CN101398379A - Phase measurement method of high-sensitivity surface plasma resonance and measuring system thereof - Google Patents

Abstract

The invention discloses a measurement method and a measurement system thereof used for measuring the high-sensitiveness surface plasma resonance. The method and the system utilize a principle that output power of a DC light laser near the vale value thereof is affected obviously by the loss change in chamber and lead the surface plasma resonance measurement instrument in an active laser, thus leading the loss of the fixed wavelength caused by a SPR effect to be in the internal loss of the laser chamber and leading the slight change of the SPR loss to be amplified by the acute changes of the output power of the laser and the like, thereby greatly improving the sensitiveness of the surface plasma resonance measurement.

Description

A kind of measuring method and measuring system thereof of high-sensitivity surface plasma resonance

Technical field

The present invention relates to sensor and field of sensing technologies.The present invention is specifically related to the surface plasma resonance measuring method, and the measuring system that realizes this method.

Background technology

Surface plasma (Surface Plasmon abbreviates SP as) is the vibration mode that forms along the collective oscillation by the metal surface electric charge that propagate at interface between metal and dielectric; Surface plasma-wave is present on the material interface of two kinds of dielectric constants opposite (being generally metal and medium).The field intensity of this pattern is reaching maximum at the interface, and all is exponential decay along the direction perpendicular to the interface in the both sides, interface, thereby the mould field is limited near interface.The surface plasma-wave dispersion relation can be expressed as:

$k_{\mathrm{sp}}=\frac{2\mathrm{\π}}{\mathrm{\λ}}{\left(\frac{{\mathrm{\ϵ}}_1{\mathrm{\ϵ}}_2}{{\mathrm{\ϵ}}_1+{\mathrm{\ϵ}}_2}\right)}^{1/2}=\frac{\mathrm{\ω}}{c}{\left(\frac{{\mathrm{\ϵ}}_1{\mathrm{\ϵ}}_2}{{\mathrm{\ϵ}}_1+{\mathrm{\ϵ}}_2}\right)}^{1/2}---\left(1\right)$

k _SpBe metal surface plasma wave propagation coefficient, λ, ω, c is respectively wavelength, the angular frequency and the light velocity.ε ₁And ε ₂Be respectively the dielectric coefficient of metal level, dielectric layer.

Surface plasma resonance (Surface Plasmon Resonance, abbreviate SPR as) be a kind of physical optics phenomenon, can utilize the coupling of modes such as the evanescent wave of light when prism boundary place experiences total internal reflection and metal surface plasma resonance mode, energy is coupled to plasma wave from light wave, and the free electron that causes the metal surface produces the surface plasma vibration.When the plane of linear polarization light wave that is parallel to plane of incidence when electric field component is incident on medium/metal interface with special angle, the wave vector of surface plasma and the wave vector of evanescent wave coupling, the incident light energy is coupled to surface plasma-wave, reach surface plasma resonance, thereby cause energy of reflection light significantly to reduce.The phase matching relation of SPR can be expressed as:

k _x＝ksinθ＝k _sp (2)

By equation (1) and (2) as can be seen, for testing medium of the same race, the generation condition of SPR is the function that is characterized by lambda1-wavelength and incident angle.

The measuring method a kind of commonly used of surface plasma resonance is the intensity scan method.This scan method is to fix at incident angle, under the situation that incident wavelength is fixing, by measuring the variation through the luminous power transmitance of spr sensor, detect the variation of sample characteristic.Owing to be subjected to the influence of noise sources such as detector shot noise and system's thermonoise, the subtle change of the SPR transmitance that produces for sample characteristic generation subtle change is flooded by noise easily, thereby limits its detection resolution.Wherein, the influence of thermonoise in the highest flight.

Summary of the invention

Therefore, task of the present invention provides a kind of measuring method of high-sensitivity surface plasma resonance;

Another task of the present invention provides a kind of measuring system of using above-mentioned measuring method.

On the one hand, the invention provides a kind of measuring method of high-sensitivity surface plasma resonance, may further comprise the steps:

(1) with the adjustment of SPR device and be fixed near the SPR incident angle of sample correspondence;

(2) the SPR device is connected to is operated in the resonator cavity that is operated in the direct current light laser on the specific wavelength, form resonant tank;

(3) power of adjusting pump light source makes laser works near threshold value;

(4) feed sample in sample cell, the signal of measuring according to detecting instrument changes, and obtains the variation of determinand.

