Device and method for measuring reflectivity based on self-reference of area array CCD sensor

Abstract

The present invention provides a device and method for measuring reflectivity based on self-reference of an area array CCD sensor, and belongs to the field of optical measurement. Due to the instability of the light source, when measuring the reflectivity, the light intensity of the light source will fluctuate with the changes in the environment and temperature, thereby causing fluctuations in the reflectivity measured by traditional reflectivity equipment, and further affecting the final measurement result. The present invention divides the light coming out of the light source into two paths, one of which is transmitted to the upper or lower part of the area array CCD sensor as a reference light intensity, and the other is transmitted to the sample surface, and then the reflected light is transmitted to the other part of the area array CCD sensor as a measurement light intensity, and the fluctuation of the reference light intensity is corrected to the measurement light intensity, so that the influence of the instability of the light source in the reflectivity measurement process is eliminated in real time, thereby ensuring the consistency of the wavelength and the consistency of the signal-to-noise ratio, thereby ensuring the accuracy of the measurement result.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and more specifically, relates to a self-reference reflectivity measurement device and method based on a planar array CCD sensor. Background Art

[0002] Area array CCD sensor is a sensor that converts light signals into electrical signals using the photoelectric effect of semiconductor materials. It is widely used in the fields of spectroscopy and imaging. Binning is a unique operating technology of area array CCD sensor, which can merge and move the photosensitive charges in different pixels in a certain way.

[0003] Figure 1 This is a schematic diagram of Binning in the vertical direction in Hamamatsu's area array CCD sensor. The CCD has M*N pixels, M pixels in the horizontal direction, and N pixels in the vertical direction. After the integration time is over, the charge of each pixel will be gathered in the potential well to form a two-dimensional charge information distribution. At the same time, the vertical and horizontal temporary registers receive clock pulses respectively. When the horizontal temporary register clock is paused, by applying several clock pulses to the vertical temporary register, the signal charge of each column of pixels is transferred and aggregated into each horizontal temporary register in turn. When the vertical branch of the Nth column is completed, the horizontal clock is restarted, and the aggregated signal charge is sent to the external circuit through the output stage.

[0004] like Figure 2 The figure shows the existing reflectivity measurement method. The light emitted by the wide spectrum light source passes through the collimator and beam splitter and is incident on the surface of the sample to be measured. The reflected light passes through the beam splitter again and is received by the spectrometer. The actual process of measuring the reflectivity of the sample is as follows:

[0005] 1) Measure the dark noise intensity of the spectrometer .

[0006] 2) Measure the reflected light intensity data of the standard .

[0007] 3) Measure the reflected light intensity of the sample to be tested , according to the reflectivity calculation formula:

[0008] (1)

[0009] (2)

[0010] Among them, the standard reflectivity If the reflectivity of the sample to be tested is known, the reflectivity of the sample to be tested can be calculated. .

[0011] However, as time and ambient temperature change, the light intensity of the light source will fluctuate, and the light intensity of the standard will not be measured synchronously with the sample to be tested, which will cause fluctuations in the reflectivity measured by the equipment, thereby affecting the final result. Summary of the invention

[0012] In order to solve the above problems, the embodiment of the present invention provides a device and method for measuring reflectivity based on self-reference of an area array CCD sensor, and the scheme is as follows:

[0013] On the one hand, an embodiment of the present invention provides a device for measuring reflectivity based on self-reference of an area array CCD sensor, comprising:

[0014] Light source: used to output light and split it into two;

[0015] Measurement optical path: used to send one light path directly to the spectrometer module and another light path to the sample surface and send the reflected light to the spectrometer module;

[0016] Spectrometer module: includes an area array CCD sensor, which is used to send one path of light to the upper part or the lower part of the area array CCD sensor as reference light, and send another path of light to another part of the area array CCD sensor as measurement light.

[0017] Among them, in the spectrometer module, two paths of light are sent to the upper and lower parts of the area array CCD sensor after collimated reflection, grating splitting and focused reflection.

