CN101398378B - Phase measurement method of surface plasma resonance and measuring system thereof - Google Patents

Abstract

The invention discloses a high-precision surface plasmon resonance phase measurement method and a measurement system thereof. The method and system use the polarization selectivity of the surface plasmon resonance effect to polarize and analyze the wide-spectrum light through different polarization control devices, so as to realize the interference of polarized light with different polarization directions. A certain delay difference is introduced between the polarized lights in the polarization direction to generate interference fringes on the spectrum, so as to realize the function of obtaining the frequency domain phase response information of the surface plasmon resonance effect by detecting the spectral distribution with interference fringes. The invention can accurately detect the frequency-domain phase response of the surface plasmon resonance effect under a very simple structure, avoids complex optical systems such as interferometers, increases the reliability and stability of the detection system, and facilitates the realization of integration, miniaturization and portability change. The invention can combine the wavelength scanning mode and the phase detection method to realize high system sensitivity.

Description

A phase measurement method of surface plasmon resonance and its measurement system

technical field

The invention relates to the field of sensors and sensing technology. The invention specifically relates to a surface plasmon resonance measurement method and a measurement system for realizing the method.

Background technique

Surface plasmon (Surface Plasmon, referred to as SP) is a vibration mode formed by the collective oscillation of metal surface charges propagating along the interface between metal and dielectric; ) on the material interface. The field strength of this mode reaches its maximum at the interface and decays exponentially along the direction perpendicular to the interface on both sides of the interface, so that the mode field is confined near the interface. The surface plasmon wave dispersion relation can be expressed as:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; sp</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

k _sp is the propagation coefficient of the plasmon wave on the metal surface, λ, ω, c are the wavelength, angular frequency and light speed, respectively. ε ₁ and ε ₂ are the dielectric coefficients of the metal layer and the dielectric layer, respectively.

Surface plasmon resonance (Surface Plasmon Resonance, referred to as SPR) is a physical optical phenomenon, which can use the coupling of the evanescent wave of light when total internal reflection occurs at the interface of the prism and the metal surface plasmon resonance mode to transfer energy from the light wave to the surface plasmon resonance mode. Coupled to the plasma wave, the free electrons on the metal surface are induced to generate surface plasmon oscillations. When a linearly polarized plane light wave whose electric field component is parallel to the incident plane is incident on the medium/metal interface at a specific angle, the wave vector of the surface plasmon matches the wave vector of the evanescent wave, and the incident light energy is coupled to the surface plasmon wave, reaching the surface plasmon Resonance, resulting in a significant reduction in reflected light energy, and a significant change in phase, reflected in the observed physical quantities, it will be found that the reflected light intensity decreases, and the phase of the reflected light wave also jumps accordingly. The phase matching relationship of SPR can be expressed as:

k _x ＝ksinθ＝k _sp (2)

It can be seen from equations (1) and (2) that for the same medium to be measured, the generation condition of SPR is a function characterized by the wavelength and angle of incident light. Therefore, currently applied SPR detection scanning methods are all based on changing the incident light conditions. The commonly used scanning methods mainly include angle scanning and wavelength scanning:

1. Angular Interrogation: This is the most commonly used scanning method for traditional surface plasmon resonance sensors. This method uses a light source with a fixed wavelength to find the SPR resonance angle by changing the incident angle of the incident light on the interface of the SPR detection structure.

2. Wavelength Interrogation (Wavelength Interrogation): In this method, when the incident angle of the near-plane beam is fixed, a wide-spectrum light source is incident, and a spectrometer or monochromator is used to measure the spectrum of the reflected light, thereby obtaining different incident wavelengths. The SPR spectral response is used to find the corresponding light wavelength that can generate SPR resonance.

The physical quantity used to judge the occurrence of SPR resonance in the above two methods is usually intensity. Although the phase change caused by SPR is more significant than the intensity change, it is possible to achieve a higher system sensitivity than the detection intensity, but because the experimental device and process of the phase detection currently studied are often too complicated, the current method of detecting reflected light is still commonly used. The intensity is used to judge the occurrence of SPR resonance.

Contents of the invention

Therefore, the task of the present invention is to provide a phase measurement method of surface plasmon resonance;

Another task of the present invention is to provide a measuring system using the above-mentioned measuring method.

