Microsphere laser and preparation method thereof

Abstract

The invention relates to a microsphere laser and a preparation method thereof, the microsphere laser comprises an optical fiber, microspheres and a pump light source, the microspheres are erbium-ytterbium co-doped microspheres containing erbium ions and ytterbium ions, the number of the microspheres is two, the microspheres are respectively a first microsphere and a second microsphere, the diameter of the first microsphere is smaller than that of the second microsphere, and the pump light source is arranged between the optical fiber and the pump light source. A conical area which is gradually shrunk from the two ends to the middle is arranged at the position, close to the center, of the optical fiber, the first end of the conical area is close to the pump light source, the second end of the conical area is far away from the pump light source, and the two microspheres are located on the upper side and the lower side of the conical area of the optical fiber respectively. The first microsphere is disposed proximate a first end of the tapered region to couple with a first end of the optical fiber, and the second microsphere is disposed proximate a second end of the tapered region to couple with a second end of the optical fiber. Through the arrangement form of the two microspheres, the optical fiber and the pump light source, the threshold value is reduced.

Description

Technical Field

[0001] The invention relates to a microsphere laser and a preparation method thereof. Background Art

[0002] Low-threshold lasers have broad application prospects in micro-nano optics, integrated optical devices, and micro-sensors. In particular, low-threshold lasers based on microcavities have been widely studied due to their unique characteristics and diverse applications. 1.5μm band lasers are eye-safe and have important application value in civil and military fields such as medicine, precision ranging, laser radar, and target recognition. 3+ / Yb 3+ Co-doping gain materials to prepare gallery mode (WGM) microcavities, especially microspheres, is considered to be an ideal choice for constructing low-threshold and narrow-linewidth lasers in the 1.5μm band.

[0003] In the current method of preparing 1.5μm band microsphere lasers, the oscillation threshold is as high as 60μW or more due to the low pumping efficiency. Even if glass-coated silica microspheres are prepared, the minimum laser threshold is still 30μW, and the coating material shows instability under long-term continuous optical pumping.

[0004] Therefore, further improvements to microsphere lasers are needed. Summary of the invention

[0005] The first technical problem to be solved by the present invention is to provide a microsphere laser with a lowered laser threshold in view of the current status of the above-mentioned prior art.

[0006] The second technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned microsphere laser.

[0007] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a microsphere laser, comprising:

[0008] optical fiber;

[0009] A microsphere, which is disposed on the outer peripheral wall of the optical fiber and is coupled to the optical fiber;

[0010] A pump light source is fixed to the first end of the left and right ends of the optical fiber, so that the laser is input from the first end of the optical fiber and output from the second end of the left and right ends of the optical fiber;

[0011] The invention is characterized in that the microsphere is an erbium-ytterbium co-doped microsphere containing erbium ions and ytterbium ions, and there are two of them, namely a first microsphere and a second microsphere, the diameter of the first microsphere is smaller than the diameter of the second microsphere, the position near the center of the optical fiber has a tapered area that gradually shrinks from both ends to the middle, the first end of the tapered area is close to the pump light source, and the second end of the tapered area is far away from the pump light source, the two microspheres are respectively located on the upper and lower sides of the tapered area of ​​the optical fiber, the first microsphere is arranged near the first end of the tapered area to couple with the first end of the optical fiber, and the second microsphere is arranged near the second end of the tapered area to couple with the second end of the optical fiber.

[0012] Preferably, the first microsphere is located above the conical region, and the second microsphere is located below the conical region. In addition, the first microsphere may be located below the conical region, and the second microsphere may be located above the conical region.

[0013] Preferably, the tangent line at the position where the conical region contacts the first microsphere is parallel to the equatorial plane of the first microsphere, and the tangent line at the position where the conical region contacts the second microsphere is parallel to the equatorial plane of the second microsphere. The microsphere and optical fiber cone coupling is realized by near-field coupling. The evanescent wave is first generated by other dielectric objects, and then the microsphere cavity is coupled with it, which can effectively couple the external light wave into the microsphere cavity. Therefore, if the relative position of the microsphere and the optical fiber deviates at this time, that is, it is not parallel, the efficiency of the evanescent wave coupling into the microsphere is affected, thereby increasing the threshold of laser emission.

