CN102661800A

CN102661800A - Reflection type optical reading method based on MEMS (Micro-electromechanical Systems) infrared imaging system

Info

Publication number: CN102661800A
Application number: CN2012101614139A
Authority: CN
Inventors: 惠梅; 王文娟; 赵跃进
Original assignee: Beijing Institute of Technology BIT
Current assignee: Beijing Institute of Technology BIT
Priority date: 2012-05-23
Filing date: 2012-05-23
Publication date: 2012-09-12
Anticipated expiration: 2032-05-23
Also published as: CN102661800B

Abstract

The invention provides a reflection type optical reading method based on an MEMS (Micro-electromechanical Systems) infrared imaging system. When a background environment is not provided with an infrared object, an FPA (Focal Plane Array) micro-cantilever is not bent; light reflected by an FPA is subjected to primary Fourier transformation through a concave lens to form filtering waves with a frequency spectrum which passes through a reflection filter; then the filtering waves are imaged on a CCD (Charge Coupled Device) by the Fourier transformation through the other concave lens; and the image is used as a standard image. When the environment is provided with the infrared object, the micro-cantilever in the focal plane array is bent by heating and the light reflected by the FPA is changed; and the light is certainly displaced through the frequency spectrum of the concave lens; and the light is imaged on the CCD through the filtering waves of the reflection filter and inverse Fourier transformation of the concave lens. The image and the standard image are subjected to difference operation to obtain an image with an infrared radiation object. The method folds a light path, reduces the size of an optical reading system and realizes the aims of improving the imaging quality and improving the detection sensitivity.

Description

Reflective optic reading method based on the MEMS infrared imaging system

The ■ technical field

The present invention is based on a kind of optical reading method of FPA non refrigerating infrared imaging system.This reading method is invented out a kind of new optical reading method to the present problem that the read-out system structure is too huge and sensitivity is low.This method uses catoptron to replace original lens imaging, and has used reflective filter to replace traditional wave filter, makes system compact more, and light, design freedom is bigger, and has increased the sensitivity that system surveys to a certain extent.

The ■ background technology

No matter be domestic or external, read formula FPA thermal imaging based on the novel optical of MEMS and more and more come into one's own.Light is read formula non refrigerating infrared imaging system and is compared with traditional electrical readout mode, sums up and gets up to have following several respects advantage:

1. can at room temperature work based on the core Sensitive Apparatus of the non refrigerating infrared imaging system of micro-cantilever, and not need refrigeration plant.

2. be the optics playback mode owing to what adopt, the phenomenon that does not exist electric energy to change heat energy is not so read-out system can produce additional heat energy on detector.

3. need between pixel, not carry out cross wire and electron scanning bundle, increase the quantity of pixel on the detector easily, not introduce manufacture difficulty and cost, reduce complexity and the production cost made.

4. do not need to carry out metal at shank between probe unit and connect, thereby can between probe unit and substrate, realize good heat isolation, make the heat isolation of each pixel can reach radiation limit like this.

5. therefore the micro fabrication that the present employing of micro-cantilever array can be compatible with the Si manufacture craft has reduced exploitation and cost of manufacture to a great extent.

According to several advantages of above introduction, the performance and integrated of both at home and abroad all novel optical being read formula non refrigerating infrared imaging system has now been carried out extensive probing into.

At present, the optical reading method that the non refrigerating infrared imaging system is used to read FPA micro-cantilever deflection angle is mostly based on the 4f system of transmission-type, and uses the filtering mode of the edge of a knife, aperture, slit, square hole etc.With the aperture filtering method is example: aperture filtering read-out system is through Infrared Lens infrared ray to be focused on the FPA, and FPA is in vacuum chamber, and light source is visible light LED.The light that LED sends becomes directional light behind collimating element, this directional light is radiated at FPA and upward and through FPA reflects.Become converging light from the FPA beam reflected through first imaging len, and be focused near the aperture on the focal plane.Because the deflection angle of each reflection junior unit is different, can make the converged position of these light on aperture plate different, have only when converged position and aperture position are suitable, these light can pass through aperture and second imaging len.When these light through behind second imaging len, can become directional light and on CCD, form images.When not having the infrared emanation object in the environment; The deflection angle of each semi-girder junior unit is identical; Therefore the directional light behind the collimation has identical direction after the FPA reflection, and through first imaging len post-concentration Jiao together, and the position of focus is all overlapping; The light intensity of reflected light after small holes that the FPA that CCD is received goes up each junior unit is identical, so the gray-scale value of each position of output image is identical.When having hot object in the environment; Difference and the different angle of deflection because each junior unit is heated; Cause direction difference, make this light beam focus on back focus and do not overlap that therefore the light intensity through aperture changes through first imaging len through the FPA beam reflected; The light intensity that finally causes receiving on the CCD changes, and obtains the output of gray-scale value pictures different.The detection sensitivity of this method is not only relevant with the temperature of detection of a target black matrix, and is also relevant with the sensitivity of the luminous intensity of LED and CCD.This method need not vibration isolation, is prone to realize array measurement.But the spatial resolution of this method and detection sensitivity can't improve simultaneously, and spatial resolution is not enough and not fogging clear etc.Summary is got up, and there is the defective of following several respects in the optical reading method of transmission-type:

1. the system architecture size is bigger, is unfavorable for miniaturization and portable.

