A surface wave based coherent multicore fiber probe

Abstract

The application discloses a kind of based on surface wave's coherent multicore optical fiber probe, including multicore optical fiber and metal film, metal microstructure hole is provided on the metal film, the multicore optical fiber includes optical fiber cladding and the core distributed in the optical fiber cladding inside, the core is set as at least two, the metal film covers the tip of the core, the incident light in the core inside channel is polarization state orthogonal or the same signal, surface plasmon is excited from the surface layer of the metal film or from the metal microstructure hole and is transmitted, the sensitivity of micro parameter is dynamically regulated using the phase difference between incident light.The application uses a kind of based on surface wave's coherent multicore optical fiber probe, can realize any parameter sensing according to the required environment, does not need strict spatial collimation, coupled light path, eliminates the influence of incident light oblique incidence on device performance, with low energy consumption, dynamic tuning, high integration, structure is small, system stable and the like characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nano-optics, and in particular to a coherent multicore fiber probe based on surface waves. BACKGROUND

[0002] With the advent of nanotechnology, people have higher requirements for the detection of substances in the fields of medical treatment, environment, disease prevention and biochemistry. However, there are still a series of technical problems in the detection of low content and small substances. Therefore, researching high-sensitivity, high-resolution and high-integration sensing and detection technology and developing corresponding sensing and detection instruments have become an important task in the field of sensing and detection. Surface plasmon polaritons (SPP) have attracted extensive attention and research due to their characteristics of breaking the diffraction limit at subwavelength scale, high energy localization and realizing near-field enhancement. Surface plasmon polaritons propagating in a medium are usually referred to as surface waves. The advantages mainly lie in two aspects. On the one hand, surface plasmon polaritons are a very weak decaying resonance excited by incident electromagnetic waves, which is extremely sensitive to changes in the refractive index, temperature and other changes of the medium around the metal, so it can be used to make sensors. On the other hand, surface plasmon polaritons can break the diffraction limit and realize the regulation of optical field at subwavelength scale. Based on these advantages, surface plasmon polaritons have been widely used in the fields of biological / chemical sensing, surface enhanced Raman scattering, signal transmission, enhanced nonlinear effect and super-resolution imaging.

[0003] Optical fiber as a kind of general optical device has the advantages of strong anti-interference, strong flexibility, long optical transmission distance and the like. The application and use of optical fiber has long exceeded the ability of simply transmitting information from a light source to a detector. In many applications, the most attractive feature of optical fiber is the possibility of long-distance propagation, which extends the interaction between light and matter. However, for the most advanced photon functions such as signal transmission, optical filtering and sensing, the standard solution is to rely on external optical circuits, but this method needs to reliably and accurately control the coupling between the signal transmission optical fiber and the more complex circuit. Recent fiber-on-a-chip technology provides a method to overcome this inherent limitation, i.e. using microstructures on the tip of the optical fiber to realize optical communication and detection.

[0004] In the 1970s, with the development of optical fiber communication technology, optical fiber sensing technology also emerged, which uses the interaction between the evanescent field around the optical fiber and the medium to be measured for sensing. Optical fiber sensor uses optical fiber transmission as the sensitive information of measurement, which combines the advantages of optical fiber and optical measurement. In the 21st century, micro-nano optical fiber combining optical fiber technology and micro-nano processing technology has become a research hotspot. Micro-nano optical fiber has unique optical properties such as strong light field constraint, strong evanescent field and small mass, which makes it have great application value in optical transmission, coupling and sensing detection fields. Surface plasmon optical fiber sensing technology combines the high sensitivity of surface plasmon sensing technology and the high bandwidth and low loss of optical fiber transmission technology, and can realize the regulation and sensing detection of light on the micro-nano scale, thereby breaking through the bottleneck problem of traditional sensors, and is one of the effective ways to realize the application value of the two. With the rapid development of surface plasmon related theory and application and the maturity of nano processing technology, the characteristics of surface plasmon being very sensitive to external environmental changes and the demand for micro detection in molecular detection field are not coincidental, so the surface plasmon probe based on surface plasmon is born in time, and has become a research hotspot.

