CN211826790U - Mode modulation system based on potassium tantalate niobate crystal double-line waveguide - Google Patents
Mode modulation system based on potassium tantalate niobate crystal double-line waveguide Download PDFInfo
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- CN211826790U CN211826790U CN201922307616.4U CN201922307616U CN211826790U CN 211826790 U CN211826790 U CN 211826790U CN 201922307616 U CN201922307616 U CN 201922307616U CN 211826790 U CN211826790 U CN 211826790U
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Abstract
The utility model relates to a mode modulation system based on potassium tantalate niobate crystal double-line type waveguide, its technical characterstic lies in: the laser comprises a laser light source, a focusing objective lens, a double-line type waveguide mode modulator, an imaging objective lens, a light beam quality analyzer, a temperature controller and a high-voltage power supply. The utility model discloses can realize TE among potassium tantalate niobate crystal double-line type waveguide through the plus electric field voltage who increases double-line type waveguide mode modulator00Output of the die to TE01Mode output and TE02Modulation of the die output.
Description
Technical Field
The utility model belongs to the technical field of optical function devices, and relates to a mode modulation system based on potassium tantalate niobate crystal double-line waveguide.
Background
With the development of optical communication, optical information processing and laser technology, the conventional optical system cannot meet the requirements of the development of optoelectronic technology due to large volume and low information processing speed. In 1969, miller, belll laboratory in the united states, proposed the concept of "integrated optics", which is to integrate various optical elements on the same "chip" by a method similar to a semiconductor integrated circuit, so as to realize integration, miniaturization and all-optical signal processing of an optical information processing system. The optical waveguide is a basic component of the integrated optical circuit, and the quality of the optical waveguide directly affects the performance of the whole integrated optical circuit. Therefore, the development of optical waveguide technology is a great deal in the development of integrated optics.
The dual-line waveguide is the main type of stress-induced waveguide. For a double-line waveguide, the femtosecond laser generates negative refractive index change in a focusing region in the crystal, causing lattice expansion in the region, and the nearby region is affected by the phenomenon to generate stress-induced positive refractive index change. For the double-line type waveguide, a waveguide region having an increased refractive index is formed in the middle portion of the two lines, and the region may be slightly shifted up and down. The method has the advantages of simple processing, easy control of etching and high yield. In addition, because the waveguide is positioned in the middle of the two direct-writing lines, the influence of processing is relatively small, the characteristics of the original crystal material can be kept, and experimental research is facilitated.
The electro-optical element can realize rapid and accurate control of the state of light by changing the polarization, intensity or phase of the light, and thus has wide application in the fields of optical communication, laser, sensing and the like. In addition, when a voltage or an electric field is applied, the electro-optical element can generate a refractive index change, and this phenomenon is called an electro-optical effect. Potassium tantalate niobate crystal is an excellent electro-optic crystal, and in recent years, many potential applications have been studied, including the ability to make high-speed deflectors, electro-optic modulators, photorefractive optical pins, and the ability to perform scale-free optics and diffraction-free optical wave transmission. The refractive index of the potassium tantalate-niobate crystal is changed by changing the voltage applied to the two ends of the potassium tantalate-niobate crystal, so that the conducted optical mode in the potassium tantalate-niobate double-line waveguide is modulated, the optical field mode distribution of the output end of the waveguide is changed, and the electro-optical element has quick response time.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to overcome prior art's not enough, provide a mode modulation system based on potassium tantalate niobate crystal double-line type waveguide, can utilize the electro-optic effect of electro-optic crystal, realize regulating and controlling the mode of transmission light in the crystal waveguide.
The utility model provides a its realistic problem take following technical scheme to realize:
a mode modulator system based on potassium tantalate niobate crystal double-line waveguide comprises a laser light source, a focusing objective lens, a double-line waveguide mode modulator, an imaging objective lens and a light beam quality analyzer;
the laser light source is used for generating laser beams polarized along the horizontal direction, and the output end of the laser light source is connected with the focusing objective lens; the output end of the focusing objective lens is connected with the double-line type waveguide mode modulator and used for focusing linearly polarized light on the end face of the double-line waveguide; the output end of the double-line waveguide mode modulator is connected with a light beam quality analyzer through an imaging objective lens and used for imaging light guided out by the waveguide on the light beam quality analyzer, and the light beam quality analyzer analyzes mode distribution information of the light transmitted in the double-line waveguide.
