Laser measurement system and method

Abstract

The present disclosure provides a laser measurement system and method, which is applied to the field of microwave photon technology. The system comprises an antenna, a microwave source, a laser, a polarization controller, a double parallel Mach-Zehnder modulator, an electrical coupler, a photoelectric detector and a signal processing module. The antenna is used to receive a return signal, the microwave source is used to emit a reference signal, the polarization controller controls the polarization direction of the optical carrier emitted by the laser, the return signal and the reference signal are modulated onto the optical carrier with the controlled polarization direction through the double parallel Mach-Zehnder modulator, and a modulated optical signal is output, the modulated optical signal enters the signal processing module after frequency mixing processing by the photoelectric detector, and the signal processing module outputs a final result to obtain the measurement results of Doppler shift and angle of arrival at the same time. The present disclosure can realize the simultaneous measurement of Doppler shift and angle of arrival, determine the direction of Doppler shift, and is not limited by electromagnetic interference and working bandwidth, and has a very large working bandwidth.

Description

Technical Field

[0001] This disclosure relates to the field of microwave photonics technology, and in particular to a laser measurement system and method. Background Technology

[0002] In radar ranging, autonomous driving, wireless communication, and other emerging fields, obtaining the position and velocity of moving objects is of great significance. The Doppler shift, calculated by subtracting the frequency of the received echo signal from the frequency of the transmitted radar signal, carries the velocity and direction parameters of the moving object. Measuring the angle of arrival (Angle of Arrival) of the echo signal allows for precise identification of the object's location. Therefore, in practical applications, the position, direction, and speed of a moving target can be accurately determined using Doppler shift and Angle of Arrival (AHA). Traditional measurement methods are typically based on electrical systems; however, due to limitations imposed by electronic bottlenecks such as narrow measurement bandwidth, weak anti-interference capabilities, high transmission loss, high measurement costs, and low measurement sensitivity, electrical methods are difficult to implement when the measured frequency is in the megahertz to terahertz range.

[0003] In recent years, with the development and rise of microwave photonics, researchers have begun to consider using microwave photonics technology to measure Doppler frequency shift and angle of arrival due to its many advantages, such as strong anti-electromagnetic interference capability, large bandwidth, low loss, high sensitivity, high stability, small size, and low cost. However, existing technical solutions can only measure Doppler frequency shift or angle of arrival individually, and cannot achieve simultaneous measurement of Doppler frequency shift and angle of arrival. Summary of the Invention

[0004] In view of the above problems, this disclosure provides a laser measurement system and method to solve the problems of narrow working bandwidth and inability to simultaneously measure Doppler frequency shift and angle of arrival in the prior art.

[0005] The first aspect of this disclosure provides a laser measurement system, comprising:

[0006] Antenna, microwave source, laser, polarization controller, dual parallel Mach-Zehnder modulator, photodetector and signal processing module;

[0007] The antenna is used to receive a preset echo signal;

[0008] The microwave source is used to emit a reference signal;

[0009] The laser is used to emit a first optical carrier wave;

[0010] The polarization controller is used to control the polarization direction of the first optical carrier to obtain the second optical carrier;

[0011] The dual parallel Mach-Zehnder modulator is used to modulate the preset echo signal and the reference signal onto the second optical carrier to obtain a modulated optical signal.

[0012] The photodetector is used to perform beat frequency processing on the modulated optical signal and convert the modulated optical signal into an electrical signal.

[0013] The signal processing module is used to receive the electrical signal and calculate the measurement results of Doppler frequency shift and angle of arrival.

[0014] According to embodiments of this disclosure, the preset echo signal includes a first echo signal and a second echo signal, and the antenna includes:

[0015] First antenna and second antenna;

[0016] The first antenna is used to receive the first echo signal;

[0017] The second antenna is used to receive the second echo signal.

[0018] According to an embodiment of this disclosure, the measurement system further includes an electrical coupler for combining the first echo signal and the reference signal to obtain a back-reference signal.

[0019] According to embodiments of this disclosure, the dual parallel Mach-Zehnder modulator includes:

[0020] Branch beam splitter, first sub-Mach-Zehnder modulator, second sub-Mach-Zehnder modulator and polarization beam combiner;

[0021] The branch beam splitter divides the second optical carrier into two beams on average, based on the optical power of the second optical carrier, to obtain a third optical carrier and a fourth optical carrier.