2. spatial resolution and detection sensitivity cannot improve simultaneously, and spatial resolution is not enough and image is clear inadequately.

3. wave filter uses the edge of a knife, aperture or slit etc. mostly, and system defect (such as the manufacturing defect of FPA, the aberration that form is inconsistent and optical device produces that junior unit is initial etc.) is bigger to the influence of imaging.

4. the mutually complementary wave filter in position is difficult to realize and receive easily the influence of air turbulence.

Different with the optical reading method of transmission-type, reflective optical reading method is the optical element that utilizes reflection, and the use reflective filter complementary mutually with the conventional filter position.Compare with the wave filter (like aperture, slit etc.) of traditional 4f system, reflective filter is the form complementary with conventional filter, just with the method for round dot or side's point.Use the very difficult realization of 4f system of transmission-type to use round dot, side's point, realize the form of narrow band filter than difficulty, and receive the influence of air turbulence easily as wave filter.In addition, the mode of traditional aperture filtering is not easy to find the optimum filtering position.

The ■ summary of the invention:

The objective of the invention is to utilize reflective 4f system imaging performance, use reflective filter, the corner that is heated of micro-cantilever array is converted into light intensity signal.

The objective of the invention is to be realized by following technical scheme: reflective wave filter is a round dot of on level crossing, scribing certain radius, and the round dot position is reflected light not, and the position beyond the round dot can be reflective, as the wave filter of reflective 4f system diffraction spectra.The optical reflection face of supposing each micro-cantilever unit can be reduced to regular rectangular slab and parallel to each other, and rectangular slab is lined up and just formed two-dimentional optical grating construction so one by one.When using visible illumination, each rectangular slab unit forms identical diffraction spectra on the spectrum plane, but the angle of post deflection is different because each rectangular slab is heated, and the displacement of the diffraction spectra of each unit is also just different.The corner of some micro-cantilever is bigger than normal, causes the most of retroreflective regions that moves into of diffraction of light spectrum, and the luminous energy that passes through increases; The corner of some micro-cantilever is less than normal, diffraction of light spectrum major part still in opaque zone, the degree less (vice versa) that the luminous energy that passes through increases.During original state, when not having the infrared radiation object in the environment, the initial angle of the reflector of each junior unit of focal plane arrays (FPA) FPA is the same; Directional light with certain angle incident after; The rectangular slab unit of FPA forms identical diffraction spectra through reflection 4f system on the spectrum plane, through after the filtering and concave mirror of reflective filter; Be imaged on the CCD, and look like as benchmark with this.When the infrared radiation object is arranged in the environment; Object is imaged on the FPA through Infrared Lens; Corresponding different deflection takes place in the last junior unit of FPA, and after directional light incided on the FPA, corresponding deflection also took place the light that reflects through the FPA reflector; At this moment, the diffraction of light spectrum is along with the deflection of junior unit produces certain displacement.After the filtering and concave mirror imaging through reflective filter, be imaged on the CCD once more, the luminance difference of twice imaging just can obtain the thermal-induced imagery of infrared radiation object.

The ■ beneficial effect

Adopt the present invention can replace traditional lens imaging, adopt reflecting element concave mirror and reflective filter that the corner that is heated of micro-cantilever array is converted into light intensity signal.Compare with traditional method; The design freedom of reflective filter is bigger; This method not only can reduce the size of total system; Can also improve detection sensitivity, improve the efficiency of light energy utilization to a certain extent, and system defect is littler than using traditional 4f optical pickup system to the influence of imaging.

The ■ description of drawings

Fig. 1 is with the principle schematic based on the reflective 4f optical reading method of the uncooled ir thermal imaging system of MEMS based on of the present invention

Wherein: 1-pointolite, 2-colimated light system, 3-focal plane arrays (FPA), 4-concave mirror, 5-catoptron, 6-reflective filter, 7-concave mirror, 8-photelectric receiver

The reflective filter of Fig. 2 for using in the reflective optic reading method

Wherein: 9-plane mirror, the light tight round dot of 10-

The ■ embodiment

Below in conjunction with accompanying drawing the present invention is done and to further describe:

As shown in Figure 1, when the external world did not have the infrared radiation object, the junior unit of focal plane arrays (FPA) all was in same state.At this moment, the light that pointolite 1 is launched becomes directional light and penetrates through the modulation of colimated light system 2.Directional light shines on the 3 focal plane arrays (FPA) FPA, and the reflector in the focal plane arrays (FPA) FPA junior unit reflects directional light.On by concave mirror 4, focal plane, form diffraction spot through the light of focal plane arrays (FPA) FPA reflected back at concave mirror; The frequency spectrum of object just; The frequency spectrum that forms carries out filtering through reflective filter 6; Filtered frequency spectrum passes through the process of an inverse Fourier transform of concave mirror 7 again, and focal plane arrays (FPA) FPA is formed images.Looking like with this is benchmark image.Wherein plane mirror 5 has played folded optical path, reduces the effect of system dimension.When infrared object had been placed in the external world, the light that infrared object sends was imaged on the 3 focal plane arrays (FPA) FPA through behind the Infrared Lens, and the semi-girder that 3 focal plane arrays (FPA) FPA go up corresponding junior unit deflects.At this moment; Directional light through behind the collimation lens 2 shines on the FPA, and shining in the directional light behind the corresponding junior unit that deflects also can the certain angle of deflection, passes through once more by concave mirror 4, plane mirror 5, reflective filter 6; At this moment; The most of retroreflective regions that moves into of diffraction of light spectrum, the luminous energy that passes through increases, again through concave mirror 7 imagings; CCD collects to such an extent that be a piece image that infrared object information is arranged, and this width of cloth image and original image are done the thermal imagery that difference just can obtain infrared object.

As shown in Figure 2 is the wave filter of reflective playback mode.Be on plane mirror 9, to scribe an opaque round dot 10, be used for diffraction spectra is carried out filtering.In environment, do not have infrared object to be, the diffraction spectra major part of micro-cantilever is sponged by opaque circular hole, and the fraction of diffraction spectra is through the reflection of the reflecting surface outside the circular hole.When infrared object has been placed in the external world; The part micro-cantilever is according to the different angle of heat difference deflection that absorbs, and corresponding skew takes place diffraction spectra separately, and the corner of some micro-cantilever is bigger than normal; Cause the most of retroreflective regions that moves into of diffraction of light spectrum, it is bigger that the luminous energy that passes through increases degree; The corner of some micro-cantilever is less than normal, and it is less that the diffraction of light spectrum departs from retroreflective regions, and the degree that the luminous energy that passes through increases is also less.CCD just can capture the variation of different brightness like this, increases the sensitivity of infrared imaging system.In addition, reflective wave filter also can be as required with lighttight round dot 10, and the side's of being designed to point, arrowband or arbitrary shape are to satisfy the demand of system.

Claims

1. reflective optic reading method based on the MEMS infrared imaging system; It is characterized in that: this method realizes in the MEMS infrared imaging system; System is made up of illumination path, focal plane arrays (FPA) micro-cantilever FPA, Infrared Lens, concave mirror, reflective filter, photodetector and display; Infrared Lens on surface behind the FPA, makes FPA junior unit generation temperature distortion deflection with infrared emanation target conjugate imaging, and the directional light of illumination path outgoing arrives concave mirror after the FPA front surface reflection; Concave mirror carries out Fourier transform to FPA temperature distortion deflection light field; Fourier spectrum is by reflective filter filtering, and the inverse Fourier transform through another sheet concave mirror is imaged on the photodetector again, and display shows the light field information after FPA receives thermal deflection.

2. the reflective optic reading method based on the MEMS infrared imaging system as claimed in claim 1 is characterized in that: the reflective optic reading method adopts reflective filter, and just in time the position is complementary mutually to the filtered version of the filtered version of frequency spectrum and traditional transmission-type wave filter.

3. the reflective optic reading method based on the MEMS infrared imaging system as claimed in claim 2; It is characterized in that: transmission filter all blocks the high frequency position of frequency spectrum; And the reflective filter that the reflective optic reading method adopts has only blocked most of junior unit frequency spectrum in the position of frequency spectrum low frequency part; Therefore system defect is (such as the manufacturing defect of FPA; The aberration that form is inconsistent and optical device produces that junior unit is initial etc.) frequency spectrum that produces is by all filterings, and system defect is littler to the imaging effect influence like this.

4. the reflective optic reading method based on the MEMS infrared imaging system as claimed in claim 1, it is characterized in that: the reflective optic reading method has been used reflection device fully, can not produce aberration, and therefore the requirement to light source reduces, and the influence of light source reduces.

5. the reflective optic reading method based on the MEMS infrared imaging system as claimed in claim 1; It is characterized in that: the incident light of reflective optic reading method is an off-axis ray; Compare with traditional transmission-type reading method; In the design of light path, need not use Amici prism, reduce optical energy loss to a great extent.

6. the reflective optic reading method based on the MEMS infrared imaging system as claimed in claim 1; It is characterized in that: the traditional optical reading method is coaxial transmissive system; The a plurality of faces of transmissive element in the tradition reading method all can produce partial reflection light; Reflex to FPA,, produce the fuzzy of multiple imaging and picture again by the FPA reflected back; Reflective optical reading method is the off axis reflector system, and the light that reflects from FPA all forms images through concave mirror, and image quality is better than the transmission-type reading method, and has improved the efficiency of light energy utilization.

7. like claims 1 described reflective optic reading method based on the MEMS infrared imaging system; It is characterized in that: certain angle is arranged between incident directional light and the FPA; The off-axis angle of concave mirror is identical with the angle of FPA emergent light in this reading method; The picture that infrared object is become is identical with original ratio, can not be out of shape.