CN116961765A - Photon generation method of switchable multi-format chirp signal based on DP-BPSK - Google Patents

Abstract

The invention discloses a photon generation method of a switchable multi-format chirp signal based on DP-BPSK, and relates to the technical fields of radar, optical communication and microwaves. The scheme is shown in figure 1 of the specification, and comprises a light source LD, a local oscillation signal LO, an arbitrary waveform generator AWG, a 90-degree electric phase shifter, a single-mode fiber SMF and a photoelectric detector PD. The proposal utilizes a DP-BPSK modulator to modulate and polarization multiplex the microwave local oscillation signal and the cutting parabola waveform signal, and the output optical signal can realize the flexible switching of the up-down and double chirp signals through the photoelectric detector. The invention adopts N times of split parabolic waveform signals, and improves the time bandwidth product TBWP of the generated chirp signals by N/2 times. The signal generator has multi-format switchable capability, frequency adjustability, long-distance transmission capability, attenuation resistance capability and pulse compression capability, and has potential application scenes in modern radar systems.

Description

Photon generation method of switchable multi-format chirp signal based on DP-BPSK

Technical Field

The invention relates to the technical fields of radars, optical communication and microwaves, and mainly relates to a method for generating multi-format switchable chirp signals by utilizing optical technology.

Background

Chirp signals play an important role in pulse compression in modern radar systems and have been increasingly attractive for decades. In order to provide complete insight into the target, modern radar systems increasingly require signals with multiple formats and large time-bandwidth products (TBWP). Conventional electronic devices often have problems of narrow operating bandwidth, low carrier frequency, low sampling rate, etc., and thus it is difficult to generate a chirp signal having a large TBWP in the electric domain. The generation of the chirp signal by adopting photon assistance has the characteristics of large bandwidth, small loss and good tunability, and is a signal generation technology with great development prospect.

The microwave photon has the advantages of large instantaneous bandwidth, small volume, small power consumption, strong electromagnetic interference resistance and capability of processing a plurality of information points in parallel, so that the optical generation technology of the multi-format switchable chirp signal gradually becomes the key point of research.

In order to obtain a chirp signal with a large TBWP, various schemes for photon-assisted chirp signal generation have emerged. By establishing a free space optical system based on frequency domain-time domain mapping, a chirp signal with larger TBWP is obtained, however, the system has the defects of large volume and large loss. In addition, the optical signal in the laser can be injected into two main lasers through the semiconductor, and one of the main lasers is properly controlled, so that the chirp signal can be obtained. However, the use of multiple lasers increases the phase noise of the optical link and optical path separation reduces the stability of the system. In addition, in the method of generating a large chirp signal by utilizing the characteristics of optical devices such as a linearly chirped fiber bragg grating, the frequency tunability of the obtained linearly chirped signal is poor due to the limitation of the bandwidth of the linearly chirped fiber bragg grating. Based on optical polarization multiplexing, the DP-QPSK modulator faces the problem of bias voltage drift by using the chirp signal generated by the integrated double-polarization quadrature phase shift keying DP-QPSK modulator. The frequency stepping chirp signal of large TBWP generated by the optical frequency shift ring is established, and better time delay matching is difficult to control. The parabolic waveform signal is modulated by the phase modulator PM, so that a chirp signal of limited TBWP can be generated, but the chirp signal is easily influenced by the maximum input power of the modulator, and the problem can be solved by splitting the parabolic waveform signal to carry out phase modulation, and the obtained chirp signal is related to the division times of the TBWP. Accurate phase shifting of the chirp signal is difficult, and switchable multi-format chirp signals are obtained by shifting the phase of the input signal and adjusting the bias voltage of the QP-QPSK modulator, but the QP-QPSK modulator cannot be controlled by a commercial bias controller. By adjusting the bias voltage, a switchable multi-band chirp signal can be generated using a dual parallel mach-zehnder modulator. Therefore, in order to complete the switching of the signal multi-format, the power of the input signal needs to be precisely controlled, which is also an urgent requirement of the radar system.

