Near-melting-point super-stable full-sapphire optical microcavity high-temperature sensor and preparation method thereof

Abstract

The invention discloses a near-melting-point ultra-stable full-sapphire optical microcavity high-temperature sensor and a preparation method thereof. The near-melting-point ultra-stable full-sapphire optical microcavity high-temperature sensor comprises a protective sleeve, a first insertion core, a multimode optical fiber, a sapphire optical fiber and a sapphire optical microcavity, the sapphire optical microcavity comprises a second insertion core made of sapphire and a sapphire wafer, and the sapphire wafer is fixed at the tail end of the second insertion core in a non-adhesive bonding manner; one end of the multimode optical fiber is aligned and fixedly connected with one end of the sapphire optical fiber, and the joint of the multimode optical fiber and the sapphire optical fiber is suspended in the protective sleeve; the other end of the sapphire optical fiber extends into the sapphire optical microcavity, and the distance between the other end of the sapphire optical fiber and the sapphire wafer is 50-100 microns; the protective sleeve sleeves the outer surface of a part of the sapphire optical microcavity and the outer surfaces of a part of the multimode optical fiber and the sapphire optical fiber. The temperature sensitive element of the high-temperature sensor is only a sapphire wafer, the second insertion core and the sapphire wafer are fixed through a non-adhesive process, a full-sapphire optical microcavity is manufactured, and the high-temperature consistency is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensors, and in particular relates to a near-melting-point ultra-stable all-sapphire optical microcavity high-temperature sensor for extreme environment applications and a preparation method thereof. Background Art

[0002] In the fields of aerospace, industrial metallurgy, nuclear reaction, etc., the demand for ultra-high temperature detection above 1700℃ is becoming increasingly prominent. Although traditional high-temperature thermocouples can detect temperatures above 1700℃, they have slow temperature response time, poor resistance to extreme environments, low accuracy and low lifespan, and cannot quickly and accurately sense small temperature changes. As an emerging high-temperature detection method, optical fiber high-temperature sensing technology has the advantages of small size, high accuracy, and strong resistance to environmental interference, and performs well in high-temperature detection. The optical fiber sensors working above 1400℃ are mainly sapphire optical fiber high-temperature sensors, which mainly include the following three structural types: sapphire optical fiber high-temperature sensors based on blackbody radiation cavities, but they have poor accuracy and insufficient high-temperature stability, and the blackbody cavity material and sapphire optical fiber material have poor high-temperature adaptability and are prone to breakage; sapphire optical fiber sensors based on fiber gratings have expensive manufacturing platforms and difficult processing, and when the temperature is higher than 1700℃, the grating structure is prone to degradation, resulting in sensor failure; sapphire optical fiber high-temperature sensors based on optical microcavities have high accuracy and sensitivity, simple structure, and low preparation cost, and are widely used in high-temperature detection.

[0003] However, sapphire fiber high-temperature sensors based on optical microcavities are currently difficult to use for temperature measurements above 1700°C. There are two main reasons for this: (1) Sapphire optical microcavities are usually fixed with high-temperature ceramic glue. At high temperatures, the expansion coefficients of the ceramic glue material and sapphire are inconsistent, resulting in slight changes in the position of the microcavity, which in turn reduces or even damages the sensing performance. (2) In the high-temperature section, the sapphire fiber used to transmit light in the probe must also be fixed with high-temperature ceramic glue. In an ultra-high temperature environment above 1500°C, the atomic diffusion rates of the sapphire material and the ceramic glue material increase sharply, resulting in modification of the sapphire fiber, which in turn causes a sharp increase in light transmission loss and makes the temperature probe unable to work properly.

[0004] Therefore, solving the above two problems will expand the upper limit of measurement temperature of sapphire fiber high-temperature sensor based on optical microcavity to near the melting point of sapphire, which is of great significance for practical applications. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and to propose a near-melting-point ultra-stable all-sapphire optical microcavity high-temperature sensor and a preparation method thereof for extreme environment applications. The purpose of the optical microcavity high-temperature sensor is to achieve glue-free packaging in the high-temperature zone, using a sapphire tube and a tail tube to form a protective fixing structure, and the sapphire tube is used to protect the all-sapphire optical microcavity high-temperature probe and fix the relative position of the sapphire optical fiber and the sapphire ferrule, thereby producing a sapphire optical fiber high-temperature probe that can work at a temperature above 1700°C near the sapphire melting point.

