Calibration system and method for relative spectral responsivity of optical power meter

Abstract

The invention relates to the technical field of optics, and discloses a calibration system and method for the relative spectral responsivity of an optical power meter, so as to improve the calibration efficiency and precision. The system comprises a Glan-Taylor prism and a Wollaston prism which are arranged adjacently; a group of concave mirrors with gradually increased curvatures are arranged between the Glan-Taylor prism and the monochromator light source; after the Wollaston prism, a third concave mirror and a first y cylindrical reflector which are used for projecting the first beam splitting light to the first detector, and a fourth concave mirror and a second y cylindrical reflector which are used for projecting the second beam splitting light to the second detector are arranged. Wherein the Glan-Taylor prism is used for adjusting emergent light into linearly polarized light forming an included angle of 45 degrees with the vertical direction, the y direction where the reflection cylindrical surface of the cylindrical surface reflector is located is the vertical direction, and the plane where the bread board used for deploying the device for the calibration system is located is the horizontal plane.

Description

Technical Field

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

[0002] An optical power meter is a sensor made of effective materials that converts optical radiation signals into electrical signals. The response of an optical power meter can only be within a certain spectral region and has strong spectral selectivity. Therefore, it is necessary to measure the spectral responsivity of the optical power meter.

[0003] The block diagram of the relative spectral responsivity calibration principle is as follows: Figure 1 As shown in the figure, the light emitted by the stable power supply light source passes through the front optical system (generally composed of a converging lens or a concave or flat reflector) and enters the incident slit of the monochromator. The monochromatic light output from the monochromator exit slit passes through the rear optical system and beam splitter and enters the standard detector and the detector under test respectively. The specific layout of a typical calibration device is as follows: Figure 2 shown.

[0004] Adjust the wavelength drum of the monochromator to around 550nm, and after passing through the secondary spectral filter, it is incident on the deflection reflector. The standard detector and the detector to be measured are placed at both ends of the outgoing beam, and the reflector is rotated to project the monochromatic light spot output by the monochromator to the center of the standard detector and the detector to be measured. With the standard detector as a reference, the calibration procedure is preset according to the spectral range and wavelength interval to be calibrated, and the wavelength calibration is completed. After normalization, the relative spectral responsivity value of the optical power meter to be measured can be obtained.

[0005] However, Figure 2 The limitations of the spectral calibration device shown are very obvious. When the standard detector and the detector under test are compared point by point at a certain wavelength interval from the starting wavelength to the ending wavelength using the point-by-point comparison method, the motor-controlled deflection mirror projects the light spot onto the two detectors in turn through mechanical movement, resulting in poor test 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 the environment are required to have extremely high stability to ensure that the test conditions are strictly the same. Summary of the invention

[0007] The present invention aims 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 the calibration.

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

[0009] Glan-Taylor prism and Wollaston prism set adjacent to each other;

[0010] A group of concave mirrors with increasing curvatures are provided between the Glan-Taylor prism and the monochromator light source to shrink the light beam to the light aperture of the Glan-Taylor prism;

[0011] A third concave mirror and a first y-cylindrical reflector are arranged behind the Wollaston prism for projecting the first split beam of light onto the first detector, and a fourth concave mirror and a second y-cylindrical reflector are arranged for projecting the second split beam of light onto the second detector; the first y-cylindrical reflector is located between the third concave mirror and the first detector, and the second y-cylindrical reflector is located between the fourth concave mirror and the second detector;

[0012] Among them, the Glan Taylor prism is used to adjust the outgoing light into linear polarized light with an angle of 45° with the vertical direction, the y-axis direction of the reflecting cylindrical surfaces of the first y-cylindrical reflector and the second y-cylindrical reflector is the vertical direction; and the plane where the breadboard for deploying the devices for the calibration system is located is a horizontal plane.

[0013] Preferably, a group of concave mirrors for shrinking the light beam to the light hole of the Glan-Taylor prism includes a first concave mirror and a second concave mirror arranged at an interval, and the curvature of the first concave mirror is smaller than the curvature of the second concave mirror.

[0014] To achieve the above object, 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, deploying the calibration system of the relative spectral responsivity of the optical power meter as claimed in claim 1 or 2 and completing the optical path debugging;

[0016] Step S2, using standard detectors for both the first detector and the second detector, and calibrating the splitting ratios of the two standard detectors corresponding to each wavelength;

[0017] Step S3, replacing the second detector with the detector under test, and during the calibration process of the second detector, calculating the actual optical power of the light beam detected by the detector under test according to 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 the relative spectral responsivity curve of the detector under test according to the actual optical power of the light beam detected by the detector under test.

