A feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion

Abstract

The present invention relates to a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion. The system uses an in-phase and orthogonal mixing detection scheme to extract the frequency and phase difference of two independently running narrow linewidth lasers, and uses a feedforward compensation scheme to adjust the frequency and phase information of one of the narrow linewidth lasers before optical frequency down-conversion, so that its phase and frequency characteristics follow the reference narrow linewidth laser, thereby achieving relative phase noise and frequency stability of the two lasers. This dynamic cross-correlated phase noise and frequency mechanism can avoid the terahertz signal noise deterioration problem caused by the frequency and phase noise difference of the two lasers; at the same time, high-precision frequency following can be achieved without relying on independent frequency stabilization equipment. Even if the frequency and noise characteristics of the reference laser change under the influence of the external environment, the feedforward compensation mechanism can still make the frequency and noise characteristics of the slave laser follow the reference laser.

Description

Technical Field

[0001] The present invention relates to the field of terahertz radiation generation and terahertz communication, and in particular to a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion. Background Art

[0002] In order to meet the ever-increasing demand for data traffic in wireless communications, the communication carrier frequency needs to be pushed from tens of GHz to 0.1 THz or even several THz.

[0003] Optical frequency down-conversion technology has the advantages of easy generation of high-frequency signals, good frequency tuning capability, and compatibility with current mature fiber-optic communication technologies. Optical frequency down-conversion technology generates terahertz radiation based on the basic principle of optical heterodyne detection, that is, using a high-speed photodetector to detect two optical signals with different frequencies, and then obtaining a terahertz signal of the difference between the two optical carrier frequencies at the output end of the detector. The terahertz radiation can be tuned by simply changing the frequency difference between the two optical signals. More conveniently, mature optical communication technologies can be used, such as changing the intensity or phase information of one of the optical carriers to load communication information. Terahertz radiation generated by optical frequency down-conversion can be divided into two categories.

[0004] In the scheme based on optical frequency comb, it is necessary to accurately filter the generated terahertz radiation frequency to obtain two frequency comb teeth with high spectral purity for optical heterodyne detection. Since an optical frequency comb with high frequency accuracy and stability is used as the excitation source, the terahertz radiation has excellent frequency stability and phase noise characteristics. However, since the frequency spectrum used only accounts for one percent or even one millionth of all the comb teeth of the optical frequency comb, the terahertz radiation energy generated by this technology is low.

[0005] Another optical frequency down-conversion technology based on multiple discrete lasers uses several free-running lasers to directly perform heterodyne detection to obtain terahertz radiation, which can obtain higher energy. However, since the phase noise of the two lasers is transferred to terahertz during the heterodyne process, additional frequency stabilization or phase noise suppression mechanisms are required to reduce the impact of phase and frequency noise. Although the optical sideband injection locking technology generates a frequency-stable terahertz signal by locking the modulated sideband to one sideband of the master laser, the phase difference between the master laser and the modulated sideband is affected by the detuned frequency and injection ratio. Even under stable locking conditions, the frequency noise of the two lasers will generate phase noise, requiring a complex tracking circuit to stabilize the frequency of the terahertz signal.

[0006] Therefore, there is an urgent need to develop a simple and effective noise suppression technology to improve the frequency stability of terahertz radiation. Summary of the invention

[0007] The present invention aims at solving the technical problems in the prior art and provides a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion, thereby improving the frequency stability of terahertz radiation in optical frequency down-conversion technology.

[0008] According to a first aspect of the present invention, there is provided a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion, comprising: a reference laser, a slave laser, a first optical coupler, a second optical coupler, a third optical coupler, a detection and driving unit, an IQ modulator, a fourth optical coupler and a terahertz detector;

[0009] The laser light outputted by the reference laser is divided into two beams through the first optical coupler, one beam enters the third optical coupler, and the other beam enters the fourth optical coupler;

[0010] The laser light outputted from the laser is divided into two beams through the second optical coupler, one beam enters the third optical coupler, and the other beam enters the optical input port of the IQ modulator;

[0011] The third optical coupler couples the two input optical signals into a beam of light and outputs the beam to the detection and driving unit;

[0012] The detection and driving unit detects the relative phase noise and frequency jitter between the reference laser and the slave laser, generates a corresponding driving signal, and outputs two orthogonal RF signals to the RF input port of the IQ modulator;

[0013] The IQ modulator compensates for the frequency jitter and phase noise of the slave laser relative to the reference laser under the action of the driving signal, and outputs an optical signal to the fourth optical coupler;

[0014] The fourth optical coupler couples the two input optical signals into a beam of light and outputs it to the terahertz detector;

[0015] The terahertz detector performs frequency down-conversion on two input optical signals of different frequencies, and outputs the optical signals of the two frequencies in the form of photocurrent.

