CN114285480A - Silicon-based integrated microwave photon down-conversion chip and down-conversion implementation method thereof - Google Patents
Silicon-based integrated microwave photon down-conversion chip and down-conversion implementation method thereof Download PDFInfo
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Abstract
A silicon-based integrated microwave photon down-conversion chip and a down-conversion method thereof belong to the technical field of microwave photons and solve the problems that a microwave photon down-conversion system based on a discrete device in the prior art is large in size and not beneficial to integration, and the existing microwave photon down-conversion technical scheme is high in complexity, large in energy loss and low in system conversion efficiency; the grating coupler, the two silicon-based phase modulators, the thermo-optic phase shifter, the 2 multiplied by 23 dB optical coupler and the GeSi balanced optical detector are integrated on the SOI platform compatible with the CMOS process, so that the chip is realized, the size is small, and the integration level is high; the down-conversion of the microwave photon signal can be realized by using two silicon-based phase modulators, and the microwave photon signal down-conversion device has the advantages of simple structure, low link loss and high frequency conversion efficiency; by adopting balanced difference frequency detection, two paths of optical current signals are subtracted, partial noise and direct current terms are offset, and the input noise level generated by a laser in a system is reduced.
Description
Technical Field
The invention belongs to the technical field of microwave photons, and relates to a silicon-based integrated microwave photon down-conversion chip and a down-conversion method thereof.
Background
With the increasing demand of communication, the signal bandwidth and frequency are increasing, and the signal bandwidth that can be processed by the signal processing system is limited, so that the down-conversion technology is required to convert the high-frequency signal into the medium-low frequency signal and then process the signal. Microwave photonics is a cross discipline combining microwave technology and photon technology, integrates the advantages of microwave technology and photon technology, has the advantages of low loss, high frequency band, large bandwidth, electromagnetic interference resistance and the like, and becomes a current research hotspot. The microwave photon down-conversion technology is to modulate a received high-frequency signal and a local oscillation signal on an optical signal through a modulator, and finally obtain a down-conversion signal on a detector through beat frequency. By carrying out frequency reduction processing on the microwave signals, the later-stage processing of the microwave signals can be carried out by using middle and low frequency devices with higher technical degree and lower cost. The microwave photon down-conversion technology completes the conversion from microwave high-frequency signals to medium-low frequency in an optical domain, overcomes the problems of high system complexity, large signal loss, small processing bandwidth, easy electromagnetic interference and the like in the traditional electric domain frequency conversion method, and has wide application in the fields of radar, electronic warfare, communication and the like.
Important indexes for measuring the performance of the microwave photon down-conversion link are gain and dynamic range. The gain directly affects the performance of the frequency conversion link, and particularly in long-distance transmission systems, the gain is highly required. The dynamic range describes the power range which can be processed by the system, comprehensively reflects the performance of the system and is an important index for judging the performance of the down-conversion receiver. Therefore, the research on the microwave photon down-conversion method and system with high gain and large dynamic range is of great significance.
Key devices in the microwave photon down-conversion system comprise a laser, a modulator, a detector and the like, and the conventional microwave photon down-conversion system realizes functions based on a plurality of discrete devices, and the discrete devices are large in size and high in power consumption. Because a silicon-on-insulator (SOI) technology platform device library is relatively mature, a passive device, an electro-optical modulator, a detector and the like can be integrated, and an SOI technology platform is compatible with a CMOS (complementary metal oxide semiconductor) process, optical path devices and circuit devices with various functions can be integrated on the same SOI wafer, and the system integration level can be remarkably improved, for example, relevant silicon-based optoelectronic device research work is introduced aiming at the requirements of microwave photon links in the document silicon-based photonic device research facing microwave photons (Yang, Zhejiang university) with the document publication date of 2019, and the work comprises a high-linearity modulator, a high-saturation detector, a large-range adjustable microwave real time delay line, a light beam forming network delay module and the like. Therefore, the silicon-based integrated microwave photon down-conversion chip is realized by utilizing the SOI platform to monolithically integrate the modulator, the phase shifter, the optical coupler, the detector and the like on the chip level, is applied to the microwave photon down-conversion technology, and has the advantages of miniaturization, high integration level and the like.