In the above-mentioned measuring method (1), the angle that described light incides the SPR sensing layer should be set to slightly depart from the SPR angle of laser works wavelength.

In the above-mentioned measuring method (2), described SPR device places in the resonator cavity that is operated in the direct current light laser on the specific wavelength, and the pumping condition of described direct current light laser is controlled near the threshold value.

In the above-mentioned measuring method (4), the variation of the power of the response of described SPR device by observation laser instrument output light etc. obtains.

On the other hand, the invention provides a kind of measuring system (shown in Figure 1) of high-sensitivity surface plasma resonance.Comprise pumping source 1, gain media 2, polarizer 3, SPR device 4, optical filter 5, measuring equipment 6 and optical cavity 7, pumping source 1 provides energy to gain media 2, and the gain size of adjustable gain medium 2, polarizer 3 guarantees to have only the light of the p polarization that can excite the SPR effect to incide on the SPR sensing layer, SPR device 4 is made of SPR sensing layer, optical coupling system and sample cell, and measuring equipment 6 is measured the watt level that outputs to the light signal outside the optical cavity 7.Optical cavity 7 can be that unidirectional ring cavity also can be the standing wave resonance optical cavity.

In the above-mentioned measuring system, described laser cavity can be unidirectional loop chamber or standing wave resonance laser cavity.

In the above-mentioned measuring system, the output scalable of described pumping source, pumping source can be pump light source, current source, voltage source etc.

In the above-mentioned measuring system, described gain media is a rare earth doped optical fibre or by rare earth doped optical fibre, semiconductor laser amplifier, solid laser crystal.

In the above-mentioned measuring system, described narrow band filter is grating type wave filter, film interference mode filter, grating filter or is realized by the wavelength selection effect of other element.

In the above-mentioned measuring system, described checkout equipment can be PIN photoelectric detector, APD photoelectric detector or light power meter.

The measuring method and the measuring system thereof of high-sensitivity surface plasma resonance sensing of the present invention have the following advantages:

1. the present invention's loss that will adopt the SPR device of intensity scanning to bring is incorporated in the laser chamber internal loss, when the sample refractive index changes, and the loss difference that the SPR device is produced.Because near the nonlinear operation characteristic of laser instrument threshold value, the variation meeting of cavity loss causes tremendous influence to the output of laser instrument, causes the variation of characterisitic parameters such as the output mode of laser instrument and light intensity.Therefore, the faint variation of the present invention can be brought the SPR device when detecting different sample loss produces amplification, has improved the sensitivity that SPR detects.

2. the output power size of pumping source has determined its threshold point among the present invention, and the variation of threshold value will bring the change of the enlargement factor and the sensing range of signal amplification, therefore the enlargement factor that just can regulate measurable scope or measuring-signal by the output power of regulating pump laser.

3. all components and parts in the measuring system that realizes by method of the present invention all can maintain static, and are easy to realize integrated, miniaturization and portability.

Description of drawings

Fig. 1 is a kind of high-sensitivity surface plasma resonance measuring system device synoptic diagram.

The explanation of Fig. 1 drawing

1-pumping source 2-gain media 3-polarizer 4-SPR device 5-optical filter

6-measuring equipment 7-optical cavity

Fig. 2 is a kind of high-sensitivity surface plasma resonance measuring system device synoptic diagram based on optical fiber laser structure.

The explanation of Fig. 2 drawing

1-pump light source 2-wavelength division multiplex device 3-Er-doped fiber 4-isolating device

5-narrow band filter 6-coupling prism 7-sensing layer 8-sample cell

9-SPR device 10-beam splitting device 11-light power meter 12-polaroid

Fig. 3 is the wavelength scan curve of the SPR response under the sample of different refractivity.

Fig. 4 is the correlation curve that adopts the amplitude output signal of the present invention and regular tenacity scanning SPR.

