Programmable signal processing chip based on silicon optical modulator and control method

Abstract

The application discloses a programmable signal processing chip based on a silicon optical modulator and a control method. The chip is based on silicon-on-insulator material and is manufactured by using a semiconductor processing technology. The chip mainly comprises five silicon-based end face couplers, two silicon-based carrier depletion type Mach-Zehnder push-pull modulators with the same structure, and eight silicon-based extinction ratio and center resonant wavelength adjustable micro-ring modulators with the same structure. The comb tooth number, spectral line spacing and flatness of the generated optical frequency comb are regulated by controlling the input RF signal amplitude, frequency and DC bias voltage size. The overall optical frequency comb can be regulated by adjusting the resonant peak of the cascaded micro-ring modulator at the back end to align with the specified comb center wavelength. The chip has the advantages of artificial adjustability, strong reconfigurability and high integration degree, and can be used in the fields of high-speed narrow-band Nyquist pulse sequence generation, waveform shaping, high-frequency electrical signal synthesis, digital optical communication and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to a programmable signal processing chip based on silicon optical modulator and a control method, in particular to a multi-functional programmable processing photonic integrated chip. BACKGROUND

[0002] Silicon photonics, initially considered as a revolutionary technology to combine optical communication networks and complementary metal-oxide-semiconductor (CMOS) industry, is now becoming a major technology platform including optoelectronic integrated circuits (OEICs), nonlinear optics, lidar, mid-infrared sensors, and quantum photonic circuits. Photonic integration is the dominant technology in high-bandwidth communications and dominates many areas of photonics, while photonic integrated circuits (PICs) have become a powerful technology in the past few decades due to their unique advantages of ultra-wideband, high-precision, compact, low-power consumption, and low-cost manufacturing. Therefore, these characteristics enable PICs to be applied to various applications such as high-speed digital optical communication, analog optical signal processing, chemical and biological thermal sensing, etc.

[0003] However, most of these photonic integrated circuits are designed to perform a single or a few functions to meet the needs of a certain specific application, and they are called application-specific photonic integrated circuits (ASPICs). In recent years, with the continuous development of silicon-based optoelectronic integration technology, the demand for multiple optical signal processing capabilities supporting multiple application scenarios has been growing, and programmable PICs have emerged as the times require. Programmable PICs fabricated on a number of different material integration platforms have been reported, with the most representative material platforms being indium phosphide (InP), silicon nitride (Si3N4), and silicon-on-insulator (SOI).

[0004] The above-mentioned material platforms are supported by literature, for example, W. Liu et al. proposed and demonstrated an InP-based programmable PIC that can be used for time integration, time differentiation, and Hilbert transform. However, due to the large transmission loss of the waveguide, a semiconductor optical amplifier is needed to compensate for the loss, which increases the power consumption and complexity of the waveguide. Similarly, D. Lin et al. and Y. Xie et al. proposed Si3N4-based programmable PICs that are widely used for analog beam forming, frequency discriminators, and optical pulse processing functions. However, due to the low refractive index contrast waveguide, such PICs are large in size. In addition, it cannot manufacture active photonic components such as modulators and germanium photodiodes (GePD), which hinders the expansion of more desired functions.

[0005] Compared with these two materials, silicon photonics technology based on silicon-on-insulator (SOI) is considered as the most attractive platform for programmable PICs due to its compatibility, high integration, and potential for seamless integration with electronic devices. Therefore, in recent years, a large number of functionally rich silicon-based programmable PICs have emerged, which can be used for advanced analog radio frequency systems, complex-valued pulse shaping, photonic integrated field programmable disk arrays, and other applications. The above programmable PICs are based on the idea of manipulating the transmission of optical fields on the chip through electrically controlled beam couplers or disks. However, they are mostly unable to be used for digital optical modulation, signal generation, and complex optical signal processing. SUMMARY

[0006] In order to expand the application scenarios and avoid functional deficiencies, the present application proposes a programmable signal processing chip based on silicon optical modulator and a control method based on the SOI photonic integrated platform. By adjusting the working state of the modulator, this PIC can be used for the generation of Nyquist pulses, the generation of high-frequency microwave signals, and digital optical communication.

[0007] The technical solutions of the present application are as follows:

[0008] The present application provides a programmable signal processing chip based on a silicon optical modulator; the chip comprises five silicon-based edge couplers (Silicon-based Edge Coupler) Si-EC1-Si-EC5, two silicon-based carrier depletion Mach-Zender push-pull modulators (Silicon-based carrier depletion Mach-Zender push-pull modulator) Si-MZM1-Si-MZM2 of the same structure, and a series microring modulation unit composed of eight silicon-based extinction ratio and central resonant wavelength adjustable microring modulators (Silicon-based extinction ratio and central resonant wavelength adjustable microring modulator) Si-MRM1-Si-MRM8 of the same structure, wherein Si-MRM1-Si-MRM8 are connected in series by bus waveguides.

