CN116482802A - Reflective optical electric field sensor based on lithium niobate thin film material - Google Patents
Reflective optical electric field sensor based on lithium niobate thin film material Download PDFInfo
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- 230000005684 electric field Effects 0.000 title claims abstract description 81
- 230000003287 optical effect Effects 0.000 title claims abstract description 78
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 title claims abstract description 44
- 239000010409 thin film Substances 0.000 title claims abstract description 38
- 239000000463 material Substances 0.000 title claims abstract description 34
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- 239000011159 matrix material Substances 0.000 claims abstract description 7
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 13
- 239000013078 crystal Substances 0.000 claims description 9
- 239000000758 substrate Substances 0.000 claims description 9
- 238000000034 method Methods 0.000 claims description 8
- 229910052710 silicon Inorganic materials 0.000 claims description 8
- 239000010703 silicon Substances 0.000 claims description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 7
- 239000000377 silicon dioxide Substances 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 235000012239 silicon dioxide Nutrition 0.000 claims description 6
- 238000001514 detection method Methods 0.000 claims description 5
- 238000005530 etching Methods 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 238000000691 measurement method Methods 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 abstract description 3
- 238000010586 diagram Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 6
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- 238000012360 testing method Methods 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 238000005253 cladding Methods 0.000 description 2
- 239000012792 core layer Substances 0.000 description 2
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/124—Geodesic lenses or integrated gratings
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
- G01R29/12—Measuring electrostatic fields or voltage-potential
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/105—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type having optical polarisation effects
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/125—Bends, branchings or intersections
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/126—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind using polarisation effects
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12035—Materials
- G02B2006/1204—Lithium niobate (LiNbO3)
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12138—Sensor
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12133—Functions
- G02B2006/12142—Modulator
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B2006/12166—Manufacturing methods
- G02B2006/12176—Etching
Abstract
The invention relates to a reflective optical electric field sensor based on a lithium niobate thin film material, which adopts the lithium niobate thin film material as a sensor matrix, and sequentially etches the lithium niobate thin film material along the light path propagation direction to form a gradual coupling structure, a polarization selection structure, a reflective MZ electro-optic modulator, a broadband high-gain electrode and an antenna structure, wherein the reflective MZ electro-optic modulator only comprises a Y-branch optical waveguide, and a Bragg reflection grating is arranged on a parallel waveguide arm of the Y-branch optical waveguide; the electric field signal can be modulated on the laser by inputting the laser signal to the sensor, and the modulated laser is transmitted by using the long optical fiber; the rear end is demodulated by a photoelectric detector and is sent into a receiver for measurement, and the electric field information to be measured can be obtained. The sensor has the advantages of simple structure, output optical fiber saving, small size, high sensitivity, small interference, accurate electric field measurement result and high measurement repeatability.
Description
Technical Field
The invention belongs to the technical field of broadband rapid electric field detection, and particularly relates to a reflective optical electric field sensor based on a lithium niobate thin film material.
Background
The development of electronic technology has prompted the need for electromagnetic field detection technology, from the initial antenna plus spectrometer test mode to the current optical electric field sensor system test mode, the development of electric field test technology has been deepened continuously, and a number of problems are exposed in the process.
The optical electric field sensor is a sensor which modulates an electric field signal to be detected on laser by utilizing the electro-optical effect of an electro-optical crystal and reversely pushes electric field information by detecting the intensity of the laser. Most of the existing optical electric field sensors use bulk lithium niobate crystals as sensing crystals, and a channel waveguide sensing structure is manufactured on the bulk lithium niobate to realize sensing and measurement of an electric field. The bulk lithium niobate has a certain thickness, is not film-shaped, has high etching difficulty, is generally realized by adopting a titanium diffusion or proton exchange process, and the refractive index difference between a core layer and a cladding layer of the optical waveguide structure prepared on the bulk lithium niobate material based on the technology is smaller, usually in order of magnitude, so that the waveguide width is larger (usually 6-7 mu m for single-mode optical waveguide) and the light beam capacity is weaker. The large waveguide width results in large electrode spacing, resulting in smaller inter-electrode electric field, low modulation efficiency, and longer structures needed to accomplish modulation. The weak beam light capability results in a large turning radius of the branched structures in the waveguide, and thus longer structures are also required to accomplish the modulation. And the overlong structure can aggravate the photoelectric speed mismatch effect, thereby influencing the bandwidth of the probe. Therefore, the existing optical electric field sensor still has the problems of large volume and narrow bandwidth.