Disclosure of Invention

In order to solve the problems in the technical background, the invention utilizes a dual-polarization binary phase shift keying modulator DP-BPSK to realize a photon generation method of the switchable multi-format chirp signal. The method uses two parallel double-drive Mach-Zehnder modulators DD-MZMs, wherein the upper-path DD-MZM1 works at the minimum point, and phase shift is introduced by adjusting the bias voltage of DD-MZM2A chirp signal of various formats can be obtained. When the phase shift is->When the chirp signals are respectively set to pi/2, -pi/2 and 0, the lower, upper and double chirp signals can be generated, and the generation of the multi-format switchable chirp signals is realized. The use of N split parabolic waveform signals increases the resulting time-bandwidth product by a factor of N/2.

The technical scheme adopted for solving the technical problems is as follows: the device comprises a laser LD 1, a dual polarization binary phase shift keying modulator DP-BPSK 2, an arbitrary waveform generator AWG 3, a local oscillation signal LO 4, an electric phase shifter 590 DEG, a single-mode optical fiber SMF 6 and a photoelectric detector PD 7. The method is characterized in that linearly polarized light generated by a laser LD is sent into DP-BPSK, split parabolic waveform signals generated by an AWG drive DD-MZM1 and DD-MZM2 modulators respectively, one path of local oscillation signal LO is directly connected into the DD-MZM1, the other path of local oscillation signal LO is connected into the DD-MZM2 after 90-degree phase shift, the DD-MZM1 works at a minimum transmission point MITP, and the format of an output signal can be changed by adjusting the bias voltage of the DD-MZM2. After photoelectric conversion is completed on the modulated signal through high-speed PD, chirp signals with various formats can be obtained, and finally, the modulated signal can be connected with an oscilloscope or a spectrometer for analysis.

The dual-polarization binary phase shift keying modulator DP-BPSK consists of a Y-type optical splitter, two parallel dual-drive terahertz Zehnder modulators DD-MZMs respectively named DD-MZM1 and DD-MZM2, a 90-degree polarization rotator PR and a polarization beam combiner PBC.

The bias voltage of the modulator can be controlled by a bias controller on the market, so that the whole structure is stable and easy to control. The anti-interference performance of the invention on power attenuation enables the system to improve the survivability of the radar system in distributed deployment. In addition, the generation of the chirp signal using a split parabolic waveform signal can greatly increase the TBWP of the signal.

The invention comprises the following steps in working:

(1) A continuous optical carrier wave having a wavelength lambda from a laser is injected into the DP-BPSK modulator.

(2) One path of the cutting parabolic signal generated by the arbitrary waveform generator AWG is directly connected into the DD-MZM1, and the other path of the cutting parabolic signal is directly connected into the DD-MZM2. The TBWP of the chirp signal is obtained by phase modulating the split parabolic waveform signal.

(3) One path of local oscillation LO signal is directly connected into DD-MZM1, and the other path of local oscillation LO signal is connected into DD-MZM2 after 90-degree phase shift, the DD-MZM1 works at the minimum point, and the flexible switching of the up-down and double chirp signals can be realized by adjusting the working point of the DD-MZM2. The signals modulated by the DD-MZM1 and the DD-MZM2 are combined through PBC polarization to form a polarization multiplexing signal.

(4) The polarization beam combiner in the DP-BPSK combines the optical signals modulated by the upper path and the lower path into polarization multiplexing light, and the output modulator is injected into a Single Mode Fiber (SMF) to realize remote transmission.

(5) Finally, the polarization multiplexing signal output by the DP-BPSK enters the PD to carry out photoelectric detection, and the PD belongs to coherent detection, and after the polarization multiplexing signal is input, beat frequency can be carried out on the same polarization state, and the PD belongs to one polarization state, so that the PD is not interfered with each other.

