Calibration System and Method for Relative Spectral Responsivity of Optical Power Meters

Abstract

This invention relates to the field of optical technology, and discloses a calibration system and method for the relative spectral responsivity of an optical power meter to improve calibration efficiency and accuracy. The system includes: a GranTaylor prism and a Wollaston prism arranged adjacent to each other; a set of concave mirrors with increasing curvature positioned between the GranTaylor prism and the monochromator light source; and, following the Wollaston prism, a third concave mirror and a first y-cylindrical mirror for projecting a first beam of light onto a first detector, and a fourth concave mirror and a second y-cylindrical mirror for projecting a second beam of light onto a second detector; wherein the GranTaylor prism is used to adjust the outgoing light into linearly polarized light with an angle of 45° to the vertical direction, and the y-direction of the reflecting cylinder of the cylindrical mirror is the vertical direction, while the plane on which the breadboard used to deploy the calibration system components is located is a horizontal plane.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to a calibration system and method for the relative spectral responsivity of an optical power meter. Background Technology

[0002] An optical power meter is a sensor that uses materials with effects to convert optical radiation signals into electrical signals. The response of an optical power meter is limited to a certain spectral range and has strong spectral selectivity. Therefore, it is necessary to measure the spectral responsivity of the optical power meter.

[0003] The principle block diagram of relative spectral responsivity calibration is as follows: Figure 1 As shown, light emitted from a stably powered light source enters the monochromator's entrance slit via the front optical system (typically composed of a converging lens or concave / plane mirrors). The monochromatic light exiting the monochromator's exit slit passes through the rear optical system and a beam splitter before entering the standard detector and the detector under test, respectively. A typical calibration setup is arranged as follows: Figure 2 As shown.

[0004] The monochromator's wavelength drum is tuned to around 550 nm, and the light is incident on the deflecting mirror after passing through a second-order spectral filter. The standard detector and the detector under test are placed at opposite ends of the output beam. The mirror is rotated so that the monochromatic light spot output by the monochromator is projected onto the centers of the standard detector and the detector under test, respectively. Using the standard detector as a reference, a calibration program is preset according to the required spectral range and wavelength interval, and wavelength calibration is completed. After normalization, the relative spectral responsivity value of the optical power meter under test can be obtained.

[0005] However, Figure 2 The limitations of the spectral calibration device shown are very obvious. When using the point-by-point comparison method to compare the standard detector and the detector under test at certain wavelength intervals from the starting wavelength to the ending wavelength, the deflecting mirror controlled by the motor projects the light spot onto the two detectors in sequence through mechanical movement, resulting in poor testing efficiency.

[0006] As a variation, if the substitution method is used to test the wavelength response of the standard detector and the detector under test under the same conditions, the light source and environment must have extremely high stability to ensure that the test conditions are strictly the same. Summary of the Invention

[0007] The purpose of this invention is to disclose a calibration system and method for the relative spectral responsivity of an optical power meter, so as to improve the efficiency and accuracy of calibration.

[0008] To achieve the above objectives, the present invention discloses a calibration system for the relative spectral responsivity of an optical power meter, comprising:

[0009] Adjacent GranTylene and Wollaston prisms;

[0010] A set of concave mirrors with increasing curvature is provided between the GranTaylor prism and the monochromator light source to compress the light beam into the light aperture of the GranTaylor prism.

[0011] Following the Wollaston prism, a third concave mirror and a first y-cylindrical mirror are deployed for projecting a first beam of light onto a first detector, and a fourth concave mirror and a second y-cylindrical mirror are deployed for projecting a second beam of light onto a second detector; the first y-cylindrical mirror is located between the third concave mirror and the first detector, and the second y-cylindrical mirror is located between the fourth concave mirror and the second detector.

[0012] The GranTaylor prism is used to adjust the outgoing light into linearly polarized light with an angle of 45° to the vertical direction. The y-axis direction of the reflecting cylinders of the first and second y-cylindrical mirrors is the vertical direction. The plane on which the breadboard used to deploy the devices of the calibration system is located is a horizontal plane.

[0013] Preferably, the set of concave mirrors for constricting the light beam to the light aperture of the GlanTell prism includes a first concave mirror and a second concave mirror arranged at intervals, wherein the curvature of the first concave mirror is less than the curvature of the second concave mirror.

