A point diffraction light source based on tapered micro-nano optical fiber and its preparation method

Abstract

The present invention discloses a point light source based on a tapered micro-nano optical fiber and a preparation method thereof. The coating layer of the optical fiber is removed at the end portion. One end of the optical fiber and a tapered micro-nano optical fiber having a waist region are coaxially butted and the coating layers of both are removed. A hollow sleeve is sleeved outside the tapered micro-nano optical fiber. One end of the hollow sleeve is flush with the waist of the tapered micro-nano optical fiber. The low refractive index glue is filled in the gap between the hollow sleeve and the tapered micro-nano optical fiber, and the end face of the low refractive index glue is flush with the end face of the hollow sleeve. The present invention utilizes the low-loss transmission of the tapered micro-nano optical fiber to efficiently convert free-space light into a guided wave mode with strong field confinement in the micro-nano optical fiber, and then further limits the spot size by using a metal film to form a sub-wavelength point diffraction light source with low loss, having advantages such as a high numerical aperture, a low wavefront error, high brightness, and high stability.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano photonic devices, and particularly to a point diffraction light source based on a tapered micro-nano optical fiber and a preparation method thereof, which can achieve a high numerical aperture, low wavefront error, high brightness and high stability, and can promote the development of the fields of precision detection systems and lithography systems. Background Art

[0002] Point diffraction light sources play an important role in the fields of optical precision detection systems, high-precision processing technologies, etc. However, traditional pinhole diffraction point light sources and single-mode fiber point light sources are difficult to simultaneously meet the requirements in multiple aspects such as numerical aperture, wavefront error, and brightness. Micro-nano optical fibers have advantages such as small size, ultra-low propagation loss, and seamless connection with fiber systems, and have attracted a large amount of in-depth research in many fields such as sensors and optical interconnections. However, due to being dielectric waveguides, it is difficult to achieve sub-wavelength field confinement. Surface plasmon structures have the ability to confine light fields beyond the diffraction limit, and thus can be used to realize sub-wavelength point light sources. For example, a metal film is deposited on the surface of a tapered micro-nano optical fiber to form a structure similar to the probe of an optical scanning tunneling microscope; and a technique for realizing a high numerical aperture point light source by further processing a finer tapered structure at the tip of the micro-nano optical fiber and coating it with a metal film. However, the high loss and thermal effect of surface plasmons greatly limit the brightness of point light sources based on this. How to improve the structure preparation to simultaneously meet the requirements of high numerical aperture and high brightness of point light sources is still a technical problem. In addition, to achieve low-loss transmission from a standard optical fiber to a micro-nano optical fiber, the tapered region needs to have a gentle transition to meet the adiabatic condition, but this also prolongs the transition region, resulting in the tapered micro-nano optical fiber being easily affected by air flow and other factors and jittering, affecting the stability of the point light source. Therefore, it is also very important to provide good support and protection for the tapered micro-nano optical fiber without affecting the transmission characteristics. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, the present invention discloses a point diffraction light source based on a tapered micro-nano optical fiber and a preparation method thereof. The point diffraction light source has the advantages of high numerical aperture, high brightness, high mechanical strength and stability, etc. The point diffraction light source is expected to promote the development of fields such as large-size optical precision detection systems and high-precision micro-nano processing.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] 1. A point light source based on a tapered micro-nano optical fiber:

[0006] The point light source includes an optical fiber, a hollow sleeve, a tapered micro-nano optical fiber, a low-refractive-index glue, and a metal film; the coating layer of the optical fiber is removed at the end, one end of the optical fiber is coaxially butted with the tapered micro-nano optical fiber having a waist region and both are removed of the coating layer, and the tapered micro-nano optical fiber is sleeved with a hollow sleeve; one end of the hollow sleeve is flush with the waist of the tapered micro-nano optical fiber, the low-refractive-index glue is filled in the gap between the hollow sleeve and the tapered micro-nano optical fiber, and the low-refractive-index glue is flush with the end face of the hollow sleeve, and is arranged on the end face of the low-refractive-index glue and the hollow sleeve.

[0007] The tip of the tapered micro-nano optical fiber penetrates through the metal film, and the end face of the tip is flush with the surface of the metal film.

[0008] The tapered micro-nano optical fiber is prepared from an optical fiber by the fused biconical taper method, forming a structure that gradually transitions from the diameter of the optical fiber to its own waist region.

[0009] The outer contour of the tapered micro-nano optical fiber satisfies or nearly satisfies the adiabatic condition in the low-refractive-index glue environment.

[0010] The tip diameter of the tapered micro-nano optical fiber is in the sub-wavelength dimension.

[0011] The hollow sleeve is a hollow optical fiber or a hollow capillary, and the inner diameter is larger than the diameter of the optical fiber after removing the coating layer.

