CN111548005A - A kind of preparation method of laser-drawn silicon germanium core fiber - Google Patents

Abstract

The invention belongs to the technical field of optical fibers, and in particular relates to a preparation method for preparing a silicon germanium core optical fiber by laser wire drawing; The invention adopts single crystal silicon and single crystal germanium to form inner filling materials, and fills the quartz hollow tube with one end closed in advance, and assembles it into a prefabricated rod; single crystal silicon and single crystal germanium can be spliced by semi-cylindrical rods and alternately stacked with slices. The combined structure is evenly mixed with the powder, and the flexibility is high. The present invention uses laser to heat the preform until the quartz tube is softened and drawn, the silicon material and the germanium material reach a molten state through the quartz conduction heat, and the two materials are mixed into an infinite solid solution to form a silicon germanium alloy. The preparation method provided by the invention solves the problem of segregation of silicon germanium alloy in the prior art, realizes a binary single-phase alloy material with uniform composition, obtains a silicon germanium fiber core in a single crystal form, and improves the silicon germanium core fiber performance.

Description

A kind of preparation method of laser-drawn silicon germanium core fiber

technical field

The invention belongs to the technical field of optical fibers, and in particular relates to a preparation method of a laser-drawn silicon-germanium core optical fiber.

Background technique

Pure silicon core fiber and pure germanium core fiber have the characteristics of high thermal conductivity, wide transparent window and high refractive index, and are widely used in infrared transmission, sensing and all-optical systems. Silicon and germanium are miscible solid solutions in any ratio, and the miscible bodies they constitute are called silicon germanium alloys. Many physical properties of silicon-germanium alloys are directly affected by the composition, and its energy gap can be precisely set by adjusting the composition. Therefore, it is called "the second generation of silicon microelectronic materials". In the field of optics, silicon germanium alloys have good optoelectronic properties, nonlinear properties, and transparent transmission in the mid-infrared. The introduction of this material into the optical fiber waveguide structure will expand the function of the optical fiber and has the potential to prepare all-optical network devices.

The traditional method of preparing silica fiber usually uses a graphite furnace drawing tower, which has the characteristics of mature technology and stable temperature. Graphite drawing technology is now also used to prepare SiGe core fibers. For example, the document "Silicon-germanium core fiber F-P cavity temperature sensor based on optical fiber fusion and polishing technology" (optical communication technology, 2020) discloses a preparation method of a silicon-germanium core fiber: it is drawn by a tube rod method; The silicon half-round rod and the single-crystal germanium half-round rod are spliced together and placed in a quartz preform closed at one end, and one end of the preform is connected to a vacuum pump and fixed on the upper end of the drawing tower; it is made by melting in a graphite furnace and an optical fiber drawing process. out of silicon germanium fiber. However, due to the long length of the graphite furnace temperature zone and the low temperature gradient in the furnace, the distance between the solid-liquid interface of the SiGe alloy and the highest temperature in the liquid phase is relatively large, and the temperature gradient at the front of the growth interface is relatively low. Moreover, the solidus and liquidus of silicon-germanium alloys have great separation. When the temperature gradient at the front of the growth interface is low, the components are easily cooled, resulting in component segregation. Therefore, the SiGe core fiber is drawn by a graphite furnace drawing tower. The composition of the SiGe core fiber is very segregated. The uneven composition causes the core refraction to fluctuate, causing high scattering loss and affecting the performance of the SiGe core fiber. .

With the development of high-power technology, laser wire drawing technology is gradually used in optical fiber preparation. Compared with graphite furnace wire drawing technology, laser wire drawing technology has the advantages of easy control of heating energy, short action time and small action area. Laser drawing technology has been used in single crystal silicon core fiber and single crystal germanium core fiber.

For example, the patent with publication number CN109669232A discloses a single crystal semiconductor core fiber and a preparation method thereof; the core is made of semiconductor materials such as Si or Ge, and the cladding is formed by shrinking glass capillaries, and has a good core-wrapping structure. The preparation method is as follows: (1) preparation of single crystal semiconductor core: wet etching single crystal semiconductor rod; (2) treatment of cladding capillary: low borosilicate glass capillary is used for germanium material, and silicon fiber core is selected with a higher softening temperature. High borosilicate glass capillary, before treatment, the capillary can be ultrasonically cleaned. After the treatment is completed, select a quartz pigtail or single-mode fiber of suitable size and plug it from one end of the capillary to 1/4-1/3 of the length of the tube, then The end is softened and sealed by heat treatment; (3) Assembling of optical fiber preform: The corroded single crystal hexagonal fine core is filled into the glass capillary after one end is sealed. The middle of the tube is parked, and the upper end of the tube does not need to be sealed; the upper end of the tube is tied to the end of the thin quartz rod with high temperature tape, and the upper end of the thin quartz rod is connected to a small section of thick quartz rod. On the fixture with two-dimensional adjustment frame, the fixture is fixed on the rod feeding device of the drawing tower; (4) Optical fiber forming based on CO ₂ laser drawing system.