(6) The format of the final output photocurrent is phase shifted by the DD-MZM2 bias voltageIs a function of (a) and (b). As the phase shift->Part of the output photocurrent is eliminated. By adjusting the phase shift introduced by the bias voltage of DD-MZM2, a chirp signal of various formats can be realized.

(7) The frequency of the local oscillator signal LO is changed and an SMF transmission modulated optical signal with a length of 25km is used.

The invention provides a photon generation method of switchable multi-format chirp signals based on DP-BPSK, which adopts a dual-polarization binary phase shift keying modulator DP-BPSK to modulate local oscillation signals LO and cutting parabolic signals and then carry out polarization multiplexing, and adjusts bias voltage of DD-MZM2 to introduce phase shift by determining that DD-MZM1 works at a minimum transmission point MITP, and carries out photoelectric conversion by a photoelectric detector PD, thereby realizing flexible switching of upper, lower and dual-chirp signals resisting power fading.

The multi-format chirp signal generator provided by the invention has multi-format switchable capability, frequency adjustability, long-distance transmission capability, attenuation resistance capability and pulse compression capability. A bias controller may also be applied in this scheme to make the bias voltage of the modulator more stable. The invention is more suitable for integration due to the simple link structure.

Drawings

Fig. 1 is a schematic diagram of the generation of a switchable multi-format chirp signal having power fading resistance.

Fig. 2 (a) is a schematic diagram of a conventional parabolic waveform signal (b) divided parabolic waveform signal having a division number of 10.

In fig. 3, (a) is a chirp spectrum diagram with pi/2 phase shift introduced for the bias voltage of DD-MZM2, (b) is a chirp spectrum diagram with-pi/2 phase shift introduced for the bias voltage of DD-MZM2, and (c) is a chirp spectrum diagram with 0 phase shift introduced for the bias voltage of DD-MZM2.

In fig. 4, (a) is a chirp signal time-frequency diagram with pi/2 phase shift introduced by the bias voltage of DD-MZM2, (b) is a chirp signal time-frequency diagram with-pi/2 phase shift introduced by the bias voltage of DD-MZM2, and (c) is a chirp signal time-frequency diagram with 0 phase shift introduced by the bias voltage of DD-MZM2.

In fig. 5, (a) a phase curve of a chirp signal with a phase shift of pi/2, (b) a phase curve of a chirp signal with a phase shift of-pi/2, and (c) a phase curve of a chirp signal with a phase shift of 0.

In fig. 6, (a_i), (b_i), and (c_i) are waveform diagrams of the up, down, and double chirp signals, respectively, and (a_ii), (b_ii), and (c_ii) are autocorrelation results of the up, down, and double chirp signals, respectively.

The square solid line in FIG. 7 (a) represents the power of the chirp signal at different frequencies in the case of no optical fiber transmission, the circle solid line represents the power of the chirp signal at different frequencies in the case of 25km optical fiber transmission (b) the triangle solid line represents the power difference between the two structures of no optical fiber transmission and 25km optical fiber transmission

Fig. 8 shows the frequency spectrum of the (a), (b) and (c) double chirp signals obtained when the division number is changed from 2500 to 5000.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the attached drawings: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation flow are provided, but the protection scope of the invention is not limited to the following embodiment.

Fig. 1 is a schematic diagram of the generation of a switchable multi-format chirp signal having power fading resistance. The device comprises a laser LD 1, a dual-polarization binary phase shift keying modulator DP-BPSK 2, an arbitrary waveform generator AWG 3, a local oscillation signal LO 4, an electric phase shifter 590 DEG, a single-mode fiber SMF 6 and a photoelectric detector PD 8. The output port of the laser is connected with the optical input port of the DP-BPSK modulator, and two dual-drive Mach-Zehnder modulators DD-MZM1 and DD-MZM2 are respectively arranged on the upper arm and the lower arm of the DP-BPSK modulator. The cut parabolic waveform signal is directly injected into the upper arm and the lower arm of the DP-BPSK modulator, and then the modulated signal is injected into the single mode fiber SM to complete transmission. And after the high-speed photoelectric detector PD is used as a mixer and the modulation signal is injected into the PD to realize photoelectric conversion, the multi-format switchable chirp signal resistant to power fading can be obtained.