For the microwave photon down-conversion technical scheme based on the heterodyne frequency mixing technology, the microwave photon down-conversion technical scheme mainly comprises an external modulation scheme based on a serial Mach-Zehnder modulator, a double-parallel Mach-Zehnder modulator structure, a double-polarization double-parallel Mach-Zehnder modulator and the like, and differential frequency detection is realized on a detector by respectively loading a microwave signal RF and a local oscillator signal L0 on the two modulators, for example, the Chinese invention patent application document 'a microwave photon down-conversion system with low local oscillator frequency', the publication date of which is 2019, 8, 23 and the publication number of which is CN 110166133A; however, the above schemes all realize the microwave photon down-conversion based on the complex modulator structure, the system structure complexity is high, and after the microwave signal is modulated twice, the energy loss is large, and the system conversion efficiency is not high.
Disclosure of Invention
The invention aims to design a silicon-based integrated microwave photon down-conversion chip and a down-conversion method thereof, and aims to solve the problems that a microwave photon down-conversion system based on a discrete device in the prior art is large in size and not beneficial to integration, and the existing microwave photon down-conversion technical scheme is high in complexity, large in energy loss and low in system conversion efficiency.
The invention solves the technical problems through the following technical scheme:
a silicon-based integrated microwave photonic down conversion chip, comprising: the system comprises a grating coupler (10), a 1 x 2 optical beam splitter (11), a thermo-optic phase shifter (12), a first silicon-based phase modulator (13), a second silicon-based phase modulator (14), a 2 x 2 optical coupler (15), a GeSi balanced optical detector (16) and a silicon waveguide (17) which are integrated on an SOI platform compatible with a CMOS process;
the output end of the grating coupler (10) is connected with the input end of a 1 × 2 optical beam splitter (11) through a silicon waveguide (17), the first output end of the 1 × 2 optical beam splitter (11) is connected with the input end of a thermo-optic phase shifter (12) through the silicon waveguide (17), the output end of the thermo-optic phase shifter (12) is connected with the input end of a first silicon-based phase modulator (13) through the silicon waveguide (17), the output end of the first silicon-based phase modulator (13) is connected with the first input end of a 2 × 2 optical coupler (15) through the silicon waveguide (17), and the first output end of the 2 × 2 optical coupler (15) is connected with the first input end of a GeSi balanced optical detector (16) through the silicon waveguide (17); the second output end of the 1 × 2 optical beam splitter (11) is connected with the input end of a second silicon-based phase modulator (14) through a silicon waveguide (17), the output end of the second silicon-based phase modulator (14) is connected with the second input end of a 2 × 2 optical coupler (15) through the silicon waveguide (17), and the second output end of the 2 × 2 optical coupler (15) is connected with the second input end of a GeSi balanced optical detector (16) through the silicon waveguide (17);
the grating coupler (10) couples the input optical signal into a silicon waveguide (17), and the optical signal respectively enters a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14) after being subjected to power splitting by a 1 multiplied by 2 optical beam splitter (11); the thermo-optic phase shifter (12) is used for controlling the first silicon-based phase modulator (13) to work at a pi/2 bias point; the direct current bias voltage DC and the microwave signal RF are loaded on a first silicon-based phase modulator (13), and the direct current bias voltage DC and the local oscillator signal L0 are loaded on a second silicon-based phase modulator (14); microwave signals RF are subjected to electro-optical conversion of a first silicon-based phase modulator (13) to obtain optical-carrier microwave signals, local oscillator signals L0 are subjected to electro-optical conversion of a second silicon-based phase modulator (14) to obtain optical-carrier local oscillator signals, the optical-carrier microwave signals and the optical-carrier local oscillator signals are coupled and split by a 2 x 2 optical coupler (15) and respectively enter two input ends of a GeSi balanced optical detector (16), and after differential frequency photoelectric conversion detection of the GeSi balanced optical detector (16), the coupled optical-carrier microwave signals and the optical-carrier local oscillator signals are converted into medium and low frequency signals IF.