Disclosure of Invention
The technical problems to be solved are as follows:
aiming at the problems in the prior art, the invention provides a reflective optical electric field sensor based on a lithium niobate thin film material, which is formed by etching a waveguide structure and the like on the lithium niobate thin film material. The sensor has the advantages of simple structure, small size, no need of output optical fibers in a reflective structure, high sensitivity, small interference, accurate electric field measurement result and high measurement repeatability.
The technical scheme adopted is as follows:
the invention provides a reflective optical electric field sensor based on a lithium niobate thin film material, which can modulate an electric field signal to be measured on laser by inputting the laser signal to the sensor and transmit the electric field signal by using a long optical fiber; the rear end is demodulated by a photoelectric detector and is sent into a receiver for measurement, and the electric field information to be measured can be obtained.
A reflective optical electric field sensor based on a lithium niobate thin film material adopts the lithium niobate thin film material as a sensor matrix, and is formed by sequentially etching the lithium niobate thin film material along the light path propagation direction: a gradual coupling structure, a polarization selection structure, a reflective MZ electro-optic modulator, a broadband high-gain electrode and an antenna structure; the gradual change coupling structure is arranged at a port of the sensor and couples laser with larger light spots in input laser into a single-mode optical waveguide with smaller light spots so as to realize single-mode transmission of the laser; the polarization selection structure eliminates TM mode in the single-mode optical waveguide to realize single polarization transmission of laser; the reflection type MZ electro-optic modulator only comprises a Y-branch optical waveguide, wherein the Y-branch optical waveguide comprises two sections of parallel waveguide arms, and Bragg reflection gratings are arranged at the distal ends of the two sections of parallel waveguide arms; the reflection type MZ electro-optic modulator is connected behind the single-mode optical waveguide and is used for modulating an electric field to be detected in space onto transmitted laser; the high-gain electrode increases the intensity of an electric field to be detected acting on a waveguide arm of the reflective MZ electro-optic modulator; the Bragg reflection grating reflects waveguide light, and the reflected light is combined and output through the Y-branch optical waveguide.
Further, the lithium niobate thin film material matrix takes a silicon wafer as a support, a silicon dioxide substrate with the thickness of 2-5 mu m is attached to the silicon wafer, and a lithium niobate single crystal thin film with the thickness of 300-600nm is attached to the silicon dioxide substrate.
Further, the gradual change coupling structure is a conical gradual change transmission channel arranged at a sensor port, one end of the conical gradual change transmission channel, which faces the port, is wider and is used for being connected with an input optical fiber, the other end of the conical gradual change transmission channel is narrower and is connected with a single-mode optical waveguide, and laser of the input optical fiber is gradually coupled into the single-mode optical waveguide with the width of 1 mu m.
Furthermore, the polarization selection structure is characterized in that a metal coating is arranged on the single-mode optical waveguide, and a high-loss plasma surface mode is excited, so that TE mode guided waves pass through with low loss, TM mode guided waves attenuate with high loss, and the single-polarization working state of the sensor is realized.
Further, the reflective MZ electro-optic modulator adopts a biased MZ electro-optic modulation structure, so that the sensor works at a linear working point of the MZ electro-optic modulator.
Further, the high-gain electrode adopts a broadband micro-nano high-gain electrode, and comprises 2 electrodes with the same size, the electrode spacing is within 2 mu m, and the high-gain electrode is integrated on a waveguide arm of the MZ electro-optic modulator.
The measuring system for measuring based on the lithium niobate thin film material optical electric field sensor comprises: the laser is input to the optical electric field sensor through the polarization maintaining optical fiber and the circulator, an external electric field to be detected is applied to the sensor, laser subjected to intensity modulation is output to be incident into the optical detector through the circulator and the single-mode optical fiber and converted into an electric signal, and finally the electric signal is input to the spectrometer for detection, so that the frequency and the amplitude of the electric field intensity to be detected are obtained.
