A wavelength calibration method for optical fiber spectrometer

Abstract

The invention discloses a wavelength calibration method for a fiber optic spectrometer, and belongs to the field of measurement technology. The method first measures at least two standard samples through the fiber optic spectrometer to be calibrated, obtains a measured reflected light intensity-pixel number sequence, and calculates the measured normalized reflected light intensity-pixel sequence ratio of any two standard samples; then, the normalized reflected light intensity-wavelength sequence of the standard samples is theoretically calculated to obtain the theoretical normalized reflected light intensity-wavelength sequence ratio of any two standard samples; finally, by comparing the measured normalized reflected light intensity-pixel number sequence ratio and the theoretical normalized reflected light intensity-wavelength sequence ratio, the relationship between the wavelength and the fiber optic spectrometer pixel number is solved, thereby realizing the wavelength calibration of the fiber optic spectrometer. The wavelength calibration method in the present invention will not be limited by the detection wavelength range of the fiber optic spectrometer to be calibrated, and can realize the accurate wavelength calibration of the fiber optic spectrometer within any spectral range.

Description

Technical Field

[0001] The invention belongs to the field of measurement, and in particular relates to a wavelength calibration method for an optical fiber spectrometer. Background Art

[0002] A spectrometer is a general optical measuring instrument that uses a dispersion spectrometer to split the incident light beam introduced by an optical fiber into different wavelengths at different angles, and receives it through a linear array detector to measure and obtain the intensity distribution characteristics of the incident light beam at different wavelengths. In the early days, due to the limitations of processing technology, prisms were usually used as spectrometers. Due to the limited spectrometer capability of the prism, the spectrometer based on prism spectrometry was relatively large in size and its spectral resolution was not high. In recent decades, with the rapid development of micro-nano manufacturing technology, gratings, as a more efficient spectrometer, have been introduced more and more into the design and manufacture of spectrometers, and spectrometers are gradually developing towards miniaturization and miniaturization. Since Ocean Optics invented the miniature spectrometer in 1992, the miniature fiber optic spectrometer that uses optical fiber to introduce the light beam to be detected has gradually become the first choice for people to build spectral analysis instruments due to its size advantage and the convenience of optical fiber connection.

[0003] The fiber optic spectrometer essentially detects and obtains the intensity distribution of light on different pixels on the linear array detector. In order to convert the intensity distribution of light on the pixels into the intensity distribution at different wavelengths, the pixels in the fiber optic spectrometer need to be calibrated in wavelength. The commonly used wavelength calibration method is to introduce a standard light source with known characteristic spectral lines (such as a mercury lamp light source, an argon lamp light source, etc.) into the fiber optic spectrometer. Certain pixel positions in the fiber optic spectrometer will obtain specific characteristic spectral line responses. Through the correspondence between multiple characteristic spectral line wavelengths and pixel positions, the correspondence between pixel positions and wavelengths in the fiber optic spectrometer can be obtained by solving polynomial equations.

[0004] For many application fields, fiber optic spectrometers are required to achieve ultra-high spectral resolution. However, due to the size of fiber optic spectrometers, it is usually impossible to achieve high spectral resolution and wide spectral detection range at the same time. When calibrating the wavelength of such fiber optic spectrometers (high resolution), it is impossible to find enough characteristic spectral lines of the standard light source within its narrow spectral detection range, and thus the wavelength of the fiber optic spectrometer cannot be calibrated using the standard light source. Summary of the invention

[0005] In view of the situation that it is impossible to find enough characteristic spectral lines for wavelength calibration in the above-mentioned narrow spectral range and high spectral resolution fiber optic spectrometer, the wavelength calibration method of the fiber optic spectrometer based on the comparison of the reflected light intensity of the standard sample provided by the present invention can perform calculation comparison and wavelength calibration in any spectral range and will not be limited by the detection spectral range of the fiber optic spectrometer.

[0006] An embodiment of the present invention provides a wavelength calibration method for a fiber optic spectrometer, comprising:

[0007] At least two groups of standard samples are measured by the optical fiber spectrometer to be calibrated to obtain a reflected light intensity-pixel number sequence, and a measured normalized reflected light intensity-pixel sequence ratio of any two standard samples is calculated;

[0008] The theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated, and the ratio of the theoretical normalized reflected light intensity-wavelength sequence of any two standard samples is calculated;

[0009] The corresponding relationship between the pixel number and the wavelength of the fiber optic spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio.

[0010] Wherein, measuring at least two groups of standard samples by using the optical fiber spectrometer to be calibrated includes: connecting a light source and the optical fiber spectrometer to be calibrated by using Y-type optical fibers to measure the standard samples.