[0005] The optical fiber surface plasmon probe is a kind of high-efficiency optical fiber sensing technology based on the principle of surface plasmon, which has the advantages of high efficiency, sensitivity, good biological compatibility and real-time monitoring. Due to the diversification of the target to be detected, the single-channel surface plasmon probe cannot meet the demand. The development of multi-channel surface plasmon probe has become a research hotspot, which is more accurate in measurement than multi-channel. Peng et al. studied the double-channel surface plasmon fiber probe (Opt. Lett., 2005, 30(17):2218-2220), which can detect different surface plasmon signals on the two sides of a probe. Liu et al. studied the double-channel surface plasmon probe, which plated a gold film with a thickness of 50 nm on the inclined surface of the optical fiber, and obtained a sensitivity of up to 6463 nm / RIU by reducing the mode noise (Opt. Lett. 40, 2015, 2826-2829). The use of gratings on a single optical fiber to make multiple-channel surface plasmon probes has been studied (Opt. Lett., 2015, 40(1):115-118), but there is still a lack of sensitivity. The use of fiber optic laboratory technology on a nanoscale scale to develop high-performance new optical fiber probes plays an important role in improving the level of medical diagnosis, strengthening the detection of food safety, and preventing harmful substances, which cannot be ignored. SUMMARY

[0006] The application aims to provide a surface wave based coherent multi-core optical fiber probe, which can realize sensing of any parameter of an environment as required, does not need strict spatial collimation and coupling light path, eliminates influence of oblique incidence of incident light on device performance, and has low energy consumption, dynamic tuning, high integration, small structure, system stability and the like.

[0007] To achieve the above object, the application provides a surface wave based coherent multi-core optical fiber probe, which comprises a multi-core optical fiber and a metal film, the metal film is provided with a metal microstructure hole, the multi-core optical fiber comprises a fiber cladding and a core distributed inside the fiber cladding, the core is provided as at least two, the core is single mode and has the same refractive index, and the metal film covers a tip of the core.

[0008] The incident light in the core internal passage is a signal with orthogonal or same polarization state, surface plasmons are excited from a surface layer of the metal film or from the metal microstructure hole and are transmitted, and sensitivity of a micro parameter is dynamically regulated by using phase difference between the incident light.

[0009] Preferably, the incident light is two linearly polarized lights with same frequency and propagation speed, and orthogonal or same polarization direction.

[0010] Preferably, the core is one of double core, triple core and ring core, and signals between the cores do not interfere with each other.

[0011] Preferably, the metal microstructure hole is one of H shape, U shape, rectangle, trapezoid, rhombus and circle, and is arranged as a periodic or non-periodic structure to meet a condition of exciting surface waves by metal nano hole array.

[0012] Preferably, the metal film and the metal microstructure hole are selected from one of gold, silver and aluminum, a metal film with certain thickness is prepared on a treated core end face by using electron beam evaporation technology, and a microstructure on the metal surface is processed by using focused ion beam etching technology.

[0013] Preferably, the end face of the core is one of wedge shape, inclined end face and cone.

[0014] Therefore, the application provides a surface wave based coherent multi-core optical fiber probe, which can realize sensing of any parameter of an environment as required, does not need strict spatial collimation and coupling light path, eliminates influence of oblique incidence of incident light on device performance, and has low energy consumption, dynamic tuning, high integration, small structure, system stability and the like.

[0015] In addition, compared with the prior art, the application has the following advantages:

[0016] 1. The multi-core optical fiber probe is efficient and sensitive, and the device is easy to realize.

[0017] 2. The flexible design of the metal microstructure hole can make the sensing characteristics of the multi-core optical fiber probe easy to control.

[0018] 3. The sensitivity of the multi-core optical fiber probe is only related to the metal material and the microstructure design, and the sensing characteristics are not affected by other factors.

[0019] The technical solutions of the present application will be further described in detail below with the help of the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 A flowchart of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0021] Figure 2 A sensing diagram of a metal microstructure hole at the end face of an optical fiber of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0022] Figure 3 A sensing diagram of a metal thin film at the tip of an optical fiber of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0023] Figure 4 A schematic diagram of a circular metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0024] Figure 5 A schematic diagram of a double-circular metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0025] Figure 6 A schematic diagram of a trapezoidal metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0026] Figure 7 A schematic diagram of an H-shaped metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0027] Figure 8 A schematic diagram of a rectangular metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0028] Figure 9 A schematic diagram of a U-shaped metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0029] Figure 10 A schematic diagram of a rectangular metal microstructure hole of an embodiment of the present application, a coherent multi-core optical fiber probe based on surface waves;

[0030] Figure 11L-shaped metal microstructure hole arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0031] Figure 12 H-shaped metal microstructure hole arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0032] Figure 13 Circular metal microstructure hole arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0033] Figure 14 Double-core fiber core arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0034] Figure 15 Three-core fiber core arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0035] Figure 16 Annular core fiber core arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0036] Figure 17 Four-core fiber core arrangement diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0037] Figure 18 Single-face side polishing schematic diagram of a fiber tip of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0038] Figure 19 Double-face side polishing schematic diagram of a fiber tip of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0039] Figure 20 δ=0 phase control sensing effect diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0040] Figure 21 δ=π / 2 phase control sensing effect diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0041] Figure 22 δ=π phase control sensing effect diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0042] Figure 23 δ=3π / 2 phase control sensing effect diagram of a surface wave based coherent multi-core optical fiber probe embodiment of the present application;

[0043] 1, metal microstructure hole; 2, detection object; 3, fiber core; 4, optical fiber cladding; 5, incident light signal. DETAILED DESCRIPTION

[0044] The technical solutions of the present application are further described below by means of the accompanying drawings and examples.