[0019] Preferably, the specific calculation formula of step S3 is:

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

[0021] Among them, P S(350-1100) is the power value of the standard detector, P T(350-1100) is the power value of the detector under test collected by the standard detector, R 350-1100 is the splitting ratio; the actual power value of the measured detector 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 under different wavelengths of light is collected. (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] Among them, the relative spectral responsivity coefficient is obtained after the absolute spectral responsivity is normalized.

[0025] The present invention can realize synchronous detection of a standard detector and a detector to be measured, use two standard optical power meters to calibrate the system splitting ratio point by point, and then calculate the relative spectral response of the optical power meter to be measured according to the calibrated splitting ratio; it has at least the following beneficial effects:

[0026] 1. Through Glan Taylor prism and Wollaston prism, it can split the light with wavelength of 300-2300nm, and synchronously measure the spectral response of the standard power meter and the power meter to be tested; it can achieve efficient splitting of a wide spectrum.

[0027] Common passive beam splitting methods include beam splitting or bifurcated fiber optic splitting. For beam splitters, their operating wavelength is limited by the coating process and cannot be applied to high spectral bands. Light beyond the allowable range of the working band of the beam splitter or anti-reflection film will produce artifacts or interference fringes, affecting the final result of spectral calibration. The splitting scheme of bifurcated fiber can use a y-type fiber bundle divided into two, which can reduce the complexity of the system to a great extent, but two points need to be considered. One is the coupling efficiency between the optical fiber and the monochromator slit. The traditional circular fiber bundle does not match the height of the monochromator output slit, and there is a very large room for improvement in the utilization rate in the height direction. The second is the divergence of the monochromator light source and the matching degree of the numerical aperture of the fiber bundle. Since the vertical and horizontal divergence angles of the monochromator are inconsistent, there will be a large energy loss. Thus, compared with common beam splitting, the present invention is based on the combination of Glan Taylor prism and Wollaston prism in the specific scenario of detector calibration, and the sorting performance that can be achieved is better.

[0028] 2. Use a concave reflector and a cylindrical reflector to maximize the utilization of the monochromatic light source. 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. Different from the limitations of linear polarizers and polarization beam splitters in the working spectrum, the passive polarization splitting module composed of Glan-Taylor prism and Wollaston prism transmits the light source to the standard detector and the detector under test respectively. While ensuring high calibration efficiency, the wide spectrum applicability and high extinction ratio ensure the reliability of the calibration data.

[0030] 4. Based on the present invention, under the premise of ensuring the same-position measurement, sampling is performed nanometer by nanometer from 350nm to 1100nm. The repeatability comparison results of two independent samplings show that the repeatability difference of most sampling points is less than 1% and all are less than 1.5%, which proves the stability of the system.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

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

[0034] Figure 2 It 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 It is a schematic diagram of the optical path based on the x-direction of the calibration system of the relative spectral responsivity of the optical power meter disclosed in the embodiment of the present invention.

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

[0037] Figure 5 This is a result diagram of the splitting ratio obtained by sampling nanometer by nanometer from 350nm to 1100nm disclosed in an embodiment of the present invention.

[0038] Figure 6 The embodiment of the present invention discloses Figure 5 Schematic diagram of the relative spectral responsivity curve of the detector under test obtained by the splitting ratio shown. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are 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. Figure 3 and Figure 4 The calibration principle is described in detail as follows:

[0042] Figure 3 and Figure 4 The directions of the light paths in the x and y directions are respectively indicated. Turn on the monochromator and adjust the wavelength to 532nm as a reference light source for adjusting the light path. First, based on the two concave reflectors, concave mirror 1 and concave mirror 2, the diameter of the light beam is reduced so that all the light sources emitted by the monochromator can enter the Glan Taylor prism. The two concave reflectors need a large enough target surface 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 light beam to concave mirror 2 at a slower speed. The focal length of concave mirror 2 is 50m, which quickly shrinks the speed of light to the size of the prism aperture.

[0043] Glan Taylor prism is a polarizing prism. Glan Taylor prism adjusts the outgoing light into linear polarized light with an angle of 45° with the vertical direction to ensure that the amplitudes of the two polarized light beams after polarization beam splitting are similar, which is conducive to spectroscopic detection. The linear polarized light is divided into two orthogonal linear polarized light beams after passing through Wollaston prism, which are projected on concave mirror 3 and concave mirror 4 respectively; and then projected to two detectors at the same time through a cylindrical reflector with a focal length of 50mm. Among them, the cylindrical lens focuses the light in the vertical direction and limits the divergence angle of the light in the vertical direction to make it almost consistent with the horizontal direction.