[0022] The first sub-Mach-Zehnder modulator is used to receive the third optical carrier and the second echo signal to obtain the first pre-modulated optical signal;

[0023] The second sub-Mach-Zehnder modulator is used to receive the fourth optical carrier and the back-reference signal to obtain the second pre-modulated optical signal;

[0024] The polarization combiner is used to combine the first pre-modulated optical signal and the second pre-modulated optical signal to obtain a modulated optical signal.

[0025] According to embodiments of this disclosure, both the first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator are push-pull Mach-Zehnder modulators.

[0026] The first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator are connected in parallel.

[0027] Both the first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator have an RF input port and a DC bias port.

[0028] According to embodiments of this disclosure, the dual parallel Mach-Zehnder modulator further includes a main DC bias port;

[0029] The main DC bias port is used to adjust the phase between the first pre-modulated optical signal and the second pre-modulated optical signal.

[0030] According to embodiments of this disclosure, the branch beam splitter is a 3dB Y-branch beam splitter.

[0031] According to an embodiment of this disclosure, the first optical carrier is continuously linearly polarized light.

[0032] A second aspect of this disclosure provides a laser measurement method applied to the laser measurement system described in the first aspect above, the method comprising:

[0033] Receive a preset echo signal using an antenna;

[0034] A reference signal is emitted using a microwave source;

[0035] The first optical carrier wave is emitted using a laser;

[0036] The polarization direction of the first optical carrier is controlled by a polarization controller to obtain the second optical carrier;

[0037] The preset echo signal and the reference signal are modulated onto the second optical carrier using a dual parallel Mach-Zehnder modulator to obtain a modulated optical signal;

[0038] The modulated optical signal is processed by a photodetector to convert it into an electrical signal.

[0039] The electrical signal is received using a signal processing module, and the measurement results of Doppler frequency shift and angle of arrival are calculated.

[0040] According to the laser measurement system and method provided in this disclosure, the optical carrier is modulated by a dual parallel Mach-Zehnder modulator. It can simultaneously measure the Doppler frequency shift and angle of arrival without the need for filtering elements such as filters and wavelength division multiplexing. It can also determine the direction of the Doppler frequency shift. The measurement system is simple and has a very large working bandwidth. Attached Figure Description

[0041] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0042] Figure 1 A schematic diagram of the structure of a laser measurement system according to an embodiment of the present disclosure is shown.

[0043] Figure 2 The schematic diagram illustrates a flow chart of a laser measurement method according to an embodiment of the present disclosure;

[0044] Figure labeling: 1-Laser; 2-Polarization controller; 3-First sub-Mach-Zehnder modulator; 4-Second sub-Mach-Zehnder modulator; 5-Photodetector; 6-First antenna; 7-Second antenna; 8-Signal processing module. Detailed Implementation

[0045] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0046] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0047] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0048] Figure 1 A schematic diagram of the structure of a laser measurement system according to an embodiment of the present disclosure is shown, such as... Figure 1 As shown, it includes:

[0049] Antenna, microwave source, laser, polarization controller, dual parallel Mach-Zehnder modulator, photoelectric detection and signal processing module;

[0050] This antenna is used to receive a preset echo signal;

[0051] This microwave source is used to emit a reference signal;

[0052] The laser 1 is used to emit the first optical carrier;

[0053] The polarization controller 2 is used to control the polarization direction of the first optical carrier to obtain the second optical carrier;

[0054] The dual parallel Mach-Zehnder modulator is used to modulate the preset echo signal and the reference signal onto the second optical carrier to obtain a modulated optical signal.

[0055] The photodetector 5 is used to perform beat frequency processing on the modulated optical signal and convert the modulated optical signal into an electrical signal.

[0056] The signal processing module 8 is used to receive the electrical signal and calculate the measurement results of Doppler frequency shift and angle of arrival.

[0057] In one embodiment of this disclosure, the preset echo signal includes a first echo signal and a second echo signal; the antenna includes a first antenna 6 and a second antenna 7, the first antenna 6 being used to receive the first echo signal; and the second antenna 7 being used to receive the second echo signal.