[0014] Specifically, the optical fiber includes two straight sections, the tapered region is located between the two straight sections, and the left and right ends of the tapered region are respectively connected to the straight sections on the corresponding sides.

[0015] Preferably, the optical fiber is a quartz optical fiber, and the pump light source is a 976nm semiconductor laser.

[0016] In order to observe the laser output from the second end of the optical fiber, the second end of the optical fiber is used to connect to a spectrometer.

[0017] Preferably, the microspheres are erbium-ytterbium co-doped phosphate glass microspheres.

[0018] The technical solution adopted by the present invention to solve the above second technical problem is: a method for preparing the microsphere laser, characterized in that it includes the following steps in sequence:

[0019] 1) preparing erbium-ytterbium co-doped microspheres doped with erbium ions and ytterbium ions;

[0020] 2) Preparing an optical fiber with a tapered region: taking a section of communication optical fiber, removing the coating layer from the middle part of the communication optical fiber and wiping it clean to obtain a semi-bare optical fiber; then fixing the two ends of the semi-bare optical fiber on a motor, using an oxyhydrogen flame electrically controlled fire sweeping gun head to move left and right along the optical fiber, repeatedly heating the central area of ​​the semi-bare optical fiber, and gradually stretching the motor controlled by a computer program to prepare an optical fiber with a tapered region; after the tapered optical fiber is drawn, the upward movement of the U-shaped bracket is achieved through a three-dimensional platform, so that the two ends of the optical fiber are respectively in contact with the two ends of the U-shaped bracket, and a reagent that can fix the two ends of the optical fiber to the corresponding ends of the U-shaped bracket is respectively added at the two contact positions;

[0021] 3) Attach one end of the optical fiber to the inner surface of the glass tube by ultraviolet curing glue, use the other end of the optical fiber to pick out two erbium-ytterbium co-doped microspheres in turn, and then fix the two erbium-ytterbium co-doped microspheres at the corresponding positions of the optical fiber, and then insert the glass tube into the gap of the three-dimensional adjustment frame. At this time, the glass tube is fixed on a rotating shaft that can rotate 360 ​​degrees; fix the rotating shaft on the three-dimensional platform, and adjust the three-dimensional platform so that the two erbium-ytterbium co-doped microspheres are respectively coupled with the corresponding ends of the tapered optical fiber, thereby obtaining a microsphere laser.

[0022] Preferably, the preparation method of the erbium-ytterbium co-doped microspheres in step 1) comprises the following steps in sequence:

[0023] S1. Putting phosphate glass doped with erbium ions and ytterbium ions into a grinding dish and grinding it into glass powder, and selecting a punch frame standard sieve with a corresponding aperture according to actual needs to screen the glass powder to obtain glass powder of a desired size;

[0024] S2. After the screened glass powder is mixed evenly, it is collected in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine for repeated shaking, and the anhydrous ethanol in the beaker is continuously replaced for cleaning, and then the cleaned powder is subjected to high-temperature drying treatment;

[0025] S3, transferring the dried powder to a funnel-shaped glass device with a switch valve, placing the glass device at the feed inlet above the high-temperature vertical furnace, connecting the collecting tube to the microsphere outlet of the high-temperature vertical furnace, heating the furnace chamber of the high-temperature vertical furnace, and after the furnace chamber reaches a preset temperature, filling with sufficient inert protective gas, opening the switch valve of the glass device to allow the glass powder to enter the furnace chamber through the feed inlet;

[0026] S4. After being subjected to high temperature and surface tension, the glass powder in the furnace cavity finally falls into the collecting tube and forms solidified glass microspheres of the required size.

[0027] In order to clean the microspheres, after step S4, the microspheres are placed in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine to be repeatedly shaken and the anhydrous ethanol in the beaker is continuously replaced for cleaning.

