CN113281550A - Straight waveguide phase modulator, integrated assembly and preparation method - Google Patents
Straight waveguide phase modulator, integrated assembly and preparation method Download PDFInfo
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Abstract
The invention discloses a straight waveguide phase modulator, an integrated component and a preparation method, wherein lithium tantalate crystals with smaller birefringence effect are used as substrate crystals of the straight waveguide phase modulator, the optical path difference of orthogonal polarized light waves is smaller, and the transmission loss and the coupling loss related to polarization are lower. In addition, the Y-branch waveguide coupler with the functions of the polarizer and the coupler and the straight waveguide phase modulator are integrated on the same lithium tantalate wafer. The optical fiber current transformer system based on the integrated assembly has the advantages of higher reliability, lower assembly complexity and lower manufacturing cost.
Description
Technical Field
The invention can be applied to the technical field of optical fiber current transformers, and particularly relates to a straight waveguide phase modulator, an integrated component and a preparation method.
Background
The all-fiber current transformer based on the Faraday magneto-optical effect has the characteristics of strong insulativity, small volume, light weight, large dynamic range, full digitalization and the like, and has more outstanding advantages in a power electrical system with higher relay protection requirement, higher electrical equipment automation requirement and higher insulation capability requirement compared with the traditional electromagnetic induction type current transformer. The common optical fiber current transformer mainly comprises three technical schemes of a Sagnac interference type optical path based on a Y waveguide phase modulator, a collinear optical path based on the Y waveguide phase modulator and a collinear optical path based on a straight waveguide phase modulator, wherein the optical path of the collinear optical fiber current transformer based on the straight waveguide has the best space anisotropy and time anisotropy and the minimum temperature error.
Referring to fig. 1, a schematic diagram of an optical path structure of a collinear fiber current transformer using a straight waveguide phase modulator is shown. The working principle of the optical fiber current transformer is as follows: light waves are emitted from a laser light source and then pass through an optical fiber coupler and an optical fiber polarizer to form linearly polarized light, and the light power is evenly distributed to two polarization axes of the polarization maintaining optical fiber after 45-degree optical fibers are adopted for welding. The two linearly polarized light wave modes are transmitted to the 1/4 wave plates through the transmission optical fiber and are respectively converted into left-handed circularly polarized light and right-handed circularly polarized light, and a non-mutually different phase difference is formed under the action of a closed magnetic field when the two linearly polarized light wave modes are transmitted in the sensing optical fiber loop. The returned circularly polarized light is converted into linearly polarized light again through the 1/4 wave plate, and an interference light signal is generated when the circularly polarized light passes through the optical fiber polarizer again. The phase modulator is connected to the optical path of the optical fiber current transformer, so that phase information contained in the interference optical signal, namely a current value on the current-carrying conductor, can be demodulated.
As can be seen from fig. 1 and the basic working principle of the collinear optical fiber current transformer, the optical path difference, the polarization-dependent transmission loss difference, the polarization-dependent coupling loss difference, and the like caused by the refractive index difference and the optical waveguide mode distribution difference between the two polarization modes of the straight waveguide phase modulator have important influences on the non-dissimilar phase error of the optical fiber current transformer, the contrast of the interference optical signal, and the like.
In the prior art, a titanium diffusion technology is generally adopted to prepare a titanium diffusion optical waveguide in a lithium niobate crystal, and a straight waveguide phase modulator is prepared on the basis of the titanium diffusion optical waveguide. Compared with proton exchange of another common lithium niobate optical waveguide preparation technology, the titanium diffusion optical waveguide can simultaneously transmit orthogonal polarization light wave modes, and the proton exchange optical waveguide can only transmit a single polarization light wave mode. However, the straight waveguide phase modulator based on the lithium-titanium niobate diffusion waveguide has the following problems:
(1) the lithium niobate crystal has obvious birefringence effect. According to Sellmeier's equation, at 1310nm operating wavelength and at 25 ℃ room temperature, the refractive indices no and ne of lithium niobate crystals with the same composition are 2.220 and 2.145 respectively, so that the refractive index difference is 0.075. Generally, the waveguide chip length of the lithium niobate straight waveguide phase modulator applied to the optical fiber current transformer is about 40mm, so that the optical path difference of two orthogonally polarized light waves transmitted in the lithium niobate crystal is 3 mm. The existence of the optical path difference between the two linearly polarized light waves inevitably influences the time mutual difference of the optical paths of the optical fiber current transformer.
(2) Because of the difference of the ion diffusion rates along the ordinary optical crystal axis and the abnormal optical crystal axis of the lithium niobate crystal, the TE and TM optical waveguide mode distributions (namely the spot sizes) have differences, on one hand, the transmission losses of the optical waves in different polarization states in the waveguide are different, on the other hand, the coupling efficiency of the optical waves in different polarization states at the optical fiber coupling point is different, and finally, the contrast of interference optical signals of the orthogonal polarization optical waves is greatly influenced.
(3) To utilize the maximum electro-optic coefficient gamma of lithium niobate crystal33The straight waveguide phase modulator generally adopts an X-cut crystal and selects the Y-axis direction as the beam propagation direction of the optical waveguide. The X-cut Z-transfer lithium niobate crystal has small birefringence effect but cannot utilize the maximum electro-optic coefficient gamma33This results in a large increase in the half-wave voltage of the modulator.
(4) Referring to fig. 1, in the assembly of the optical path system of the fiber current transformer, it is necessary to perform fiber fusion interconnection on each discrete fiber passive device or active device in the dashed box in fig. 1, and in particular, it is necessary to perform 45 ° fiber-to-shaft fusion on a fiber polarizer and a straight waveguide phase modulator. Too many fusion points of optical fibers and too many discrete passive/active optical fiber devices inevitably have great influence on the reliability, the assembly complexity and the manufacturing cost of the optical fiber current transformer.