The technical scheme of the invention integrates the grating coupler, the two silicon-based phase modulators, the thermo-optic phase shifter, the 2 multiplied by 23 dB optical coupler and the GeSi balanced optical detector on the SOI platform compatible with the CMOS process, thereby realizing chip formation, small size and high integration level; the down-conversion of the microwave photon signal can be realized by using two silicon-based phase modulators, and the microwave photon signal down-conversion device has the advantages of simple structure, low link loss and high frequency conversion efficiency; by adopting balanced difference frequency detection, two paths of optical current signals are subtracted, partial noise and direct current terms are offset, and the input noise level generated by a laser in a system is reduced.
The first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are carrier depletion type modulators.
The electrode structures of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are coplanar waveguide traveling wave electrodes, the electrodes on two sides are grounding electrodes G, the middle electrode is a signal electrode S, and a direct current bias voltage DC is loaded on the middle signal electrode S, so that the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are ensured to work in a carrier depletion state.
The 2 x 2 optical coupler (15) adopts a 3dB 2 x 2 multimode interference type (MMI) coupler or a 2 x 2 directional coupler.
A down-conversion implementation method based on the silicon-based integrated microwave photon down-conversion chip comprises the following steps:
s11, inputting an optical signal;
s12, the microwave signal and the local oscillator signal are subjected to electro-optical conversion to generate an optical carrier microwave signal and an optical carrier local oscillator signal;
and S13, mixing the microwave signal and the local oscillator signal into a medium and low frequency signal.
The method for inputting the optical signal in step S11 includes:
the input optical signal is coupled into a silicon waveguide (17) through a grating coupler (10), and after being subjected to equal-power beam splitting through a 1 multiplied by 2 optical beam splitter (11), the input optical signal respectively enters a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14);
according to the transmission principle of light in the silicon-based phase modulator, the optical field expression of the modulated light signals output by the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) is obtained as follows:
wherein the optical field of the input optical signal is
Wherein EcIs the amplitude of the light field, wcIs the frequency of the optical signal; a isA、aBRespectively representing the optical transmission loss coefficients of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14); phi is aA、φBRespectively representing the modulation phase shift of a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14); delta phi denotes the phase difference of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14).
The method for generating the optical carrier microwave signal and the optical carrier local oscillator signal through the electro-optical conversion of the microwave signal and the local oscillator signal in the step S12 includes: controlling direct current voltage loaded on a thermo-optic phase shifter (12), and regulating and controlling phase shift of the thermo-optic phase shifter (12), so that a first silicon-based phase modulator (13) works at a pi/2 bias point, direct current bias voltage DC and microwave signals RF are loaded on a middle signal electrode S of the first silicon-based phase modulator (13) through a first T-shaped biaser (21), and direct current bias voltage DC and local oscillator signals L0 are loaded on a middle signal electrode S of a second silicon-based phase modulator (14) through a second T-shaped biaser (22); the microwave signal RF is subjected to electro-optical conversion of a first silicon-based phase modulator (13) to obtain an optical carrier microwave signal, and the local oscillator signal L0 is subjected to electro-optical conversion of a second silicon-based phase modulator (14) to obtain an optical carrier local oscillator signal; the optical carrier microwave signal and the optical carrier local oscillator signal are coupled and split by a 2X 2 optical coupler (15) to obtain two modulated optical signals.