[0014] To achieve the above objectives, the present invention also discloses a method for calibrating the relative spectral responsivity of an optical power meter, comprising the following steps:

[0015] Step S1: Deploy the calibration system for the relative spectral responsivity of the optical power meter as described in claim 1 or 2 and complete the optical path debugging;

[0016] Step S2: Select standard detectors for both the first and second detectors, and calibrate the splitting ratios of the two standard detectors at each wavelength.

[0017] Step S3: Replace the second detector with the detector under test, and during the calibration process of the second detector, calculate the actual optical power of the beam detected by the detector under test based on the optical power detected by the standard detector and the calibrated splitting ratio of the corresponding wavelength.

[0018] Step S4: Calculate the absolute spectral responsivity curve and relative spectral responsivity curve of the detector under test based on the actual optical power of the beam detected by the detector under test.

[0019] Preferably, the specific calculation formula for step S3 is as follows:

[0020] R 350-1100 =P S(350-1100) / P T(350-1100) ;

[0021] Among them, P S(350-1100) P represents the power value of a standard detector. T(350-1100) R is the power value of the detector under test acquired using a standard detector. 350-1100 The splitting ratio is given; the actual power value of the detector under test is 1 / R of the measured value of the standard detector. 350-1100 That is: P RT(350-1100) =P S(350-1100) / R 350-1100 ;

[0022] In step S4, the power response value P of the detector under test is acquired under different wavelengths of light illumination. (350-1100) Then calculate the absolute spectral responsivity K of the detector under test. (350-1100) The calculation formula is as follows:

[0023] K (350-1100) =P RT(350-1100) / P (350-1100) ;

[0024] The relative spectral response coefficient is obtained by normalizing the absolute spectral response.

[0025] This invention enables synchronous detection by a standard detector and the detector under test, uses two standard optical power meters to calibrate the system's beam splitting ratio point by point, and then calculates the relative spectral response of the optical power meter under test based on the calibrated beam splitting ratio; it has at least the following beneficial effects:

[0026] 1. By using a GranTaylor prism and a Wollaston prism, light in the wavelength range of 300-2300nm can be split, and the spectral response of a standard power meter and the power meter under test can be measured simultaneously; thus, efficient spectral splitting across a wide spectrum can be achieved.

[0027] Common passive beam splitting methods include beam splitters or bifurcated fiber beam splitting. For beam splitters, their operating wavelength is limited by the coating process, preventing application in the high spectral range. Light exceeding the allowable operating wavelength range of the beam splitter or antireflection coating will produce artifacts or interference fringes, affecting the final spectral calibration results. Bifurcated fiber beam splitting can use a Y-shaped fiber bundle split into two, significantly reducing system complexity. However, two points need consideration: first, the coupling efficiency between the fiber and the monochromator slit; traditional circular fiber bundles do not match the height of the monochromator output slit, leaving significant room for improvement in the height direction; second, the matching degree between the monochromator light source divergence and the numerical aperture of the fiber bundle. Due to the inconsistent divergence angles of the monochromator in the vertical and horizontal directions, there will be significant energy loss. Therefore, compared to common beam splitting methods, this invention, in the specific scenario of detector calibration, achieves superior beam splitting performance based on a combination of Glan Taylor and Wollaston prisms.

[0028] 2. The combination of concave and cylindrical mirrors maximizes the utilization of monochromatic light sources. At any wavelength, the detector position has a light intensity of more than microwatts, and the beam size can be constrained to 3-5mm at the power detector. It is suitable for most optical power detectors (detection target surface 5-10mm), and the light energy utilization rate is relatively high.

[0029] 3. Unlike the limitations of linear polarizers and polarizing beam splitters in the working spectrum, the passive polarizing beam splitter module composed of a GranTylene prism and a Wollaston prism transmits the light source to the standard detector and the detector under test respectively. While ensuring high calibration efficiency, the wide spectral range applicability and high extinction ratio ensure the reliability of calibration data.