Disclosure of Invention
The first objective of the present invention is to provide a straight waveguide phase modulator, which uses lithium tantalate crystal with smaller birefringence effect as the substrate wafer of the straight waveguide phase modulator, and the optical path difference of orthogonal polarized light wave is smaller, and the transmission loss and coupling loss related to polarization are lower.
The invention has a second object to provide an integrated component, wherein a Y-branch waveguide coupler with polarizer and coupler functions and a straight waveguide phase modulator are integrated on the same lithium tantalate wafer, a single port of the Y-branch waveguide coupler is connected with an input port of a straight waveguide by adopting a polarization-maintaining optical fiber, a slow axis of the polarization-maintaining optical fiber at the single port of the Y-branch waveguide coupler is at an angle of 45 degrees to an axis, and two ports of the Y-branch waveguide coupler can be respectively used for connecting a laser light source and a photoelectric detector through optical fibers. The optical fiber current transformer system based on the integrated assembly has the advantages of higher reliability, lower assembly complexity and lower manufacturing cost.
The third objective of the present invention is to provide a method for manufacturing a straight waveguide phase modulator.
A fourth object of the present invention is to provide a method for manufacturing an integrated component.
In order to achieve the first purpose of the invention, the technical scheme provided by the invention is as follows:
a straight waveguide phase modulator comprises a straight waveguide, a metal electrode, an optical fiber crystal carrier block, a polarization maintaining optical fiber and a lithium tantalate substrate wafer, wherein the straight waveguide is formed in the lithium tantalate substrate wafer, the metal electrode is placed on the upper surface of the lithium tantalate substrate wafer, the optical fiber crystal carrier block is in coupling connection with the straight waveguide, and the polarization maintaining optical fiber is placed in the optical fiber crystal carrier block.
The lithium tantalate substrate wafer is an optical-grade X-cut Y-pass lithium tantalate crystal, the thickness of the lithium tantalate substrate wafer is not less than 0.5mm, and the polishing angle of the lithium tantalate substrate wafer is 0-11 degrees.
The straight waveguide is a zinc oxide optical waveguide, and the strip zinc oxide film forming the straight waveguide has a width of no more than 10 μm and a thickness of no more than 250 nm.
The metal electrode is of a lumped electrode structure and is composed of a first electrode branch and a second electrode branch, and the first electrode branch and the second electrode branch are symmetrically arranged on two sides above the straight waveguide respectively.
The optical fiber crystal carrier block is made of lithium tantalate crystals, and the polishing angle of the optical fiber crystal carrier block is 0-16 degrees; the slow axis of the polarization maintaining optical fiber and the X-axis direction of the lithium tantalate substrate wafer form a 0-degree or 90-degree counter-axis angle.
Compared with the prior art, the beneficial effect of the above technical scheme lies in:
(1) the lithium tantalate crystal has a lower birefringence effect, n being lower than that of the lithium niobate crystal used in the prior artoAnd neThe difference value of the optical fiber current transformer is lower by one order of magnitude, so that the straight waveguide phase modulator prepared by adopting the lithium tantalate crystal has smaller optical path difference, and the time non-mutually-different error of the optical path system of the optical fiber current transformer is lower.
(2) Compared with lithium niobate crystal adopted in the prior art, the ion diffusion rate of the lithium tantalate crystal along the ordinary optical crystal axis and the abnormal optical crystal axis is closer, so that the difference of the optical waveguide mode distribution of the TE mode and the TM mode is smaller, the waveguide transmission loss and the optical fiber coupling loss related to polarization are lower, and better interference optical signal contrast can be obtained after the optical fiber current transformer passes through the polarizer in the optical path system.
(3) The zinc oxide diffusion technology adopted by the invention can prepare the optical waveguide at the Curie temperature lower than about 610 ℃ of the lithium tantalate, and avoids the phenomenon of depolarization of the lithium tantalate crystal caused by the high diffusion temperature of about 1000 ℃ of the existing titanium diffusion technology.
In order to achieve the second object of the present invention, the technical solution provided by the present invention is as follows:
an integrated assembly comprising the straight waveguide phase modulator and the Y-branch waveguide coupler,
the Y-branch waveguide coupler is formed on the lithium tantalate substrate wafer, an optical waveguide of the Y-branch waveguide coupler is an annealed proton exchange waveguide, a double port of the Y-branch waveguide coupler is used as an input end, one end of the Y-branch waveguide coupler is used for being connected with a laser light source through a polarization maintaining optical fiber, and the other end of the Y-branch waveguide coupler is used for being connected with a photoelectric detector through the polarization maintaining optical fiber; and a single port of the Y-branch waveguide coupler is used as an output end and is connected with the straight waveguide through a polarization maintaining fiber.
Wherein, at the single port of the Y-branch waveguide coupler, the slow axis of the polarization maintaining optical fiber and the X-axis direction of the lithium tantalate substrate wafer form a 45-degree counter-axis angle; and at the double ports of the Y-branch waveguide coupler and the input ports and the output ports of the straight waveguides, the slow axis of the polarization-maintaining optical fiber and the X-axis direction of the lithium tantalate substrate wafer still form a 0-degree or 90-degree counter-axis angle, and the optical fiber crystal carrier block with the polarization-maintaining optical fiber is respectively coupled and bonded with each optical waveguide port of the integrated assembly.
The optical fiber crystal carrier block is provided with a plurality of grooves with channels on the surface in advance or a plurality of round holes in the center, the grooves or the round holes of each channel are respectively provided with a polarization maintaining optical fiber, and the distance between every two channels is not less than 82 mu m.
