and then perform Fourier transform to obtain the frequency of the beat signal. , and then get the absolute distance information .

[0052] Specifically, in step S1, the pulse width of the femtosecond pulse laser is and 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 splittings respectively.

[0053] Furthermore, due to the frequency-time mapping effect caused by the dispersion fiber, the pulses split into two optical paths are broadened in the time domain;

[0054] Therefore, in step S1, the pulse expression of the two new light paths is for:

[0055] , i=1, 2;

[0056] Where t is the time offset of the average delay of the two optical path splitting; For femtosecond pulse laser, it is the Fourier transform of the optical signal after passing through the optical coupler; is the corresponding constant of optical path splitting; is the center frequency of the optical pulse relative to the optical path splitting Angular frequency deviation; is the Fourier transform operator; is the imaginary unit; exp is the exponential function; and then we get and .

[0057] Will and Convert to absolute angular frequency This means:

[0058] , i=1, 2;

[0059] t=n×T, n=2, 3, 4, 5;

[0060] Therefore, the time delay of the two independent light path splits is adjusted to an integer multiple of the pulse period T of the two independent light path splits, which means that the light pulses of the two independent light path splits can reach the optical coupler in step S2 at the same time and interfere with each other.

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

[0062]

[0063] in, ; is the responsivity of photodetection; is the light field intensity when i=1; is the light field intensity when i=2; is the conjugate operator; is a constant; is the light field intensity amplitude when i=1; is a constant; is the light field intensity amplitude when i=2; For phase.

[0064] According to the differential relationship between the phase factor and the 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, is the central wavelength of the femtosecond pulse laser, is the wavelength width of the femtosecond pulse laser, The speed of light.

[0072] Specifically, the linear chirped microwave pulse generated in step S3 is used as a microwave source, transmitted through an antenna, and converted into a transmission signal and a reference signal. The principle here is that the reference signal and the transmission signal will produce a time delay. ( ), where R represents the absolute distance information of the target object and c represents the speed of light. Therefore, the subsequent , 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. , and then get the absolute distance information .

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

[0075]

[0076]

[0077] .

[0078] In addition, if Figure 1 As shown, the present invention also proposes a high time response ranging device based on optically generated microwave chirped pulses; wherein, the solid line represents light wave 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] Femtosecond laser 101 generates femtosecond pulsed laser light and is internally provided with a 50:50 optical coupler (not shown in the figure) that splits the femtosecond pulsed laser light into two optical branches. Of course, the optical coupler can also be provided external to femtosecond laser 101, and this is not a limitation here. Those skilled in the art can configure it according to actual circumstances.

[0081] The first dispersion-compensating fiber 102 and the second dispersion-compensating 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 disposed therein. The optical coupler of the photodetector 104 is connected to the first dispersion-compensating optical fiber 102 and the second dispersion-compensating optical fiber 103, respectively, to convert the optical signal into a linear frequency-modulated microwave signal. The optical coupler can also be disposed outside the photodetector 104, and this is not limited here. Persons skilled in the art can configure the optical coupler according to actual circumstances.

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

[0084] A microwave circulator 106, comprising a first port 1, a second port 2, and a third port 3, wherein the first port 1, the second port 2, and the third port 3 are interconnected; the first port 1 is connected to the power divider 105 for receiving a transmission signal;

[0085] The antenna 107 is connected to the second port 2, receives the transmission signal and transmits it to the target 111 to be measured, and receives the echo signal of the target 111 to be measured;

[0086] 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;

[0087] an oscilloscope 109 connected to the mixer 108 to collect the mixed signal and obtain a beat frequency signal;

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

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

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

[0091] The bandwidth of the power divider is 6-18 GHz, the bandwidth of the antenna is 7-13 GHz, the bandwidth of the microwave circulator is 7-12.4 GHz, the bandwidth of the RF / LO of the mixer is 10-44 GHz, the bandwidth of the intermediate frequency (IF) is DC-14 GHz, the target to be measured is a metal plate, and the measurement distance is about 40 cm. The Fourier transform waveform of the beat frequency signal obtained in the experiment is as follows: Figure 3 shown.

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

[0093] In summary, it can be seen that the present invention, based on the FMCW radar ranging principle, builds a simple microwave absolute distance measurement device, which achieves absolute distance measurement with a time resolution of 50 nanoseconds and an accuracy of 100 microns.

[0094] This invention utilizes a microwave absolute distance measurement device and method with a simple structure, sub-microsecond temporal resolution, and micron-level measurement accuracy. Under unbalanced dispersion conditions, femtosecond laser interferometry generates nanosecond linear frequency-modulated microwave pulses. This is then applied using the principles of frequency-modulated continuous wave (FMCW) radar to achieve high temporal resolution absolute distance measurement. The technology described in this patent enables high temporal resolution and high-precision absolute distance measurement using existing commercial components.

