CN110907136A - Temperature-controllable electro-optic amplitude modulator and test method - Google Patents

Temperature-controllable electro-optic amplitude modulator and test method Download PDF

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CN110907136A
CN110907136A CN201911151557.4A CN201911151557A CN110907136A CN 110907136 A CN110907136 A CN 110907136A CN 201911151557 A CN201911151557 A CN 201911151557A CN 110907136 A CN110907136 A CN 110907136A
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electro
copper furnace
temperature
amplitude modulator
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CN110907136B (en
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王雅君
李瑞鑫
郑耀辉
田龙
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Shanxi University
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Shanxi University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G01M11/0207—Details of measuring devices
    • 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
    • G02F1/0305—Constructional arrangements

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  • Optics & Photonics (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The invention belongs to the technical field of laser modulation, and particularly relates to a temperature-controllable electro-optic amplitude modulator and a test method. The invention aims to improve the linear modulation performance of electro-optic amplitude modulation and reduce the influence of external temperature change on the performance of a modulator, and the electro-optic amplitude modulation device comprises a first base, wherein an insulating gasket is arranged on the first base, the edge gasket is of a cuboid structure, a second base is arranged on the insulating gasket, one side of the second base is attached to one side of the insulating gasket, and gaps are reserved on the other three sides.

Description

Temperature-controllable electro-optic amplitude modulator and test method
Technical Field
The invention belongs to the technical field of laser modulation, and particularly relates to a temperature-controllable electro-optic amplitude modulator and a test method.
Background
The electro-optical modulator is a key device for high-speed optical communication, and can modulate the amplitude or phase of light waves emitted by a laser, so that an input signal is applied to an optical carrier for transmission, and the optical modulator can not only change the intensity of the light waves, but also modulate the polarization state of the light waves. The requirements of a fiber optic communication system for modulation are: (1) high modulation rate and wide modulation bandwidth; (2) a low drive voltage; (3) high extinction ratio; (4) low insertion loss. The lithium niobate (LINBO3) crystal is used as an excellent transverse electro-optical modulation material, has the advantages of low driving voltage, small insertion loss, wide spectrum working range, high extinction ratio, easiness in large-scale production and the like, and is widely applied to the fields of optical communication, optical signal transmission, electro-optical switches and the like.
The existing electro-optical amplitude modulator in the market has no temperature control facility, and the reason is mainly that the temperature control device occupies a large space, the cost is large, the product effect is not good, and the mass production is facilitated by the configuration of directly adding electrodes to bare crystals; however, in practical experiments, the fluctuation of temperature has a great influence on the electro-optic amplitude modulation, which results in unstable amplitude modulation signals or introduction of signals into an phase modulator, and the like, so that extra useless signals are introduced into the amplitude modulation of optical field signals, which affects normal use. Therefore, a temperature control setting is very necessary.
Ideally, the light ray propagates along the optical axis of the lithium niobate crystal, and the influence of natural birefringence is not considered in theoretical analysis, but in practical application, complete alignment of the light ray and the optical axis is impossible, which causes errors between theory and practice. The transverse electro-optic effect of the lithium niobate crystal under the conditions of paraxial and non-paraxial is analyzed, and the method has guiding significance for improving the electro-optic performance by utilizing angle adjustment. Meanwhile, the electro-optical characteristics of the crystal under the paraxial and non-paraxial conditions are of great importance to a novel electro-optical device which needs to utilize the birefringence effect of the crystal to split or combine beams and also needs to utilize the electro-optical effect to generate additional phase shift. The invention provides a temperature-controlled electro-optic amplitude modulator, wherein the temperature of a crystal is controllable, and the amplitude modulation can be realized by adopting a simple device.
