CN114815037A - Dual-mode optical fiber photon nanometer jet optical field regulation and control device - Google Patents

Abstract

The invention provides a dual-mode optical fiber photonic nano-jet fiber end optical field control device, which includes a monochromatic light source, a section of dual-mode optical fiber, a medium microsphere, an optical fiber polarizer, a polarization controller, a three-dimensional high-precision displacement stage and a high-resolution CCD. The end face of the dual-mode optical fiber is adhered to the medium microsphere by the low-refractive index glue, the dual-mode optical fiber excites the LP ₁₁ mode, and the light emitted by the monochromatic light source passes through the optical fiber polarizer and the single-mode optical fiber, and then excites different modes through the dual-mode optical fiber. The spot action produces photon nanojets on the dielectric microspheres, which are finally observed by high-resolution CCD; the polarization controller on the single-mode fiber is adjusted to change the excited LP ₁₁ mode spot, thereby changing the photon nanojet characteristics of the dielectric microspheres. . The device of the invention has high efficiency, controllability and diversity of polarization states, and can realize not only single-dual multiplexing but also a fiber-tip photonic nano-jet generator with adjustable spatial position, that is, an adjustable single-fiber multi-performance fiber tip Photonic Nanojet Generator.

Description

A dual-mode fiber photonic nanojet optical field control device

technical field

The invention belongs to the technical field of optics, and in particular relates to a dual-mode optical fiber photonic nano-jet optical field control device.

Background technique

With the continuous advancement of high-precision measurement technology, the size of research objects is getting smaller and smaller. However, due to the diffraction limit of traditional optics, the focusing spot of the beam has been limited to more than half wavelength, which severely limits the research in the field of micro-nano. The photonic nanojets produced by the use of micron-scale dielectric spheres have high focusing energy, sub-wavelength half width, can break through the diffraction limit of traditional optics, and have the advantages of simple structure, easy preparation, and low cost, which have attracted extensive attention of scientists. . The development of photonic nanojets has flourished in the past few decades. At present, the photonic nanojet effect has been widely used in the fields of super-resolution imaging, nanolithography, Raman spectroscopy, nanoparticle trapping, and optical switching devices. However, in most of the existing photonic nanojet devices, the light source and the microsphere are separate, especially in the case of a single microsphere, which is not conducive to the manipulation of the microsphere. . Although there are also reports on fiber-based photonic nanojet devices, most of these fiber-based photonic nanojet devices utilize the fundamental mode of the fiber and can only generate single-beam photonic nanojets, thus lacking the control function, which greatly limits their performance.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a dual-mode optical fiber photonic nano-jet optical field control device.

The object of the present invention is achieved through the following technical solutions:

A dual-mode optical fiber photonic nano-jet optical field control device, comprising a monochromatic light source, an optical fiber polarizer, a single-mode optical fiber, a polarization controller, a dual-mode optical fiber, a dielectric microsphere, a high-magnification lens, and a high-resolution CCD;

The end face of the dual-mode optical fiber is adhered to the medium microsphere by the low-refractive index glue, the dual-mode optical fiber excites the LP ₁₁ mode, and the light emitted by the monochromatic light source passes through the optical fiber polarizer and the single-mode optical fiber, and then excites different modes through the dual-mode optical fiber. The spot effect produces photon nanojets on the dielectric microspheres, which are finally observed by a high-resolution CCD; the polarization controller on the single-mode fiber is adjusted to change the excited LP ₁₁ mode spot, thereby changing the photon nanojets generated by the dielectric microspheres characteristic.

Further, the dual-mode optical fiber is a silica optical fiber with a smaller refractive index difference between the core and the cladding, or a microstructured fiber of glass or semiconductor material with a larger refractive index difference between the core and the cladding; the end face of the dual-mode optical fiber is cut. Flattening, so that the contact area between the dielectric microspheres and the dual-mode fiber is small.

Further, when the excitation efficiency of the LP ₁₁ mode of the dual-mode fiber is comparable to the remaining fundamental mode energy, that is, the excitation efficiency of the LP ₁₁ mode of the dual-mode fiber is about 50%, the fundamental and dual-mode multiplexing photonic nanometers can be realized. injection.