[0018] Furthermore, the spectrometer module in the embodiment of the present invention also includes an input optical fiber, a slit, a plane grating, a focusing mirror and a collimating mirror. The input optical fiber, the slit, the collimating mirror, the plane grating, the focusing mirror and the area array CCD sensor are arranged in sequence along the light path direction. The input optical fiber is composed of two optical fibers arranged closely side by side. The two optical fibers are arranged side by side in the length direction of the slit and input two light beams respectively.

[0019] The area array CCD sensor in the embodiment of the present invention binns the light intensities of the upper and lower parts respectively and outputs spectrum data.

[0020] Furthermore, the self-reference reflectivity measuring device based on the area array CCD sensor of the present invention also includes:

[0021] Calculation module: used to obtain the reflectance curve of the sample to be tested based on the reflectance curve of the standard sample and the light intensity data detected under three states.

[0022] On the other hand, an embodiment of the present invention further provides a self-reference reflectivity measurement method based on an area array CCD sensor, comprising:

[0023] Obtain reference light intensity and measurement light intensity respectively under no light source, standard sample and sample to be tested;

[0024] The reflectivity of the sample to be tested is obtained according to the reflectivity of the standard sample and the light intensity data detected under three states.

[0025] Specifically, the self-reference reflectivity measurement method of the embodiment of the present invention comprises the following steps:

[0026] S101: Block the light path and obtain reference light intensity and measure light intensity .

[0027] S102: Test the standard product and obtain the reference light intensity and measure light intensity .

[0028] S103: Detect the sample to be tested and obtain the reference light intensity and measure light intensity .

[0029] S104: Calculate the reflectivity curve of the sample to be tested according to formulas Ⅰ and Ⅱ ;

[0030] (Ⅰ)

[0031] (Ⅱ)

[0032] in, is the reflectance curve of the standard product, is the horizontal pixel index, is the fluctuation factor for each pixel.

[0033] The beneficial effects of this patent are as follows: the present invention divides the light intensity coming out of the light source into two paths, one path is transmitted to the upper part of the area array CCD sensor as the reference light intensity, and the other path is transmitted to the sample surface, and then the reflected light is transmitted to the lower part of the area array CCD sensor as the measurement light intensity. By correcting the fluctuation of the reference light intensity in the upper part to the measurement light intensity in the lower part, the influence of the instability of the light source in the reflectivity measurement process is eliminated in real time, which not only ensures the consistency of the wavelength, but also ensures the consistency of the signal-to-noise ratio, thereby ensuring the accuracy of the measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of binning in the vertical direction of the area array CCD sensor;

[0035] Figure 2 is a working schematic diagram of an existing reflectivity measuring device;

[0036] Figure 3 It is a schematic diagram of the optical path of the self-reference reflectivity measuring device based on the area array CCD sensor provided by the present invention;

[0037] Figure 4 It is a side view of the optical path of the self-reference reflectivity measuring device based on the area array CCD sensor provided by the present invention;

[0038] Figure 5 This is a layered schematic diagram of the area array CCD sensor provided by the present invention;

[0039] Figure 6 1 is a schematic structural diagram of a self-reference reflectivity measuring device based on an area array CCD sensor according to an embodiment of the present invention;

[0040] Figure 7 is a flow chart of the self-reference reflectivity measurement method provided by the present invention;

[0041] Figure 8 Schematic diagram of imaging of the upper and lower parts of the area array CCD sensor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] Example 1

[0044] Embodiment 1 provides a device for measuring reflectivity based on self-reference of an area array CCD sensor, comprising:

[0045] Light source: used to output light and split it into two; specifically, an existing wide-spectrum light source is used, and the splitting method is a conventional method.

[0046] Measuring optical path: used to send one light path directly to the spectrometer module and another light path to the sample surface and send the reflected light to the spectrometer module; specifically used to send one light path into the reference light interface of the spectrometer module, send another light path to the sample and send the reflected light into the measuring light interface of the spectrometer module, mainly composed of optical fiber, probe and other necessary optical components.

[0047] Spectrometer module: includes an area array CCD sensor, which is used to send one light beam to the upper or lower part of the area array CCD sensor as reference light, and send another light beam to the other part (lower or upper part) of the area array CCD sensor as measurement light. The area array CCD sensor converts light information into electrical signal output.

[0048] Calculation module: used to obtain the reflectance curve of the sample to be tested and output (such as display) according to the reflectance curve of the standard sample (input or default value) and the light intensity data detected in three states (no light source, standard sample and sample to be tested). Figure 6 Computer shown.