Compared with the prior art, the beneficial effect of the above technical scheme lies in:
(1) the Y-branch waveguide coupler with two important functions of polarization and coupler and the straight waveguide are integrated on the single chip of the lithium tantalate wafer, and two integrated optical device structures are directly connected through the polarization maintaining optical fiber, so that two discrete optical fiber devices are reduced, two optical fiber fusion welding points are reduced, and the manufacturing cost of an optical fiber current transformer optical path system is reduced, the optical path assembly complexity is reduced, and the system reliability is improved.
(2) The optical damage threshold of the zinc oxide diffusion optical waveguide is higher than that of the titanium diffusion optical waveguide, so that the integrated component provided by the invention can transmit higher laser optical power, the signal-to-noise ratio of the photoelectric detector is higher, and the sensing performance of the optical fiber current transformer system is favorably improved.
To achieve the third object of the present invention, the present invention provides a method for manufacturing a straight waveguide phase modulator, comprising the following steps:
step 1: preparing a layer of strip-shaped zinc oxide film on the surface of a lithium tantalate substrate wafer by adopting a conventional semiconductor process;
step 2: placing the lithium tantalate substrate wafer with the prepared strip-shaped zinc oxide film in a central area of a high-temperature diffusion furnace, and charging wet oxygen, wherein the furnace temperature of the central area of the diffusion furnace does not exceed the Curie temperature of lithium tantalate crystals and keeps constant for more than 1 hour at constant temperature so as to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking out the lithium tantalate substrate wafer from the diffusion furnace when the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a metal electrode on the surface of the lithium tantalate substrate wafer with the zinc oxide straight waveguide by adopting a conventional semiconductor process, and symmetrically aligning an electrode branch I and an electrode branch II of the metal electrode relative to the straight waveguide;
and 5: respectively and precisely polishing the end face of the lithium tantalate substrate wafer and the end face of the optical fiber crystal carrier block with the polarization maintaining optical fiber;
step 6: and precisely aligning the optical fiber crystal carrier block with the polarization maintaining optical fiber with the input port and the output port of the straight waveguide in the lithium tantalate substrate wafer, filling ultraviolet glue, and performing ultraviolet exposure curing to complete coupling and bonding.
The straight waveguide phase modulator in the first object of the present invention can be prepared by the above-described method for preparing a straight waveguide phase modulator.
To achieve the fourth object of the invention, the invention provides an integrated component manufacturing method, comprising the steps of:
step 1: preparing a layer of strip-shaped zinc oxide film on the surface of a lithium tantalate substrate wafer by adopting a conventional semiconductor process;
step 2: placing the lithium tantalate substrate wafer with the prepared strip-shaped zinc oxide film in a central area of a high-temperature diffusion furnace, and charging wet oxygen, wherein the furnace temperature of the central area of the diffusion furnace does not exceed the Curie temperature of lithium tantalate crystals and keeps constant for more than 1 hour at constant temperature so as to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking out the lithium tantalate substrate wafer from the diffusion furnace after the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a layer of metal film or non-metal film on the surface of the lithium tantalate substrate wafer with the zinc oxide straight waveguide by adopting a conventional semiconductor process to serve as a proton exchange mask, wherein the pattern of an opening of the mask is a Y-branch coupler, and the opening of the mask is not more than 10 mu m;
and 5: putting the lithium tantalite substrate wafer into a quartz beaker containing pure benzoic acid solution or a quartz beaker containing mixed solution of benzoic acid and lithium benzoate, heating the quartz beaker to 150-250 ℃, and keeping the temperature for more than 0.5 hour;
step 6: corroding the metal film or the nonmetal film on the surface of the lithium tantalate substrate wafer which finishes the proton exchange process;
and 7: putting the lithium tantalate substrate wafer into a central area of an annealing furnace, annealing the area subjected to proton exchange, keeping the temperature for more than 1 hour when the temperature of the central furnace of the annealing furnace reaches 300-400 ℃, and taking the lithium tantalate substrate wafer out of the annealing furnace;
and 8: preparing a metal electrode on the surface of a lithium tantalate substrate wafer by adopting a conventional semiconductor process, and symmetrically aligning an electrode branch I and an electrode branch II of the metal electrode relative to a straight waveguide;
and step 9: respectively and precisely polishing the end face of the lithium tantalate substrate wafer and the end face of the optical fiber crystal carrier block with the polarization maintaining optical fiber;
step 10: and respectively carrying out precise alignment on the optical fiber crystal carrier block with the polarization maintaining optical fiber and each waveguide port of the lithium tantalate substrate wafer, filling ultraviolet glue, and carrying out ultraviolet exposure curing to complete coupling and bonding.
The integrated component in the second object of the present invention can be produced by the above-described integrated component production method.
Drawings
FIG. 1: the schematic diagram of the optical path structure of the collinear optical fiber current transformer in the prior art;
FIG. 2: the invention provides a structural schematic diagram of a straight waveguide phase modulator;
FIG. 3: the invention provides a structural schematic diagram of a first embodiment of an integrated assembly;
FIG. 4: the invention provides a schematic diagram of the optical fiber to axis angle of each optical waveguide port in the integrated component structure;
FIG. 5: the invention provides a structural schematic diagram of a second embodiment of an integrated assembly;
in the figure, 1, a lithium tantalate substrate wafer; 2. a straight waveguide; 2-1, an input port of a straight waveguide; 2-2, an output port of the straight waveguide; 3. a metal electrode; 3-1, electrode branch one of the metal electrode; 3-2, electrode branch II of the metal electrode; 4. a fiber crystal carrier block; 5. a polarization maintaining optical fiber; 6. a Y-branch waveguide coupler; 6-1-1, one end of a dual port of a Y-branch waveguide coupler; 6-1-2, the other end of the dual port of the Y-branch waveguide coupler; 6-2, single port of a Y-branch waveguide coupler.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The technical principle of the invention is as follows:
the collinear optical fiber current transformer based on the straight waveguide phase modulator needs to ensure that the straight waveguide phase modulator can simultaneously transmit two orthogonal polarization optical waveguide modes, and also needs to ensure that the transmission loss and the optical fiber coupling loss of the two polarization optical waveguide modes are possibly consistent, so as to ensure that the optimal interference optical signal contrast can be obtained at a 45-degree welding point at the tail fiber of the input end of the straight waveguide phase modulator. In addition, the effective refractive indexes of the two optical waveguide modes are also as close as possible so as to reduce the time non-mutually different errors of the optical paths of the fiber current transformer.