[0012] The refractive index of the low-refractive-index glue is lower than the refractive index of the material of the optical fiber.

[0013] The material of the metal film is a metal such as gold Au, silver Ag, aluminum Al, chromium Cr, or platinum Pt.

[0014] The thickness of the metal film is 50 - 500 nm.

[0015] II. A preparation method of a point light source based on a tapered micro-nano optical fiber, the method comprising the following steps:

[0016] (1) Strip about 10 cm of the coating layer near the end of the optical fiber and clean it thoroughly;

[0017] (2) Insert a hollow sleeve with an inner diameter matching the diameter of the optical fiber cladding from the end of the optical fiber after removing the coating layer and sleeve it near the optical fiber including the coating layer;

[0018] (3) Place the optical fiber after removing the coating layer on a high-precision optical fiber taper machine, and stretch the optical fiber by the fused biconical taper method at the end of the optical fiber to prepare a tapered micro-nano optical fiber with low transmission loss that satisfies or nearly satisfies the adiabatic condition and has a diameter smaller than that of the optical fiber;

[0019] (4) Move the previously sleeved hollow sleeve from the position near the optical fiber with the coating layer to the tapered micro-nano optical fiber. One end of the hollow sleeve is flush with the waist of the tapered micro-nano optical fiber, and the other end is still tightly fixed to the cladding part after the coating layer of the optical fiber is removed.

[0020] (5) Fill the gap between the hollow sleeve and the tapered micro-nano optical fiber with a low-refractive-index glue in liquid state through capillary action and cure it.

[0021] (6) Cut the tapered micro-nano optical fiber at the center of the waist, and leave a section of the tapered micro-nano optical fiber outside the end face of the low-refractive-index glue.

[0022] (7) Deposit a metal film on the end faces of the low-refractive-index glue and the hollow sleeve through processes such as magnetron sputtering or electron beam evaporation.

[0023] (8) Cut the tapered micro-nano optical fiber along the surface of the metal film so that the end face of the tapered micro-nano optical fiber is flush with the outer surface of the metal film, and complete the preparation of the point light source.

[0024] The working principle of the point light source of the present invention is as follows: After free-space light is focused, it is coupled from one end of the non-tapered optical fiber to the optical fiber for transmission. After passing through the tapered micro-nano optical fiber, a micro-nano optical fiber waveguide mode is formed, and the mode field is constrained. The metal film absorbs the evanescent fields of the leakage mode and the waveguide mode in the transition region, and the mode field is further compressed. After passing through the metal film, it diffracts to form a quasi-spherical wave with a large numerical aperture and a small wavefront error.

[0025] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0026] (1) The transition region of the tapered micro-nano optical fiber adopted in the present invention meets or is close to meeting the adiabatic condition and has low-loss transmission characteristics. The loss of the entire structure mainly comes from the absorption of the evanescent field by the metal film. Compared with the existing pinhole point light source, the tapered micro-nano optical fiber with a metal film coated on the surface, and the surface plasmon structure fabricated at the tip of the tapered micro-nano optical fiber, the point light source scheme of the present invention has a higher transmittance and realizes higher brightness.

[0027] (2) The present invention uses the metal film to absorb the leakage mode in the tapered transition region and eliminate its influence on the point light source; and absorbs the evanescent field of the waveguide mode to further limit the mode field area, having the advantages of a small output spot, a high numerical aperture, and a small wavefront error.

[0028] (3) The present invention uses the low-refractive-index glue to support and fix the tapered micro-nano optical fiber, greatly improving the mechanical strength and stability.

[0029] (4) The preparation method provided by the present invention is simple and feasible and can be realized through existing mature micro-nano processing technologies. Description of the Drawings

[0030] Figure 1 Schematic structural diagram of a point light source based on a tapered micro-nano optical fiber according to the present invention.

[0031] Figure 2 Schematic diagram of the preparation process of a point light source based on a tapered micro-nano optical fiber according to the present invention.

[0032] The reference numerals are listed as follows: 1 - optical fiber, 2 - hollow sleeve, 3 - tapered micro-nano optical fiber, 4 - low refractive index ultraviolet curable glue, 5 - metal film. Detailed implementation manners

[0033] The following further describes the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0034] As Figure 1 shown, the point light source structure includes an optical fiber 1, a hollow sleeve 2, a tapered micro-nano optical fiber 3, a low refractive index glue 4, and a metal film 5; the coating layer of the optical fiber 1 is removed at one end, one end of the optical fiber 1 and the tapered micro-nano optical fiber 3 with a waist region are coaxially butted and both have their coating layers removed, a hollow sleeve 2 is tightly sleeved outside the cladding part of the tapered micro-nano optical fiber 3, that is, the hollow sleeve 2 is nested outside the optical fiber 1 and the tapered micro-nano optical fiber 3 with the coating layers removed; one end of the hollow sleeve 2 is flush with the waist of the tapered micro-nano optical fiber 3, the low refractive index glue 4 is filled in the gap between the hollow sleeve 2 and the tapered micro-nano optical fiber 3, the low refractive index glue 4 is flush with the end face of the hollow sleeve 2, and is provided at the end face of the low refractive index glue 4 and the hollow sleeve 2.