[0016] Based on the above technical solution, the present invention can also make the following improvements.

[0017] Optionally, the reference laser and the slave laser are single longitudinal mode lasers, the working center frequency is adjustable, and a narrow linewidth optical signal with a linewidth less than 15 kHz is generated;

[0018] The operating center frequencies of the slave laser and the reference laser differ by 0.1-1 THz.

[0019] Optionally, the first optical coupler divides the input optical signal into two beams according to the ratio, the large output ratio end is connected to the fourth optical coupler, and the small output ratio end is connected to the third optical coupler. The second optical coupler divides the input optical signal into two beams according to the ratio, the large output ratio end is connected to the IQ modulator, and the small output ratio end is connected to the third optical coupler.

[0020] Optionally, an optical filter is further arranged between the fourth optical coupler and the terahertz detector.

[0021] Optionally, the detection and driving unit includes: a modulation drive generator, an optical phase modulator, a narrowband filter, a photodetector, an IQ phase detector and two low-pass filters;

[0022] The modulation drive generator is used to generate a drive signal for the optical phase modulator and a demodulation signal for the IQ phase detector;

[0023] The input end of the optical phase modulator is connected to the output end of the third optical coupler, and the electrical input end is connected to the high-frequency output of the modulation drive generator, and the drive signal is applied to the two input optical signals to generate a modulation sideband of the corresponding frequency, which is output to the narrowband filter;

[0024] The narrowband filter is an optical filter, which performs optical filtering on the input signal and then outputs it to the photodetector;

[0025] The photodetector converts the beat frequency signal of the reference laser and the overlapping part of the laser frequency sideband filtered by the narrowband filter into a current signal, and outputs it to the IQ phase detector;

[0026] The IQ phase detector extracts the in-phase and quadrature current amplitude and phase information from the input signal, and the I and Q ports output the in-phase and quadrature voltage signals to two low-pass filters respectively;

[0027] The two low-pass filters are used to filter the in-phase and quadrature voltage signals output by the IQ phase detector, and the output signals drive the IQ modulator.

[0028] Optionally, the modulation drive generator includes: a crystal oscillator, a power divider, a radio frequency divider, a filter amplifier, a radio frequency phase shifter, and a voltage amplifier;

[0029] The crystal oscillator is used to provide a stable signal source required for phase modulation and IQ phase detection, and the output end is connected to the power divider;

[0030] The power divider divides the input signal into two parts and then outputs them to the RF frequency divider and RF phase shifter respectively for connection;

[0031] The frequency division coefficient of the radio frequency divider is determined based on the overlapped portion of the sideband orders of the reference laser and the slave laser, and the output end is connected to the filter amplifier;

[0032] The filtering center frequency of the filter amplifier is the same as the operating frequency after frequency division, and the output end is connected to the IQ phase detector;

[0033] The radio frequency phase shifter is used to adjust the phase of the input electrical signal and output it to the voltage amplifier;

[0034] The voltage amplifier amplifies the low voltage obtained after frequency shifting and outputs it to the optical phase modulator.