The expression of the two modulated optical signals is as follows:
the method for mixing the microwave signal and the local oscillator signal into the medium and low frequency signal in step S13 includes:
modulating an optical signal E1，E2Respectively enter two input ends of the GeSi balance light detector (16), the responsivity of the GeSi balance light detector (16) is set as eta, and two paths of noise currents are respectively n1(t)，n2(t), after photoelectric conversion by the GeSi balance photodetector (16), the GeSi balance photodetector (16) outputs photocurrent signals I in the upper and lower paths1、I2The expression of (a) is as follows:
during balanced detection, the output current I (t) is a photocurrent signal I output by the upper and lower paths of the GeSi balanced photodetector (16)1、I2The difference of (a) to (b), namely:
setting the microwave signal RF and the local oscillator signal L0 loaded on the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) as follows: v1(t)＝υ1cos(ω1t)，V0(t)＝υ0cos(ω0t) in the formula1,υ0Amplitude, ω, of microwave signal RF and local oscillator signal LO1,ω1To it isAngular frequency. Thus a can be respectively connectedA、aBAnd phiA、φBIs shown as V1、V0A third order polynomial of (a):
substituting equation (5) into equation (4) yields:
the Talor of formula (6) is expanded to retain only the up-conversion term (ω)1+ω0) And a down conversion term (ω)1-ω0) The balanced probe photocurrent can be converted to:
the invention has the advantages that:
1) the invention integrates the grating coupler, the two silicon-based phase modulators, the thermo-optic phase shifter, the 2 multiplied by 23 dB optical coupler and the GeSi balanced optical detector on the SOI platform compatible with the CMOS process, realizes the chip of silicon-based integrated microwave photon down-conversion, and has the advantages of small size and high integration level; an SOI platform compatible with a CMOS process is adopted, so that the construction cost of the process platform is reduced, and the large-scale production is facilitated; in addition, the chip can be integrated with a circuit chip in a single chip, so that the integration level is further improved;
2) according to the microwave photon down-conversion method provided by the invention, the down-conversion of the microwave photon signal can be realized by using the two silicon-based phase modulators, the structure is simple, and the problems of large link loss, low frequency conversion efficiency and complex system in a down-conversion system with a serial and parallel multi-modulator architecture are avoided; in addition, because the coplanar waveguide traveling wave electrode structure has the characteristic of good electromagnetic shielding property, the two silicon-based phase modulators are used to avoid the crosstalk problem between microwave signals and local oscillation signals;
3) the invention adopts balanced type difference frequency detection, two paths of optical current signals of a balanced detection system are subtracted, partial noise and direct current terms are counteracted, the input noise level generated by a laser in the system is reduced, and particularly in a system with dominant input noise, the noise level of the whole system is greatly reduced; in addition, by adopting a balanced difference frequency detection scheme, two paths of intermediate frequency signal photocurrents generated on the two detectors have pi phase difference, so that the obtained intermediate frequency signal power is the sum of the intermediate frequency powers of the two detectors, and the signal-to-noise ratio of the system is favorably improved.
Drawings
FIG. 1 is a block diagram of a silicon-based integrated microwave photonic downconversion chip in accordance with an embodiment of the present invention;
FIG. 2 is a block diagram of a silicon-based phase modulator of a silicon-based integrated microwave photonic downconversion chip according to an embodiment of the present invention;
fig. 3 is a flowchart of a down-conversion implementation method of a silicon-based integrated microwave photonic down-conversion chip according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The technical scheme of the invention is further described by combining the drawings and the specific embodiments in the specification:
example one
As shown in fig. 1, a silicon-based integrated microwave photonic down-conversion chip includes: the device comprises a grating coupler 10, a 1 x 2 optical beam splitter 11, a thermo-optic phase shifter 12, a first silicon-based phase modulator 13, a second silicon-based phase modulator 14, a 2 x 2 optical coupler 15, a GeSi balanced photodetector 16, a silicon waveguide 17, an off-chip laser 20, a first T-shaped biaser 21 and a second T-shaped biaser 22. The grating coupler 10, the 1 × 2 optical beam splitter 11, the thermo-optic phase shifter 12, the first silicon-based phase modulator 13, the second silicon-based phase modulator 14, the 2 × 2 optical coupler 15, the GeSi balanced optical detector 16 and the silicon waveguide 17 are all integrated on an SOI platform compatible with a CMOS process.
