CN103245416A - Hadamard-transform near-infrared spectrograph added with light harvesting structure - Google Patents

Abstract

The invention discloses a Hadamard-transform near-infrared spectrograph added with a light harvesting structure, and relates to the field of Hadamard-transform near-infrared spectrographs. The spectrograph comprises a light source, the light harvesting structure consisting of a collimation lens and a cylindrical lens, a slit, a collimation lens, a plane grating, a DMD (digital micro mirror device), an imaging lens, a single-point detector, a static drive circuit and a spectral information acquisition and processing system. According to the Hadamard-transform near-infrared spectrograph, the light harvesting structure is added between an optical fiber and the slit, so that the energy utilization ratio of the system for light to be detected is improved greatly, and the detection for near-infrared spectrum is facilitated; appropriate slit width, grating incident angle and the like are selected, then the resolution ratio of the spectrograph is higher, simultaneously, the energy utilization ratio is higher, and the detection capacity of the spectrograph for a weak spectrum signal is improved; and a single-point photodiode is used to perform spectrum detection, accordingly, the spectrograph cost and the spectrograph size are reduced, and the detection sensitivity is improved.

Description

A kind of Hadamard transform near infrared spectrometer that adds sheet feeding type

Technical field

The present invention relates to Hadamard transform near infrared spectrometer field, be specifically related to a kind of Hadamard transform near infrared spectrometer that adds sheet feeding type.

Background technology

Near infrared spectrometer has been widely used in fields such as agricultural product, petroleum chemicals, clinical diagnosis, environment measuring at present as a kind of strong scientific analysis instrument.Along with the raising that research and application require spectrometer, microminiature spectrometer contactless, quick, low-cost, stable and reliable for performance becomes the development trend in this field gradually.At present, the digital conversion type near infrared spectrometer that declines mainly contains two kinds of Fourier transform and Hadamard transform formulas.The Fourier transform spectrometer is because there being movable member, and is higher to environmental requirement, is mainly used in lab analysis.Based on DMD(Digital Micro mirror Device, digital micromirror elements) Hadamard transform (Hadamard Transform, HT) spectrometer does not have movable member, computing and processing time are better than Fourier transform spectrometer,, can realize the perfect adaptation of high speed, high resolving power, high s/n ratio and extremely strong adaptive capacity to environment.Present commercial novel portable Hadamard changes near infrared spectrometer and uses slit as the incident diaphragm usually, uses the plane blazed grating as beam splitter.The length and width of slit, grating parameter have determined capacity usage ratio and the resolution of spectrometer to a great extent.Then the efficiency of light energy utilization is lower in order to improve systemic resolution, if improved then resolution decline of the efficiency of light energy utilization, and domestic existing near infrared spectrometer exists problems such as volume is big, cost height, be unfavorable for the commercialization of spectrometer and to the detection of faint near infrared light spectrum signal, reduced the cost performance of such Hadamard transform spectrometer.

Summary of the invention

Can not guarantee high-energy utilization factor and high resolving power simultaneously for what solve that prior art exists, can't be to the detection of faint near infrared light spectrum signal, and the high technical matters of the big cost of spectrometer volume, the invention provides a kind of Hadamard transform near infrared spectrometer that adds sheet feeding type, make the perfect adaptation that has realized high resolving power, small size, low cost and high-light-energy utilization factor based on the Hadamard transform near infrared spectrometer of DMD.

The technical scheme that technical solution problem of the present invention is taked is as follows:

A kind of Hadamard transform near infrared spectrometer that adds sheet feeding type comprises light source, slit, second collimation lens, plane grating, imaging len, DMD, condenser lens, the single-point detector, static driving circuit and spectral information acquisition processing system, it is characterized in that, this spectrometer also comprises the sheet feeding type that is made of first collimation lens and cylindrical mirror, the photometry for the treatment of that light source sends is incided first collimation lens through fiber port, be to incide cylindrical mirror behind the secondary color directional light by first collimation lens collimation, after becoming ribbon beam with circular light beam, cylindrical mirror incides slit, being to incide plane grating behind the secondary color directional light by the light beam of slit outgoing through second collimation lens collimation, is band through the plane grating chromatic dispersion; Utilize the static driving circuit to adjust the angle of DMD, make band assemble the back is incided DMD successively by the wavelength order diverse location by imaging len, after carrying out the wavelength gating, DMD focused on the single-point detector by condenser lens, the single-point detector sends the spectral information that receives to the spectral information acquisition processing system, the spectral information acquisition processing system carries out Hadamard inverse transformation decoding to the spectral information that receives, and obtains the information of original spectrum signal.

The invention has the beneficial effects as follows: this spectrometer has added sheet feeding type between optical fiber and slit, has improved the capacity usage ratio that system treats photometry greatly, is conducive to the detection near infrared spectrum; The present invention has designed suitable slit width, grating incident angle etc., makes spectrometer when resolution is higher, and high energy utilization rate is arranged, and has improved the detectability of spectrometer to the faint light spectrum signal; The present invention adopts the single-point photodiode to carry out spectrographic detection, has both reduced the spectrometer cost, has reduced the spectrometer volume again, has improved detection sensitivity.