The measuring method based on the measuring system specifically comprises the following steps:
step one, gradual change mode spot conversion coupling: the laser emitted by the laser source is transmitted to the input end of the optical electric field sensor through the polarization maintaining optical fiber, and is transmitted to the single-mode optical waveguide with the width of 1 mu m through the gradual coupling structure, so that the single-mode transmission of the laser is realized;
step two, polarization selection: when the laser transmitted in the single mode passes through the single mode optical waveguide coated with the metal coating, exciting a surface mode of the plasma, thereby removing a TM mode in the waveguide and forming single polarization transmission of the laser;
step three, phase modulation: the transmitted laser in the second step is divided into two paths at the Y branch of the reflective MZ modulator, and the two paths of laser enter two optical waveguide arms interfered by the MZ photoelectric modulator respectively, and the refractive index of the lithium niobate material is changed due to the existence of an electric field to be detected in the space, so that the phase of waveguide light transmitted in the two arms is changed, and the first phase modulation of the transmitted waveguide light is realized;
fourth, secondary phase modulation: light in the two optical waveguide arms is transmitted forward into the Bragg reflection grating and reflected; the waveguide light phase reflected by the Bragg reflection grating is modulated by the space electric field to be detected for the second time;
step five: intensity modulation: the light in the two secondarily modulated optical waveguide arms passes through the Y branch again and is combined into one path of light, so that interference occurs, and finally, the intensity modulation of the space electric field on the laser is realized; the change rule is as follows:
I out ＝I in αE
wherein I is out For backward output power of sensor, I in Inputting power for a light source, wherein alpha is a sensor modulation coefficient, and E is the electric field strength to be measured;
step six, calculating the electric field strength to be measured: the intensity modulated laser output in the fifth step is input into a photodetector to be converted into an electric signal, the obtained electric signal is input into a spectrometer, and the signal amplitude V is measured in the spectrometer rf The method comprises the steps of carrying out a first treatment on the surface of the The frequency of the electric field to be measured is the same as the frequency of the signal measured in the spectrometer, and the electric field strength amplitude of the electric field to be measured is E out ＝V rf +A F Wherein A is F The antenna coefficient of the measurement system after precision calibration.
Compared with the prior art, the invention has the following beneficial effects:
1. the refractive index difference between the core layer and the cladding layer of the single-mode optical waveguide formed by the lithium niobate thin film adopted by the invention is about 0.7, which is far higher than that of the traditional technology (titanium diffusion and proton exchange, about 6-7 mu m), so that the width of the single-mode optical waveguide is within 1 mu m, the Shu Guangneng force is strong, and the size of the sensor is reduced.
2. The high-gain broadband electrode spacing is within 2 mu m, the interelectrode electric field is larger than that of the traditional process, the modulation efficiency is improved, the electrode size and the light path size are reduced, and the bandwidth is improved.
3. The invention etches the on-chip polarization selection structure directly on the lithium niobate film, does not need to add a polarizer, reduces the complexity of the sensor, saves the cost and reduces the size.
4. The invention adopts a high-gain broadband electrode-antenna structure, increases the sensitivity and improves the bandwidth.
5. The invention adopts a reflective sensor structure, has smaller volume and is easier to hold and install; the invention designs an on-chip reflecting structure, avoids externally-arranged reflecting mirrors or plated reflecting films, and reduces the process steps.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a reflective optical electric field sensor structure of a lithium niobate thin film material;
FIG. 2 is a schematic diagram of a matrix of lithium niobate thin film material;
FIG. 3 is a schematic diagram of a measurement system of an optical electric field of a lithium niobate thin film material;
FIG. 4 (a) is an effect diagram of the polarization selection structure performing polarization selection on a TE polarized Gaussian beam;
FIG. 4 (b) is a graph showing the effect of the polarization selection structure on polarization selection of a TM polarized Gaussian beam;
fig. 5 is a graph of bragg grating reflection effects.
Reference numerals illustrate:
1-polarization-maintaining optical fiber, 2-gradual-change coupling structure, 3-polarization selection structure, 4-reflection type MZ electro-optic modulator, 5-high gain electrode, 6-Bragg reflection grating, 7-laser source, 8-lithium niobate thin film material optical electric field sensor, 9-circulator, 10-single mode optical fiber, 11-photodetector, 12-spectrometer, 13-radio frequency transmission line, 14-electric field to be measured, 15-lithium niobate single crystal thin film, 16-silicon dioxide and 17-silicon.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.