[0009] The Si-MZM1 and the Si-MZM2 both adopt a symmetric MZI (Mach-Zehnder Interferometer) structure, which comprises a beam splitter, an upper arm waveguide, a lower arm waveguide and a beam combiner; a first thermal-optic phase shifter (TOPS1) is arranged on the upper arm waveguide, a second thermal-optic phase shifter (TOPS2) is arranged on the lower arm waveguide, and a PN junction phase shifter is embedded in the center of the two arm waveguides, the inside of the waveguide is P-type doped, and the outside is N-type doped; the outside of the two arm waveguides is provided with a traveling wave electrode, and the beam splitter and the beam combiner are both 2*2 structures.

[0010] The Si-EC1 is connected with the beam splitter of the Si-MZM1 as a chip input end, and the optical carrier is output through the beam combiner of the Si-MZM1, the first output end of the beam combiner is connected with the front beam splitter of the Si-MZM2, the optical carrier is transmitted into secondary regulation, the second output end is connected with the Si-EC2, and the optical carrier is output and used for detection.

[0011] The other input end of the beam splitter of the Si-MZM2 is connected with the Si-EC3, and is used for separately inputting an optical signal; the output end of the beam combiner of the Si-MZM2 has two paths, the first output end is connected with the input end of the serial micro-ring modulation unit and is regulated; the second output end is connected with the Si-EC4, and the optical carrier is output and used for detection.

[0012] The output end of the serial micro-ring modulation unit is connected with the Si-EC5 as a chip output end, and is used for detecting an output optical field.

[0013] In another aspect, the application provides a control method of a programmable signal processing chip based on a silicon optical modulator, which can realize functions such as reconfigurable Nyquist pulse sequence generation, high-frequency microwave signal synthesis and digital optical communication according to needs, and comprises the following steps:

[0014] 1) An optical carrier signal with a frequency of f0 output by an external laser is coupled into the chip through the Si-EC1, the beam splitter of the Si-MZM1 first divides the signal into two paths with equal optical intensity and inputs them into the upper arm and the lower arm respectively, and the optical phase difference of the Si-MZM1 can be regulated by regulating the driving voltage of the TOPS1 and the TOPS2 on the upper arm and the lower arm.

[0015] A radio frequency signal RF1 with a frequency of 3f m is input into the traveling wave electrode of the Si-MZM1 through a probe, and is used for regulating the frequency component of an optical frequency comb (OFC); the PN junction on the Si-MZM1 is reversely biased by adjusting the size of the direct current bias voltage thereof; and a center frequency f0 and a frequency interval 3f ma 3-line optical frequency comb;

[0016] 2) the optical carrier signal output from the first output end of the combiner of the Si-MZM1 enters the Si-MZM2, with a frequency of f m RF2 is input to the traveling wave electrode of the Si-MZM2 through a probe, RF1 and RF2 are phase-locked, and the phase difference is controlled through an externally adjustable electric phase shifter; at the same time, TOPS1 and TOPS2 of the Si-MZM2 and the direct current bias voltage are controlled, to generate a 9-line optical frequency comb with a center frequency of f m 9 and a frequency interval of f

[0017] 3) when a reconfigurable Nyquist pulse sequence needs to be generated, the RF1, RF2, the thermo-optic phase shifter voltage of the Si-MZM1 and the Si-MZM2, and the externally adjustable electric phase shifter are controlled at the same time, so that the generated optical frequency comb has the characteristics of equal amplitude, equal frequency interval, phase linearization, and high out-of-band suppression ratio; the optical signals output by the Si-EC2 and the Si-EC4 are connected to an external high-speed PD for frequency mixing, and then connected to a real-time oscilloscope for observation, to obtain a 3-line and 9-line optical frequency comb in the time domain, which generates a sinc-type Nyquist pulse sequence with weak distortion, and the optical power of different comb teeth of the obtained optical frequency comb is suppressed by adjusting the center resonance wavelength of the Si-MRM1 to Si-MRM8, to realize time-domain waveform change and waveform shaping;

[0018] when a high-frequency microwave signal needs to be synthesized, two comb teeth are selected from the generated 9-line optical frequency comb as the synthesized microwave signal, the driving voltages of TOPS3 and TOPS4 of the Si-MRM1 to Si-MRM8 are adjusted to generate resonance peak sequences with different intervals and different extinction ratios, the extinction ratio of the Si-MRM1 to Si-MRM8 is controlled to be the largest, and the center resonance wavelength of the Si-MRM1 to Si-MRM8 is adjusted to be equal to the center frequency of the optical carrier signal output by the laser source, so that the resonance peak sequence of the micro-ring resonator is in resonance with the wavelengths of the remaining 7 comb teeth that are not selected, and the resonance is canceled, and finally the output optical signal of the Si-EC5 is connected to an external high-speed PD for frequency mixing, and the synthesized high-frequency microwave signal can be observed in a spectrum analyzer;

