Whispering gallery mode resonator based on a cylindrical cavity in an optical fiber and method of making the same

Abstract

The application belongs to the technical field of optical fiber application, and discloses an echo wall mode resonator based on an inner cylindrical cavity of an optical fiber and a manufacturing method, which comprises an optical fiber body, a cylindrical cavity is formed on the optical fiber body, the top end of the cylindrical cavity is in an open shape, and the bottom end of the cylindrical cavity is located inside the optical fiber body, wherein a part or all of the cylindrical cavity blocks part of the transmission light beam of the optical fiber body, so that the part of the transmission light beam of the optical fiber body is coupled into the inner wall of the cylindrical cavity along a tangent direction, and then the light beam periodically propagates on the inner wall of the cylindrical cavity to form an echo wall mode; the echo wall mode resonator is a WGM resonator based on the cylindrical cavity and is completely integrated with the optical fiber, and can directly couple the light propagating in the optical fiber core, thereby paving the way for many promising applications in the fields of micro-lasers and nonlinear optics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber application, and particularly relates to an echo wall mode resonator based on an inner cylindrical cavity of an optical fiber and a manufacturing method thereof. BACKGROUND

[0002] Light in the echo wall mode (WGM) resonator propagates in a closed cavity, and is totally reflected in the cavity at the same angle. After one round of propagation, when the light wave path meets certain phase matching conditions, the light waves can be superimposed to form a standing wave field and optical amplification effect. The echo wall mode (WGM) resonator is widely used in optical filters, modulators, micro-lasers, frequency comb generators, nonlinear optics and high-sensitivity sensor devices due to its high quality factor (Q), small mode volume, narrow linewidth, long photon lifetime and low power consumption.

[0003] At present, common microcavity types of the WGM resonator mainly include microsphere cavity, microbubble cavity, micro-ring cavity, micro-disc cavity, micro-ring core cavity, micro-tube cavity and bottle mouth cavity. Each microcavity type has its own advantages and disadvantages. However, the WGM resonators of the above microcavity types are mostly discrete optical devices, which cannot be directly coupled with incident light, and need to use external coupling schemes such as tapered optical fibers, side-polished optical fibers, waveguides or prisms. When the WGM resonator needs to be used in an optical fiber system, this causes difficulty.

[0004] Therefore, a WGM resonator integrated in an optical fiber and easily coupled with light propagating in the fiber core is urgently needed in practice. At present, such a device has not appeared on the market. SUMMARY

[0005] The application aims to solve the technical problems in the prior art and provides an echo wall mode resonator based on an inner cylindrical cavity of an optical fiber and a manufacturing method thereof. The WGM resonator is prepared by femtosecond laser etching and rapid hydrofluoric acid etching. The WGM resonator based on the cylindrical cavity is completely integrated with the optical fiber and can be directly coupled with light propagating in the fiber core, thereby paving the way for many promising applications in the fields of micro-lasers and nonlinear optics.

[0006] The technical scheme adopted to achieve the above purpose is as follows:

[0007] An echo-wall mode resonator based on a cylindrical cavity in an optical fiber, comprising an optical fiber body, a cylindrical cavity is opened on the optical fiber body, the central axis of the cylindrical cavity is perpendicular to the central axis of the optical fiber body, the top end of the cylindrical cavity is open, and the bottom end of the cylindrical cavity is located inside the optical fiber body, wherein a part or all of the cylindrical cavity blocks part of the transmission light beam of the optical fiber body, so that the part of the transmission light beam of the optical fiber body is coupled into the inner wall of the cylindrical cavity in a tangential direction, and then periodically propagates on the inner wall of the cylindrical cavity, thereby forming an echo-wall mode resonance in the cylindrical cavity.

[0008] Preferably, when the optical fiber body is a multimode optical fiber, the diameter of the cylindrical cavity is smaller than the core diameter of the multimode optical fiber, and the bottom end of the cylindrical cavity is located in the core of the multimode optical fiber.

[0009] Preferably, the central axis of the cylindrical cavity is perpendicular to the central axis of the multimode optical fiber.

[0010] Preferably, when the optical fiber body is a single-mode optical fiber, the diameter of the cylindrical cavity is not less than the core diameter of the single-mode optical fiber, at this time, the cylindrical cavity is arranged eccentrically with the single-mode optical fiber, and part of the side surface and part of the bottom surface of the cylindrical cavity are located in the core of the single-mode optical fiber.

