CN114137743B - High-linearity modulator chip based on cascaded silicon-based micro-ring modulator and modulation method - Google Patents
High-linearity modulator chip based on cascaded silicon-based micro-ring modulator and modulation method Download PDFInfo
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour in optical waveguides, not otherwise provided for in this subclass
- G02F1/0113—Glass-based, e.g. silica-based, optical waveguides
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
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Abstract
The invention discloses a high-linearity modulator chip based on a cascaded silicon-based micro-ring modulator and a modulation method. The two lasers with different wavelengths output optical carrier signals and are combined through an on-chip beam combiner or a wavelength division multiplexer, and as the micro-ring modulator has a wavelength selection function, the two paths of optical carriers are respectively coupled into the two silicon-based micro-ring modulators through bus waveguides. The electric modulation signal is divided into two paths through an electric power divider with adjustable power ratio and respectively modulates the two micro-ring modulators. One micro-ring modulator works at the maximum point of the first-order harmonic component and the other micro-ring modulator works at the maximum point of the third-order nonlinearity by regulating and controlling the working points of the two micro-ring modulators. Meanwhile, the distribution ratio of the electric power divider is regulated and controlled, and when the photoelectric detector end demodulates, the three-order nonlinearity in the two micro-loops can be mutually offset through the operation, and meanwhile, the first-order harmonic component is ensured to be smaller in change.
Description
Technical Field
The invention relates to a high-linearity modulator chip based on a cascaded silicon-based micro-ring modulator, in particular to a high-linearity modulator chip based on a cascaded silicon-based micro-ring modulator and a modulation method.
Background
In recent years, microwave photon technology integrating microwave technology and light wave technology is widely applied to wireless communication, optical fiber radio frequency transmission systems, radar electronics and the like. It is mainly studied how to use photoelectric devices and optical methods to realize the generation, transmission, processing, detection, etc. of microwave/millimeter wave signals. With the increasing complexity of functions and urgent need for cost reduction of microwave photonic systems, the size, weight and power consumption from device to system are required to be reduced, and miniaturization, light weight and low cost of the systems are achieved.
In a microwave photon link, it is important to achieve modulator performance for converting microwave signals from the electrical domain to the optical domain, because the transfer function of the modulator has a certain nonlinearity, which will generate higher order harmonics and intermodulation signals, in particular the third order harmonic HD3 (the 3 rd Harmonic Distortion, HD 3) and third-order intermodulation signal IMD3 (the 3) rd Inter-Modulation Distortion, IMD 3) reduces the Spurious Free Dynamic Range SFDR (SFDR) of the microwave photon system. To realize microwave signal inAnalog high-fidelity transmission in optical links, and achieving high dynamic link performance, modulator linearity is a very important indicator.
At present, most microwave photon links use lithium niobate modulators, but the lithium niobate modulators have the defects of large volume, large insertion loss, high power consumption and the like. In contrast, a silicon optical integration platform with advantages of small volume, low power consumption, CMOS (Complementary Metal Oxide Semiconductor, CMOS) compatibility, photoelectric monolithic integration and the like has great potential in the aspects of miniaturization and low cost of a microwave photon system. Silicon-based modulators as important silicon optical devices have a significant impact on link performance. Silicon-based modulators can be categorized into Silicon-based Mach-Zehnder Modulator (Si-MZM) and Silicon-based micro-ring modulators (Silicon-based Ring Modulator, si-MRM) according to the structure. Compared with Si-MZM, si-MRM has the advantages of ultra-small size, ultra-low power consumption, ultra-large bandwidth and the like, and has great potential in miniaturization of a microwave photon system. However, si-MRM is affected by lorentz modulation curves and carrier dispersion effects, which have very strong electro-optical modulation nonlinearities, i.e. very strong third-order harmonics and intermodulation nonlinear signals can be generated during the modulation process, thus reducing the dynamic range of the microwave photon link. How to improve the linearity of Si-MRM is therefore a scientific problem of great interest in current academia and industry.