[0030] 4. Based on this invention, under the premise of ensuring measurement at the same location, sampling was performed nanometer by nanometer from 350nm to 1100nm. The repeatability comparison results of two independent samplings showed that the repeatability difference of most sampling points was less than 1% and all were less than 1.5%, which proved the stability of the system.

[0031] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0032] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a block diagram illustrating the principle of relative spectral responsivity measurement disclosed in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the optical path of a typical relative spectral response calibration device disclosed in an embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of the optical path based on the x-direction of the calibration system for the relative spectral responsivity of the optical power meter disclosed in an embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the optical path based on the y-direction of the calibration system for the relative spectral responsivity of the optical power meter disclosed in an embodiment of the present invention.

[0037] Figure 5 This is a graph showing the result of the spectral ratio obtained by sampling nanometer by nanometer from 350nm to 1100nm, as disclosed in the embodiments of the present invention.

[0038] Figure 6 This is based on the embodiments of the present invention. Figure 5 The diagram shows the relative spectral response curve of the detector under test obtained by the shown spectrophotometric ratio. Detailed Implementation

[0039] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0040] Example 1

[0041] This embodiment discloses a calibration system for the relative spectral responsivity of an optical power meter, such as... Figure 3 and Figure 4 As shown, its calibration principle is detailed below:

[0042] Figure 3 and Figure 4 The x- and y-directions of the light are shown respectively. The monochromator is turned on and the wavelength is adjusted to 532nm as a reference light source for adjusting the light path. First, the beam diameter is reduced based on the two concave mirrors 1 and 2, so that all the light emitted from the monochromator can enter the Glan Taylor prism. The two concave mirrors need to have sufficiently large target surfaces to receive more than 90% of the light from the monochromator light source. Preferably, the focal length of concave mirror 1 is 500mm to converge the beam to concave mirror 2 at a relatively slow speed, and the focal length of concave mirror 2 is 50m to rapidly reduce the light speed to the size of the prism's aperture.

[0043] The Glan-Taylor prism is a polarizing prism. It adjusts the outgoing light to linearly polarized light at a 45° angle to the vertical direction, ensuring that the two polarized beams after polarization splitting have similar amplitudes, which is beneficial for beam splitting detection. The linearly polarized light is split into two orthogonally polarized linearly polarized beams by the Wollaston prism, which are projected onto concave mirrors 3 and 4, respectively. These beams are then simultaneously projected onto two detectors by cylindrical mirrors with a focal length of 50mm. The cylindrical lens focuses the vertical light rays, limiting the vertical divergence angle to be almost identical to the horizontal angle.

[0044] Alternatively, the surface detector can use a magnetic chuck to ensure that the measurement positions are highly aligned.

[0045] Based on the above optical path system, only two standard detectors are needed to calibrate the split ratio across the entire spectrum in the early stage, which can then be used to calibrate the relative spectral responsivity stably over a long period of time.

[0046] In summary, the core components of the system in this embodiment include: a GranTaylor prism and a Wollaston prism arranged adjacent to each other. A set of concave mirrors with increasing curvature (equivalent to...) are provided between the GranTaylor prism and the monochromator light source. Figure 3 and Figure 4 The combination of concave mirror 1 and concave mirror 2 (which will not be described in detail later) is used to compress the light beam into the aperture of the Glan Taylor prism. Following the Wollaston prism, a third concave mirror (equivalent to...) is deployed to project the first beam onto the first detector. Figure 3 and Figure 4 The concave mirror 3 (not described in detail later) and the first cylindrical mirror (equivalent to) Figure 3 and Figure 4 The y-cylindrical reflector 1 (which will not be described in detail later), and the fourth concave mirror and the second y-cylindrical reflector (equivalent to) used to project the second beam of light onto the second detector. Figure 3 and Figure 4 The first y-cylindrical mirror is located between the third concave mirror and the first detector, and the second y-cylindrical mirror is located between the fourth concave mirror and the second detector. The Glan Taylor prism is used to adjust the outgoing light into linearly polarized light at an angle of 45° to the vertical direction. The y-axis direction of the reflecting surfaces of the first and second y-cylindrical mirrors is the vertical direction. The plane on which the breadboard used to deploy the calibration system components is located is a horizontal plane.