Fig. 1 shows a structure diagram of a reflective optical electric field sensor made of a lithium niobate thin film material, wherein the sensor uses the lithium niobate thin film as a matrix, and a graded coupling structure 2, a polarization selection structure 3, an MZ electro-optic modulator 4, a high gain electrode 5, an antenna structure (not shown) and a bragg reflection grating 6 are sequentially etched in the direction of an optical path. The polarization maintaining optical fiber 1 of the conical lens is arranged at the left end face of the sensor 8, and only one optical fiber is arranged to be directly connected with the sensor 8, so that optical path communication is realized.
The gradual change coupling structure 2 is a conical gradual change transmission channel arranged at a port of the sensor 8, one end of the conical gradual change transmission channel, which faces the port, is wider and is used for being connected with the input polarization-maintaining optical fiber 1, the other end of the conical gradual change transmission channel is narrower and is connected with a single-mode optical waveguide inside the sensor, and laser of the input polarization-maintaining optical fiber 1 is gradually coupled into the single-mode optical waveguide with the width of 1 mu m.
The polarization selection structure 3 is characterized in that a metal coating is arranged on the single-mode optical waveguide, and a high-loss plasma surface mode is excited, so that TE mode guided waves pass through with low loss, TM mode guided waves attenuate with high loss, and the single-polarization working state of the sensor is realized.
The reflection type MZ electro-optic modulator 4 comprises a Y-branch optical waveguide, wherein the Y-branch optical waveguide comprises two sections of parallel waveguide arms, and Bragg reflection gratings 6 are arranged at the distal ends of the two sections of parallel waveguide arms; the reflective MZ electro-optic modulator 4 adopts a biased MZ electro-optic modulation structure, so that the sensor operates at a linear operating point of the MZ electro-optic modulator 4. Thereby ensuring that the dynamic range of the sensor reaches the maximum; the Bragg reflection grating 6 is adopted to realize the back propagation of waveguide light, a reflector or a reflecting film is not required to be arranged on the other end face of the waveguide, the sensor structure is simplified, the defects of inconvenient grasping, inconvenient arrangement and the like caused by the separation of input and output ends in the use process of the sensor are avoided by the reflecting structure, the optical fiber sensor is more in line with the human engineering, and the optical fiber sensor is also more suitable for various measuring environments. The reduction of the number of optical fibers is also more advantageous for the construction of complex sensor systems, since no output optical fibers are required.
The high-gain electrode 5 adopts a broadband micro-nano high-gain electrode, and comprises 2 electrodes with the same size, wherein the electrode spacing is within 2 mu m, and the high-gain electrode is integrated on a waveguide arm of the MZ electro-optic modulator. The antenna structure adopts a conventional antenna structure of the existing electric field sensor.
Fig. 2 shows a substrate of lithium niobate thin film material, which is formed by attaching a lithium niobate single crystal thin film on a silicon substrate, specifically comprises a silicon 17 supporting structure with the thickness of 0.5mm, a silicon dioxide substrate 16 with the thickness of 2-5 μm is attached on the silicon 17 supporting structure, and a lithium niobate single crystal thin film structure 15 with the thickness of 300-600nm is attached on the silicon dioxide substrate 16, wherein an x-cut y transfer lithium niobate single crystal thin film structure can be adopted. The sensor structure is etched on the lithium niobate thin film material matrix by a micro-nano processing method.