[0028] Compared with the prior art, the advantages of the present invention are: the microsphere laser is provided with microspheres on the upper and lower sides of the conical region, the first microsphere is close to the first end of the conical region adjacent to the pump light source, and the second microsphere is close to the second end of the conical region away from the pump light source. The second microsphere transfers energy to the first microsphere, and part of the energy is transferred to the first microsphere, so that the laser mode in the first microsphere is excited and strengthened, thereby achieving a low threshold; and the presence of the second microsphere weakens various losses of the first microsphere, such as the second microsphere blocks part of the scattered light from the surface of the first microsphere, thereby reducing the scattering loss of the first microsphere, the second microsphere can absorb part of the light energy transmitted in the first microsphere, reducing the absorption loss of the first microsphere, and the second microsphere can absorb and convert part of the energy, so as not to let the part of the energy leave the first microsphere in the form of radiated light, so that more light energy remains in the first microsphere, further enabling the microsphere laser to obtain a low laser threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structural principle of a microsphere laser having double microspheres according to an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the assembly structure of the optical fiber and the glass tube in an embodiment of the present invention;

[0031] Figure 3 is a single-mode laser characteristic diagram of only the first microsphere;

[0032] Figure 4 is the single-mode laser characteristic diagram of only the second microsphere;

[0033] Figure 5 for Figure 1 Single-mode laser characteristic diagram;

[0034] Figure 6 for Figure 1 Cascade laser characteristics diagram. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to the accompanying drawings.

[0036] like Figure 1As shown, the microsphere laser of this embodiment includes an optical fiber 1, a microsphere and a pump light source 5. The pump light source 5 is fixed to the first end of the left and right ends of the optical fiber 1, so that the laser is input from the first end of the optical fiber 1 and output through the second end of the left and right ends of the optical fiber 1. The second end of the optical fiber 1 is used to connect to a spectrometer. The spectrometer is used to observe the generated laser.

[0037] In this embodiment, the pump light source 5 is a 976nm semiconductor laser. The optical fiber 1 is a quartz optical fiber, and the optical fiber 1 includes a tapered region 11 and a straight section 12. There are two straight sections 12, and the tapered region 11 is located near the center of the optical fiber 1, and gradually shrinks from both ends to the middle. The tapered region 11 is located between the two straight sections 12, and the left and right ends of the tapered region 11 are respectively connected to the straight sections 12 on the corresponding sides. The first end of the tapered region 11 is close to the pump light source 5, and the second end of the tapered region 11 is far away from the pump light source 5.

[0038] The microspheres are arranged on the outer peripheral wall of the optical fiber 1 and are coupled with the optical fiber 1. In the present embodiment, the microspheres are fixed by the sticky ball method, such as by sticking the microspheres on the optical fiber through the ultraviolet glue 7. The aforementioned microspheres are erbium-ytterbium co-doped microspheres containing erbium ions and ytterbium ions, specifically erbium-ytterbium co-doped phosphate glass microspheres. There are two aforementioned microspheres, namely the first microsphere 3 and the second microsphere 4. The diameter of the first microsphere 3 is smaller than the diameter of the second microsphere 4. The two microspheres are respectively located on the upper and lower sides of the tapered region 11 of the optical fiber 1. The first microsphere 3 is arranged near the first end of the tapered region 11 to couple with the first end of the optical fiber 1, and the second microsphere 4 is arranged near the second end of the tapered region 11 to couple with the second end of the optical fiber 1. In the present embodiment, the first microsphere 3 is located above the tapered region 11, and the second microsphere 4 is located below the tapered region 11. In addition, the tangent line at the contact position between the conical region 11 and the first microsphere 3 is parallel to the equatorial plane of the first microsphere 3 , and the tangent line at the contact position between the conical region 11 and the second microsphere 4 is parallel to the equatorial plane of the second microsphere 4 .