[0058] In one embodiment of this disclosure, the measurement system further includes an electrical coupler for combining the first echo signal and the reference signal to obtain a back reference signal.

[0059] In one embodiment of this disclosure, the dual parallel Mach-Zehnder modulator includes: a branch beam splitter, a first sub-Mach-Zehnder modulator 4, a second sub-Mach-Zehnder modulator 5, and a polarization beam combiner; the branch beam splitter splits the second optical carrier into two beams equally according to the optical power of the second optical carrier, to obtain a third optical carrier and a fourth optical carrier; the first sub-Mach-Zehnder modulator 4 is used to receive the third optical carrier and the second echo signal to obtain a first pre-modulated optical signal; the second sub-Mach-Zehnder modulator 5 is used to receive the fourth optical carrier and the echo signal to obtain a second pre-modulated optical signal; the polarization beam combiner combines the first pre-modulated optical signal and the second pre-modulated optical signal to obtain a modulated optical signal.

[0060] In one embodiment of this disclosure, both the first sub-Mach-Zehnder modulator 4 and the second sub-Mach-Zehnder modulator 5 are push-pull Mach-Zehnder modulators. The first sub-Mach-Zehnder modulator 4 and the second sub-Mach-Zehnder modulator 5 are connected in parallel. Both the first sub-Mach-Zehnder modulator 4 and the second sub-Mach-Zehnder modulator 5 have an RF input port and a DC bias port.

[0061] In one embodiment of this disclosure, the dual parallel Mach-Zehnder modulator further includes a main DC bias port for adjusting the phase between the first pre-modulated optical signal and the second pre-modulated optical signal.

[0062] In one embodiment of this disclosure, the branch beam splitter is a 3dB Y-branch beam splitter.

[0063] In one embodiment of this disclosure, the first optical carrier is continuously linearly polarized light.

[0064] Figure 2 The schematic diagram illustrates a flow chart of a laser measurement method according to an embodiment of the present disclosure, which utilizes, for example... Figure 1 The measurement system shown is implemented.

[0065] The laser measurement method includes steps S201-S207.

[0066] In operation S201, the antenna is used to receive a preset echo signal;

[0067] In operation S202, a reference signal is emitted using a microwave source;

[0068] In operation S203, the first optical carrier is emitted using a laser;

[0069] In operation S204, the polarization direction of the first optical carrier is controlled by a polarization controller to obtain the second optical carrier;

[0070] In operation S205, the preset echo signal and the reference signal are modulated onto the second optical carrier using a dual parallel Mach-Zehnder modulator to obtain a modulated optical signal.

[0071] In operation S206, the modulated optical signal is processed by a photodetector to convert the modulated optical signal into an electrical signal.

[0072] In operation S207, the electrical signal is received by the signal processing module, and the measurement results of Doppler frequency shift and angle of arrival are calculated.

[0073] The specific principles and steps of this method are as follows:

[0074] Let E0 denote the amplitude of the continuous linearly polarized light generated by the laser, and ω denote its angular frequency. c Then the continuous linearly polarized light can be represented as:

[0075]

[0076] The amplification factors of the reference signal and the echo signal are denoted as V. r and V eThe angular frequencies of the reference signal and the echo signal are denoted as ω. r and ω e Let θ be the phase difference between the two echo signals. Then the reference signal, the first echo signal, and the second echo signal can be expressed as follows:

[0077]

[0078] θ is the phase difference caused by the time delay τ in the arrival of the echo signal at the two antennas due to the different positions of the first and second antennas. Therefore, the phase difference θ can be expressed as θ = ω. e τ, since the angle of arrival α will have the following relationship with the time delay τ:

[0079]

[0080] Where c is the velocity of the microwave signal in vacuum, d is the distance between the two antennas, and α is the angle of arrival of the echo signal to the antenna. Setting d to λ / 2, where λ is the wavelength of the optical carrier, the relationship between the angle of arrival α and the phase difference θ between the two echo signals is established as follows:

[0081]

[0082] Among them, due to Therefore, the relationship between the angle of arrival α and the phase difference θ between the two echo signals can be transformed into:

[0083]

[0084] The angle of arrival α can be calculated by solving for the phase difference θ between the two echo signals.