[0047] Example 2

[0048] Corresponding to the above embodiments, this embodiment discloses a method for calibrating the relative spectral responsivity of an optical power meter, including the following steps:

[0049] Step S1: Deploy the calibration system for the relative spectral responsivity of the optical power meter as described in Example 1 and complete the optical path debugging.

[0050] Step S2: Select standard detectors for both the first and second detectors, and calibrate the splitting ratios of the two standard detectors at each wavelength.

[0051] It is worth noting that the wavelength used for optical path adjustment can be 532nm, corresponding to the aforementioned reference light source. However, during the actual calibration process, the beam splitting ratio of each wavelength in the 300-2300nm range needs to be calibrated individually according to the minimum wavelength adjustment unit of the monochromator to improve accuracy. For example... Figure 5 The diagram shows the spectrophotometric ratio (i.e., the ratio of the power measured by the two standard detectors) obtained after sampling nanometer by nanometer from 350nm to 1100nm. Wherein, if Figure 3 and Figure 4 If the layout of the optical components in the system shown has changed, recalibration is required.

[0052] Step S3: Replace the second detector with the detector under test, and during the calibration process of the second detector, calculate the actual optical power of the beam detected by the detector under test based on the optical power detected by the standard detector and the calibrated splitting ratio of the corresponding wavelength.

[0053] Step S4: Calculate the absolute spectral responsivity curve and relative spectral responsivity curve of the detector under test based on the actual optical power of the beam detected by the detector under test.

[0054] The principles behind the above two steps are summarized as follows:

[0055] exist Figure 5 In the diagram, the horizontal axis represents the wavelength value; the vertical axis represents the power ratio, i.e., the system's splitting ratio R. 350-1100 The calculation formula is as follows:

[0056] R 350-1100 =P S(350-1100) / P T(350-1100) ;

[0057] Among them, P S(350-1100) P represents the power value of a standard detector. T(350-1100) The power value of the detector under test is obtained using a standard detector. Therefore, when performing spectral response calibration, the actual power value of the detector under test is 1 / R of the measured value from the standard detector. 350-1100 That is: P RT(350-1100) =P S(350-1100) / R 350-1100 .

[0058] Therefore, if the absolute power values ​​P of light at different wavelengths are known... RT(350-1100) The power response values ​​P of the detector under test were collected under different wavelengths of light illumination. (350-1100) The absolute spectral responsivity K of the detector under test can then be calculated. (350-1100) The calculation formula is as follows:

[0059] K (350-1100) =P RT(350-1100) / P (350-1100) .

[0060] Furthermore, after normalizing the absolute spectral responsivity, the relative spectral responsivity coefficient is obtained, i.e., the response coefficient-wavelength curve. Further, if a 532nm light source is used as the normalization reference, the following is obtained: Figure 6 The relative spectral response curve of the detector under test is shown.

[0061] Optionally, the "detector" mentioned above in this embodiment includes, but is not limited to, photoelectric detectors such as optical power meters, spectrometers, and photocells.

[0062] In summary, the systems and methods disclosed in the embodiments of the present invention can achieve synchronous detection by the standard detector and the detector under test, calibrate the system's beam splitting ratio point by point using two standard optical power meters, and then calculate the relative spectral response of the optical power meter under test based on the calibrated beam splitting ratio; it has at least the following beneficial effects:

[0063] 1. By using a GranTaylor prism and a Wollaston prism, light in the wavelength range of 300-2300nm can be split, and the spectral response of a standard power meter and the power meter under test can be measured simultaneously; thus, efficient spectral splitting across a wide spectrum can be achieved.

[0064] Common passive beam splitting methods include beam splitters or bifurcated fiber beam splitting. For beam splitters, their operating wavelength is limited by the coating process, preventing application in the high spectral range. Light exceeding the allowable operating wavelength range of the beam splitter or antireflection coating will produce artifacts or interference fringes, affecting the final spectral calibration results. Bifurcated fiber beam splitting can use a Y-shaped fiber bundle split into two, significantly reducing system complexity. However, two points need consideration: first, the coupling efficiency between the fiber and the monochromator slit; traditional circular fiber bundles do not match the height of the monochromator output slit, leaving significant room for improvement in the height direction; second, the matching degree between the monochromator light source divergence and the numerical aperture of the fiber bundle. Due to the inconsistent divergence angles of the monochromator in the vertical and horizontal directions, there will be significant energy loss. Therefore, compared to common beam splitting methods, this invention, in the specific scenario of detector calibration, achieves superior beam splitting performance based on a combination of Glan Taylor and Wollaston prisms.