Disclosure of Invention
The invention aims to improve the linear modulation performance of electro-optical amplitude modulation and reduce the influence of external temperature change on the performance of a modulator. As shown in fig. 12, by analyzing the change of the principal axis of the refractive index of the crystal by applying voltages to different principal axes of the crystal, a lithium niobate crystal which has strong modulation performance and is convenient and economical is selected as a modulation crystal, and the lithium niobate crystal has no natural birefringence effect when the electric field is applied to the Z axis and the X or Y axis (natural birefringence is the change of the refractive index of the crystal just before the electric field is applied, that is, when no external electric field is applied, there is a phase difference between o light and e light passing through the crystal), but after the electric field is applied, the X and Y axes become biaxial crystals, and only the voltage applied to the X axis has two cross terms according to a formula, so that the crystal undergoes two coordinate transformations, one rotation of 45 ° around the Z axis, and the later transformation is the same as the Y axis. When the electro-optical amplitude modulator is actually designed, lithium niobate crystals are adopted, voltage is applied to an X axis, a Z axis passes light, natural birefringence is avoided, but the X axis and the Z axis rotate around a Y axis by a small angle, namely in one direction of X 'and Y', the amplitude is projected, but the Y axis does not rotate, so that the projection difference can be eliminated by adopting a mode that two crystals are arranged side by side and are mutually connected in series by 90 degrees. Because the lithium niobate crystal has no natural birefringence when light passes through the Z axis and voltage is applied to the other axes, after coordinate transformation, the fact that when voltage is applied to the X axis direction of the crystal main axis and light is transmitted along the Z axis, the change of the crystal refractive index main axis meets the linear requirement of amplitude modulation is found, theoretical research finds that the main axis of the crystal refractive index ellipsoid can be transformed twice when voltage is applied to the X axis direction, but the useful transformation for amplitude modulation is only the coordinate transformation around the Z axis of the light-passing axis, and the coordinate transformation around the Y axis is a little transformation angle, but still can be one of the important factors influencing the amplitude modulation, therefore, the invention utilizes two lithium niobate crystals with completely same size and performance, the optical axes of the lithium niobate crystals are arranged in series at 90 degrees to compensate the amplitude projection along the Y axis after the voltage is applied to the crystals; the temperature control design part is characterized in that a crystal is wrapped by an insulating and heat-conducting material, a designed heat-preservation copper furnace is wrapped by the material wrapping the crystal at the periphery of the material, a thermistor is inserted into the heat-preservation copper furnace in the middle of the crystal, a thermistor is inserted into the heat-preservation copper furnace, a temperature controller is used for monitoring the temperature change of the crystal, a semiconductor cooler (TEC) for feeding back temperature control is completely attached to the upper cross section and the lower cross section of the heat-preservation copper furnace, and an electro-optic crystal fixing the temperature control device is designed.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a temperature-controllable electro-optic amplitude modulator comprises a first base, wherein an insulating gasket is arranged on the first base, the edge gasket is of a cuboid structure, a second base is arranged on the insulating gasket, one side of the second base is attached to one side of the insulating gasket, gaps are reserved among the other three sides, a plurality of first semiconductor refrigerators are arranged on the second base side by side, heat-insulating copper furnaces are arranged on the first semiconductor refrigerators, a plurality of second semiconductor refrigerators are arranged on the heat-insulating copper furnaces side by side, a first heat-insulating layer and a second heat-insulating layer are fixedly arranged on the front end face and the rear end face of the heat-insulating copper furnaces respectively, a third heat-insulating layer and a third heat-insulating layer are fixedly arranged on the left end face and the right end face of each heat-insulating copper furnace, a plurality of joint holes are formed in the upper end face of an outer shell, and a plurality of light through holes are symmetrically formed in the left end face and the right, the insulating gasket is arranged between the first base and the second base and is mainly used for placing electric heat exchange between the platform and the second base; gaps left on three sides of the insulating gasket are used for placing an outer shell sleeve, so that the outer shell sleeve and the second base form a cuboid box perfectly; the first semiconductor refrigerators are closely arranged on the second base side by side, one side of each first semiconductor refrigerator is closely contacted with the second base, the other side of each first semiconductor refrigerator is completely adhered to the copper furnace through glue, the first semiconductor refrigerators connected in series completely cover one side of the copper furnace to prevent heat loss, the temperature of the copper furnace can be controlled through the cold and heat regulation capacity of the first semiconductor refrigerators, and the second semiconductor refrigerators on opposite sides of the first semiconductor refrigerators have the same function; the first heat insulation layer is provided with a countersunk hole which is fixed on the copper furnace by plastic screws, and one surface of the first heat insulation layer is completely covered for heat conduction; the second heat-insulating layer is similar to the first heat-insulating layer, and the only difference is that a hole for leading out a line between crystal electrodes and a hole for leading out a thermistor line are formed and are completely consistent with a plurality of wire outlet holes on the side wall of the copper furnace; the third heat-insulating layers on the front and rear end surfaces of the copper furnace are provided with countersunk holes which are fixed on the copper furnace by plastic screws to prevent heat conduction, and the middle of the third heat-insulating layers is provided with a hole which is completely consistent with the light through hole of the outer shell; the purpose of better temperature control can be achieved by the design that the external six surfaces of the copper furnace are fully covered (two sides are used for controlling the temperature of the semiconductor refrigerator, and the rest four surfaces are fully covered with heat-insulating layers for preventing heat conduction with the outside).
