CN203629684U - Spectrum measurement device based on electrooptical effect - Google Patents

Abstract

The utility model discloses a spectrum measurement device based on the electrooptical effect. The spectrum measurement device comprises a first polaroid, an electrooptical effect crystal, a second polaroid, and a light detector which are disposed along an incident light direction, wherein the polarization direction of the first polaroid is not parallel to the direction of an induction main shaft of the electrooptical effect crystal under an external electric field. The spectrum measurement device is used in such a way that: the optical powers detected by the light detector when different external voltages are applied to the electrooptical effect crystal are measured, and the obtained optical power data is used as an augmented matrix to build a linear equation set by combining with a coefficient matrix which is composed of detection rates of the spectrum measurement device under different voltages for incident light with different frequencies; the linear equation seat is solved to obtain optical powers of each component in different frequencies of an incident light to be tested, linear fitting is carried out, spectrum radiation calibration is carried out, and the spectrum of the incident light to be tested is obtained. The spectrum measurement device has advantages of being strong in anti-vibration capability, being high in resolution, and being wide in spectrum measurement range.

Description

A kind of spectral measurement device based on electrooptical effect

Technical field

The utility model relates to a kind of spectral measurement device, relates in particular to a kind of spectral measurement device based on electrooptical effect, belongs to field of spectral analysis technology.

Background technology

Spectrometer is a kind of important optical instrument.It is that optical means is combined with hyundai electronics data handling system, carrys out the basic equipment of structure, composition and the content of Accurate Analysis material by obtaining the spectral information of studied material.Spectrometer has the advantages such as analysis precision is high, measurement range is large, speed is fast; be widely used in the fields such as metallurgy, geology, petrochemical complex, medical and health, environmental protection; also be that the requisite remote sensing equipments such as military surveillance, universe exploration, resource and hydrology detection are (referring to document [Li Quanchen, Jiang Yuejuan.Spectral instrument principle [M], Beijing; Publishing house of Beijing Institute of Technology, 1999]).The application nearly cover of spectral technique all scientific domains, comprise medicine, chemistry, geology, physics and uranology etc., from the bottom of ocean to remote universe, spectrometer is the information that we collect world around.

But, along with scientific and technical fast development, spectrometer is had higher requirement.Particularly as some special occasions such as geological and mineral exploration, micro-fluidic and spaceborne analyses, need that the wavelength coverage that spectrometer energy vibration and interference resistance is strong, spectral measurement resolution is high, measure is large, power consumption is little and can obtain fast, in real time, intuitively spectral signal, obviously, traditional spectral instrument is difficult to reach above-mentioned requirements simultaneously, for example current commercial Fourier transform spectrometer, not only volume large, to vibration sensing, measurement range mainly at infrared band, and its resolution affects by index glass moving range, be therefore unsuitable for the particular surroundingss such as field and measure; And grating spectrograph resolution is not high, price is also high (referring to document [Yang Jae-chang, et al.Micro-electro-mechanical-systems-based infrared spectrometer composed of multi-slit grating and bolometer array, Jap.J.of Appl.Phys.47 (8), 6943-6948 (2008)]).

Therefore, for spectrometer, require it in thering is anti-vibration, can reduce costs, in performance, can reach higher spectral resolution, simple in structure and be easy to make, with existing technology be difficult to realization.

Utility model content

Technical problem to be solved in the utility model be to overcome the existing cost of prior art higher, make difficulty, to technical matterss such as vibration sensing, resolution are not high, spectral measurement ranges is narrower, a kind of spectrometer based on electrooptical effect is provided.

Spectral measurement device based on electrooptical effect of the present utility model, comprises the first polaroid, electrooptical effect crystal, the second polaroid, the photo-detector that set gradually along incident light direction; Wherein, the polarization direction of the first polaroid and the induction major axes orientation of described electrooptical effect crystal under extra electric field are not parallel.

Further, described spectral measurement device also comprises the optical collimator being arranged at before the first polaroid.

