WO2022000243A1

WO2022000243A1 - Imaging system based on fabry-perot cavity

Info

Publication number: WO2022000243A1
Application number: PCT/CN2020/099162
Authority: WO
Inventors: 郭斌; 黄锦标
Original assignee: 深圳市海谱纳米光学科技有限公司
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2022-01-06
Also published as: CN113614633B; CN113614633A

Abstract

An imaging system based on a Fabry-Perot cavity. The system comprises a monochromatic imaging chip, and a bandpass filter and a Fabry-Perot cavity, which are arranged in an upstream optical path of the monochromatic imaging chip, wherein the bandpass filter and the Fabry-Perot cavity are separate elements, and the bandpass filter is configured to have a first optical response range from 430 nm to 760 nm, and the Fabry-Perot cavity is tunable such that an optical response peak thereof can be within the first optical response range or completely beyond the first optical response range. By using a tunable Fabry-Perot cavity covered by a wide spectrum and a bandpass filter with a first optical response range from 430 nm to 760 nm, and by means of a monochromatic imaging chip, an imaging system for RGB imaging, IR imaging and ON-OFF imaging can be realized, and a spectral image of any waveband can be parsed.

Description

Imaging system based on Fabry-Perot cavity

technical field

The present invention relates to the technical field of optical imaging, and in particular, to an imaging system based on a Fabry-Perot cavity.

Background technique

The tunable filter device based on Fabry-Perot cavity interference can be used in miniature spectrometers, small hyperspectral cameras and mini hyperspectral cameras. Compared with other solutions, the Fabry-Perot cavity provides the simplest optical path and system structure, so the cost and volume of the hyperspectral camera are greatly reduced.

In consumer applications, especially in portable imaging applications such as mobile phones, CMOS imaging devices are increasingly required to provide imaging in both RGB (color) and IR (far-infrared) spectral ranges, but the current mainstream color imaging chips based on filters are only R (red), G (green), B (blue) three channels. In application, the imaging chip based on RGB filter film will cooperate with IR-CUT filter to remove the influence of near-infrared wavelength light on color imaging. The color response (RGB) usually refers to the filter covering the R, G or B channels on a single pixel, and its response is the quantum efficiency of the pixel itself superimposed on the spectral response of the corresponding filter. To achieve IR imaging, a single RGB chip cannot be completed, and an additional imaging chip needs to be added to collect images at near-infrared wavelengths. The imaging chip is generally a monochromatic response device with a near-infrared filter attached.

In addition, CMOS imaging chips on mobile phones use electronic shutters, including rolling shutters and global shutters, while driven mechanical shutters are generally not used in portable imaging applications such as mobile phones due to their large size and low lifespan. Global shutter imaging chips usually have low pixels and also Rarely appears in portable applications such as mobile phones, while rolling shutter imaging chips have problems such as image tilt during high-speed imaging. And in applications such as high-quality imaging and spectral image analysis, it is usually desirable to cover the entire imaging chip to obtain the black frame reference at that time, but the black frame reference is very difficult to achieve in practical applications without a mechanical shutter.

SUMMARY OF THE INVENTION

In order to solve the technical problem in the prior art that it is not easy to use a single Fabry-Perot cavity and a single imaging chip to obtain a spectral imaging range that can cover RGB and IR and simultaneously achieve turn-off effect imaging under typical device structures and operating modes, The present invention proposes an imaging system based on a Fabry-Perot cavity, which solves the problem that a single Fabry-Perot cavity and a single imaging chip cannot be used to obtain an imaging system that can cover RGB under typical device structures and working modes in the prior art. and IR spectral imaging range and at the same time realize the technical problem of switching off effect imaging.

According to an aspect of the present invention, an imaging system based on a Fabry-Perot cavity is proposed, comprising a monochromatic imaging chip and a bandpass filter and a Fabry disposed in the upstream optical path of the monochromatic imaging chip a Perot cavity, the bandpass filter and the Fabry Perot cavity being separate elements, and the bandpass filter being configured to have a first optical response including from 430nm to 760nm range, and the Fabry-Perot cavity is tunable such that its optical response peak can be within the first optical response range or completely outside the first optical response range.