[0019] when a digital optical communication function needs to be implemented, the driving voltage of TOPS3 of the Si-MRM1 to Si-MRM8 is controlled, so that the center resonance wavelengths of the Si-MRM1 to Si-MRM8 are equal to f m; the i-th Si-MRM is selected as an electro-optical modulator, and the other 7 Si-MRMs are selected as optical filters, the driving voltage of the TOPS4 is adjusted so that the extinction ratio of the i-th Si-MRM is 5dB, and the extinction ratios of the other 7 Si-MRMs are equal to 20dB; at this time, the frequency of the light carrier signal output by the laser source is adjusted to f0 ’ ; the comb peaks of the optical frequency comb are aligned with the center resonant wavelengths of the 8 Si-MRMs; at this time, the direct current reverse bias voltage and the NRZ or PAM4 signals of different codes and rates output by the Arbitrary Waveform Generators (AWG) are applied to the metal pad of the i-th Si-MRM through the Bias-Tee and the probe, so as to modulate the optical field at the resonant peak of the i-th Si-MRM, the output optical signal of the Si-EC5 is connected to an external low-noise Erbium-doped Optical Fiber Amplifier (EDFA) to amplify the optical power, and then connected to a high-speed PD and a real-time oscilloscope, the amplitude and rate of the signal in the AWG are adjusted, the size of the direct current reverse bias voltage on the i-th Si-MRM is adjusted, and the center resonant wavelength is finely adjusted so that the i-th Si-MRM is located at the best working point, and the NRZ and PAM4 eye diagrams of different rates can be observed in the real-time oscilloscope.

[0020] According to the preferred scheme of the application, the Si-MRM1 to Si-MRM8 each include a partially bent bus waveguide and a micro-ring resonant cavity in which a PN junction phase shifter is embedded, the partially bent bus waveguide is coupled to the micro-ring resonant cavity at two points, the coupling region length can be obtained by simulation, the micro-ring resonant cavity is provided with a third thermo-optic phase shifter TOPS3 at the top away from the bus waveguide, and the partially bent bus waveguide is provided with a fourth thermo-optic phase shifter TOPS4; the inside of the micro-ring resonant cavity is an N-type doped region, and part of the outside is a P-type doped region, the two doped regions are connected with a metal layer and a metal pad, and the driving voltage applied thereto can be changed to change the waveguide refractive index and realize modulation.

[0021] Further, by adjusting the frequency and amplitude of the modulation signal, and the size of the direct current bias voltage, different types of optical frequency combs can be generated, and more applications of the chip can be realized through subsequent frequency mixing or micro-ring filtering modulation functions.

[0022] Most of the conventional photonic integrated circuits can only support a specific function or application, which are called as application-specific photonic integrated circuits (ASPICs). In recent years, programmable PICs have emerged as an urgent need to support various optical signal processing capabilities in various application scenarios. SOI silicon photonics is considered as the most attractive programmable PIC platform due to its compatibility, high integration and potential for seamless integration with electronic devices. The present application provides a new type of silicon photonic programmable PIC, which is composed of two cascaded Si-MZMs and eight series Si-MRMs, which is innovatively used for the generation of narrowband Nyquist pulses, the synthesis of high-frequency microwave signals and digital optical communication. In summary, most of the programmable PICs in the past cannot be used for digital optical modulation, signal generation and complex optical signal processing. The chip of the present application combines the reconfigurability of optical frequency comb with multiple types of applications, which paves the way for the development of general-purpose silicon photonic integrated circuits including analog optical signal processing and digital communication systems. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Fig. 1 is a structural schematic diagram of the programmable signal processing chip based on silicon optical modulator according to the present application;

[0024] Figure 2 Fig. 2 is a schematic diagram of optical frequency comb generation;

[0025] Figure 3 Fig. 3 is a simulation result diagram of generating a 9-line optical frequency comb according to the required experimental conditions;

[0026] Figure 4 Fig. 4 is a test result diagram of the silicon-based extinction ratio and center resonant wavelength adjustable micro-ring modulator, (a) is the test result of the extinction ratio adjustable of a single micro-ring modulator, (b) is the test result diagram of the resonant peak sequence of the 8 micro-ring modulators in series with equal interval and equal extinction ratio;

[0027] Figure 5 Fig. 5 is a simulation result diagram of micro-ring filtering the middle comb teeth of the optical frequency comb, and the remaining two comb teeth on the left and right; DETAILED DESCRIPTION

[0028] The present application will be further described and explained with specific embodiments. The embodiments are only exemplary and do not circumscribe the scope of the disclosure. The technical features of each embodiment in the present application can be combined accordingly without conflict.

[0029] The present embodiment provides a programmable signal processing chip based on silicon optical modulator, which is prepared based on the CMOS compatible processing technology of silicon on insulator (SOI). In one specific embodiment of the present application, the chip is made on a 220nm SOI wafer and a 750Ω-cm silicon substrate.