At present, there is no research on the preparation of SiGe core fiber by laser wire drawing technology to solve the segregation of SiGe alloy.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems existing in the prior art, the present invention provides a silicon-germanium alloy which uses a laser as a heating source to improve the temperature gradient at the front of the growth interface of the silicon-germanium alloy, and draws the preform of the elemental silicon and germanium mixed material. Core fiber preparation method.

The specific technical solutions are as follows:

A method for preparing a laser-drawn silicon-germanium core fiber, comprising the following steps:

(1) Quartz tube treatment: uniformly heated by a graphite furnace, the lower end of the quartz hollow core tube is narrowed and sealed;

(2) Assembly of preforms: splicing semi-cylindrical silicon rods and semi-cylindrical germanium rods into cylindrical shapes or alternate stacking of silicon and germanium wafers or evenly mixing silicon and germanium powders as inner filling materials, loading step (1) The quartz hollow core tube is assembled into a preform;

(3) Preform processing: The quartz tube at the upper end of the assembled preform is sealed with the vacuum pump pipeline, and the pressure in the tube is adjusted to avoid oxidation of the core material;

(4) Laser wire drawing:

a. Put the preform into the laser drawing tower, set a constant laser power to heat the preform until it softens, and draw under the action of its own gravity;

b. Adjust the laser power to reduce the increase in laser power density due to the thinning of the preform, avoid the occurrence of fusing, and achieve stable wire drawing;

c. Maintain the laser power during stable drawing to make the temperature gradient reach about 10 ⁴ ℃/cm. The drawing speed is adjusted according to the component ratio, and the fastest drawing speed does not exceed 50mm/min;

In the present invention, laser heat treatment is used for non-uniform silicon germanium core fiber, and it is found that laser heat treatment can suppress component segregation, and the laser wire drawing conditions are screened and studied by simulation model, and verified by component supercooling theory. It was found that when the laser power was maintained during stable drawing, the temperature gradient reached about 10 ⁴ ℃/cm, and the drawing speed did not exceed 50 mm/min, a SiGe core fiber with uniform composition could be obtained.

Preferably, the inner layer filling material is single crystal silicon with a purity of 99.999% and single crystal germanium with a purity of 99.999%.

Preferably, the laser drawing tower includes a carbon dioxide laser and an optical path module, and the size of the laser action area can be adjusted. As a heat source, the laser has high temperature gradient and fast temperature response, and can provide a high temperature gradient at the front of the growth interface.

It should be noted that in the preparation of silicon-germanium core optical fibers with silicon content of less than 25 at% or germanium content of less than 25 at%, it is advisable to use the powder uniformly mixed form; Two forms (half-cylindrical silicon rods and germanium rods are spliced into cylindrical shapes, and silicon and germanium wafers are alternately stacked), so that silicon and germanium can be heated and melted at the same time.

It should be noted that the quartz hollow tube of the preform can be doped, and the thermal parameters such as the melting point and viscosity of the quartz material can be modified to adapt to the drawing of silicon-germanium core fibers with different composition ratios and reduce the reduction of silicon-germanium alloy materials. The problem of large strain with the quartz layer due to the mismatch of the expansion coefficient.

It should be noted that the laser wire drawing process can be carried out multiple times. During the second wire drawing, since the diameter of the silicon germanium preform is reduced, the required length of the laser action area can be further reduced, thereby increasing the temperature gradient and further optimizing the silicon germanium fiber. performance.

The invention also provides a silicon germanium optical fiber prepared by the above preparation method, comprising a core and a cladding, the core is a silicon germanium alloy, and the cladding is quartz; the interface between the core layer and the cladding is smooth, and the fiber size is uniform.

The beneficial effects of the present invention are:

Silicon-germanium alloy is a binary single-phase material that is prone to component segregation. Serious segregation will cause the coexistence of silicon, germanium and silicon-germanium alloy materials, which affects the performance of silicon-germanium core fibers. The invention provides a preparation method of silicon germanium core optical fiber through research on preform and laser technology, solves the problem of silicon germanium alloy segregation in the prior art, realizes the binary single-phase alloy material with uniform composition, and makes The silicon germanium fiber core in single crystal form is obtained, and the electrochemical and optical properties of the silicon germanium core fiber are improved.

