CN108683458B - Time domain ghost imaging device and method based on orthogonal frequency division multiplexing - Google Patents
Time domain ghost imaging device and method based on orthogonal frequency division multiplexing Download PDFInfo
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- CN108683458B CN108683458B CN201810497391.0A CN201810497391A CN108683458B CN 108683458 B CN108683458 B CN 108683458B CN 201810497391 A CN201810497391 A CN 201810497391A CN 108683458 B CN108683458 B CN 108683458B
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Abstract
The invention discloses a time domain ghost imaging device and a method based on orthogonal frequency division multiplexing, wherein the device comprises a continuous laser CW, random waveform generators AWG1 and AWG2, Mach-Zehnder modulators MZM1 and MZM2, and polarization controllers PC1 and PC 2. The invention encodes the time domain intensity waveform based on the Hadamard matrix onto the OFDM electrical signal. Modulating the carrier to obtain an OFDM optical signal, modulating the OFDM optical signal by a time domain signal to be detected, receiving the modulated waveform by an oscilloscope, calculating the total power of each subcarrier by using the received waveform, and performing correlation calculation on the total power and the time domain intensity waveform of each subcarrier of the original OFDM electric signal so as to restore the waveform of the time domain signal to be detected with high quality and high resolution. The invention has the advantages of lower cost, simple structure, insensitivity to damage between a signal to be detected and a detector, capability of recovering a monopulse time domain signal and good application prospect in high-speed real-time signal detection.
Description
Technical Field
The invention belongs to the field of optical signal processing, and particularly relates to a time domain ghost imaging device and method based on orthogonal frequency division multiplexing.
Background
The ghost imaging technology is an indirect imaging technology, and a time domain ghost imaging technology has a new development recently. And integrating the optical carrier modulated by the time domain signal to obtain the total power of each subcarrier, and performing correlation calculation on the total power and the intensity waveform of each subcarrier to reconstruct the time domain signal to be detected. The time domain ghost imaging technology is insensitive to damage between a time domain signal to be detected and a detector, namely, insensitive to distortion caused by detection, and extremely beneficial to reconstruction of a fast time domain signal.
In general, time-domain ghost imaging requires a large number of repeated measurements, so that a periodic signal needs to be repeatedly transmitted, and the time-domain ghost imaging cannot be used for recovering a real-time signal. The single time domain ghost imaging by utilizing wavelength multiplexing only needs one-time measurement, signals do not need to be sent repeatedly, and the single pulse time domain signals can be restored, so that the real-time signals are restored. However, to improve temporal resolution, wavelength-multiplexed single-pass time-domain ghost imaging must use a large number of high-speed electro-optical modulators and photodetectors, which can greatly increase cost and complexity of the system.
Disclosure of Invention
In view of the above drawbacks and needs of the prior art, the present invention provides an apparatus and method for orthogonal frequency division multiplexing-based time domain ghost imaging, which solves the technical problems of increased cost and system complexity due to the necessity of using a large number of high-speed electro-optical modulators and photodetectors in single time domain ghost imaging using wavelength multiplexing.
To achieve the above object, according to an aspect of the present invention, there is provided an orthogonal frequency division multiplexing-based time domain ghost imaging apparatus, including: the system comprises a continuous laser, a first arbitrary waveform generator, a first Mach-Zehnder modulator, a second arbitrary waveform generator, a second Mach-Zehnder modulator and a processing module;
the continuous laser is used for generating a carrier wave of an Orthogonal Frequency Division Multiplexing (OFDM) optical signal;
the first arbitrary waveform generator is configured to generate an OFDM electrical signal, and after the OFDM electrical signal is modulated by the first mach-zehnder modulator, modulate the OFDM electrical signal onto a carrier of the OFDM optical signal to generate a first OFDM optical signal, where the OFDM electrical signal is obtained by waveform coding of time domain intensity based on a hadamard matrix;
the second arbitrary waveform generator is used for generating a time domain signal to be measured, and after the time domain signal to be measured is modulated by the second Mach-Zehnder modulator, the time domain signal to be measured is modulated onto the first OFDM optical signal to obtain a second OFDM optical signal;
the processing module is configured to calculate a total power of each subcarrier of the second OFDM optical signal according to the time domain intensity waveform of each subcarrier of the second OFDM optical signal, and reconstruct the time domain signal to be detected based on the subcarrier intensity waveform of the OFDM electrical signal.
