Summary of the invention
Technical matters to be solved by this invention is to overcome the technical matters such as cost existing for prior art is higher, making is difficult, not high to vibration sensing, resolution, wavelength measurement scope is narrower, provides a kind of spectral measurement device based on magneto-optic modulation and spectral measurement method.
Spectral measurement device based on magneto-optic modulation of the present invention, comprises the first polaroid, magneto-optic modulation device, the second polaroid, the photo-detector that set gradually along incident light direction.
Further, the described spectral measurement device based on magneto-optic modulation also comprises the optical collimator be arranged at before the first polaroid.
Further, the described spectral measurement device based on magneto-optic modulation also comprises the calculation processing unit be connected with described photodetector signal.
Further, described calculation processing unit is connected with the control end of described magneto-optic modulation device, can control the magnetic field intensity of magneto-optic modulation device.
The present invention is based on the spectral measurement method of magneto-optic modulation, use the spectral measurement device based on magneto-optic modulation described in above arbitrary technical scheme, comprise the following steps:
Step 1, the frequency range that described photo-detector can detect to be divided into
nindividual frequency range is Δ
ffrequency band,
nfor being greater than the integer of 10, 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, magneto-optic modulation device, the second polaroid, and undertaken by described magneto-optic modulation device
nthe magneto-optic modulation of individual different magnetic field intensity, uses this
nafter the value that under individual magnetic field intensity, described photo-detector detects deducts neighbourhood noise respectively, obtain one group of numerical value, be designated as
p 1 ,
p 2 ,
p n ;
Step 3, obtain each frequency component in incident light to be measured by solving following system of equations
f 1 ,
f 2 ,
f n size
p(
f 1 ),
p(
f 2 ) ...,
p(
f n ):
In formula,
c ij (
i=1,2 ... n) (
j=1,2 ... n) represent the
junder individual magnetic field intensity, frequency is
f i light through with without in the first polaroid, magneto-optic modulation device, the second polaroid situation, the value that photo-detector detects deducts both ratio after neighbourhood noise respectively, records in advance by experiment;
Step 4, right
p(
f 1 ),
p(
f 2 ),
p(
f n ) carry out linear fit, and through spectral calibration, obtain the spectrum of incident light to be measured.
Compared to existing technology, technical scheme of the present invention has following beneficial effect:
1, spectral measurement device anti-vibration ability of the present invention is strong, without the need to mobile optical device when carrying out spectral measurement, therefore vibrates its impact less, stable performance, can be used for the real-time measurement in complex environment.
2, spectral measurement device of the present invention is easy to make, with low cost: the magnet-optical medium required for it, polaroid, photo-detector etc. are all very ripe products, needing complexity, expensive equipment, making more easily simple compared to making other spectrometers.
3, spectral measurement device resolution of the present invention is high, and spectral measurement ranges is wide.
4, spectral measurement device of the present invention can eliminate distortion, realizes spectrum and measures in real time: the method adopting Tikhonov regularization to solve large linear systems restores spectrum, can eliminate distortion, realizes quick real time spectrum and restores.Meanwhile, the invalid data that the photo-detector caused due to a variety of causes collects, by casting out the method solving equation group of these invalid datas, can make new system of equations full rank and meeting solving condition, avoiding the larger distortion of spectrum recovering.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is described in detail:
Thinking of the present invention utilizes magneto-optic modulation device to treat survey incident light to carry out magneto-optic modulation, changed and propagate polarisation of light state in magnet-optical medium, thus reach the object changing light intensity by magneto-optic effect.By measuring the intensity of the light modulated under one group of different magnetic field intensity, and obtain the frequency spectrum of incident light to be measured by solving system of linear equations.
Magneto-optic effect refers to be between the material of magnetized state and light and occurs to interact and the various optical phenomenas that cause, comprise Faraday effect, Kerr magnetooptical effect, Zeeman effect, Cotton-Mouton effet etc., wherein, Faraday effect refers to: when linearly polarized light is by Cucumber under magnetic fields, its plane of polarization is subject to being proportional to externally-applied magnetic field and is parallel to the effect of direction of propagation component and deflects; Also Faraday rotation effect or magnetic circular birefringence effect can be called.And usual said magneto-optic modulation is exactly the light modulation techniques utilizing Faraday effect.
In order to carry out optical shaping to incident light, first make incident light by an optical collimator in this example, the structure of this optical collimator as shown in Figure 1, comprise confocal lens 2 and lens 4, lens 2 and the common focus place of lens 4 are provided with aperture 3, and the light that incident light source 1 sends is by changing directional light into after this optical collimator.So not only make to only have directional light just can incide magneto-optic modulation spectrometer, and define the width of light beam of incident light, be conducive to improving the accuracy of measuring.