Description of drawings

Fig. 1 adds the structural representation of the Hadamard transform near infrared spectrometer of sheet feeding type for the present invention.

Fig. 2 is the sheet feeding type simulation drawing among the present invention.

Fig. 3 is the simulation of optical systems figure of spectrometer of the present invention.

Embodiment

The present invention is further described below in conjunction with drawings and Examples.

As shown in Figure 1, the present invention's Hadamard transform near infrared spectrometer of adding sheet feeding type sheet feeding type, slit 4, second collimation lens 5, plane grating 6, imaging len 7, DMD8, condenser lens 9, single-point detector 10, static driving circuit and spectral information acquisition processing system of comprising light source 1, being constituted by first collimation lens 2 and cylindrical mirror 3.The photometry for the treatment of that light source 1 sends is incided first collimation lens 2 through fiber port, be to incide cylindrical mirror 3 behind the secondary color directional light by first collimation lens 2 collimation, after becoming ribbon beam with circular light beam, cylindrical mirror 3 incides slit 4, being to incide plane grating 6 behind the secondary color directional light by the light beam of slit 4 outgoing through second collimation lens, 5 collimations, is band through plane grating 6 chromatic dispersions; Utilize the static driving circuit to adjust the angle of DMD 8, make band assemble the back is incided DMD 8 successively by the wavelength order diverse location by imaging len 7, after carrying out the wavelength gating, DMD 8 focused on the single-point detector 10 by condenser lens 9, single-point detector 10 sends the spectral information that receives to the spectral information acquisition processing system, the spectral information acquisition processing system carries out Hadamard inverse transformation decoding to the spectral information that receives, and obtains the information of original spectrum signal.

The present invention use the single-point photodiode as detector to spectroscopically detectable, guaranteed small size and the low cost of spectrometer, the marketing that is beneficial to spectrometer is used.

The present invention is by analyzing the slit length and width to the influence of spectrometer resolution and capacity usage ratio, grating parameter such as grating constant, incident angle etc. are to the influence of spectrometer resolution and capacity usage ratio, appropriate design collimation lens and imaging len, adopt light path segmentation optimization, make optical system that the high-resolution high energy utilization rate that has simultaneously be arranged.Specific design is as follows:

The width of slit 4 is designed to 50 μ m, and Design of length is 1mm.

The relational expression of the grating constant d of grating and diffraction light spectrum level time m and spectral resolution R is:

$\frac{\mathrm{dR}}{d(\mathrm{dl}/\mathrm{d\λ})}>0,\frac{\mathrm{dl}}{\mathrm{d\λ}}=\frac{d}{m\cos \mathrm{\θ}}{f}_{2---\left(1\right)}$

Wherein, θ is angle of diffraction, f ₂Be the focal length of imaging len 7, R is spectral resolution, and dl/d λ is the grid stroke dispersive power.

By formula (1) as can be known, d is more little, and m is more big, and spectral resolution is more high.But reducing d can make the off-axis aberration of image-forming objective lens increase; The m value is limited by grating equation also.Get m=1 according to the diffraction grating theory, d=300l/mm.According to air midplane diffraction efficiency of grating formula:

${\mathrm{\η}}_m={\sin c}^2\{m-\frac{h}{\mathrm{\λ}}[\sqrt{n^2\left(\mathrm{\λ}\right)-{\sin }^{2}i}-\cos i\left]\right\}---\left(2\right)$

Can draw the diffraction efficiency of different wave length when different incidence angles, wherein, h is the grating maximum height, and n (λ) is the substrate refractive index of grating when wavelength X, and i is incident angle.The result shows that different wave length reaches the diffraction efficiency maximum simultaneously in a certain incident angle, and selecting best grating incident angle thus is 12.6 °, makes the capacity usage ratio of system reach maximum.

Because the focal distance f of collimation lens ₁More long, the collimated ray depth of parallelism is more good, but under the constant situation of numerical aperture, increasing focal length can make system aberration increase, parasitic light increase, reduce spectral resolution, the increase of spectrometer volume, cost are increased, the contradiction that need have it both ways is selected suitable collimation focal length.The focal length of imaging len then can basis

$\frac{\mathrm{dl}}{\mathrm{d\λ}}=\frac{\mathrm{d\θ}}{\mathrm{d\λ}}\frac{f_2}{\cos \mathrm{\σ}}=\frac{m}{d\cos \mathrm{\θ}}\frac{f_2}{\cos \mathrm{\σ}}---\left(3\right)$

(σ is the angle of imaging len central shaft and focal plane normal) determined.For making DMD be operated in optimum condition, light should become 12 ° of angle incidents with the DMD surface normal of " on " attitude, gets σ=12 ° herein.The DMD that the present invention uses is of a size of 14mm*10mm, and the direction length of spectral distribution is 14mm, i.e. dl=14mm; The nm=600nm of d λ=(1600-1000); Calculate the diffraction angle at centre wavelength 1300nm place by grating equation 2dsin θ=m λ, bring the value of each parameter into formula (3) and can calculate f ₂=53.5mm.Among the present invention, the focal length of second collimation lens 5 is got 25mm, and the focal length of imaging len 7 is got 50mm.System adopts the cemented doublet aberration correction, adopts light path segmentation optimization in optical design software ZEMAX, and the single lens of first design optimization to the total system complex optimum, reach optimum efficiency at last.