Preferably, the first mach-zehnder modulator and the second mach-zehnder modulator both work in a push-pull mode, polarization is at an orthogonal point, and an electric signal changes an internal refractive index to influence phase distribution of an optical signal, further influence intensity distribution, and realize electro-optic modulation.
Preferably, the apparatus further comprises: a first polarization controller and a second polarization controller;
the first polarization controller is positioned between the continuous laser and the first Mach-Zehnder modulator, and the second polarization controller is positioned between the first Mach-Zehnder modulator and the second polarization controller;
the first polarization controller is used for changing the polarization state of the OFDM optical signal carrier to be consistent with the polarization state of the first Mach-Zehnder modulator;
the second polarization controller is used for changing the polarization state of the first OFDM optical signal to be consistent with the polarization state of the second Mach-Zehnder modulator.
According to another aspect of the present invention, there is provided a time-domain ghost imaging method based on orthogonal frequency division multiplexing, including:
generating a carrier of an orthogonal frequency division multiplexing, OFDM, optical signal;
mapping each preset row vector based on a Hadamard matrix to a time domain intensity waveform of each subcarrier of an OFDM electric signal, then generating the OFDM electric signal by utilizing fast inverse Fourier transform and parallel-serial conversion, and modulating the OFDM electric signal to a carrier of the OFDM optical signal to generate a first OFDM optical signal;
modulating the first OFDM optical signal by a time domain signal to be detected, and modulating the time domain signal to be detected onto the first OFDM optical signal to obtain a second OFDM optical signal;
and calculating the total power of each subcarrier of the second OFDM optical signal according to the time domain intensity waveform of each subcarrier of the second OFDM optical signal, and reconstructing the time domain signal to be detected based on the intensity waveform of each subcarrier of the OFDM electric signal.
Preferably, before reconstructing the time-domain signal to be measured, the method further includes:
and adding a random phase uniformly distributed between 0 and pi into the intensity waveform of each subcarrier of the OFDM electric signal.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
the time domain intensity waveform based on the Hadamard matrix is coded on the OFDM electric signal and used for modulating the carrier of the OFDM signal, the carrier is secondarily modulated by the time domain signal to be measured, the modulated waveform is received by an oscilloscope, the total power of each subcarrier is calculated by using the received waveform, and the total power and the time domain intensity waveform of each subcarrier of the original OFDM electric signal are subjected to correlation calculation, so that the waveform of the time domain signal to be measured with high quality and high resolution is recovered.
The method provided by the invention has the advantages of low cost, simple structure, insensitivity to damage between the signal to be detected and the detector, capability of realizing single-pulse time domain signal ghost imaging, and good application prospect in high-speed real-time signal detection.
Drawings
Fig. 1 is a schematic structural diagram of a time-domain ghost imaging apparatus based on orthogonal frequency division multiplexing according to an embodiment of the present invention;
fig. 2 is a diagram of intensity code patterns of subcarriers based on a hadamard matrix according to an embodiment of the present invention, where black is bit '1' and white is bit '-1' in the 16 × 16 hadamard matrix shown in fig. 2 (a); FIG. 2(b) shows the corresponding HTH, superscript T represents transposition;
FIG. 3 illustrates an original image and a ghost image of three signals provided by an embodiment of the present invention; wherein, fig. 3(a) is a square wave; FIG. 3(b) is a sine wave; fig. 3(c) shows a triangular wave.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a time domain ghost imaging device and a time domain ghost imaging method based on orthogonal frequency division multiplexing. The advantage of the ofdm technology over wavelength multiplexing is that only one electro-optical modulator and one detector are needed, and Inverse Fast Fourier Transform (IFFT) is used to complete the multi-path modulation of the sub-carriers, and the intensity waveforms of the sub-carriers can be strictly synchronized. The invention can realize the detection of the high-resolution high-quality time domain signal, reduces the cost, has simple structure, is insensitive to the damage between the signal to be detected and the detector, realizes the ghost imaging of the monopulse time domain signal and has good application prospect in the high-speed real-time signal detection.