[0035] The tip of the tapered micro-nano optical fiber 3 passes through the low refractive index glue 4 and the metal film 5, and the end face of the tip is flush with the surface of the metal film 5.

[0036] The optical fiber 1 is an ordinary optical fiber.

[0037] The tapered micro-nano optical fiber 3 is prepared from the optical fiber 1 by the fused biconical taper method, forming a structure that gradually transitions from the cladding diameter of the optical fiber 1 to its own waist region.

[0038] The outer contour of the tapered micro-nano optical fiber 3 satisfies or approximately satisfies the adiabatic condition in the environment of the low refractive index ultraviolet curable glue 4, and has the characteristic of low transmission loss.

[0039] The tip diameter of the tapered micro-nano optical fiber 3 is in the sub-wavelength size, and the diffracted quasi-spherical wave has a large numerical aperture and a low wavefront error.

[0040] The hollow sleeve 2 is a hollow optical fiber or a hollow capillary tube, the inner diameter is slightly larger than the diameter of the optical fiber 1 with the coating layer removed, and its inner diameter is slightly larger than the diameter of the optical fiber with the coating layer removed, and it can slide on the optical fiber and maintain a certain frictional force.

[0041] The refractive index of the low refractive index glue 4 is lower than that of the material of the optical fiber 1. Its refractive index determines the length of the transition region required for the tapered micro-nano optical fiber to meet the adiabatic condition. The lower the refractive index, the shorter the transition region.

[0042] The low refractive index glue 4 can fix and support the tapered micro-nano optical fiber 3 at the same time, enhance the mechanical strength of the tapered micro-nano optical fiber, and improve the stability of the point light source.

[0043] The material of the metal film 5 is a metal such as gold Au, silver Ag, aluminum Al, chromium Cr or platinum Pt.

[0044] The thickness of the metal film 5 is 50 - 500 nm. Its thickness needs to be able to completely absorb the leakage mode in the tapered transition region, eliminate its influence on the point light source, and at the same time fully absorb the evanescent field of the guided mode of the tapered micro-nano optical fiber, further compress the mode field area, and achieve sub-wavelength point diffraction; on this basis, its thickness should be as thin as possible to improve the overall transmittance of the point light source.

[0045] As Figure 2 shown, the above-mentioned point light source based on the tapered micro-nano optical fiber can be prepared according to the following method, and the steps are as follows:

[0046] (1) As shown in attachment Figure 2 (a), strip about 10 cm of the coating near the optical fiber end, and clean the optical fiber surface with an alcohol cotton ball;

[0047] (2) As shown in attachment Figure 2 (b), insert a hollow sleeve with an inner diameter matching the optical fiber cladding diameter from the end of the optical fiber with the coating removed until it is near the optical fiber with the coating;

[0048] (3) As shown in attachment Figure 2 (c), place the optical fiber with the coating removed on a high-precision optical fiber taper machine, and prepare a tapered micro-nano optical fiber with low transmission loss that meets or is close to meeting the adiabatic condition by the method of fused tapering;

[0049] (4) As shown in attachment Figure 2 (d), move the pre-inserted hollow sleeve to the tapered micro-nano optical fiber. One end of the hollow sleeve is flush with the waist of the tapered micro-nano optical fiber, and the other end is still tightly fixed to the un-tapered optical fiber;

[0050] (5) As shown in attachment Figure 2 (e), fill the gap between the hollow sleeve and the tapered micro-nano optical fiber with a liquid low refractive index ultraviolet curable glue through capillary action, and cure it under ultraviolet lamp irradiation to support and fix the tapered micro-nano optical fiber, and improve the mechanical strength and stability;

[0051] (6) As shown in attachment Figure 2 (f), cut off the tapered micro-nano optical fiber and leave a section outside the low refractive index ultraviolet curable glue;

[0052] (7) As shown in Figure 2 (g), a metal film is deposited on the end faces of the low refractive index ultraviolet curable glue and the hollow sleeve through processes such as magnetron sputtering or electron beam evaporation. The metal film can be made of metal materials such as gold (Au), silver (Ag), aluminum (Al), chromium (Cr), platinum (Pt), etc., and the thickness is 50 - 500 nm;

[0053] (8) As shown in Figure 2 (h), the micro - nano fiber is cut along the surface of the metal film through processing techniques such as focused ion beam (FIB) and femtosecond laser cutting, so that the end face of the micro - nano fiber is flush with the surface of the metal film.