[0085] Specifically, the laser measurement method includes the following steps:

[0086] E, the continuous linearly polarized light generated by the laser in (t) is used as the first optical carrier. After the polarization direction is controlled by the polarization controller, it is used as the second optical carrier and input to the dual parallel Mach-Zehnder modulator. The 3dBY branch beam splitter in the dual parallel Mach-Zehnder modulator distributes the second optical carrier equally to the first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator according to the power, so as to obtain the third optical carrier and the fourth optical carrier respectively.

[0087] The first sub-Mach-Zehnder modulator connects the second echo signal received by the second antenna to its input RF port. Adjusting the DC bias voltage ensures the first sub-Mach-Zehnder modulator operates at its minimum transmission point, thus achieving phase modulation of the third optical carrier to obtain the first pre-modulated optical signal. Simultaneously, the second sub-Mach-Zehnder modulator receives the fourth optical carrier. An electrocoupler combines the reference signal emitted by the microwave source with the first echo signal received by the first antenna, and then directly inputs this combination to the RF input port of the second sub-Mach-Zehnder modulator. Adjusting the DC bias voltage also ensures the second sub-Mach-Zehnder modulator operates at its minimum transmission point, thus achieving phase modulation of the fourth optical carrier to obtain the second pre-modulated optical signal.

[0088] Since the second-order and higher sidebands can be directly ignored due to their low power under small-signal modulation, the first pre-modulated optical signal and the second pre-modulated optical signal can be expressed as follows:

[0089]

[0090]

[0091] Where, β e ,β r These are the modulation depths of the echo signal and the reference signal in the dual parallel Mach-Zehnder modulator, β. e =πV e / V π ,β r =πV r / V π V π J represents the half-wave voltage of the dual parallel Mach-Zehnder modulator. n (β) is a Bessel function of the first kind of nth order, where j is the imaginary unit.

[0092] Adjusting the main DC bias port of the dual-parallel Mach-Zehnder modulator to operate at the quadrature bias point achieves phase modulation between the first and second pre-modulated optical signals. Then, the phase-modulated first and second pre-modulated optical signals are combined by the polarization combiner in the dual-parallel Mach-Zehnder modulator to obtain the modulated optical signal. Therefore, the modulated optical signal can be expressed as E3(t) = E1(t) + E2(t), i.e.

[0093]

[0094] The modulated optical signal is converted into an electrical signal by a photodetector, which is then input into the signal processing system. Since the photodetector is a low-speed photodetector, the high-frequency signal is directly filtered out, retaining only the low-frequency signal. Therefore, the detected electrical signal can be expressed as:

[0095]

[0096] in,

[0097] A=2J0(β e )J1(β e )J1(β r )

[0098] B = J0(β) e )J0(β r )J1(β e )J1(β r )

[0099]

[0100] ω IF =ω r -ω e

[0101] ω IF It is the angular frequency of the output photocurrent. This is due to the difference between the echo signal and the reference signal f. DFS f t f e , and f r These are the Doppler frequency shift, the frequencies of the transmitted signal, the echo signal, and the reference signal, respectively. A 3MHz low-frequency signal is mixed with the transmitted signal using an electrical mixer to set the reference signal frequency to be 3MHz higher than the transmitted signal frequency.

[0102] f DFs =f e -f t

[0103] f r =f t +3MHz

[0104] Therefore, it can be deduced from this disclosure that:

[0105] f DFs =3MHz-f IF

[0106] Among them, f IF This is the frequency of the output electrical signal. From this, the magnitude of the Doppler frequency shift can be calculated, and f... IF It can also determine the sign of the Doppler frequency shift. When the IF is between 2 and 3 MHz, it corresponds to a positive Doppler frequency shift, indicating that the object is close to the radar antenna. When the IF is between 3 and 4 MHz, it corresponds to a negative Doppler frequency shift, indicating that the object is moving away from the radar antenna.

[0107] The power of an electrical signal can be calculated from the electrical signal itself.