The input end of the grating coupler 10 is connected with the output end of the off-chip laser 20, the output end of the grating coupler 10 is connected with the input end of the 1 × 2 optical beam splitter 11 through a silicon waveguide 17, the first output end of the 1 × 2 optical beam splitter 11 is connected with the input end of the thermo-optic phase shifter 12 through a silicon waveguide 17, the output end of the thermo-optic phase shifter 12 is connected with the input end of the first silicon-based phase modulator 13 through a silicon waveguide 17, the output end of the first silicon-based phase modulator 13 is connected with the first input end of the 2 × 2 optical coupler 15 through a silicon waveguide 17, and the first output end of the 2 × 2 optical coupler 15 is connected with the first input end of the GeSi balanced optical detector 16 through a silicon waveguide 17; the second output end of the 1 × 2 optical beam splitter 11 is connected to the input end of the second silicon-based phase modulator 14 through a silicon waveguide 17, the output end of the second silicon-based phase modulator 14 is connected to the second input end of the 2 × 2 optical coupler 15 through a silicon waveguide 17, and the second output end of the 2 × 2 optical coupler 15 is connected to the second input end of the GeSi balanced optical detector 16 through a silicon waveguide 17.
The 2 × 2 optical coupler 15 is a 3dB 2 × 2 multimode interference MMI coupler or a 2 × 2 directional coupler, and the phase difference between the output ports of the 2 × 2 optical coupler 15 is constant pi/2.
The GeSi balanced optical detector 16 is composed of 2 same detectors on a chip, and each detector performs difference frequency detection on an optical carrier microwave signal and an optical carrier local oscillator signal which are coupled together to realize microwave photon down-conversion; in order to realize the subtraction of two paths of photocurrent with pi phase difference, reverse bias voltage needs to be applied to two ends of the cascaded detector, so that direct current components are mutually counteracted and only modulation signals are reserved.
As shown in fig. 2, the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14 are prepared based on an SOI platform compatible with a CMOS process, and are carrier depletion type modulators; the electrode structure of the silicon-based phase modulator is a coplanar waveguide traveling wave electrode which has the characteristic of good electromagnetic shielding property, the problem of crosstalk between a microwave signal RF and a local oscillation signal L0 can be avoided by using the electrode, the two side electrodes are grounding electrodes G, and the middle electrode is a signal electrode S.
The working principle of the silicon-based integrated microwave photon down-conversion chip is as follows: the grating coupler 10 couples an optical signal input by the off-chip laser 20 into the silicon waveguide 17, and the optical signal is divided into a first silicon-based phase modulator 13 and a second silicon-based phase modulator 14 by the 1 × 2 optical beam splitter 11 with equal power; the thermo-optic phase shifter 12 is used for controlling the working point of the first silicon-based phase modulator 13, and the phase shift of the thermo-optic phase shifter 12 is regulated and controlled by controlling the direct-current voltage loaded on the thermo-optic phase shifter 12, so that the first silicon-based phase modulator 13 works at a pi/2 bias point; the direct current bias voltage DC and the microwave signal RF are loaded on the middle signal electrode S of the first silicon-based phase modulator 13 through the first T-shaped biaser 21, the direct current bias voltage DC and the local oscillation signal L0 are loaded on the middle signal electrode S of the second silicon-based phase modulator 14 through the second T-shaped biaser 22, wherein the loading of the direct current back bias voltage DC ensures that the phase-shifting arms of the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14 work in a carrier depletion state; the microwave signal RF is subjected to electro-optical conversion by the first silicon-based phase modulator 13 to obtain an optical carrier microwave signal, and the local oscillator signal RF is subjected to electro-optical conversion by the second silicon-based phase modulator 14 to obtain an optical carrier local oscillator signal; the optical carrier microwave signal and the optical carrier local oscillator signal are coupled by a 2 x 2 optical coupler 15 and subjected to equal-power splitting to obtain two modulated optical signals, the two modulated optical signals respectively enter two input ends of a GeSi balanced optical detector 16, and after the two modulated optical signals are detected by difference frequency photoelectric conversion of the GeSi balanced optical detector 16, the optical carrier microwave signal and the optical carrier local oscillator signal which are coupled together are down-converted into a medium-low frequency signal IF, so that microwave photon down-conversion is realized.