The double-line waveguide mode modulator comprises a potassium tantalate-niobate crystal coated with electrodes on two sides and a refrigerating sheet arranged below the potassium tantalate-niobate crystal, wherein the electrodes on the two sides of the potassium tantalate-niobate crystal are connected with a high-voltage power supply, and the refractive index of the potassium tantalate-niobate crystal can be quickly changed by controlling the voltage of the high-voltage power supply; the refrigerating plate is connected with a temperature controller, and the temperature controller can control the temperature of the potassium tantalate niobate crystal at a set temperature.
The utility model has the advantages and beneficial effect:
1. the utility model discloses propose for the first time and utilize potassium tantalate niobate crystal's secondary electro-optic effect, realize carrying out the modulation system that adjusts and control to the mode of transmission light in the potassium tantalate niobate crystal double-line type waveguide.
2. The utility model discloses can be in visible light to near infrared wavelength range, through the change of plus electric field voltage, realize the modulation of potassium tantalate niobate crystal double-line type waveguide single mode output to multimode output to the regulation and control of electric field to the light field has been realized.
3. The utility model discloses can realize stable single mode and multimode output, and have good output effect.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention;
fig. 2 is a schematic end view of a double-line waveguide according to the present invention;
FIG. 3 is a schematic diagram of the end face of a double-line waveguide for the practical femtosecond laser processing of potassium tantalate niobate crystal of the present invention;
fig. 4 is the light field pattern distribution diagram of the waveguide output end detected by the middle light beam quality analyzer.
Detailed Description
The embodiments of the present invention will be described in detail with reference to the accompanying drawings:
a mode modulator system based on a potassium tantalate niobate crystal double-line waveguide is shown in figure 1 and comprises a laser light source A, a focusing objective lens B, a double-line waveguide mode modulator C, an imaging objective lens D, a light beam quality analyzer E, a temperature controller F and a high-voltage power supply G;
the laser light source is used for generating laser beams polarized along the horizontal direction, and the output end of the laser light source is connected with the focusing objective lens; the output end of the focusing objective lens is connected with the double-line type waveguide mode modulator and used for focusing linearly polarized light on the end face of the double-line waveguide; the output end of the double-line waveguide mode modulator is connected with a light beam quality analyzer through an imaging objective lens and used for imaging light guided out by the waveguide on the light beam quality analyzer, and the light beam quality analyzer analyzes mode distribution information of the light transmitted in the double-line waveguide.
In this example, the double-line waveguide mode modulator comprises a potassium tantalate-niobate crystal coated with electrodes on two sides and a refrigerating sheet arranged below the potassium tantalate-niobate crystal, wherein the electrodes on two sides of the potassium tantalate-niobate crystal are connected with a high-voltage power supply, and the refractive index of the potassium tantalate-niobate crystal can be rapidly changed by controlling the voltage of the high-voltage power supply; the refrigerating plate is connected with a temperature controller, and the temperature controller can control the temperature of the potassium tantalate niobate crystal at a set temperature.
The utility model discloses a work flow does:
firstly, a laser generates a laser beam polarized along the horizontal direction, then the beam passes through a focusing objective and enters a double-line waveguide mode modulator, the beam coming out of the double-line waveguide mode modulator passes through an imaging lens, then the beam enters a beam quality analyzer, and the beam quality analyzer records the light field mode distribution information of the outgoing beam.
