CN1215152A - High-resolution surface plasma wave angle/refractive index sensor - Google Patents

Abstract

The present invention belongs to the field of precision measurement technology, including laser, polarizer, magnetic-optical modulator, angle sensor component, polarization analyzer, photoelectric detector, signal source, lock-in amplifier, A/D converter, PC computer signal processing and display unit, in which the angle sensor component is a rectangular prism placed on the tested material, and the oblique angle surface of the prism is arranged opposite the laser, and a rectangular surface is coated with metal film with laser surface plasma wave. The polarizer and magnetic-optical modulator are placed in the incident light circuit between prism and laser. Said invention is high in resolution, simple in structure, small in valume, specially suitable for use in limited space.

Description

High-resolution surface plasma wave angle/refractive index sensor

The invention belongs to the Technology of Precision Measurement field, particularly based on the angle of optics total internal reflection principle and excitating surface plasma ripple principle or refraction Design of Sensor.

Interferometer and autocollimator are used in accurate measurement of angle usually, though these instruments provide very high resolution, and most of inaccessible 1 * 10 ^-7The requirement of radian, and sensor bulk is bigger.Multi-functional as everyone knows two-frequency laser interferometer (as HP5528), measurement of angle resolution are 3 * 10 ^-7Radian.Sensor bulk is also big, is difficult to be used for occasions with limited space (as nano-machine).

Recently, receive publicity based on the angular transducer of optics total internal reflection principle and excitating surface plasma ripple principle, their common feature is that sensor bulk is little, and goodish resolution can be provided, and is specially adapted to the situation of limited space.People such as Huang utilize the amplitude characteristic of total internal reflection to develop the high sensitivity angular transducer, but this sensor is subjected to the influence of extraneous light intensity.People such as Chiu utilize the phase place characteristics of total internal reflection P ripple and S ripple to develop another kind of angular transducer, can not be subjected to the influence of ambient lighting.Angular transducer based on total internal reflection principle has a common shortcoming, i.e. severe nonlinear, and its sensing element must cooperate with two identical prisms just can work.People such as Margheri utilize excitating surface plasma ripple principle to make angular transducer, overcome non-linear, its sensor element as long as a prism promptly can work.

Input light only contains P ripple (claiming the TM ripple again) in the Margheri scheme, utilizes the relation of P ripple excitating surface plasma wave reflection light intensity with incident angle, measures the purpose that reflective light intensity reaches angle measurement.The resolution that the people reached such as Margheri are 0.1 rad, close 4.87 * 10 ^-7Radian, their device only are experimental provisions, as the total reflection prism of sensing element light beam are carried out primary event, as shown in Figure 1.When sensing element transmission θ angle, the reflected light direction is rotated 2 θ angles, its receiver just must change 2 θ, receiver promptly can not be motionless together with light source like this, can not rotate with sensing element, and must rotate separately, in practice because the θ angle is unknown before measurement, so this device practicality is very poor.

Surface plasma wave sensor is used to reflect flat rate mostly and measures, the molecular conecentration that derives from is measured thus, refractometry is the measurement of a chemico-analytic important parameter, but the resolution inaccessible 1 * 10 of present surface plasma wave index sensor ^-6Refractive index unit.

The objective of the invention is to overcome the weak point of prior art, propose a kind of novel angle/index sensor.Utilize the same incident angle/refractive index of variation of P ripple excitating surface plasma wave phase relevant, the S ripple can not the excitating surface plasma ripple, the feature that the same incident angle/refractive index of its phase change has nothing to do in interested scope, obtain the variation of reflected light polarization state, cooperate the high sensitivity polarized interferometer, make the resolution height of its angle measurement/refractive index, and it is simple in structure, its sensing element only is a prism, and volume is little, is specially adapted to occasions with limited space.

A kind of high-resolution surface plasma wave angle degree sensor that the present invention proposes, comprise that laser instrument, the polarizer, magneto-optic modulator, angle sensor parts, analyzer, photodetector, signal source, lock-in amplifier, A/D A/D converter, PC Computer signal are handled, display unit, it is characterized in that, said angle sensor parts are a right-angle prism that places on the measured object, and the oblique angle face of this prism and said laser instrument are oppositely arranged the metal film that edged surface always is coated with the excitating surface plasma wave; The said polarizer, magneto-optic modulator place among the input path between said prism and the laser instrument, and said analyzer, photodetector place among the reflected light path between said prism and the laser instrument; Said lock-in amplifier, A/D A/D converter, PC computing machine link to each other with said photodetector successively, and said signal source is connected between said magneto-optic modulator and the lock-in amplifier; Store signal handler in said PC Computer signal processing, the display unit.