[0039] The preparation method of the microsphere laser comprises the following steps in sequence:

[0040] 1) preparing erbium-ytterbium co-doped microspheres doped with erbium ions and ytterbium ions;

[0041] 2) Prepare an optical fiber 1 with a tapered region 11: take a section of communication optical fiber 1, remove the coating from the middle part of the communication optical fiber 1 and wipe it clean to obtain a semi-bare optical fiber 1; then fix the two ends of the semi-bare optical fiber 1 on a motor, use an oxyhydrogen flame electrically controlled fire sweeping gun head to move left and right along the optical fiber 1, repeatedly heat the central area of ​​the semi-bare optical fiber 1, and gradually stretch the motor controlled by a computer program to prepare an optical fiber 1 with a tapered region 11; after the tapered optical fiber 1 is drawn, the upward movement of the U-shaped bracket is achieved through a three-dimensional platform, so that the two ends of the optical fiber 1 are respectively in contact with the two ends of the U-shaped bracket, and a reagent that can fix the two ends of the optical fiber 1 to the corresponding ends of the U-shaped bracket is added at the two contact positions, and the reagent is salicylic acid; the structure of the aforementioned U-shaped bracket and the installation method with the optical fiber 1 are specifically referred to in the patent application number CN201810116351.7, entitled "A Holmium and Ytterbium Co-doped Microsphere Cavity Laser and Preparation Method" Figure 2 In this embodiment, the diameter of the tapered region of the optical fiber 1 is 1.05 um;

[0042] 3) Attach one end of the optical fiber 1 to the inner surface of the glass tube 6 by UV curing glue, and pick out two erbium-ytterbium co-doped microspheres with good sphericity and smooth surface from the other end of the optical fiber 1 in turn, and then paste the two erbium-ytterbium co-doped microspheres to the corresponding positions of the optical fiber 1, and then insert the glass tube into the gap of the three-dimensional adjustment frame. At this time, the glass tube is fixed on a rotating shaft that can rotate 360°; fix the rotating shaft on the three-dimensional platform, and the rotating shaft rotates under the drive of the three-dimensional platform; adjust the three-dimensional platform so that the two erbium-ytterbium co-doped microspheres are respectively coupled with the corresponding ends of the tapered optical fiber 1, so as to obtain a microsphere laser. Under a microscope, by adjusting the angle of the three-dimensional platform, the diameters of the two microspheres are parallel to the tangents at the contact points of the corresponding positions of the tapered area; at this time, a 976nm laser is used as a pump light source, input from the first end of the optical fiber, and a laser of about 1.5μm is output from the second end. By adjusting the coupling by adjusting the three-dimensional platform as mentioned above, single-mode lasers and multi-mode lasers can be obtained. The characteristics of single-mode lasers are as follows: Figure 5 shown.

[0043] Depend on Figure 5 It can be seen that the laser power of the microsphere laser with the first microsphere and the second microsphere is significantly reduced compared with that of the microsphere laser with only a single microsphere (i.e., one of the first microsphere and the second microsphere), that is, the laser threshold is reduced. Figure 6 It can be seen that the microsphere laser having the first microsphere and the second microsphere obtains two types of lasers, namely, cascade lasers.

[0044] The preparation method of the erbium-ytterbium co-doped microspheres in step 1) above includes the following steps:

[0045] S1. Put phosphate glass doped with erbium ions and ytterbium ions into a grinding dish and grind it into glass powder. Select a punch frame standard sieve with a corresponding aperture according to actual needs to screen the glass powder to obtain glass powder of a desired size. In this embodiment, the diameter of the microspheres is 50 μm-200 μm.

[0046] S2. After the screened glass powder is mixed evenly, it is collected in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine for repeated shaking, and the anhydrous ethanol in the beaker is continuously replaced for cleaning, and then the cleaned powder is subjected to high-temperature drying treatment;

[0047] S3, transferring the dried powder to a funnel-shaped glass device with a switch valve, placing the glass device at the feed inlet above the high-temperature vertical furnace, connecting the collecting tube to the microsphere outlet of the high-temperature vertical furnace, heating the furnace chamber of the high-temperature vertical furnace, and after the furnace chamber reaches a preset temperature, filling with sufficient inert protective gas, opening the switch valve of the glass device to allow the glass powder to enter the furnace chamber through the feed inlet;

[0048] S4. After being subjected to high temperature and surface tension, the glass powder in the furnace cavity finally falls into the collection tube and forms solidified glass microspheres of the required size. The microspheres are then placed in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine for repeated shaking and continuous replacement of anhydrous ethanol in the beaker for cleaning.