[0011] Preferably, the cylindrical cavity is a plurality of cylindrical cavities, and the plurality of cylindrical cavities are arranged in sequence along the light transmission direction in the optical fiber body.

[0012] Preferably, the diameters of each cylindrical cavity are not completely the same.

[0013] Also disclosed is a method for manufacturing the echo-wall mode resonator as described above, comprising the following steps:

[0014] Step A: femtosecond laser micro-machining process, the optical fiber body is placed on a three-dimensional micro-moving platform controlled by computer software, the micro-machining process is monitored by a CCD camera, after the focusing adjustment of the optical fiber body and the femtosecond laser is completed, the femtosecond laser pulse etches a ring structure with the required diameter on the surface of the optical fiber; when the ring structure is etched, the femtosecond laser beam steps in the direction of the inside of the optical fiber body at an interval of 2 μm, to continuously etch the same ring structure, and recursively step by step until the cylindrical structure with the required depth is etched;

[0015] Step B: etching process of hydrofluoric acid solution, one end of the optical fiber body is connected with a red light pen, the waveguide position in the optical fiber body, i.e. the position of the cylindrical structure, is found by red light display, and then the part of the optical fiber body where the cylindrical structure is located is immersed in the hydrofluoric acid solution for a period of time;

[0016] Step C: Put the cylindrical cavity after the etching treatment in step B into an ultrasonic cleaning machine for a certain period of time, so that the inner wall of the cylindrical cavity becomes smooth, which is helpful to form the whispering gallery mode.

[0017] Preferably, step A comprises the following steps:

[0018] Step A1: After the etching of the first cylindrical structure, the three-dimensional micro-moving platform drives the optical fiber body to move along the axial direction by a certain distance, and then the etching of the first cylindrical structure is repeated to complete the etching of the second cylindrical structure, and so on, so as to complete the etching of all cylindrical structures and form a hierarchical whispering gallery mode structure on the optical fiber body; wherein the diameters of each cylindrical structure are not completely the same.

[0019] Preferably, when multiple cylindrical structures need to be made, step A further comprises the following steps: the optical fiber body is a multimode optical fiber, the center wavelength of the femtosecond laser is 800 nm, the pulse energy is 500 μJ, the pulse duration is 35 fs, the repetition frequency is 5 kHz, and the scanning speed of the laser beam is 10 μm / s,

[0020] Preferably, in step B, the part of the optical fiber body where the cylindrical structure is located is immersed in a 40% concentration of hydrofluoric acid solution for 150 s.

[0021] The echo wall mode resonator of the present application is based on a WGM resonator with a cylindrical cavity and is fully integrated with an optical fiber, which can directly couple with the light propagating in the core of the optical fiber, thereby paving the way for many promising applications in the fields of micro-lasers and nonlinear optics.

[0022] The present application is a cylindrical cavity formed by improving the structure of the optical fiber body itself, and the cylindrical cavity is integrated in the optical fiber without the need for cooperation with other components, so the overall device is solid and stable in operation.

[0023] The echo wall mode resonator has low cost, simple manufacturing process, high integration, and high Q value, and the experimental results show that the quality factor (Q) is 1.06x10 4 , which provides a new direction for the development of integrated optics and photon chips.

[0024] The method for manufacturing the echo wall mode resonator of the present application has the characteristics of simplicity, speed, flexibility and stability, and can simply and effectively manufacture a hierarchical whispering gallery mode structure to improve the application potential of the system. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Figure 1 is a structure diagram of a multimode optical fiber echo wall mode resonator in embodiment 1.

[0026] Figure 2 for Figure 1 Schematic diagram of the AA section structure along the middle;

[0027] Figure 3 for Figure 2 A schematic diagram of the three-dimensional structure;

[0028] Figure 4 This is a magnified microscope diagram of the multimode fiber whispering-gallery mode resonator in Specific Embodiment 1;

[0029] Figure 5 This is a magnified microscope diagram of the multimode fiber whispering-gallery mode resonator when red light is applied in specific embodiment 1.