The said magneto-optic modulator of the present invention is open magneto-optic modulator, this magneto-optic modulator comprises the identical ferrite magnetic material of two block size shapes that is oppositely arranged, relative position on these two blocks of magnetic materials winds the coil with the identical number of turn, places a magneto-optic memory technique on its central shaft.

Principle of work of the present invention is: surface plasma wave is a kind of transverse magnetic wave of propagating along the interface (TM), in its intensity index decay of vertical interface direction.Because at both direction all is index decay, thus the capable ripple of surface plasma only on the interface of both sides refractive index real part contrary sign, can excite, promptly on metal and the dielectric interphase.The excitating surface plasma ripple must satisfy energy and momentum conservation simultaneously, thereby condition is quite harsh.When subtle change takes place external condition (as refractive index, lambda1-wavelength and incident angle), the fierce variation will take place in exciting characteristic.Because energy conservation, part projectile energy will convert surface plasma wave to during the excitating surface plasma ripple, so reflected energy is less than projectile energy, reflectivity is a sharp concave with the variation R (θ) or the reflectivity of incident angle with variations in refractive index R (n).Fierce variation also takes place in catoptrical phase place.

Surface plasma wave Maxwell equation group commonly used and boundary condition are described, and try to achieve its strict solution with separating multilayer technique.This is separated and coincide fairly goodly with experiment.To simple trilamellar membrane system, reflection coefficient is: $r_q=\frac{r_{01}^q+r_{12}^q\exp \left(2i{k}_{\mathrm{lz}}d\right)}{1+r_{01}^q{r}_{12}^q\exp \left(2i{k}_{\mathrm{lz}}d\right)},q=p,s---\left(1\right)$ Wherein $r_{i,l+1}^q=\frac{X_i^q+X_{i+1}^q}{X_1^q+X_{i=1}^q},i=\mathrm{0,1}---\left(2\right)$

$K_{\mathrm{iz}}=\sqrt{{(\mathrm{\ω}/c)}^2{\mathrm{\ϵ}}_i-k_{11}^2}$ $k_{11}=\frac{\mathrm{\ω}}{c}\sqrt{{\mathrm{\ϵ}}_0}\sin \mathrm{\θ}$ P wherein, S represents P ripple and S ripple respectively, θ is an incident angle.

In fact have only the P ripple just can the excitating surface plasma ripple, the S ripple can not the excitating surface plasma ripple.Because the incident angle of excitating surface plasma ripple always greater than the critical angle of total internal reflection, so in interested scope, S wave reflection coefficient is approximately 1, has a fixing phase shift.P wave reflection coefficient presents a sharp concave, and its phase-shift characterisitc more complicated is divided film and thick film two classes, and the minimum value of the theoretical reflection coefficient of critical thickness is zero, and angular transducer always is to use film.Theoretical Calculation as shown in Figure 1, curve a represents the relation of phase place and incident angle among the figure, curve b represents the relation of reflection coefficient amplitude and incident angle.

Be not difficult from Fig. 1 to find that when surface plasma wave excited, the subtle change of incident angle can cause that the fierceness of phase place changes.The value of Φ/ θ can be up to hundreds of.Because the phase change of S ripple here can be ignored.Contain S ripple and P ripple simultaneously as incident wave, when incident angle changed, the polarization of reflected light attitude will have greatly changed.Because polarized interferometer can expect to reach 1 * 10 to the high resolution that plane of polarization detects ^-6Radian is so can make high-resolution angle/index sensor with the method for excitating surface plasma ripple.

With the Qiong Shi matrix method can obtain when angle sensor parts corner be Δ θ ' time, the size that records signal is: $U\∝\mathrm{\ρ}\frac{Q}{n_0}\sin \left(2a\right)J_1\left(2M\right)\mathrm{\Δ\θ}\′---\left(4\right)$ Relatively the signal of polarized interferometer survey plane of polarization Δ θ ' is:

U?∝sin(2a)JI(2M)Δθ′ (5)

Can think $\mathrm{\ρ}\frac{\mathrm{\θ}}{n_0}$ For adopting the sensitivity enhancer of surface plasma wave technology.