Laser wire drawing has the characteristics of small action area and high temperature gradient. The invention greatly improves the temperature gradient at the front of the growth interface of the silicon-germanium alloy by researching the core excitation of the optically drawn silicon-germanium alloy, can achieve the effect of suppressing the supercooling of the components, reduce the component segregation of the silicon-germanium alloy, and is beneficial to Single crystal growth improves the performance of the fiber; the feature of adjustable beam improves the flexibility of drawing temperature zone control; and the viscosity of the molten silicon germanium material is lower than that of the fused silica material, so it can maintain good fluidity during the drawing process , forming a SiGe core fiber that perfectly fits with the silica cladding to form a smooth core-clad interface. The preparation method provided by the invention has good applicability to different semiconductor core optical fibers, and improves the problem that the temperature gradient is not high when the crystal core optical fibers are grown by graphite furnace drawing.

In the technical scheme provided by the present invention, various combinations of preform filling materials enrich the composition ratio of SiGe alloy; the core component of SiGe core fiber has a low degree of supercooling, and the fiber performance is more superior; the preparation method is flexible higher.

Description of drawings

Figure 1 shows the three combined structures of single-crystal silicon and single-crystal germanium in the preform, 1- pre-reduced and sealed quartz hollow tube, 2- semi-cylindrical germanium rod, 3- semi-cylindrical silicon rod, 4- germanium sheet, 5-silicon flakes, 6-silicon powder particles, 7-germanium powder particles.

FIG. 2 is a flow chart of the preparation process of the silicon germanium core optical fiber.

Fig. 3 is a graph showing the segregation of components in graphite furnace drawing.

FIG. 4 is a graph showing the results of laser heat treatment for inhibiting component segregation.

Detailed ways

The technical solutions of the present invention will be further limited below in conjunction with specific embodiments, but the scope of protection is not limited to the description.

Example 1

A method for preparing a laser-drawn silicon-germanium core fiber, comprising the following steps:

(1) Quartz tube treatment: take a quartz hollow core tube with an outer diameter of 6 mm and an inner diameter of 1 mm, uniformly heat it through a graphite furnace, and narrow and seal the lower end of the quartz hollow core tube;

(2) preform assembly: the semi-cylindrical silicon rod and the semi-cylindrical germanium rod are spliced into a cylindrical shape, which is used as an inner filling material, and is loaded into the quartz hollow tube of step (1), and assembled into a preform; wherein half of the inner filling material is half The content of cylindrical silicon rod is 47at%;

(3) Preform treatment: the upper end of the assembled preform is filled with a plug, and then connected to a vacuum pump for vacuum treatment to avoid oxidation of the core material;

(4) Laser wire drawing:

a. Put the preform into the laser drawing tower, set the laser power to 210W, convert the laser beam into a halo, the length of the action area is 13mm, the halo evenly illuminates the surface of the preform, and heat the preform until it softens. Drawing under the action of gravity;

b. Slowly adjust the laser power to 180W, reduce the increase in laser power density due to the thinning of the preform, and avoid the occurrence of fusing; adjust the feeding speed of the preform to 0.2mm/min to achieve stable wire drawing;

c. During stable drawing, the laser power makes the temperature gradient reach about 10 ⁴ ℃/cm, the drawing speed is set to 46 mm/min, the drawing is completed, and the silicon germanium core fiber is formed by cooling.

A simulation experiment was carried out according to the technical solution of Example 1, and a silicon germanium core optical fiber was prepared. The prepared silicon-germanium core fiber is measured and verified by optical microscope and EDS. The results show that the microscope optical image contrast of the silicon-germanium core fiber is consistent, and the EDS energy spectrum shows that the silicon and germanium elements are uniformly distributed; the technology provided by the present invention is explained. The solution effectively solves the problem of silicon germanium alloy segregation, and the prepared silicon germanium core optical fiber has a uniform composition.

The present invention conducts simulation experiments on preforms with two combined structures in the form of silicon and germanium powder mixed uniformly and in the form of alternate stacking of silicon and germanium wafers: adjusting the power of the laser drawing tower and the feeding speed of the preform to soften the preform, and then Adjust the laser rate and preform feeding speed to achieve stable drawing of the preform; maintain the laser power during stable drawing so that the temperature gradient reaches about 10 ⁴ ℃/cm, and the fastest drawing speed does not exceed 50mm/min; after drawing is completed, cool to form silicon germanium core fiber. Optical microscope measurement and EDS inspection and verification of the prepared silicon-germanium core fiber were carried out. The results showed that the preform of the two combined structures in the form of a uniform mixture of silicon and germanium powders and the form of alternate stacking of silicon and germanium discs could obtain uniform composition. SiGe core fiber.