In the prior art, a titanium diffusion technology is generally adopted to prepare a guided wave structure used in a straight waveguide phase modulator in a lithium niobate crystal. However, the ordinary refractive index and the extraordinary refractive index of the lithium niobate crystal are 2.220 and 2.145 (at 1310nm operating wavelength), respectively, and the refractive index difference is 0.075. Considering that the waveguide length of the lithium niobate straight waveguide phase modulator is about 40mm, the optical path difference of two orthogonally polarized light waves transmitted in the lithium niobate crystal is 3 mm.
Lithium tantalate is a material having a crystal structure very similar to that of lithium niobate, belongs to a trigonal crystal, and has a plurality of excellent integrated optical characteristics such as electro-optic, acousto-optic, piezoelectric, pyroelectric and nonlinear optics. According to the Sellmeier equation of lithium tantalate crystals, at a 1310nm operating wavelength, the ordinary refractive index and the extraordinary refractive index of lithium tantalate are 2.126 and 2.130, respectively, and the difference between the refractive indices is only 0.004. Therefore, for a straight waveguide with the length of 40mm, the optical path difference of the two polarized light waves transmitted in the lithium tantalate crystal is 0.167mm, which is much smaller than that in the lithium niobate crystal. Therefore, the time reciprocity of the collinear optical fiber current transformer based on the lithium tantalate crystal straight waveguide phase modulator is more excellent.
The optical waveguide prepared by adopting the titanium diffusion technology in the lithium niobate crystal has the phenomenon of larger difference of optical waveguide mode distribution of a TE mode and a TM mode. This phenomenon results in a large difference in transmission loss caused by absorption, scattering, reflection, etc. encountered by the two polarized optical waveguide modes during transmission in the optical waveguide, and also results in a large difference in coupling loss caused by different mode matching degrees at the optical fiber coupling point. Although the difference between the optical waveguide mode distributions of the TE mode and the TM mode of the optical waveguide prepared by adopting the titanium diffusion technology in the lithium tantalate crystal is small, the formation temperature of the titanium diffusion optical waveguide is generally more than 1000 ℃ and is far higher than the Curie temperature of the lithium tantalate crystal, which is about 600 ℃, so that the depolarization phenomenon of the crystal can be caused. The zinc oxide diffusion optical waveguide can be manufactured under the condition that the Curie temperature of the lithium tantalate crystal is lower, the optical waveguide mode distribution difference of a TE mode and a TM mode of transmission is small, and the transmission loss and the coupling loss related to polarization are also low.
Referring to fig. 1, a schematic diagram of an optical path structure of a collinear fiber current transformer based on a straight waveguide phase modulator in the prior art is shown. The light wave emitted from the laser light source forms high-polarization linearly polarized light after passing through the optical fiber polarizer, the light wave is subjected to average beam splitting at a 45-degree fusion point, and the power of the light wave is averagely coupled into a fast axis and a slow axis of an input tail fiber of the straight waveguide phase modulator. Since the slow axis of the input pigtail is parallel to the TE (or TM) mode of the optical waveguide, the linearly polarized light modes traveling along the fast and slow axes of the polarization maintaining fiber couple with the TE or TM mode of the optical waveguide, respectively.
The preparation of proton exchange optical waveguide can be realized in lithium tantalate crystal, and the waveguide has natural polarization characteristic, and the polarization extinction ratio can reach over 50dB, so that the lithium tantalate crystal is an excellent material for preparing waveguide polarizer. Therefore, the monolithic integration of a plurality of active or passive optical device structures such as a coupler, a polarizer, a straight waveguide phase modulator and the like can be realized on the same lithium tantalate crystal, and the optical devices can be reasonably connected through the polarization-maintaining optical fiber.
Based on the above technical principles, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Example 1
Referring to fig. 2, a schematic structural diagram of the straight waveguide phase modulator provided in this embodiment is shown. A straight waveguide phase modulator comprising: a lithium tantalate substrate wafer 1 having an electro-optical effect; the straight waveguide 2 is a zinc oxide diffusion optical waveguide and is formed in the lithium tantalate substrate wafer 1; the metal electrode 3 is used for modulating the light wave transmitted in the straight waveguide 2; the surface of the optical fiber crystal carrier block 4 is provided with grooves or the center is provided with a round hole for placing the polarization-maintaining optical fiber 5, and the optical fiber crystal carrier block is coupled and bonded with the straight waveguide 2 formed in the lithium tantalate substrate wafer 1 after being polished.
The lithium tantalate base wafer 1 is an optical-grade crystalline material as a base wafer and a substrate medium for forming an optical waveguide. The same composition of lithium tantalate crystalline material is preferred, but special lithium tantalate crystalline materials such as metal magnesium doped lithium tantalate, magnesium oxide doped lithium tantalate, near stoichiometric lithium tantalate, etc. may also be used. In order to ensure sufficient fiber coupling bonding area and bonding strength, the lithium tantalate substrate wafer 1 of the present embodiment has a thickness of not less than 0.5mm, and preferably 1 mm. The crystal tangential direction of the lithium tantalate substrate wafer 1 can be selected from X-cut or Z-cut, and the Y-axis direction of the crystal is selected as the transmission direction of the light wave in order to utilize the maximum electro-optic coefficient of the lithium tantalate crystal. The preferred embodiment is an X-cut Y-cut crystal tangent.