Further, in the case where the monochromatic light source is not controlled by the polarization controller, the dual-mode fiber will excite the hollow annular mode spot in the middle, and act on the dielectric microsphere to generate annular or single-point photon nanojets; In the case where the monochromatic light source is controlled by the polarization controller, the dual-mode fiber will excite a symmetrically distributed double-lobed mode spot, that is, the linearly polarized LP ₁₁ mode. When the polarization direction of the LP ₁₁ mode is perpendicular to the symmetry axis of the mode spot, One-photon nanojets with large sidelobes will be generated, and when the polarization direction of the LP ₁₁ mode is parallel to the symmetry axis of the mode spot, a symmetrical distribution of two-photon nanojets will be generated.

Further, the method for exciting the LP ₁₁ mode of the dual-mode fiber is a method of writing a long-period fiber grating, melting taper and dislocation welding.

Further, the wavelength range of the monochromatic light source is 400-1600 nm.

Further, the size range of the medium microspheres is 2λ-40λ.

The beneficial effects of the present invention are:

1. The present invention utilizes a dual-mode optical fiber to realize an adjustable single/multiplexing photonic nano-jet generating device, and uses a three-dimensional high-precision displacement stage to control the microsphere, so that the microsphere is attached to the end face of the dual-mode optical fiber to make a photon. Nanojet generator. The high-order mode is excited by writing a long-period fiber grating on the side of the dual-mode fiber by a carbon dioxide laser, and a hollow annular mode spot or a high-order double-lobed LP ₁₁ mode spot with different polarization states is generated. The annular mode spot or the LP ₁₁ modes of different polarization states can generate spatially tunable and single/multiplexed photon nanojets on the microspheres, realizing a highly integrated and controllable single/multiphoton nanojet. Nanojet light field control device.

2. The invention integrates the microspheres on the end face of the optical fiber, and solves the problems that the traditional single-photon nano-jet light source is not easy to couple and the microspheres are not easy to control.

3. The present invention combines the polarization characteristics of the LP ₁₁ mode with the photonic nanojet, the controllability of the polarization state of the linearly polarized LP ₁₁ mode, and the diversity of photonic nanojets generated by the action of different linearly polarized LP ₁₁ modes on the microspheres , to realize a single/multiplexed photonic nanojet optical field control device with tunable spatial position.

4. The two-photon nanojet produced by the present invention has high intensity and narrower sub-wavelength beam waist compared with the traditional single-photon nanojet, and has wider application range.

Description of drawings

Fig. 1 is the system schematic diagram of the dual-mode optical fiber photonic nano-jet optical field control device of the present invention;

2 is a schematic structural diagram of the dual-mode fiber photonic nano-jet optical field control device of the present invention writing a long-period fiber grating and integrating microspheres on its end face;

Figure 3 (a) is the annular light field output by the dual-mode fiber without polarization control in the present invention;

Fig. 3 (b) is the adjusting polarization controller of the present invention, the linearly polarized LP ₁₁ mode that the dual-mode fiber outputs;

4(a)-(e) are schematic diagrams of the mode field distribution of the annular light field in the non-polarized state of the present invention and the linearly polarized LP ₁₁ mode in different polarization states;

Fig. 5 is the simulation schematic diagram of the single-point photon nano-jet in three directions of xoz, yoz and xoy produced by the annular light field of the present invention without polarization control;

Fig. 6 is the light field simulation schematic diagram of the single-photon nano-jet with two larger side lobes in the three directions of xoz, yoz and xoy produced by the LP ₁₁ mode polarization direction perpendicular to the symmetry axis of the present invention;

7 is a schematic diagram of the simulation of the symmetric two-photon nanojet produced in the xoz, yoz and xoy planes by the LP ₁₁ mode polarization direction parallel to the symmetry axis of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings.

Referring to Figure 1, a dual-mode fiber photonic nanojet optical field control device includes a monochromatic light source 1, a fiber polarizer 2, a single-mode fiber 3, a polarization controller 4, a dual-mode fiber 5, a dielectric microsphere 6, a high magnification Lens 7, high resolution CCD8 and computer 9. The dielectric microspheres 6 are adhered to the end face of the dual-mode optical fiber 5 coated with low-refractive index glue under the control of a three-dimensional high-precision displacement stage to form a fiber-end photonic nanojet generator. The thickness of the low-refractive index glue should be as thin as possible. The side of the dual-mode fiber 5 is written with a long-period fiber grating by a carbon dioxide laser, which excites the LP ₁₁ mode in the fiber, and is adjusted by the polarization controller 4; The higher-order modes form a hollow annular mode spot in the middle, and a ring-shaped or single-point photon nanojet will be generated after the dielectric microsphere 6 , which is related to the relative size and position of the annular mode spot and the microsphere. When polarization control is applied, the dual-mode fiber 5 excites a symmetrically distributed dual-lobed mode spot, namely the linearly polarized LP ₁₁ mode. When the polarization direction is perpendicular to the mode spot symmetry axis, single-photon nanojets with larger sidelobes will be generated; when the polarization direction is parallel to the mode spot symmetry axis, it will generate two-photon nanojets with symmetrical distribution. Under the control of the polarization controller 4, the polarization state of the excited linearly polarized LP ₁₁ mode is changed, and the photonic nanojet produced by the dielectric microspheres 6 is changed accordingly, so as to realize the regulation of the photonic nanojet. When the dual-mode excitation efficiency is comparable to the remaining fundamental mode energy, that is, the dual-mode excitation efficiency is about 50%, the fundamental and dual-mode multiplexing photonic nanojets can also be realized. A high-resolution CCD is used to monitor the optical field of the photonic nanojets produced by the dual-mode fiber, and to determine the spatial position and single/double morphology of the generated photonic nanojets.