As shown in fig. 3, this embodiment further provides a down-conversion method for a silicon-based integrated microwave photonic down-conversion chip, which includes the following steps:
a) input of optical signals
The optical signal output by the off-chip laser 20 is coupled into the silicon waveguide 17 through the grating coupler 10, and is 1 aThe optical beam splitter 11 with equal power beam splitting respectively enters a first silicon-based phase modulator 13 and a second silicon-based phase modulator 14; let the optical field of the optical signal output by the off-chip laser 20 be
Wherein EcIs the amplitude of the light field, wcAs for the frequency of the optical signal, according to the principle of optical transmission in the silicon-based phase modulator, the optical field expression of the modulated optical signal output by the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14 is obtained as follows:
due to the carrier absorption effect, the silicon-based phase modulator can introduce different optical loss coefficients at different driving voltages, aA、aBRespectively representing the optical transmission loss coefficients of the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14; phi is aA、φBRespectively representing the modulation phase shifts of the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14; and delta phi denotes the phase difference between the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14, which is controlled by the thermo-optic phase shifter 12.
b) The microwave signal and the local oscillator signal are subjected to electro-optical conversion to generate an optical carrier microwave signal and an optical carrier local oscillator signal
Controlling the direct current voltage loaded on the thermo-optic phase shifter 12, and regulating the phase shift of the thermo-optic phase shifter 12, so that the first silicon-based phase modulator 13 works at a pi/2 bias point, the direct current bias voltage DC and the microwave signal RF are loaded on a middle signal electrode S of the first silicon-based phase modulator 13 through a first T-shaped biaser 21, and the direct current bias voltage DC and the local oscillation signal L0 are loaded on a middle signal electrode S of the second silicon-based phase modulator 14 through a second T-shaped biaser 22; the microwave signal RF is subjected to electro-optical conversion by the first silicon-based phase modulator 13 to obtain an optical carrier microwave signal, and the local oscillator signal L0 is subjected to electro-optical conversion by the second silicon-based phase modulator 14 to obtain an optical carrier local oscillator signal; the optical carrier microwave signal and the optical carrier local oscillator signal pass through a 2X 2 optical coupler15 coupling and beam splitting to obtain two modulated optical signals E1、E2The expression of (a) is as follows:
c) down-conversion of microwave signals and local oscillator signals to medium and low frequency signals
Modulating an optical signal E1，E2Respectively enter two input ends of the GeSi balance light detector 16, the responsivity of the GeSi balance light detector 16 is set as eta, and two paths of noise currents are respectively set as n1(t)，n2(t), after photoelectric conversion by the GeSi balance photodetector 16, the GeSi balance photodetector 16 outputs photocurrent signals I in upper and lower paths1、I2The expression of (a) is as follows:
during balanced detection, the output current I (t) is a photocurrent signal I output by the upper and lower paths of the GeSi balanced photodetector 161、I2The difference of (a) to (b), namely:
the microwave signal RF and the local oscillator signal L0 loaded on the first silicon-based phase modulator 13 and the second silicon-based phase modulator 14 are respectively: v1(t)＝υ1cos(ω1t)，V0(t)＝υ0cos(ω0t) in the formula1,υ0Amplitude, ω, of microwave signal RF and local oscillator signal LO1,ω1Is its angular frequency. Thus a can be respectively connectedA、aBAnd phiA、φBIs shown as V1、V0A third order polynomial of (a):
substituting equation (5) into equation (4) yields:
the Talor of formula (6) is expanded to retain only the up-conversion term (ω)1+ω0) And a down conversion term (ω)1-ω0) The balanced probe photocurrent can be converted to:
in the prior art, when the direct detection method is adopted, only the up-conversion term (omega) is reserved1+ω0) And a down conversion term (ω)1-ω0) The photocurrent expression is:
comparing the equation (7) with the equation (8), it can be seen that the photocurrent part noise and the dc term output by the GeSi balanced photodetector 16 are cancelled out, so that the input noise generated by the off-chip laser 20 can be reduced; in addition, compared with single-tube direct detection, the amplitude of the intermediate frequency signal output by adopting balanced detection is approximately doubled, namely the power of the intermediate frequency component is improved by approximately 4 times, and the down-conversion of the microwave photons with large dynamic range and high gain is realized.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. A silicon-based integrated microwave photonic down conversion chip, comprising: the system comprises a grating coupler (10), a 1 x 2 optical beam splitter (11), a thermo-optic phase shifter (12), a first silicon-based phase modulator (13), a second silicon-based phase modulator (14), a 2 x 2 optical coupler (15), a GeSi balanced optical detector (16) and a silicon waveguide (17) which are integrated on an SOI platform compatible with a CMOS process;
the output end of the grating coupler (10) is connected with the input end of a 1 × 2 optical beam splitter (11) through a silicon waveguide (17), the first output end of the 1 × 2 optical beam splitter (11) is connected with the input end of a thermo-optic phase shifter (12) through the silicon waveguide (17), the output end of the thermo-optic phase shifter (12) is connected with the input end of a first silicon-based phase modulator (13) through the silicon waveguide (17), the output end of the first silicon-based phase modulator (13) is connected with the first input end of a 2 × 2 optical coupler (15) through the silicon waveguide (17), and the first output end of the 2 × 2 optical coupler (15) is connected with the first input end of a GeSi balanced optical detector (16) through the silicon waveguide (17); the second output end of the 1 × 2 optical beam splitter (11) is connected with the input end of a second silicon-based phase modulator (14) through a silicon waveguide (17), the output end of the second silicon-based phase modulator (14) is connected with the second input end of a 2 × 2 optical coupler (15) through the silicon waveguide (17), and the second output end of the 2 × 2 optical coupler (15) is connected with the second input end of a GeSi balanced optical detector (16) through the silicon waveguide (17);
the grating coupler (10) couples the input optical signal into a silicon waveguide (17), and the optical signal respectively enters a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14) after being subjected to power splitting by a 1 multiplied by 2 optical beam splitter (11); the thermo-optic phase shifter (12) is used for controlling the first silicon-based phase modulator (13) to work at a pi/2 bias point; the direct current bias voltage DC and the microwave signal RF are loaded on a first silicon-based phase modulator (13), and the direct current bias voltage DC and the local oscillator signal L0 are loaded on a second silicon-based phase modulator (14); microwave signals RF are subjected to electro-optical conversion of a first silicon-based phase modulator (13) to obtain optical-carrier microwave signals, local oscillator signals L0 are subjected to electro-optical conversion of a second silicon-based phase modulator (14) to obtain optical-carrier local oscillator signals, the optical-carrier microwave signals and the optical-carrier local oscillator signals are coupled and split by a 2 x 2 optical coupler (15) and respectively enter two input ends of a GeSi balanced optical detector (16), and after differential frequency photoelectric conversion detection of the GeSi balanced optical detector (16), the coupled optical-carrier microwave signals and the optical-carrier local oscillator signals are converted into medium and low frequency signals IF.
2. The silicon-based integrated microwave photonic downconversion chip according to claim 1, wherein the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are carrier depletion type modulators.
3. The silicon-based integrated microwave photon down-conversion chip according to claim 2, wherein the electrode structures of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are coplanar waveguide traveling wave electrodes, the two electrodes are grounding electrodes G, the middle electrode is a signal electrode S, and the direct current bias voltage DC is loaded on the middle signal electrode S, so that the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) are ensured to work in a carrier depletion state.
4. The silicon-based integrated microwave photonic downconversion chip according to claim 1, wherein the 2 x 2 optical coupler (15) employs a 3dB 2 x 2 multimode interference type (MMI) coupler or a 2 x 2 directional coupler.