[0049] The above-mentioned anhydrous ethanol is anhydrous ethanol with a high purity of 99.9%.

[0050] The microsphere laser has a lower threshold value from the following two perspectives:

[0051] 1. Laser mode (subjective): When the second microsphere 4 approaches the first microsphere 3, the second microsphere 4 transfers energy to the first microsphere 3 (it is known that the first microsphere 3 has a lower threshold. Due to the wave nature of light, light will seek the path with the lowest energy, that is, the light energy is more likely to be concentrated on the first microsphere 3), and part of the energy is transmitted to the first microsphere 3, so that the laser mode in the first microsphere 3 is excited and strengthened, thereby achieving a low threshold.

[0052] 2. Loss mode (objective):

[0053] For scattering loss, the second microsphere 4 can be regarded as a "shield" for the first microsphere 3, blocking part of the scattered light from being scattered from the surface of the first microsphere 3, thereby reducing the scattering loss of the first microsphere 3. For absorption loss, the second microsphere 4 has a strong absorption capacity and can absorb part of the light energy transmitted in the first microsphere 3, reducing the absorption loss of the first microsphere 3. For radiation loss, the second microsphere 4 can absorb and convert part of the energy instead of letting this part of the energy leave the first microsphere 3 in the form of radiant light, so that more light energy remains in the first microsphere 3. In short, the presence of the second microsphere 4 weakens all kinds of losses of the first microsphere 3 and reduces the total loss of the first microsphere 3. The closer the distance, the lower the total loss, so that its laser mode can be excited at a lower power threshold.

[0054] This embodiment uses a 976nm laser as a pump light source, which is input from the first end of the tapered optical fiber and forms a very strong evanescent wave in the tapered region of the tapered optical fiber. The present invention uses a tapered optical fiber to effectively couple with two erbium-ytterbium co-doped microspheres, and the evanescent wave of the 976nm laser is coupled into the microspheres, exciting the ytterbium ions in the microspheres, and the ytterbium ions, as sensitizers, absorb the energy of the 976nm laser and transfer it to the erbium ions, thereby generating a laser near 1.5μm and outputting from the second end of the tapered optical fiber.

[0055] In the specification and claims of the present invention, terms indicating directions, such as "front", "rear", "up", "down", "left", "right", "side", "top", "bottom", etc., are used to describe various exemplary structural parts and elements of the present invention, but these terms are used here only for the purpose of convenience of description and are determined based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in the present invention can be arranged in different directions, these terms indicating directions are only used as explanations and should not be regarded as limitations. For example, "up" and "down" are not necessarily limited to directions opposite to or consistent with the direction of gravity.

Claims

1. A microsphere laser comprising: optical fiber; A microsphere, which is disposed on the outer peripheral wall of the optical fiber and is coupled to the optical fiber; A pump light source is fixed to the first end of the left and right ends of the optical fiber, so that the laser is input from the first end of the optical fiber and output from the second end of the left and right ends of the optical fiber; It is characterized in that The microsphere is an erbium-ytterbium co-doped microsphere containing erbium ions and ytterbium ions, and there are two of them, namely a first microsphere and a second microsphere. The diameter of the first microsphere is smaller than the diameter of the second microsphere. The optical fiber has a tapered area near the center that gradually shrinks from both ends to the middle. The first end of the tapered area is close to the pump light source, and the second end of the tapered area is far away from the pump light source. The two microspheres are respectively located on the upper and lower sides of the tapered area of ​​the optical fiber. The first microsphere is arranged near the first end of the tapered area to couple with the first end of the optical fiber, and the second microsphere is arranged near the second end of the tapered area to couple with the second end of the optical fiber.

2. The microsphere laser according to claim 1, Features: The first microsphere is located above the conical region, and the second microsphere is located below the conical region.