The modulation method of the mode modulator system based on the potassium tantalate niobate crystal double-line waveguide comprises the following steps:
step 1, opening a temperature controller, setting the temperature of a potassium tantalate-niobate crystal, and carrying out the next step after the temperature controller displays that the temperature tends to be stable;
step 2, adjusting the double-line waveguide mode modulator based on the potassium tantalate-niobate crystal, and detecting by using a beam quality analyzer to ensure that the waveguide output end mode is stable TE00A base mold;
step 3, increasing the voltage value V of the double-line waveguide mode modulator which is arranged on the refrigerating sheet and is based on the potassium tantalate-niobate crystal until the beam quality analyzer can detect stable TE01A mode for recording voltage values and light field mode information;
and 4, continuing to increase the voltage until the beam quality analyzer can detect stable TE02Recording voltage value and light field mode information, and finishing a complete modulation process;
and 5, repeating the steps 2 to 4 for multiple times to see whether the same result can be obtained or not, and finally, sorting and corresponding the recorded voltage values and the light field mode distribution.
The functions of the components of the wavelength scanning light source system of the present invention are further described below:
A. the laser light source is used for generating a laser beam which is required in an experiment and is polarized along the horizontal direction;
B. the focusing objective lens is used for focusing the light beams on the end face of the double-line waveguide;
C. a double-line waveguide mode modulator based on potassium tantalate-niobate crystal arranged on a refrigerating sheet, wherein the potassium tantalate-niobate has a double-line waveguide required by femtosecond laser writing experiment, and the double-line waveguide is arranged along with the tantalum-niobiumThe voltage on two sides of the potassium crystal is increased, and the mode of transmitting light in the double-line waveguide is changed from TE00Conversion of fundamental mode to TE01First order mode and TE02A second order mode;
D. an imaging objective for imaging the light guided out by the waveguide on a beam analyzer;
E. beam quality analyzer (WinCamD)TMSeries) for analyzing the mode of light transmitted in the two-wire waveguide;
F. a temperature controller (Arroyo Instruments, 5305, 5A/12V) for controlling the temperature of the two-wire waveguide mode modulator of the potassium tantalate niobate crystal;
G. and a high-voltage power supply (BOHER HV, 70210P) for supplying required voltage to the double-line waveguide mode modulator of the potassium tantalate niobate crystal.
The utility model discloses a function process of transmission optical mode modulation in potassium tantalate niobate crystal double-line waveguide does:
firstly, a high-voltage power supply G is turned on, the temperature of a double-line waveguide mode modulator which is arranged on a refrigerating piece and is based on potassium tantalate-niobate crystals and connected with a temperature controller is set to be 18 ℃, after the temperature tends to be stable (the temperature fluctuation range is within 0.03 ℃), a laser A is turned on, a laser beam polarized along the horizontal direction is generated by the laser A, and the laser beam enters a double-line waveguide mode modulator C based on the potassium tantalate-niobate crystals after passing through a focusing objective B;
secondly, the light beam coming out of the C passes through an imaging objective lens D, then enters a light beam quality analyzer E connected with a PC end, and receives light field mode information passing through the double-linear waveguide mode modulator C by the light beam quality analyzer E;
secondly, the potassium tantalate niobate crystal in the double-line waveguide mode modulator C is a typical secondary electro-optic crystal and has obvious electro-optic effect, the voltage applied to two ends of the double-line waveguide mode modulator C is controlled by the high-voltage power supply G, the refractive index of the potassium tantalate niobate crystal can be changed rapidly, so that the refractive index of the double-line waveguide is changed correspondingly, and the mode of transmitting light in the waveguide is changed by TE while the refractive index of the waveguide is changed00Change of fundamental mode to TE01First order mode and TE02A second order mode;
finally, when the voltage applied to both ends of the double-wire waveguide mode modulator C is controlled by the high-voltage power supply G to change, the change in the transmission mode of the double-wire waveguide in the double-wire waveguide mode modulator C is detected and recorded by the beam quality analyzer E.
The modulation method of the mode modulator system based on the potassium tantalate niobate crystal double-line waveguide comprises the following steps:
step 1, opening a temperature controller, setting the temperature of a potassium tantalate-niobate crystal, and carrying out the next step after the temperature controller displays that the temperature tends to be stable;
step 2, adjusting the double-line waveguide mode modulator based on the potassium tantalate-niobate crystal, and detecting by using a beam quality analyzer to ensure that the waveguide output end mode is stable TE00A base mold;
step 3, increasing the voltage value V of the double-line waveguide mode modulator which is arranged on the refrigerating sheet and is based on the potassium tantalate-niobate crystal until the beam quality analyzer can detect stable TE01A mode for recording voltage values and light field mode information;
and 4, continuing to increase the voltage until the beam quality analyzer can detect stable TE02Recording voltage value and light field mode information, and finishing a complete modulation process;
and 5, repeating the steps 2 to 4 for multiple times to see whether the same result can be obtained or not, and finally, sorting and corresponding the recorded voltage values and the light field mode distribution.