[0006] The first aspect of the present invention relates to an all-sapphire optical microcavity high temperature sensor, comprising a protective sleeve, a first ferrule, a multimode optical fiber, a sapphire optical fiber and a sapphire optical microcavity;

[0007] The sapphire optical microcavity comprises a second ferrule and a sapphire wafer, wherein the sapphire wafer is fixed to the end of the second ferrule by a non-adhesive bonding method; and the second ferrule is made of sapphire;

[0008] One end of the multimode optical fiber and the sapphire optical fiber are aligned and fixedly connected, and the connection between the multimode optical fiber and the sapphire optical fiber is suspended in the protective sleeve;

[0009] The other end of the sapphire optical fiber extends into the sapphire optical microcavity and is 50-100 μm away from the sapphire wafer and is perpendicular to the sapphire wafer;

[0010] The protective sleeve is sleeved on a portion of the outer surface of the sapphire optical microcavity, a portion of the multimode optical fiber and the outer surface of the sapphire optical fiber; wherein one end of the sapphire optical microcavity having the sapphire wafer is exposed to the outside of the protective sleeve.

[0011] Furthermore, the sapphire optical microcavity and sapphire optical fiber form a sapphire optical microcavity high-temperature probe, both of which are made of sapphire material, and the sapphire optical fiber has no glue contact, which can ensure the detection of high temperatures of 1700°C to 2000°C close to the melting point of sapphire.

[0012] Furthermore, the second ferrule and the sapphire wafer are connected by a method selected from carbon dioxide laser welding or high-temperature hot pressing bonding.

[0013] Furthermore, the protective sleeve includes a sapphire sleeve and a tail tube, wherein the sapphire sleeve is used to protect the sapphire optical microcavity high-temperature probe formed by the sapphire optical microcavity and the sapphire optical fiber and fix the relative position of the sapphire optical fiber and the second ferrule, and the tail tube protects the multimode optical fiber to prevent breakage.

[0014] Furthermore, the multimode optical fiber and the sapphire optical fiber are discharged and fused by an arc fusion splicer, and the fusion point is 5 mm to 15 mm away from one end of the first ferrule facing the sapphire optical microcavity.

[0015] Furthermore, the first core insert material is ceramic, and the tail pipe material is selected from one of the following: stainless steel, aluminum alloy, alumina ceramic and zirconia ceramic.

[0016] Furthermore, the multimode optical fiber and the first ferrule, the first ferrule and the tail tube, the tail tube and the sapphire sleeve, and the sapphire sleeve and the second ferrule are bonded with high-temperature ceramic glue, and the high-temperature ceramic glue has a temperature resistance of 2200°C.

[0017] Furthermore, the diameter of the sapphire wafer is between 300um and 3mm, the thickness is between 30μm and 200μm, and it is double-sided polished; the outer diameter of the second ferrule is between 1mm and 2.5mm, the inner diameter is between 100μm and 130μm, and both end faces are polished.

[0018] The sapphire optical fiber has a diameter between 75 μm and 125 μm, and a length between 15 cm and 200 cm; the multimode optical fiber has an outer diameter of 125 μm, and a core diameter between 62.5 μm and 105 μm.

[0019] The first ferrule matches the diameter of the tail tube, and the inner diameter of the first ferrule is between 125μm and 400μm; the inner diameter of the tail tube is between 1.3mm and 1.5mm; the length of the sapphire sleeve is between 15cm and 200cm, the inner diameter is between 2mm and 3mm, and the outer diameter is between 3mm and 10mm.

[0020] A second aspect of the present invention relates to a method for preparing an all-sapphire optical microcavity high temperature sensor, comprising:

[0021] Step 1: Grind both ends of the sapphire optical fiber flat, align the axis of the sapphire optical fiber with the multimode optical fiber, and then weld them by arc discharge;

[0022] Insert one end of the multimode optical fiber into the first ferrule, and use high-temperature ceramic glue to bond the first ferrule and the multimode optical fiber; then insert the connected first ferrule and the multimode optical fiber into the tail tube and bond them with high-temperature ceramic glue;

[0023] Step 2: aligning the axes of the second ferrule and the sapphire wafer and fixing them by adhesive-free bonding to form a full sapphire optical microcavity;