[0035] The present invention provides a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion. The system uses an in-phase and orthogonal mixing detection scheme to extract the frequency and phase difference of two independently running narrow linewidth lasers, and uses a feedforward compensation scheme to adjust the frequency and phase information of one of the narrow linewidth lasers before optical frequency down-conversion, so that its phase and frequency characteristics follow the reference narrow linewidth laser, thereby achieving relative phase noise and frequency stability of the two lasers. This dynamic cross-correlated phase noise and frequency mechanism can avoid the problem of terahertz signal noise deterioration caused by the difference in frequency and phase noise of the two lasers; at the same time, high-precision frequency following can be achieved without relying on independent frequency stabilization equipment. Even if the frequency and noise characteristics of the reference laser change under the influence of the external environment, the feedforward compensation mechanism can still make the frequency and noise characteristics of the slave laser follow the reference laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A structural diagram of an embodiment of a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion provided by the present invention;

[0037] Figure 2 A structural diagram of an embodiment of a detection and driving unit in a feedforward compensation technology for suppressing terahertz radiation noise generated by optical frequency down-conversion provided by the present invention;

[0038] Figure 3 A structural diagram of an embodiment of a modulation driver in a feed-forward compensation technology for suppressing terahertz radiation noise generated by optical frequency down-conversion;

[0039] In the accompanying drawings, the names of the components represented by the numbers are as follows:

[0040] 101. reference laser, 102. slave laser, 103. first optical coupler, 104. second optical coupler, 105. third optical coupler, 106. detection and driving unit, 107. IQ modulator, 108. fourth optical coupler, 109. optical filter, 110. terahertz detector;

[0041] 201, optical phase modulator, 202, narrowband filter, 203, photodetector, 204, modulation drive generator, 205, IQ phase detector, 207, low-pass filter 1, 208, low-pass filter 2;

[0042] 301. Crystal oscillator, 302. Power divider, 303. RF frequency divider, 304. Filter amplifier, 305. RF phase shifter, 306. Voltage amplifier. DETAILED DESCRIPTION

[0043] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0044] Figure 1 A structural diagram of an embodiment of a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion provided by the present invention, such as Figure 1 As shown, the feedforward compensation system includes: a reference laser 101, a slave laser 102, a first optical coupler 103, a second optical coupler 104, a third optical coupler 105, a detection and driving unit 106, an IQ modulator 107, a fourth optical coupler 108 and a terahertz detector 110.

[0045] The laser light outputted by the reference laser 101 is divided into two beams by the first optical coupler 103 , one beam enters the third optical coupler 105 , and the other beam enters the fourth optical coupler 108 .

[0046] The laser light output from the laser 102 is divided into two beams by the second optical coupler 104 , one beam enters the third optical coupler 105 , and the other beam enters the optical input port of the IQ modulator 107 .

[0047] The third optical coupler 105 couples the two input optical signals into a beam of light and outputs the beam to the detection and driving unit 106 . In a specific implementation, the coupling mode can be polarization-dependent or polarization-independent.

[0048] The detection and driving unit 106 detects the relative phase noise and frequency jitter between the reference laser 101 and the slave laser, generates a corresponding driving signal, and outputs two orthogonal RF signals to the RF input port of the IQ modulator 107 .

[0049] Under the action of the driving signal, the IQ modulator 107 compensates for the frequency jitter and phase noise of the slave laser 102 relative to the reference laser 101 , and outputs an optical signal to the fourth optical coupler 108 .

[0050] The optical input port of the IQ modulator 107 is connected to the second optical coupler, and the optical output port is connected to the fourth optical coupler 108 ; the two RF input ports are connected to the modulation output end of the detection and driving unit 106 .

[0051] The fourth optical coupler 108 couples the two input optical signals into a beam of light and outputs it to the terahertz detector 110 . In a specific implementation, the coupling mode can be polarization-dependent or polarization-independent.

[0052] The terahertz detector 110 performs frequency down-conversion on two input optical signals of different frequencies and outputs the optical signals of the two frequencies in the form of photocurrent.

[0053] The present invention provides a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion, and its implementation principle includes:

[0054] The reference laser 101 and the slave laser 102 provide optical frequencies of f 1 and f 2 optical carrier signal, the frequency difference between the two lasers is the frequency of the terahertz radiation ( f 1- f 2, the range is 0.1-1THz), the two lasers are connected to the first optical coupler 103 and the second optical coupler 104 respectively, wherein the large splitting ratio port of the first optical coupler 103 is connected to the fourth optical coupler 108, the large splitting ratio port of the second optical coupler 104 is connected to the IQ modulator 107, and the output end of the IQ modulator 107 is connected to the fourth optical coupler 108; the fourth optical coupler 108 is used to couple the latter two narrow linewidth lasers and input them to the optical filter 109; the small splitting ratio ports are respectively connected to the third optical coupler 105; the third optical coupler 1 The output end of 05 is connected to the detection and driving unit 106, which is used to detect the frequency and phase noise between the slave laser 102 and the reference laser 101; the detection and driving unit 106 is a photoelectric conversion module, and its output is an electrical signal, which is used to drive the IQ modulator 107 to dynamically compensate the frequency and phase noise of the slave laser 102 relative to the reference laser 101; the frequency jitter and phase noise of the slave laser 102 signal after feedforward compensation are consistent with those of the reference laser 101, and optical frequency conversion occurs in the terahertz detector 110 to generate a frequency of f 1- f 2 terahertz radiation.

[0055] The frequency and phase difference of two independently running narrow linewidth lasers are extracted by using the in-phase and orthogonal mixing detection schemes, and the frequency and phase information of one of the narrow linewidth lasers is adjusted by using the feedforward compensation scheme before the optical frequency conversion, so that its phase and frequency characteristics follow the reference narrow linewidth laser, and the relative phase noise and frequency stability of the two lasers are achieved. This dynamic cross-correlated phase noise and frequency mechanism can avoid the terahertz signal noise deterioration problem caused by the frequency and phase noise differences of the two lasers; at the same time, high-precision frequency following can be achieved without relying on independent frequency stabilization equipment. Even if the frequency and noise characteristics of the reference laser change under the influence of the external environment, the feedforward compensation mechanism can still make the frequency and noise characteristics of the slave laser follow the reference laser.

[0056] Example 1

[0057] Embodiment 1 provided by the present invention is an embodiment of feedforward compensation for suppressing terahertz radiation noise generated by optical frequency down-conversion provided by the present invention, combined with Figure 1 It can be seen that an embodiment of the feedforward compensation system includes: a reference laser 101, a slave laser 102, a first optical coupler 103, a second optical coupler 104, a third optical coupler 105, a detection and driving unit 106, an IQ modulator 107, a fourth optical coupler 108 and a terahertz detector 110.

[0058] The laser light outputted by the reference laser 101 is divided into two beams by the first optical coupler 103 , one beam enters the third optical coupler 105 , and the other beam enters the fourth optical coupler 108 .

[0059] In a possible embodiment, the first optical coupler 103 divides the input optical signal into two beams according to a ratio, the large output ratio end is connected to the fourth optical coupler 108, and the small output ratio end is connected to the third optical coupler 105. In a specific implementation, the ratio can be 1:9, 2:8, 3:7, etc.

[0060] The laser light output from the laser 102 is divided into two beams by the second optical coupler 104 , one beam enters the third optical coupler 105 , and the other beam enters the optical input port of the IQ modulator 107 .

[0061] In a possible embodiment, the second optical coupler 104 divides the input optical signal into two beams according to a ratio, the large output ratio end is connected to the IQ modulator 107, and the small output ratio end is connected to the third optical coupler 105. In a specific implementation, the ratio can be 1:9, 2:8, 3:7, etc.

[0062] In a possible embodiment, the reference laser 101 and the slave laser 102 are single longitudinal mode lasers, the operating center frequency is adjustable, and a narrow linewidth optical signal with a linewidth less than 15 kHz is generated.

[0063] The operating center frequencies of the slave laser 102 and the reference laser 101 differ by 0.1-1 THz.

[0064] In a specific implementation, the reference laser 101 and the slave laser 102 can be single-frequency lasers of any system.

[0065] The third optical coupler 105 couples the two input optical signals into a beam of light and outputs the beam to the detection and driving unit 106 . In a specific implementation, the coupling mode can be polarization-dependent or polarization-independent.

[0066] The detection and driving unit 106 detects the relative phase noise and frequency jitter between the reference laser 101 and the slave laser, generates a corresponding driving signal, and outputs two orthogonal RF signals to the RF input port of the IQ modulator 107 .

