CN109781262B - Calibration and correction method and device for center wavelength of liquid crystal tunable filter - Google Patents
Calibration and correction method and device for center wavelength of liquid crystal tunable filter Download PDFInfo
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Abstract
The invention relates to the technical field of filters, and discloses a calibration and correction method and a calibration and correction device for the center wavelength of a liquid crystal tunable filter.
Description
Technical Field
The invention relates to the technical field of filters, in particular to a method and a device for calibrating and correcting the center wavelength of a liquid crystal tunable filter.
Background
The liquid crystal tunable filter is a programmable narrow-band optical filter, can decompose visible light/near-infrared continuous spectrum into nearly 1000 independent wave bands, and the high-spectrum imaging system formed by combining the liquid crystal tunable filter and an image sensor can obtain high-resolution spatial information and spectral information of a detection target in a wave band time-sharing scanning mode. The hyperspectral imaging system based on the liquid crystal tunable filter greatly improves the target identification capability, and plays an important role in the fields of camouflage identification, counterfeit identification, ground feature classification, environment monitoring and evaluation, resource remote sensing investigation, medical diagnosis and the like which need to identify the detailed optical intensity, polarization state and spectral characteristics of targets.
The liquid crystal tunable filter usually employs a plurality of liquid crystal polarization interference units to realize optical filtering in cascade, that is, only light of a narrow band spectrum centered on a certain wavelength is allowed to pass through and light of other wavelengths is cut off, so that when the liquid crystal tunable filter works, each stage of liquid crystal polarization interference unit needs to have maximum transmittance at a specified central wavelength, and at least one stage of liquid crystal polarization interference unit outside the central wavelength has a wavelength cut-off capability. The calibration of the liquid crystal tunable filter is to find the optimal driving voltage with the maximum transmittance of each level of liquid crystal polarization interference unit at the specified central wavelength, so that the liquid crystal tunable filter combined in a cascade mode has good optical performance.
Because the equivalent phase delay amounts of all levels of polarization interference units of the liquid crystal tunable filter are different, the transmission spectrum curves of all levels of polarization interference units usually cannot meet the maximum transmittance condition at the same time at the set wavelength, and meanwhile, the transmission spectrum curves of all levels of polarization interference units of the liquid crystal tunable filter have a plurality of maximum values and minimum values. Therefore, how to select one of the maximum values of each level of polarization interference unit and drive the selected maximum value to the set central wavelength position is a key problem of the calibration of the liquid crystal tunable filter, and plays a decisive role in the quality of key performance parameters of the liquid crystal tunable filter, such as wavelength accuracy, transmittance, bandwidth (FWHM), out-of-band cut-off and the like.
In the calibration process of the central wavelength of the liquid crystal tunable filter, because the transmission spectrum curve of each level of polarization interference unit has a plurality of maximum values and a plurality of maximum and minimum values generated by Fabry-Perot interference of the liquid crystal phase retarder exist, a computer is used for automatically judging the central wavelength of a peak value, so that a large error is usually generated, and the calibration of the central wavelength of the liquid crystal tunable filter is mainly manual calibration at present. The method comprises the steps of firstly appointing a central wavelength, adjusting a driving voltage, driving a wavelength corresponding to a peak value of a transmission spectrum of each level of polarization interference unit to reach the appointed value, then appointing another central wavelength, adjusting the driving voltage, driving a wavelength corresponding to a peak value of a transmission spectrum of each level of polarization interference unit to reach the appointed value, and circulating in sequence to finish the appointed central wavelength calibration in the working range of the liquid crystal tunable filter. The wavelength accuracy of the calibration method depends on manual interpretation, and along with the improvement of the tuning resolution of the liquid crystal tunable filter, if the tuning resolution of 0.1nm is needed, the accuracy of the manual interpretation is difficult to guarantee, and meanwhile, the number of the calibrated central wavelengths reaches 103-104, and the calibration workload is increased sharply.
In addition, for each level of polarization interference unit, different transmission spectrum maximum values are selected, which correspond to different bandwidths (FWHM), out-of-band cut-off, transmittances and the like of the cascaded liquid crystal tunable filter. With the improvement of the spectral resolution of the liquid crystal tunable filter, the number of required polarization interference units increases, the number of maximum combinations brought by each increase of one level increases in an order of magnitude manner, only a few combinations can be extracted in the maximum combinations of the polarization interference units of each level with huge number, parameters such as bandwidth (FWHM), out-of-band cut-off and transmittance of the liquid crystal tunable filter in the cascade combination cannot meet the requirements easily, and at present, the calibration of the central wavelength becomes a key constraint factor for research and development of the high-resolution liquid crystal tunable filter with more cascade levels.