Comparative Example 1 Preparation of SiGe Fiber by Graphite Drawing

The first is the production of the preform. A pure quartz tube with an outer diameter of about 12mm is prepared, and one end of the quartz tube is closed for wire drawing, and at the same time, the molten silicon germanium material is prevented from flowing out of the quartz tube during drawing. Then, a semi-circular germanium rod with a purity of 99.999% and a diameter of 2.5 mm is placed into the preform together with the silicon rod. The other end of the preform is connected to the vacuum pump and fixed on the drawing tower. The vacuum pump provides an approximate vacuum state during drawing to prevent the large core from generating oxides at high temperatures. The graphite furnace was heated to 2200°C, and the preform was slowly put into the graphite furnace through the drawing tower control system. After the wire is formed by the wire rod, the optical fiber is passed through the pulling wheel, the wire diameter meter, the coating device, the wire drawing wheel and the wire take-up disk in sequence.

The simulation experiment was carried out according to the technical scheme of Comparative Example 1; the SiGe core fiber as shown in Figure 3 can be obtained. It can be seen from Figure 3 that the SiGe core fiber has bright and dark areas with different sizes; The germanium core fiber has obvious segregation phenomenon.

In the present invention, the laser heat treatment method is used to treat the silicon-germanium core fiber with uneven composition prepared in Comparative Example 1, and it is found that the composition segregation can be suppressed by laser heat treatment; and the optimization of the laser heat treatment conditions is carried out. , the laser heat treatment conditions are as follows: the laser spot size is 160 microns, the laser power is 0.7 W, and the scanning speed is 0.3 mm/s (18 mm/min), which can suppress the segregation of components to the greatest extent, and obtain the silicon germanium core fiber as shown in Figure 4; It can be seen from Fig. 4 that there are no bright and dark regions of different sizes in the SiGe core fiber, which verifies that the laser heat treatment can suppress the composition segregation of the SiGe core fiber.

It is necessary to point out here that the above examples and test examples are only for further elaboration and understanding of the technical solutions of the present invention, and should not be construed as further limiting the technical solutions of the present invention. Inventions and creations with sexual characteristics and significant progress still belong to the protection scope of the present invention.

Claims (8)

1. a laser wire drawing silicon germanium core optical fiber preparation method, comprising quartz tube processing, preform assembly, preform processing, laser wire drawing steps, it is characterized in that, maintain laser power to make temperature gradient reach during stable wire drawing in the described laser wire drawing process About 10 ⁴ ℃/cm, the wire drawing speed is adjusted according to the composition ratio of silicon and germanium, and the fastest wire drawing speed does not exceed 50mm/min. 2. The preparation method of laser wire drawing silicon germanium core fiber as claimed in claim 1, it is characterized in that, the concrete steps of laser wire drawing are: a, preform is put into laser wire drawing tower, set constant power to make preform soften, in itself Under the action of gravity, a necking area is formed, and the wire drawing is completed; b. Reduce the laser power to adjust the laser power density that is rapidly increased due to the thinning of the preform, so as to avoid the occurrence of fusing and achieve stable wire drawing; c. Maintain the laser power to make the temperature The gradient reaches about 10 ⁴ ℃/cm, the wire drawing speed is adjusted according to the component ratio, and the fastest wire drawing speed does not exceed 50 mm/min. 3 . The method for preparing a laser-drawn silicon-germanium core fiber according to claim 2 , wherein the laser-drawing tower comprises a carbon dioxide laser and an optical path module, and the size of the laser action area can be adjusted. 4 . 4. the preparation method of laser-drawn silicon germanium core fiber as claimed in claim 1, is characterized in that, described preform is assembled as: adopt purity 99.999% monocrystalline silicon and purity 99.999% monocrystalline germanium to form inner filling material, fill to Quartz hollow core tubes, assembled into preforms. 5. The method for preparing a laser-drawn silicon-germanium core fiber according to claim 4, wherein the combined structure of silicon and germanium in the preform can be splicing of silicon and germanium semi-cylindrical rods, alternating stacking of silicon and germanium flakes, and Silicon and germanium powders are uniformly mixed. 6 . The method for preparing a laser-drawn silicon-germanium core optical fiber according to claim 4 , wherein the lower end of the quartz hollow core tube is narrowed and sealed. 7 . 7. The method for preparing a laser-drawn silicon-germanium core optical fiber according to claim 1, wherein the preform is processed as follows: the quartz tube at the upper end of the assembled preform is sealed and connected to the vacuum pump pipeline, the pressure in the tube is adjusted, and the fiber is avoided. Core material oxidizes. 8. A silicon-germanium core optical fiber prepared by the method for preparing a laser-drawn silicon-germanium core optical fiber according to any one of claims 1-7, characterized in that, comprising a core and a cladding, and the core is a silicon-germanium alloy , the cladding is quartz.

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