[0011] Among them, the theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated by Fresnel formula I:

[0012] (I)

[0013] Where λ is the wavelength, d is the film thickness, and n(λ) represents the refractive index of the film.

[0014] Among them, the corresponding relationship between the pixel number and the wavelength is shown in formula II:

[0015] (Ⅱ)

[0016] Among them, i=1,2,3,…,K is the pixel number, m represents the order of the polynomial, C0,C1,C2,…C m Represents the coefficients of the polynomial.

[0017] The corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio, including: using a nonlinear regression algorithm based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio to iteratively obtain the corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated.

[0018] Specifically, the wavelength calibration method of the optical fiber spectrometer provided by the embodiment of the present invention includes:

[0019] S101: The fiber optic spectrometer to be calibrated measures standard samples A and B respectively to obtain a reflected light intensity-pixel number sequence and , calculate the measured normalized reflected light intensity-pixel sequence ratio of standard samples A and B / ;

[0020] in, , 1,2,3,…,k are the pixel numbers of the fiber optic spectrometer;

[0021] S102: Obtain the measured normalized reflected light intensity-wavelength sequence ratio from formula II and formula III ;

[0022] (III)

[0023] S103: Calculate the theoretical normalized reflected light intensity-wavelength sequence of standard samples A and B according to formula I and , get the theoretical normalized reflected light intensity-wavelength sequence ratio / ;

[0024] S104: Comparison by nonlinear regression method and , the corresponding relationship between the pixel number and wavelength of the fiber optic spectrometer to be calibrated is calculated.

[0025] Furthermore, step S104 specifically includes:

[0026] S401: Taking the design wavelength of the fiber spectrometer to be calibrated as the initial value, the coefficients of the initial polynomial are calculated by formula II ;

[0027] S402: Substitute the coefficients of the initial polynomial into equations II and III to calculate the measured normalized reflected light intensity-wavelength sequence ratio ;

[0028] S403: Comparison and , the polynomial coefficients are iteratively solved by nonlinear regression algorithm C 0, C 1, C 2,… C m ;when and When the difference is the smallest, it is the final polynomial coefficient corresponding to the calibration of the fiber optic spectrometer to be calibrated. C 0, C 1, C 2,… C m .

[0029] The beneficial effects of the present invention are as follows: the key to the method proposed in the example of the present invention is to compare the normalized reflected light intensity-wavelength sequence ratio of the measured standard sample with the normalized reflected light intensity-wavelength sequence ratio of the theoretically calculated standard sample, and to use a nonlinear regression iteration method to obtain the correspondence between the pixel number and the wavelength. The spectral range to which the method is applicable is limited only by the wavelength range of the known refractive index of the standard sample. At present, silicon, silicon dioxide, etc., which are commonly used as standard sample materials, have a known refractive index range ranging from deep ultraviolet to mid-to-far infrared, far exceeding the spectral detection range that can be achieved by the fiber optic spectrometer. Therefore, the wavelength calibration method proposed in the present invention can theoretically calibrate the wavelength of the fiber optic spectrometer of any spectral range. In addition, the example of the present invention measures two groups of standard samples to obtain their ratios in order to eliminate the influence of the incident light intensity, and the method of using more groups of standard samples to obtain the ratios is also applicable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the fiber optic spectrometer detecting the standard sample;

[0031] Figure 2 is a flow chart of the wavelength calibration method of the optical fiber spectrometer provided in Example 2;

[0032] Figure 3 It is a flow chart of calculating the corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated by nonlinear regression method;

[0033] Figure 4 The invention is a principle block diagram of calculating the corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated by using the nonlinear regression method.

[0034] Among them, 1Y-type optical fiber, 2 light sources, 3 fiber optic spectrometers, and 4 standard samples. DETAILED DESCRIPTION

[0035] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Example 1

[0037] Embodiment 1 provides a wavelength calibration method for a fiber optic spectrometer, comprising:

[0038] The fiber optic spectrometer to be calibrated measures at least two groups of standard samples to obtain the reflected light intensity-pixel number sequence, and calculates the measured normalized reflected light intensity-pixel sequence ratio of any two standard samples. The influence of the incident light intensity can be eliminated by measuring the normalized reflected light intensity-pixel sequence ratio of any two standard samples.

[0039] The theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated, and the ratio of the theoretical normalized reflected light intensity-wavelength sequence of any two standard samples is calculated.

[0040] The corresponding relationship between the pixel number and the wavelength of the fiber optic spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio.

[0041] The reflected light intensity-pixel number sequence represents the corresponding relationship between the reflected light intensity and the pixel number, and is expressed as a discrete sequence.