[0067] The detection and driving unit 106 is a key link in realizing the feedforward compensation technology to suppress the terahertz radiation noise generated by optical frequency down conversion, such as Figure 2 FIG. 1 is a structural diagram of an embodiment of a detection and driving unit in a feedforward compensation technology for suppressing terahertz radiation noise generated by optical frequency down-conversion provided by the present invention, combined with FIG. Figure 1 and Figure 2 It can be seen that in a possible embodiment, the detection and driving unit 106 includes: a modulation driving generator 204, an optical phase modulator 201, a narrowband filter 202, a photodetector 203, an IQ phase detector 205 and two low-pass filters 207 and 208.

[0068] The modulation drive generator 204 is used to generate the drive signal of the optical phase modulator 201 and the demodulation signal of the IQ phase detector 205. f LO .

[0069] The input end of the optical phase modulator 201 is connected to the output end of the third optical coupler 105, and the electrical input end is connected to the high-frequency output of the modulation drive generator 204. The drive signal is loaded on the two input optical signals to generate a modulation sideband of the corresponding frequency, which is output to the narrowband filter 202.

[0070] The narrowband filter 202 is an optical filter, which performs optical filtering on the input signal and then outputs the signal to the photodetector 203 .

[0071] In a specific implementation, the working bandwidth of the narrowband filter 202 covers the frequency range in which the frequency sidebands generated by two narrow linewidth lasers under the modulation of the optical phase modulator 201 just overlap.

[0072] The photodetector 203 converts the beat frequency signal of the overlapping portion of the frequency sidebands of the reference laser 101 and the slave laser 102 filtered out by the narrowband filter 202 into a current signal, and outputs the current signal to the IQ phase detector 205 .

[0073] The IQ phase detector 205 extracts the in-phase and quadrature current amplitude and phase information from the input signal, and the I and Q ports output in-phase and quadrature voltage signals to two low-pass filters respectively.

[0074] The two low-pass filters are used to filter the in-phase and quadrature voltage signals output by the IQ phase detector 205 , and the output signals drive the IQ modulator 107 .

[0075] The implementation principle of the detection and driving unit includes: the two narrow line width lasers output by the third optical coupler 105 are coupled into the optical phase modulator 201, and the electrical drive port of the optical phase modulator 201 is connected to the modulation drive generator 204, and its drive signal is a frequency of Sine wave, assuming that the light field of two narrow linewidth lasers is:

[0076] .

[0077] and Represent the light fields of two narrow linewidth lasers, and Represent two narrow linewidth lasers, and represent the frequencies of two narrow linewidth lasers, and They represent the phase noise of two narrow linewidth lasers respectively; i is the imaginary part of the light field, which represents the light field component orthogonal to the phase in the complex space, and t is the time.

[0078] Under the action of the driving signal, the frequency sidebands corresponding to the generation of the two narrow linewidth lasers form new frequency components with their own frequency and phase noise characteristics within the spectrum range. After passing through a narrowband filter 202 of a specific wavelength, the area where the two modulated frequency sidebands just overlap is filtered out, and a mixed light field can be obtained. After being coupled to the photodetector 203, when the modes of the corresponding sidebands of the two narrow linewidth lasers are m and n respectively, the corresponding photocurrent and the modulation signal (The corresponding phase noise is ) is:

[0079] .

[0080] As can be seen from the above equation, the detected photocurrent includes the relative phase noise of the two lasers and relative frequency jitter , so when the frequency and phase information is known, the relative frequency and phase noise can be compensated. (The corresponding phase noise is ), the in-phase and quadrature current and phase information can be extracted using the IQ phase detector 205. The in-phase and quadrature voltage signals output by the I and Q ports of the IQ phase detector 205 are:

[0081]

[0082] When the two orthogonal signals VI and VQ filtered by the two low-pass filters 207 and 208 are applied to the IQ modulator 107 biased at the zero transmission point, the phase of the input slave laser is modulated. At this time, the electric field at the output of the IQ modulator can be expressed as:

[0083] .