ρ=｜r _p｜=0.2

n ₀For the prismatic refraction rate gets 2

θ=φ/θ=400

So enhancer is about 40.Cooperating resolution is 1 * 10 ^-6The polarized interferometer of radian, angle resolution are expected to reach 2.5 * 10 ^-8Radian.

Sensing element of the present invention promptly can be as index sensor and the chemistry, the biomolecule concentration sensor that derive from thus as long as improve a little.The resolution of index sensor can be obtained by following formula: $\mathrm{\δn}=\frac{\∂n}{\∂\mathrm{\φ}}\mathrm{\δ\φ}=\mathrm{\δ\φ}/\frac{\∂\mathrm{\φ}}{\∂n}---\left(11\right)$ φ/ n is the variation that variations in refractive index causes resonance angle.δ φ is an angular resolution.Because φ/ n is about 1 radian/refractive index unit, so the resolution of survey refractive index is for being better than 1 * 10 ^-7Refractive index unit.

Excitation wavelength of the present invention can be selected within a large range, and this selects not influence the enforcement of scheme, but excitation wavelength should be stable monochromatic light.The thickness of metal film can select in the larger context equally (30nm～40nm), this selectivity in a big way have utilize implement in coating process.The refractive index of prism also can be selected in the larger context, and the prism that refractive index is big more helps the enforcement of scheme.

Characteristics of the present invention:

One, high resolving power: point out that as theoretical analysis the present invention utilizes the surface plasma wave technology to obtain being about 40 sensitivity enhancer, (resolution is 1 * 10 to cooperate the high sensitivity polarized interferometer ^-6Radian), reach and be better than 1 * 10 ^-7The measurement of angle resolution of radian.Same principle is used for refractometry resolution can reach 1 * 10 ^-7Refractive index unit.

Two, volume is little, and is simple in structure: the present invention only needs a prism as sensing element, can be used for occasions with limited space.

Three, practicality height: the angle measuring system reflected light is parallel all the time with incident light, is not breadboard principle device, can be directly used in the scene.Survey the refractive index sensing parts and be designed to probe-type, also can be directly used in the scene.

Four, good stability: adopted open novel magneto-optic modulator in embodiments, overcome traditional magneto-optic modulation interferometer resolution height but the shortcoming of poor stability.Because there is stress birefrin in magneto-optic memory technique, when temperature variation, stress birefrin changes, thereby has drift.The tradition magneto-optic memory technique is placed in the coil, and when modulator was worked, the heat that is produced by electric current raise the magneto-optic memory technique temperature.The present invention has designed open magneto-optic modulator, though make magneto-optic memory technique in magnetic field not in coil, effectively reduce temperature rise, improved stability.

Brief Description Of Drawings:

Fig. 1 is the SPR amplitude and the phase shift feature of Theoretical Calculation.

Fig. 2 is an embodiment of the invention overall construction drawing.

The open magneto-optic modulator structural drawing that Fig. 3 adopts for the embodiment of the invention.

Fig. 4 is used for the on-the-spot sensing element structural drawing of surveying refractive index for the present invention.

Fig. 5 is used for the sensing element structural drawing that refractive index is surveyed in the laboratory for the present invention.

Below in conjunction with accompanying drawing, introduce embodiments of the invention in detail.

The present embodiment general structure as shown in Figure 2, laser instrument 1 is a semiconductor laser, wavelength is 670nm, the light beam that laser instrument sends through the collimation after throw on the polarizer 2.Collimation is necessary, and the angle of divergence of light beam should be less than 0.1 degree.The polarizer 2 and analyzer 4 are used Glan prism, and extinction ratio is the bigger the better.The effect of the polarizer not only makes the incident light polarization characteristic better, and guarantees that S light and P light have certain proportion, and its proportional control is about 1: 10.Being subjected to amplitude through magneto-optic modulator 3 rear polarizer attitudes is M, and frequency is the modulation of Ω.The size of M and Ω is obtained by experiment.Present embodiment is to add 24V AC signal 10, becomes series resonance through an electric capacity with the magneto-optic modulator coil groups, and frequency is 248Hz.Light beam incides on the sensing element 5.This sensing element is a right-angle prism, the prismatic refraction rate is 1.746, is coated with golden film on prism one right-angle side, and its thickness is 40nm, incident beam reflects in prism twice, because drift angle is the right angle, so the reflected light direction changes 180 ° of angles, even when prism rotates, reflected light is also parallel with incident beam, so not only can be directly used in the scene, and make only prism of sensing element, reduce volume.When sensor element rotates Δ θ ' angle, incident angle Δ θ ' change Δ θ '/n, corresponding P wave phase is changed into $\frac{\∂\mathrm{\φ}}{\∂\mathrm{\θ}}\mathrm{\Δ\θ}$ , the phase place of S ripple does not have to change substantially.Like this, reflected light has the information that the sensing element angle changes.This information becomes relevant electric signal through analyzer and photoelectric commutator 6, and this signal frequency is that the AC compounent of Ω is shown in (4) formula.Detect through lock-in amplifier 7 and to become direct current signal.Convert digital signal to by A/D converter 8 at last,, handle and demonstration, directly provide corner Δ θ ' by computing machine 9 records.