[0030] Figure 6 This is a schematic diagram of the single-mode fiber whispering-gallery mode resonator in specific embodiment 2;

[0031] Figure 7 for Figure 6 Schematic diagram of the cross-sectional structure along the middle BB line;

[0032] Figure 8 This is a schematic diagram of the structure when the optical fiber body is a multi-stage series cylindrical cavity structure. Detailed Implementation

[0033] The invention will now be further described with reference to the accompanying drawings. Specific Implementation Example 1:

[0035] like Figures 1 to 4 As shown, a whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber includes an optical fiber body. A cylindrical cavity 4 is formed on the optical fiber body. The central axis of the cylindrical cavity 4 is perpendicular to the central axis of the optical fiber body. The top of the cylindrical cavity 4 is open, and the bottom of the cylindrical cavity 4 is located inside the optical fiber body. Part or all of the cylindrical cavity 4 blocks part of the transmitted light beam of the optical fiber body, so that part of the transmitted light beam of the optical fiber body is tangentially coupled to the inner wall of the cylindrical cavity 4 in the form of an evanescent wave or in the form of direct coupling. Then, it propagates periodically on the inner wall of the cylindrical cavity 4, thereby forming a whispering-gallery mode resonance within the cylindrical cavity 4.

[0036] like Figure 1 As shown, when the optical fiber body is a multimode optical fiber, the diameter of the cylindrical cavity 4 is smaller than the diameter of the multimode optical fiber core 2, and the cylindrical cavity 4 penetrates the multimode optical fiber cladding 1 from top to bottom and is embedded in the multimode optical fiber core 2. The bottom end of the cylindrical cavity 4 is located inside the multimode optical fiber core 2, and the central axis of the cylindrical cavity 4 intersects perpendicularly with the central axis of the multimode optical fiber core 2.

[0037] likeFigure 5 As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same.

[0038] As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same. Specific embodiment 2:

[0040] As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same. Figure 6 and Figure 7 As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same.

[0041] As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same. Specific embodiment 3:

[0043] As shown in the embodiment, when the multi-mode optical fiber is replaced by the coreless optical fiber, since both of them are multi-mode transmission, the cross section of the transmission light beam is relatively large, and the cylindrical cavity 4 is located entirely within the transmission light beam, so the working process and working principle of the two are the same. Figure 8 As shown in the embodiment, the difference between the above two specific embodiments is that the cylindrical cavity is a plurality of cylindrical cavities 4, 11, 12, 13, which are arranged in sequence along the direction of light transmission in the multi-mode optical fiber; wherein the diameters of the plurality of cylindrical cavities 4, 11, 12, 13 are not completely the same, thereby forming a hierarchical acoustic resonator structure on the multi-mode optical fiber, which can multiplex multiple resonators on one optical fiber, and expand and enrich the application range of the device.

[0044] The application also discloses a manufacturing method of the acoustic resonator as described above, comprising the following steps:

[0045] Step A: femtosecond laser microprocessing process, the optical fiber body is placed on a three-dimensional micro-moving platform controlled by computer software, the microprocessing process is monitored by a CCD camera, after the focusing adjustment of the optical fiber body and the femtosecond laser is completed, the femtosecond laser pulse etches a ring structure of the required diameter on the surface of the optical fiber body; when the ring structure is etched, the femtosecond laser beam steps in the direction of the optical fiber body at an interval of 2 μm to continuously etch the same ring structure, and the step is repeated in turn until a cylindrical structure of the required depth is etched;

[0046] Step B: corrosion process of hydrofluoric acid solution, one end of the optical fiber body is connected with a red light pen, the waveguide position in the optical fiber body, i.e. the position of the cylindrical structure, is found by red light display, and then a small amount of hydrofluoric acid solution is dropped at the position of the cylindrical structure for soaking and corrosion for a period of time;

[0047] Step C: the cylindrical cavity treated by the corrosion process in Step B is placed in an ultrasonic cleaning machine for cleaning for a period of time, so that the inner wall of the cylindrical cavity becomes smooth, which is helpful for forming the whispering gallery mode; for example, Figure 4 Figure 1 is a microscope magnified schematic diagram of a multimode optical fiber whispering gallery mode resonator, which shows that the diameter of the cylindrical cavity is 38 μm and the depth is 65 μm.

[0048] In Step A, the optical fiber body is a multimode optical fiber, the center wavelength of the femtosecond laser is 800 nm, the pulse energy is 500 μJ, the pulse duration is 35 fs, the repetition frequency is 5 kHz, and the scanning speed of the laser beam is 10 μm / s; in Step B, a 40% concentration of hydrofluoric acid solution is dropped at the position of the cylindrical structure for soaking and corrosion for 150 s.