[0054] After free - space light is coupled to the optical fiber and propagates with low loss through the tapered micro - nano fiber, the formed micro - nano fiber guided - wave mode still has a high transmittance under the constraint of the metal mode, and forms a sub - wavelength light spot, diffracting a quasi - spherical wave with a large numerical aperture and low wavefront error.

[0055] It can be seen from the above implementation that the present invention uses the low - loss transmission of the tapered micro - nano fiber to efficiently convert free - space light into a guided - wave mode with strong field confinement in the micro - nano fiber, and then uses the metal film to further limit the light spot size, constituting a low - loss sub - wavelength point diffraction light source, which has advantages such as a high numerical aperture, low wavefront error, high brightness, and high stability, and can promote the development of fields such as precision detection systems and lithography systems.

[0056] The above is only a specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be subject to the claims.

Claims

1. A point light source based on a tapered micro-nano optical fiber, characterized in that: It includes an optical fiber (1), a hollow sleeve (2), a tapered micro-nano optical fiber (3), a low-refractive-index glue (4) and a metal film (5); the coating layer of the optical fiber (1) is removed at the end, one end of the optical fiber (1) and the tapered micro-nano optical fiber (3) with a waist region are coaxially butted and both have their coating layers removed, and a hollow sleeve (2) is sleeved outside the tapered micro-nano optical fiber (3); one end of the hollow sleeve (2) is flush with the waist of the tapered micro-nano optical fiber (3), and the low-refractive-index glue (4) is filled in the gap between the hollow sleeve (2) and the tapered micro-nano optical fiber (3), and the end face of the low-refractive-index glue (4) is flush with the end face of the hollow sleeve (2); The tip of the tapered micro-nano optical fiber (3) penetrates through the metal film (5), and the end face of the tip is flush with the surface of the metal film (5); The outer contour of the tapered micro-nano optical fiber (3) satisfies or nearly satisfies the adiabatic condition in the environment of the low-refractive-index glue (4); The tip diameter of the tapered micro-nano optical fiber (3) is in the sub-wavelength size; The refractive index of the low-refractive-index glue (4) is lower than the refractive index of the material of the optical fiber (1).

2. The point light source based on a tapered micro-nano optical fiber according to claim 1, characterized in that: The tapered micro-nano optical fiber (3) is prepared from the optical fiber (1) by the fused biconical taper method, forming a structure that gradually transitions from the diameter of the optical fiber (1) to its own waist region.

3. The point light source based on a tapered micro-nano optical fiber according to claim 1, characterized in that: The hollow sleeve (2) is a hollow optical fiber or a hollow capillary, and its inner diameter is larger than the diameter of the optical fiber (1) with the coating layer removed.

4. A point light source based on a tapered micro-nano optical fiber according to claim 1, characterized in that: The material of the metal film (5) is gold Au, silver Ag, aluminum Al, chromium Cr or platinum Pt.

5. A point light source based on a tapered micro-nano optical fiber according to claim 1, characterized in that: The thickness of the metal film (5) is 50 - 500 nm.

6. A preparation method applied to the point light source according to any one of claims 1 to 5, characterized in that, The method includes the following steps: (1) Strip the coating layer near the end of the optical fiber (1) and clean it; (2) Insert a hollow sleeve (2) with an inner diameter matching the cladding diameter of the optical fiber (1) from the end of the optical fiber (1) with the coating layer removed and sleeve it near the optical fiber (1) including the coating layer; (3) Stretch the optical fiber (1) at the end of the optical fiber (1) by the fused biconical taper method to prepare a tapered micro-nano optical fiber (3) with a diameter smaller than that of the optical fiber (1); (4) Move the previously inserted hollow sleeve (2) to the tapered micro-nano optical fiber (3), one end of the hollow sleeve (2) is flush with the waist of the tapered micro-nano optical fiber (3), and the other end is still tightly sleeved and fixed with the part of the optical fiber (1) after the coating layer is removed; (5) Fill the gap between the hollow sleeve (2) and the tapered micro-nano optical fiber (3) with the liquid low-refractive-index glue (4) by capillary action and cure it; (6) Cut off the tapered micro-nano optical fiber (3), and leave a section of the tapered micro-nano optical fiber (3) outside the end face of the low-refractive-index glue (4); (7) Deposit a metal film (5) on the end faces of the low-refractive-index glue (4) and the hollow sleeve (2) by magnetron sputtering or electron beam evaporation process; (8) Cut off the tapered micro-nano optical fiber (3) along the surface of the metal film (5) so that the end face of the tapered micro-nano optical fiber (3) is flush with the outer surface of the metal film (5), and complete the preparation of the point light source.

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