[0030] As Figure 1 shown, the chip mainly integrates five silicon-based end-face couplers Si-EC1-Si-EC5, two silicon-based carrier-depletion Mach-Zehnder push-pull modulators Si-MZM1 and Si-MZM2 of the same structure, and eight silicon-based extinction ratio and center resonant wavelength adjustable micro-ring modulators Si-MRM1-Si-MRM8 of the same structure in series.

[0031] Referring Figure 1 to the drawings, the silicon-based carrier-depletion Mach-Zehnder push-pull modulators Si-MZM1 and Si-MZM2 both adopt a symmetric MZI structure and are completely identical in structure. According to one specific embodiment of the present application, it includes two 2×2 multimode interferometers (MMI) respectively serving as a beam splitter and a beam combiner, an upper arm waveguide and a lower arm waveguide; the beam splitter and the beam combiner both have two output ends and an input end; the upper arm waveguide and the lower arm waveguide are respectively provided with a first thermo-optic phase shifter TOPS1 (TOPS1, a = 1, 2, indicating the a-th Si-MZM) and a second thermo-optic phase shifter TOPS2 (TOPS2, a = 1, 2, indicating the a-th Si-MZM), and both the arm waveguides are embedded with a PN junction phase shifter at the center, with P-type doping inside and N-type doping outside; the outside of the two arm waveguides is provided with a traveling wave electrode. 1a 2a a = 1, 2, indicating the a-th Si-MZM), and both the arm waveguides are embedded with a PN junction phase shifter at the center, with P-type doping inside and N-type doping outside; the outside of the two arm waveguides is provided with a traveling wave electrode.

[0032] According to one specific embodiment of the present application, the Si-MZM is composed of two 4-mm-long active waveguides, and a 50-ohm terminal matching resistance based on TiN is connected to the end of the traveling wave electrode of each Si-MZM as an on-chip terminator. Both the waveguides are embedded with a carrier-depletion PN junction for high-speed modulation at the center, with P-type doping inside and N-type doping outside. The inside flat plate area of the two arms of the MZI is a high-concentration P-type heavily doped area, which connects the two PN junctions and the DC bias electrode. The outside flat plate layer of the two arms of the MZI is a high-concentration N-type heavily doped area connected with the traveling wave electrode, and the traveling wave electrode adopts a coplanar microstrip line structure. The two traveling wave electrodes are located at the outside of the MZI and are respectively a signal line (S) and a ground line (G). The two traveling wave electrodes are connected with a metal pad and adopt a single-port microwave input, so as to realize push-pull driving.

[0033] As Figure 1 ​As shown, the Si-MRM is composed of a partially bent straight waveguide and a micro-ring resonator with embedded PN junction phase shifters, the partially bent straight waveguide is coupled with the micro-ring resonator at points A and B, and the length of the coupling region can be obtained by simulation. Here, the third and fourth thermal-optic phase shifters (TOPS3, TOPS4) based on TiN are respectively placed on the top of the micro-ring resonator away from the bus waveguide and at the partially bent bus waveguide, and are respectively used for independently tuning the center resonant wavelength and the coupling ratio (extinction ratio) between the bus waveguide and the micro-ring resonator. The inside of the micro-ring resonator is an N-type doped region, and part of the outside is a P-type doped region, the two doped regions are connected through a metal layer and a metal pad, and changing the driving voltage applied thereto can change the waveguide refractive index and thus achieve modulation. By adjusting the extinction ratio and the center resonant wavelength, the two-point coupled MRM can be used as an electro-optic modulator or a bandwidth and resonant point adjustable optical filter.

[0034] As shown in Figure 1 Si-EC1 and Si-EC3 are mainly input functions, used for external laser and polarization controller; Si-EC2, Si-EC4 and Si-EC5 are mainly output functions, used for external optical power splitter, photodetector (PD) and oscilloscope. The connection relationship of the components in the silicon-based optoelectronic programmable processor chip is as follows: Si-EC1 is connected with the beam splitter of Si-MZM1 as the input end of the chip, the optical carrier is output through the beam combiner of Si-MZM1, the first output end of the beam combiner is connected with the front beam splitter of Si-MZM2, the optical carrier is transmitted into the secondary regulation and control, the second output end is connected with Si-EC2, and the optical carrier is output and used for detection; the other input end of the beam splitter of Si-MZM2 is connected with Si-EC3, used for separately inputting optical signal; the output end of the beam combiner of Si-MZM2 has two paths, the first output end is connected with the input end of the serial micro-ring modulation unit and is regulated and controlled; the second output end is connected with Si-EC4, and the optical carrier is output and used for detection; the output end of the serial micro-ring modulation unit is connected with Si-EC5 as the output end of the chip, used for detecting the output optical field.

