CN112415791B - Method for quickly and accurately selecting optimal modulation point of crystal electro-optic modulation - Google Patents

Method for quickly and accurately selecting optimal modulation point of crystal electro-optic modulation Download PDF

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CN112415791B
CN112415791B CN202011292552.6A CN202011292552A CN112415791B CN 112415791 B CN112415791 B CN 112415791B CN 202011292552 A CN202011292552 A CN 202011292552A CN 112415791 B CN112415791 B CN 112415791B
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electric field
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CN112415791A (en
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杜小平
吕潇磊
赵继广
宋一铄
王阳
张建伟
杨步一
郜魏柯
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Peoples Liberation Army Strategic Support Force Aerospace Engineering University
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0012—Optical design, e.g. procedures, algorithms, optimisation routines
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
    • G02F1/0327—Operation of the cell; Circuit arrangements
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The invention discloses a method for selecting an optimal modulation point for crystal electro-optic modulation, which comprises the following steps: determining the phase change of the bias electric field and the modulation electric field based on a phase modulation theory; calculating the electro-optical modulation transmission amplitude value under any electric field input based on a modulation transmission theory by utilizing the phase change of the bias electric field and the modulation electric field; measuring a dynamic dielectric response function of the crystal material under a bias electric field based on the dielectric tester; integrating the dynamic phase changes of the bias electric field and the modulation electric field based on an integral upper limit function; the highest point of the modulation transmission amplitude is calculated by software to be the maximum modulation amplitude of the modulator, and the corresponding bias field intensity is the optimal modulation point. The invention provides the analysis expression form and the acquisition method of each parameter required by calculating the crystal electro-optic modulation point, has the advantage of rapidly and accurately acquiring the electro-optic modulation point, and can exert the maximum modulation performance under the modulation point, and generate the maximum output signal of the modulator with the minimum modulation voltage.