Further, the second base comprises a fixed seat and a baffle, the fixed seat and the baffle are integrally formed into an L shape, a first convex edge is arranged in the middle of the fixed seat, a first heat conduction inclined surface is arranged between the baffle and the first convex edge, and the first heat conduction inclined surface is inclined downwards from the baffle to the first convex edge, the front end of the first ridge is provided with a platform, the inner wall of the front panel of the outer shell is provided with a second ridge and a second heat conduction inclined plane, and the second heat conduction inclined plane is tightly attached to the second semiconductor refrigerator, the heat-conducting inclined plane is arranged between the baffle and the convex edge, so that the heat-insulating copper furnace can be arranged on the inclined plane, thereby not only being convenient for placing the polarizer, because only the light modulation in the horizontal direction and the vertical direction is considered, the surface of the copper furnace is not contacted with the outer shell completely, the heat exchange between the copper furnace and the outer shell is avoided, and the space saving is facilitated.
Still further, the heat preservation copper stove includes copper stove body and copper stove lid, the copper stove lid is fixed to be set up on the copper stove body, the copper stove body is for controlling both ends open-ended flute profile structure the recess inner wall and the bottom of copper stove body all are equipped with the arch the preceding terminal surface of copper stove body is equipped with wire hole and thermistor mounting hole be equipped with the thermistor in the thermistor mounting hole to seal the thermistor mounting hole with thermal-insulating material, be used for gathering the temperature of heat preservation copper stove.
The copper furnace body and the cover can be separated mainly for facilitating crystal installation and crystal arrangement of electrode wires, the protrusions arranged on the inner wall and the bottom of the groove of the copper furnace body are used for adhering crystals (the protrusion positions are different because X, Y shafts of the two crystals are in reverse parallel), the wire outlet hole of the copper furnace body is formed in the middle of the side wall and mainly used for leading out a wire between the two crystal electrodes, and the arrangement is most space-saving and the wire arrangement layout is more suitable.
A test method for applying a modulation signal to an optical field amplitude component by a temperature-controllable electro-optic amplitude modulator comprises the following steps:
step 1, respectively sticking two lithium niobate crystals with the same size in a heat preservation copper furnace, feeding temperature signals back to a first semiconductor refrigerator and a second semiconductor refrigerator in an electro-optical amplitude modulator through a temperature controller through the temperature of the lithium niobate crystals acquired by a thermistor, carrying out constant temperature control on the temperature of the lithium niobate crystals, and simultaneously applying modulation signals by a signal generator to modulate the amplitude of an optical field;
step 2, assembling the electro-optical amplitude modulator, and collimating a beam of stably running single-frequency laser;
step 3, inserting a polarizing film/half-wave plate in the collimated laser path to enable the laser beam to transmit along the center of the polarizing film, and rotating the vibration transmission direction to ensure that linearly polarized light in the vertical or horizontal direction is obtained after the linearly polarized light is transmitted through the polarizing film;
step 4, after the linearly polarized light in the vertical or horizontal direction in the step 3 is obtained, an electro-optical amplitude modulator is placed behind the linearly polarized light, and the light beam is ensured to be transmitted and output by a light transmission central shaft of the lithium niobate crystal;
step 5, passing the laser passing through the electro-optical amplitude modulator in the step 4 through an 1/4 lambda wave plate to perform pi/2 phase delay;
step 6, the light which is subjected to the phase delay of pi/2 in the step 5 passes through a second polaroid/polarization beam splitter prism;
step 7, inputting the laser transmitted by the second polarizing film/polarization splitting prism in the step 6 into a photoelectric detector, converting an optical signal into a photocurrent signal, and inputting the photocurrent signal into an oscilloscope to observe a transmission signal; when the waveform of the output signal is completely consistent with that of the input signal, namely if the input is a sine wave signal, the output is a complete sine wave with regular symmetry, the test of the electro-optical amplitude modulation signal is completed.
By combining the device and the test method, the linear working area and the signal amplitude of the amplitude modulator are optimized, the linear modulation performance of amplitude modulation is improved, a better amplitude modulation signal is obtained, and the implementation effect of the modulator is enhanced.
Further, the rotational transmission direction of the first polarizer/half-wave plate in the step 3 is consistent with the direction of the X axis or the Y axis when no voltage is applied to the lithium niobate crystal.
Still further, the main axis direction of the wave plate in the step 5 is consistent with the X and Y axis directions in the coordinate system.
Furthermore, the light transmission direction of the second polarizer/polarization splitting prism in the step 6 is perpendicular to the light transmission direction of the first polarizer/half-wave plate.