Preferably, described optical collimator comprises two confocal lens, and is arranged at the aperture at the common focus place of described two lens.

Further, described spectral measurement device also comprises the calculation processing unit being connected with described photodetector signal.Thereby can automatically calculate and export according to the measurement data of photo-detector the spectrum of incident light to be measured.

The spectral measurement method that uses spectral measurement device described in as above any one, comprises the following steps:

Step 1, the frequency range that described photo-detector can be surveyed are divided into the frequency band that n frequency range is Δ f, and n is greater than 1 integer, and the centre frequency of each frequency band is f ₁, f ₂... f _n;

Step 2, make incident light to be measured successively by the first polaroid, electrooptical effect crystal, the second polaroid, and with the power of described photo-detector detection emergent light;

Step 3, described electrooptical effect crystal is applied to one group of n different voltage, and record the emergent light power that under different voltage, photo-detector detects, be designated as respectively P ₁, P ₂... P _n;

Step 4, be f by solving the frequency that following system of equations obtains comprising in incident light to be measured ₁, f ₂... f _nluminous power P(f ₁), P(f ₂) ..., P(f _n):

In formula, C _ij(i=1,2 ... n) (j=1,2 ... n), while being illustrated in the voltage that electrooptical effect crystal is applied and getting j value, frequency is f _ilight by after the first polaroid, electrooptical effect crystal, the second polaroid with by before power ratio, record in advance by experiment;

Step 5, to P (f ₁), P (f ₂) ... P (f _n) carry out linear fit, and through spectral radiometric calibration, obtain the spectrum of incident light to be measured.

Preferably, utilize the method for Tikhonov regularization to solve described equation.

Compared to existing technology, the utlity model has following beneficial effect:

1, spectral measurement device anti-vibration ability of the present utility model is strong, while carrying out spectral measurement, without mobile optical device, therefore vibrates its impact littlely, and stable performance, can be used for the real-time measurement in complex environment.

2, spectral measurement device of the present utility model is easy to make, with low cost: its needed electrooptical effect crystal, polaroid, photo-detector etc. are all very ripe products, need the equipment of complexity, costliness than making other spectrometers, make more easily simple.

3, spectral measurement device resolution of the present utility model is high, and spectral measurement ranges is wide: adopt and dwindle the method that frequency partition scope repeatedly restores and can in obtaining wide spectrum detection scope, reach high spectral resolution.

4, spectral measurement device of the present utility model can be eliminated distortion, realizes spectrum and measures in real time: the method that adopts Tikhonov regularization to solve large linear systems is restored spectrum, can eliminate distortion, realizes quick real time spectrum and restores.Meanwhile, the invalid data that the photo-detector causing due to a variety of causes collects, can, by casting out the method solving equation group of these invalid datas, make new system of equations full rank and meet solving condition, avoids the larger distortion of spectrum recovering.

Accompanying drawing explanation

Fig. 1 is the optical collimator structural representation shown in embodiment, wherein: 1 represents incident light source, and 2 is lens, and 3 is aperture, and 4 is lens;

Fig. 2 is the structural representation of the spectral measurement device shown in embodiment; Wherein, 5 is polaroid, and 6 is electrooptical effect crystal, and 7 is polaroid, and 8 is photo-detector;

Fig. 3 is the incident light spectral frequency division methods that the utility model adopts, and in figure, horizontal ordinate represents frequency, and unit is hertz; Ordinate is normalization spectral power, and unit is watt/hertz.

Embodiment

Below in conjunction with accompanying drawing, the technical solution of the utility model is elaborated:

Thinking of the present utility model is to utilize electrooptical effect crystal under identical DC Electric Field, the linearly polarized light of different frequency is by the phase differential between two bundle birefringent lights after electrooptical effect crystal also different principle, light intensity impact in conjunction with polaroid on incident polarized light, construct one by two polaroids and the electrooptical modulation parts that electrooptical effect crystal forms, measure incident light to be measured under different extra electric fields and pass through the luminous power after these electrooptical modulation parts, and obtain the frequency spectrum of incident light to be measured by solving system of linear equations.