Description

Method for quickly and accurately selecting optimal modulation point of crystal electro-optic modulation
Technical Field
The invention belongs to the technical field of electro-optic modulation, and particularly relates to a method for quickly and accurately selecting an optimal modulation point of crystal electro-optic modulation.
Background
The electro-optic crystal is a key component element of an electro-optic modulation system, realizes the regulation and control of output signals by adding alternating current and direct current signals at two ends of the crystal to light, aims to generate large output signals through small modulation signals, and is widely applied in the fields of high-speed optical communication, high-speed optical deflection and the like. In the prior art, the electro-optic modulation usually selects the median point of half-wave voltage of a crystal as the electro-optic modulation point, and the electro-optic modulation is realized by DC bias to the electro-optic modulation point and then applying an AC modulation signal, but the relaxation characteristic causes dynamic response of the dielectric constant of part of the crystal under the action of an electric field, which causes the deviation of the median point of half-wave voltage compared with the static dielectric constant, and then the electro-optic modulation according to the method causes the weakening of modulation performance and the increase of power consumption. In recent years, as the preparation process of novel crystal materials is mature, crystals with large size and good optical quality are gradually introduced, and the crystal electro-optic modulation has a wide application prospect in the fields of free space optical communication and laser three-dimensional imaging. In free-space optical communication and laser three-dimensional imaging, the power consumption of an electro-optical modulator is directly related to the load of the system, and the modulation voltage becomes an important factor for limiting the application and development of the electro-optical modulator. Therefore, the research on the optimal modulation point of the crystal electro-optic modulation has very important practical significance and application value by applying a small modulation voltage to realize a large modulation amplitude.
Disclosure of Invention
In view of the above-mentioned current situation, the invention provides a method for quickly and accurately selecting the optimal modulation point of crystal electro-optic modulation, which can be used for optimally designing the working state of the electro-optic modulation equipment.
A method for quickly and accurately selecting an optimal modulation point of crystal electro-optic modulation comprises the following steps:
the first step: determining phase change of bias electric field and modulation electric field based on phase modulation theory
For a secondary electro-optic crystal, when the laser propagates in the x-direction, an electric field is applied in the z-direction, and the transmittance of the electro-optic modulator is expressed as:
Figure GDA0004139472340000021
wherein I is o Represents the intensity of incident light, I represents the light of emergent lightThe intensity, Φ, represents the phase change of the light, and this parameter is the response of the applied electric field, which can be expressed as
Figure GDA0004139472340000022
Medium dc bias signal E DC Phase change Φ of (2) DC And an alternating current modulation signal E AC Phase change Φ of (2) AC Can be expressed as
Figure GDA0004139472340000023
Figure GDA0004139472340000024
Wherein n is 0 Represents the refractive index of ordinary ray in unpressurized condition g 11 -g 12 Represents the secondary electro-optic coefficient, L represents the light transmission length of the crystal, lambda represents the laser wavelength, and epsilon (E) represents the dynamic dielectric constant under the action of an electric field.
And a second step of: calculating the electro-optical modulation transmission amplitude value under any electric field input based on the modulation transmission theory by utilizing the phase change of the bias electric field and the phase change of the modulation electric field obtained in the first step
The crystal modulation transmission amplitude Δt under electrical parameter modulation can be expressed as:
Figure GDA0004139472340000025
and a third step of: measuring dynamic dielectric response function of crystal material under bias electric field based on dielectric tester
The range of the bias field is set based on the half-wave voltage value of the crystal material, and the dynamic dielectric parameter epsilon (E) is measured by a dielectric tester
Fourth step: integrating the dynamic phase change of the bias electric field and the modulation electric field based on the integral upper limit function by utilizing the dynamic dielectric response function obtained in the third step
Will modulate the electric field E AC The dynamic dielectric function and the bias electric field E are integrated based on an integral upper limit formula, and the direct current bias phase change and the alternating current modulation phase change can be respectively expressed as
Figure GDA0004139472340000031
Figure GDA0004139472340000032
Fifth step: substituting the dynamic phase change obtained in the fourth step into the modulation transmission amplitude obtained in the second step, and calculating the highest point of the modulation transmission amplitude by software to obtain the maximum modulation amplitude of the modulator, wherein the corresponding bias field intensity is the optimal modulation point
The modulation transmission amplitude delta' T of the crystal under the dynamic response of the electrical parameter can be expressed as:
Figure GDA0004139472340000033
the maximum value of the modulation transmission amplitude is simulated by Matlab, a corresponding E value is selected as an optimal modulation point, and E is applied AC The small voltage of (2) can realize the large modulation amplitude of delta T.
Drawings
FIG. 1 is a schematic diagram of a KTN electro-optic modulator according to an embodiment of the present invention;
FIG. 2 is a graph showing the dynamic dielectric constant of KTN crystals under the action of an electric field in an embodiment of the present invention;
FIG. 3 is a graph of simulation results of the modulation performance of a KTN electro-optic modulator under the action of an electric field in an embodiment of the present invention;
fig. 4 is a graph showing actual modulation performance of a KTN electro-optic modulator according to an embodiment of the present invention.
Detailed description of the preferred embodiments
The invention is further described below with reference to the drawings and examples.
With the current relatively popular potassium tantalate niobate (KTN) crystal electro-optic modulation as an embodiment, the incident light of the laser 1 forms polarized light along the direction 2 through the polarizer 3, and enters the analyzer 5 through the KTN crystal 4, and finally is received by the photodetector 6, and the bias voltage V DC And modulating voltage V AC Is loaded in direction 8 across the crystal by means of a biaser 7.
The first step: determining phase change of bias electric field and modulation electric field based on phase modulation theory
For a secondary electro-optic crystal, when the laser propagates in the x-direction, an electric field is applied in the z-direction, and the transmittance of the electro-optic modulator is expressed as:
Figure GDA0004139472340000041
wherein I is o Representing the intensity of the incident light, I representing the intensity of the exiting light, Φ representing the phase change of the light, the parameter being the response of the applied electric field, may be expressed as
Figure GDA0004139472340000042
Wherein the DC offset signal E DC Phase change Φ of (2) DC And an alternating current modulation signal E AC Phase change Φ of (2) AC Can be expressed as
Figure GDA0004139472340000043
Figure GDA0004139472340000044
Wherein n is 0 Represents the refractive index of ordinary ray in unpressurized condition g 11 -g 12 Represents the secondary electro-optic coefficient, L represents the crystal light-on length, lambda represents the laser wavelength, and ε (E) represents the dielectric constant.
And a second step of: calculating the electro-optical modulation transmission amplitude value under any electric field input based on the modulation transmission theory by utilizing the phase change of the bias electric field and the phase change of the modulation electric field obtained in the first step
The crystal modulation transmission amplitude Δt under electrical parameter modulation can be expressed as:
Figure GDA0004139472340000051
and a third step of: measuring dynamic dielectric response function of crystal material under bias electric field based on dielectric tester
The range of the bias field is set based on the half-wave voltage value of the crystal material, the capacitance of the crystal material is measured by an impedance analyzer, the dynamic dielectric parameter epsilon (E) is obtained by data processing, and the dynamic dielectric constant curve of figure 2 is obtained by processing the capacitance curve measured by a steady state 6500B precision impedance analyzer.
Fourth step: and (3) integrating the dynamic phase change of the bias electric field and the modulation electric field based on the integral upper limit function by utilizing the dynamic dielectric response function obtained in the third step.
Will modulate the electric field E AC The dynamic dielectric function and the bias electric field E are integrated based on an integral upper limit formula, and the direct current bias phase change and the alternating current modulation phase change can be respectively expressed as
Figure GDA0004139472340000052
Figure GDA0004139472340000053
Fifth step: substituting the dynamic phase change obtained in the fourth step into the modulation transmission amplitude obtained in the second step, and calculating the highest point of the modulation transmission amplitude by software to obtain the maximum modulation amplitude of the modulator, wherein the corresponding bias field intensity is the optimal modulation point
The modulation transmission amplitude delta' T of the crystal under the dynamic response of the electrical parameter can be expressed as:
Figure GDA0004139472340000054
the maximum value of the modulation transmission amplitude is simulated by Matlab, a corresponding E value is selected as an optimal modulation point, and E is applied AC The small voltage of (2) can realize the large modulation amplitude of delta T.
As a specific example, the calculation result of the optimal modulation point of the KTN electro-optic modulator is shown in FIG. 3 by applying 9.4X10 4 The direct current bias electric field of V/m can realize large modulation amplitude of 0.32 pi by adopting small voltage of 1V, 32mV modulation is realized under the same condition by constructing an experimental system, and 0.28 pi is modulated relative to 114mV transmittance, and the frequency sweep diagram of the modulation amplitude of the electro-optical modulator in the range of 0-200kHz is shown in fig. 4. We pass the test 9.3×10 4 V/m and 9.5X10 4 The modulation performance of the V/m bias electric field verifies that this point is the optimal modulation point, but the partial attenuation of the modulation amplitude is due to the inherent errors of the system components.
The foregoing is merely one embodiment of the invention, and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims (5)