Because the wavelength corresponding to the maximum value of the transmission spectrum of the liquid crystal polarization interference unit is changed due to the manufacturing process of the liquid crystal phase retarder in the liquid crystal polarization interference unit or the change of the environmental temperature, the current calibration method does not have the capability of correcting the wavelength change, and therefore, each liquid crystal tunable filter needs to be calibrated independently.
Disclosure of Invention
The invention mainly aims to provide a calibration and correction method and a calibration and correction device for the center wavelength of a liquid crystal tunable filter, which improve the accuracy and efficiency of the calibration of the center wavelength of the liquid crystal tunable filter.
In order to achieve the above object, the present invention provides a calibration and correction method for center wavelength of a liquid crystal tunable filter, which includes:
calculating to obtain a driving coefficient according to a function of the phase retardation along with the wavelength and a function of the liquid crystal phase retardation along with the driving voltage;
setting central wavelengths for all levels of liquid crystal polarization interference units in the liquid crystal tunable filter, and calculating driving voltages of all levels of liquid crystal polarization interference units according to driving coefficients corresponding to the preset central wavelengths;
acquiring an actual measurement center wavelength under the driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
judging whether the deviation value is smaller than a deviation threshold value, if so, taking the driving voltage as the driving voltage of the central wavelength of the liquid crystal tunable filter;
otherwise, calculating a correction coefficient according to the actually measured central wavelength and the preset central wavelength;
updating the driving voltage according to the correction coefficient until the deviation value is less than the deviation threshold.
Optionally, the obtaining of the driving coefficient by calculating according to the function of the phase retardation along with the wavelength and the function of the liquid crystal phase retardation along with the driving voltage includes:
acquiring a function of phase retardation along with wavelength change, wherein the function of phase retardation along with wavelength change comprises a function of liquid crystal phase retardation along with wavelength change and a function of fixed phase retardation along with wavelength change;
acquiring a function of liquid crystal phase delay variation along with the driving voltage;
and calculating to obtain a driving coefficient according to the function of the phase retardation along with the wavelength and the function of the liquid crystal phase retardation along with the driving voltage.
Optionally, the obtaining the measured central wavelength under the driving voltage, and calculating a deviation value between the measured central wavelength and the preset central wavelength includes:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
Optionally, the updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value comprises:
multiplying the driving coefficient corresponding to the preset central wavelength by the correction coefficient to obtain an updated driving coefficient;
calculating to obtain updated driving voltage according to the updated driving coefficient;
acquiring the actual measurement center wavelength under the updated driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
and returning to the step of judging whether the deviation value is smaller than the deviation threshold value or not until the deviation value is smaller than the deviation threshold value.
Optionally, the liquid crystal phase retardation amount as a function of wavelength is expressed as: Δ ndLC(λ)；
The fixed phase delay amount as a function of wavelength is expressed as: Δ ndQ(λ)；
The driving coefficients corresponding to the liquid crystal polarization interference units at all levels are expressed as follows:
......
the correction coefficient is expressed as:
wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is the filter function.
As another aspect of the present invention, a calibration and correction apparatus for center wavelength calibration of a liquid crystal tunable filter is provided, which includes:
the driving coefficient acquisition module is used for calculating and obtaining a driving coefficient according to a function of the phase delay along with the wavelength and a function of the liquid crystal phase delay along with the driving voltage;
the driving voltage calculation module is used for setting a central wavelength for each level of liquid crystal polarization interference unit in the liquid crystal tunable filter and calculating the driving voltage of each level of liquid crystal polarization interference unit according to a driving coefficient corresponding to the preset central wavelength;
the calibration module is used for acquiring an actual measurement center wavelength under the driving voltage and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
the judging module is used for judging whether the deviation value is smaller than a deviation threshold value, and if so, the driving voltage is used as the driving voltage of the central wavelength of the liquid crystal tunable filter;
the correction coefficient calculation module is used for calculating a correction coefficient according to the measured central wavelength and the preset central wavelength when the deviation value is not less than a deviation threshold value;
and the correction module is used for updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value.
Optionally, the driving coefficient obtaining module includes:
a first function obtaining unit, configured to obtain a function of phase retardation as a function of wavelength, where the function of phase retardation as a function of wavelength includes a function of liquid crystal phase retardation as a function of wavelength and a function of fixed phase retardation as a function of wavelength;
the second function acquisition unit is used for acquiring a function of the liquid crystal phase delay amount changing along with the driving voltage;
and the driving coefficient acquisition unit is used for calculating and acquiring a driving coefficient according to the function of the phase delay along with the wavelength and the function of the liquid crystal phase delay along with the driving voltage.