[0035] According to a specific embodiment of the present application, the TOPS1-TOPS4 are led out through on-chip metal wires and gathered into a pad array, which can be connected with a PCB board through wire bonding, connected with an external direct current voltage source through an adapter plate and a flexible flat cable, and directly regulate and control the driving voltage of the thermal-optic phase shifter.

[0036] The programmable signal processing chip based on the silicon optical modulator can realize multiple functions by control, for example, can realize the reconfigurable Nyquist pulse sequence generation function, realizes the high frequency microwave signal synthesis function and realizes the digital optical communication function. The control method of the chip in realizing different functions is introduced below, wherein steps 1) to 4) are the basic steps required to realize each function.

[0037] 1) The optical carrier signal with the frequency f0 output by the external laser is adjusted to the TE mode by the external polarization controller, and then coupled into the optical chip through the on-chip silicon end-coupler Si-EC1, at this time, the frequency spectrum output at Si-EC5 of the optical chip is as shown in (a) of Figure 2 ;

[0038] 2) The input signal is divided into two paths with equal light intensity by MMI_11 and input into the upper and lower arms of Si-MZM1 respectively, and the DC bias voltage of Si-MZM1 is set, generally-3V, so that the PN junction is reverse biased. At this time, the driving voltage of TOPS 11 and TOPS 21 can control the optical phase difference of Si-MZM1, that is, the light power distribution ratio of the two output ports of the tail end MMI_12 thereof, generally one of TOPS 11 and TOPS 21 is selected for control;

[0039] 3) The radio frequency signal RF1 with the frequency 3f m is input into the traveling wave electrode of Si-MZM1 through the probe, the power of RF1 and the driving voltage of TOPS 11 (TOPS 21 ) are adjusted, so that the modulation index (m=πV RF / V π )<1, wherein ω RF is the angular frequency of the radio frequency signal, V RF is the amplitude of the radio frequency signal, the amplitudes of the carrier and the positive and negative first-order sidebands are equal, that is, a relatively flat 3-line optical frequency comb with the center frequency f0 and the frequency interval 3f m can be generated, and the frequency spectrum output at Si-EC2 is as shown in (b) of Figure 2 ;

[0040] In one specific embodiment of the application, step 3) is specifically: assuming that the input optical field where ω c is the optical wave angular frequency, the radio frequency signal is V m (t)=V RF sin(ω RF t), and the DC bias voltage of the modulator is Vdc The output optical field of Si-MZM1 is:

[0041]

[0042] where Jn(x) is the n-th order Bessel function of the first kind; the modulation index m = πV RF / V π ; the phase shift caused by the DC bias voltage The optical carrier and the first-order sidebands are:

[0043]

[0044]

[0045] The general method for generating optical frequency comb is to set the modulation index <1, and the amplitudes of the carrier and the first-order sidebands are equal, that is, where is the phase shift caused by the DC bias voltage, When the positive and negative values are taken respectively, the phases of the negative first-order, optical carrier, and positive first-order sidebands form an arithmetic sequence, and the common difference is and At this time, a 3-line optical frequency comb can be obtained.

[0046] 4) The optical signal is then input to Si-MZM2, and a DC bias voltage is applied to make the PN junction of Si-MZM2 reverse biased, and the frequency is f m The RF signal RF2 (the two RF signals RF1 and RF2 are phase-locked, and the phase difference is controlled by an adjustable electric phase shifter) with a frequency of f 11 is input to the traveling wave electrode of Si-MZM2 through the probe, and the TOPS 21 (TOPS 12 (TOPS 22 ) driving voltages of the two-stage Si-MZM1 and Si-MZM2 and the powers of RF1 and RF2 are controlled, a relatively flat 9-line optical frequency comb with a center frequency of f0 and a frequency interval of f m can be generated, and the frequency spectrum output at Si-EC4 is shown in (c) of Figure 2 Further, the frequency of the RF (RF2) signal input to Si-MZM2 is set to f m , and is to ensure that the interval between adjacent spectral components of the generated 9-line optical frequency comb is equal. We use numerical analysis software MATLAB to model and simulate the generation of a 9-line optical frequency comb according to the required experimental conditions, and the simulation results are shown in Figure 3 .

[0047] 5) The implementation of each function is as follows:

[0048] a) to achieve the function of reconfigurable Nyquist pulse sequence generation: simultaneously adjust the power of two RF signals, the driving voltage of the thermo-optic phase shifter of the two-stage Si-MZM, the electrical phase shifter (make the phase difference of RF1 and RF2 be 0), the driving voltage of the electrical phase shifter of the two-stage Si-MZM, and the driving voltage of the electrical phase shifter of the two-stage Si-MZM, so that the driving voltage of the Si-MZM1 is negative, the driving voltage of the Si-MZM2 is positive, that is, the direct current bias values of the two stages are opposite in sign. Finally, the generated optical frequency comb has the characteristics of equal amplitude, equal spectral spacing, phase linearization, and high out-of-band suppression ratio. The optical signals output by the Si-EC2 and Si-EC4 are connected to external high-speed PDs for frequency mixing, and then connected to a real-time oscilloscope for observation. In the time domain, a sinc-type Nyquist pulse sequence with weak distortion can be obtained;

