An optical phase detection method and device using SPR to enhance nonlinear effect

Abstract

The application discloses an optical phase detection method and device using SPR to enhance nonlinear effect, and the method comprises the following steps: forming interference by coherent light beams with different phases to generate a fundamental frequency light interference fringe image; and the interference fringe image is incident on a Kretschmann structure with a gold film on a slope at a resonance angle to excite surface plasmon resonance, reduce the intensity of reflected light, and improve nonlinear conversion effect; and the fundamental frequency light in the reflected light is filtered out, and interference fringe images or power data of high-order harmonics are collected to perform interference phase detection. The application converts phase difference information into optical nonlinear information, uses surface plasmon resonance to enhance nonlinear effect, completes enhancement of nonlinear effect, and the phase detection capability is amplified by the square and the cube, so that the contrast of bright and dark fringes of the interference image is enhanced, and the precision and resolution of phase measurement are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the fields of sensing technology and optical phase detection, and particularly to a method and device for optical phase detection using SPR enhanced nonlinear effect. BACKGROUND

[0002] Surface plasmon resonance (SPR) is originated from the coherent resonance of electrons and light field, which can greatly localize the light field on the metal surface and form extremely high local electromagnetic field intensity. The SPR sensing technology has the advantages of label-free, real-time monitoring, low sample consumption, high sensitivity and high throughput detection, and has wide applications in the fields of environmental monitoring, food safety, genomics and proteomics research.

[0003] Accurate detection of light beam phase is the core of optical technology and the key prerequisite for realizing coherent synthesis of high-energy short pulse laser. Therefore, developing a method for accurately detecting light beam phase with high sensitivity has forward-looking strategic significance for realizing ultra-high peak power laser. The main methods for phase detection include heterodyne method, Hansch-Couillaud (H-C) polarization detection, shearing interference, reference light interference and interference image, etc. However, these methods have certain shortcomings. When the phase difference between two light beams is small, the accuracy of these methods is not high, the resolution is insufficient, and it is difficult to realize accurate detection. The frequency sweeping or frequency offset phase detection method is relatively complex and troublesome. The phase-type SPR sensing technology has quite high sensitivity and response speed. The present technology uses ATR structure to excite surface plasmon resonance and uses SPR to enhance nonlinear effect. The purpose is to convert the change of optical phase into the signal change of second-order and third-order nonlinear response of plasmonic, which is expected to improve the measurement accuracy and contrast of the current interference phase measurement, and provides a new idea for accurate measurement of optical phase of coherent light. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method and device for optical phase detection using SPR enhanced nonlinear effect, which converts the phase information of light into optical nonlinear information based on high-order nonlinear effect, and then enhances the nonlinear effect through surface plasmon resonance to improve the visibility of interference fringe pattern, amplify the light intensity difference of dark and bright fringes of interference fringe, and improve the resolution of phase detection.

[0005] The technical solution of the present application is as follows:

[0006] In one aspect, the present application provides a method for optical phase detection using SPR enhanced nonlinear effect, comprising:

[0007] The coherent light beams with different phases form interference to produce a base frequency light interference fringe image.

[0008] The Kretschmann structure with the gold film plated on the inclined surface is incident at the resonance angle to excite the surface plasmon resonance, reduce the reflected light intensity, and improve the nonlinear conversion effect.

[0009] The fundamental light in the reflected light is filtered out, and the interference fringe image or light power of the high-order harmonic is collected to perform interference phase detection, so that the detection of the phase difference of the coherent light beam is realized, and the visibility of the interference fringe is significantly improved.

[0010] On the other hand, the application also provides an optical phase detection device using SPR to enhance nonlinear effect, comprising:

[0011] A polarization adjustment module is configured to adjust the polarization of different phase coherent light beams to be detected.

[0012] An SPR generation module is configured to generate surface plasmon resonance for the incident coherent light beam, reduce the reflected light intensity, excite interference fringes, and improve the nonlinear conversion effect.

[0013] A filtering module is configured to filter out the fundamental light in the reflected light.

[0014] A collection module is configured to collect data of the high-order harmonic, such as interference fringe images, light powers, etc.

[0015] A data processing system is configured to perform interference phase detection on the collected interference fringe images.

[0016] Preferably, the SPR generation module is a coupling prism with a gold film plated on the inclined surface.

[0017] Preferably, the data collection module is a CCD camera or a light power meter.

[0018] The principle of the application is as follows:

[0019] The nonlinear effect principle is used: nonlinear optics refers to the response of a material to an external light field in a nonlinear manner, which is closely related to the intensity of the external light field. This relationship can be described by the relationship between the material polarizability (P) and the light field intensity (E), that is:

[0020] P = ε0[x (1) E+x (2) E 2 +x (3) E 3 +…]

[0021] In the formula, ε0 is the vacuum dielectric constant, x (n)The n-order nonlinear optical coefficient of the material is a linear term, and the response of the material is linearly related to the intensity of the light field. When the intensity of the external light field is large enough, the nonlinear response of the polarization intensity to the light field becomes obvious. The second-order nonlinear effect is proportional to the square of the intensity of the light field, and the third-order nonlinear effect is proportional to the cube of the intensity of the light field. Surface plasmon resonance can enhance the nonlinear effect, and high-order harmonics are more easily excited. The reflected light after the SPR is filtered and collected, and the interference fringes of the high-order harmonics can be collected. By using the surface plasmon resonance to enhance the nonlinear effect, the phase difference of the light beams can be accurately detected with high sensitivity.