Optionally, the calibration module includes:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
Optionally, the correction module comprises:
the drive coefficient updating unit is used for multiplying the drive coefficient corresponding to the preset central wavelength by the correction coefficient to obtain an updated drive coefficient;
the driving voltage updating unit is used for calculating to obtain updated driving voltage according to the updated driving coefficient;
the offset value updating unit is used for acquiring the actual measurement center wavelength under the updated driving voltage and calculating the offset value between the actual measurement center wavelength and the preset center wavelength;
and the circulating unit is used for returning to the step of judging whether the deviation value is smaller than the deviation threshold value until the deviation value is smaller than the deviation threshold value.
Optionally, the liquid crystal phase retardation amount as a function of wavelength is expressed as: Δ ndLC(λ)；
The fixed phase delay amount as a function of wavelength is expressed as: Δ ndQ(λ)；
The driving coefficients corresponding to the liquid crystal polarization interference units at all levels are expressed as follows:
......
the correction coefficient is expressed as:
wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is the filter function.
The invention provides a calibration and correction method and a device for the center wavelength of a liquid crystal tunable filter, wherein the method comprises the following steps: calculating to obtain a driving coefficient according to a function of the phase retardation along with the wavelength and a function of the liquid crystal phase retardation along with the driving voltage; setting central wavelengths for all levels of liquid crystal polarization interference units in the liquid crystal tunable filter, and calculating driving voltages of all levels of liquid crystal polarization interference units according to driving coefficients corresponding to the preset central wavelengths; acquiring an actual measurement center wavelength under the driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength; judging whether the deviation value is smaller than a deviation threshold value, if so, taking the driving voltage as the driving voltage of the central wavelength of the liquid crystal tunable filter; otherwise, calculating a correction coefficient according to the actually measured central wavelength and the preset central wavelength; and updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value, generating the driving voltage of each level of polarization interference units of the liquid crystal tunable filter by calibrating a function of the phase delay amount changing along with the wavelength and a function of the liquid crystal phase delay amount changing along with the driving voltage and utilizing simulation calculation on the basis of the driving coefficient, and calculating to obtain the correction coefficient according to the deviation of the actually measured central wavelength and the set central wavelength, so that the driving voltage corresponding to the central wavelength of the liquid crystal tunable filter is automatically corrected, and the accuracy and the efficiency of the calibration of the central wavelength of the liquid crystal tunable filter are improved.
Drawings
Fig. 1 is a flowchart of a calibration method for center wavelength calibration of a liquid crystal tunable filter according to an embodiment of the present invention;
FIG. 2 is a flowchart of the method of step S10 in FIG. 1;
FIG. 3 is a schematic diagram of a transmission spectrum curve of the liquid crystal phase retardation according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a liquid crystal phase retardation dispersion function curve according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating a transmission spectrum curve with a fixed phase retardation according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating a dispersion function curve with a fixed phase delay according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a driving voltage curve corresponding to any wavelength of a liquid crystal polarization interference unit according to an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating an offset detection function according to an embodiment of the present invention;
FIG. 9 is a diagram illustrating deviation values of center wavelengths according to an embodiment of the present invention;
FIG. 10 is a flowchart of the method of step S70 of FIG. 1;
fig. 11 is a block diagram illustrating an exemplary structure of a calibration and correction device for center wavelength calibration of a liquid crystal tunable filter according to a second embodiment of the present invention;
FIG. 12 is a block diagram illustrating an exemplary structure of the driving coefficient obtaining module shown in FIG. 11;
FIG. 13 is a block diagram of an exemplary structure of the correction module of FIG. 11.
The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the following description, suffixes such as "module", "component", or "unit" used to denote elements are used only for facilitating the explanation of the present invention, and have no specific meaning in themselves. Thus, "module" and "component" may be used in a mixture.
As shown in fig. 1, in this embodiment, a method for calibrating and correcting a center wavelength of a liquid crystal tunable filter includes:
s10, calculating to obtain a driving coefficient according to a function of phase retardation along with wavelength change and a function of liquid crystal phase retardation along with driving voltage change;
s20, setting a center wavelength for each level of liquid crystal polarization interference unit in the liquid crystal tunable filter, and calculating the driving voltage of each level of liquid crystal polarization interference unit according to the driving coefficient corresponding to the preset center wavelength;
s30, acquiring an actual measurement center wavelength under the driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
s40, judging whether the deviation value is smaller than a deviation threshold value, if so, entering a step S50, and taking the driving voltage as the driving voltage of the central wavelength of the liquid crystal tunable filter;
otherwise, step S60 is performed, and a correction coefficient is calculated according to the measured center wavelength and the preset center wavelength;
and S70, updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value.