The terms "first" and "second," and the like in the description and in the claims of the present invention, are used for distinguishing between different objects and not for describing a particular order.
In the embodiment of the present invention, as shown in fig. 1, a schematic diagram of a time-domain ghost imaging apparatus based on Orthogonal Frequency Division Multiplexing (OFDM) may first generate a carrier of an Orthogonal Frequency Division Multiplexing (OFDM) optical signal by using a 1550nm continuous laser CW 1. The OFDM electrical signal may be generated by an arbitrary waveform generator AWG 12 (tektronixwg 7122C may be used) with a bandwidth of 3.2GHz, and the OFDM electrical signal is modulated by a mach-zehnder modulator MZM 13, so as to modulate the OFDM electrical signal onto a carrier of the OFDM optical signal to generate a first OFDM optical signal. The first OFDM optical signal is then modulated by a time domain signal to be measured, which may be generated by another 300MHz bandwidth AWG 24 (Tektronix AWG5012C may be employed) and another mach-zehnder modulator MZM25, to generate a second OFDM optical signal. Wherein MZM 13 and MZM25 operate in push-pull mode, are biased at quadrature points, and achieve electro-optic modulation. The polarization states of input light of the Mach-Zehnder modulators MZM 13 and MZM25 are manually adjusted by adopting two polarization controllers PC 16 and PC 27 respectively to be consistent with the polarization states of the Mach-Zehnder modulators MZM 13 and MZM25 respectively, and the transmissivity of the modulators is improved. Finally, the transmitted light waveform modulated by the OFDM electric signal and the time domain signal to be detected can be received by a 4GHz real-time Oscilloscope 8 (TektronixCS A7404B can be adopted), the total power of each subcarrier modulated by the signal to be detected is calculated according to the received waveform, the total power and the intensity waveform of each subcarrier of the original OFDM electric signal are subjected to correlation calculation, and the time domain signal to be detected is reconstructed.
The polarization controllers PC 16 and PC 27 are composed of polarization maintaining fibers and a tri-slurry mechanical rotation structure, and the polarization state of light can be changed by manually adjusting the tri-slurry mechanical rotation structure to be consistent with the polarization states of Mach-Zehnder modulators MZM1 and MZM2, so that the transmissivity of the modulators is improved.
In an embodiment of the present invention, there is further provided a time domain ghost imaging method based on orthogonal frequency division multiplexing, including:
generating a carrier of an OFDM optical signal;
mapping each preset row vector based on a Hadamard matrix to a time domain intensity waveform of each subcarrier of an OFDM electric signal, then generating the OFDM electric signal by utilizing fast inverse Fourier transform and parallel-serial conversion, and modulating the OFDM electric signal to a carrier of the OFDM optical signal to generate a first OFDM optical signal;
modulating the first OFDM optical signal by the time domain signal to be measured, and modulating the time domain signal to be measured onto the first OFDM optical signal to obtain a second OFDM optical signal;
and calculating the total power of each subcarrier modulated by the time domain signal to be detected according to the time domain intensity waveform of each subcarrier of the second OFDM optical signal, and reconstructing the time domain signal to be detected based on the intensity waveform of each subcarrier of the OFDM electric signal.
Preferably, before reconstructing the time-domain signal to be measured, the method further comprises:
and adding a random phase uniformly distributed between 0 and pi into the intensity waveform of each subcarrier of the OFDM electric signal.
The added random phase can destroy the in-phase superposition of each subcarrier, and reduce the peak-to-average ratio. In addition, because the random phase can be eliminated by a digital calculation method after being detected, the orthogonality of the time domain intensity waveforms of the subcarriers can be maintained, and therefore high quality of the recovered signals is guaranteed, and imaging quality is improved.
As shown in fig. 2, a time domain pattern based on a hadamard matrix is encoded to subcarriers of an OFDM signal. Where a 16 x 16 hadamard matrix is used as shown in fig. 2(a), which means that there are 16 sub-carriers and 16 signal samples. Where black is the bit '1' and white is the bit '-1'. As can be seen in FIG. 2(b), HTH is a scalar matrix, which is advantageous for perfectly restoring the time-domain signal.