Embodiment

The present invention will adopt the SPR device of intensity scanning to be incorporated in the laser resonant cavity, i.e. the loss of SPR device becomes the part of laser chamber internal loss.When the sample refractive index changes, the loss difference that the SPR device is produced.Because near the nonlinear operation characteristic of laser instrument threshold value, the variation meeting of cavity loss causes tremendous influence to the output of laser instrument, causes the variation of the characterisitic parameters such as output intensity of laser instrument.Therefore, the faint variation of the present invention can be brought the SPR device when detecting different sample loss produces amplification, thereby realizes that high sensitivity SPR detects.

In common SPR intensity scanister, when the variations in refractive index of establishing sample was Δ n, the detection power that is caused by variations in refractive index was changed to Δ I _Signal, establishing the detection signal noise that causes with the irrelevant extraneous thermonoise of signal power is I _Noise, establish k=Δ n/ Δ I _Signal, then the detection sensitivity of system is S=k/I _NoiseIf establish the variations in refractive index of sample among the present invention when being Δ n, detection power changes and is enlarged into A Δ I _Signal(A〉1), then the detection sensitivity S=Ak/I of system of the present invention _Noise=AS, i.e. it is original A times that sensitivity increases.

So the present invention adopts the SPR device is connected to method in the laser resonant cavity, the sensitivity that can improve SPR measuring method and system.

Be example to adopt Er-doped fiber as the ring laser of gain media below, near the amplification characteristic of continuous dc laser device threshold value of deriving.

Fiber laser can come approximate representation with the rate equation of three-level structure

$\frac{{\mathrm{<figure-callout\; id="3"\; label="dN"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">dN</figure-callout>}}_3}{\mathrm{dt}}=W_P{N}_1-\frac{{\mathrm{<figure-callout\; id="3"\; label="N"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">N</figure-callout>}}_3}{{\mathrm{\&tau;}}_3}---\left(3\right)$

$\frac{{\mathrm{<figure-callout\; id="2"\; label="dN"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">dN</figure-callout>}}_2}{\mathrm{dt}}=\frac{{\mathrm{<figure-callout\; id="3"\; label="N"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">N</figure-callout>}}_3}{{\mathrm{\&tau;}}_3}-\frac{{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">N</figure-callout>}}_2}{{\mathrm{\&tau;}}_2}-\frac{{\mathrm{\&eta;}}_S}{{\mathrm{S\&tau;}}_e}({\mathrm{\&sigma;}}_c{N}_2-{\mathrm{\&sigma;}}_a{N}_1)---\left(4\right)$

N ₁＝N ₀-N ₂-N ₃ (5)

$\frac{{\mathrm{<figure-callout\; id="1"\; label="dN"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">dN</figure-callout>}}_1}{\mathrm{dt}}=\frac{{\mathrm{\&eta;}}_S{I}_a}{{\mathrm{\&tau;}}_c}({\mathrm{\&sigma;}}_e{N}_2-{\mathrm{\&sigma;}}_a{N}_1)N_1-\frac{\mathrm{\&delta;}}{{\mathrm{\&tau;}}_c}{N}_1---\left(6\right)$

N wherein ₀Be erbium ion-doped concentration, N ₁, N ₂And N ₃Be the population of each energy level, W _P=P _pσ _Ap/ A _EffHv _pBe pumping efficiency, P _pBe pump power, hv _pBe pump photon energy, A _EffBe the useful area of pump light, σ _ApBe the absorption cross section of pump light, η _sBe the ratio of flashlight in the fiber cores, S is the fibre core area, σ _eAnd σ _aBe the emission and the absorption cross section of laser, N ₁Be the photon number in the laser cavity, τ ₃Be the non-radiative die-away time of pumping level, τ ₂Be the photon lifetime of last energy level, τ _cFor photon transmits time in a week in the chamber, δ is a cavity loss, I _aBe Er-doped fiber length, in order to simplify computing, we have ignored a spot of spontaneous radiation.