The current methods for improving the linearity of Si-MRM can be divided into two categories: the first is the integration of a linear electro-optic material film, such as a silicon-based lithium niobate thin film micro-ring modulator, on a silicon photo-chip. Compared with Si-MRM based on carrier dispersion effect, the method has a certain degree of improvement on linearity due to the use of linear electro-optic materials. However, this approach introduces very complex processing techniques and would introduce very high costs. In addition, the method can not realize the monolithic integration of the photoelectric device, and is not beneficial to the further integration and miniaturization of a microwave photon system. The second method is to use the nonlinearity of the DC-Kerr effect to offset the nonlinearity of the carrier dispersion effect, thereby realizing the high linearity modulation of Si-MRM. However, the method changes the process flow of the chip foundry and improves the complexity and cost of chip processing.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a high-linearity modulation chip and a modulation method based on a cascaded silicon-based micro-ring modulator, which are characterized in that two optical carrier signals with the same power are input and respectively coupled into corresponding Si-MRMs, and the working points of the two Si-MRMs are regulated and controlled, so that one Si-MRM works at the relative maximum working point of a first-order harmonic HD1, the other Si-MRM works at the relative maximum working point of a third-order harmonic HD3, and the phase difference pi between the two working points is ensured. By regulating and controlling the power ratio of the modulation signals loaded on the two Si-MRMs, the complete cancellation of the HD3 component can be realized, and the power of the HD1 component is kept unchanged basically.
The technical scheme of the invention is as follows:
the invention first provides a high-linearity modulator chip based on a cascaded silicon-based micro-ring modulator, which comprises: the laser device comprises two input end couplers for coupling optical carrier signals output by a laser into a Modulator chip, a beam combiner for combining the optical signals of the two input end couplers into one path, a bus waveguide connected with the beam combiner and used for transmitting the optical signals, two cascaded Silicon-based Micro-Ring modulators 1, si-MRM1 and an output end coupler connected with the bus waveguide;
the two cascaded silicon-based micro-ring modulators comprise a first silicon-based micro-ring modulator and a second silicon-based micro-ring modulator, and the two silicon-based micro-ring modulators are identical and are coupled on the same bus waveguide.
As a preferable scheme of the invention, the input end coupler is a grating coupler or an end face coupler; the output end coupler is a grating coupler or an end surface coupler.
As a preferred scheme of the invention, the beam combiner for combining the optical signals of the two input end couplers into one path is a beam combiner or a wavelength division multiplexer.
As a preferable scheme of the invention, the silicon-based micro-ring modulator is a straight-through micro-ring modulator and comprises a micro-ring resonant cavity embedded with a PN junction phase shifter, and the silicon-based micro-ring modulator is integrated with a thermo-optical phase shifter for regulating and controlling a working point; the resonant cavities of the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator are distributed on one side of the same bus waveguide.
The invention also discloses a modulation method of the high-linearity modulator chip, which comprises the following steps:
1) Two wavelengths are respectively lambda 1 And lambda (lambda) 2 Optical carrier signals output by the external laser are respectively coupled into the modulator chip through the input end coupler;
2) Two paths of optical carrier signals with different wavelengths of two input end couplers are combined into one path of optical signal through a beam combiner and transmitted in a bus waveguide;
3) Regulating and controlling reverse bias voltage V of PN junction phase shifter on two silicon-based micro-ring modulators DC1 And V DC2 PN junction modulation arms on the two silicon-based micro-ring modulators work in a reverse bias area;
4) Regulating and controlling the thermo-optical phase shifters on the two silicon-based micro-ring modulators to enable the first silicon-based micro-ring modulator to work at the relative maximum point of HD1, and the second silicon-based micro-ring modulator to work at the relative maximum point of HD3, wherein the phase difference between the two working points is pi;
5) A radio frequency signal generator is used for generating a double-tone modulation signal and dividing the double-tone modulation signal into two paths through a radio frequency power divider with adjustable power ratio; the two paths of double-tone signals and two paths of direct current reverse Bias voltages generated by a voltage source are loaded on two corresponding silicon-based micro-ring modulators through two Bias-tee respectively;
6) By regulating the power ratio of the radio frequency power divider, the three-order nonlinear HD3 generated by the two silicon-based micro-ring modulators are mutually offset at the photoelectric detector end, the HD1 component power variation is within 3dB, and the dynamic range of the link is improved.
As a preferable scheme of the invention, the optical signal modulated by the high-linearity modulator chip is amplified by the optical fiber amplifier before being connected into the photoelectric detector for demodulation, so as to compensate the coupling loss of the chip.