[0022] Interference fringe visibility:

[0023] Wherein, E Max , E Min are the maximum and minimum values of the interference fringe light intensity, respectively. When K=1, the interference fringe visibility is best, and this is called complete coherence; when K=0, the interference fringe visibility is worst, and this is called incoherence. The interference fringe light intensity is amplified through the nonlinear effect, thereby amplifying the visibility difference and improving the phase detection accuracy of the interference image.

[0024] At the same time, the light field intensities of the fundamental light I 1ω , the second harmonic I2 ω and the third harmonic I3 ω are measured by an optical power meter. The optical power is proportional to the size of the light field intensity, and measuring the optical power is equivalent to measuring the light intensity. The change of the high-order harmonic has a certain mathematical rule with the phase difference. The intensities of the second harmonic and the third harmonic are enhanced by the surface plasmon resonance to enhance the nonlinear effect, and the power of the high-order harmonic can be accurately measured. By measuring the third harmonic I3 ω and the second harmonic I2 ω , the ratio K between them can be calculated, and the phase difference value of the different phase interference light can be accurately calculated.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] 1. The phase difference information is converted into optical nonlinear information, and the surface plasmon resonance is used to enhance the nonlinear effect, so that the nonlinear effect is enhanced, the phase detection capability is amplified by the square and the cube, and the contrast of the bright and dark fringes of the interference image is enhanced, and the precision and resolution of the phase measurement are improved.

[0027] 2. The surface plasmon resonance is used to detect the phase of coherent light, and the SPR phase detection is the most accurate method for measuring precision in SPR.

[0028] 3. The application uses interference fringes to measure the phase of coherent light, and measures the high-order harmonic of the interference fringes, and uses ATR attenuated total reflection structure to enhance the generation of high-order harmonic, thereby improving the sensitivity of the measurement; the non-contact measurement does not scratch the measured sample; the sensitivity is high, and the efficiency is high; the structure is simple, and the operation is simple;

[0029] 4. The application uses an optical power meter to measure the optical power of coherent light, and uses surface plasmon resonance to enhance the light intensity of high-order harmonic, thereby amplifying the response of high-order harmonic; the experimental structure is simple, and the operation is simple; the sensitivity is high, and the efficiency is high;

[0030] 5. The entire device is built by discrete optical elements, without complex mechanical structure and electronic structure; the experiment is easy to build, and the application range is wide. The method has high measurement sensitivity, high precision, fast response speed, real-time nondestructive measurement, and simple structure. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a measurement system schematic diagram for detecting phase based on SPR enhanced nonlinear effect according to the embodiment of the application;

[0032] Figure 2 It is a flow chart of the implementation steps for detecting phase by using SPR enhanced nonlinear effect according to the application.

[0033] Figure 3 It is an ATR structure schematic diagram of incident light on a sensing prism;

[0034] Fig. 4 is an interference schematic diagram of fundamental light generated without SPR enhancement, wherein a is an interference intensity distribution curve diagram of the fundamental light, and b is an interference fringe pattern generated by the fundamental light.

[0035] Fig. 5 is an interference schematic diagram of nonlinear second harmonic enhanced by SPR, wherein a is an interference intensity distribution curve diagram of the second harmonic, and b is an interference fringe pattern generated by the second harmonic.

[0036] Fig. 6 is an interference schematic diagram of nonlinear third harmonic enhanced by SPR, wherein a is an interference intensity distribution curve diagram of the third harmonic, and b is an interference fringe pattern generated by the third harmonic.

[0037] In the figure: 1-different phase coherent light beams 2-polarization control device 3-focusing lens 4-coupling prism 5-metal film 6-filter 7-CCD camera / optical power meter DETAILED DESCRIPTION

[0038] The application will be further described in detail below in combination with the drawings and embodiments, but it is not used as the basis for limiting the application.

[0039] The SPR effect can only be excited by p-polarized incident light, and s-polarized incident light cannot produce the SPR effect, so the light source should emit coherent beams with different phases. When the incident fundamental light produces interference, interference fringes on the spectrum are produced.

[0040] Figure 1 A phase detection system based on the SPR enhanced nonlinear effect and a working principle schematic diagram are given. The system includes coherent beams with different phases 1 arranged in sequence on the optical path, a polarization control device 2 for controlling the polarization of the beams, a focusing lens 3, a coupling prism 4, a metal film 5, a filter 6 and a CCD camera / power meter 7.