The structure of spectral measurement device of the present invention as shown in Figure 2, comprises the polaroid 5, magneto-optic modulation device, polaroid 9, the photo-detector 10 that set gradually along incident light direction.In the present invention, photo-detector 10 is used to measure the luminous power being irradiated to its surface, can adopt existing various photo-detector, such as modal silicon detector.In order to automatically realize numerical value collection in spectrum recovering process and calculating, in the present embodiment, also comprise the calculation processing unit (not shown in Fig. 2) be connected with photo-detector 10 signal.
Magneto-optic modulation device contains magnet-optical medium 6, can adopt cerous fluoride crystal, YIG or the material such as the YIG mixing Ga; Spiral winding 7, it is looped around on magnet-optical medium 6; Driving power 8.During work, the electric current that driving power 8 changes will induce magnetic field by spiral winding 7.Utilize Faraday rotation effect, when a branch of linearly polarized light is by Propagation under externally-applied magnetic field effect, its polarization direction can rotate, the anglec of rotation
size with along the magnetic field intensity of beam direction
hwith the length that light is propagated in media as well
lamassing is directly proportional, that is:
In formula,
vfor Theresa Weld constant, determined by medium and frequency of light wave, represent the angle that linearly polarized light is rotated by the magnet-optical medium rear polarizer direction of unit length under unit magnetic strengths.
Particularly, as shown in Figure 2, when the linearly polarized light by polaroid 5 be parallel to magnetic direction incide magnet-optical medium 6 in magneto-optic modulation device surperficial time, polarized light can resolve into dextrorotation and left-handed two bundle polarized lights, and corresponding electric vector is
e r with
e l , both sense of rotation are contrary.Here dextrorotation and left-handed be for magnetic direction.Under the influence of a magnetic field, because magnet-optical medium 6 has different refractive indexes to both
n r with
n l , the velocity of propagation of right-circularly polarized light
c/n r with the velocity of propagation of left circularly polarized light
c/n l not etc., so when they by thickness are
dmagnet-optical medium 6 after, create different phase delays:
In formula,
λfor the wavelength in vacuum.
When they are after magnet-optical medium 6 outgoing, the synthesis electric vector of two circularly polarized lights
evibration plane have rotated an angle relative to original vibration plane
θ:
Cause
So
When the angle of polaroid 5 and polaroid 9 is
αduring angle, according to Marlu's principle, incident light by the output intensity after polaroid 5, magneto-optic modulation device, polaroid 9 is successively:
In formula,
i ofor incident light is by the output intensity after polaroid 5,
n r -
n l be proportional to the magnetic field intensity along beam direction
h.
From above formula, at the angle of polaroid 5 and polaroid 9
αone timing, is placed in the wavelength of light intensity that the photo-detector 10 after polaroid 9 detects and incident light
and magnetic field intensity
hrelevant.Therefore, under identical magnetic field intensity, the incident light of different frequency is by after polaroid 5, magneto-optic modulation device, polaroid 9, and photo-detector 10 will detect different light intensities; And the incident light of same frequency is by after the magneto-optic modulation device under polaroid 5, different magnetic field intensity, polaroid 9, the light intensity that photo-detector 10 detects is also different.Treat survey incident ray polarized light at magneto-optic modulation device to carry out
nduring the magneto-optic modulation of individual different magnetic field intensity, photo-detector 10 just can record a series of data, and a series of values obtained after the data detected by photo-detector 10 remove neighbourhood noise are respectively as augmented matrix; The frequency range that photo-detector 10 can detect evenly is divided into
npart, the size of every a centre frequency in incident light spectrum is as unknown number; Record photo-detector 10 in advance in magneto-optic modulation device
ndetectivity to each frequency component under the magnetic field intensity that kind is different, and using this detectivity as matrix of coefficients.By solving this matrix equation, and acquired results is carried out the spectrum that linear fit, spectral calibration just can obtain treating light-metering.Spectral measurement of the present invention (spectrum recovering) method can be obtained based on this principle, specific as follows:
Step 1, the frequency range that described photo-detector 10 can detect to be divided into
nindividual frequency range is Δ
ffrequency band,
nfor being greater than the integer of 10, 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 10, the curve of spectrum is evenly divided into
nsection.Whole spectrum area is just divided into multiple elongated rectangle by approximate, supposes that every a centre frequency is
f 1 , f 2 ... f n , frequency range is Δ
f,
p (f i )for frequency
f i corresponding watt level (
i=1,2 ... n), the power in incident light corresponding to each frequency band is the area of each little rectangle, according to infinitesimal analysis principle, and the general power of incident light
p 0 can be approximated to be the summation of each little rectangular area below curve in figure, i.e. the superposition of each frequency component power.If represented with mathematical formulae, can be expressed as:
P 0 = P(
f 1 )
Δf + P(
f 2 )
Δf + …
+ P(
f n )
Δf
Step 2, make incident light to be measured successively by polaroid 5, magneto-optic modulation device, polaroid 9, by magneto-optic modulation device, the incident light to be measured through polaroid 5 is carried out
nthe magneto-optic modulation of individual different magnetic field intensity, uses this
nafter the value that under individual magnetic field intensity, described photo-detector detects deducts neighbourhood noise respectively, obtain one group of numerical value, be designated as
p 1 ,
p 2 ,
p n .