[0044] Optionally, the detection surface detector can use a magnetic attraction plate to ensure a high degree of coincidence of the measurement positions.

[0045] Based on the above optical path system, it is only necessary to use two standard detectors to calibrate the splitting ratio of the entire spectrum in advance, so that the relative spectral response can be calibrated stably over a long period of time.

[0046] In summary, the core components of the system of this embodiment include: adjacently arranged Glan Taylor prisms and Wollaston prisms. A group of concave mirrors with increasing curvature (equivalent to Figure 3 and Figure 4 After the Wollaston prism, a third concave mirror (equivalent to Figure 3 and Figure 4 The concave mirror 3 in (not described in detail later) and the first y cylindrical reflector (equivalent to Figure 3 and Figure 4 y cylindrical reflector 1 in the figure, which will not be described in detail later), and a fourth concave mirror and a second y cylindrical reflector (equivalent to Figure 3 and Figure 4 The first y cylindrical reflector is located between the third concave mirror and the first detector, and the second y cylindrical reflector is located between the fourth concave mirror and the second detector. The Glan Taylor prism is used to adjust the emitted light to linear polarized light with an angle of 45° with the vertical direction, and the y-axis direction of the reflection cylinders of the first y cylindrical reflector and the second y cylindrical reflector is the vertical direction; the plane where the breadboard for deploying the components of the calibration system is located is the horizontal plane.

[0047] Example 2

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

[0049] Step S1, deploying the calibration system of the relative spectral responsivity of the optical power meter as described in Example 1 and completing the optical path debugging.

[0050] Step S2: select standard detectors for both the first detector and the second detector, and calibrate the splitting ratios of the two standard detectors corresponding to each wavelength.

[0051] It is worth noting that the wavelength used for optical path debugging can be 532nm corresponding to the above-mentioned reference light source. However, in the specific calibration process, it is necessary to calibrate the beam splitting ratio of each wavelength in the range of 300-2300nm one by one according to the minimum wavelength adjustment unit of the monochromator to improve the precision. Figure 5 As shown in the figure, the splitting ratio (i.e. the ratio of the power measured by two standard detectors) obtained after sampling from 350nm to 1100nm by nanometer is shown. Figure 3 and Figure 4 If the layout of the optical components in the system shown is changed, recalibration is required.

[0052] Step S3, replacing the second detector with the detector under test, and during the calibration process of the second detector, calculating the actual optical power of the light beam detected by the detector under test according to 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 the relative spectral responsivity curve of the detector under test according to the actual optical power of the light beam detected by the detector under test.

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

[0055] exist Figure 5 In the figure, the horizontal axis is the wavelength value; the vertical axis is the power ratio, that is, the system splitting ratio R 350-1100 , and its calculation formula is as follows:

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

[0057] Among them, P S(350-1100) is the power value of the standard detector, P T(350-1100) R is the power value of the detector under test collected by the standard detector. Therefore, when spectral response calibration is performed, the actual power value of the detector under test is 1 / R of the value measured by the standard detector. 350-1100 , that is: P RT(350-1100) =P S(350-1100) / R 350-1100 .

[0058] Thus, if the absolute power value P of light of different wavelengths is known RT(350-1100) , collect the power response value P of the detector under test under different wavelengths of light (350-1100) The absolute spectral responsivity K of the detector under test can be calculated (350-1100) The calculation formula is as follows:

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

[0060] Furthermore, the absolute spectral responsivity is normalized to obtain the relative spectral responsivity coefficient, that is, the response coefficient-wavelength curve. Further, if the 532nm light source is used as the normalization reference, Figure 6 The relative spectral responsivity curve of the tested detector is shown.

[0061] Optionally, the above-mentioned “detector” in this embodiment includes but is not limited to photoelectric detectors such as an optical power meter, a spectrometer, and a photoelectric amplification tube.

[0062] In summary, the system and method respectively disclosed in the embodiments of the present invention can realize synchronous detection of the standard detector and the detector to be measured, use two standard optical power meters to calibrate the system splitting ratio point by point, and then calculate the relative spectral response of the optical power meter to be measured according to the calibrated splitting ratio; it has at least the following beneficial effects:

[0063] 1. Through Glan Taylor prism and Wollaston prism, it can split the light with wavelength of 300-2300nm, and synchronously measure the spectral response of the standard power meter and the power meter to be tested; it can achieve efficient splitting of a wide spectrum.