[0049] like Figure 6 As shown, the spectrometer module is provided with a reference light interface and a measurement light interface respectively.

[0050] Among them, in the spectrometer module, both light beams are sent to the upper and lower parts of the area array CCD sensor after collimated reflection, grating splitting and focused reflection. Correspondingly, the spectrometer module in the embodiment of the present invention also includes an input optical fiber, a slit, a plane grating, a focusing mirror and a collimating mirror, etc. The input optical fiber, the slit, the collimating mirror, the plane grating, the focusing mirror and the area array CCD sensor are arranged in sequence along the light path direction, and the arrangement method is well known to those skilled in the art. The input optical fiber is composed of two optical fibers arranged closely side by side, and the two optical fibers are arranged side by side in the length direction of the slit and input the two light beams respectively. Specifically, two optical fibers can form a Y-shaped structure (the output ends are as close as possible (can be directly wrapped together), and the input ends are far away from each other) to improve the light coupling efficiency; the slit is used to limit the height of the light and control the size of the light beam entering the spectroscopic system; the plane grating is the key spectroscopic element, which separates light of different wavelengths according to the diffraction principle, so that the light deflects in different directions according to the wavelength; the collimator plays the role of collimating the light, so that the light is collimated parallel light when it is directed to the grating, improving the grating spectroscopic effect; the focusing mirror is used to gather and reflect the split light signal to the area array CCD sensor; the area array CCD sensor is used to record the light intensity and convert the light information into an electrical signal output. Finally, a pixel-light intensity spectrum is formed.

[0051] Of course, the input optical fiber may also adopt other structures to introduce light, and the structure between the input optical fiber and the area array CCD sensor may also be adjusted or optimized as needed.

[0052] The area array CCD sensor in the embodiment of the present invention bins the light intensities of the upper and lower parts respectively and outputs spectral data. Generally, the area array CCD sensor can implement the binning function through hardware.

[0053] Among them, the pixel ratio of the upper and lower parts of the area array CCD sensor is not limited to 1:1. Considering that the light intensity of the light source is directly transmitted to the area array CCD sensor, the light intensity is relatively strong. When designing the optical path, it is possible to consider irradiating the reference light to a smaller area on the area array CCD sensor and measuring the light intensity in a larger area, thereby ensuring better response and signal-to-noise ratio. Alternatively, the upper and lower areas can be divided on the CCD pixel array, and each area can independently control the integration time to obtain data with different integration times in different areas in the same frame image.

[0054] Example 2

[0055] Embodiment 2 provides a self-reference reflectivity measurement method based on an area array CCD sensor, using the self-reference reflectivity measurement device based on an area array CCD sensor provided in Embodiment 1. The method includes:

[0056] The reference light intensity and the measured light intensity are obtained respectively in the absence of light source, standard sample and sample to be tested; the process of no light source, standard sample and sample to be tested is consistent with the prior art, the difference of this patent is that the reference light intensity needs to be obtained at the same time.

[0057] The reflectivity of the sample to be tested is obtained according to the reflectivity of the standard sample and the light intensity data detected in three states (under no light source, standard sample and sample to be tested, respectively).

[0058] Specifically, see Figure 7 The self-reference reflectivity measurement method of the embodiment of the present invention comprises the following steps:

[0059] S101: Block the light path and obtain reference light intensity (for reference dark noise) and measured light intensity (To measure dark noise).

[0060] S102: Test the standard product and obtain the reference light intensity (initial light intensity data) and measured light intensity (Measured light intensity data of standard product).

[0061] S103: Detect the sample to be tested and obtain the reference light intensity (Real-time reference light intensity data) and measured light intensity (Real-time measured light intensity data of the sample to be tested).

[0062] S104: Calculate the reflectivity curve of the sample to be tested according to formulas Ⅰ and Ⅱ ;

[0063] (Ⅰ)

[0064] (Ⅱ)

[0065] Among them, is the reflectivity curve of the standard product, is the horizontal pixel index, is the fluctuation factor of each pixel.