[0095] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. After reading the above description, various modifications and substitutions of the present invention will become apparent to those skilled in the art. 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 optically generated microwave chirped pulses, characterized in that: For calculating the absolute distance information R of the object to be measured; the method comprises: Step S1: input a femtosecond pulse laser and split it into two independent optical path beams through an optical coupler; connect dispersive optical fibers with different dispersion amounts to the two independent optical path beams to obtain two new optical path beams; Step S2, splitting the two new optical paths and coupling them through an optical coupler to convert them into linear frequency modulated microwave signals; Step S3, using the linear frequency modulated microwave signal as a microwave source to convert it into a transmission signal and a reference signal; Step S4: Send the transmission signal to the object to be measured, and receive its echo signal, mix the echo signal with the reference signal to obtain a beat signal, and then perform Fourier transform to obtain the frequency of the beat signal. , and then get the absolute distance information .

2. The high time response ranging method based on optically generated microwave chirped pulses according to claim 1, characterized in that: In step S1, the pulse width of the femtosecond pulse laser is and 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 splittings respectively.

3. The high time response ranging method based on optically generated microwave chirped pulses according to claim 2, characterized in that: In step S1, the pulse expression of the two new light paths is for: ，i=1、2； Where t is the time offset of the average delay of the two optical path splitting; For femtosecond pulse laser, it is the Fourier transform of the optical signal after passing through the optical coupler; is the corresponding constant of optical path splitting; is the center frequency of the optical pulse relative to the optical path splitting Angular frequency deviation; is the Fourier transform operator; is the imaginary unit; exp is the exponential function.

4. The high time response ranging method based on optically generated microwave chirped pulses according to claim 3, characterized in that: In step S1, and The absolute angular frequency Expressed as: ，i=1、2； t=n×T, n=2, 3, 4, 5; Where T is the pulse period.

5. The high time response ranging method based on optically generated microwave chirped pulses according to claim 4, characterized in that: In step S2, the linear frequency modulated microwave signal is: in, ; is the responsivity of photodetection; is the light field intensity when i=1; is the light field intensity when i=2; is the conjugate operator; is a constant; is the light field intensity amplitude when i=1; is a constant; is the light field intensity amplitude when i=2; For phase.

6. The high time response ranging method based on optically generated microwave chirped pulses according to claim 5, 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 pulse and bandwidth for: in, is the central wavelength of the femtosecond pulse laser, is the wavelength width of the femtosecond pulse laser, The speed of light.

7. The high time response ranging method based on optically generated microwave chirped pulses according to claim 6, characterized in that: In step S4, the absolute distance information for: 。 8. A high time response ranging device based on optically generated microwave chirped pulses, characterized in that: The device is used to implement a high time response ranging method based on photogenerated microwave chirped pulses as described in any one of claims 1 to 7, and the device is used to measure a target (111) to be measured, and the device comprises: A femtosecond laser (101) generates femtosecond pulse laser light, wherein an optical coupler is provided inside the femtosecond laser light, and the optical coupler divides the femtosecond pulse laser light into two optical path branches; The first dispersion-compensating optical fiber (102) and the second dispersion-compensating optical 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; A photodetector (104) is provided with an optical coupler therein, wherein the optical coupler of the photodetector (104) is connected to the first dispersion-compensating optical fiber (102) and the second dispersion-compensating optical fiber (103) respectively to convert the optical signal into a linear frequency-modulated microwave signal; A power divider (105) is connected to the photodetector (104), wherein the linear frequency modulated microwave pulse is used as a microwave source, and the power divider (105) divides the microwave signal into a transmission signal and a reference signal; A microwave circulator (106), the microwave circulator (106) comprising a first port (1), a second port (2) and a third port (3), wherein the first port (1), the second port (2) and the third port (3) are interconnected; the first port (1) is connected to the power distributor (105) and is used to receive a transmission signal; An antenna (107) is connected to the second port (2), receives a transmission signal and transmits it to the target to be measured (111), and receives an echo signal from the target to be measured (111); A 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 the mixer (108) to collect the mixed signal and obtain a beat frequency signal; The computer (110) is connected to the oscilloscope (109) and performs Fourier transform on the generated beat frequency signal to obtain a frequency value, thereby calculating and obtaining absolute distance information.

9. The high time response ranging device based on optically generated microwave chirped pulses according to claim 8, characterized in that: The optical coupler of the femtosecond laser (101) is 50:50; the optical coupler of the photodetector (104) is 50:50.

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