[0064] Common passive beam splitting methods include beam splitting or bifurcated fiber optic splitting. For beam splitters, their operating wavelength is limited by the coating process and cannot be applied to high spectral bands. Light beyond the allowable range of the working band of the beam splitter or anti-reflection film will produce artifacts or interference fringes, affecting the final result of spectral calibration. The splitting scheme of bifurcated fiber can use a y-type fiber bundle divided into two, which can reduce the complexity of the system to a great extent, but two points need to be considered. One is the coupling efficiency between the optical fiber and the monochromator slit. The traditional circular fiber bundle does not match the height of the monochromator output slit, and there is a very large room for improvement in the utilization rate in the height direction. The second is the divergence of the monochromator light source and the matching degree of the numerical aperture of the fiber bundle. Since the vertical and horizontal divergence angles of the monochromator are inconsistent, there will be a large energy loss. Thus, compared with common beam splitting, the present invention is based on the combination of Glan Taylor prism and Wollaston prism in the specific scenario of detector calibration, and the sorting performance that can be achieved is better.

[0065] 2. Use a concave reflector and a cylindrical reflector to maximize the utilization of the monochromatic light source. 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. Different from the limitations of linear polarizers and polarization beam splitters in the working spectrum, the passive polarization splitting module composed of Glan-Taylor prism and Wollaston prism transmits the light source to the standard detector and the detector under test respectively. While ensuring high calibration efficiency, the wide spectrum applicability and high extinction ratio ensure the reliability of the calibration data.

[0067] 4. Based on the present invention, under the premise of ensuring the same-position measurement, sampling is performed nanometer by nanometer from 350nm to 1100nm. The repeatability comparison results of two independent samplings show that the repeatability difference of most sampling points is less than 1% and all are less than 1.5%, which proves the stability of the system.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A calibration system for relative spectral responsivity of an optical power meter, characterized in that: include: Glan-Taylor prism and Wollaston prism set adjacent to each other; A group of concave mirrors with increasing curvatures are provided between the Glan-Taylor prism and the monochromator light source to shrink the light beam to the light aperture of the Glan-Taylor prism; A third concave mirror and a first y-cylindrical reflector are arranged behind the Wollaston prism for projecting the first split beam of light onto the first detector, and a fourth concave mirror and a second y-cylindrical reflector are arranged for projecting the second split beam of light onto the second detector; the first y-cylindrical reflector is located between the third concave mirror and the first detector, and the second y-cylindrical reflector is located between the fourth concave mirror and the second detector; Among them, the Glan Taylor prism is used to adjust the outgoing light into linear polarized light with an angle of 45° with the vertical direction, the y-axis direction of the reflecting cylindrical surfaces of the first y-cylindrical reflector and the second y-cylindrical reflector is the vertical direction; and the plane where the breadboard for deploying the devices for the calibration system is located is a horizontal plane.

2. The calibration system for relative spectral responsivity of an optical power meter according to claim 1, characterized in that: A group of concave mirrors for shrinking a light beam to a light-through hole of the Glan-Taylor prism comprises a first concave mirror and a second concave mirror arranged at an interval, wherein the curvature of the first concave mirror is smaller 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: The following steps are involved: Step S1, deploying the calibration system of the relative spectral responsivity of the optical power meter as claimed in claim 1 or 2 and completing the optical path debugging; Step S2, using standard detectors for both the first detector and the second detector, and calibrating the splitting ratios of the two standard detectors corresponding to each wavelength; Step S3, replacing the second detector with the detector under test, and during the calibration process of the second detector, calculating the actual optical power of the light beam detected by the detector under test according to 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 the relative spectral responsivity curve of the detector under test according to the actual optical power of the light beam detected by the detector under test.

4. The method according to claim 3, characterized in that: The specific calculation formula of step S3 is: R 350-1100 =P S(350-1100) / P T(350-1100) ; Among them, P S(350-1100) is the power value of the standard detector, P T(350-1100) is the power value of the detector under test collected by the standard detector, R 350-1100 is the splitting ratio; the actual power value of the measured detector 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 under different wavelengths of light is collected. (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) ; Among them, the relative spectral responsivity coefficient is obtained after the absolute spectral responsivity is normalized.

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