[0042] Among them, see Figure 1 , measuring at least two groups of standard samples by the optical fiber spectrometer to be calibrated includes: connecting the light source 2 and the optical fiber spectrometer to be calibrated 3 by Y-type optical fiber 1 to measure the standard sample 4. The present invention connects the light source and the optical fiber spectrometer to be calibrated by Y-type optical fiber to measure the standard sample, which is only a simple way to measure and obtain the pixel number-reflection light intensity sequence. The method of measuring the standard sample by building a reflected light intensity measurement optical path is also applicable to this method.

[0043] Among them, the theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated by Fresnel formula I:

[0044] (I)

[0045] Where λ is the wavelength, d is the film thickness, and n(λ) represents the refractive index of the film. R 01 The intensity of light reflected partially at the film interface is R 12 The intensity of the light reflected again by the substrate is the intensity of the transmitted light. According to the Fresnel formula, the incident light enters the film from the air and is partially reflected at the film interface. R 01 And partial transmission, the transmitted light is reflected again on the substrate R 12 The light reflected by the film and the substrate is the normalized reflected light intensity. R cal .

[0046] Among them, the corresponding relationship between the pixel number and the wavelength is shown in formula II:

[0047] (Ⅱ)

[0048] Among them, i=1,2,3,…,K is the pixel number; m represents the order of the polynomial, usually 3 to 7; C0,C1,C2,…C m Represents the coefficients of the polynomial.

[0049] The corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio, including: using a nonlinear regression algorithm based on the measured normalized reflected light intensity-pixel sequence ratio (converted into the reflected light intensity-wavelength sequence ratio through formula II) and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio, iteratively obtaining the corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated.

[0050] Example 2

[0051] Embodiment 2 provides a wavelength calibration method for a fiber optic spectrometer, the method comprising the following steps:

[0052] See also Figure 1 , the two forked optical fibers of the Y-type optical fiber 1 are connected to the light source 2 and the optical fiber spectrometer 3 to be tested, and the standard sample 4 is measured by the other end of the optical fiber. The reflected light intensity-pixel number sequence of the standard sample 4 can be measured by the optical fiber spectrometer 3 to be tested:

[0053] (1)

[0054] Where 1, 2, 3, ..., k are the pixel numbers of the fiber optic spectrometer.

[0055] Fiber optic spectrometers use grating splitting, and the relationship between wavelength and pixel position can usually be expressed by a polynomial:

[0056] (2)

[0057] in i =1,2,3,…,k is the pixel number, m Indicates the order of the polynomial, usually 3 to 7, C 0, C 1, C 2,… C m Represents the coefficient of the polynomial. Then, the wavelength corresponding to the pixel number can be calculated by equation (2), and the measured reflected light intensity-pixel number sequence of the standard sample 4 can be obtained by substituting it into equation (1):

[0058] (3)

[0059] In the present invention, the measured reflected light intensity of the standard sample 4 will change with the change of the incident light intensity, and its normalized measured reflected light intensity-wavelength sequence R mear It can be expressed as:

[0060] (4)

[0061] in, I 0 is the incident light intensity. Therefore, the normalized measured reflected light intensity-wavelength series is calculated by calculating the ratio of the two standard sample measurements , which can eliminate the incident light intensity I 0 Impact:

[0062] (5)

[0063] For standard sample 4, according to the Fresnel reflection law, the incident light enters the film from the air and is partially reflected at the film interface. R 01 And partial transmission, the transmitted light is reflected again on the substrate R 12 The light reflected by the film and substrate is the theoretical normalized reflected light intensity-wavelength sequence. R cal :

[0064] (6)

[0065] in, λ is the wavelength, d is the film thickness, n ( λ ) represents the refractive index of the film.

[0066] The theoretical normalized reflected light intensity-wavelength sequence of standard samples A and B can be calculated by formula (6): R cal A ( λ )and R cal B ( λ ), and nonlinear regression was used to compare and , the polynomial coefficients in formula (2) can be calculated C 0, C 1, C 2,… C m Specifically, a nonlinear regression method was used to compare and The method steps are as follows Figure 3 and 4As shown:

[0067] 1) Taking the design wavelength of the fiber spectrometer to be calibrated as the initial value, the initial polynomial coefficients can be calculated by combining equation (2) with the undetermined coefficient method: .

[0068] 2) Substituting the initial polynomial coefficients into formulas (2) and (5), we can obtain the measured normalized reflected light intensity-wavelength sequence ratio: .