In this embodiment, the driving voltages of the polarization interference units of the liquid crystal tunable filter at each stage are generated by calibrating the function of the phase retardation along with the wavelength variation and the function of the liquid crystal phase retardation along with the driving voltage, and by using simulation calculation based on the driving coefficients, the correction coefficients are calculated according to the deviation between the actually measured center wavelength and the set center wavelength, so as to automatically correct the driving voltage corresponding to the center wavelength of the liquid crystal tunable filter, thereby improving the accuracy and efficiency of the calibration of the center wavelength of the liquid crystal tunable filter.
As shown in fig. 2, in the present embodiment, the step S10 includes:
s11, acquiring a function of phase retardation along with wavelength, wherein the function of phase retardation along with wavelength comprises a function of liquid crystal phase retardation along with wavelength and a function of fixed phase retardation along with wavelength;
s12, acquiring a liquid crystal phase retardation variation function along with the driving voltage;
and S13, calculating to obtain a driving coefficient according to the function of the phase retardation along with the wavelength and the function of the liquid crystal phase retardation along with the driving voltage.
In this embodiment, the method for obtaining the function of the liquid crystal phase retardation along with the wavelength variation includes:
a. parallel polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzer, enabling the polarization directions of the polarizing plate and the analyzer to be parallel, inserting a liquid crystal phase delay plate into the polarizing plate and the analyzer, enabling the included angle between the crystal axis direction of the liquid crystal phase delay plate and the polarizing direction to be 45 degrees, and forming a parallel polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line A in figure 3;
b. vertical polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to be vertical, inserting a liquid crystal phase retarder into the polarizing plate and the analyzing polarization to ensure that the included angle between the crystal axis direction of the liquid crystal phase retarder and the polarizing direction is 45 degrees, and forming a vertical polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line B in figure 3;
c. liquid crystal phase retardation dispersion calculation
Calculating to obtain a liquid crystal phase retardation dispersion function curve delta nd based on the polarization interference principle by utilizing the wavelength value corresponding to the maximum value of the parallel polarization interference transmission spectrum and the wavelength value corresponding to the maximum value of the vertical polarization interference transmission spectrumLC(λ) as shown in FIG. 4.
In this embodiment, the method for obtaining the function of the fixed phase delay amount with the wavelength variation includes:
a. parallel polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to enable the polarization directions of the polarizing plate and the analyzing polarization to be parallel, inserting a fixed phase delay plate into the polarizing plate and the analyzing polarization to enable the included angle between the crystal axis direction of the fixed phase delay plate and the polarizing direction to be 45 degrees, and forming a parallel polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line A in figure 5;
b. vertical polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to be vertical, inserting a liquid crystal phase retarder into the polarizing plate and the analyzing polarization to ensure that the included angle between the crystal axis direction of the fixed phase retarder and the polarizing direction is 45 degrees, and forming a vertical polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line B in figure 5;
c. fixed phase delay dispersion calculation
Calculating to obtain a dispersion function curve delta nd of a fixed phase retardation based on a polarization interference principle after normalization by using a wavelength value corresponding to a maximum value of a parallel polarization interference transmission spectrum and a wavelength value corresponding to a maximum value of a vertical polarization interference transmission spectrumQ(λ) as shown in FIG. 6.
In this embodiment, a driver is used to generate a sequential driving voltage to drive the liquid crystal polarization interference unit, and a transmission spectrum curve corresponding to the sequential voltage is measured by a spectrometer. The wavelength value change corresponding to the maximum value and the minimum value of the transmission spectrum curve is tracked and recorded, the discrete data of the wavelength value changing along with the voltage is fitted into a function of the wavelength changing along with the voltage, and the driving voltage corresponding to any wavelength of the liquid crystal polarization interference unit is obtained through the function relation of the wavelength changing along with the voltage, as shown in fig. 7.
In the present embodiment, according to Δ ndLC(lambda) calculation
Maximum of transmission spectral curve
When the driving voltage is from ViIncrease to VjThe wavelength corresponding to the maximum is from λiChange to lambdajI.e. by
By driving factor
To show the variation of the liquid crystal phase retardation amount with the driving voltage. Due to zero voltage
Has a maximum value, the wavelength corresponding to the maximum value decreases as the driving voltage increases, and
is a decreasing function, the driving coefficient is a dimensionless value in the interval (0, 1).
In this embodiment, the liquid crystal tunable filter is formed by combining multiple stages of liquid crystal polarization interference units, and the filter function of each stage of liquid crystal polarization interference unit can be equivalent to:
......
selecting fixed phase delay delta of each stage of liquid crystal polarization interference unitiThen, the driving coefficient alpha corresponding to any maximum wavelength of each level of liquid crystal polarization interference unit is obtained through calculationiI.e. by
......