[0045] To make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and illustrated in the accompanying drawings herein can be arranged and designed in various different configurations.

[0046] Embodiments

[0047] The present application provides a surface wave based coherent multicore fiber probe, comprising a multicore fiber and a metal film, the metal film is provided with a metal microstructure hole 1, the multicore fiber comprises a fiber cladding 4 and a core 3 distributed inside the fiber cladding 4, the core 3 is single mode and has the same refractive index, and the metal film covers the tip of the core. The metal film completely covers the fiber tip, the incident light is transmitted to the metal film to generate evanescent waves by total internal reflection, the surface waves are excited by the metal film, are locally enhanced at the fiber tip, form an energy hot spot, and realize high-sensitivity sensing of multiple parameters such as temperature, refractive index, concentration and perturbation. The metal film and the metal microstructure hole are selected from one of gold, silver and aluminum, a metal film with a certain thickness is prepared on the treated core end face by using electron beam evaporation technology, and a microstructure on the metal surface is processed by using focused ion beam etching technology. The metal microstructure hole is one of H-shaped, U-shaped, rectangular, trapezoidal, rhombic and circular, and the spatial distribution is set as a periodic or non-periodic structure to meet the surface wave excitation condition of the metal nano-hole array.

[0048] The end face of the core 3 is one of wedge-shaped, beveled, and conical, the core 3 is set as one of double-core, three-core and ring-shaped core, and the signals between the cores 3 do not interfere with each other.

[0049] The incident light in the internal channel of fiber core 3 is a signal with orthogonal or identical polarization states. The incident light excites surface plasmons from the surface of the metal thin film or from the microstructure holes of the metal and propagates. The sensitivity of microparameters is dynamically controlled by utilizing the phase difference between the incident light beams. The incident light excites surface plasmons on the surface of the metal thin film or in the microstructure holes of the metal and propagates, forming hot spots at the tip or exciting surface plasmons in the microstructure holes of the fiber end face. This allows for the study of field enhancement or resonance peak phenomena of the fiber probe and the exploration of the interaction between surface waves and the external environment. This can be applied to the field of micro-sensing by dynamically controlling the sensitivity of different microparameters using the phase difference between the incident light beams. The intensity of the metal surface plasmons excited by incident light with different phase differences varies, thus achieving the monitoring of multiple parameters of the external environment. Surface wave sensing can utilize the phase difference between the incident light beams to dynamically control the sensitivity of different microparameters. The intensity of the metal surface plasmons excited by incident light with different phase differences varies, thus achieving the monitoring of multiple parameters of the external environment.

[0050] The principle of surface plasmon excitation by metal microstructure pores: When light shines on a metal film with a nanopore array, the pore array on the metal film has a scattering effect, and the incident electromagnetic waves will also interfere with each other. In both cases, diffracted waves will be generated, and the diffracted waves localized on the metal surface will excite surface plasmons.

[0051] This surface wave-based coherent multi-core fiber optic probe utilizes the different phase differences between the incident light signals in the fiber cores to achieve multi-parameter sensing. This sensor can be extended to biochemical detection, environmental gas monitoring, and refractive index applications.

[0052] In this embodiment, the fiber core serves as the carrier of incident light. Upon reaching the metal microstructure hole or metal surface, surface plasmons are excited. On the surface of the metal microstructure hole, there is a probe 2 of a coherent multi-core fiber optic probe based on surface waves. The surface plasmons propagate and converge at the fiber tip, which will excite a localized enhanced field effect. When the refractive index, concentration, or refractive index of the external environment changes, the change in microparameters can be identified by utilizing the change in the field effect. Figure 2 , 3 The images present examples of metal microstructured holes placed on the fiber end face and metal thin film-coated fiber tips. Different metal microstructured holes can induce different surface plasmon resonances. Figures 4-9 The unit shape of the pores in the metallic microstructure is provided. Different spatial arrangements can also determine the resonance intensity of plasmons. Figures 10-13 A reference schematic diagram of the arrangement of pores in the metal microstructure is provided. Since multi-channel technology can add new degrees of freedom for microparameter probing, some reference schematic diagrams of the fiber core distribution are listed here, such as... Figures 14-17 As shown. Considering different applications, the characteristics of the fiber tip vary. Figure 18 This is a schematic diagram of a multi-core fiber optic sensing system during single-sided side-throwing of the fiber tip. Figure 19A schematic diagram of a multi-core optical fiber sensing probe with double-side polished fiber tip.