Compared with the prior art, the invention has the following beneficial effects:
1. the first base is provided with an insulating gasket which is mainly used for placing electric heat exchange between the platform and the second base; gaps left on three sides of the insulating gasket are used for placing the outer shell sleeve, so that a cuboid box is formed between the outer shell sleeve and the second base; the semiconductor refrigerators I are closely arranged on the base II side by side, one side of each semiconductor refrigerator is not in close contact with the base II, the other side of each semiconductor refrigerator is adhered to the heat preservation copper furnace in a gluing or welding mode, the semiconductor refrigerators I connected in series and one side of the heat preservation copper furnace are completely covered to prevent heat loss, the temperature of the heat preservation copper furnace can be controlled through the cold and heat regulation capacity of the semiconductor refrigerators I, and the semiconductor refrigerators II on the opposite side of the semiconductor refrigerators have the same function; the first heat insulation layer is provided with a countersunk hole which is fixed on the heat insulation copper furnace by a plastic screw, and one surface of the first heat insulation layer is completely covered for heat conduction; the second heat-insulating layer is similar to the first heat-insulating layer, and the only difference is that a lead hole between crystal electrodes and a thermistor lead hole are formed and correspond to a plurality of wire outlet holes on the side wall of the heat-insulating copper furnace; the third heat insulation layers on the front and rear end surfaces of the heat insulation copper furnace are provided with countersunk holes which are fixed on the heat insulation copper furnace by plastic screws to prevent heat conduction, and the middle of the third heat insulation layers is provided with a hole which is completely consistent with the light through hole of the outer shell; through the design, the six external surfaces of the heat-preservation copper furnace are fully covered (two side surfaces are used for controlling the temperature of the semiconductor refrigerator, and the other four surfaces are fully covered with the heat-insulation heat-preservation layer on the copper surface to prevent heat conduction with the outside), so that the aim of better temperature control can be achieved.
2. The second base comprises a fixed seat and a baffle, the fixed seat and the baffle are integrally formed, the baffle is arranged at the rear end of the fixed seat, a first projecting edge is arranged in the middle of the fixed seat, a first heat conduction inclined surface is arranged between the baffle and the first projecting edge, the first heat conduction inclined surface is enabled to incline downwards from the baffle to the first projecting edge, a platform is arranged at the front end of the first projecting edge, a second projecting edge and a second heat conduction inclined surface are arranged on the inner wall of a front panel of an outer shell sleeve, the second heat conduction inclined surface is enabled to be tightly attached to a second semiconductor refrigerator, a heat preservation copper furnace can be arranged on the inclined surface by arranging the first heat conduction inclined surface between the baffle and the projecting edge, so that a polarizer is conveniently placed, and the surface of the copper furnace can not be in contact with the outer shell sleeve completely only by considering light modulation in the horizontal direction and the vertical direction, avoid heat exchange between the two and is beneficial to saving space.
3. The heat preservation copper furnace comprises a copper furnace body and a copper furnace cover, wherein the copper furnace cover is fixedly arranged on the copper furnace body, the copper furnace body is of a groove-shaped structure with openings at the left end and the right end, bulges are arranged on the inner wall and the bottom of a groove of the copper furnace body, and a plurality of wire outlet holes are formed in the side wall of the copper furnace body. The copper furnace body and the cover can be separated mainly for facilitating crystal installation and crystal arrangement of electrode wires, the protrusions arranged on the inner wall and the bottom of the groove of the copper furnace body are used for adhering crystals (the protrusion positions are different because X, Y shafts of the two crystals are in reverse parallel), the wire outlet hole of the copper furnace body is formed in the middle of the side wall and mainly used for leading out a wire between the two crystal electrodes, and the arrangement is most space-saving and the wire arrangement layout is more suitable.
4. The invention optimizes the linear working area and the signal amplitude of the amplitude modulator by combining the device and the test method, improves the linear modulation performance of the amplitude modulation, obtains a better amplitude modulation signal and enhances the implementation effect of the modulator.