3. The microsphere laser according to claim 1, Features: The tangent line at the contact position between the conical region and the first microsphere is parallel to the equatorial plane of the first microsphere, and the tangent line at the contact position between the conical region and the second microsphere is parallel to the equatorial plane of the second microsphere.

4. The microsphere laser according to claim 1, Features: The optical fiber includes two straight sections, the tapered area is located between the two straight sections, and the left and right ends of the tapered area are respectively connected to the straight sections on the corresponding sides.

5. The microsphere laser according to claim 1, Features: The optical fiber is a quartz optical fiber, and the pump light source is a 976nm semiconductor laser.

6. The microsphere laser according to claim 1, Features: The second end of the optical fiber is used to connect to a spectrometer.

7. The microsphere laser according to claim 1, Features: The microspheres are erbium-ytterbium co-doped phosphate glass microspheres.

8. A method for preparing the microsphere laser according to any one of claims 1 to 6, It is characterized in that The following steps are included in sequence: 1) preparing erbium-ytterbium co-doped microspheres doped with erbium ions and ytterbium ions; 2) Preparing an optical fiber with a tapered region: taking a section of communication optical fiber, removing the coating layer from the middle part of the communication optical fiber and wiping it clean to obtain a semi-bare optical fiber; then fixing the two ends of the semi-bare optical fiber on a motor, using an oxyhydrogen flame electrically controlled fire sweeping gun head to move left and right along the optical fiber, repeatedly heating the central area of ​​the semi-bare optical fiber, and gradually stretching the motor controlled by a computer program to prepare an optical fiber with a tapered region; after the tapered optical fiber is drawn, the upward movement of the U-shaped bracket is achieved through a three-dimensional platform, so that the two ends of the optical fiber are respectively in contact with the two ends of the U-shaped bracket, and a reagent that can fix the two ends of the optical fiber to the corresponding ends of the U-shaped bracket is respectively added at the two contact positions; 3) Attach one end of the optical fiber to the inner surface of the glass tube by ultraviolet curing glue, use the other end of the optical fiber to pick out two erbium-ytterbium co-doped microspheres in turn, and then fix the two erbium-ytterbium co-doped microspheres at the corresponding positions of the optical fiber, and then insert the glass tube into the gap of the three-dimensional adjustment frame. At this time, the glass tube is fixed on a rotating shaft that can rotate 360 ​​degrees; fix the rotating shaft on the three-dimensional platform, and adjust the three-dimensional platform so that the two erbium-ytterbium co-doped microspheres are respectively coupled with the corresponding ends of the tapered optical fiber, thereby obtaining a microsphere laser.

9. The preparation method according to claim 8, Features: The preparation method of the erbium-ytterbium co-doped microspheres in step 1) comprises the following steps in sequence: S1. Putting phosphate glass doped with erbium ions and ytterbium ions into a grinding dish and grinding it into glass powder, and selecting a punch frame standard sieve with a corresponding aperture according to actual needs to screen the glass powder to obtain glass powder of a desired size; S2. After the screened glass powder is mixed evenly, it is collected in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine for repeated shaking, and the anhydrous ethanol in the beaker is continuously replaced for cleaning, and then the cleaned powder is subjected to high-temperature drying treatment; S3, transferring the dried powder to a funnel-shaped glass device with a switch valve, placing the glass device at the feed inlet above the high-temperature vertical furnace, connecting the collecting tube to the microsphere outlet of the high-temperature vertical furnace, heating the furnace chamber of the high-temperature vertical furnace, and after the furnace chamber reaches a preset temperature, filling with sufficient inert protective gas, opening the switch valve of the glass device to allow the glass powder to enter the furnace chamber through the feed inlet; S4. After being subjected to high temperature and surface tension, the glass powder in the furnace cavity finally falls into the collecting tube and forms solidified glass microspheres of the required size.

10. The preparation method according to claim 9, Features: After step S4, the microspheres are placed in a small beaker filled with anhydrous ethanol, and then placed in an ultrasonic cleaning machine for repeated shaking while continuously replacing the anhydrous ethanol in the beaker for cleaning.

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