The straight waveguide 2 needs to have the capability of simultaneously transmitting two optical waveguide modes of orthogonal polarization. The forming method for realizing the optical waveguide in the lithium niobate or lithium tantalate crystal comprises the following steps: titanium diffusion, zinc diffusion and zinc oxide diffusion. In consideration of the curie temperature of the lithium tantalate crystal and the roughness of the surface of the crystal after diffusion, the present embodiment preferably employs a zinc oxide diffusion process to prepare the straight waveguides 2 on the surface of the lithium tantalate substrate wafer 1. In order to ensure that the optical waveguide mode transmitted in the straight waveguide 2 is a fundamental mode, the width of the strip-shaped zinc oxide thin film for forming the zinc oxide diffusion waveguide is not more than 10 μm, and the thickness is not more than 250 nm.
The metal electrode 3 is used for electro-optically modulating the light wave transmitted in the straight waveguide 2. Common metal electrode structures are: the lumped type and the traveling wave type, wherein the former is mainly used for the electro-optical modulator with low modulation rate or modulation bandwidth, and the latter is mainly used for the electro-optical modulator with high modulation rate or modulation bandwidth. Considering that the working bandwidth of the optical fiber current transformer is generally in the order of kHz to MHz and the manufacturing process of the traveling wave type electrode structure is more complicated, the lumped type modulation electrode structure is preferred in this embodiment.
The metal electrode 3 is placed on the upper surface of the lithium tantalate substrate wafer 1, and an electrode branch one 3-1 (such as a positive electrode or a negative electrode) and an electrode branch two 3-2 (such as a negative electrode or a positive electrode) which form the metal electrode 3 are respectively and symmetrically placed on two sides above the straight waveguide 2. The metal thin film material constituting the metal electrode 3 may be any one of aluminum metal, titanium/gold double-layer metal, chromium/gold double-layer metal, titanium/platinum/gold multilayer metal, and the like, and titanium or chromium serves as a transition metal layer to improve the adhesion between the gold thin film and the lithium tantalate substrate wafer. The thickness of the aluminum film layer is not less than 100nm, the thickness of the titanium film layer or the chromium film layer is not less than 10nm, and the thickness of the gold film layer is not less than 100 nm. Preferably, the metal film material is a chromium/gold double-layer metal, the thickness of the chromium film layer is 10nm to 50nm, and the thickness of the gold film layer is 300nm to 700 nm. The metal film can be prepared by coating methods such as magnetron sputtering, electron beam evaporation, thermal evaporation, electroplating and the like. In this embodiment, an oxide thin film buffer layer such as silicon dioxide may be disposed on the surface of the lithium tantalate wafer 1 after the straight waveguides 2 are formed, as required, so as to avoid the absorption of the light wave energy by the metal thin film at the intersection of the metal electrode 3 and the straight waveguides 2.
The optical fiber crystal carrier block 4 may be a square or rectangular crystal with a groove of one shape of V, square, semi-circle, etc. pre-fabricated on the surface, or a circular crystal or D-shaped crystal with a circular hole formed at the center, and is mainly used for placing optical fibers and increasing the bonding area and bonding strength when coupling optical fibers. The optical fibers are typically placed in the following manner: firstly, a groove with a specific shape, such as a V shape, a square shape, a semicircular shape and the like, is made in advance on the surface of the optical fiber crystal carrier block 4, or a round hole is made in advance in the center of the optical fiber crystal carrier block 4; then, the polarization maintaining optical fiber 5 is placed in the groove or the round hole, and the counter-axis angle of the slow axis of the polarization maintaining optical fiber 5 is placed according to the requirement; and filling ultraviolet glue in the gap between the groove or the round hole and the optical fiber and exposing the ultraviolet glue by ultraviolet light to be fully cured. The optical fiber crystal carrier block 4 and the polarization maintaining optical fiber 5 placed therein are ground and polished together, and then can be coupled and bonded with the optical waveguide.
The optical fiber crystal carrier 4 may be made of a crystal material such as lithium niobate, lithium tantalate, quartz, glass, or silicon, but is not particularly limited to this, and a lithium tantalate crystal material is preferable. The polishing inclination angle of the optical fiber crystal carrier block 4 is 0-11 degrees, and the polishing inclination angle of the lithium tantalate substrate wafer 1 is 0-16 degrees.
The slow axis of the polarization maintaining optical fiber 5 and the X-axis direction of the lithium tantalate substrate wafer 1 form an angle of 0 degree or 90 degrees with respect to the axis, the polarization maintaining optical fiber is placed in a groove or a round hole of the optical fiber crystal carrier block 4, a gap between the optical fiber and the groove or the round hole is filled with epoxy glue and completely cured, and the polarization maintaining optical fiber is respectively coupled and bonded with the input port 2-1 and the output port 2-2 containing the straight waveguide 2 after being polished.
In order to obtain the best optical fiber coupling efficiency and reduce the back reflection of the optical device, the polishing inclination angle of the optical fiber crystal carrier block 4 is 14.7 degrees +/-0.5 degrees, and the polishing inclination angle of the lithium tantalate substrate wafer 1 is 10 degrees +/-0.5 degrees.
Example 2
Referring to fig. 3, a schematic structural diagram of an embodiment of an integrated component provided in this embodiment is shown. An integrated assembly, comprising: lithium tantalate substrate wafer 1, straight waveguide 2, metal electrode 3, fiber crystal carrier 4, polarization maintaining fiber 5, Y-branch waveguide coupler 6. The structures of the lithium tantalate substrate wafer 1, the straight waveguide 2, the metal electrode 3, the fiber crystal carrier block 4, and the like are the same as those of embodiment 1, and detailed description thereof is omitted.