[0084] Under the action of IQ modulator 107, the frequency of slave laser 102 follows the frequency of reference laser , its frequency variation and jitter are only related to the frequencies of the two modulation signals, and similarly, the phase noise has the same characteristics. Therefore, the field distribution of the terahertz signal after optical frequency down-conversion can be expressed as:

[0085] 。

[0086] like Figure 3 The structure diagram of the embodiment of the modulation driver in the feedforward compensation technology for suppressing the terahertz radiation noise generated by optical frequency down conversion is shown. Figure 1-Figure 3 It can be seen that in a possible embodiment, the modulation drive generator 204 includes: a crystal oscillator 301 , a power divider 302 , a radio frequency divider 303 , a filter amplifier 304 , a radio frequency phase shifter 305 , and a voltage amplifier 306 .

[0087] The crystal oscillator 301 is used to provide a stable signal source required for phase modulation and IQ phase detection, and its output end is connected to the power divider 302 .

[0088] In a specific implementation, the crystal oscillator 301 is synchronized with an external clock to meet clock synchronization and frequency synthesis requirements. Its operating frequency is 20-40 GHz, and a YIG crystal oscillator can be preferably used.

[0089] The power divider 302 divides the input signal into two parts and outputs them to the RF frequency divider 303 and the RF phase shifter 305 respectively.

[0090] The frequency division coefficient of the RF frequency divider 303 is based on the overlapping sideband orders of the reference laser 101 and the slave laser 102 ( m and n ), and the output end is connected to the filter amplifier 304.

[0091] Specifically, taking the overlapping bandwidth of the two levels at 11 GHz as an example, it is necessary to adjust the crystal oscillator 301 to 40 GHz and set the frequency division coefficient to 2 to obtain a driving frequency of 1 GHz.

[0092] The filtering center frequency of the filter amplifier 304 is the same as the working frequency after the frequency division, so as to avoid interference from other harmonics and baseband signals. The amplified signal is output to the IQ phase detector 205 for IQ phase detection.

[0093] The RF phase shifter 305 is used to adjust the phase of the input electrical signal and output it to the voltage amplifier 306 to meet the phase requirements of phase modulation and IQ phase detection.

[0094] The voltage amplifier 306 amplifies the low voltage obtained after the frequency shift and outputs it to the optical phase modulator 201 to meet the requirement of driving the optical phase modulator 201 .

[0095] Under the action of the driving signal, the IQ modulator 107 compensates for the frequency jitter and phase noise of the slave laser 102 relative to the reference laser 101 , and outputs an optical signal to the fourth optical coupler 108 .

[0096] The optical input port of the IQ modulator 107 is connected to the second optical coupler, and the optical output port is connected to the fourth optical coupler 108 ; the two RF input ports are connected to the modulation output end of the detection and driving unit 106 .

[0097] The fourth optical coupler 108 couples the two input optical signals into a beam of light and outputs it to the terahertz detector 110 . In a specific implementation, the coupling mode can be polarization-dependent or polarization-independent.

[0098] The terahertz detector 110 performs frequency down-conversion on two input optical signals of different frequencies and outputs the optical signals of the two frequencies in the form of photocurrent.

[0099] In a possible embodiment, an optical filter 109 is further disposed between the fourth optical coupler 108 and the terahertz detector 110 .

[0100] The embodiment of the present invention provides a feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion. It uses in-phase and orthogonal mixing detection schemes to extract the frequency and phase difference of two independently running narrow linewidth lasers, and before optical frequency down-conversion, uses a feedforward compensation scheme to adjust the frequency and phase information of one of the narrow linewidth lasers so that its phase and frequency characteristics follow the reference narrow linewidth laser, thereby achieving relative phase noise and frequency stability of the two lasers. This dynamic cross-correlated phase noise and frequency mechanism can avoid the terahertz signal noise deterioration problem caused by the frequency and phase noise differences of the two lasers; at the same time, high-precision frequency following can be achieved without relying on independent frequency stabilization equipment. Even if the frequency and noise characteristics of the reference laser change under the influence of the external environment, the feedforward compensation mechanism can still make the frequency and noise characteristics of the slave laser follow the reference laser.