[0024] Step 3: inserting the sapphire optical fiber in the optical fiber material containing the tail tube, the first ferrule, the multimode optical fiber and the sapphire optical fiber prepared in step 1 into the all-sapphire optical microcavity prepared in step 2, and the end of the sapphire optical fiber not connected to the second ferrule is 50 to 100 μm away from the sapphire wafer and is perpendicular to the sapphire wafer;

[0025] The positions of the tail tube and the second ferrule are adjusted so that the axes of the tail tube and the second ferrule are aligned, and then a sapphire sleeve is sleeved on the outer surface of part of the tail tube and part of the second ferrule and fixed with high-temperature ceramic glue, thereby obtaining a preliminarily prepared all-sapphire optical microcavity high-temperature sensor; wherein the connection between the multimode optical fiber and the sapphire optical fiber is suspended in the sapphire sleeve, and the end of the all-sapphire optical microcavity with the sapphire wafer extends out of the sapphire sleeve;

[0026] Step 4: Place the all-sapphire optical microcavity high-temperature sensor prepared in step 3 into a high-temperature furnace for high-temperature static aging, with the temperature setting range being 1500°C to 1600°C and the holding time being 2 to 6 hours;

[0027] Step 5: subject the all-sapphire optical microcavity high-temperature sensor obtained in step 4 to high-temperature static aging to temperature cycle aging, with the temperature linearly increasing from 500°C to 1800°C at a rate of 5°C / min to 10°C / min, and then slowly cooling to about 500°C at a rate of less than 10°C / min; after the above temperature cycle is repeated for no less than 5 times, the preparation is completed.

[0028] Optionally, the step 2 specifically includes:

[0029] The second ferrule and the sapphire wafer are placed together with a high-temperature fixture in a high-temperature furnace. The high-temperature fixture applies a pressure of not less than 200 kPa, heats to 1200° C., and keeps the temperature for 52 hours to achieve bonding, thereby obtaining an all-sapphire optical microcavity.

[0030] Optionally, the step 2 specifically includes:

[0031] The second ferrule and the sapphire wafer are fixed on a high temperature resistant fixture, and the sapphire wafer and the ferrule are brought into close contact by the fixture to ensure axis alignment; a carbon dioxide laser light source is used to heat and melt the edge portion of the sapphire wafer and the second ferrule in contact, so that the edge portion is melted and bonded, thereby fixing the second ferrule and the sapphire wafer to be connected, thereby obtaining a full sapphire optical microcavity.

[0032] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0033] 1. The ultra-stable all-sapphire optical microcavity high-temperature sensor near the melting point provided by the present invention has a temperature sensitive element consisting of only a sapphire wafer, which has the advantages of high sensitivity, rapid response and stable optical interference performance; the sapphire ferrule and the sapphire wafer are fixed by a glue-free process to form an all-sapphire optical microcavity with good high-temperature consistency and stable temperature measurement performance;

[0034] 2. The high-temperature area of ​​the temperature probe is made of sapphire, including sapphire optical fiber for optical signal transmission, sapphire tube for overall protection and all-sapphire optical microcavity. The sapphire optical fiber has no contact with any glue, which avoids the great deterioration of transmission performance caused by high-temperature diffusion of impurity components and ensures ultra-stable detection of high temperatures of 1700℃ to 2000℃ near the melting point of sapphire.

[0035] 3. The present invention provides a method for manufacturing a near-melting-point ultra-stable all-sapphire optical microcavity high-temperature sensor. The all-sapphire optical microcavity is manufactured using a glue-free process, is suitable for mass production, and has good mechanical properties and consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is an axial cross-sectional view of the all-sapphire optical microcavity high temperature sensor described in the present invention.

[0037] In the figure:

[0038] 1: Tail tube 2: First ferrule 3: Multimode optical fiber

[0039] 4: Sapphire sleeve 5: Sapphire optical fiber 6: Second ferrule

[0040] 7: Sapphire wafer 8: High temperature ceramic glue DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The described specific embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0042] like Figure 1 As shown, a near-melting-point ultra-stable all-sapphire optical microcavity high-temperature sensor comprises a tail tube 1, a first ferrule 2, a multimode optical fiber 3, a sapphire sleeve 4 and a sapphire optical microcavity high-temperature probe.