The Y-branch waveguide coupler 6 integrates two important functions of a waveguide coupler and a waveguide polarizer, among which: the waveguide coupler function is realized through a Y-branch structure; the waveguide polarizer function is achieved by using the high polarization-rising characteristic of the annealed proton-exchanged optical waveguide.
Referring to fig. 3, the present embodiment can realize monolithic integration of each discrete optical fiber device in the dashed-line block diagram of fig. 1 in a lithium tantalate wafer. In the integrated package provided in this embodiment, the optical waveguide of the Y-branch waveguide coupler is an annealed proton-exchanged waveguide, which includes a dual port and a single port, where: one end 6-1-1 of the double port can be used for being connected with a laser light source through an optical fiber, the other end 6-1-2 of the double port can be used for being connected with a photoelectric detector through the optical fiber, and the single port 6-2 is connected with the straight waveguide 2 through the polarization maintaining optical fiber 5.
The annealed proton exchange waveguide is a polarizing optical waveguide, and the output optical waveguide mode is a high-polarization linearly polarized light mode. As shown in fig. 4, the same function as that of the 45 ° optical fiber fusion splice angle shown in fig. 1 can be obtained by setting the counter-axis angle of the polarization maintaining fiber 5 at the single port 6-2 of the Y-branch waveguide coupler 6 to 45 °, that is, the slow axis direction is 45 ° relative to the X axis direction of the lithium tantalate substrate wafer 1. At the remaining optical waveguide ports, including the two ports 6-1-1 and 6-1-2 of the Y-branch waveguide coupler 6 and the two ports 2-1 and 2-2 of the straight waveguide 2, the slow axis direction of the polarization maintaining fiber 5 and the X axis direction of the lithium tantalate substrate wafer 1 both form an on-axis angle of 0 ° or 90 °. And the fiber crystal carrier block 4 with the polarization maintaining fiber 5 is respectively coupled and bonded with each optical waveguide port of the integrated assembly.
Example 3
Referring to fig. 5, a schematic structural diagram of the integrated component provided in this embodiment is shown. In order to further improve the integration level of the integrated component, improve the reliability of the component, and reduce the assembly difficulty and manufacturing cost, on the basis of embodiment 2, in this embodiment, the optical fiber crystal carrier block 4 is improved, and a multi-channel optical fiber array is formed by using the multi-channel optical fiber crystal carrier block 4 and placing one polarization maintaining optical fiber 5 in each channel.
Specifically, the method comprises the following steps: lithium tantalate substrate wafer 1, straight waveguide 2, metal electrode 3, fiber crystal carrier 4, polarization maintaining fiber 5, Y-branch waveguide coupler 6. The structures of the lithium tantalate substrate wafer 1, the straight waveguide 2, the metal electrode 3, the Y-branch waveguide coupler 6, and the like are the same as those of embodiment 2, and detailed description thereof will not be provided.
The fiber crystal carrier block 4 arranged on one side of the single port 6-2 of the Y-branch waveguide coupler 6 comprises 2 channels, namely 2 grooves or 2 round holes, which are respectively used for arranging 2 polarization-maintaining fibers, and the distance between every two channels is not less than 82 μm. The slow axis direction of the polarization maintaining optical fiber arranged at the single port 6-2 of the Y-branch waveguide coupler 6 and the X-axis direction of the lithium tantalate substrate wafer 1 form an angle of 45 degrees to the axis, and the slow axis direction of the polarization maintaining optical fiber arranged at the port 2-1 of the straight waveguide 2 and the X-axis direction of the lithium tantalate substrate wafer 1 form an angle of 0 degree or 90 degrees to the axis.
The fiber crystal carrier block 4 placed on the side of the two ports 6-1-1 and 6-1-2 of the Y-branch waveguide coupler 6 contains 3 channels, i.e., 3 grooves or 3 round holes, respectively for placing 3 polarization-maintaining fibers, and the space between each channel is not less than 82 μm. The slow axis directions of the 3 polarization maintaining optical fibers and the X axis direction of the lithium tantalate substrate wafer 1 form 0-degree or 90-degree counter axis angles.
The polishing inclination angle of the optical fiber crystal carrier block containing multiple channels is 14.7 degrees +/-0.5 degrees. The polishing angle of the lithium tantalate substrate wafer was 10 ° ± 0.5 °.
Example 4
The invention also provides a manufacturing method of the straight waveguide phase modulator. The manufacturing method is used for manufacturing the straight waveguide phase modulator in embodiment 1, and specifically comprises the following steps:
step 1: preparing a strip-shaped zinc oxide film with the width not more than 10 mu m and the thickness not more than 250nm on the surface of the lithium tantalate substrate wafer 1 by adopting a photoetching stripping process or a photoetching corrosion process and combining film coating processes such as magnetron sputtering or chemical vapor deposition and the like;
step 2: putting the lithium tantalate substrate wafer 1 with the prepared strip-shaped zinc oxide film into a central area of a high-temperature diffusion furnace, charging wet oxygen, keeping the furnace temperature of the central area of the diffusion furnace constant without exceeding the Curie temperature of lithium tantalate crystals, and keeping the temperature for more than 1 hour to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking the lithium tantalate substrate wafer 1 out of the diffusion furnace after the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a metal electrode 3 on the surface of the lithium tantalate substrate wafer 1 with the zinc oxide straight waveguide 2 by adopting a photoetching stripping process or a photoetching electroplating process in combination with a metal film coating process such as magnetron sputtering or evaporation plating, and symmetrically registering an electrode branch I3-1 and an electrode branch II 3-2 of the metal electrode 3 relative to the straight waveguide 2;
and 5: respectively and precisely polishing the end face of a lithium tantalate substrate wafer 1 and the end face of an optical fiber crystal carrier block 4 with a polarization maintaining optical fiber 5, wherein the optical fiber crystal carrier block 4 is polished to an inclination angle of 14.7 degrees +/-0.5 degrees, and the polishing angle of the lithium tantalate substrate wafer 1 is 10 degrees +/-0.5 degrees;
step 6: and precisely aligning the optical fiber crystal carrier block 4 with the polarization maintaining optical fiber 5, the input port 2-1 and the output port 2-2 of the straight waveguide 2 of the lithium tantalate substrate wafer 1, filling ultraviolet glue between the optical fiber crystal carrier block and the end face of the optical waveguide, and completing coupling and bonding after the ultraviolet glue is fully exposed and cured by ultraviolet light.