Drawings
FIG. 1 is a schematic view of the overall structure of the present invention;
FIG. 2 is a rear view of the overall structure of the present invention;
FIG. 3 is an exploded view of the present invention;
FIG. 4 is a schematic view of the present invention with the outer shell removed;
FIG. 5 is a schematic structural view of a second base of the present invention;
FIG. 6 is a schematic view of the construction of the outer shell of the present invention;
FIG. 7 is a schematic three-dimensional structure of the copper furnace body according to the present invention;
FIG. 8 is a schematic top view of the copper furnace body according to the present invention;
FIG. 9 is a schematic view showing the structure of a copper furnace lid according to the present invention;
FIG. 10 is a graph showing the transmittance of an electro-optic amplitude modulator to an optical signal according to the present invention;
FIG. 11 is a test state diagram of the present invention;
FIG. 12 is a schematic diagram of the electro-optic amplitude modulation principle;
FIG. 13 is a graph of the test results of a small amplitude sine wave modulation signal applied by a signal generator of the present invention to an electro-optic amplitude modulator;
FIG. 14 is a graph of the test results of the light intensity modulation wave output by the electro-optic amplitude modulator of the present invention;
in the figure: 1-first base, 2-insulating spacer, 3-second base, 301-fixing base, 302-baffle, 303-first heat conduction inclined plane, 304-platform, 4-outer casing, 401-joint hole, 402-light through hole, 403-second ridge, 404-second heat conduction inclined plane, 5-first semiconductor refrigerator, 6-heat preservation copper furnace, 601-copper furnace body, 602-copper furnace cover, 603-bulge, 604-wire outlet, 605-thermistor mounting hole, 7-second semiconductor refrigerator, 8-first heat insulation layer, 9-second heat insulation layer, 10-third heat insulation layer, 11-electro-optical amplitude modulator, 12-first polarizer/half-wave plate, 13-wave plate, 14-second polarizer/polarizing beam splitter prism, 15-a photoelectric detector, 16-an oscilloscope, 17-a temperature controller and 18-a signal generator.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
Examples
As shown in fig. 1 to 14, a temperature-controllable electro-optical amplitude modulator includes a first base 1, an insulating spacer 2 is disposed on the first base 1, the edge spacer 2 is a rectangular parallelepiped structure, a second base 3 is disposed on the insulating spacer 2, one side of the second base 3 is attached to one side of the insulating spacer 2, and the remaining three sides leave a gap, a plurality of first semiconductor refrigerators 5 are disposed on the second base 3 side by side, a heat-insulating copper furnace 6 is disposed on the plurality of first semiconductor refrigerators 5, a plurality of second semiconductor refrigerators 7 are disposed on the heat-insulating copper furnace 6 side by side, a first heat-insulating layer 8 and a second heat-insulating layer 9 are respectively fixed on front and rear end faces of the heat-insulating copper furnace 6, a third heat-insulating layer 10 is fixed on left and right end faces of the heat-insulating copper furnace 6, a plurality of joint holes 401 are disposed on an upper end face of a housing 4, the left end face and the right end face of the outer shell 4 are symmetrically provided with a plurality of light through holes 402, the insulating gasket 2 is provided with the outer shell 4, the edge of the outer shell 4 is tightly attached to the edge of the insulating gasket 2, and the outer shell 4 is sleeved outside the second base 3.
Base 3 includes fixing base 301 and baffle 302, fixing base 301 and baffle 302 integrated into one piece are the L shape fixing base 301's middle part is equipped with abrupt edge 305 No. one be equipped with heat conduction inclined plane 303 between baffle 302 and abrupt edge 305, and make a heat conduction inclined plane 303 follow baffle 302 to abrupt edge 305 orientation downward sloping No. one the front end of abrupt edge 305 is equipped with platform 304 the front panel inner wall of outer shell 4 is equipped with No. two abrupt edges 403 and No. two heat conduction inclined planes 404, and makes No. two heat conduction inclined planes 404 and No. two semiconductor 7 closely laminate the refrigerator.
The heat preservation copper furnace 6 comprises a copper furnace body 601 and a copper furnace cover 602, wherein the copper furnace cover 602 is fixedly arranged on the copper furnace body 601, the copper furnace body 601 is of a groove structure with openings at the left end and the right end, protrusions 603 are arranged on the inner wall and the bottom of a groove of the copper furnace body 601, a wire outlet 604 and a thermistor mounting hole 605 are arranged on the front end face of the copper furnace body 601, a thermistor is arranged in the thermistor mounting hole 605, and the thermistor mounting hole 605 is sealed by a heat insulating material and used for collecting the temperature of the heat preservation copper furnace 6.