As shown in Figure 2, (glass material is F2 to first collimation lens 2 in the sheet feeding type of the present invention's interpolation, and K9), focal length is 4mm, and diameter is about 4mm for two gummed mirrors.Cylindrical mirror 3 is the planoconvex cylindrical lenses, and glass material is F2, and focal length is 4.9mm.The 6mm that is spaced apart of first collimation lens 2 and cylindrical mirror 3.The length of whole sheet feeding type is 18mm.

Fibre diameter is 100um, and numerical aperture is 0.22.When light is directly incident on slit 4 from optical fiber, enter the energy Φ of slit 4 ₁≈ 6.4% Φ ₀, Φ ₀Luminous energy for the optical fiber outgoing.After before entrance slit 4, adding sheet feeding type, be the secondary color directional light from the photometry for the treatment of of fiber port outgoing through first collimation lens, 2 collimations, focus on slit 4 places by cylindrical mirror 3 then, circular incident light becomes and slit direction parallel ribbon light, the length of banded light and slit length approach, width of light beam W '=143nm, the numerical aperture of the numerical aperture of outgoing beam and second collimation lens 5 is complementary, so the numerical aperture NA=0.18 of outgoing beam.Enter the luminous energy of slit 4 this moment ${\mathrm{\Φ}}_2=\frac{W}{W^{\′}}{\left({\mathrm{\τ}}_1\right)}^2{\mathrm{\τ}}_2{\mathrm{\Φ}}_0=\frac{50}{143}{\left(0.96\right)}^{2}0.95{\mathrm{\Φ}}_0=30.6\%{\mathrm{\Φ}}_0,$ τ ₁, τ ₂Be the transmitance of glass, W is slit width.Φ ₂Φ ₁, this sheet feeding type can increase the luminous flux that enters slit greatly under the same terms, improves the capacity usage ratio for the treatment of photometry, improves signal to noise ratio (S/N ratio), improves the spectrometer performance.

Fig. 3 is the parameter according to each element, simulates the spectrometer optical system structure that obtains with optical design software ZEMAX.The wavelength coverage of optical fiber emergent light is 1000～1600nm; Slit 4 width are 50 μ m; The focal length of second collimation lens 5 is 25mm, and the focal length of imaging len 7 is 50mm; The pixel number of DMD 8 is 1024*768, and pixel dimension is 13.68*13.68 μ m, and is rotatable under the driving of static driving circuit ± 12 °.Analog result shows that the optical resolution of system on the DMD surface is 4nm, and the focal beam spot geometric diameter on the single-point detector 10 is less than 3mm, the small size that meets design requirement, low cost, high resolving power and high-energy utilization factor.

Claims (4)

1. a Hadamard transform near infrared spectrometer that adds sheet feeding type comprises light source (1), slit (4), second collimation lens (5), plane grating (6), imaging len (7), DMD(8), condenser lens (9), single-point detector (10), static driving circuit and spectral information acquisition processing system, it is characterized in that, this spectrometer also comprises the sheet feeding type that is made of first collimation lens (2) and cylindrical mirror (3), the photometry for the treatment of that light source (1) sends is incided first collimation lens (2) through fiber port, incide cylindrical mirror (3) by first collimation lens (2) collimation for behind the secondary color directional light, after becoming ribbon beam with circular light beam, cylindrical mirror (3) incides slit (4), inciding plane grating (6) through second collimation lens (5) collimation for behind the secondary color directional light by the light beam of slit (4) outgoing, is band through plane grating (6) chromatic dispersion; Utilize the static driving circuit to adjust DMD(8) angle, make band assemble the back by imaging len (7) and incide DMD(8 successively by the wavelength order) diverse location, through DMD(8) carry out being focused on the single-point detector (10) by condenser lens (9) behind the wavelength gating, single-point detector (10) sends the spectral information that receives to the spectral information acquisition processing system, the spectral information acquisition processing system carries out Hadamard inverse transformation decoding to the spectral information that receives, and obtains the information of original spectrum signal.

2. a kind of Hadamard transform near infrared spectrometer that adds sheet feeding type as claimed in claim 1 is characterized in that described single-point detector (10) is the single-point photodiode.

3. a kind of Hadamard transform near infrared spectrometer that adds sheet feeding type as claimed in claim 1 is characterized in that, described first collimation lens (2), second collimation lens (5) and imaging len (7) are cemented doublet.

4. a kind of Hadamard transform near infrared spectrometer that adds sheet feeding type as claimed in claim 1 is characterized in that, the width of described slit (4) is 50 μ m, and length is 1mm.

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