1. A method for quickly and accurately selecting the optimal modulation point of crystal electro-optic modulation is characterized in that the modulation point of the crystal can be quickly and accurately determined, and the optimal modulation performance of an electro-optic modulator is fully exerted, and the method comprises the following steps:
the first step: determining the phase change of the bias electric field and the modulation electric field based on a phase modulation theory;
and a second step of: calculating the electro-optical modulation transmission amplitude value under any electric field input based on the modulation transmission theory by utilizing the phase change of the bias electric field and the phase change of the modulation electric field obtained in the first step;
and a third step of: measuring a dynamic dielectric response function epsilon (E) of the crystal material under a bias electric field based on the dielectric tester;
fourth step: integrating the dynamic phase change of the bias electric field and the modulation electric field based on the integral upper limit function by utilizing the dynamic dielectric response function obtained in the third step;
fifth step: and substituting the dynamic phase change obtained in the fourth step into the modulation transmission amplitude obtained in the second step, and calculating the highest point of the modulation transmission amplitude by software to obtain the maximum modulation amplitude of the modulator, wherein the corresponding bias field intensity is the optimal modulation point.
2. A method for fast and accurate selection of optimal modulation points for crystal electro-optic modulation according to claim 1, wherein in the first step:
bias electric field E DC The phase change of (a) is:
Figure FDA0004139472330000011
modulating electric field E AC The phase change of (a) is:
Figure FDA0004139472330000012
wherein n is 0 Represents the refractive index of ordinary ray in unpressurized condition g 11 -g 12 Represents the secondary electro-optic coefficient, L represents the light transmission length of the crystal, lambda represents the laser wavelength, epsilon (E) represents the dielectric constant, and E is the applied electric field.
3. The method for quickly and accurately selecting an optimal modulation point for electro-optic modulation of a crystal according to claim 2, wherein the transmission amplitude of the electro-optic modulation under any electric field input in the second step is:
Figure FDA0004139472330000021
4. a method for fast and accurate selection of optimal modulation point for electro-optic modulation of crystal according to claim 3 wherein the dc bias phase variation and ac modulation phase variation in the fourth step are expressed as respectively
Figure FDA0004139472330000022
Figure FDA0004139472330000023
5. The method for quickly and accurately selecting optimal modulation point for electro-optic modulation of crystal according to claim 4, wherein the modulation transmission amplitude ΔΔt of the crystal in the electrical parameter dynamic response in the fifth step is expressed as:
Figure FDA0004139472330000024
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Citations (6)

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JPS6059321A (en) * 1983-09-13 1985-04-05 Matsushita Electric Ind Co Ltd Optical modulating element
CN101216518A (en) * 2007-12-29 2008-07-09 上海亨通光电科技有限公司 Y wave-guide half-wave voltage test method
CN101825656A (en) * 2009-12-31 2010-09-08 上海亨通光电科技有限公司 Method for rapidly testing half-wave voltage value of lithium niobate optical modulator
CN205353175U (en) * 2015-12-23 2016-06-29 南昌航空大学 Voltage detector based on vertical electro -optical crystal modulation
WO2016103633A1 (en) * 2014-12-24 2016-06-30 日本電気株式会社 Optical transmitter and method for controlling optical transmitter
CN109975998A (en) * 2019-02-02 2019-07-05 中国科学院国家授时中心 Electric light Polarization Modulation system and electric light polarization modulation method

Patent Citations (6)

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Publication number Priority date Publication date Assignee Title
JPS6059321A (en) * 1983-09-13 1985-04-05 Matsushita Electric Ind Co Ltd Optical modulating element
CN101216518A (en) * 2007-12-29 2008-07-09 上海亨通光电科技有限公司 Y wave-guide half-wave voltage test method
CN101825656A (en) * 2009-12-31 2010-09-08 上海亨通光电科技有限公司 Method for rapidly testing half-wave voltage value of lithium niobate optical modulator
WO2016103633A1 (en) * 2014-12-24 2016-06-30 日本電気株式会社 Optical transmitter and method for controlling optical transmitter
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Non-Patent Citations (1)

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Title
Modeling and Analysis of the Electro-Optic Modulator With Alignment Errors;PENG ZHANG 等;《IEEE Access》;20191225;第8卷;第2023-2031页 *

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