Further, the imaging system further includes a collimating lens group disposed at an upstream optical path position of the bandpass filter.

Further, the bandpass filter is arranged in the upstream optical path of the Fabry-Perot cavity.

Further, the reflective mirror surface in the Fabry-Perot cavity is made of a broad-spectrum reflective material.

Preferably, the mirror surface in the Fabry-Perot cavity is made of silver.

Further, the optical distance between the two mirror surfaces of the Fabry-Perot cavity is adjustable between 300-1125 nm.

Further, the peak order m of the incident light is adjusted by the Fabry-Perot cavity through the voltage change, the optical distance between the two mirror surfaces of the Fabry-Perot cavity is d, and the bandpass filter The wavelength of the optical response of the sheet is λ, m=2d/λ.

Further, the number of wave peaks in the optical response of the Fabry-Perot cavity in the first optical response range is 0, 1, 2, or 3.

Further, the optical distance d between the two mirror surfaces of the Fabry-Perot cavity is when the first-order peak (m=1) appears at λ>750nm, and the second-order peak (m=2) appears at λ<450nm. position, the imaging system is off.

Further, the collimating lens group collimates the incident light into incident light less than 30°.

Further, the monochromatic imaging chip adopts a silicon-based optical imaging chip.

Further, the spectral response range of the monochromatic imaging chip is 380nm-1050nm.

The present invention utilizes a tunable Fabry-Perot cavity with wide spectral coverage and a bandpass filter with a first optical response range from 430 nm to 760 nm, and can realize RGB imaging, IR imaging and IR imaging through a monochromatic imaging chip. Imaging system for imaging and ON-OFF imaging, and can resolve spectral images of any wavelength band. Thus, a single Fabry-Perot cavity and a single imaging chip are used to obtain an imaging system and method that can cover the spectral imaging range of RGB and IR and simultaneously realize the imaging of the turn-off effect.

Description of drawings

The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain the principles of the invention. Other embodiments and many of the intended advantages of the embodiments will be readily recognized as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale to each other. Like reference numerals designate corresponding similar parts.

1 is a schematic diagram according to an embodiment of the present invention;

FIG. 2 is a graph of quantum efficiency of an imaging chip according to an embodiment of the present invention.

3 is a schematic diagram of a voltage control curve of a Fabry-Perot cavity according to a specific embodiment of the present invention;

4 is a calculation table of spectral response data of an imaging system according to a specific embodiment of the present invention;

FIG. 5 is a spectral response curve diagram of a Fabry-Perot cavity according to a specific embodiment of the present invention;

detailed description

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof and are shown by way of illustrative specific embodiments in which the invention may be practiced. In this regard, directional terms such as "top," "bottom," "left," "right," "top," "bottom," etc. are used with reference to the orientation of the figures being described. Because components of an embodiment may be positioned in several different orientations, directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description should not be taken in a limiting sense, and the scope of the invention is defined by the appended claims.

As shown in FIG. 1 is a specific embodiment of an imaging system based on a Fabry-Perot cavity.

An imaging system based on a Fabry-Perot cavity, comprising a band-pass filter, a Fabry-Perot cavity and a monochromatic imaging chip, wherein the band-pass filter and the Fabry-Perot cavity are separate components, And set in the upstream optical path of the monochromatic imaging chip, the band-pass filter is set in the upstream optical path of the Fabry-Perot cavity, the incident light first passes through the band-pass filter and passes through the first optical response range. The incident light, then enters the Fabry-Perot cavity, the Fabry-Perot cavity is tunable so that its optical response peak can be within the first optical response range or completely within the first optical response range In addition, the incident light exits from a tunable Fabry-Perot cavity and enters a monochromatic imaging chip for imaging.

In a specific embodiment, the bandpass filter is configured to have a first optical response range including from 430 nm to 760 nm, and the Fabry-Perot cavity is tunable such that its optical response peak can be Within the first optical response range or completely outside the first optical response range.