[0066] Example 3

[0067] Example 3 provides a self-reference reflectivity measurement method based on a linear array CCD sensor. Taking the CCD sensors of Hamamatsu Corporation in Japan, such as S11420 and S7031, as examples, M = 1024, 2048, etc., N = 64, 128, etc. Appropriate sensors can be selected according to actual measurement requirements. The band range can be freely designed within the range of 190nm - 1100nm. Typical band ranges are 350nm - 1000nm, 245nm - 1000nm, 190nm - 1000nm, etc. It can be achieved by modifying the grating and optical path in the spectrometer according to requirements.

[0068] As Figure 5 shown, the CCD area array sensor has a total of M * N pixels. Horizontally, there are M pixels, and vertically, there are N pixels. The vertical direction is divided into a and b pixels, where N = a + b, a is the number of rows in the upper part, and b is the number of rows in the lower part. Since in the design of this patent, the light source divides a path of light intensity directly to the upper half of the CCD, and the reflected light intensity is transmitted to the lower half of the CCD, which results in the response of the upper half of the CCD being much higher than that of the lower half of the CCD. There are two methods to handle this problem: 1) Add an optical filter in the optical path transmitted to the upper half of the CCD; 2) Reduce the value of a so that a < b. This patent mainly considers method 2. The calculation formulas for the light intensity of the CCD are shown in (3) and (4):

[0069] (3)

[0070] (4)

[0071] Among them, is the index of the horizontal pixel, and the horizontal pixel represents the wavelength dimension; is the index of the pixel in the vertical direction, and the light intensity of each column is the sum of the light intensities of its respective columns. Through circuit design, the reference light intensity and the measured light intensity can be extracted separately. During the actual operation process, the allocation of a and b is adjusted according to the magnitude of the measured light intensity.

[0072] Figure 6The figure shows the process of the self-reference reflectivity measurement method disclosed in the present invention. Compared with the traditional reflectivity measurement, there is an additional step of reference light intensity measurement and correction process. During the measurement process, the influence of light source fluctuation on reflectivity is eliminated in real time, ensuring the accuracy of reflectivity measurement results.

[0073] Specifically, the self-reference reflectivity measuring device based on the area array CCD sensor in this embodiment is as follows: Figure 6 As shown. The light source is used to output a light beam with a spectral range of 190nm-1000nm. The spectrometer module includes a housing, an input optical fiber, a slit, a plane grating, a focusing mirror, a collimating mirror, an array CCD sensor, and necessary electrical components. The slit, plane grating, focusing mirror, collimating mirror, and array CCD sensor are inside the housing. The input optical fiber has two input ends, namely a reference light interface and a measurement light interface. The number of pixels of the array CCD sensor is M*N; the computer is installed with control software, which is connected to the spectrometer module through a network cable to provide a graphical interface for the user.

[0074] After the measurement begins, the light output by the light source is divided into two paths. One path is directly connected to the reference light interface of the spectrometer module and forms an image on the upper half of the area array CCD sensor. The other path reaches the sample surface through the Y-type optical fiber, and the reflected light is connected to the measurement light interface of the spectrometer module and forms an image on the lower half of the area array CCD sensor. The final imaging effect of the reference light and the measurement light on the area array CCD sensor is shown in the figure below. Figure 8 shown.

[0075] Through circuit design, the upper half of the area array CCD sensor can be binned into one row, and the lower half can be binned into another row, outputting data with a length of M*2 pixels. If the area array CCD sensor does not support the hardware binning function, you can also achieve a similar binning effect by performing pixel merging in software. The specific steps are as follows:

[0076] 1) Read the complete image of CCD in normal mode and obtain M*N raw image data.

[0077] 2) In the software code, traverse the first a rows of data of the image, calculate the average or sum of each column, and generate the first row of data.

[0078] 3) Similarly, the last b rows of image data are processed to generate the second row of data.

[0079] In this way, by using software pixel summation, the line binning function of the hardware can be simulated to process M*N data into M*2.

[0080] The disadvantage of software binning is that it requires a lot of computation and is not as efficient as hardware binning. At the same time, noise will be accumulated. The main reason is that hardware binning accumulates signals in the analog domain, so the amplitude of the read signal can be significantly increased, while the noise amplitude is relatively fixed, and the signal-to-noise ratio (SNR) is improved. However, software binning is performed in the digital domain, where both the signal and the noise are accumulated equally, and the signal-to-noise ratio cannot be increased. In order to mitigate this noise doubling effect, the following can be considered when implementing software binning:

[0081] 1) When summing, use a sliding average instead of a simple sum.