For incident light is carried out to optical shaping, in this example, first make incident light pass through an optical collimator, the structure of this optical collimator as shown in Figure 1, comprise confocal lens 2 and lens 4, the common focus place of lens 2 and lens 4 is provided with aperture 3, and the light that incident light source 1 sends can change directional light into after by this optical collimator.So not only make to only have directional light just can incide electrooptical modulation spectrometer, and define the width of light beam of incident light, be conducive to improve the accuracy of measuring.

The structure of spectral measurement device of the present utility model as shown in Figure 2, comprises the polaroid 5, electrooptical effect crystal 6, polaroid 7, the photo-detector 8 that set gradually along incident light direction; The polarization direction of polaroid 5 and the electrooptical effect crystal 6 induction major axes orientation under extra electric field is not parallel.In the utility model, photo-detector 8 is to be irradiated to its surperficial luminous power for measuring, and can adopt existing various photo-detector, for example modal silicon detector.In order automatically to realize numerical value collection and the calculating in spectrum recovering process, in the present embodiment, also comprise the calculation processing unit (not shown in Fig. 2) being connected with photo-detector 8 signals.

So-called electrooptical effect refers under DC Electric Field, the effect that the refractive index of some crystal (electrooptical effect crystal) changes.When incident light passes through electrooptical effect crystal, due to the motion of electronics in molecule or atom under DC Electric Field of electrooptical effect crystal, or the structure of crystal changes, thereby cause its refractive index and change by the polarization state of crystal, result produces birefringence.If the variation of crystal refractive index is directly proportional to electric field, this electrooptical effect is called Pockels effect.If square being directly proportional of the variation of refractive index and electric field, this electrooptical effect is called Kerr effect.

When electrooptical effect crystal 6 is while having non-centrosymmetrical crystal, as lithium niobate (LiNbO ₃), bismuth silicate (Bi ₁₂siO ₂₀), bismuth germanium oxide (Bi ₄ge ₃o ₁₂) and potassium dihydrogen phosphate (KH ₂pO ₄₎deng, under extra electric field, can produce Pockels effect, now the extra electric field direction of electrooptical effect crystal 6 can be consistent with the direction of propagation of light, also can be vertical with the direction of propagation of light, be that electric field can be added on two electrodes of crystal 6 opposite faces, or be added on two electrodes of same of electrooptical effect crystal 6.And when electrooptical effect crystal 6 be while thering is any symmetric crystal, as nitrotoluene (C ₇h ₇nO ₂), nitrobenzene (C ₆h ₅nO ₂) etc., just there is Kerr effect, now the direction of propagation of the extra electric field direction Ying Yuguang of electrooptical effect crystal 6 is vertical.

As shown in Figure 2, the crystal 6 adopting meets Pockels effect, below with potassium dihydrogen phosphate (KH ₂pO ₄) crystal is that example is analyzed.When after the z direction of principal axis added electric field along electrooptical effect crystal 6, electrooptical effect crystal 6 is responded to main shaft x ' and y ' and is rotated to respectively and the direction of former main shaft x and y angle at 45 °.Electrooptical effect crystal 6 is placed between two polaroids, wherein the polarization direction of polaroid 5 becomes α angle (α can not equal 0 ° and 90 °) with the induction main shaft x ' axle of electrooptical effect crystal 6, and the polarization direction of polaroid 7 becomes β angle with the induction main shaft x ' axle of electrooptical effect crystal 6.Therefore, become the linearly polarized light that becomes α angle with the induction main shaft x ' axle of electrooptical effect crystal 6 along the light of z axle incident after by polaroid 5, be broken down into two component E along x ' and y ' direction after entering electrooptical effect crystal 6 _x' and E _y', their amplitude and phase place are respectively:

$E_{x^{\′}}\left(0\right)=A\cos \mathrm{\α}{e}^{{\mathrm{i\ω}}_{c}t}$

$E_{y^{\′}}\left(0\right)=A\sin \mathrm{\α}{e}^{{\mathrm{i\ω}}_{c}t}$

When after the crystal that light is L by length, due to the refractive index n of two polarized components _{x '}and n _{y '}difference, the light path of two polarized components is respectively n _{x '}l and n _{y '}l, phase delay is respectively:

Therefore, these two light waves will produce a phase differential through after electrooptical effect crystal 6:

In formula, U=E _zl is along the added voltage of z axle; λ is optical wavelength; n ₀for the refractive index of electrooptical effect crystal 6; r ₆₃for electrooptical effect crystal 6 electrooptical coefficients.

With complex representation be:

E _x'(L)=Acosα

So, be that two polarized components are becoming the projection sum on β angular direction with the induction main shaft x ' axle of electrooptical effect crystal 6 by the electric field intensity after polaroid 7:

If the amplitude of two polarized components is respectively:

A _x'=Acosαcosβ

A _y'=Asinαsinβ

Due to light intensity be proportional to electric field square, therefore output intensity is:

Because input light intensity be again:

I _i=E·E ^*=E _x'(0) ²+E _y'(0) ²=2A ²

So the light intensity of output is:

Will substitution above formula, get final product:

$I_o=\frac{1}{2}{I}_i\{{\cos }^2(\mathrm{\α}+\mathrm{\β})+\frac{1}{2}\sin 2a\sin 2\mathrm{\β}(1-\cos \left(\frac{2\mathrm{\π}}{\mathrm{\λ}}{n_0}^3{r}_{63}U\right))\}---\left(2\right)$

As the electrooptical effect crystal 6 being adopted meets Kerr effect, now the direction of propagation of the extra electric field direction Ying Yuguang of electrooptical effect crystal 6 is vertical, the polarization direction of polaroid 5 becomes α angle (α can not equal 0 ° and 90 °) with the x axle of electro-optic crystal 6, the polarization direction of polaroid 7 becomes β angle with the x axle of electro-optic crystal 6.Become the linearly polarized light that becomes α angle with the x axle of electro-optic crystal 6 along the light of z axle incident after by polaroid 5, linearly polarized light is broken down into along x axle and axial two components of y after entering electrooptical effect crystal 6.Due to the propagation phase velocity difference of these two components in electrooptical effect crystal 6, these two components are through having produced phase differential after electrooptical effect crystal 6:

In formula, l is electrooptical effect crystal 6 optical direction length; K is Kerr coefficient, relevant with incident light wavelength; D is electrooptical effect crystal 6 thickness along extra electric field direction; U is at the electrooptical effect crystal 6 added magnitudes of voltage in two ends.Two components will synthesize elliptically polarized light after by electrooptical effect crystal 6, so just have part light by polaroid 7, and its reasoning is the same.Now, the light intensity of output is:

$I_o=\frac{1}{2}{I}_i\{{\cos }^2(\mathrm{\α}+\mathrm{\β})+\frac{1}{2}\sin 2a\sin 2\mathrm{\β}(1-\cos \left(\frac{2\mathrm{\πlK}{U}^2}{d^2}\right))\}---\left(4\right)$

As the above analysis, no matter meet Pockels effect or Kerr effect, in the time that the light of characteristic frequency passes through electrooptical effect crystal 6, due under the effect of extra electric field, the refractive index of electrooptical effect crystal 6 changes, the variation of its refractive index will cause from the variation of phase differential between two birefringent lights of electrooptical effect crystal 6 outgoing, and the variation of phase differential will cause by the variation of output light intensity after electrooptical modulation parts.Can adopt voltage to regulate and control because of the variation of refractive index again, thereby can utilize impressed voltage can modulate the variation of output light intensity, the luminous power detecting in fixed range on photo-detector 8 is also changed.