计算得到1310nm单色光下，激发LP₁₁模的光栅周期为146.9μm。根据所得到的光栅周期，利用二氧化碳激光器在双模光纤4侧面刻写长周期光纤光栅，通过高分辨率CCD8测量模场并对高阶模转换效率进行评价，直到得到输出稳定的线偏振LP₁₁模。The core diameter of the dual-mode fiber 5 is 14 μm, the cladding diameter is 125 μm, and the core refractive index is 1.4485 at 1550 nm. The microspheres 6 are polystyrene pellets with a diameter of 10 μm and a refractive index of 1.59. The wavelength of the monochromatic light source 1 used is 1310 nm, and the high-resolution CCD 8 used is an infrared camera. First, according to the coupled mode theory, the grating period that can excite the LP ₁₁ mode is calculated at the wavelength of 1310nm-1550nm. According to the fiber parameters, the effective refractive index difference between the fundamental mode LP ₀₁ mode and the LP ₁₁ mode in the fiber is calculated to be 0.008916, and then according to the grating cycle

It is calculated that the grating period for exciting the LP ₁₁ mode is 146.9 μm under the monochromatic light of 1310 nm. According to the obtained grating period, a carbon dioxide laser is used to write a long-period fiber grating on the side of the dual-mode fiber 4, and the mode field is measured by a high-resolution CCD8 and the conversion efficiency of high-order modes is evaluated until a stable linearly polarized LP ₁₁ mode is obtained.

FIG. 2 is a schematic diagram of the structure of a dual-mode optical fiber with a long-period fiber grating written on the side face and a dielectric microsphere 6 integrated on the end face. After the dual-mode fiber 5 is written into the long-period fiber grating, if the polarization of the incident light is not controlled, the four degenerate vector modes are superimposed to obtain a ring mode field.

As shown in Figure 3(a), the polarization controller 4 is used to change the polarization state of the linearly polarized LP ₁₁ mode to obtain a linearly polarized LP ₁₁ mode with two symmetrically distributed mode spots. As shown in Figure 3(b), cut the end face of the dual-mode optical fiber 5 flat, dip a little low-refractive index glue on the end face of the dual-mode optical fiber 5, and use another optical fiber to repeatedly adhere to the adhesive layer to reduce the thickness of the adhesive layer to the order of microns. Then use a three-dimensional high-precision displacement stage (with an accuracy of nm order) to precisely control the glass slide carrying the microspheres, and align the center of the sphere with the axis of the fiber in two orthogonal directions, that is, to ensure that the center of the microsphere is aligned with the center of the fiber, and the medium The microspheres 6 are adhered to the end face of the dual-mode optical fiber 5 , and then cured by ultraviolet light irradiation, so that the medium microspheres 6 are adhered to the end face of the dual-mode optical fiber 5 .

Fig. 4(a) shows the hollow annular spot excited in the dual-mode fiber without applying polarization, and Fig. 4(b)(c)(d)(e) shows the existence and polarization of the LP ₁₁ mode after applying polarization, respectively. Direction: Figure 4(b) shows that the mode spot is symmetrical up and down, and the polarization direction is perpendicular to the symmetry axis. Figure 4(c) shows that the mode spot is vertically symmetrical, and the polarization direction is parallel to the symmetry axis. Figure 4(d) shows that the mode spot is left-right symmetrical, and the polarization The direction is perpendicular to the axis of symmetry. Figure 4(e) shows that the mode spot is left-right symmetrical, and the polarization direction is parallel to the axis of symmetry.