Drive factor alphaiBy T (λ) ═ T1(λ)T2(λ)......TnThe performance parameters such as full width at half maximum (FWHM), out-of-band rejection ratio, transmittance and the like are analyzed and obtained through a (lambda) curve, and the driving coefficient alpha is optimized through maximum value selectioniAccording to the driving coefficient alphaiThe corresponding driving voltage is searched. Namely, the driving voltage of each stage of liquid crystal polarization interference unit required by any central wavelength of the liquid crystal tunable filter can be automatically generated through simulation calculation.
In this embodiment, the step S30 includes:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
As shown in fig. 8, the driving coefficient α of each level of liquid crystal polarization unit at the arbitrarily set center wavelength is obtained by PC-side simulation calculationiThen, the corresponding driving voltage value V is searchediGenerating a voltage V by using a liquid crystal driving controlleriThe liquid crystal polarization interference units at each stage are driven, and the deviation value between the wavelength corresponding to the maximum value of the transmission spectrum curve and the set central wavelength is detected by the spectrometer, as shown in fig. 9.
As shown in fig. 10, in the present embodiment, the step S70 includes:
s71, multiplying the drive coefficient corresponding to the preset center wavelength by the correction coefficient to obtain an updated drive coefficient;
s72, calculating to obtain an updated driving voltage according to the updated driving coefficient;
s73, acquiring the actual measurement center wavelength under the updated driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
returning to the step of determining whether the deviation value is less than the deviation threshold at step S40 until the deviation value is less than the deviation threshold.
In this embodiment, if the center wavelength of the tunable filter is set to λdThen there is
The wavelength corresponding to the maximum value of the transmission spectrum curve of a certain-level polarization interference unit of the actually measured tunable filter is lambdarSince the amount of the fixed phase delay does not vary with the driving voltage, there are
The polarization interference unit transmits the wavelength lambda corresponding to the maximum value of the spectral curverCorrected to λdNeed to satisfy
Wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is the filter function.
In the embodiment, the driving coefficient alpha of the liquid crystal polarization unit at the arbitrarily set central wavelength is obtained through simulation calculationiMultiplying by a correction coefficient c to obtain c alphaiFinding the drive coefficient c αiCorresponding driving voltage Vi1The driving voltage is used as the driving voltage of the central wavelength set by the liquid crystal tunable filter, the liquid crystal driver is used for generating the voltage to drive each level of liquid crystal polarization interference unit, the deviation value of the wavelength corresponding to the maximum value of the transmission spectrum curve and the set central wavelength is detected through the spectrometer, and if the deviation value of the wavelength corresponding to the maximum value of the transmission spectrum curve of the liquid crystal polarization interference unit and the set central wavelength meets the design requirement, V is usedi1A drive voltage as a set center wavelength of the tunable liquid crystal filter. If the deviation value exceeds the design range, correcting according to the method, and correcting the deviation value for N times to meet the V of the design requirementiNA drive voltage as a set center wavelength of the tunable liquid crystal filter.
Example two
As shown in fig. 11, in this embodiment, a device for calibrating and correcting the center wavelength of a liquid crystal tunable filter includes:
the driving coefficient obtaining module 10 is configured to calculate a driving coefficient according to a function of the phase retardation varying with the wavelength and a function of the liquid crystal phase retardation varying with the driving voltage;
the driving voltage calculation module 20 is configured to set a center wavelength for each level of liquid crystal polarization interference units in the liquid crystal tunable filter, and calculate a driving voltage of each level of liquid crystal polarization interference units according to a driving coefficient corresponding to the preset center wavelength;
the calibration module 30 is configured to obtain an actual measurement center wavelength under the driving voltage, and calculate a deviation value between the actual measurement center wavelength and the preset center wavelength;
the judging module 40 is configured to judge whether the deviation value is smaller than a deviation threshold, and if so, use the driving voltage as a driving voltage of a center wavelength of the liquid crystal tunable filter;
a correction coefficient calculation module 50, configured to calculate a correction coefficient according to the measured center wavelength and the preset center wavelength when the deviation value is not smaller than a deviation threshold;
a correction module 60, configured to update the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold.
In this embodiment, the driving voltages of the polarization interference units of the liquid crystal tunable filter at each stage are generated by calibrating the function of the phase retardation along with the wavelength variation and the function of the liquid crystal phase retardation along with the driving voltage, and by using simulation calculation based on the driving coefficients, the correction coefficients are calculated according to the deviation between the actually measured center wavelength and the set center wavelength, so as to automatically correct the driving voltage corresponding to the center wavelength of the liquid crystal tunable filter, thereby improving the accuracy and efficiency of the calibration of the center wavelength of the liquid crystal tunable filter.