[0065] 2. The combination of concave and cylindrical mirrors maximizes the utilization of monochromatic light sources. At any wavelength, the detector position has a light intensity of more than microwatts, and the beam size can be constrained to 3-5mm at the power detector. It is suitable for most optical power detectors (detection target surface 5-10mm), and the light energy utilization rate is relatively high.

[0066] 3. Unlike the limitations of linear polarizers and polarizing beam splitters in the working spectrum, the passive polarizing beam splitter module composed of a GranTylene prism and a Wollaston prism transmits the light source to the standard detector and the detector under test respectively. While ensuring high calibration efficiency, the wide spectral range applicability and high extinction ratio ensure the reliability of calibration data.

[0067] 4. Based on this invention, under the premise of ensuring measurement at the same location, sampling was performed nanometer by nanometer from 350nm to 1100nm. The repeatability comparison results of two independent samplings showed that the repeatability difference of most sampling points was less than 1% and all were less than 1.5%, which proved the stability of the system.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A calibration system for the relative spectral responsivity of an optical power meter, characterized in that, include: Adjacent GranTylene and Wollaston prisms; A set of concave mirrors with increasing curvature is provided between the GranTaylor prism and the monochromator light source to compress the light beam into the light aperture of the GranTaylor prism. Following the Wollaston prism, a third concave mirror and a first y-cylindrical mirror are deployed for projecting a first beam of light onto a first detector, and a fourth concave mirror and a second y-cylindrical mirror are deployed for projecting a second beam of light onto a second detector; the first y-cylindrical mirror is located between the third concave mirror and the first detector, and the second y-cylindrical mirror is located between the fourth concave mirror and the second detector. The GranTaylor prism is used to adjust the outgoing light into linearly polarized light with an angle of 45° to the vertical direction. The y-axis direction of the reflecting cylinders of the first and second y-cylindrical mirrors is the vertical direction. The plane on which the breadboard used to deploy the devices of the calibration system is located is a horizontal plane.

2. The calibration system for the relative spectral responsivity of an optical power meter according to claim 1, characterized in that, A set of concave mirrors for constricting the light beam to the aperture of the GlanTell prism includes a first concave mirror and a second concave mirror arranged at intervals, wherein the curvature of the first concave mirror is less than the curvature of the second concave mirror.

3. A method for calibrating the relative spectral responsivity of an optical power meter, characterized in that, Includes the following steps: Step S1: Deploy the calibration system for the relative spectral responsivity of the optical power meter as described in claim 1 or 2 and complete the optical path debugging; Step S2: Select standard detectors for both the first and second detectors, and calibrate the splitting ratios of the two standard detectors at each wavelength. Step S3: Replace the second detector with the detector under test, and during the calibration process of the second detector, calculate the actual optical power of the beam detected by the detector under test based on the optical power detected by the standard detector and the calibrated splitting ratio of the corresponding wavelength. Step S4: Calculate the absolute spectral responsivity curve and relative spectral responsivity curve of the detector under test based on the actual optical power of the beam detected by the detector under test.

4. The method according to claim 3, characterized in that, The specific calculation formula for step S3 is as follows: R 350-1100 =P S(350-1100) / P T(350-1100) ; Among them, P S(350-1100) P represents the power value of a standard detector. T(350-1100) R is the power value of the detector under test acquired using a standard detector. 350-1100 The splitting ratio is given; the actual power value of the detector under test is 1 / R of the measured value of the standard detector. 350-1100 That is: P RT(350-1100) =P S(350-1100) / R 350-1100 ; In step S4, the power response value P of the detector under test is acquired under different wavelengths of light illumination. (350-1100) Then calculate the absolute spectral responsivity K of the detector under test. (350-1100) The calculation formula is as follows: K (350-1100) =P RT(350-1100) / P (350-1100) ; The relative spectral response coefficient is obtained by normalizing the absolute spectral response.

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