[0082] 2) Perform low-pass filtering on the output image to suppress high-frequency noise.

[0083] Specifically, the reflectivity measurement process is as follows:

[0084] 1) First, block the reference light path and the measurement light path, and collect a set of data output by the area array CCD sensor, which are the reference dark noise and measure dark noise .

[0085] 2) Select the standard sample bare silicon. The reflectivity of the standard sample is known and is recorded as After placing the standard sample, a set of data output by the area array CCD sensor is obtained by measuring once, which are the initial light intensity data of the reference light Measure light intensity data with standard products .

[0086] 3) Remove the standard, place the sample to be tested, and measure again to obtain a set of data output by the area array CCD sensor, which are the real-time light intensity data of the reference light and Real-time measurement of light intensity data of the sample to be tested .

[0087] 4) Real-time fluctuation factor of light source , can be expressed as:

[0088] (5)

[0089] Then the reflectivity calculation formula (5) considering the light source fluctuation can be modified as follows:

[0090] (6)

[0091] According to formulas (5) and (6), the real-time reflectivity curve of the sample to be tested can be obtained: Formula (5) is the fluctuation factor of each pixel. In the actual calculation process, the fluctuation factor can also be averaged. Formula (6) can be improved to formula (8):

[0092] (7)

[0093] (8)

[0094] in is the average value of the wavelength factor, then is the horizontal pixel index.

[0095] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for measuring reflectivity based on self-reference of an area array CCD sensor, characterized in that: include: Light source: used to output light and split it into two; Measurement optical path: used to send one light path directly to the spectrometer module and another light path to the sample surface and send the reflected light to the spectrometer module; Spectrometer module: including an area array CCD sensor, used for sending one path of light to the upper part or the lower part of the area array CCD sensor as reference light, and sending another path of light to another part of the area array CCD sensor as measurement light; The area array CCD sensor bins the light intensity of the upper and lower parts respectively and outputs spectral data; the upper part of the area array CCD sensor is binned into one row, and the lower part is binned into another row through hardware implementation, and data with a length of M*2 pixels is output; the calculation formula of the light intensity of the CCD is shown in (3) and (4): (3) (4) in, is the index of the horizontal pixel, which represents the wavelength dimension; is the index of the vertical pixel, and the light intensity of each column is the sum of the light intensities of the respective columns; the CCD area array sensor has a total of M*N pixels, M pixels in the horizontal direction and N pixels in the vertical direction, and the vertical direction is divided into a and b pixels, where N=a+b, a is the number of rows in the upper part, and b is the number of rows in the lower part; The self-reference reflectivity measurement method of the device for self-reference reflectivity measurement based on the area array CCD sensor comprises the following steps: S101: Block the light path and obtain reference light intensity and measure light intensity ; S102: Test the standard product and obtain the reference light intensity and measure light intensity ; S103: Detect the sample to be tested and obtain the reference light intensity and measure light intensity ; S104: Calculate the reflectivity curve of the sample to be tested according to formulas Ⅰ and Ⅱ ; (Ⅰ) (Ⅱ) in, is the reflectance curve of the standard product, is the horizontal pixel index, is the fluctuation factor for each pixel.

2. The device for measuring reflectivity based on self-reference of area array CCD sensor according to claim 1, characterized in that: In the spectrometer module, both light beams are sent to the upper and lower parts of the area array CCD sensor after collimated reflection, grating splitting and focused reflection.

3. The device for measuring reflectivity based on self-reference of area array CCD sensor according to claim 2, characterized in that: The spectrometer module also includes an input optical fiber, a slit, a plane grating, a focusing mirror and a collimating mirror. The input optical fiber, the slit, the collimating mirror, the plane grating, the focusing mirror and the area array CCD sensor are arranged in sequence along the light path direction. The input optical fiber consists of two optical fibers arranged closely side by side. The two optical fibers are arranged side by side in the length direction of the slit and input two light beams respectively.

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