[0041] The light source outputs coherent beams with different phases along the same direction, and after passing through the polarization control device 2, it becomes linearly polarized light with p-polarization. The coherent light is focused by the focusing lens 3 to be incident on the coupling prism 4 at a resonance angle θ, and the surface plasmon resonance is excited in the Kretschmann structure. At this time, the reflected light intensity is greatly reduced, and the nonlinear effect is greatly enhanced. After the fundamental light is filtered out by the filter 6, the reflected light is sent into the CCD camera / power meter 7 to form an image, and the interference fringe image and the power data of the high-order harmonic are collected. The obtained data is transmitted to the data processing system 8 for processing. The nonlinear process can enhance the light field intensity, amplify the light intensity difference, improve the sensitivity of the interference image method for phase detection, or enhance the intensity of the high-order harmonic.

[0042] The surface plasmon effect originates from the coherent resonance of electrons and light fields, and can greatly confine the light field on the metal surface to form a very high local electromagnetic field strength. Exciting surface plasmon resonance can greatly enhance the nonlinear process, and the interference pattern produced by the second and third harmonics can be used for phase detection, which can break through the current bottleneck and realize ultra-high sensitivity and accurate phase detection. The present application uses the SPR characteristic nonlinear phase detection method to directly measure the phase of coherent light, providing a new method for accurate phase detection of coherent light.

[0043] Figure 2 The implementation steps of the present application for detecting phase by using the SPR enhanced nonlinear effect are shown in the flowchart. The coherent beams with different phases form interference and produce interference fringe patterns. The coherent beams enter the Kretschmann structure with a gold film on the inclined surface to excite surface plasmon resonance. The phase information of the light can be converted into optical nonlinear information by processing the interference fringe image of the high-order harmonic. The optical phase information is converted into interference fringe information, and then the SPR enhanced linear effect is used to obtain interference fringe images with higher resolution. The light power method is used for phase detection, the nonlinear effect is enhanced by surface plasmon resonance to enhance the intensity of the second and third harmonics, and the power of the high-order harmonic can be accurately measured. The third harmonic I3ω : second harmonic I2 ω , calculate the ratio K between them, and can solve the phase difference of different phase interference light.

[0044] Figure 3 is the ATR structure diagram of the incident light in the sensing prism.

[0045] Two coherent beams with different phases can produce interference.

[0046] The coherent light is polarized by a polarization control device to p-polarized light, and a convex lens group is used to form a focusing structure, which is incident to the sensing prism with a gold film structure on the hypotenuse at the resonance angle. In the Kretschmann structure single-layer metal film structure, surface plasmon resonance is excited, and under the resonance state, the energy of the electromagnetic field light is effectively converted into the collective vibration energy of free electrons, and the electromagnetic field is localized in a small range and enhanced. Due to the excitation of surface plasmon resonance to enhance the nonlinear effect of the gold film, the intensity of the reflected light high harmonic wave will increase.

[0047] After the reflected light is filtered through the low-pass filter to filter out the fundamental frequency light in the reflected light, it is incident to the CCD camera, and the interference patterns of the second and third harmonics are observed and displayed as digital images (as shown in Figures 5 and 6). The interference patterns generated by the second and third harmonics generated by the SPR enhancement are transmitted to the data processing system, and the interference image method is used to phase.

[0048] As can be seen from Figure 5, the interference image of the high harmonic wave enhanced by the SPR is phase detected, which significantly improves the contrast of the interference fringe image. According to the detection of the interference phase, the phase information of the coherent light beams with different phases can be accurately obtained.

[0049] Finally, it should be pointed out that the above examples are only used to illustrate the structure and technical scheme of the surface plasmon resonance sensing nonlinear enhancement interference phase measurement method and its measurement system of the present application, but not limited. Although the present application is described in detail with reference to the examples, those skilled in the art should understand that the technical method of the present application can be modified or replaced by equivalent, without departing from the spirit and scope of the technical scheme of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. An optical phase detection method using SPR enhanced nonlinear effect, characterized in that, The steps include the following: Step one: different phase coherent beams form interference to produce a fundamental frequency light interference fringe image; Step two: incident to a prism with a gold film on the slope at a resonance angle to excite surface plasmon resonance through Kretschmann structure, and to produce second and third harmonics, reduce the reflected light intensity, and improve the nonlinear conversion effect; Step three (1): filter out the fundamental frequency light in the reflected light, collect the interference fringe image of the high-order harmonic to perform interference phase detection; Step three (2): filter out the fundamental frequency light in the reflected light, collect the light power of the high-order harmonic to perform phase detection; Step four: calculate the phase difference value through the interference fringe image or the light power data of the high-order harmonic to realize high-sensitivity and high-resolution phase measurement.

2. An optical phase detection device using SPR enhanced nonlinear effect, characterized by, It includes: A polarization adjustment module for adjusting the polarization of different phase coherent beams to be measured to ensure that the incident light is p-polarized light; An SPR generation module, a coupling prism with a gold film on the slope, for producing surface plasmon resonance in the incident coherent light beam, producing second and third harmonics, reducing the reflected light intensity, exciting interference fringes, and improving the nonlinear conversion effect; A filtering module for filtering out the fundamental frequency light in the reflected light; An acquisition module for acquiring data of the fundamental frequency light and the high-order harmonic; A data processing system for performing interference phase detection on the collected interference fringe image.

3. The optical phase detection device using SPR enhanced nonlinear effect according to claim 2, wherein, The detection module is a CCD camera or an optical power meter.

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