5. A down-conversion implementation method of the silicon-based integrated microwave photonic down-conversion chip according to any one of claims 1 to 4, comprising the following steps:
s11, inputting an optical signal;
s12, the microwave signal and the local oscillator signal are subjected to electro-optical conversion to generate an optical carrier microwave signal and an optical carrier local oscillator signal;
and S13, mixing the microwave signal and the local oscillator signal into a medium and low frequency signal.
6. The method of claim 5, wherein the step S11 is implemented by inputting the optical signal:
the input optical signal is coupled into a silicon waveguide (17) through a grating coupler (10), and after being subjected to equal-power beam splitting through a 1 multiplied by 2 optical beam splitter (11), the input optical signal respectively enters a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14);
according to the transmission principle of light in the silicon-based phase modulator, the optical field expression of the modulated light signals output by the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14) is obtained as follows:
wherein the optical field of the input optical signal is
Wherein EcIs the amplitude of the light field, wcIs the frequency of the optical signal; a isA、aBRespectively representing the optical transmission loss coefficients of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14); phi is aA、φBRespectively representing the modulation phase shift of a first silicon-based phase modulator (13) and a second silicon-based phase modulator (14); delta phi denotes the phase difference of the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14).
7. The method of claim 6, wherein the step S12 of performing the electro-optical conversion on the microwave signal and the local oscillator signal to generate the optical carrier microwave signal and the optical carrier local oscillator signal comprises: controlling direct current voltage loaded on a thermo-optic phase shifter (12), and regulating and controlling phase shift of the thermo-optic phase shifter (12), so that a first silicon-based phase modulator (13) works at a pi/2 bias point, direct current bias voltage DC and microwave signals RF are loaded on a middle signal electrode S of the first silicon-based phase modulator (13) through a first T-shaped biaser (21), and direct current bias voltage DC and local oscillator signals L0 are loaded on a middle signal electrode S of a second silicon-based phase modulator (14) through a second T-shaped biaser (22); the microwave signal RF is subjected to electro-optical conversion of a first silicon-based phase modulator (13) to obtain an optical carrier microwave signal, and the local oscillator signal L0 is subjected to electro-optical conversion of a second silicon-based phase modulator (14) to obtain an optical carrier local oscillator signal; the optical carrier microwave signal and the optical carrier local oscillator signal are coupled and split by a 2X 2 optical coupler (15) to obtain two modulated optical signals.
8. The method of claim 7, wherein the two modulated optical signals are expressed as follows:
9. the method for implementing downconversion according to claim 7, wherein the step S13 is implemented by mixing the microwave signal and the local oscillator signal into a medium-low frequency signal by:
modulating an optical signal E1，E2Respectively enter two input ends of the GeSi balance light detector (16), the responsivity of the GeSi balance light detector (16) is set as eta, and two paths of noise currents are respectively n1(t)，n2(t), after photoelectric conversion by the GeSi balance photodetector (16), the GeSi balance photodetector (16) outputs photocurrent signals I in the upper and lower paths1、I2The expression of (a) is as follows:
during balanced detection, the output current I (t) is a photocurrent signal I output by the upper and lower paths of the GeSi balanced photodetector (16)1、I2The difference of (a) to (b), namely:
setting the microwave signal RF and local oscillator loaded on the first silicon-based phase modulator (13) and the second silicon-based phase modulator (14)The signals L0 are: v1(t)＝υ1cos(ω1t)，V0(t)＝υ0cos(ω0t) in the formula1,υ0Amplitude, ω, of microwave signal RF and local oscillator signal LO1,ω1Is its angular frequency; thus a can be respectively connectedA、aBAnd phiA、φBIs shown as V1、V0A third order polynomial of (a):
substituting equation (5) into equation (4) yields:
the Talor of formula (6) is expanded to retain only the up-conversion term (ω)1+ω0) And a down conversion term (ω)1-ω0) The balanced probe photocurrent can be converted to:
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