[0049] b) to achieve the function of Nyquist pulse waveform shaping: the optical signal finally enters the bus waveguide of the serial micro-ring modulation unit. The extinction ratio of the Si-MRM can be adjusted by adjusting the driving voltage on the TOPS4. The varying extinction ratio is as shown in (a) of Figure 4 Meanwhile, the center resonance wavelength of the Si-MRM can be adjusted by adjusting the driving voltage on the TOPS3. The center resonance wavelength is as shown in (b) of Figure 4 In (b) of , the extinction ratios of the eight micro-rings are adjusted to 10 dB or 20 dB, and the center resonance wavelength spacing is equal to 0.16 nm. By adjusting the extinction ratio and the center resonance wavelength of one or more micro-rings, the optical power of each comb tooth of the obtained optical frequency comb can be suppressed, that is, the waveform shaping of the Nyquist pulse can be achieved.

[0050] c) to achieve the function of high-frequency microwave signal synthesis: two comb teeth can be selected from the generated 9-line optical frequency comb, and the spacing between them is the synthesized high-frequency signal. Seven Si-MRMs are selected, the driving voltages of the TOPS3 and TOPS4 of the Si-MRMs are adjusted, the extinction ratios of the Si-MRMs are controlled to be maximum, and the center resonance wavelength of the Si-MRM is adjusted to be equal to the center frequency of the optical carrier signal output by the laser source. The resonance peaks of the micro-ring are aligned with the center wavelengths of the remaining seven comb teeth that are not selected, and the resonance is cancelled. Finally, the output optical signal of the Si-EC5 is connected to an external high-speed PD for frequency mixing, and the synthesized high-frequency microwave signal can be observed in a spectrum analyzer. We also simulated the micro-ring filtering, and the simulation results are shown in Figure 5 .

[0051] d) to achieve the function of digital optical communication: the driving voltages of the TOPS3 of the eight Si-MRMs in the serial micro-ring modulation unit are adjusted, so that the center resonance wavelength spacing of the eight Si-MRMs is equal to about f m . The i-th Si-MRM (Si-MRM i) as an electro-optical modulator, the extinction ratio of the Si-MRM is 5dB, and the extinction ratios of the other 7 Si-MRMs are equal and maximum. At this time, the frequency of the laser source output optical carrier signal is adjusted to f0 i , and the center resonant wavelengths of the 8 Si-MRMs are aligned with the comb tooth peaks of the optical frequency comb. At this time, the DC reverse bias voltage and the NRZ or PAM4 signals of different codes and rates emitted by the Arbitrary Waveform Generators (AWG) are applied to the PN junction of the Si-MRM ’ through the Bias-Tee and the probe, so as to modulate the comb tooth where the resonant peak of the Si-MRM i is located. i The output optical signal of the Si-EC5 is connected to an external low-noise Erbium-doped Optical Fiber Amplifier (EDFA) to amplify the optical power, followed by a high-speed PD and a real-time oscilloscope. The amplitude and rate of the signal in the AWG are adjusted, and at the same time, the size of the DC reverse bias voltage on the Si-MRM i is adjusted, and the center resonant wavelength is finely adjusted, so that the optical power of the comb tooth where the resonant peak of the Si-MRM i is located is reduced by 3-8dB. The NRZ and PAM4 eye diagrams of different rates can be observed in the real-time oscilloscope, that is, the function of digital optical communication is realized. The maximum rate of the AWG output signal is 50Gaud. The bandwidth of the external high-speed PD is greater than 100GHz.