A test method for applying a modulation signal to an optical field amplitude component by a temperature-controllable electro-optic amplitude modulator comprises the following steps:
step 1, respectively sticking two lithium niobate crystals with the same size in a heat preservation copper furnace 6, feeding temperature signals back to a first semiconductor refrigerator 5 and a second semiconductor refrigerator 7 in an electro-optical amplitude modulator 11 through a temperature controller 17 through the temperature of the lithium niobate crystals collected by a thermistor, carrying out constant temperature control on the temperature of the lithium niobate crystals, and simultaneously applying modulation signals by a signal generator 18 to modulate the amplitude of an optical field;
step 2, assembling the electro-optical amplitude modulator 11, and collimating a beam of stably operating single-frequency laser;
step 3, inserting a first polarizing film/half-wave plate 12 into the collimated laser path to enable the laser beam to transmit along the center of the polarizing film, and rotating the transmission direction to ensure that linearly polarized light in the vertical or horizontal direction is obtained after the linearly polarized light is transmitted through the polarizing film; the rotational transmission direction of the first polaroid/half-wave plate 12 is consistent with the X-axis or Y-axis direction of the lithium niobate crystal when no voltage is applied;
step 4, after the linearly polarized light in the vertical or horizontal direction in the step 3 is obtained, an electro-optical amplitude modulator 11 is placed behind the linearly polarized light, and the light beam is ensured to be transmitted and output by a light passing central shaft of the lithium niobate crystal;
step 5, passing the laser light passing through the electro-optical amplitude modulator 11 in the step 4 through an 1/4 lambda wave plate 13 to perform phase delay of pi/2; the main axis direction of the wave plate 13 is consistent with the X-axis direction and the Y-axis direction in the coordinate system.
Step 6, the light which is subjected to the phase delay of pi/2 in the step 5 passes through a second polaroid/polarization beam splitter prism 14; the light transmission direction of the second polarizer/polarizing beam splitter prism transmission 14 is vertical to the light transmission direction of the first polarizer/half-wave plate 12;
step 7, inputting the laser emitted from the polarizing plate II/polarization splitting prism transmission 14 in the step 6 into a photoelectric detector 15, converting an optical signal into a photocurrent signal, and inputting the photocurrent signal into an oscilloscope 16 to observe a transmission signal; when the waveform of the output signal is completely consistent with that of the input signal, namely if the input is a sine wave signal, the output is a complete sine wave with regular symmetry, the test of the electro-optical amplitude modulation signal is completed.
The method is characterized in that incident light firstly passes through a polarizer parallel to an X axis of a coordinate system, then passes through a lithium niobate crystal with voltage applied in the X axis direction of the crystal, passes through the crystal, then passes through an X' axis with voltage applied in the X axis direction of the lithium niobate crystal through a fast axis parallel to the X axis of the lithium niobate crystal, and finally passes through an analyzer parallel to the Y axis of the coordinate system, which is the basic principle of electro-optic amplitude modulation, the direction of an external electric field is parallel to the X axis of the crystal, modulated light is emergent light, the direction of the emergent light is parallel to the Y axis of the coordinate system, the intermediate crystal is an electro-optic modulated crystal, and the specification of the intermediate crystal is 3 mm; the two crystals have identical size properties and are arranged in series with their optical axes at 90 ° to each other, i.e. the Y 'axis and the X axis of one crystal are parallel to the X' axis and the Y axis of the other crystal, respectively.
FIG. 12 is a schematic diagram showing the principle of electro-optical amplitude modulation, in which a lithium niobate crystal (two optical axes arranged at 90 to each other between two polarizers orthogonal to each other, wherein the polarization direction of the polarization actuator 1 is parallel to the X-axis of the coordinate axes shown in the figure, the polarization direction of the analyzer 2 is parallel to the Y-axis of the coordinate axes shown in the figure, and a λ/4 glass is inserted between the crystal and the analyzer 2. when an electric field is applied to the crystal in the X-axis direction, the principal axes X 'and Y' of induction of the crystal are rotated to the directions forming angles of 45 to the original principal axes X and Y, respectively, so that a light beam incident along the Z-axis passes through the polarization actuator 1 to become linearly polarized light in the X-axis direction of the coordinate system shown in the figure, and after entering the crystal, is decomposed into two components in the X 'and Y' directions, the amplitude and phase are the same, and it can be understood from the relationship between the transmittance and the modulation voltage as shown in FIG. 2 that in the general case, the relationship between the output characteristic of the modulator and the, the modulated light intensity will be distorted; to achieve linear modulation, the voltage bias of the modulator can be made at the 50% transmittance operating point by introducing a fixed pi/2 phase delay; a lambda/4 slide is inserted in the optical path of the modulator, the fast and slow axes of which are at an angle of 45 DEG to the principal X axis of the crystal, so that a fixed phase difference of pi/2 is produced between the two components.