In this example, the method specifically includes the following steps:

step one: the laser LD generates a continuous light wave with an operating wavelength of 1550nm and a power of 16dBm, which is injected into the DP-BPSK modulator.

Step two: an Arbitrary Waveform Generator (AWG) generates a cut parabolic waveform signal with a duration of 5 mus, split number 2500, and then amplifies the peak-to-peak value of the signal to about 7V. The cutting parabolic waveform signal power is divided into two paths to drive DD-MZM1 and DD-MZM2 in the DP-BPSK modulator respectively.

Step three: the local oscillation signal source outputs a single-frequency signal continuous optical carrier with the frequency of 16GHz, after power is divided into two paths, one path directly drives one radio frequency port of the DD-MZM1, the other path drives one radio frequency port of the DD-MZM2 after phase shifting by 90 degrees, and the DD-MZM1 modulator works at the minimum transmission point MITP to realize the suppression of carrier double-sideband (CS-DSB) modulation.

Step four: adjusting the bias voltage of DD-MZM2 to change the format of the output signal

Step five: and then, the upper and lower paths of modulated optical signals are compounded into polarization multiplexing light through a polarization beam combiner in the DP-BPSK modulator, and the polarization multiplexing light is output to the modulator.

Step six: the output optical signal is photoelectrically converted by a high-speed PD with a responsivity of 0.65A/W.

Step seven: in order to verify the frequency tunability and long-distance transmission capability of the proposed multi-format chirp signal generator. 25km optical fibers are added for transmission, 16GHz power of an input radio frequency signal is kept unchanged, the frequency of a local oscillator LO signal is changed, and an output electric spectrum is observed. With the change of the local oscillation signal frequency, observing the power of the downlink chirp signal before and after long-distance transmission and no optical fiber transmission

Step eight: to further verify the ability to segment the parabolic waveform signal to increase TBWP for the chirp signal, the number of segments of the parabolic waveform signal was increased from 2500 to 5000. Repeating the first to sixth steps.

As can be seen from FIG. 3, when DD-MZM1 is operated at the MITP point, the phase shift is pi/2, -pi/2 by adjusting the bias voltage of DD-MZM2, respectively, the down-chirp signal and up-chirp signal with the bandwidth of 1GHz can be obtained, and the bandwidth of 2G can be obtained when the phase shift is 0Hz double chirp signal. The signal quality can be analyzed in the time-frequency dimension using a short-time Fourier transform as shown in FIG. 4, which shows the DD-MZM2 phase shift as shown in FIG. 4 (a)At pi/2, a down-chirp signal may be generated; by adjusting the phase shift +.>The down-chirp signal is eliminated and the up-chirp signal is generated; it can be seen that fig. 4 (a) and (b) can observe a single chirp signal with a signal bandwidth of 1GHz and a time period of 5 mus, as shown in fig. 4 (c), when the phase shift +.>At 0, a double chirp signal with a signal bandwidth of 2GHz and a time period of 5 mus can be observed. As shown in fig. 5, which shows an instantaneous phase curve of the multi-format chirp signal recovered by the hilbert transform, it can be found that the phase curve is parabolic. In addition, the pulse compression capability of the resulting chirp signal was also evaluated, as shown in (a_i), (b_i), and (c_i) of fig. 6, in which TBWPs of the resulting downstream, upstream, and double chirp signals were 5000, and 10000, respectively, in a period of 5 μs, and as can be seen in (a_ii), (b_ii), and (c_ii) of fig. 6, the autocorrelation half maximum full widths FWHM of the resulting downstream, upstream, and double chirp signals were 1.035ns,1.058ns, and 0.509ns, respectively, the peak-to-peak suppression ratios PSR of the autocorrelation peaks were 6.37dB, 6.29dB, and 6.70dB, respectively, and the corresponding Pulse Compression Ratios (PCR) were 4831, 4726, and 9823. In order to verify the frequency adjustability and long-distance transmission capability of the proposed multi-format chirp signal generator, the frequency of the LO signal is changed, a 25km long Single Mode Fiber (SMF) is used to transmit the modulated optical signal, and the result of the downlink chirp signal before and after long-distance transmission is obtained, after long-distance transmission, the optical power fed back to the PD is reduced from-4.41 dBm to-10.82 dBm, and the transmission loss is 6.41dB. FIG. 7 (a) is a table showing the power of local oscillation LO signalsThe signal is shown to have good frequency tunability and power fading resistance, and as shown in fig. 7 (b), the power difference caused by transmission loss between the two structures is about 8.8dB, and the power difference fluctuates by about 0.8dB in the range of 4 to 18 GHz. To verify the ability of dividing the parabolic waveform signal to increase the TBWP of the resulting chirp signal, the number of divisions was increased from 2500 to 5000, and comparing fig. 3 and 8 revealed that the resulting signal bandwidth was proportional to the number of divisions of the parabolic waveform signal. After the division times are doubled, the bandwidth of the single chirp signal is increased from 1GHz to 2GHz, and the bandwidth of the obtained double chirp signal is 4GHz. Meanwhile, after doubling the division number, the power of the obtained signal is reduced by about 3dB.