[0043] The sapphire optical microcavity high temperature probe is composed of a sapphire optical fiber 5, a second ferrule 6 and a sapphire wafer 7, which constitute the high temperature region of the optical microcavity high temperature sensor. Since all components in the sapphire optical microcavity high temperature probe are made of sapphire, they have a high temperature expansion coefficient consistency, and the sapphire wafer 7, as a temperature sensitive element, has the advantages of high sensitivity, fast response and stable optical interference performance. The high temperature region of the sapphire optical microcavity high temperature probe in the present invention is all made of sapphire material, including sapphire optical fiber for optical signal transmission, sapphire sleeves for overall protection and all-sapphire optical microcavity. The sapphire optical fiber is completely free of any glue contact, which avoids the great transmission performance deterioration caused by the high temperature diffusion of impurity components, and ensures ultra-stable detection of high temperatures of 1700℃ to 2000℃ near the melting point of sapphire. One end of the sapphire optical fiber 5 is fixedly connected to the multimode optical fiber 3, and the outer surface of the other end of the sapphire optical fiber 5 is wrapped with a second core 6, which is vertically fixed to the sapphire wafer 7 and is 50 to 100 um away from the sapphire wafer, that is, the sapphire wafer 7 is fixed to the end of the second core 6 by high-temperature hot pressing bonding.

[0044] The sapphire sleeve 4 and the tail tube 1 form a protective fixing structure, wherein the sapphire sleeve 4 is used to protect the sapphire optical microcavity high-temperature probe and fix the relative position of the sapphire optical fiber 5 and the second ferrule 6, and the tail tube 1 protects the multimode optical fiber 3 to prevent breakage, and dissipates heat and cools the end where the first ferrule is located to prevent high-temperature damage to the multimode optical fiber 3.

[0045] The sapphire wafer 7 has a diameter of 1 mm, a thickness of 50 μm, and is polished on both sides; the second ferrule 6 is made of sapphire, has an outer diameter of 1.5 mm, an inner diameter of 125 μm, and has two end surfaces polished.

[0046] The outer surface of the multimode optical fiber 3 wraps the first ferrule 2 . The first ferrule 2 is made of ceramic material. The outer diameter of the first ferrule 2 is 1.25 mm and the inner diameter is 220 μm.

[0047] The multimode optical fiber 3 and the sapphire optical fiber 5 are discharged and fused by an arc fusion machine, and the fusion point is located at the front end of the first core 2 (i.e., the end facing the sapphire optical microcavity high-temperature probe), 5mm to 15mm away from the front end of the first core 2. Part of the outer surface of the first core 2 wraps the tail tube 1, and the outer diameter of the first core 2 is adapted to the inner diameter of the tail tube. Specifically, the outer diameter of the first core 2 is 1.25mm, and the inner diameter is 220μm; the inner diameter of the tail tube 1 is 1.3mm, and the outer diameter is 1.9mm, and the manufacturing material is zirconia ceramic.

[0048] The sapphire sleeve 4 has a length of 15 cm, an inner diameter of 2 mm, and an outer diameter of 5 mm. The sapphire sleeve 4 is sleeved on the outside of part of the tail tube 1 and part of the second ferrule 6, and the sapphire sleeve 4, the tail tube 1 and the second ferrule 6 are bonded with high-temperature ceramic glue 8. Part of the second ferrule 6 and the sapphire wafer 7 protrude from the sapphire sleeve 4, and part of the multimode optical fiber 3 and the sapphire optical fiber 5 located inside the sapphire optical microcavity high-temperature probe are suspended.

[0049] The high temperature ceramic glue 8 is used to bond and fix the multimode optical fiber 3 and the first ferrule 2, the first ferrule 2 and the tail tube 1, the tail tube 1 and the sapphire sleeve 4, and the sapphire sleeve 4 and the second ferrule 6, and the high temperature ceramic glue 8 is temperature resistant to 2200°C.

[0050] When in use, the all-sapphire optical microcavity high temperature sensor is connected to the LED light source and the spectrometer through the optical fiber jumper from one end of the multimode optical fiber 3. The light emitted by the LED light source enters the all-sapphire optical microcavity high temperature sensor through the optical fiber jumper, and is emitted from the end face of the sapphire optical fiber 5 close to the sapphire wafer 7 through the fusion point of the multimode optical fiber 3 and the sapphire optical fiber 5. The divergent light irradiates the two reflection surfaces of the sapphire wafer 7 to form two beams of reflected light carrying optical path difference information; the two beams of reflected light are coupled to the sapphire optical fiber for output, forming a Fabry-Perot interference signal, and the optical path difference between the two beams of reflected light changes with temperature, thereby causing changes in the interference signal; the interference signal is transmitted back to the spectrometer through the sapphire optical fiber, the multimode optical fiber, the optical fiber jumper, and then transmitted back to the spectrometer.