The transverse electro-optical effect of the electro-optical crystal can be utilized to realize electro-optical amplitude modulation, for example, as shown in fig. 1, the incident light is changed into linearly polarized light parallel to the X axis after passing through the polarization starter, the projection and the phase on the crystal are equal, and the projection and the phase are respectively set as follows:
Ex′＝Ey′＝Acosδ (1)
or by a complex amplitude method, the light wave of the surface with the incident crystal Z being 0 is expressed as:
Ex′(0)＝Ey′(0)＝A (2)
the intensity of the incident light is:
Ii＝|Ex′(0)|2+|Ey′(0)|2＝2A2(3)
when light passes through two lithium niobate crystals with the total length of l, the phase difference delta is generated between X 'and Y':
Ex′(l)＝A,Ey′(l)＝Aeiδ(4)
the light exiting through the analyzer when the λ/4 slide is not considered is the sum of the projections of the two components on the Y-axis:
Figure BDA0002283670350000121
its corresponding output light intensity ItCan be written as:
Figure BDA0002283670350000122
the light intensity transmittance T is:
Figure BDA0002283670350000123
the following steps are provided:
Figure BDA0002283670350000124
it can be seen that δ is related to the voltage applied to the crystal, and when the voltage is increased to a certain value, the polarized light in the X 'and Y' directions can generate a phase difference δ ═ pi when passing through the crystal, the light intensity transmittance T is 100%, and the voltage applied to the crystal is called half-wave voltage, usually VπIs represented by VπIs an important parameter for describing the electro-optic effect of the crystal,
Figure BDA0002283670350000125
wherein V0Is a direct voltage, V, applied to the crystalmsin ω t is an AC modulation signal applied simultaneously to the crystal, VmIs its amplitude, ω is the modulation frequency, and as can be seen from the above equation, V is varied0Or VmThe output characteristics will vary accordingly. For monochromatic light and defined crystals, VπIs constant and thus T will only vary with the voltage applied to the crystal.
The following is a consideration of the effect of the dc bias on the output characteristics:
when in use
Figure BDA0002283670350000131
Vm<<VπWhen the working point is selected at the center of the linear working area, the linear modulation with higher efficiency can be obtained
Figure BDA0002283670350000132
Substitution (9) is given by:
Figure BDA0002283670350000133
due to Vm<<Vπ
Figure BDA0002283670350000134
Namely, it is
T∝sinωt (12)
In this case, although the amplitude of the signal output from the modulator is different from that of the modulated signal, the frequencies of the two signals are the same, and the output signal is not distorted, i.e., linear modulation.
The test results of the device are shown in fig. 13 and fig. 14, wherein fig. 13 is a small-amplitude sine wave modulation signal applied to the electro-optical amplitude modulator by the signal generator, and fig. 14 is a light intensity modulation wave output after passing through the electro-optical amplitude modulator; it can be seen that the frequency and waveform fidelity of the optical field modulation signal are high, proving that the modulator works in the linear region as described in fig. 10, and the modulation effect completely meets the application requirement.
The first base 1, the insulating gasket 2, the second base 3, the fixed base 301, the baffle 302, the first heat conducting inclined plane 303, the platform 304, the outer shell 4, the joint hole 401, the light through hole 402, the second protruded ridge 403, the second heat conducting inclined plane 404, the first semiconductor refrigerator 5, the heat preservation copper furnace 6, the copper furnace body 601, the copper furnace cover 602, the protrusion 603, the wire outlet hole 604, the thermistor mounting hole 605, the second semiconductor refrigerator 7, the first heat insulation layer 8, the second heat insulation layer 9, the third heat insulation layer 10, the electro-optical amplitude modulator 11, the first polarizer/half-wave plate 12, the wave plate 13, the second polarizer/polarization splitting prism 14, the photoelectric detector 15, the oscilloscope 16, the temperature controller 17 and the signal generator 18 of the invention are all common standard parts or parts known by technicians in the field, the structure and principles are known to the skilled person from technical manuals or by routine experimentation.
While there have been shown and described what are at present considered the fundamental principles and essential features of the invention and its advantages, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but is capable of other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims (7)

1. A temperature-controllable electro-optic amplitude modulator, characterized by: comprises a first base (1), an insulating gasket (2) is arranged on the first base (1), the edge gasket (2) is of a cuboid structure, a second base (3) is arranged on the insulating gasket (2), one side of the second base (3) is attached to one side of the insulating gasket (2), gaps are reserved on the other three sides, a plurality of first semiconductor refrigerators (5) are arranged on the second base (3) side by side, a heat preservation copper furnace (6) is arranged on the first semiconductor refrigerators (5), a plurality of second semiconductor refrigerators (7) are arranged on the heat preservation copper furnace (6) side by side, a first heat insulation layer (8) and a second heat insulation layer (9) are respectively and fixedly arranged on the front end surface and the rear end surface of the heat preservation copper furnace (6), a third heat insulation layer (10) is fixedly arranged on the left end surface and the right end surface of the heat preservation copper furnace (6), the up end of outer cover (4) is equipped with a plurality of joint holes (401) the left and right sides terminal surface symmetry of outer cover (4) is equipped with a plurality of logical unthreaded holes (402) be equipped with outer cover (4) on insulating gasket (2), and make the edge of outer cover (4) closely laminate with the edge of insulating gasket (2) to make outer cover (4) cover establish the outside at No. two base (3).