As a preferred embodiment of the present invention, the step 6) specifically includes: the optical signal is connected into a photoelectric detector for demodulation, the demodulated signal is led into a frequency spectrograph, the power ratio of a radio frequency power divider is regulated and controlled to regulate and control the power ratio of two-tone modulation signals loaded on two silicon-based micro-ring modulators, meanwhile, the power of first-order harmonic HD1 and third-order intermodulation signals IMD3 on the frequency spectrograph is observed until the power difference between the HD1 and the IMD3 is maximum, meanwhile, the power of the HD1 is ensured to be larger than the power of the IMD3, the power change of an HD1 component is within 3dB, and the power is the optimal linear working point of a modulator chip.
As a preferred embodiment of the present invention, the step 4) specifically includes:
4.1 Regulating and controlling thermo-optic phase shifter on two modulators of silicon-based micro-ring to make wavelength be lambda 1 And lambda (lambda) 2 The optical carrier of the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator are respectively coupled into the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator;
4.2 Regulating and controlling a thermo-optic phase shifter of the first silicon-based micro-ring modulator to enable the thermo-optic phase shifter to work at the maximum slope of a transfer function of the modulator, wherein the maximum point corresponds to a first-order harmonic component HD 1;
4.3 The thermo-optical phase shifter of the second silicon-based micro-ring modulator is regulated and controlled to work at the third-order nonlinear maximum point, and meanwhile, the direction opposite to the working point of the first silicon-based micro-ring modulator is guaranteed, and the third-order harmonic component HD3 is the maximum.
Compared with the method for improving the linearity of the Si-MRM by changing the chip processing technology, the method has the advantages that the minimum working point of the third-order intermodulation IMD3 can be found by simply regulating and controlling the distribution ratio of modulation signals loaded on two Si-MRMs on the premise of not changing the technological parameters and the flow of a foundry of the chip, and the first-order harmonic HD1 basically keeps the maximum value under the condition that the minimum of the third-order intermodulation signal IMD3 is found. The method does not bring high processing complexity and cost due to process change, and can realize the high-linearity microwave photon link based on the high-linearity silicon-based modulator by only changing the power ratio of the modulation signals loaded on the two Si-MRMs. The chip manufacturing process is based on a CMOS process, namely the photon chip and the electronic chip can be manufactured on the same chip, and the peripheral control chip can be integrated on the same chip, so that the size and the power consumption of the whole system are greatly reduced, and the production cost is also saved.
Drawings
Fig. 1 is a schematic diagram of a modulator structure and a test flow according to the present invention.
Fig. 2 is a schematic diagram of the modulation principle of the micro-ring modulator.
Fig. 3 is a simulation result of the variation of the components of the micro-ring modulators HD1 and HD3 with wavelength. The abscissa is the wavelength mismatch relative to the resonance wavelength (Frequency Detuning), and "0" represents the operating point as the resonance wavelength point.
Detailed Description
The invention is further described below with reference to the drawings and examples.
As shown in fig. 1, a high linearity modulator chip based on a cascaded silicon-based micro-ring modulator includes: the laser device comprises two input end couplers for coupling optical carrier signals output by a laser into a modulator chip, a beam combiner for combining the optical signals of the two input end couplers into one path, a bus waveguide connected with the beam combiner and used for transmitting the optical signals, two cascaded silicon-based micro-ring modulators (Si-MRM 1) and an output end coupler connected with the bus waveguide;
the two cascaded silicon-based micro-ring modulators comprise a first silicon-based micro-ring modulator and a second silicon-based micro-ring modulator, and the two silicon-based micro-ring modulators are identical and are coupled on the same bus waveguide. In the figure, "1" is the coupler of the modulator chip and the optical fiber, typically a grating coupler or an end-face coupler. "2" is an on-chip optical combiner or wavelength division multiplexer, and "3" is a bus waveguide.