In equation (3)-(6), establish dNt _l/ dt=0 (i=1,2,3) can obtain the steady state solution that laser instrument is exported

${\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="A200810056954E00091.png,A200810056954E00092.png"\; state="\{\{state\}\}">N</figure-callout>}}_1=\frac{A}{\mathrm{\&delta;}}-B---\left(7\right)$

$A=\frac{{\mathrm{S\&tau;}}_c{l}_a{N}_0(W_p{\mathrm{\&tau;}}_2{\mathrm{\&sigma;}}_c-{\mathrm{\&sigma;}}_a)}{{\mathrm{\&tau;}}_2[{\mathrm{\&sigma;}}_a+{\mathrm{\&sigma;}}_e(1+W_p{\mathrm{\&tau;}}_3)]}---\left(8\right)$

Output power is directly proportional with N1 and is expressed as follows

$I\&Proportional;\frac{A}{\mathrm{\&delta;}}-B=\frac{A-\mathrm{B\&delta;}}{\mathrm{\&delta;}}---\left(10\right)$

Wherein A-B δ=0 is corresponding to the threshold status of laser instrument, and definition K is

$K=\ln \frac{I_0}{I}---\left(11\right)$

The variable quantity of light intensity when the laser instrument output intensity when wherein I and I0 represent respectively to have or not spr sensor spare in the laser chamber, Δ I change for the cavity loss that causes when this device, when the loss variation is very little, Δ I＜＜I ₀, equation (11) can be written as

$K\&ap;\frac{\mathrm{\&Delta;I}}{I_0}---\left(12\right)$

Obtain the sensitivity enhancer according to equation (10) and (12)

$\mathrm{\&xi;}=\frac{K}{\mathrm{\&Delta;\&delta;}}=\frac{A}{\mathrm{\&delta;}(A-\mathrm{B\&delta;})}---\left(13\right)$

This shows that laser instrument near threshold value A-B δ=0, can reach maximum measurement sensitivity.By changing the laser pumping power P _p, can change its threshold condition, thereby regulate the enlargement factor or the measurement range of the measurement result of SPR.

Fig. 2 has provided a kind of high sensitivity SPR measuring system synoptic diagram that adopts annular direct current light optical fiber laser structure to realize.This system is included in semiconductor pumped light source 1, wavelength division multiplex device 2, Er-doped fiber 3, isolator 4, narrow band filter 5, spr sensor spare 6, light-splitting device 10, light power meter 11 and the polaroid 12 of power-adjustable.

The pumping semiconductor laser centre wavelength of wherein said power controlled is 980nm, and its power is controlled by laser diode current, and the electric current of pump laser is set in the native system, makes laser works near threshold value;

The length of described Er-doped fiber is 11m;

Described isolator 4 makes the light in the optical fiber cavity transmit along single direction;

The passband centre wavelength of described narrow band filter is 1534.26nm, and the 10dB bandwidth is 0.4nm.In this central wavelength, the small variations in refractive index in the optical loss that the SPR device is produced and its sample cell in the sample is linear, as shown in Figure 3.It will be appreciated by those skilled in the art that this narrow band filter can be grating type optical fiber wave filter, film interference mode filter or grating filter, also can realize by the wavelength selectivity of other element in the optical cavity;

Described SPR device, thereby scioptics are coupled into out optical fiber and connect into the fiber laser optical cavity, adopt traditional prism-coupled Kretschmann structure, and the material of coupling prism 5 is ZF-7, its refractive index is 1.763 (on the 1550nm wavelength), and sensing layer 8 is the golden film of thickness 50nm;

Sample in the described sample cell 9 is the NaCl aqueous solution of variable concentrations;

The beam split ratio of described light-splitting device 10 is 1: 9, and 90% light is got back in the ring cavity, and 10% light is input to light power meter 11.

The printing opacity direction of described polaroid 12 is the p polarization direction;

Described SPR device is mainly the SPR structural system of the various SPR of generation effects, and test substance is detected.The detection method that the present invention relates to is applicable to various SPR structures, and conventional monolayers metal SPR structure, long-distance surface plasma resonance (LRSPR), coupling plasma Wave guide resonance (CPWR), Wave-guide coupling surface plasma resonance (WCSPR) etc. all can directly apply in the middle of the above-mentioned measuring system.Also comprise in the SPR device the optical devices of incident beam and folded light beam coupling turnover SPR structure, be used for special angle, will detect light and incide on the SPR sensing layer to excite corresponding SPR effect with the p polarization state.