[0052] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. For ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A programmable signal processing chip based on silicon optical modulator, characterized in that: the chip comprises five silicon-based end-couplers (Si-EC1-Si-EC5), two silicon-based carrier-depletion Mach-Zehnder push-pull modulators (Si-MZM1-Si-MZM2) of the same structure, and a series micro-ring modulation unit composed of eight silicon-based extinction ratio and center resonant wavelength adjustable micro-ring modulators (Si-MRM1-Si-MRM8) of the same structure; the Si-MZM1 and Si-MZM2 both adopt a symmetric MZI structure, a first thermo-optic phase shifter (TOPS1) is arranged on the upper arm waveguide, a second thermo-optic phase shifter (TOPS2) is arranged on the lower arm waveguide, and a PN junction phase shifter is embedded in the center of both arm waveguides, the inside of the waveguide is P-doped, and the outside is N-doped; a traveling wave electrode is arranged on the outside of both arm waveguides; wherein the Si-EC1 is connected to the front beam splitter of the Si-MZM1 as the input end of the chip, the optical carrier is output through the rear beam combiner of the Si-MZM1, the first output end of the beam combiner is connected to the front beam splitter of the Si-MZM2 to pass the optical carrier into the second regulation, the second output end is connected to the Si-EC2 to output the optical carrier for detection; the other input end of the front beam splitter of the Si-MZM2 is connected to the Si-EC3 to input the optical signal alone; the first output end of the rear beam combiner of the Si-MZM2 is connected to the input end of the series micro-ring modulation unit for regulation; the second output end is connected to the Si-EC4 to output the optical carrier for detection; the output end of the series micro-ring modulation unit is connected to the Si-EC5 as the output end of the chip for detection of the output optical field. The Si-MZM1 and Si-MZM2 both comprise a beam splitter, an upper arm waveguide, a lower arm waveguide and a beam combiner, the beam splitter and the beam combiner are both of a 2×2 structure, the beam splitter is an input end, and the beam combiner is an output end; a DC bias electrode is connected to the P-doped region of the Si-MZM1-Si-MZM2; a terminal matching resistor is connected to the end of the traveling wave electrode as an on-chip terminator; the traveling wave electrode adopts a coplanar microstrip line structure, both traveling wave electrodes are located on the outside of the MZI and serve as a signal line S and a ground line G respectively, both traveling wave electrodes are connected to a metal pad, and single-port microwave input is adopted to realize push-pull driving. The Si-MRM1-Si-MRM8 each comprise a partially curved bus waveguide and a micro-ring resonant cavity embedded with a PN junction phase shifter, the partially curved bus waveguide is coupled to the micro-ring resonant cavity at two points, the micro-ring resonant cavity is provided with a third thermo-optic phase shifter (TOPS3) at the top away from the bus waveguide, and the partially curved bus waveguide is provided with a fourth thermo-optic phase shifter (TOPS4) ; the inside of the micro-ring resonant cavity is an N-doped region, and the outside is a P-doped region, both doped regions are connected to a metal pad through a metal layer, and changing the driving voltage applied thereto can change the refractive index of the waveguide to realize modulation; the Si-MRM1-Si-MRM8 are connected in series by bus waveguides. ​ ​ ​ 2. The programmable signal processing chip based on silicon optical modulators according to claim 1, wherein, ​ 3. The programmable signal processing chip based on silicon optical modulators as claimed in claim 1, wherein, ​ 4. The programmable signal processing chip based on silicon optical modulators according to claim 3, wherein, The center resonant wavelength of the Si-MRM1-Si-MRM8 is regulated by regulating the driving voltage of the TOPS3 on the Si-MRM1-Si-MRM8; and the extinction ratio of the Si-MRM1-Si-MRM8 is regulated by regulating the driving voltage of the TOPS4 on the Si-MRM1-Si-MRM8.

5. The programmable signal processing chip based on silicon optical modulators of claim 1, wherein, The chip is prepared based on a CMOS compatible silicon-on-insulator processing technology, and is manufactured on a 220 nm SOI wafer.

6. The programmable signal processing chip based on silicon optical modulators of claim 1, wherein, The Si-EC1 and Si-EC3 are input ports, and are used for externally connecting a laser and a polarization controller; and the Si-EC2, Si-EC4 and Si-EC5 are output ports, and are used for externally connecting an optical power splitter, a photodetector and an oscilloscope.

7. The programmable signal processing chip based on silicon optical modulators as claimed in claim 3, wherein, The TOPS1-TOPS4 are led out through on-chip metal wires and are collected into a pad array, and can be connected with a PCB board through wire bonding, and are connected with an external direct current voltage source through an adapter plate and a flexible flat cable, so as to directly regulate the driving voltage of the thermo-optic phase shifter.