[0049] Further, when a multi-stage whispering gallery mode structure needs to be made, the following steps can also be included in Step A:

[0050] Step A1: after the etching of the first cylindrical structure is completed, the three-dimensional micro-moving platform moves the optical fiber body along the axial direction by a set distance, and then the etching of the first cylindrical structure is repeated to complete the etching of the second cylindrical structure, and so on, so that the etching of all cylindrical structures is completed, thereby forming a multi-stage whispering gallery mode structure on the optical fiber body; wherein the diameters of the cylindrical structures are not completely the same.

[0051] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced equivalently, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber, characterized in that, The device includes an optical fiber body, on which a cylindrical cavity is formed. The central axis of the cylindrical cavity is perpendicular to the central axis of the optical fiber body. The top of the cylindrical cavity is open, and the bottom of the cylindrical cavity is located inside the optical fiber body. Part or all of the cylindrical cavity blocks part of the transmitted light beam of the optical fiber body, so that part of the transmitted light beam of the optical fiber body is tangentially coupled to the inner wall of the cylindrical cavity, and then periodically propagates on the inner wall of the cylindrical cavity to form a whispering-gallery mode resonance. When the optical fiber body is a single-mode optical fiber, the diameter of the cylindrical cavity is not less than the diameter of the single-mode optical fiber core. In this case, the cylindrical cavity and the single-mode optical fiber are eccentrically set, and part of the side surface and part of the bottom surface of the cylindrical cavity are located inside the single-mode optical fiber core.

2. The whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber according to claim 1, characterized in that, When the optical fiber body is a multimode optical fiber, the diameter of the cylindrical cavity is smaller than the diameter of the multimode optical fiber core, and the bottom end of the cylindrical cavity is located inside the multimode optical fiber core.

3. The whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber according to claim 2, characterized in that, The central axis of the cylindrical cavity intersects perpendicularly with the central axis of the multimode optical fiber.

4. The whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber according to any one of claims 1 to 3, characterized in that, There are multiple cylindrical cavities, which are arranged sequentially along the light transmission direction within the optical fiber body.

5. The whispering-gallery mode resonator based on an inner cylindrical cavity of an optical fiber according to claim 4, characterized in that, The diameter of each cylindrical cavity is not exactly the same.

6. A method for manufacturing a whispering-gallery mode resonator as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step A: Femtosecond laser micromachining process. The fiber body is placed on a three-dimensional micro-movement platform controlled by computer software. The micromachining process is monitored by a CCD camera. After the fiber body and the femtosecond laser are focused and adjusted, the femtosecond laser pulse etches a ring structure of the required diameter on the fiber surface. After the ring structure is etched, the femtosecond laser beam moves inward toward the fiber body at 2μm intervals to continuously etch the same ring structure. This process is repeated until a cylindrical structure of the required depth is etched. Step B: The corrosion process of hydrofluoric acid solution. Connect a red light pen to one end of the optical fiber body and use the red light to locate the waveguide position in the optical fiber body, that is, the position of the cylindrical structure. Then, immerse the part of the optical fiber body where the cylindrical structure is located in the hydrofluoric acid solution for a period of time. Immerse the part of the optical fiber body where the cylindrical structure is located in a 40% concentration hydrofluoric acid solution for 150 seconds. Step C: Place the cylindrical cavity, which has undergone corrosion treatment in step B, into an ultrasonic cleaner for a certain period of time to make the inner wall of the cylindrical cavity smooth, which helps to form a sounding wall mode.

7. The method for fabricating a whispering-gallery mode resonator according to claim 6, characterized in that, When multiple cylindrical structures need to be fabricated, step A also includes the following steps: Step A1: After the first cylindrical structure is etched, the three-dimensional micro-moving platform moves the optical fiber body along the axial direction by a set distance, and then repeats the first cylindrical structure etching step to complete the etching of the second cylindrical structure, and so on, to complete the etching of all cylindrical structures, thereby forming a cascaded whispering gallery mode structure on the optical fiber body; wherein, the diameter of each cylindrical structure is not exactly the same.

8. The method for fabricating a whispering-gallery mode resonator according to claim 6 or 7, characterized in that, In step A, the optical fiber body is a multimode optical fiber, the center wavelength of the femtosecond laser is 800 nm, the pulse energy is 500 μJ, the pulse duration is 35 fs, the repetition frequency is 5 kHz, and the scanning speed of the laser beam is 10 μm / s.

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