In one aspect, the present invention provides a phase measurement method of surface plasmon resonance, comprising the following steps:

(1) The broad-spectrum light with a certain linear polarization direction is incident on the surface of the SPR sample to be tested at a fixed angle. The linear polarization direction should make the incident light contain both s-light and p-light components. This direction can be in the same direction as the s-light polarization direction 45°, the incident light is reflected on the surface of the SPR sample;

(2) introducing a certain delay difference between s-light and p-light through a polarization-dependent delay element for the incident broad-spectrum light and/or the SPR reflected light;

(3) Analyzing the above-mentioned SPR reflected light in another specific linear polarization direction, the linear polarization direction should be between the s-light and p-light polarization directions, and this direction can be 45° with the s-light polarization direction;

(4) Measure the spectrum of the optical signal passing through the polarizer, and obtain the phase information of the SPR effect by analyzing the spectrum signal.

Further, the method further includes step (4) using a data processing method of phase detection under wavelength scanning to determine information such as changes in the refractive index of the SPR measured sample.

In the above method, the certain linear polarization direction is a linear polarization direction that includes both the s-light component and the p-light component, preferably a 45-degree linear polarization direction that makes the intensity of the s-light component and the p-light component the same.

In the above method, the other specific linear polarization direction is a linear polarization direction that includes both the s-light component and the p-light component, preferably a 45-degree linear polarization direction that makes the intensity of the s-light component and the p-light component the same.

In the above method, the linear polarization directions of the polarizer and the analyzer can be different, so that the phenomenon of spectral interference obviously occurs.

In the above method, the delay difference between the s-light and p-light introduced by the polarization-dependent time-delay element makes the spectral interference phenomenon in the spectral range of the broad-spectrum light source used obvious and easy to measure accurately, that is, the number of interference fringes is relatively small. At the same time, it is advisable not to exceed the accuracy range of the spectral measurement equipment.

In the above method, the broad-spectrum light is incident on the surface of the SPR sample to be measured at a fixed angle.

On the other hand, the present invention also provides a phase measurement system for surface plasmon resonance, including a wide-spectrum light source, a first polarization control device capable of generating linearly polarized light, a polarization-dependent delay device capable of generating a fixed delay difference, and a waiting time An SPR measuring device, a second polarization control device capable of transmitting linearly polarized light, a spectral detection device for receiving SPR reflected light, and a data processing system for processing the detection results of the spectral detector device, the polarization-dependent time delay The device is arranged on the light path between the wide-spectrum light source and the spectrum detection equipment.

In the above measurement system, the broadband light source may be a coherent broadband light source or an incoherent broadband light source.

The wide-spectrum light source can be selected from a white light source, a stimulated spontaneous emission (ASE) light source, a superluminescent diode (SLD) light source, a supercontinuum light source, a mode-locked laser, and the like.

The polarization-dependent time-delay device may select a device capable of producing a fixed time-delay difference between s-light and p-light.

The polarization-dependent delay device can be selected from birefringent crystals, polarization-maintaining fibers, etc.; the birefringent crystals can be calcite (CaCO ₃ ), rutile (TiO ₂ ), yttrium vanadate (YVO ₄ ), etc.

The detection equipment can use a spectrometer, a monochromator, a fiber grating demodulator, and the like.

The phase measurement method and measurement system of the surface plasmon resonance of the present invention have the following advantages:

1. The present invention can achieve high-sensitivity detection under a very simple structure by introducing a polarization-related delay element. Compared with the previous phase detection method, it avoids the limitation of complex optical systems such as double-arm interferometers and mostly single-point detection , the present invention can obtain the phase wavelength scanning curve by using a simple detection method, which increases the reliability and stability of the detection system.

2. The light source, detection structure, detection equipment, etc. of the scanning part in the sensing system realized by the method of the present invention can be fixed, which is convenient for realizing integration, miniaturization and portability.

3. The light source, detection structure, detection equipment, etc. in the sensing system realized by the method of the present invention can all realize optical fiber, which is convenient for integration and miniaturization.

4. The sensing system realized by the method of the present invention adopts the wavelength scanning method and the phase detection method at the same time, so it has higher sensitivity than the existing SPR system products of angle scanning and intensity detection.

5. The sensing system realized by the method of the present invention is different from the traditional spatial coherent phase detection method, and adopts the frequency domain interference method for phase detection. The wavelength scanning curve of the phase is obtained at one time, so that the detection accuracy and sensitivity can be further improved through data processing methods such as curve fitting and smoothing, and the influence of errors and noises in single-point phase detection can be reduced.

Description of drawings

Fig. 1 is a device schematic diagram of a high-precision SPR phase measurement system.