As shown in fig. 12, in this embodiment, the driving coefficient obtaining module includes:
a first function obtaining unit 11, configured to obtain a function of a phase retardation as a function of wavelength, where the function of the phase retardation as a function of wavelength includes a function of a liquid crystal phase retardation as a function of wavelength and a function of a fixed phase retardation as a function of wavelength;
a second function obtaining unit 12, configured to obtain a function of a variation of the liquid crystal phase retardation with the driving voltage;
and the driving coefficient obtaining unit 13 is configured to calculate and obtain a driving coefficient according to the function of the phase retardation varying with the wavelength and the function of the liquid crystal phase retardation varying with the driving voltage.
In this embodiment, the method for obtaining the function of the liquid crystal phase retardation along with the wavelength variation includes:
a. parallel polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzer, enabling the polarization directions of the polarizing plate and the analyzer to be parallel, inserting a liquid crystal phase delay plate into the polarizing plate and the analyzer, enabling the included angle between the crystal axis direction of the liquid crystal phase delay plate and the polarizing direction to be 45 degrees, and forming a parallel polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line A in figure 3;
b. vertical polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to be vertical, inserting a liquid crystal phase retarder into the polarizing plate and the analyzing polarization to ensure that the included angle between the crystal axis direction of the liquid crystal phase retarder and the polarizing direction is 45 degrees, and forming a vertical polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line B in figure 3;
c. liquid crystal phase retardation dispersion calculation
Calculating to obtain a liquid crystal phase retardation dispersion function curve delta nd based on the polarization interference principle by utilizing the wavelength value corresponding to the maximum value of the parallel polarization interference transmission spectrum and the wavelength value corresponding to the maximum value of the vertical polarization interference transmission spectrumLC(λ) as shown in FIG. 4.
In this embodiment, the method for obtaining the function of the fixed phase delay amount with the wavelength variation includes:
a. parallel polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to enable the polarization directions of the polarizing plate and the analyzing polarization to be parallel, inserting a fixed phase delay plate into the polarizing plate and the analyzing polarization to enable the included angle between the crystal axis direction of the fixed phase delay plate and the polarizing direction to be 45 degrees, and forming a parallel polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line A in figure 5;
b. vertical polarization interference transmission spectrum curve collection
Setting the polarization directions of a polarizing plate and an analyzing polarization to be vertical, inserting a liquid crystal phase retarder into the polarizing plate and the analyzing polarization to ensure that the included angle between the crystal axis direction of the fixed phase retarder and the polarizing direction is 45 degrees, and forming a vertical polarization interference unit. Collecting a polarization interference transmission spectrum curve by using a spectrometer, and marking a wavelength value corresponding to a maximum value of the transmission spectrum curve, as shown by a line B in figure 5;
c. fixed phase delay dispersion calculation
Calculating to obtain a dispersion function curve delta nd of a fixed phase retardation based on a polarization interference principle after normalization by using a wavelength value corresponding to a maximum value of a parallel polarization interference transmission spectrum and a wavelength value corresponding to a maximum value of a vertical polarization interference transmission spectrumQ(λ) as shown in FIG. 6.
In this embodiment, a driver is used to generate a sequential driving voltage to drive the liquid crystal polarization interference unit, and a transmission spectrum curve corresponding to the sequential voltage is measured by a spectrometer. The wavelength value change corresponding to the maximum value and the minimum value of the transmission spectrum curve is tracked and recorded, the discrete data of the wavelength value changing along with the voltage is fitted into a function of the wavelength changing along with the voltage, and the driving voltage corresponding to any wavelength of the liquid crystal polarization interference unit is obtained through the function relation of the wavelength changing along with the voltage, as shown in fig. 7.
In the present embodiment, according to Δ ndLC(lambda) calculation
Maximum of transmission spectral curve
When the driving voltage is from ViIncrease to VjThe wavelength corresponding to the maximum is from λiChange to lambdajI.e. by
By driving factor
To show the variation of the liquid crystal phase retardation amount with the driving voltage. Due to zero voltage
Has a maximum value, the wavelength corresponding to the maximum value decreases as the driving voltage increases, and
is a decreasing function, the driving coefficient is a dimensionless value in the interval (0, 1).
In this embodiment, the liquid crystal tunable filter is formed by combining multiple stages of liquid crystal polarization interference units, and the filter function of each stage of liquid crystal polarization interference unit can be equivalent to:
......
selecting fixed phase delay delta of each stage of liquid crystal polarization interference unitiThen, the driving coefficient alpha corresponding to any maximum wavelength of each level of liquid crystal polarization interference unit is obtained through calculationiI.e. by
......