Example 5
The present invention also provides a manufacturing method of an integrated component for manufacturing the integrated components in embodiments 2 and 3, specifically, the manufacturing method includes the steps of:
step 1: preparing a strip-shaped zinc oxide film with the thickness of not more than 250nm on the surface of the lithium tantalate substrate wafer 1 by adopting a photoetching stripping process or a photoetching corrosion process and combining film coating processes such as magnetron sputtering or chemical vapor deposition and the like;
step 2: putting the lithium tantalate substrate wafer 1 with the prepared strip-shaped zinc oxide film into a central area of a high-temperature diffusion furnace, charging wet oxygen, keeping the furnace temperature of the central area of the diffusion furnace constant without exceeding the Curie temperature of lithium tantalate crystals, and keeping the temperature for more than 1 hour to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking the lithium tantalate substrate wafer 1 out of the diffusion furnace after the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a layer of silicon dioxide film or metal film or nonmetal film such as metal titanium or metal chromium on the surface of the lithium tantalate substrate wafer 1 with the zinc oxide straight waveguide 2 by adopting a photoetching stripping process or a corrosion photoetching process and combining film coating processes such as magnetron sputtering, chemical vapor deposition or evaporation and the like, wherein the silicon dioxide film or the metal film or the nonmetal film is used as a proton exchange mask, the pattern of an opening of the mask is a Y-branch coupler, and the opening of the mask is not more than 10 mu m;
and 5: putting the lithium tantalate substrate wafer 1 into a quartz beaker containing pure benzoic acid solution or a quartz beaker containing mixed solution of benzoic acid and lithium benzoate, heating the quartz beaker to 150-250 ℃, and keeping the temperature for not less than 0.5 hour;
step 6: corroding the metal film or the nonmetal film on the surface of the lithium tantalate substrate wafer 1 which finishes the proton exchange process;
and 7: putting the lithium tantalate substrate wafer 1 into the central area of an annealing furnace, annealing the area subjected to proton exchange, keeping the temperature for more than 1 hour when the temperature of the central furnace of the annealing furnace reaches 300-400 ℃, and taking the lithium tantalate substrate wafer 1 out of the annealing furnace;
and 8: preparing a metal electrode 3 on the surface of the lithium tantalate substrate wafer 1 by adopting a photoetching stripping process or a photoetching electroplating process and combining a magnetron sputtering process or a vapor deposition process and other metal film coating processes, and symmetrically aligning an electrode branch I3-1 and an electrode branch II 3-2 of the metal electrode 3 relative to the straight waveguide 2;
and step 9: respectively and precisely polishing the end face of a lithium tantalate substrate wafer 1 and the end face of an optical fiber crystal carrier block 4 with a polarization maintaining optical fiber 5, wherein the optical fiber crystal carrier block 4 is polished to an inclination angle of 14.7 degrees +/-0.5 degrees, and the polishing angle of the lithium tantalate substrate wafer 1 is 10 degrees +/-0.5 degrees;
step 10: and (3) precisely aligning the optical fiber crystal carrier block 4 with the polarization maintaining optical fiber 5 and each waveguide port of the lithium tantalate substrate wafer 1, filling ultraviolet glue between the optical fiber crystal carrier block and the end face of the optical waveguide, and completing coupling and bonding after the ultraviolet glue is completely exposed and cured by ultraviolet light.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A straight waveguide phase modulator comprises a straight waveguide (2), a metal electrode (3), a fiber crystal carrier block (4) and a polarization maintaining fiber (5),
the polarization maintaining optical fiber polarization maintaining device is characterized by further comprising a lithium tantalate substrate wafer (1), wherein the straight waveguide (2) is formed in the lithium tantalate substrate wafer (1), the metal electrode (3) is placed on the upper surface of the lithium tantalate substrate wafer (1), the optical fiber crystal carrier block (4) is in coupling connection with the lithium tantalate substrate wafer (1), and the polarization maintaining optical fiber (5) is placed in the optical fiber crystal carrier block (4).
2. The straight waveguide phase modulator according to claim 1, wherein the lithium tantalate substrate wafer (1) employs optical-grade, X-cut, Y-pass lithium tantalate crystals with a thickness of not less than 0.5mm, and the polishing angle of the lithium tantalate substrate wafer (1) is 0 ° to 11 °.
3. The straight waveguide phase modulator according to claim 1 or 2, characterized in that the straight waveguide (2) is a zinc oxide optical waveguide, and the width of the strip-shaped zinc oxide thin film forming the straight waveguide (2) is not more than 10 μm and the thickness is not more than 250 nm.
4. The straight waveguide phase modulator according to claim 1 or 2, characterized in that the metal electrode (3) is a lumped electrode structure, and the metal electrode (3) is composed of a first electrode branch and a second electrode branch, which are respectively symmetrically disposed on two sides above the straight waveguide (2).