As shown in FIG. 1, the invention cascades two Si-MRMs based on carrier depletion, and the resonant cavities of the two Si-MRMs are distributed on one side of the same bus waveguide. Two paths of optical carriers with different wavelengths are synthesized by an on-chip optical combiner or a wavelength division multiplexer, transmitted by the same bus waveguide and respectively coupled into corresponding Si-MRM. The two Si-MRMs respectively work at the relative maximum point of HD1 and the relative maximum point of HD3 by regulating and controlling the thermo-optic phase shifters on the two Si-MRMs, and the phases of the two working points are different by pi. On a sub-basis, the power distribution ratio of the radio frequency power divider is regulated, so that the HD3 component generated by the two-stage modulator is mutually offset when the high-speed detector demodulates, and the power of the outputted HD1 component is changed less.
The high-linearity modulation method based on the cascaded silicon-based micro-ring modulator comprises the following steps:
1) Two paths of unmodulated optical carrier signals output by two lasers with different wavelengths are coupled into a modulator chip through a structure '1' in fig. 1;
2) As shown in fig. 1, two optical signals are synthesized into one optical signal by a structure "2" and transmitted by a bus waveguide "3";
3) As shown in fig. 1, two dc power supplies generate two paths of reverse Bias voltages (generally-2V), the rf dual-tone modulation signal is split into two paths by an rf power splitter with adjustable power ratio, and the two paths of rf electrical signals and the corresponding reverse Bias voltages are respectively loaded on PN junction phase shifters of Si-MRM1 and Si-MRM2 after being combined by two Bias-tee paths. After the modulation signal is loaded on the micro-ring modulator, the resonance wavelength of the micro-ring modulator is changed, so that the output optical power of the bus waveguide is changed, and the modulation function is realized. FIG. 2 is a schematic diagram of the Lorentz transfer curve, modulated signal and modulated optical signal principle including a micro-ring modulator;
4) The thermo-optic phase shifters TOPS1 and TOPS2 on Si-MRM1 and Si-MRM2 are controlled to couple two optical carrier signals with corresponding wavelengths of lambda 1 and lambda 2 into Si-MRM1 and Si-MRM2 respectively, and the working points of the two modulators are respectively operated at the relative maximum point of HD1 and the relative maximum point of IMD3, and the relation between the wavelengths of the HD1 and IMD3 and the micro-ring modulator. It can be seen that HD1 and IMD3 components at the non-pass wavelengths are of different relative magnitudes;
5) The modulated optical signal is output by the structure '1', amplified by the EDFA and compensated by the coupling loss of the chip, and finally input into a high-speed photoelectric detector for demodulation;
6) Inputting the demodulated electric signal into an electric spectrometer, regulating and controlling the power ratio gamma of the radio frequency power divider, and observing the relative sizes of HD1 and IMD3 components, namely the carrier distortion suppression ratio CDR (Carrier to Distortion Ratio) through the electric spectrometer;
7) Repeating the step '6') until the CDR reaches the maximum and the HD1 component does not change much, which is the optimal linear modulation point. The method comprises the following steps: introducing the demodulated signals into a frequency spectrograph, regulating and controlling the power ratio of the radio frequency power divider to regulate and control the power ratio of the two-tone modulation signals loaded on two Si-MRMs, and simultaneously observing the power of first-order harmonic HD1 and third-order intermodulation signals IMD3 on the frequency spectrograph until the power difference between the HD1 and the IMD3 is maximum (simultaneously ensuring that the power of the HD1 is greater than that of the IMD 3), and the HD1 is basically unchanged, wherein the power difference is the optimal linear working point of the modulator chip.
According to the time domain coupling mode theory, the linearity theory of the single micro-ring modulator considering the influence of third-order harmonic waves is deduced:
assuming angular frequency omega RF Amplitude v 0 RF modulated signal v of (2) 0 cosω RF t is loaded on the micro-ring modulator, and the generated AC alternating current signal is:
in f (omega) RF ) Andrespectively representing the modulus and phase of the frequency response.