Fig. 2 is the spectral intensity curve obtained by measuring the ASE light source through two polarization control devices, a birefringent crystal and an SPR device respectively.

Fig. 3 is the SPR phase response obtained after analyzing the results of the measured spectra under different refractive indices of the detected layers (the refractive index difference n between the samples is 1.2*10 ^-4 RIU).

Illustration

1-broad-spectrum light source 2-first polarization control device 3-polarization-dependent delay element 4-SPR device 5-coupling prism 6-sensing layer 7-sample cell 8-second polarization control device 9-spectrum detection device 10 -Data processing system

Detailed ways

The SPR effect can only be excited by the p-polarized incident light, and the s-polarized incident light will not produce the SPR effect, so when s-light and p-light are incident on the SPR element at the same time, the p-polarized reflected light near the SPR condition Significant amplitude and phase changes occur in the complex amplitude, while the s-polarized reflected light changes little. When the incident s-light and p-light are broad-spectrum and the incident spectrum of the two is the same, it can be expressed by the following formula:

A _s (ω)＝A ₀ (ω)*R _s (ω)≈A ₀ (ω)R _{s, 0} A _p (ω)＝A ₀ (ω)*R _p (ω) (3)

where A ₀ (ω) is the complex amplitude of the incident spectrum, A _s (ω) and A _p (ω) are the complex amplitudes of the reflected s-light and p-light spectra respectively, R _s (ω) and R _p (ω) are the light field reflection functions of the SPR element for s-light and p-light, respectively. Since R _s (ω) changes very little, it can be approximated as a constant R _s,0 .

The phase response of the SPR effect can be obtained by comparing the phase difference between the reflected s-light and p-light. When s-light and p-light pass through an analyzer whose transmission direction is between the polarization directions of the two, the projection components of s-light and p-light in the transmission direction will undergo coherent superposition, that is, interference. The spectral intensity function S(ω) of the above interference signal can be expressed as:

S(ω)∝|A ₀ (ω)| ² (|R _s (ω)| ² +|R _p (ω)| ² )+2|R _s (ω)|·|R _p (ω)|· |A ₀ (ω)| ² cos(ωτ-φ(ω)) (4)

Where φ(ω) is the phase difference between R _s (ω) and R _p (ω), and when R _s (ω) is approximately unchanged, it is equal to the phase response of R _p (ω), that is, the phase of the SPR effect response. Therefore, it can be seen from the above formula that S(ω) has a cos interference modulation item, and the phase function is the phase response of the SPR effect. By measuring the spectral intensity function, the phase response of the SPR effect can be obtained by analyzing the variation law of the interference fringes in the frequency domain.

Figure 1 shows a schematic diagram of a high-precision SPR phase detection system and its working principle. The system includes a wide-spectrum light source 1, a first polarization control device 2, a polarization-related delay element 3, an SPR device 4, a second polarization control device 8, a spectrum detection device 9 and a data processing system 10 arranged sequentially on the optical path, The wide-spectrum light output by the wide-spectrum light source 1 passes through the first polarization control device 2, and becomes linearly polarized light having both s-light and p-light components, passes through the polarization-related delay element 3, and introduces the difference between the s-light and p-light The fixed delay difference is incident on the SPR device 3 at a fixed angle, and after the reflection of the SPR device 3, the phase difference caused by the SPR response of the s light and the p light is introduced, and then passes through the second polarization control device 8 to make the s light and the p light The light is projected in the same direction to generate interference, and is received by the detection device 9, and the obtained data is transmitted to the data processing system 11 for processing.

Wherein said broadband light source 1 adopts ASE light source, its output spectrum width (3dB) is 35nm, and center wavelength is 1545nm;

The polarization control devices described in this example all adopt Glan prisms, adjusted to a 45-degree linear polarization state, and the front and rear polarization control devices are in the same direction or perpendicular; those skilled in the art should understand that the polarization control devices can also use polarizers, etc. And the polarization direction is not limited to 45 degrees, it is better to produce obvious interference.

The polarization-related delay element 3 adopts a 35mm thick birefringent crystal yttrium vanadate to provide a delay difference of 23ps; those skilled in the art should understand that different types of birefringent crystals, such as calcite rutile, etc., can also be used, and Polarization maintaining fiber.