5. The straight waveguide phase modulator according to claim 1 or 2, characterized in that the fiber crystal carrier block (4) is made of lithium tantalate crystal, and the polishing angle of the fiber crystal carrier block (4) is 0-16 °; the slow axis of the polarization maintaining optical fiber (5) and the X-axis direction of the lithium tantalate substrate wafer (1) form a 0-degree or 90-degree counter-axis angle.
6. An integrated package comprising a straight waveguide phase modulator according to claim 1 or 2 and a Y-branch waveguide coupler,
the Y-branch waveguide coupler is formed on the lithium tantalate substrate wafer (1), the optical waveguide of the Y-branch waveguide coupler (6) is an annealed proton exchange waveguide, the two ports of the Y-branch waveguide coupler (6) are used as input ports, one end of the Y-branch waveguide coupler is used for being connected with a laser light source through a polarization maintaining optical fiber, and the other end of the Y-branch waveguide coupler is used for being connected with a photoelectric detector through the polarization maintaining optical fiber; and a single port of the Y-branch waveguide coupler (6) is used as an output end and is connected with the straight waveguide (2) through a polarization maintaining optical fiber.
7. An integrated assembly according to claim 6,
at the single port of the Y-branch waveguide coupler (6), the slow axis of the polarization-maintaining optical fiber (5) and the X-axis direction of the lithium tantalate substrate wafer (1) form a 45-degree counter-axis angle; and at the double port of the Y-branch waveguide coupler (6) and the input port and the output port of the straight waveguide (2), the slow axis of the polarization-maintaining optical fiber (5) and the X-axis direction of the lithium tantalate substrate wafer still form a 0-degree or 90-degree counter-axis angle, and the optical fiber crystal carrier block provided with the polarization-maintaining optical fiber is respectively coupled and bonded with each optical waveguide port of the integrated assembly.
8. An integrated assembly according to claim 7,
the fiber crystal carrier block (4) is provided with a plurality of grooves with channels on the surface in advance or a plurality of round holes in the center, each groove or round hole of each channel is provided with a polarization maintaining fiber, and the distance between every two channels is not less than 82 mu m.
9. A method for preparing a straight waveguide phase modulator is characterized by comprising the following steps:
step 1: preparing a layer of strip-shaped zinc oxide film on the surface of a lithium tantalate substrate wafer;
step 2: placing the lithium tantalate substrate wafer with the prepared strip-shaped zinc oxide film in a central area of a high-temperature diffusion furnace, and charging wet oxygen, wherein the furnace temperature of the central area of the diffusion furnace does not exceed the Curie temperature of lithium tantalate crystals and keeps constant for more than 1 hour at constant temperature so as to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking out the lithium tantalate substrate wafer from the diffusion furnace when the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a metal electrode on the surface of the lithium tantalate substrate wafer with the zinc oxide straight waveguide, and symmetrically aligning an electrode branch I and an electrode branch II of the metal electrode relative to the straight waveguide;
and 5: respectively and precisely polishing the end face of the lithium tantalate substrate wafer and the end face of the optical fiber crystal carrier block with the polarization maintaining optical fiber;
step 6: and precisely aligning the optical fiber crystal carrier block with the polarization maintaining optical fiber with the input port and the output port of the straight waveguide in the lithium tantalate substrate wafer, filling ultraviolet glue, and performing ultraviolet exposure curing to complete coupling and bonding.
10. A method of making an integrated component, comprising the steps of:
step 1: preparing a layer of strip-shaped zinc oxide film on the surface of a lithium tantalate substrate wafer;
step 2: placing the lithium tantalate substrate wafer with the prepared strip-shaped zinc oxide film in a central area of a high-temperature diffusion furnace, and charging wet oxygen, wherein the furnace temperature of the central area of the diffusion furnace does not exceed the Curie temperature of lithium tantalate crystals and keeps constant for more than 1 hour at constant temperature so as to ensure that the strip-shaped zinc oxide film is fully diffused in the lithium tantalate crystals;
and step 3: closing the diffusion furnace after the diffusion is finished, and taking out the lithium tantalate substrate wafer from the diffusion furnace after the temperature of the central furnace of the diffusion furnace is reduced to room temperature;
and 4, step 4: preparing a layer of metal film or non-metal film on the surface of the lithium tantalate substrate wafer with the zinc oxide straight waveguide as a proton exchange mask, wherein the pattern of an opening of the mask is a Y-branch coupler, and the opening of the mask is not more than 10 mu m;
and 5: putting the lithium tantalite substrate wafer into a quartz beaker containing pure benzoic acid solution or a quartz beaker containing mixed solution of benzoic acid and lithium benzoate, heating the quartz beaker to 150-250 ℃, and keeping the temperature for more than 0.5 hour;
step 6: corroding the metal film or the nonmetal film on the surface of the lithium tantalate substrate wafer which finishes the proton exchange process;
and 7: putting the lithium tantalate substrate wafer into a central area of an annealing furnace, annealing the area subjected to proton exchange, keeping the temperature for more than 1 hour when the temperature of the central furnace of the annealing furnace reaches 300-400 ℃, and taking the lithium tantalate substrate wafer out of the annealing furnace;
and 8: preparing a metal electrode on the surface of the lithium tantalate substrate wafer, and symmetrically aligning an electrode branch I and an electrode branch II of the metal electrode relative to the straight waveguide;
and step 9: respectively and precisely polishing the end face of the lithium tantalate substrate wafer and the end face of the optical fiber crystal carrier block with the polarization maintaining optical fiber;
step 10: and respectively carrying out precise alignment on the optical fiber crystal carrier block with the polarization maintaining optical fiber and each waveguide port of the lithium tantalate substrate wafer, filling ultraviolet glue, and carrying out ultraviolet exposure curing to complete coupling and bonding.
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