The measuring method of above-mentioned high sensitivity SPR measuring system is as follows:

At first, use the narrow-band light source close, be coupled into and be mapped on prism and the SPR device the certain sample of injection in the sample cell of SPR device with narrow band filter centre wavelength.Adjust its incident angle according to the optical characteristics of sample, laser incides on coupling prism and the SPR device with this fixing incident angle, makes this incident wavelength near the wavelength that satisfies the SPR condition.

When the sample refraction index changing, as the transmittance curve (shown in Figure 3) of different wave length under this angle that measures, as seen transmitance changes thereupon on narrow band filter centre wavelength.

Then, the above SPR device is connected in the described laserresonator, its incident beam and folded light beam connect in the chamber by coupling device, and the incident angle of SPR device remains unchanged.Adjust pump laser power, make that laser works is near threshold value when in the sample cell of SPR device sample being arranged.

At last, inject different samples, measure the reading variation of described power meter before and after injecting, obtain sample change of refractive size.

In the present embodiment fixing incident angle is chosen to be 52.411 degree, this angle is near the angle that on the 1550nm wavelength specimen in use is produced the SPR response.

The power of pump laser is 20mW in the present embodiment, makes laser works near threshold value.Those skilled in the art should select suitable pump power according to different cavity losses and gain media characteristic.

In the present embodiment SPR device is connected in the resonator cavity of annular optical fiber laser, above-mentioned pump power is set after, respectively refractive index is had small different detected solution to inject spr sensor spare, and the output power of measuring optical fiber laser instrument.The curve of the laser output power that is obtained by light power meter 11 as shown in Figure 4.The output intensity change curve of the traditional SPR intensity scan mode that measures under identical SPR device and same wavelength and incident angle with identical sample is compared, with respect to SPR intensity scan mode, the present invention can change the light intensity that is caused by variations in refractive index and amplify 9.6 times, has greatly improved the sensitivity of SPR scanning.

It should be noted that above embodiment at last only in order to the measuring method that high-sensitivity surface plasma of the present invention resonance is described and the structure and the technical scheme of measuring system thereof, but unrestricted.Although the present invention is had been described in detail with reference to embodiment, those of ordinary skill in the art is to be understood that, technical scheme of the present invention is made amendment or is equal to replacement, do not break away from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of the claim scope of the present invention.

Claims (10)

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

(1) with the adjustment of spr sensor spare and be fixed near the SPR incident angle of sample correspondence;

(2) spr sensor spare is connected to is operated in the resonator cavity that is operated in the direct current light laser on the specific wavelength, form resonant tank;

(3) power of adjusting pump light source makes laser works near threshold value;

(4) feed sample in sample cell, the signal of measuring according to detecting instrument changes, and obtains the variation of determinand.

2. measuring method according to claim 1 is characterized in that, in the described step (1), the angle that light incides the SPR sensing layer should be set to slightly depart from the SPR angle of laser works wavelength.

3. measuring method according to claim 1 is characterized in that, in the described step (2), the SPR device places in the resonator cavity that is operated in the direct current light laser on the specific wavelength, and the pumping condition of described this direct current light laser is controlled near the threshold value.

4. measuring method according to claim 1 is characterized in that, in the described step (4), the variation of the power of the response of SPR device by observation laser instrument output light etc. obtains.

5. the measuring system of high-sensitivity surface plasma resonance comprises pumping source, gain media, narrow band filter, optical cavity, SPR device, Polarization Control device and is used to measure the measuring equipment of output light intensity.

6. measuring system according to claim 5 is characterized in that, the laser cavity in this measuring system can be unidirectional loop chamber or standing wave resonance laser cavity.

7. measuring system according to claim 5 is characterized in that, the output scalable of described pumping source, and pumping source can be pump light source, current source, voltage source etc.

8. measuring system according to claim 5 is characterized in that, described gain media is a rare earth doped optical fibre or by rare earth doped optical fibre, semiconductor laser amplifier, solid laser crystal.

9. measuring system according to claim 5 is characterized in that, described narrow band filter is grating type wave filter, film interference mode filter, grating filter or is realized by the wavelength selection effect of other element.

10. measuring system according to claim 5 is characterized in that described checkout equipment can be PIN photoelectric detector, APD photoelectric detector or light power meter.

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