[0053] In addition, taking a double-channel conical fiber tip optical fiber as an example, the conical fiber tip is covered by a metal film, two incident lights are perpendicularly incident, surface plasmons are excited on the metal film, a locally enhanced hot spot is formed after transmission along the fiber tip, and the change of the external environment micro-parameters (temperature, refractive index, etc.) is determined by using the field effect change of the hot spot. The two incident lights are linearly polarized lights without polarization limitation, the phase difference of the incident light can change the intensity of different surface plasmons. Under different phase differences, the incident light signals E1 and E2 can be expressed as

[0054] E1=A1cos(wt-kz) (1)

[0055] E2=A2cos(wt-kz+δ) (2)

[0056] Wherein, A is the amplitude, k is the angular wave number, δ is the phase difference, t is the time;

[0057] It can be seen that by changing the phase difference of the incident light, the transmission wave intensity can be modulated. Figures 20-23 The surface plasmon intensity images under several special phase differences are shown.

[0058] When δ=0, the surface plasmon intensity image is as shown in Figure 20 ;

[0059] When δ=π / 2, the surface plasmon intensity image is as shown in Figure 21 ;

[0060] When δ=π, the surface plasmon intensity image is as shown in Figure 22 ;

[0061] When δ=3π / 2, the surface plasmon intensity image is as shown in Figure 23 .

[0062] The optical fiber and the metal microstructure hole in the embodiment are only schematic diagrams, and do not limit the size and shape of the microstructure hole.

[0063] Therefore, the coherent multi-core optical fiber probe based on surface waves can realize sensing of any environmental parameters according to the needs, and does not need strict spatial collimation, coupling light path, eliminates the influence of oblique incidence of incident light on the performance of the device, has the characteristics of low energy consumption, dynamic tuning, high integration, small structure, stable system, etc.

[0064] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A coherent multi-core fiber probe based on surface waves, characterized in that: The system includes a multi-core optical fiber and a metal thin film. The metal thin film has metal microstructure holes. The multi-core optical fiber includes an optical fiber cladding and fiber cores distributed inside the optical fiber cladding. There are at least two fiber cores. The fiber cores are single-mode and have the same refractive index. The metal thin film covers the tip of the fiber cores and completely covers the tip of the optical fiber. When incident light is transmitted to the metal thin film, the evanescent wave generated by total internal reflection passes through the metal film and excites a surface wave, which is locally enhanced at the tip of the optical fiber to form an energy hotspot, thereby realizing high-sensitivity sensing of multiple parameters. The incident light in the internal channel of the fiber core is a signal with orthogonal or identical polarization states. The incident light excites surface plasmons from the surface of the metal thin film or from the metal microstructure pores and is transmitted. The sensitivity of micro-parameters is dynamically controlled by the phase difference between the incident light. The fiber core is the carrier of the incident light. When it reaches the metal microstructure pores or the metal surface, it excites surface plasmons. There is a probe of a coherent multi-core fiber optic probe based on surface waves on the surface of the metal microstructure pores. The transmission and convergence of surface plasmons at the fiber tip will excite a localized enhanced field effect. When the refractive index, concentration or refractive index of the external environment changes, the change of micro-parameters is identified by the change of the field effect. The fiber core is one of a dual-core, triple-core, or ring-shaped core; the metal microstructure pores are one of an H-shape, U-shape, rectangular, trapezoidal, rhomboid, or circular, and their spatial distribution is set as a periodic or non-periodic structure to meet the conditions for exciting surface waves from the metal nanopore array; the end face of the fiber core is one of a wedge shape, an oblique end face, or a cone shape.

2. The coherent multi-core fiber probe based on surface waves according to claim 1, characterized in that: The incident light consists of two linearly polarized beams with the same frequency, propagation speed, and polarization directions that are orthogonal or identical.

3. A surface wave-based coherent multi-core fiber probe according to claim 2, characterized in that: Both the metal thin film and the metal microstructure pores are made of gold, silver, or aluminum. A metal film of a certain thickness is prepared on the treated fiber core end face using electron beam evaporation technology, and the microstructure on the metal surface is processed using focused ion beam etching technology.

Images