[0101] It should be noted that in the above embodiments, the description of each embodiment has its own emphasis, and for parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0102] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0103] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded computer, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0104] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0105] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0106] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0107] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A feedforward compensation system for suppressing terahertz radiation noise generated by optical frequency down-conversion, characterized in that: The feedforward compensation system comprises: a reference laser, a slave laser, a first optical coupler, a second optical coupler, a third optical coupler, a detection and driving unit, an IQ modulator, a fourth optical coupler and a terahertz detector; The laser light outputted by the reference laser is divided into two beams through the first optical coupler, one beam enters the third optical coupler, and the other beam enters the fourth optical coupler; The laser light outputted from the laser is divided into two beams through the second optical coupler, one beam enters the third optical coupler, and the other beam enters the optical input port of the IQ modulator; The third optical coupler couples the two input optical signals into a beam of light and outputs the beam to the detection and driving unit; The detection and driving unit detects the relative phase noise and frequency jitter between the reference laser and the slave laser, generates a corresponding driving signal, and outputs two orthogonal RF signals to the RF input port of the IQ modulator; The IQ modulator compensates for the frequency jitter and phase noise of the slave laser relative to the reference laser under the action of the driving signal, and outputs an optical signal to the fourth optical coupler; The fourth optical coupler couples the two input optical signals into a beam of light and outputs it to the terahertz detector; The terahertz detector performs frequency down-conversion on two input optical signals of different frequencies, and outputs the optical signals of the two frequencies in the form of photocurrent.

2. The feedforward compensation system according to claim 1, characterized in that: The reference laser and the slave laser are single longitudinal mode lasers, the working center frequency is adjustable, and a narrow line width optical signal with a line width less than 15 kHz is generated; The operating center frequencies of the slave laser and the reference laser differ by 0.1-1 THz.

3. The feedforward compensation system according to claim 1, characterized in that: The first optical coupler divides the input optical signal into two beams according to the ratio, the large output ratio end is connected to the fourth optical coupler, and the small output ratio end is connected to the third optical coupler.

4. The feedforward compensation system according to claim 1, characterized in that: The second optical coupler divides the input optical signal into two beams according to the ratio, the large output ratio end is connected to the IQ modulator, and the small output ratio end is connected to the third optical coupler.

5. The feedforward compensation system according to claim 1, characterized in that: An optical filter is also arranged between the fourth optical coupler and the terahertz detector.

6. The feedforward compensation system according to claim 1, characterized in that: The detection and driving unit comprises: a modulation driving generator, an optical phase modulator, a narrowband filter, a photodetector, an IQ phase detector and two low-pass filters; The modulation drive generator is used to generate a drive signal for the optical phase modulator and a demodulation signal for the IQ phase detector; The input end of the optical phase modulator is connected to the output end of the third optical coupler, and the electrical input end is connected to the high-frequency output of the modulation drive generator, and the drive signal is applied to the two input optical signals to generate a modulation sideband of the corresponding frequency, which is output to the narrowband filter; The narrowband filter is an optical filter, which performs optical filtering on the input signal and then outputs it to the photodetector; The photodetector converts the beat frequency signal of the reference laser and the overlapping part of the laser frequency sideband filtered by the narrowband filter into a current signal, and outputs it to the IQ phase detector; The IQ phase detector extracts the in-phase and quadrature current amplitude and phase information from the input signal, and the I and Q ports output the in-phase and quadrature voltage signals to two low-pass filters respectively; The two low-pass filters are used to filter the in-phase and quadrature voltage signals output by the IQ phase detector, and the output signals drive the IQ modulator.

7. The feedforward compensation system according to claim 6, characterized in that: The modulation drive generator includes: a crystal oscillator, a power divider, a radio frequency divider, a filter amplifier, a radio frequency phase shifter, and a voltage amplifier; The crystal oscillator is used to provide a stable signal source required for phase modulation and IQ phase detection, and the output end is connected to the power divider; The power divider divides the input signal into two parts and then outputs them to the RF frequency divider and RF phase shifter respectively for connection; The frequency division coefficient of the radio frequency divider is determined based on the overlapped portion of the sideband orders of the reference laser and the slave laser, and the output end is connected to the filter amplifier; The filtering center frequency of the filter amplifier is the same as the operating frequency after frequency division, and the output end is connected to the IQ phase detector; The radio frequency phase shifter is used to adjust the phase of the input electrical signal and output it to the voltage amplifier; The voltage amplifier amplifies the low voltage obtained after frequency shifting and outputs it to the optical phase modulator.

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