The multi-format chirp signal generator provided by the invention has the advantages of simple structure and good stability, and the system adopts an electronic device with stable frequency response and a modulator with uniform half-wave voltage. The scheme provided by the invention is easy to integrate because of the simple link structure. In addition, the signal generator provided by the invention provides an effective method for acquiring the large TBWP chirp signal, so that the anti-interference performance of the radar system is greatly improved, the survivability of the radar system is improved, and the signal generator has potential application scenes in modern radar systems.

In summary, the above-described embodiments are merely examples of the present invention, not intended to limit the scope of the present invention, and it should be noted that several equivalent modifications and substitutions can be made by those skilled in the art in light of the present disclosure. For example, the number of divisions of the parabolic waveform signal is not limited to 2500, and may be other division numbers. In addition, in the final experimental result, the uneven chirp signal power spectrum density caused by the non-ideal parabolic cutting, the uneven frequency response of the electronic device and the fixed half-wave voltage steps of the modulator under different frequencies can be solved by replacing the electronic device with more stable frequency response and the modulator with more uniform half-wave voltage. In general, a bias controller may also be used in the system to stabilize the bias voltage of the modulator.

Claims (1)

1. A photon generation method of switchable multi-format chirp signals based on DP-BPSK comprises a laser LD, a dual-polarization binary phase shift keying modulator DP-BPSK, an arbitrary waveform generator AWG, a local oscillation signal LO, a 90-degree electric phase shifter, a single-mode fiber SMF and a photoelectric detector PD, wherein the dual-polarization binary phase shift keying modulator DP-BPSK is internally integrated with two parallel dual-drive Mach-Zehnder modulators DD-MZM1 and DD-MZM2, a polarization rotator PR and a polarization beam combiner PBC; the method is characterized in that: the linearly polarized light generated by the laser LD is sent into a DP-BPSK modulator, a cutting parabolic waveform signal generated by the AWG drives a DD-MZM1 modulator and a DD-MZM2 modulator respectively, one path of a local oscillation signal LO is directly connected into the DD-MZM1, the other path of the local oscillation signal LO is connected into the DD-MZM2 after 90-degree phase shift, the DD-MZM1 works at a minimum transmission point MITP to realize carrier rejection double-sideband CS-DSB modulation, the DD-MZM2 works at-pi/2, pi/2 and 0 working points respectively by adjusting the bias voltage of the DD-MZM2, polarized multiplexed light is output by the DP-BPSK modulator, and photoelectric conversion is carried out by a photoelectric detector PD to realize switchable up-down double-chirp signals resisting power fading.