Known based on above principle, for the incident light of a certain characteristic frequency, be added to the magnitude of voltage on electrooptical effect crystal 6 by changing in electrooptical modulation parts, photo-detector 8 just will detect different luminous powers; And for the incident light of different frequency, in the time that electrooptical effect crystal 6 is applied to identical impressed voltage, the luminous power size detecting by photo-detector 8 after electrooptical modulation parts is also different.When voltage on electrooptical effect crystal 6 is got the different value of n kind, photo-detector 8 just can record a series of power data, and the luminous power that photo-detector 8 is detected is as augmented matrix; 8 frequency ranges that can survey of photo-detector are evenly divided into n part, and the normalized power of the centre frequency of every portion in incident light is as unknown number; When recording in advance the voltage of photo-detector 8 on electrooptical effect crystal 6 and getting the different value of n kind for the detectivity of each frequency component, and using this detectivity as matrix of coefficients.By regularization method solution matrix equation, and the spectrum that acquired results is carried out to linear fit, spectral calibration and just can obtain treating photometry.Can obtain spectral measurement of the present utility model (spectrum recovering) method based on this principle, specific as follows:

Step 1,8 frequency ranges that can survey of described photo-detector are divided into the frequency band that n frequency range is Δ f, n is greater than 1 integer, and the centre frequency of each frequency band is f ₁, f ₂... f _n.

As shown in Figure 3, within the scope of the survey frequency of photo-detector 8, the curve of spectrum is evenly divided into n section.Whole spectrum area is just divided into multiple elongated rectangles by approximate, and the centre frequency of supposing every portion is f ₁, f ₂... f _n, frequency range is Δ f, P (f _i) be frequency f _icorresponding watt level (i=1,2 ... n), in incident light, the corresponding power of each frequency band is the area of each little rectangle, according to infinitesimal analysis principle, and the general power P of incident light ₀can be approximated to be in figure the summation of each little rectangular area, the i.e. superposition of each frequency component power below curve.If represent with mathematical formulae, can be expressed as:

$P_0=\underset{k=1}{\overset{n}{\mathrm{\Σ}}}P\left(f_n\right)\mathrm{\Δf}---\left(5\right)$

Step 2, make incident light to be measured successively by polaroid 5, electrooptical effect crystal 6, polaroid 7, and survey the power of emergent light with photo-detector 8.

In the time of electrooptical modulation parts that incident light consists of polaroid 5, electrooptical effect crystal 6, polaroid 7, to get j value at the voltage being added on electrooptical effect crystal 6, the power that photo-detector 8 measures should be:

$P_j=\underset{k=1}{\overset{n}{\mathrm{\Σ}}}{C}_{\mathrm{nj}}P\left(f_n\right)\mathrm{\Δf}---\left(6\right)$

Wherein, C _1j, C _2j... C _njbeing respectively frequency is f ₁, f ₂... f _nlight through the detectivity of electrooptical modulation parts.

Step 3, electrooptical effect crystal 6 is applied to one group of n different voltage, and record the emergent light power that under different voltage, photo-detector 8 detects, be designated as respectively P ₁, P ₂... P _n.

In the time being added to voltage on electrooptical effect crystal 6 and getting the different value of n kind, photo-detector 8 just can record a series of power data, and these power are expressed as to system of linear equations:

P ₁=C ₁₁P(f ₁)Δf+C ₁₂P(f ₂)Δf+…+C _1nP(f _n)Δf，

P ₂=C ₂₁P(f ₁)Δf+C ₂₂P(f ₂)Δf+…+C _2nP(f _n)Δf，（7）

…

P _n=C _n1P(f ₁)Δf+C _n2P(f ₂)Δf+…+C _nnP(f _n)Δf，

Wherein, C _ij(i=1,2 ... n) (j=1,2 ... n) while being illustrated in the voltage that electrooptical effect crystal is applied and getting j value, the light that frequency is fi by after polaroid 5, electrooptical effect crystal 6, polaroid 7 with by before power ratio.After spectral measurement device is made, C _ijbe one group of definite value, can record by experiment, for example, can adopt with the following method: in darkroom, be first irradiated on monochromator with incident light light source, survey the different frequency f being obtained by monochromator with photo-detector 8 ₁, f ₂... f _nluminous power; Then at the front placement electrooptical modulation of photo-detector 8 parts, get j value at the voltage being added on electrooptical effect crystal 6, measure the light of the different frequency being obtained by monochromator by after electrooptical modulation parts, the luminous power that photo-detector 8 detects, the luminous power recording and the ratio that does not add the luminous power that electrooptical modulation parts measure, the light that is different frequency under this voltage for the detectivity C of photo-detector 8 _1j, C _2j... C _nj.Change the magnitude of voltage being added on crystal 6, repeat above-mentioned steps, can obtain one group of data C _ij(i=1,2 ... n) (j=1,2 ... n).These group data can form matrix of coefficients C:

Matrix of coefficients C is the intrinsic parameter of spectral measurement device, the corresponding constant matrix of coefficients C of each specific spectral measurement device.

If matrix form y=Cx expression (7) for step 4, if x represents the size of the each centre frequency luminous power of incident light, C represents the matrix of coefficients of detectivity composition, and the received corresponding luminous power of photo-detector 8 is as augmented matrix y, and the available following form of formula (7) represents:

Solve above-mentioned system of linear equations and obtain x, and further calculate according to following formula:

$\tilde{x}=x/\mathrm{\Δf}=\left(\begin{array}{c}P\left(f_1\right)\\ P\left(f_2\right)\\ \·\\ \·\\ \·\\ P\left(f_n\right)\end{array}\right)---\left(9\right)$

Just can be in the hope of the corresponding power P (f of each frequency component in incident light spectrum _i) size.

Step 5, to P (f ₁), P (f ₂) ... P (f _n) carry out linear fit, and through spectral radiometric calibration, obtain the spectrum of incident light to be measured.

In practical devices manufacturing process, the size of device, shape, material behavior etc. may have certain deviation with initial designing requirement, but after device is carried out, photo-detector 8 is for the incident light of certain impressed voltage value and certain wavelength, and its detectivity is a fixed value.As long as for the incident light of different magnitudes of voltage and different wavelength, the detectivity difference of photo-detector 8, just can solving equations.In solving equation group process, the luminous power that photo-detector 8 collects and be all measured value to the detectivity of electrooptical modulation parts.Due to reasons such as measuring error, this system of equations is real is ill-condition equation group, add in system of equations the quantity of equation more, solve with commonsense method is more difficult, and the method that adopts Tikhonov regularization solves, this system of linear equations can be eliminated obvious distortion and the speed that solves is fast, after this solving equations, get final product to obtain normalization spectral power corresponding to the each frequency of incident light, finally carry out spectral radiometric calibration and just obtained the recovery spectrum of incident light.

Above computation process can utilize calculation processing unit automatically to carry out, and can further utilize calculation processing unit impressed voltage to be controlled automatically simultaneously, thereby realizes spectral measurement fast automatically.

Claims (4)

1. the spectral measurement device based on electrooptical effect, is characterized in that, comprises the first polaroid, electrooptical effect crystal, the second polaroid, the photo-detector that set gradually along incident light direction; Wherein, the polarization direction of the first polaroid and the induction major axes orientation of described electrooptical effect crystal under extra electric field are not parallel.

2. the spectral measurement device based on electrooptical effect as claimed in claim 1, is characterized in that, also comprises the optical collimator being arranged at before the first polaroid.

3. the spectral measurement device based on electrooptical effect as claimed in claim 2, is characterized in that, described optical collimator comprises two confocal lens, and is arranged at the aperture at the common focus place of described two lens.

4. the spectral measurement device based on electrooptical effect as claimed in claim 1, is characterized in that, also comprises the calculation processing unit being connected with described photodetector signal.

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