Fig. 3 shows a schematic diagram of the measuring system of the electric field sensor 8. The laser emitted by the laser source 7 is input from one end of the circulator through the polarization maintaining optical fiber 1 and enters the sensor 8 from the other end; the laser is modulated by an electric field to be measured in the sensor and reflected; the downlink laser enters the circulator 9 again and is separated from the uplink laser, and enters the photodetector 11; the optical detector 11 outputs an electric signal carrying electric field information to be detected, and inputs the electric signal to the spectrometer 12 for detection through the radio frequency transmission line 13; and obtaining the frequency and the amplitude of the electric field strength to be measured. The specific measurement method comprises the following steps:
step one, gradual change mode spot conversion coupling: the laser emitted by the laser source is transmitted to the input end of the optical electric field sensor through the polarization maintaining optical fiber, and is transmitted to the single-mode optical waveguide with the width of 1 mu m through the gradual coupling structure, so that the single-mode transmission of the laser is realized;
step two, polarization selection: when the laser transmitted in the single mode passes through the single mode optical waveguide coated with the metal coating, exciting a surface mode of the plasma, thereby removing a TM mode in the waveguide and forming single polarization transmission of the laser;
step three, phase modulation: the transmitted laser in the second step is divided into two paths at the Y branch of the reflective MZ modulator, and the two paths of laser enter two optical waveguide arms interfered by the MZ photoelectric modulator respectively, and the refractive index of the lithium niobate material is changed due to the existence of an electric field to be detected in the space, so that the phase of waveguide light transmitted in the two arms is changed, and the first phase modulation of the transmitted waveguide light is realized;
fourth, secondary phase modulation: light in the two optical waveguide arms is transmitted forward into the Bragg reflection grating and reflected; the waveguide light phase reflected by the Bragg reflection grating is modulated by the space electric field to be detected for the second time;
step five: intensity modulation: the light in the two secondarily modulated optical waveguide arms passes through the Y branch again and is combined into one path of light, so that interference occurs, and finally, the intensity modulation of the space electric field on the laser is realized; the change rule is as follows:
I out ＝I in αE
wherein I is out For backward feeding of the sensorOutput power, I in Inputting power for a light source, wherein alpha is a sensor modulation coefficient, and E is the electric field strength to be measured;
step six, calculating the electric field strength to be measured: the intensity modulated laser output in the fifth step is input into a photodetector to be converted into an electric signal, the obtained electric signal is input into a spectrometer, and the signal amplitude V is measured in the spectrometer rf Units dB μv; the frequency of the electric field to be measured is the same as the frequency of the signal measured in the spectrometer, and the electric field strength amplitude of the electric field to be measured is E out ＝V rf +A F Wherein A is F The antenna coefficient of the measuring system after precision calibration is the known parameter of the measuring system, and is the transmission coefficient of the electric field sensor, and the unit is dB/m.
Fig. 4 shows a polarization selection effect of the polarization selection structure 3. Wherein, in fig. 4 (a), a propagation field distribution diagram of a TE polarized gaussian beam is input to an end face of the sensor, and in fig. 4 (b), a propagation field distribution diagram of a TM polarized gaussian beam is input to an end face of the sensor. It can be seen from the figure that TM polarized light has a larger attenuation, whereas TE polarized light can pass through the polarization selection structure with a lower attenuation, thereby realizing single polarization transmission. In fact, the extinction ratio for TM polarization and TE polarization can reach more than 20 dB.
Fig. 5 is a graph of the reflection effect of the bragg reflection grating structure. The left end inputs a gaussian beam and enters the bragg reflection grating. As can be seen from fig. 5, the incoming beam is not transmitted to the far right, but is reflected back to the beginning, and the reflectivity can reach 85%.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (8)
1. A reflection type optical electric field sensor based on a lithium niobate thin film material is characterized in that the lithium niobate thin film material is adopted as a sensor matrix, and the reflection type optical electric field sensor is formed by sequentially etching the lithium niobate thin film material along the light path propagation direction: a gradual coupling structure, a polarization selection structure, a reflective MZ electro-optic modulator, a broadband high-gain electrode and an antenna structure; the gradual change coupling structure is arranged at a port of the sensor and couples laser with larger light spots in input laser into a single-mode optical waveguide with smaller light spots so as to realize single-mode transmission of the laser; the polarization selection structure eliminates TM mode in the single-mode optical waveguide to realize single polarization transmission of laser; the reflection type MZ electro-optic modulator only comprises a Y-branch optical waveguide, wherein the Y-branch optical waveguide comprises two sections of parallel waveguide arms, and Bragg reflection gratings are arranged at the distal ends of the two sections of parallel waveguide arms; the reflection type MZ electro-optic modulator is connected behind the single-mode optical waveguide and is used for modulating an electric field to be detected in space onto transmitted laser; the high-gain electrode increases the intensity of an electric field to be detected acting on a waveguide arm of the reflective MZ electro-optic modulator; the Bragg reflection grating reflects waveguide light, and the reflected light is combined and output through the Y-branch optical waveguide of the reflection type MZ electro-optical modulation.
2. The reflective optical electric field sensor based on a lithium niobate thin film material according to claim 1, wherein the substrate of the lithium niobate thin film material is supported by a silicon wafer, a silicon dioxide substrate with a thickness of 2 μm to 5 μm is attached to the silicon wafer, and a lithium niobate single crystal thin film with a thickness of 300nm to 600nm is attached to the silicon dioxide substrate.