As shown in fig. 3, ghost imaging experimental results for 16 sampling points of three different single time domain signals (square, sine, and triangle) are shown, with a sampling interval of 22.5 ns. The waveform of the recovered target is well matched with that of the design target, and the method provided by the invention is shown to be capable of reconstructing a high-quality and high-resolution (22.5ns) single time domain signal. The orthogonality of the hadamard matrix ensures high temporal resolution and high quality imaging.
By using the time domain ghost imaging device and method based on orthogonal frequency division multiplexing provided by the invention, the detection of the time domain signal to be detected with high quality and high resolution can be realized, the cost is lower, the structure is simple, the device is insensitive to the damage between the signal to be detected and a detector, the single-pulse time domain ghost imaging can be realized, and the device and method have good application prospect in high-speed real-time signal detection.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. A time-domain ghost imaging apparatus based on orthogonal frequency division multiplexing, comprising: the continuous laser, the first polarization controller, the first arbitrary waveform generator, the first Mach-Zehnder modulator, the second polarization controller, the second arbitrary waveform generator, the second Mach-Zehnder modulator and the processing module;
the first polarization controller is positioned between the continuous laser and the first Mach-Zehnder modulator, and the second polarization controller is positioned between the first Mach-Zehnder modulator and the second polarization controller;
the continuous laser is used for generating a carrier wave of an Orthogonal Frequency Division Multiplexing (OFDM) optical signal;
the first polarization controller is used for changing the polarization state of the OFDM optical signal carrier to be consistent with the polarization state of the first Mach-Zehnder modulator;
the first arbitrary waveform generator is configured to generate an OFDM electrical signal, and after the OFDM electrical signal is modulated by the first mach-zehnder modulator, modulate the OFDM electrical signal onto a carrier of the OFDM optical signal to generate a first OFDM optical signal, where the OFDM electrical signal is obtained by waveform coding of time domain intensity based on a hadamard matrix;
the second polarization controller is used for changing the polarization state of the first OFDM optical signal to be consistent with the polarization state of the second Mach-Zehnder modulator;
the second arbitrary waveform generator is used for generating a time domain signal to be measured, and after the time domain signal to be measured is modulated by the second Mach-Zehnder modulator, the time domain signal to be measured is modulated onto the first OFDM optical signal to obtain a second OFDM optical signal;
the processing module is configured to calculate a total power of each subcarrier of the second OFDM optical signal according to the time domain intensity waveform of each subcarrier of the second OFDM optical signal, and reconstruct the time domain signal to be detected based on the subcarrier intensity waveform of the OFDM electrical signal.
2. The device according to claim 1, wherein the first Mach-Zehnder modulator and the second Mach-Zehnder modulator operate in a push-pull mode, polarization is in an orthogonal point, and an electric signal changes an internal refractive index to influence phase distribution of an optical signal, further influence intensity distribution, and realize electro-optical modulation.
3. A time domain ghost imaging method based on orthogonal frequency division multiplexing is characterized by comprising the following steps:
generating a carrier of an orthogonal frequency division multiplexing, OFDM, optical signal;
mapping each preset row vector based on a Hadamard matrix to a time domain intensity waveform of each subcarrier of an OFDM electric signal, then generating the OFDM electric signal by utilizing fast inverse Fourier transform and parallel-serial conversion, and modulating the OFDM electric signal to a carrier of the OFDM optical signal to generate a first OFDM optical signal;
modulating the first OFDM optical signal by a time domain signal to be detected, and modulating the time domain signal to be detected onto the first OFDM optical signal to obtain a second OFDM optical signal;
and calculating the total power of each subcarrier of the second OFDM optical signal according to the time domain intensity waveform of each subcarrier of the second OFDM optical signal, and reconstructing the time domain signal to be detected based on the intensity waveform of each subcarrier of the OFDM electric signal.
4. The method of claim 3, wherein before reconstructing the time-domain signal under test, the method further comprises:
and adding a random phase uniformly distributed between 0 and pi into the intensity waveform of each subcarrier of the OFDM electric signal.
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