[0051] The method for preparing the all-sapphire optical microcavity high temperature sensor comprises the following steps:

[0052] Step 1: Cut the sapphire optical fiber 5 of the required length, use the optical fiber cutter to cut the multimode optical fiber 3 of the required length, place the sapphire optical fiber 5 on the optical fiber polishing platform, and ensure that the optical fiber end face of the sapphire optical fiber 5 is perpendicular to the polishing plane; turn on the power, manually push the sapphire optical fiber 5 to make it contact with the polishing sandpaper, and stop after grinding the two ends of the sapphire optical fiber 5 flat with the grinder;

[0053] Then, the sapphire optical fiber 5 is fused with one end of the multimode optical fiber 3 by arc discharge. Specifically, the process includes: fixing the polished sapphire optical fiber 5 and the multimode optical fiber 3 in the left and right clamps of the large optical fiber fusion platform, adjusting the relative positions of the optical fiber end faces and ensuring the axis alignment; setting appropriate power and discharging to heat the multimode optical fiber 3 to a molten state, using a stepper motor to control the clamp to axially move the sapphire optical fiber 5, and controlling the stepper motor's advancement amount to make the sapphire optical fiber and the multimode optical fiber overlap and then stop; aligning the axis of the sapphire optical fiber 5 and the multimode optical fiber 3 after fixation.

[0054] After the fusion splicing is completed, the multimode optical fiber 3 is inserted into the first core 2, and the first core 2 and the multimode optical fiber 3 are bonded using high-temperature ceramic glue 8; and the fusion splicing point between the multimode optical fiber 3 and the sapphire optical fiber 5 is 5mm to 15mm away from the front end of the first core 2 (i.e., the end facing the sapphire optical microcavity high-temperature probe); and then the connected first core 2 and multimode optical fiber 3 are inserted into the tail tube 1 and bonded using the high-temperature ceramic glue 8.

[0055] Step 2: Fix the second ferrule 6 and the sapphire wafer 7 on a high-temperature resistant fixture, and use the fixture to make the sapphire wafer and the sapphire ferrule in close contact to ensure the axis alignment; put the second ferrule 6 and the sapphire wafer 7 together with the high-temperature fixture into a high-temperature furnace, apply a pressure of not less than 200 kPa with the high-temperature fixture, heat to 1200°C, and keep warm for 52 hours to achieve bonding, thereby obtaining a full sapphire optical microcavity.

[0056] Step 3: insert the sapphire optical fiber 5 in the optical fiber material containing the tail tube 1, the first ferrule 2, the multimode optical fiber 3 and the sapphire optical fiber 5 prepared in step 1 into the full sapphire optical microcavity prepared in step 2, and fine-tune the positions of the tail tube 1 and the second ferrule 6 so that the axes of the tail tube 1 and the second ferrule 6 are aligned to achieve high optical coupling power and good interference signal; then sleeve the sapphire sleeve 4 on the outer surface of part of the tail tube 1 and part of the second ferrule 6, and fix the tail tube 1, the sapphire sleeve 4 and the second ferrule 6 with the high-temperature ceramic glue 8, so as to obtain a full sapphire optical microcavity high-temperature sensor;

[0057] Step 4: Place the prepared all-sapphire optical microcavity high temperature sensor into a high temperature furnace for high temperature static aging, with the temperature setting range of 1500°C to 1600°C and the holding time of 2 to 6 hours;

[0058] Step 5: subject the all-sapphire optical microcavity high-temperature sensor obtained in step 4 to high-temperature static aging to temperature cycle aging, with the temperature linearly increasing from 500°C to 1800°C at a rate of 5°C / min to 10°C / min, and then slowly cooling to about 500°C at a rate of less than 10°C / min; after the above temperature cycle is repeated for no less than 5 times, the preparation is completed.

[0059] In the method for preparing the all-sapphire optical microcavity high temperature sensor described in this embodiment, the all-sapphire optical microcavity prepared in step 2 is manufactured using a glue-free process, which is suitable for mass production and has good mechanical properties and consistency.