In a specific embodiment, the mirror surface in the Fabry-Perot cavity is made of a broad-spectrum reflective material. For example, the mirror surface is made of silver and can work over the entire response range of a typical imaging device from 380nm to 1050nm.

In a specific embodiment, the optical distance d between the two mirror surfaces of the Fabry-Perot cavity is adjustable between 300-1125 nm, and the Fabry-Perot cavity can be adjusted by decreasing or increasing the optical distance d The position of the filtered peaks can be adjusted in the spectral response.

In a specific embodiment, the monochromatic imaging chip adopts a silicon-based optical imaging chip, and monochromatic imaging means that there is no RGB filter film on a single imaging unit (pixel), so the spectral response range of the monochromatic imaging chip can be 380nm-1050nm, And its ability to respond to light of any wavelength is determined by the quantum efficiency of the monochromatic imaging chip. As shown in the quantum efficiency curve in Figure 2, it can be seen that the quantum efficiency of the monochromatic imaging chip is higher than that of the RGB imaging chip, so its responsiveness to light of any wavelength is higher than that of the RGB imaging chip.

In a specific embodiment, the imaging system further includes a collimating lens group, which is arranged at the upstream optical path position of the bandpass filter, and the collimating lens group collimates the incident light with a large angle into an incident light with a small angle Light, incident light mainly includes ambient light and object reflected light. The light is complex and the light angle is usually greater than 60°. The incident light after the collimating lens group is collimated into the incident light with a light angle of less than 30°, which is conducive to light collection.

As shown in FIG. 3 , the control curve of the Fabry-Perot cavity adjusted by voltage control in this specific embodiment is shown. The optical distance d between the two mirror surfaces of a Fabry-Perot cavity decreases or increases by increasing or decreasing the driving voltage. Specifically, the relationship between the driving voltage V and the optical distance d between the mirror surfaces is:

where V is the driving voltage, d is the current optical distance between the mirrors, d ₀ is the initial optical distance between the mirrors, k is the elastic coefficient of the Fabry-Perot cavity, and ε ₀ is the dielectric constant in vacuum. The decrease or increase of the optical distance d can adjust the position of the wave peak filtered by the Fabry-Perot cavity, thereby realizing the tunability of the spectral response. However, when V is greater than a certain value V ₂ , the adsorption force between the mirror surfaces is greater than the elastic restoring force, the mirror surface will have an adsorption effect, and the two mirror surfaces will be attracted together. At this time, the Fabry-Perot cavity fails and cannot continue to work.

Figure 4 shows the calculation table of the spectral response data of the imaging system, in which the peak order m of the incident light adjusted by the Fabry-Perot cavity through voltage changes, the optical density between the two mirrors of the Fabry-Perot cavity The distance is d, the wavelength of the optical response of the bandpass filter is λ, and the relationship between the three can be simplified as m=2d/λ.

It can be seen from the data in Fig. 4 that when the optical response wavelength λ of the bandpass filter is set at 450nm-750nm, when the optical distance d=1125nm, the peak order m=3 in the optical response wavelength range appears; When the optical distance d=900nm, the peak order m=2 in the optical response wavelength range appears; when the optical distance d=825nm, 600nm, 500nm and 450nm, the wave peak order m=1 in the optical response wavelength range; When the optical distance between the two mirror surfaces of the Fabry-Perot cavity is different, the collected images correspond to 1-3 wavelengths of the response, which can satisfy RGB imaging and IR imaging. On the other hand, from the combination of these images, a spectral image of any wavelength in the optical response range of 450nm-750nm can be calculated.

When the optical distance d is 380nm-440nm, the first-order wave peak (m=1) of the Fabry-Perot cavity appears at the position of λ>750nm, and the second-order wave peak (m=2) appears at the position of λ<450nm, That is, the optical response wavelength λ of the bandpass filter is 0 in the range of 450nm-750nm, so the optical response of the imaging system is OFF. That is, the optical distance d between the two mirror surfaces of the Fabry-Perot cavity is at the position where the 1st-order peak (m=1) appears at λ>750nm, and the second-order peak (m=2) appears at the position where λ<450nm. The system is OFF.