Fig. 2 is a schematic view of an end face of a double-line type waveguide. The double-line waveguide is the main type of stress generating waveguide, in the figure, a is the waveguide width, d is the femtosecond laser notch length, and in the system, the waveguide width a is 20 μm and the notch length is 40 μm. For a twin-line waveguide, the femtosecond laser generates a negative refractive index (Δ n <0) change in a focusing region within the crystal, causing lattice expansion of the region, and the nearby region is affected by this phenomenon to generate a stress-induced positive refractive index change (Δ n > 0). For the double-line type waveguide, a waveguide region having an increased refractive index is formed in the middle portion of the two lines, and the region may be slightly shifted up and down. And because the waveguide is positioned in the middle of the two direct-writing lines, the influence of processing is relatively small, and the characteristics of the original crystal material can be maintained.
FIG. 3 is an end-view microscope picture of a duplex waveguide for actually processing potassium tantalate niobate crystals in an experiment.
In fig. 4, the three light guiding mode modulation output results of the dual-line waveguide are from left to right, and are respectively TE under TE polarization00Base mold, TE01First order mode and TE02The second order mode.
The utility model discloses a theory of operation does:
the mode modulator system based on the potassium tantalate niobate crystal double-line waveguide is designed based on the obvious quadratic electro-optic effect of potassium tantalate niobate crystal. The electro-optic effect is a phenomenon that the refractive index of a material is adjusted by an external electric field, and the potassium tantalate-niobate crystal is a known crystal with the largest quadratic electro-optic coefficient in the world and has the outstanding characteristics of low half-wave voltage, high electro-optic modulation response speed, large effective electro-optic modulation field of view and the like.
The femtosecond laser is used for processing the double-line waveguide in the potassium tantalate-niobate crystal, the refractive index of a laser ablation area is reduced, so that the lattice expansion of the area nearby the laser ablation area is caused, and the refractive index is correspondingly increased, therefore, the refractive index of the middle part of two processed lines is increased, light can be well limited in the area, and the information transmission of the light is realized. When no voltage is applied to the upper end and the lower end of the potassium tantalate niobate crystal, the potassium tantalate niobate crystal can be regarded as a common optical fiber system, and incident light is bound inside a waveguide to be totally reflected for transmission. Experimental results show that in this case, the waveguide allows only light with the polarization direction of the TE mode to be transmitted, and does not support TM mode transmission.
The photoelectric effect involved in the present invention is caused by injecting charges into the crystal by the electrodes, and this method can be named as space charge controlled photoelectric effect. The change in the refractive index inside the crystal caused by this effect exhibits a linear change between the two electrodes, and the change in the refractive index Δ n can be expressed as:
Δn(x)＝-9n3sijxV2/8d3(1)
wherein n is the effective refractive index of the crystal，sijIs the quadratic electro-optic coefficient of the crystal, x is the distance from the electrodes, V is the voltage of the applied electric field, and d is the distance between the two electrodes. It can be seen that inside the crystal, the refractive index change exhibits a linear change between the two electrodes.
When voltage is applied to two ends of the potassium tantalate niobate crystal, the variation of the refractive index presents gradient change as the formula (1) along the directions of the two electrodes, and the gradient change is in direct proportion to the square of the applied voltage, so that when the voltage of an applied electric field is increased, the refractive index difference between the upper part and the lower part at the same position in the bifilar waveguide is also increased, and thus, a first-order mode and a second-order mode appear in a light wave mode of an emergent end of the waveguide along with the increase of the voltage, and the regulation and control of the light field by the electric field are realized.
In the following, the meaning of each parameter in equation (1) is summarized again:
in equation (1): Δ n is the amount of change in refractive index, n is the effective refractive index of the crystal, sijIs the quadratic electro-optic coefficient of the crystal, x is the distance from the electrodes, V is the voltage of the applied electric field, and d is the distance between the two electrodes.