[0060] Example 2

[0061] An all-sapphire optical microcavity high temperature sensor is basically the same as the all-sapphire optical microcavity high temperature sensor described in Example 1. Only the differences are described below, and the same parts are not repeated again.

[0062] The sapphire wafer 7 is fixed to the ends of the second ferrule 6 and the sapphire optical fiber 5 in the same direction by means of carbon dioxide laser welding. Moreover, only step 2 in the preparation method of the all-sapphire optical microcavity high temperature sensor is different from that in embodiment 1, and step 2 is specifically as follows:

[0063] Step 2: Fix the second ferrule 6 and the sapphire wafer 7 on a high-temperature resistant fixture, and use the fixture to make the sapphire wafer and the sapphire ferrule tightly contact to ensure the axis alignment; use a carbon dioxide laser light source to heat and melt the edge part of the sapphire wafer 7 and the second ferrule 6 that are in contact, so that they melt and bond, thereby fixing the second ferrule 6 and the sapphire wafer 7.

[0064] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. An all-sapphire optical microcavity high temperature sensor, characterized in that It comprises a protective sleeve, a first ferrule (2), a multimode optical fiber (3), a sapphire optical fiber (5) and a sapphire optical microcavity; The sapphire optical microcavity comprises a second ferrule (6) and a sapphire wafer (7), wherein the sapphire wafer (7) is fixed to the end of the second ferrule (6) by means of adhesive-free bonding; and the second ferrule (6) is made of sapphire; One end of the multimode optical fiber (3) and the sapphire optical fiber (5) are aligned and fixedly connected, and the connection between the multimode optical fiber (3) and the sapphire optical fiber (5) is suspended in the protective sleeve; The other end of the sapphire optical fiber (5) extends into the interior of the sapphire optical microcavity and is 50 to 100 μm away from the sapphire wafer (7) and is perpendicular to the sapphire wafer (7); The protective sleeve is sleeved on a portion of the outer surface of the sapphire optical microcavity, a portion of the multimode optical fiber (3) and the outer surface of the sapphire optical fiber (5); wherein one end of the sapphire optical microcavity having the sapphire wafer (7) is exposed to the outside of the protective sleeve.

2. The all-sapphire optical microcavity high temperature sensor according to claim 1, characterized in that: The sapphire optical microcavity and the sapphire optical fiber (5) form a sapphire optical microcavity high-temperature probe, both of which are made of sapphire material, and the sapphire optical fiber (5) has no glue contact, which can ensure the detection of high temperatures of 1700°C to 2000°C close to the melting point of sapphire; and the connection method of the second ferrule (6) and the sapphire wafer (7) is selected from carbon dioxide laser welding or high-temperature hot pressing bonding.

3. The all-sapphire optical microcavity high temperature sensor according to claim 2, characterized in that: The protective sleeve comprises a sapphire sleeve (4) and a tail tube (1), wherein the sapphire sleeve (4) is used to protect a sapphire optical microcavity high-temperature probe formed by the sapphire optical microcavity and the sapphire optical fiber (5) and to fix the relative position of the sapphire optical fiber (5) and the second ferrule (6), and the tail tube (1) protects the multimode optical fiber (3) to prevent breakage.

4. The all-sapphire optical microcavity high temperature sensor according to claim 2, characterized in that: The multimode optical fiber (3) and the sapphire optical fiber (5) are discharged and fused by an arc fusion splicer, and the fusion point is 5 mm to 15 mm away from one end of the first ferrule (2) facing the sapphire optical microcavity.

5. The all-sapphire optical microcavity high temperature sensor according to claim 2, characterized in that: The material of the first insert (2) is ceramic; the material of the tail pipe (1) is selected from one of the following: stainless steel, aluminum alloy, alumina ceramic and zirconium oxide ceramic.

6. The all-sapphire optical microcavity high temperature sensor according to claim 2, characterized in that: The multimode optical fiber (3) and the first ferrule (2), the first ferrule (2) and the tail tube (1), the tail tube (2) and the sapphire sleeve (4), and the sapphire sleeve (4) and the second ferrule (6) are bonded using high-temperature ceramic glue (8), and the high-temperature ceramic glue (8) is temperature-resistant to 2200°C.