2. A temperature controllable electro-optic amplitude modulator as claimed in claim 1, characterized in that: base No. two (3) are including fixing base (301) and baffle (302), fixing base (301) and baffle (302) integrated into one piece are the L shape the middle part of fixing base (301) is equipped with abrupt edge (305) No. one be equipped with heat conduction inclined plane (303) between baffle (302) and abrupt edge (305), and make heat conduction inclined plane (303) from baffle (302) to abrupt edge (305) orientation downward sloping No. one the front end of abrupt edge (305) is equipped with platform (304) the front panel inner wall of outer shell (4) is equipped with No. two abrupt edges (403) and No. two heat conduction inclined planes (404), and makes No. two heat conduction inclined planes (404) and No. two semiconductor refrigerator (7) closely laminate.
3. A temperature controllable electro-optic amplitude modulator as claimed in claim 1, characterized in that: the heat preservation copper furnace (6) comprises a copper furnace body (601) and a copper furnace cover (602), wherein the copper furnace cover (602) is fixedly arranged on the copper furnace body (601), the copper furnace body (601) is of a groove-shaped structure with openings at the left end and the right end, protrusions (603) are arranged on the inner wall and the bottom of a groove of the copper furnace body (601), a wire outlet hole (604) and a thermistor mounting hole (605) are arranged on the front end face of the copper furnace body (601), a thermistor is arranged in the thermistor mounting hole (605), and the thermistor mounting hole (605) is sealed by heat insulation materials and used for collecting the temperature of the heat preservation copper furnace (6).
4. A test method for applying a modulation signal to an optical field amplitude component by an electro-optic amplitude modulator capable of controlling temperature is characterized by comprising the following steps: the method comprises the following steps:
step 1, two lithium niobate crystals with the same size are respectively stuck in a heat preservation copper furnace (6), temperature signals are fed back to a first semiconductor refrigerator (5) and a second semiconductor refrigerator (7) in an electro-optical amplitude modulator (11) through a temperature controller (17) through the temperature of the lithium niobate crystals collected by a thermistor, the temperature of the lithium niobate crystals is controlled at constant temperature, and meanwhile, a signal generator (18) applies modulation signals to modulate the amplitude of an optical field;
step 2, assembling the electro-optical amplitude modulator (11) and collimating a beam of stably running single-frequency laser;
step 3, inserting a first polaroid/half-wave plate (12) into the collimated laser path to enable the laser beam to transmit along the center of the polaroid, and rotating the transmission direction to ensure that linearly polarized light in the vertical or horizontal direction is obtained after the linearly polarized light is transmitted through the polaroid;
step 4, after the linearly polarized light in the vertical or horizontal direction in the step 3 is obtained, an electro-optical amplitude modulator (11) is placed behind the linearly polarized light, and the light beam is ensured to be transmitted and output by a light-passing central shaft of the lithium niobate crystal;
step 5, passing the laser light passing through the electro-optical amplitude modulator (11) in the step 4 through an 1/4 lambda wave plate (13) to perform phase delay of pi/2;
step 6, the light which is subjected to the phase delay of pi/2 in the step 5 passes through a second polaroid/polarization beam splitter prism (14);
step 7, inputting the laser emitted by the polarizing plate II/polarization beam splitter prism transmission (14) in the step 6 into a photoelectric detector (15), converting an optical signal into a photocurrent signal, and inputting the photocurrent signal into an oscilloscope (16) to observe a transmission signal; when the waveform of the output signal is completely consistent with that of the input signal, namely if the input is a sine wave signal, the output is a complete sine wave with regular symmetry, the test of the electro-optical amplitude modulation signal is completed.
5. The method of claim 4 for testing a temperature controllable electro-optic amplitude modulator, comprising: the rotating and transmitting direction of the first polaroid/half-wave plate (12) in the step 3 is consistent with the X-axis or Y-axis direction when no voltage is applied to the lithium niobate crystal.
6. The method of claim 4 for testing a temperature controllable electro-optic amplitude modulator, comprising: and in the step 5, the main axis direction of the wave plate (13) is consistent with the X-axis direction and the Y-axis direction in the coordinate system.
7. The method of claim 4 for testing a temperature controllable electro-optic amplitude modulator, comprising: the light transmission direction of the second polarizer/polarizing beam splitter prism (14) in the step 6 is perpendicular to the light transmission direction of the first polarizer/half-wave plate (12).
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