3. The reflective optical electric field sensor based on lithium niobate thin film material according to claim 2, wherein the graded coupling structure is a tapered graded transmission channel disposed at a sensor port, the tapered graded transmission channel being wider toward one end of the port for connection with an input optical fiber and narrower toward the other end for engagement with a single mode optical waveguide, and gradually coupling laser light of the input optical fiber into the single mode optical waveguide having a width of 1 um.
4. The reflective optical electric field sensor based on lithium niobate thin film material according to claim 3, wherein the polarization selection structure is configured to realize a single polarization operation state of the sensor by arranging a metal coating on the single-mode optical waveguide, and exciting a high-loss plasma surface mode to enable a TE mode guided wave to pass through with low loss while enabling a TM mode guided wave to attenuate with high loss.
5. The reflective optical electric field sensor based on lithium niobate thin film material according to claim 4, wherein the reflective MZ electro-optic modulator adopts a biased MZ electro-optic modulation structure, so that the sensor operates at a linear operating point of the MZ electro-optic modulator.
6. The reflective optical electric field sensor based on lithium niobate thin film material according to claim 5, wherein the high gain electrode is a broadband micro-nano high gain electrode, comprising 2 electrodes with the same size and an electrode spacing of less than 2um, and the high gain electrode is integrated on a waveguide arm of the MZ electro-optic modulator.
7. A measurement system for performing measurements based on a reflective optical electric field sensor according to any of claims 1-6, characterized by comprising: the laser is input to the optical electric field sensor through the polarization maintaining optical fiber and the circulator, an external electric field to be detected is applied to the sensor, laser subjected to intensity modulation is output to be incident into the optical detector through the circulator and the single-mode optical fiber and converted into an electric signal, and finally the electric signal is input to the spectrometer for detection, so that the frequency and the amplitude of the electric field intensity to be detected are obtained.
8. The measurement method based on the measurement system of claim 7, specifically comprising the following steps:
step one, gradual change mode spot conversion coupling: the laser emitted by the laser source is transmitted to the input end of the optical electric field sensor through the polarization maintaining optical fiber, and is transmitted to the single-mode optical waveguide with the width of 1um through the gradual coupling structure, so that the single-mode transmission of the laser is realized;
step two, polarization selection: when the laser transmitted in the single mode passes through the single mode optical waveguide coated with the metal coating, exciting a surface mode of the plasma, thereby removing a TM mode in the waveguide and forming single polarization transmission of the laser;
step three, phase modulation: the transmitted laser in the second step is divided into two paths at the Y branch of the reflective MZ modulator, and the two paths of laser enter two optical waveguide arms interfered by the MZ photoelectric modulator respectively, and the refractive index of the lithium niobate material is changed due to the existence of an electric field to be detected in the space, so that the phase of waveguide light transmitted in the two arms is changed, and the first phase modulation of the transmitted waveguide light is realized;
fourth, secondary phase modulation: light in the two optical waveguide arms is transmitted forward into the Bragg reflection grating and reflected; the waveguide light phase reflected by the Bragg reflection grating is modulated by the space electric field to be detected for the second time;
step five: intensity modulation: the light in the two secondarily modulated optical waveguide arms passes through the Y branch again and is combined into one path of light, so that interference occurs, and finally, the intensity modulation of the space electric field on the laser is realized; the change rule is as follows:
I out ＝I in αE
wherein I is out For backward output power of sensor, I in Inputting power for a laser light source, wherein alpha is a sensor modulation coefficient, and E is the electric field strength to be measured;
step six, calculating the electric field strength to be measured: the intensity modulated laser output in the fifth step is input into a photodetector to be converted into an electric signal, the obtained electric signal is input into a spectrometer, and the signal amplitude V is measured in the spectrometer rf The method comprises the steps of carrying out a first treatment on the surface of the The frequency of the electric field to be measured is the same as the frequency of the signal measured in the spectrometer, and the electric field strength amplitude of the electric field to be measured is E out ＝V rf +A F Wherein A is F The antenna coefficient of the measurement system after precision calibration.
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| CN116930629A (en) * | 2023-09-15 | 2023-10-24 | 清华大学 | Electric field sensing device and method |
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| CN116930629A (en) * | 2023-09-15 | 2023-10-24 | 清华大学 | Electric field sensing device and method |
| CN116930629B (en) * | 2023-09-15 | 2023-12-22 | 清华大学 | Electric field sensing device and method |
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