7. The all-sapphire optical microcavity high temperature sensor according to claim 2, characterized in that: The diameter of the sapphire wafer (7) is between 300 μm and 3 mm, the thickness is between 30 μm and 200 μm, and both sides are polished; the outer diameter of the second ferrule (6) is between 1 mm and 2.5 mm, the inner diameter is between 100 μm and 130 μm, and both end faces are polished; The sapphire optical fiber (5) has a diameter between 75 μm and 125 μm, and a length between 15 cm and 200 cm; the multimode optical fiber (3) has an outer diameter of 125 μm, and a core diameter between 62.5 μm and 105 μm; The first ferrule (2) matches the diameter of the tail tube (1), the inner diameter of the first ferrule is between 125 μm and 400 μm; the inner diameter of the tail tube is between 1.3 mm and 1.5 mm; the length of the sapphire sleeve (4) is between 15 cm and 200 cm, the inner diameter is between 2 mm and 3 mm, and the outer diameter is between 3 mm and 10 mm.

8. The method for preparing the all-sapphire optical microcavity high temperature sensor according to claim 2, comprising: Step 1: grinding both ends of the sapphire optical fiber (5) flat, aligning the axes of the sapphire optical fiber (5) and the multimode optical fiber (3), and then welding them by arc discharge; Inserting one end of the multimode optical fiber (3) into the first ferrule (2), and bonding the first ferrule (2) and the multimode optical fiber (3) using a high-temperature ceramic glue (8); then inserting the connected first ferrule (2) and the multimode optical fiber (3) into the tail tube (1) and bonding them using a high-temperature ceramic glue (8); Step 2: aligning the axes of the second ferrule (6) and the sapphire wafer (7) and fixing them by adhesive-free bonding to form a full sapphire optical microcavity; Step 3: inserting the sapphire optical fiber (5) in the optical fiber material comprising the tail tube (1), the first ferrule (2), the multimode optical fiber (3) and the sapphire optical fiber (5) prepared in step 1 into the all-sapphire optical microcavity prepared in step 2, and the end of the sapphire optical fiber (5) not connected to the second ferrule is 50 to 100 um away from the sapphire wafer (7) and is perpendicular to the sapphire wafer (7); The positions of the tail tube (1) and the second ferrule (6) are adjusted so that the axes of the tail tube (1) and the second ferrule are aligned, and then a sapphire sleeve (4) is sleeved on the outer surface of part of the tail tube (1) and part of the second ferrule (6) and fixed with a high-temperature ceramic glue (8), thereby obtaining a preliminarily prepared all-sapphire optical microcavity high-temperature sensor; wherein the connection between the multimode optical fiber (3) and the sapphire optical fiber (5) is suspended in the sapphire sleeve (4), and the end of the all-sapphire optical microcavity having the sapphire wafer (7) extends out of the sapphire sleeve (4); Step 4: Place the all-sapphire optical microcavity high-temperature sensor prepared in step 3 into a high-temperature furnace for high-temperature static aging, with the temperature setting range being 1500°C to 1600°C and the holding time being 2 to 6 hours; Step 5: subject the all-sapphire optical microcavity high-temperature sensor obtained in step 4 to high-temperature static aging to temperature cycle aging, with the temperature linearly increasing from 500°C to 1800°C at a rate of 5°C / min to 10°C / min, and then slowly cooling to about 500°C at a rate of less than 10°C / min; after the above temperature cycle is repeated for no less than 5 times, the preparation is completed.

9. The all-sapphire optical microcavity high temperature sensor according to claim 8, characterized in that: The step 2 specifically includes: The second ferrule (6) and the sapphire wafer (7) are placed together with a high-temperature fixture in a high-temperature furnace. The high-temperature fixture applies a pressure of not less than 200 kPa, and is heated to 1200° C. and kept warm for 52 hours to achieve bonding, thereby obtaining an all-sapphire optical microcavity.

10. The all-sapphire optical microcavity high temperature sensor according to claim 8, characterized in that: The step 2 specifically includes: The second ferrule (6) and the sapphire wafer (7) are fixed on a high temperature resistant fixture, and the sapphire wafer and the ferrule are brought into close contact by means of the fixture to ensure axis alignment; a carbon dioxide laser light source is used to heat and melt the edge portion of the sapphire wafer (7) and the second ferrule (6) in contact, so that the edge portion is melted and bonded, thereby fixing the second ferrule (6) and the sapphire wafer (7), thereby obtaining a full sapphire optical microcavity.

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