[0069] 3) Comparison measurement of normalized reflected light intensity-wavelength sequence ratio Ratio of the theoretical normalized reflected light intensity-wavelength series , the polynomial coefficients are iteratively solved by nonlinear regression algorithm C 0, C 1, C 2,… C m ; When measuring the normalized reflected light intensity-wavelength series ratio Ratio of the theoretical normalized reflected light intensity-wavelength series When the difference is the smallest, it is the final polynomial coefficient corresponding to the calibration of the fiber optic spectrometer. C 0, C 1, C 2,… C m .

[0070] The present invention is not limited to the above-mentioned specific implementation modes. A person skilled in the art can implement the present invention in various other specific implementation modes based on the contents disclosed in the present invention. Therefore, any design that adopts the design structure and concept of the present invention and makes some simple changes or modifications shall fall within the scope of protection of the present invention.

Claims

1. A wavelength calibration method for a fiber optic spectrometer, characterized in that: include: At least two groups of standard samples are measured by the optical fiber spectrometer to be calibrated to obtain a reflected light intensity-pixel number sequence, and a measured normalized reflected light intensity-pixel sequence ratio of any two standard samples is calculated; The theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated, and the ratio of the theoretical normalized reflected light intensity-wavelength sequence of any two standard samples is calculated; The corresponding relationship between the pixel number and the wavelength of the fiber optic spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio.

2. The wavelength calibration method of the optical fiber spectrometer according to claim 1, characterized in that: The measuring of at least two groups of standard samples by the optical fiber spectrometer to be calibrated comprises: connecting a light source and the optical fiber spectrometer to be calibrated respectively by Y-type optical fibers to measure the standard samples.

3. The wavelength calibration method of the optical fiber spectrometer according to claim 1, characterized in that: The theoretical normalized reflected light intensity-wavelength sequence of the standard sample is calculated by Fresnel formula I: (I) Where λ is the wavelength, d is the film thickness, and n(λ) represents the refractive index of the film. The intensity of light reflected partially at the film interface is The intensity of the light reflected again by the substrate is is the normalized reflected light intensity.

4. The wavelength calibration method of the optical fiber spectrometer according to claim 3, characterized in that: The corresponding relationship between the pixel number and the wavelength is shown in Formula II: (Ⅱ) Among them, i=1,2,3,…,k is the pixel number, m represents the order of the polynomial, C0,C1,C2,…C m Represents the coefficients of the polynomial.

5. The wavelength calibration method of the optical fiber spectrometer according to claim 1, characterized in that: The corresponding relationship between the pixel number and the wavelength of the optical fiber spectrometer to be calibrated is calculated based on the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio, including: According to the measured normalized reflected light intensity-pixel sequence ratio and the corresponding theoretical normalized reflected light intensity-wavelength sequence ratio, a nonlinear regression algorithm is used to iteratively obtain the corresponding relationship between the pixel number and the wavelength of the fiber optic spectrometer to be calibrated.

6. The wavelength calibration method of the optical fiber spectrometer according to claim 4, characterized in that: The method comprises: S101: The fiber optic spectrometer to be calibrated measures standard samples A and B respectively to obtain a reflected light intensity-pixel number sequence and , calculate the measured normalized reflected light intensity-pixel sequence ratio of standard samples A and B / ; in, , 1,2,3,…,k are the pixel numbers of the fiber optic spectrometer, Represents the reflected light intensity-pixel number sequence; calculate the wavelength corresponding to the pixel number through formula II and substitute it into That is, the measured reflected light intensity-pixel number sequence of the standard sample can be expressed as: ； S102: Obtain the measured normalized reflected light intensity-wavelength sequence ratio from formula II and formula III ; (Ⅲ) S103: Calculate the theoretical normalized reflected light intensity-wavelength sequence of standard samples A and B according to formula I and , get the theoretical normalized reflected light intensity-wavelength sequence ratio / ; S104: Comparison by nonlinear regression method and , the corresponding relationship between the pixel number and wavelength of the fiber optic spectrometer to be calibrated is calculated.

7. The wavelength calibration method of the optical fiber spectrometer according to claim 6, characterized in that: Step S104 specifically includes: S401: Taking the design wavelength of the fiber spectrometer to be calibrated as the initial value, the coefficients of the initial polynomial are calculated by formula II ; S402: Substitute the coefficients of the initial polynomial into equations II and III to calculate the measured normalized reflected light intensity-wavelength sequence ratio ; S403: Comparison and , the polynomial coefficients are iteratively solved by nonlinear regression algorithm C 0, C 1, C 2,… C m ;when and When the difference is the smallest, it is the final polynomial coefficient corresponding to the calibration of the fiber optic spectrometer to be calibrated. C 0, C 1, C 2,… C m .

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