8. A method of controlling a programmable signal processing chip based on the silicon optical modulator of claim 3, characterized by, The method comprises the following steps: 1) an optical carrier signal with a frequency of f0 output by an external laser is coupled into the chip through the Si-EC1, a beam splitter of the Si-MZM1 divides the signal into two paths with equal light intensity and inputs the two paths into upper and lower arms respectively, and the light phase difference of the Si-MZM1 can be regulated by regulating the driving voltages of the TOPS1 and TOPS2 on the upper and lower arms; The frequency of the radio frequency signal RF1 is 3f m The radio frequency signal RF1 is input to the traveling wave electrode of the Si-MZM1 through the probe, and is used to control the optical comb frequency component. By adjusting the direct current bias voltage of the Si-MZM1, the PN junction is reversely biased. The 3-line optical comb with the center frequency f0 and the frequency interval 3f m is generated by control. 2) the optical carrier signal output from the first output end of the combiner of the Si-MZM1 enters the Si-MZM2, with a frequency of f m The radio frequency signal RF2 is input to the traveling wave electrode of the Si-MZM2 through a probe, the radio frequency signals RF1 and RF2 are phase-locked, and the phase difference is controlled through an external adjustable electric phase shifter; at the same time, the TOPS1, the TOPS2 and the direct current bias voltage of the Si-MZM2 are controlled, and a 9-line optical frequency comb with a center frequency of f0 and a frequency interval of f m enters the serial micro-ring modulation unit through the first output end of the combiner of the Si-MZM2. 3) when a reconfigurable Nyquist pulse sequence needs to be generated, the voltages of the thermo-optic phase shifters of the RF1, RF2, Si-MZM1 and Si-MZM2 and an external adjustable electric phase shifter are simultaneously regulated, so that the generated optical frequency comb has the characteristics of equal amplitude, equal spectral spacing, phase linearization and high out-of-band suppression ratio; the optical signals output by the Si-EC2 and Si-EC4 are connected into external high-speed PDs for frequency mixing, and then are connected into a real-time oscilloscope for observation, so that a sinc-type Nyquist pulse sequence with weak distortion generated by 3-line and 9-line optical frequency combs is obtained in the time domain, and the light power of different comb teeth of the obtained optical frequency comb is suppressed by regulating the center resonant wavelengths of the Si-MRM1-Si-MRM8, so that time-domain waveform change and waveform shaping are realized; when a high-frequency microwave signal needs to be synthesized, two comb teeth in the generated 9-line optical frequency comb are selected as the synthesized microwave signal, the driving voltages of the TOPS3 and TOPS4 of the Si-MRM1-Si-MRM8 are adjusted to generate a micro-ring resonant peak sequence with different spacings and different extinction ratios, the extinction ratio of the Si-MRM1-Si-MRM8 is controlled to be maximum, the center resonant wavelengths of the Si-MRM1-Si-MRM8 are adjusted to be consistent with the center frequency of the optical carrier signal output by the laser source, the micro-ring resonant peak sequence is resonated and cancelled with the wavelengths of the peaks of the remaining seven comb teeth which are not selected, and finally the output optical signal of the Si-EC5 is connected into an external high-speed PD for frequency mixing, and a synthesized high-frequency microwave signal is observed in a spectrum analyzer; When the function of digital optical communication needs to be realized, the driving voltage of the TOPS3 of the Si-MRM1-Si-MRM8 is regulated, so that the center resonance wavelength spacing of the Si-MRM1-Si-MRM8 is equal to f m ; the i-th Si-MRM is selected as an electro-optical modulator, and the other 7 Si-MRMs are selected as optical filters, the driving voltage of the TOPS4 is adjusted so that the extinction ratio of the i-th Si-MRM is 5dB, and the extinction ratios of the other 7 Si-MRMs are equal to 20dB; at this time, the frequency of the laser source output optical carrier signal is adjusted to f0 ’ , so that the comb tooth peak value of the optical frequency comb is aligned with the center resonance wavelength of the 8 Si-MRMs; at this time, the direct current reverse bias voltage and the NRZ or PAM4 signal of different codes and rates output by the arbitrary waveform generator AWG are applied to the metal pad of the i-th Si-MRM through the Bias-Tee and the probe, the optical field at the resonance peak of the i-th Si-MRM is modulated, the output optical signal of the Si-EC5 is connected to the external low-noise doped optical fiber amplifier EDFA to amplify the optical power, and then connected to the high-speed PD and the real-time oscilloscope, the amplitude and rate of the signal in the AWG are adjusted, and the size of the direct current reverse bias voltage on the i-th Si-MRM is adjusted, so that the NRZ and PAM4 eye diagrams of different rates can be observed in the real-time oscilloscope.

9. The control method according to claim 8, characterized by, In step 1), the direct current bias voltage is set to -3V to make the PN junction of the Si-MZM1 reverse biased; assuming the input optical field of the Si-EC1 is where ω c is the optical wave angular frequency, the radio frequency signal RF1 is V m (t) = V RF sin(ω RF t), where ω RF is the radio frequency signal angular frequency, V RF is the amplitude of the radio frequency signal, and the direct current bias voltage of the Si-MZM1 is V dc ; at this time, the output optical field E out of the Si-MZM1 is: where Jn(x) is the n-th order first kind Bessel function; the modulation index m = πV RF / V π ; phase shift caused by direct current bias voltage The optical carrier, positive and negative first-order sidebands are: n＝0， n＝1, The method for regulating the generation of the optical frequency comb is: setting the modulation index m to be <1, the amplitude of the carrier and the positive and negative first-order sidebands are equal, that is When the positive and negative values are taken respectively, the phases of the negative first-order, optical carrier and positive first-order sidebands are in an arithmetic sequence, and the common difference is and At this time, a 3-line optical frequency comb is obtained.

10. The control method according to claim 8, characterized by, In step 3), in order to generate a 9-line optical frequency comb with linearly changing phases of spectral components, the DC bias voltage of the Si-MZM1 needs to take a negative value, and the DC bias voltage of the Si-MZM2 needs to take a positive value, i.e., the DC bias voltages of the two stages are opposite in sign.

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