According to the time domain coupled mode theory, the energy amplitude α (t) stored in the micro-ring satisfies:
wherein ω and A m Angular frequency and amplitude, ω, representing the amplitude of the incident light field, respectively 0 Representing the micro-ring modulator resonant angular frequency. 1/τ represents the amplitude decay rate of the optical field within the entire micro-ring resonator. Omega can be adjusted by controlling PN junction design parameters 0 And 1/τ, thus the designed and fabricated micro-ring modulator has a fixed ω 0 And 1/τ (Haifeng Shao, hui Yu, xia Li, yan Li, jianfei J)iang,Huan Wei,Gencheng Wang,Tingge Dai,Qimei Chen,Jianyi Yang,and Xiaoqing Jiang.On-chip microwave signal generation based on a silicon microring modulator[J].Optics Letters,2015,40(14):3360-3363)。
For a single silicon-based micro-ring modulator, the transmission light field S (t) =ae of the bus waveguide thereof jωt -j μa (t). To obtain third-order nonlinearity of micro-ring modulator and simplify calculation, for omega 0 And 1/τ Taylor expansion to the fourth term, yielding:
wherein omega DC And 1/τ DC The resonance frequency and the amplitude decay rate at the dc bias point are shown, respectively. k (k) 1 、k 2 、k 3 Is omega 0 Coefficients of corresponding first-order term, second-order term and third-order term when the DC bias point is unfolded, r 1 、r 2 、r 3 Is the coefficient of the first order term, the second order term and the third order term corresponding to 1/tau when the DC bias point is unfolded. These coefficients are determined by the coupling state of the microring and the waveguide mode and can be obtained by fitting experimental test results.
Bringing equations (3) - (4) into equation (2) yields:
the expression of α (t) can be obtained from the differential equation in equation (5):
wherein the expressions A, B, C, D are as follows:
bringing equation (6) into S (t) can obtain the transmitted light field S (t) in the time domain, and the corresponding light power is |S (t) | 2 . Because the receiving end uses the high-speed photoelectric detector for square law detection to demodulate the modulated optical signal, the first-order harmonic component HD1 and the second-order harmonic HD (the 2) can be calculated according to the formulas (2) - (4) nd Harmonic Distortion, HD 2) and third harmonic HD3 have optical powers of:
HD1＝∫|S(t)| 2 cos(ω RF t)dt+∫|S(t)| 2 sin(ω RF t)dt (8)
HD2＝∫|S(t)| 2 cos(2ω RF t)dt+∫|S(t)| 2 sin(2ω RF t)dt (9)
HD3＝∫|S(t)| 2 cos(3ω RF t)dt+∫|S(t)| 2 sin(3ω RF t)dt (10)
from the literature and the characteristics of square law detection of photodetectors, it is known that the demodulated third-order intermodulation nonlinear IMD3 (the 3 rd Inter-modulated Distortion, IMD 3) is 9.5dB higher than the electrical power of HD3, i.e., P IMD3 ＝P HD3 +9.5dB. Finding the HD3 minimum operating point is therefore also the minimum operating point for finding IMD 3.
Based on the nonlinear theory, the relationship between the relative sizes of HD1 and HD3 and the operating wavelength in the normalized micro-ring modulator can be obtained, as shown in fig. 3. Based on the simulation results, TOPS1 and TOPS2 on Si-MRM1 and Si-MRM2 are regulated to enable Si-MRM1 to work at the maximum point of HD1 relative to HD3 and Si-MRM2 to work at the maximum point of HD3 relative to HD 1. Let the optical powers of HD1 and HD3 outputted by Si-MRM1 at this time be P HD1-MRM1 And P HD3-MRM1 The optical powers of HD1 and HD3 output by Si-MRM2 are P respectively HD1-MRM2 And P HD3-MRM2 . The power ratio gamma of the modulation signals loaded on the Si-MRM1 and the Si-MRM2 can be regulated and controlled, so that the optical powers of the HD1 component and the HD3 component output by the two silicon-based micro-ring modulators can be flexibly controlled. Since the working points of the two modulators are out of phase by pi, this can be achievedHD3 counteracts each other while HD1 is essentially unchanged.