Owing to more or less can there is noise effect in measurement environment, actual measurement, in order to improve the accuracy of results of spectral measurements, is obtained light intensity data and calibrates, namely deduct neighbourhood noise by the present invention.For specific measurement environment, neighbourhood noise is well-determined definite value, is not namely having under incident light condition to be measured, the light intensity data in the measurement environment that photo-detector 10 detects.
Magnetic field intensity in magneto-optic modulation device gets
jwhen individual value, the luminous power that photo-detector 10 measures should be after deducting noise power:
P j = C 1j P(
f 1 )
Δf + C 2j P(
f 2 )
Δf + …
+ C nj P(
f n )
Δf
Wherein,
c 1j , C 2j ... C nj be respectively
junder individual magnetic field intensity, frequency is
f i light when through with without polaroid 5, magneto-optic modulation device, polaroid 9, the value that photo-detector 10 detects deducts both ratio after neighbourhood noise respectively, records in advance by experiment.
When the magnetic field intensity in magneto-optic modulation device is got
nduring individual different value, photo-detector 10 just can record a series of power data, and these power are expressed as system of linear equations:
P 1 = C 11 P(f 1 )Δf +C 21 P(f 2 )Δf + … + C n1 P(f n )Δf ,
P 2 = C 12 P(f 1 )Δf +C 22 P(f 2 )Δf + … + C n2 P(f n )Δf,
…
P n = C 1n P(f 1 )Δf +C 2n P(f 2 )Δf + … + C nn P(f n )Δf ,
Wherein,
c ij (
i=1,2 ... n) (
j=1,2 ... n) represent the
junder individual magnetic field intensity, frequency is
f i light when through with without polaroid 5, magneto-optic modulation device, polaroid 9, the value that photo-detector 10 detects deducts both ratio after neighbourhood noise respectively.After spectral measurement device is made, then
c ij be one group of definite value, record in advance by experiment, such as, can adopt with the following method: in darkroom, first utilize monochromator to produce different frequency
f 1 , f 2 ... f n incident light, detect the luminous power of different frequency incident light with photo-detector 10, suppose to be designated as
; Then before photo-detector 10, place polaroid 5, magneto-optic modulation device, polaroid 9 successively, the magnetic field intensity in magneto-optic modulation device gets a certain value, measure the different frequency obtained by monochromator
f 1 , f 2 ... f n incident light after polaroid 5, magneto-optic modulation device, polaroid 9, the luminous power that photo-detector 10 detects, supposes to be designated as
.Then
, be frequency
f 1 , f 2 ... f n incident light under this magnetic field intensity for the detectivity of photo-detector 10, wherein
for neighbourhood noise, namely do not having under incident light condition to be measured, the luminous power in the measurement environment that photo-detector 10 detects.Change magnetic field intensity, repeat above-mentioned steps, one group of detectivity data can be obtained
c ij (i=1,2 ... n) (j=1,2 ... n).These group data can form matrix of coefficients
c :
Matrix of coefficients
c be the intrinsic parameter of spectral measurement device, for each specific spectral measurement device, this matrix of coefficients is well-determined.
Step 3, obtain each frequency component in incident light to be measured by solving following system of equations
f 1 ,
f 2 ,
f n luminous power
p(
f 1 ),
p(
f 2 ) ...,
p(
f n ):
If use matrix form
y=Cx represent, if
x the size of the every a normalized power of centre frequency in incident light of representative,
c represent the matrix of coefficients of detectivity composition, and the received corresponding luminous power of photo-detector 10 deducts after noise power as augmented matrix
y , then system of linear equations can be expressed as above matrix form.Solve above-mentioned system of linear equations to obtain
x , and calculate further according to following formula:
Just can in the hope of power corresponding to frequency component each in incident light spectrum
p(
f i ) size.
Step 4, right
p(
f 1 ),
p(
f 2 ),
p(
f n ) carry out linear fit, and through spectral calibration, obtain the spectrum of incident light to be measured.
In practical devices manufacturing process, the size, shape, material behavior etc. of device may have certain deviation with initial designing requirement, but after device is carried out, photo-detector 10 is for the incident light of magnetic field intensity certain in magneto-optic modulation device and certain wavelength, and its detectivity is a fixed value.As long as the incident light of different magnetic field intensitys and different wavelength, the detectivity of photo-detector 10 is different, just can solving equations.In solving equation group process, the luminous power that photo-detector 10 collects and the detectivity to different frequency light are all measured values.Due to reasons such as measuring error, this system of equations is real is ill-conditioned linear systems, add the quantity of equation in system of equations more, solve with commonsense method is more difficult, and adopt the method for Tikhonov regularization solve this system of linear equations can eliminate obvious distortion and also solving speed fast, after this solving equations normalization spectral power corresponding to each frequency of incident light, finally carry out the recovery spectrum that spectral calibration just obtains incident light.