In the SPR sensor device, the traditional prism coupling Kretschmann structure is adopted, the material of the coupling prism 5 is ZF-7, and its refractive index is 1.763 (at a wavelength of 1550nm), the sensing layer 6 is a gold film with a thickness of 50nm, and 7 is the sample cell ;

The measured solutions in the sample pool 7 are NaCl aqueous solutions of different concentrations, and the difference in refractive index of each adjacent sample is 1.2*10-4RIU;

The detection device 9 is a spectrometer with a wavelength resolution of 0.01 nm. Those skilled in the art should understand that other spectral detection devices such as a monochromator can also be used.

In the entire measurement system, the broadband light source can also use other coherent or incoherent broadband light sources, such as white light source, stimulated spontaneous emission (ASE) light source, superfluorescent diode (SLD) light source, supercontinuum light source, lock Mode lasers, etc., the role of the broadband light source mainly includes: (i) its output spectrum contains the corresponding spectral components that can excite the surface plasmon resonance effect in the SPR device, (ii) its output spectrum has a certain spectral width and contains rich frequency components, (iii) whose output spectral width determines the detection range.

The first polarization control device can also use a polarizer, a wave plate group, etc., and the main functions of the polarization control device are: (i) make the incident light before the SPR device have components in two directions of s and p, for the SPR In response, the phase difference of the s-light component and the p-light component is modulated; (ii) its polarization direction is preferably a 45-degree polarization direction such that the s-light and p-light components have the same intensity.

The second polarization control device can also use a polarizer, etc. The main functions of the polarization control device are: (i) make the s light component and the p light component projected in a direction, which is located between the s light component and the p light component Between the polarization directions, so that the output polarized light interferes due to the fixed delay difference on the two components and the phase difference introduced by SPR; (ii) the polarization direction preferably makes the projection intensity of s-light and p-light the same4 5-degree polarization, that is, the same or perpendicular to the polarization direction of the first polarization control device; (iii) It is advisable to choose the polarization directions of the first polarization control device and the second polarization control device so that interference occurs obviously.

The polarization-related time-delay element can also use birefringent crystal calcite, rutile, polarization-maintaining fiber, etc. The main functions of the polarization-related time-delay element are: (i) make the s light component before reaching the second polarization control device and The p-light component has a certain phase difference or delay difference; (ii) for the delay element composed of optical crystals, the direction of its optical axis is preferably the way that makes the delay difference between s-light and p-light the largest, even if s-light and p-light Respectively incident on the direction of the o-light and e-light of the crystal; (iii) the introduced phase difference or delay difference should make the projection of the s-light component and the p-light component in the direction determined by the second polarization control device produce obvious interference, And it is better that the number of coherent fringes is denser on the spectrum detection equipment.

The polarization-related delay element can be placed between the light source and the SPR device, first introduce a fixed delay difference, and then stimulate the SPR effect, and introduce the phase difference of the SPR modulation, or the polarization-related delay element can be placed between the SPR device and the spectrum Between detection devices, the SPR effect is excited first, the SPR phase difference is introduced, and then the fixed delay difference is introduced. Alternatively, one or more polarization-related delay elements are respectively arranged before and after the SPR device, and work together to introduce a suitable fixed delay difference cumulatively.

The SPR devices are mainly various SPR structural systems that can generate SPR effects, and detect substances to be tested. The detection method involved in the present invention is applicable to various SPR device structures, such as traditional single-layer metal SPR structure, long-range surface plasmon resonance (LRSPR), coupled plasmon waveguide resonance (CPWR), waveguide coupled surface plasmon resonance (WCSPR), etc. can be directly applied in the above measurement system. The SPR device also includes an optical device for coupling the incident beam and the reflected beam into and out of the SPR structure, and incident the incident light on the SPR sensing layer in the polarization state generated by the first polarization control device at a specific angle to excite the corresponding SPR effect.

The main functions of the detection equipment are: (i) to measure the frequency-domain spectral intensity distribution formed after the interference of different polarization components; (ii) to choose equipment with higher wavelength resolution, which is convenient for measuring the small changes in the phase of each cycle so as to extract The phase change information due to the SPR effect is obtained.

The main functions of the data collection and processing unit can include: (i) collecting the spectral distribution curve output by the detection device; (ii) calculating the detected spectral intensity distribution curve, extracting the fixed delay difference SPR phase response.

The detection method of the above frequency domain SPR phase detection system is as follows:

Firstly, the broadband light output by the broadband light source is sequentially passed through the first polarization control device adjusted to a 45-degree linear polarization state with respect to the s-light polarization direction, the birefringent yttrium vanadate crystal, the light transmission direction and the first polarization control device. The second polarization control device with the same polarization direction of the device, that is, a direction of 4 to 5 degrees to the polarization direction of s light, is injected with the SPR device of the sample to be measured, and is detected and received by the spectrometer to obtain the frequency domain signal i _SPR (λ) ;

In the above steps, the birefringent crystal can also be placed on the optical path after the SPR device, that is, between the SPR device and the second polarization controller.