The magneto-optic modulator of present embodiment adopts open magneto-optic modulator.The structure of open magneto-optic modulator as shown in Figure 3, coil 33,34, the two coils series connection of winding on the identical half elliptic ferrite magnetic material 31,32 of two block size shapes with the identical number of turn guarantees to pass to identical electric current.Series connection polarity is: when leading to direct current, the magnetic field of generation is plane symmetry.To form approximate uniformly axial high-intensity magnetic field like this in the central area.With electric capacity and coil series connection, form resonance during indirect current to obtain stronger magnetic field.Magneto-optic memory technique flint glass 35 centering zones.Coil and magnetic material place in the aluminium shell (not shown), so that importing base plate as early as possible, the heat that produces during coil working dissipates, flint glass places on the heat insulated supporter (not shown), and the temperature rise of magneto-optic memory technique has reduced drift when having reduced magneto-optic modulator work so effectively.

The present embodiment device is tested on the shockproof platform in laboratory, and experimental result is as follows: resolution is 3 * 10 ^-8Radian is 2.6 * 10 in the angle measurement scope ^-4In the scope of radian, linearly dependent coefficient is 0.998.

The laboratory of the present invention's design is with surveying the refractive index sensing parts as shown in Figure 4.This sensor element comprises a right-angle prism 41, metal-plated membrane layer 43 on the edged surface always 42 of this prism, and a bonding flow chamber 44 is connected with liquid conduits 45 on this right angle face on this chamber.On-the-spot use sensing element as shown in Figure 5.This sensor element is a rectangle glass cylinder 51, and the one end is two inclined-planes 52,53 of form right angle, wherein is coated with metallic film 54 on the inclined-plane 52, and this sensing element can directly insert in the testing medium.

When being used to survey chemistry or biomolecule concentration, outside metal film, also need increase one deck functional membrane, the functional membrane of some particular molecule has open report.

Because sensitive high, it is little that the present invention is used for the index sensor measurement range, is about 1 * 10 ^-4Refractive index unit.So be more suitable for gas refracting index sensor.Because refractive index is synthermal relevant, the measured value of same medium under different temperatures can be different, and the present invention provides the measurement of real-time refractive index.

Claims (2)

1. high-resolution surface plasma wave angle degree/refraction sensor, comprise that laser instrument, the polarizer, magneto-optic modulator, angle sensor parts, analyzer, photodetector, signal source, lock-in amplifier, A/D A/D converter, PC Computer signal are handled, display unit, it is characterized in that, said angle sensor parts are a right-angle prism that places on the measured object, and the oblique angle face and the said laser instrument of this prism are oppositely arranged; Edged surface is coated with the metal film of excitating surface plasma ripple always; The said polarizer, magneto-optic modulator place among the input path between said prism and the laser instrument, and said analyzer, photodetector place among the reflected light path between said prism and the laser instrument; Said lock-in amplifier, A/D A/D converter, PC computing machine link to each other with said photodetector successively, and said signal source is connected between said magneto-optic modulator and the lock-in amplifier; Store signal handler in said PC Computer signal processing, the display unit.

2, sensor as claimed in claim 1, it is characterized in that said magneto-optic modulator is open magneto-optic modulator, this magneto-optic modulator comprises the identical ferrite magnetic material of two block size shapes that is oppositely arranged, relative position on these two blocks of magnetic materials winds the coil with the identical number of turn, places a magneto-optic memory technique on its central shaft.

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