According to the simulation calculation, when no polarization is applied, the annular hollow mode spot can produce photon nanojets with annular or single-point distribution. Figure 5 shows the simulation diagram of the single-photon nanojets generated by the hollow annular mode spot in the xoy, xoz, and yoz directions. When the polarization direction of the LP ₁₁ mode is perpendicular to the symmetry axis, it can generate single-photon nanojets with two larger side lobes. Figure 6 is the simulation diagram of the single-photon nanojets generated by the LP ₁₁ mode in the xoy, xoz, yoz directions . When the polarization direction of the LP ₁₁ mode is parallel to the symmetry axis, it can produce two-photon nanojets with symmetrical distribution. Figure 7 is a simulation diagram of the two-photon nanojets generated by the LP ₁₁ mode in the xoy, xoz, and yoz directions. When the outgoing light of the monochromatic light source 1 passes through the fiber polarizer 2, and then passes through the polarization controller 4, it enters the dual-mode fiber 5 with the long-period fiber grating written on it, and directly acts on the medium microspheres 6. The photonic nanojet light field generated by post-detection of the microspheres 6. Adjust the polarization controller 4 to change the polarization state of the LP ₁₁ mode excited by the long-period fiber grating, that is, to realize the adjustment of the optical field of the dual-mode fiber photonic nanojet.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. a dual-mode optical fiber photonic nano-jet optical field control device is characterized in that: comprising a monochromatic light source (1), an optical fiber polarizer (2), a single-mode optical fiber (3), a polarization controller (4), a dual Mode fiber (5), dielectric microspheres (6), high magnification lens (7) and high resolution CCD (8); The end face of the dual-mode optical fiber (5) adheres to the medium microspheres (6) through a low-refractive index glue, the dual-mode optical fiber (5) excites the LP ₁₁ mode, and the light emitted by the monochromatic light source (1) passes through the optical fiber polarizer ( 2) and the single-mode fiber (3) and then excited by the dual-mode fiber (5) to generate photon nano-jets on the dielectric microspheres (6) by different mode spots, and finally observed by a high-resolution CCD (8); The polarization controller (4) on the mode fiber (3) changes the excited LP ₁₁ mode spot, thereby changing the photon nanojet characteristics produced by the dielectric microspheres (6). 2. a kind of dual-mode optical fiber photonic nano-jet optical field control device according to claim 1, is characterized in that: described dual-mode optical fiber (5) is a silica optical fiber with a smaller refractive index difference between core and cladding, or Microstructure optical fiber of glass or semiconductor material with a large refractive index difference between the core and the cladding; the end face of the dual-mode optical fiber (5) is cut flat, so that the contact area between the dielectric microspheres (6) and the dual-mode optical fiber (5) is small. 3. The dual-mode optical fiber photonic nanojet optical field control device according to claim 1 or 2, characterized in that: when the excitation efficiency of the dual-mode optical fiber (5) LP ₁₁ mode is equivalent to the remaining fundamental mode energy, that is, the dual-mode optical fiber (5) When the excitation efficiency of the LP ₁₁ mode is about 50%, the fundamental mode and dual-mode multiplexing photonic nanojet can be realized. 4. a kind of dual-mode optical fiber photonic nano-jet optical field control device according to claim 1, is characterized in that: under the situation that described monochromatic light source (1) does not carry out polarization control by polarization controller (4), The dual-mode optical fiber (5) will excite the hollow annular mode spot in the middle, and act on the dielectric microspheres (6) to generate annular or single-point photon nanojets; in the monochromatic light source (1), the polarization controller (4) is used for In the case of polarization control, the dual-mode fiber (5) will excite a symmetrically distributed double-lobed mode spot, that is, the linearly polarized LP ₁₁ mode. When the polarization direction of the LP ₁₁ mode is perpendicular to the symmetry axis of the mode spot, there will be a The one-photon nanojet of the lobe, when the polarization direction of the LP ₁₁ mode is parallel to the axis of symmetry of the mode spot, produces a symmetrically distributed two-photon nanojet. 5. a kind of dual-mode optical fiber photonic nano-jet optical field control device according to claim 1, is characterized in that: the method that described dual-mode optical fiber (5) excites LP ₁₁ mode is writing long-period fiber grating, melting taper and dislocation welding method. 6 . The dual-mode optical fiber photonic nanojet optical field control device according to claim 1 , wherein the wavelength range of the monochromatic light source ( 1 ) is 400-1600 nm. 7 . 7 . The dual-mode optical fiber photonic nanojet optical field control device according to claim 1 , wherein the size of the dielectric microspheres ( 6 ) ranges from 2λ to 40λ. 8 .

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