In a specific embodiment, the half-wave width of the peak of the Fabry-Perot cavity can reach 20-30 nm, and the width of the bottom of the peak can even be greater than 50 nm. the above margin. In the data in the table in Figure 3, when the spectral range of the bandpass filter is 450nm-750nm, it can meet the spectral response requirements of RGB imaging, IR imaging and shutdown at the same time, but considering the above margin, the spectral range of the bandpass filter is selected. 430nm-760nm meets the actual requirement, that is, the first optical response range of the bandpass filter.

It can also be deduced from the table in Figure 4 that when the optical distance d=200nm and the wavelength λ=400nm of the Fabry-Perot cavity response, the peak order m=1, so theoretically the optical distance below 200nm can be Treated as another off (OFF) position. However, in practical applications, the optical distance of the Fabry-Perot cavity is usually difficult to reach 200 nm and below stably. At the same time, when the driving voltage is greater than a certain value, the adsorption effect will occur, and the distance below 200 nm is usually regarded as the distance that will produce the adsorption effect. , so the optical distance of the Fabry-Perot cavity needs to be kept above 200 nm.

Fig. 5 is a spectral response curve of a Fabry-Perot cavity in a specific embodiment of the present invention, and positions 1 to 4 correspond to the optical distance ranges in the table of Fig. 4. It can be seen that when the cut-off wavelength of the bandpass filter is at In the range of 450nm-750nm, the Fabry-Perot cavity has only 1 peak at

position

1, 2 peaks at

position

2, 3 peaks at position 3, and all peaks at position 4 at 450nm. Beyond -750nm, the optical response of the imaging system is OFF at this time.

It will be apparent to those skilled in the art that various modifications and changes can be made to the embodiments of the present invention without departing from the spirit and scope of the invention. In this manner, the present invention is also intended to cover such modifications and changes if they come within the scope of the claims of the present invention and their equivalents. The word "comprising" does not exclude the presence of other elements or steps not listed in a claim. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

An imaging system based on a Fabry-Perot cavity, characterized in that it includes a monochromatic imaging chip, a bandpass filter and a Fabry-Perot cavity arranged in the upstream optical path of the monochromatic imaging chip, and the the bandpass filter and the Fabry-Perot cavity are mutually separate elements, and the bandpass filter is configured to have a first optical response range including from 430 nm to 760 nm, and the The Fabry-Perot cavity is tunable such that its optical response peak can be within the first optical response range or completely outside the first optical response range.
The imaging system based on a Fabry-Perot cavity according to claim 1, characterized in that, the imaging system further comprises a collimating lens group arranged at an upstream optical path position of the bandpass filter.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the bandpass filter is arranged in the upstream optical path of the Fabry-Perot cavity.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the mirror surface in the Fabry-Perot cavity is made of a broad-spectrum reflective material.
The imaging system based on a Fabry-Perot cavity according to claim 4, wherein the mirror surface in the Fabry-Perot cavity is made of silver.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the optical distance between the two mirror surfaces of the Fabry-Perot cavity is adjustable between 300-1125 nm.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the Fabry-Perot cavity adjusts the peak order m of the incident light through voltage changes, the Fabry-Perot The optical distance between the two mirror surfaces of the cavity is d, the wavelength of the optical response of the bandpass filter is λ, and m=2d/λ.
The imaging system based on a Fabry-Perot cavity according to claim 7, wherein the number of wave peaks in the optical response of the Fabry-Perot cavity in the first optical response range is 0, 1, 2, or 3.
The imaging system based on a Fabry-Perot cavity according to claim 7, wherein the optical distance d between two mirror surfaces of the Fabry-Perot cavity can be adjusted so that the Fabry-Perot The first-order peak (m=1) of the optical response of the Luo cavity appears at the position of λ>750nm, and the second-order peak (m=2) appears at the position of λ<450nm, so as to realize the shutdown of the imaging system.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the collimating lens group collimates the incident light into incident light less than 30°.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the monochromatic imaging chip adopts a silicon-based optical imaging chip.
The imaging system based on a Fabry-Perot cavity according to claim 1, wherein the spectral response range of the monochromatic imaging chip is 380nm-1050nm.