The utility model discloses can be near visible light to near infrared wavelength, through electric field regulation and control, with double-line waveguide transmission mode by TE00Fundamental mode, change to stable TE01First order mode and TE02And the second-order mode realizes the regulation and control of the optical field mode in the double-line waveguide. Pure potassium tantalate-niobate crystals (silver colloid is coated on the upper end face and the lower end face of the crystals to serve as conducting electrodes, and a double-line waveguide processed by femtosecond laser is arranged inside the crystals) are used as core materials of the double-line waveguide mode modulator (because the pure potassium tantalate-niobate crystals are the crystals with the largest electrooptical coefficient at present, the characteristics enable the potassium tantalate-niobate crystals to achieve the largest refractive index modulation range theoretically). By applying different voltages to two ends of the double-line waveguide mode modulator, the refractive index difference (namely delta n in equation (1)) in the waveguide along the electrode direction is adjusted, and because the refractive index difference delta n at a specific position is in direct proportion to the square of the voltage, and the refractive index difference presents gradient change along the electrode direction under the same voltage, the refractive index difference between the upper position and the lower position in the waveguide is also in direct proportion to the square of the voltage of an applied electric field. Thus, when the applied electric field voltage increasesThe mode of guiding light in the waveguide gradually changes from a basic mode to a first-order mode and a second-order mode, and the regulation and control of the electric field on the optical field mode are realized.
The utility model discloses can realize the conversion between the different modes of double-line waveguide and stabilize the transmission. When the voltage at two ends of the crystal is 0-400V, the double-line waveguide transmission light mode is TE mode TE00The fundamental mode increases the voltage to 400-500V, and the stable TE can appear in the output end mode01In the first-order mode, the voltage is continuously increased to 500-700V, and stable TE appears in the output end mode02And the second-order mode realizes the modulation of the external electric field on the transmission optical mode in the potassium tantalate niobate crystal double-line waveguide.
It should be emphasized that the embodiments of the present invention are illustrative and not restrictive, and thus the present invention includes but is not limited to the embodiments described in the detailed description, and all other embodiments that can be derived from the technical solutions of the present invention by those skilled in the art also belong to the scope of the present invention.
Claims (2)
1. A mode modulation system based on potassium tantalate niobate crystal double-line type waveguide is characterized in that: the device comprises a laser light source, a focusing objective lens, a double-line waveguide mode modulator, an imaging objective lens and a light beam quality analyzer;
the laser light source is used for generating laser beams polarized along the horizontal direction, and the output end of the laser light source is connected with the focusing objective lens; the output end of the focusing objective lens is connected with the double-line type waveguide mode modulator and used for focusing linearly polarized light on the end face of the double-line waveguide; the output end of the double-line waveguide mode modulator is connected with a light beam quality analyzer through an imaging objective lens and used for imaging light guided out by the waveguide on the light beam quality analyzer, and the light beam quality analyzer analyzes mode distribution information of the light transmitted in the double-line waveguide.
2. The mode modulation system based on the potassium tantalate niobate crystal double-line waveguide as claimed in claim 1, wherein: the double-line waveguide mode modulator comprises a potassium tantalate-niobate crystal coated with electrodes on two sides and a refrigerating sheet arranged below the potassium tantalate-niobate crystal, wherein the electrodes on the two sides of the potassium tantalate-niobate crystal are connected with a high-voltage power supply, and the refractive index of the potassium tantalate-niobate crystal is rapidly changed by controlling the voltage of the high-voltage power supply; the refrigerating plate is connected with a temperature controller, and the temperature controller can control the temperature of the potassium tantalate niobate crystal to be at a set temperature.
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| CN201922307616.4U CN211826790U (en) | 2019-12-20 | 2019-12-20 | Mode modulation system based on potassium tantalate niobate crystal double-line waveguide |
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| CN201922307616.4U CN211826790U (en) | 2019-12-20 | 2019-12-20 | Mode modulation system based on potassium tantalate niobate crystal double-line waveguide |
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