[0108] P(θ)∝A 2 +B 2 +2ABcos(θ)

[0109] As can be seen, the output electrical signal power is maximized when the phase difference θ between the two echo signals is 0°. As the phase difference increases, the output electrical signal power gradually decreases, reaching its minimum when θ equals 180°. The output electrical signal power depends not only on system factors such as optical power, modulator insertion loss, and detector responsivity, but also on the input signal power. Therefore, normalization of the output electrical signal power is necessary. The output electrical signal power P is calculated when the phase difference is 0°. θ＝0° And the output electrical signal power P when the phase difference is 180° θ＝180° The normalized output power function can be expressed as:

[0110]

[0111] As can be seen from the above formula, normalizing the output electrical signal power eliminates the influence of the above factors. The normalized output power function is only related to the phase difference θ. Therefore, by constructing a mapping curve between the output electrical signal power and the phase difference of the echo signal, and combining it with the relationship between the phase difference and the angle of arrival, the angle of arrival of the echo signal can be calculated from the output electrical signal power.

[0112] In summary, the laser measurement system and method provided in this embodiment can simultaneously measure Doppler frequency shift and angle of arrival, and also determine the direction of Doppler frequency shift. The system has a simple structure, does not require the use of filters or wavelength division multiplexing and other filtering components, is not limited by electromagnetic interference, improves the system's operating frequency band, and gives the system a large operating bandwidth.

[0113] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0114] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A laser measurement system, characterized in that, include: First antenna, second antenna, microwave source, laser, polarization controller, dual parallel Mach-Zehnder modulator, photodetector, signal processing module and electrical coupler; The first antenna is used to receive the first echo signal; The second antenna is used to receive the second echo signal; The microwave source is used to emit a reference signal; The electrical coupler is used to combine the first echo signal and the reference signal to obtain the echo reference signal; The laser is used to emit a first optical carrier wave; The polarization controller is used to control the polarization direction of the first optical carrier to obtain the second optical carrier; The dual-parallel Mach-Zehnder modulator includes: a beam splitter, a first sub-Mach-Zehnder modulator, a second sub-Mach-Zehnder modulator, and a polarization combiner; the beam splitter is used to split the second optical carrier into two beams equally according to the optical power of the second optical carrier, to obtain a third optical carrier and a fourth optical carrier; the first sub-Mach-Zehnder modulator is used to receive the third optical carrier and the second echo signal to obtain a first pre-modulated optical signal; the second sub-Mach-Zehnder modulator is used to receive the fourth optical carrier and the echo signal to obtain a second pre-modulated optical signal; the polarization combiner is used to combine the first pre-modulated optical signal and the second pre-modulated optical signal to obtain a modulated optical signal; The photodetector is used to perform beat frequency processing on the modulated optical signal and convert the modulated optical signal into an electrical signal. The signal processing module is used to receive the electrical signal and calculate the measurement results of Doppler frequency shift and angle of arrival.

2. The laser measurement system according to claim 1, characterized in that, Both the first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator are push-pull Mach-Zehnder modulators. The first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator are connected in parallel. Both the first sub-Mach-Zehnder modulator and the second sub-Mach-Zehnder modulator have an RF input port and a DC bias port.

3. The laser measurement system according to claim 1, characterized in that, The dual parallel Mach-Zehnder modulator also includes a main DC bias port; The main DC bias port is used to adjust the phase between the first pre-modulated optical signal and the second pre-modulated optical signal.

4. The laser measurement system according to claim 1, characterized in that, The type of branch beam splitter is a 3dB Y-branch beam splitter.

5. The laser measurement system according to claim 1, characterized in that, The first optical carrier is continuously linearly polarized light.

6. A laser measurement method, characterized in that, The method, applied to the laser measurement system according to any one of claims 1-5, comprises: Receive preset echo signals using an antenna; A reference signal is emitted using a microwave source; The first optical carrier wave is emitted using a laser; The polarization direction of the first optical carrier is controlled by a polarization controller to obtain the second optical carrier; The preset echo signal and the reference signal are modulated onto the second optical carrier using a dual parallel Mach-Zehnder modulator to obtain a modulated optical signal; The modulated optical signal is processed by a photodetector to convert it into an electrical signal. The electrical signal is received using a signal processing module, and the measurement results of Doppler frequency shift and angle of arrival are calculated.

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