Drive factor alphaiBy T (λ) ═ T1(λ)T2(λ)......TnThe performance parameters such as full width at half maximum (FWHM), out-of-band rejection ratio, transmittance and the like are analyzed and obtained through a (lambda) curve, and the driving coefficient alpha is optimized through maximum value selectioniAccording to the driving coefficient alphaiThe corresponding driving voltage is searched. Namely, the driving voltage of each stage of liquid crystal polarization interference unit required by any central wavelength of the liquid crystal tunable filter can be automatically generated through simulation calculation.
In this embodiment, the calibration module includes:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
As shown in fig. 13, in the present embodiment, the correction module includes:
a driving coefficient updating unit 71, configured to multiply the driving coefficient corresponding to the preset center wavelength by the correction coefficient to obtain an updated driving coefficient;
a driving voltage updating unit 72, configured to calculate an updated driving voltage according to the updated driving coefficient;
an offset value updating unit 73, configured to obtain an actual measurement center wavelength under the updated driving voltage, and calculate an offset value between the actual measurement center wavelength and the preset center wavelength;
and a looping unit 74, configured to return to the step of determining whether the deviation value is smaller than the deviation threshold value until the deviation value is smaller than the deviation threshold value.
In this embodiment, if the center wavelength of the tunable filter is set to λdThen there is
The wavelength corresponding to the maximum value of the transmission spectrum curve of a certain-level polarization interference unit of the actually measured tunable filter is lambdarFromWhen the delay amount of the fixed phase does not change with the driving voltage, the method comprises
The polarization interference unit transmits the wavelength lambda corresponding to the maximum value of the spectral curverCorrected to λdNeed to satisfy
Wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is the filter function.
In the embodiment, the driving coefficient alpha of the liquid crystal polarization unit at the arbitrarily set central wavelength is obtained through simulation calculationiMultiplying by a correction coefficient c to obtain c alphaiFinding the drive coefficient c αiCorresponding driving voltage Vi1The driving voltage of the central wavelength set by the liquid crystal tunable filter is generated by a liquid crystal driver to drive each level of liquid crystal polarization interference unit, the deviation value of the wavelength corresponding to the maximum value of the transmission spectrum curve and the set central wavelength is detected by a spectrometer, if the transmission spectrum curve of the liquid crystal polarization interference unit is detectedThe deviation value of the wavelength corresponding to the maximum value of the line and the set central wavelength meets the design requirement, and then V is seti1A drive voltage as a set center wavelength of the tunable liquid crystal filter. If the deviation value exceeds the design range, correcting according to the method, and correcting the deviation value for N times to meet the V of the design requirementiNA drive voltage as a set center wavelength of the tunable liquid crystal filter.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (6)
1. A calibration and correction method for the center wavelength of a liquid crystal tunable filter is characterized by comprising the following steps:
calculating to obtain a driving coefficient according to a function of the phase retardation along with the wavelength and a function of the liquid crystal phase retardation along with the driving voltage;
setting central wavelengths for all levels of liquid crystal polarization interference units in the liquid crystal tunable filter, and calculating driving voltages of all levels of liquid crystal polarization interference units according to driving coefficients corresponding to the preset central wavelengths;
acquiring an actual measurement center wavelength under the driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
judging whether the deviation value is smaller than a deviation threshold value, if so, taking the driving voltage as the driving voltage of the central wavelength of the liquid crystal tunable filter;
otherwise, calculating a correction coefficient according to the actually measured central wavelength and the preset central wavelength;
updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value;
the step of obtaining the driving coefficient by calculating according to the function of the phase retardation along with the wavelength and the function of the liquid crystal phase retardation along with the driving voltage comprises the following steps:
acquiring a function of phase retardation along with wavelength change, wherein the function of phase retardation along with wavelength change comprises a function of liquid crystal phase retardation along with wavelength change and a function of fixed phase retardation along with wavelength change;
acquiring a function of liquid crystal phase delay variation along with the driving voltage;
calculating to obtain a driving coefficient according to the function of the phase retardation along with the wavelength and the function of the liquid crystal phase retardation along with the driving voltage;
the liquid crystal phase retardation is expressed as a function of wavelength: Δ ndLC(λ)；
The fixed phase delay amount as a function of wavelength is expressed as: Δ ndQ(λ)；
The driving coefficients corresponding to the liquid crystal polarization interference units at all levels are expressed as follows:
......
the correction coefficient is expressed as:
wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is a filter function; lambda [ alpha ]dIs the set center wavelength of the tunable filter; lambda [ alpha ]rThe wavelength corresponding to the maximum value of the transmission spectrum curve of a polarization interference unit of a certain level of the actually measured tunable filter.