Claims (7)
1. A high-linearity modulation method of a high-linearity modulator chip based on a cascaded silicon-based micro-ring modulator,
the high-linearity modulator chip based on the cascaded silicon-based micro-ring modulator comprises: the device comprises two input end couplers for coupling optical carrier signals output by a laser into a modulator chip, a beam combiner for combining the optical signals of the two input end couplers into one path, a bus waveguide connected with the beam combiner and used for transmitting the optical signals, two cascaded silicon-based micro-ring modulators and an output end coupler connected with the bus waveguide;
the two cascaded silicon-based micro-ring modulators comprise a first silicon-based micro-ring modulator and a second silicon-based micro-ring modulator, and the two silicon-based micro-ring modulators are identical and are coupled on the same bus waveguide;
the modulation method is characterized by comprising the following steps:
1) Two same power and wavelength lambda 1 And lambda (lambda) 2 Optical carrier signals output by the external laser are respectively coupled into the modulator chip through the input end coupler;
2) Two paths of optical carrier signals with different wavelengths of two input end couplers are combined into one path of optical signal through a beam combiner and transmitted in a bus waveguide;
3) Regulating and controlling reverse bias voltage V of PN junction phase shifter on two silicon-based micro-ring modulators DC1 And V DC2 PN junction modulation arms on the two silicon-based micro-ring modulators work in a reverse bias area;
4) Regulating and controlling the thermo-optical phase shifters on the two silicon-based micro-ring modulators to enable the first silicon-based micro-ring modulator to work at the relative maximum point of HD1, and the second silicon-based micro-ring modulator to work at the relative maximum point of HD3, wherein the phase difference between the two working points is pi;
5) A radio frequency signal generator is used for generating a double-tone modulation signal and dividing the double-tone modulation signal into two paths through a radio frequency power divider with adjustable power ratio; the two paths of double-tone signals and two paths of direct current reverse Bias voltages generated by a voltage source are loaded on two corresponding silicon-based micro-ring modulators through two Bias-tee respectively;
6) By regulating the power ratio of the radio frequency power divider, the three-order nonlinear HD3 generated by the two silicon-based micro-ring modulators are mutually offset at the photoelectric detector end, the HD1 component power variation is within 3dB, and the dynamic range of the link is improved.
2. The modulation method of claim 1, wherein the input coupler is a grating coupler or an end-face coupler; the output end coupler is a grating coupler or an end surface coupler.
3. The modulation method according to claim 1, wherein the combiner for combining the optical signals of the two input couplers into one path is a combiner or a wavelength division multiplexer.
4. The modulation method according to claim 1, wherein the silicon-based micro-ring modulator is a through-type micro-ring modulator, and comprises a micro-ring resonant cavity embedded with a PN junction phase shifter, and the silicon-based micro-ring modulator is integrated with a thermo-optic phase shifter for regulating and controlling an operating point; the resonant cavities of the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator are distributed on one side of the same bus waveguide.
5. The method of claim 1, wherein the optical signal modulated by the high-linearity modulator chip further comprises the step of amplifying the optical signal modulated by the high-linearity modulator chip by an optical fiber amplifier to compensate for coupling loss of the chip before the optical signal is coupled to the photodetector for demodulation.
6. The modulation method according to claim 1, wherein the step 6) specifically comprises: the optical signal is connected into a photoelectric detector for demodulation, the demodulated signal is led into a frequency spectrograph, the power ratio of a radio frequency power divider is regulated and controlled to regulate and control the power ratio of two-tone modulation signals loaded on two silicon-based micro-ring modulators, meanwhile, the power of first-order harmonic HD1 and third-order intermodulation signals IMD3 on the frequency spectrograph is observed until the power difference between the HD1 and the IMD3 is maximum, meanwhile, the power of the HD1 is ensured to be larger than the power of the IMD3, the power change of an HD1 component is within 3dB, and the power is the optimal linear working point of a modulator chip.
7. The modulation method according to claim 1, wherein the step 4) specifically comprises:
4.1 Regulating and controlling thermo-optic phase shifter on two modulators of silicon-based micro-ring to make wavelength be lambda 1 And lambda (lambda) 2 The optical carrier of the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator are respectively coupled into the first silicon-based micro-ring modulator and the second silicon-based micro-ring modulator;
4.2 Regulating and controlling a thermo-optic phase shifter of the first silicon-based micro-ring modulator to enable the thermo-optic phase shifter to work at the maximum slope of a transfer function of the modulator, wherein the maximum point corresponds to a first-order harmonic component HD 1;
4.3 The thermo-optical phase shifter of the second silicon-based micro-ring modulator is regulated and controlled to work at the third-order nonlinear maximum point, and meanwhile, the direction opposite to the working point of the first silicon-based micro-ring modulator is guaranteed, and the third-order harmonic component HD3 is the maximum.
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