In this example, the method of selecting a fixed incident angle is as follows: adjust the transmission angles of the first polarization controller and the second polarization controller to the p polarization direction, move the birefringent crystal out of the optical path, and first set the When a light source with a fixed wavelength is incident, the incident angle is adjusted to find the position corresponding to the SPR response of the solution to be tested. Those skilled in the art should be able to select a suitable incident angle according to different incident wavelengths and solutions to be tested.

Figure 2 shows the shape of the spectrum of the ASE light source after passing through two polarization control devices, a birefringent crystal and an SPR device.

Figure 3 shows the phase curves in the frequency domain obtained from the spectral intensity curves similar to those in Figure 2 under different sample conditions. The refractive index change difference of each adjacent sample is 1.2*10-4RIU, and it can be seen that the SPR phase curve shifts obviously after the change of the sample refractive index causes the SPR resonance wavelength to change. According to the movement of the phase curve, the SPR and the change information of the measured sample can be obtained accurately.

Finally, it should be noted that the above embodiments are only used to illustrate the structure and technical solution of the surface plasmon resonance sensing phase measurement method and its measurement system of the present invention, but are not limiting. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent replacements to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all of them should be included in the scope of the present invention. within the scope of the claims.

Claims (8)

1. the measuring method of a surface plasma resonance may further comprise the steps:

(1) wide range light is risen partially through first Polarization Controller that can produce linear polarization state, make it have polarization direction between s direction and p direction;

(2) described linear polarization wide range light is incided SPR device to be measured with fixed angle;

(3) described wide range light is before passing through described SPR device and/or afterwards by the relevant time delay device of polarization, it is poor to make that the light component of the light of the s direction polarization in the wide range light and p direction polarization has constant time lag, and detected spectrum produces a plurality of spectrum interference fringes in this time-delay official post step (4) in the accuracy rating of spectral measurement equipment;

(4) the wide range light with above-mentioned delay inequality is carried out analyzing a certain line polarization direction, its analyzing direction must make the s direction of linearly polarized light and p durection component partly pass through simultaneously, carrying out spectral intensity afterwards detects, and the one group of frequency domain interference fringe that obtains according to detection, utilize data processing method, obtain the frequency domain phase information of SPR effect, in the process that obtains described frequency domain phase information, the light source of sweep test, detection architecture, checkout equipment all maintain static.

2. measuring method according to claim 1 is characterized in that, the linear polarization wide range light that produces in the described step (1) preferably makes the s direction 45 degree linearly polarized lights identical with p durection component size.

3. measuring method according to claim 1 is characterized in that, the preferred 45 degree polarization directions of the analyzing direction in the described step (4).

4. the measuring system of a surface plasma resonance, comprise wide spectrum light source, can make wide range light produce first Polarization Controller of the linear polarization state of the polarization direction between s direction and p direction, can produce the relevant time delay device of polarization of the constant time lag difference between the different polarization light, SPR device to be measured, second Polarization Controller that is used for analyzing, be used to detect light spectrum detecting apparatus and the data handling system that is used to handle described checkout equipment testing result through the light of SPR device, described time delay device is arranged on the light path between described first and second Polarization Controllers, its relevant time-delay extent of polarization to s direction and p durection component makes the spectrum through the light of second Polarization Controller produce a plurality of spectrum interference fringes, the light source in the measuring process in the measuring system in the accuracy rating of spectral measurement equipment, detection architecture, checkout equipment maintains static.

5. measuring system according to claim 4 is characterized in that, described wide spectrum light source is incoherent or relevant wide spectrum light source, comprises white light source, is excited spontaneous radiation light source, superfluorescence diode light-source, super continuum source or mode-locked laser.

6. measuring system according to claim 4 is characterized in that, described Polarization Control device comprises polaroid or Glan prism.

7. measuring system according to claim 4 is characterized in that, the time delay device that described polarization is relevant comprises birefringece crystal or polarization maintaining optical fibre.

8. measuring system according to claim 4 is characterized in that described light spectrum detecting apparatus is the spectral intensity checkout equipment, comprises spectrometer, monochromator or fiber Bragg grating (FBG) demodulator.

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