2. The method for calibrating and correcting the center wavelength of the liquid crystal tunable filter according to claim 1, wherein the obtaining a measured center wavelength under the driving voltage, and the calculating a deviation value between the measured center wavelength and the preset center wavelength comprises:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
3. The method for calibrating and correcting the center wavelength of the liquid crystal tunable filter according to claim 2, wherein the updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value comprises:
multiplying the driving coefficient corresponding to the preset central wavelength by the correction coefficient to obtain an updated driving coefficient;
calculating to obtain updated driving voltage according to the updated driving coefficient;
acquiring the actual measurement center wavelength under the updated driving voltage, and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
and returning to the step of judging whether the deviation value is smaller than the deviation threshold value or not until the deviation value is smaller than the deviation threshold value.
4. A calibration and correction device for the center wavelength of a liquid crystal tunable filter is characterized by comprising:
the driving coefficient acquisition module is used for calculating and obtaining a driving coefficient according to a function of the phase delay along with the wavelength and a function of the liquid crystal phase delay along with the driving voltage;
the driving voltage calculation module is used for setting a central wavelength for each level of liquid crystal polarization interference unit in the liquid crystal tunable filter and calculating the driving voltage of each level of liquid crystal polarization interference unit according to a driving coefficient corresponding to the preset central wavelength;
the calibration module is used for acquiring an actual measurement center wavelength under the driving voltage and calculating a deviation value between the actual measurement center wavelength and the preset center wavelength;
the judging module is used for judging whether the deviation value is smaller than a deviation threshold value, and if so, the driving voltage is used as the driving voltage of the central wavelength of the liquid crystal tunable filter;
the correction coefficient calculation module is used for calculating a correction coefficient according to the measured central wavelength and the preset central wavelength when the deviation value is not less than a deviation threshold value;
the correction module is used for updating the driving voltage according to the correction coefficient until the deviation value is smaller than the deviation threshold value;
the drive coefficient acquisition module includes:
a first function obtaining unit, configured to obtain a function of phase retardation as a function of wavelength, where the function of phase retardation as a function of wavelength includes a function of liquid crystal phase retardation as a function of wavelength and a function of fixed phase retardation as a function of wavelength;
the second function acquisition unit is used for acquiring a function of the liquid crystal phase delay amount changing along with the driving voltage;
the driving coefficient obtaining unit is used for calculating and obtaining a driving coefficient according to the function of the phase delay along with the wavelength and the function of the liquid crystal phase delay along with the driving voltage;
the liquid crystal phase retardation is expressed as a function of wavelength: Δ ndLC(λ)；
The fixed phase delay amount as a function of wavelength is expressed as: Δ ndQ(λ)；
The driving coefficients corresponding to the liquid crystal polarization interference units at all levels are expressed as follows:
......
the correction coefficient is expressed as:
wherein λ is the wavelength;
is the maximum value of the transmission spectrum curve, and k is a natural number; deltaiThe phase delay is fixed for each level of liquid crystal polarization interference unit; t is a filter function; lambda [ alpha ]dIs the set center wavelength of the tunable filter; lambda [ alpha ]rThe wavelength corresponding to the maximum value of the transmission spectrum curve of a polarization interference unit of a certain level of the actually measured tunable filter.
5. The calibration device for calibrating and correcting the center wavelength of the liquid crystal tunable filter according to claim 4, wherein the calibration module comprises:
and the liquid crystal driver is used for generating the driving voltage to drive each level of liquid crystal polarization interference unit, the spectrometer is used for detecting the central wavelength corresponding to the maximum value of the transmission spectrum curve as an actual measurement central wavelength, and a deviation value between the actual measurement central wavelength and the preset central wavelength is calculated.
6. The calibration and correction device for center wavelength calibration of liquid crystal tunable filter according to claim 5, wherein said correction module comprises:
the drive coefficient updating unit is used for multiplying the drive coefficient corresponding to the preset central wavelength by the correction coefficient to obtain an updated drive coefficient;
the driving voltage updating unit is used for calculating to obtain updated driving voltage according to the updated driving coefficient;
the offset value updating unit is used for acquiring the actual measurement center wavelength under the updated driving voltage and calculating the offset value between the actual measurement center wavelength and the preset center wavelength;
and the circulating unit is used for returning to the step of judging whether the deviation value is smaller than the deviation threshold value until the deviation value is smaller than the deviation threshold value.
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| CN101464576A (en) * | 2009-01-14 | 2009-06-24 | 北京航空航天大学 | Characteristic parameters scaling system for liquid crystal phase variable delay device |
| JP2010224572A (en) * | 2010-05-28 | 2010-10-07 | Seiko Epson Corp | Tunable filter |
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| CN101464576A (en) * | 2009-01-14 | 2009-06-24 | 北京航空航天大学 | Characteristic parameters scaling system for liquid crystal phase variable delay device |
| JP2010224572A (en) * | 2010-05-28 | 2010-10-07 | Seiko Epson Corp | Tunable filter |
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