CN107356914B - Calibration system for satellite-borne laser radar detector - Google Patents
Calibration system for satellite-borne laser radar detector Download PDFInfo
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- CN107356914B CN107356914B CN201710637431.2A CN201710637431A CN107356914B CN 107356914 B CN107356914 B CN 107356914B CN 201710637431 A CN201710637431 A CN 201710637431A CN 107356914 B CN107356914 B CN 107356914B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
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Abstract
A calibration system for a satellite-borne laser radar detector is used for realizing calibration of sensitivity, linearity and time response of the detector; the light which is emitted by an LED and has lower intensity, stable work and easily adjustable intensity is converted into light which is irrelevant to an angle by utilizing an integrating sphere, the light which is irrelevant to the angle in the integrating sphere is coupled into an optical fiber through a coupling lens, the light in the optical fiber passes through a collimating mirror to form collimated light which is easy to establish a light path, the collimated light is attenuated after being split by an optical fiber beam splitter and is introduced into each detector, and the calibration of sensitivity and linearity is realized; the calibration of the time response of the detector needs a light source with ultra-fast response time, the laser can generate narrow pulses with ns-level width, and the time response information of the detector can be conveniently extracted by using the laser generating ns-level, so that the calibration of the time response is realized.
Description
Technical Field
The invention relates to a calibration system for a satellite-borne laser radar detector, which is suitable for calibrating the sensitivity, the linearity and the time response of the satellite-borne laser radar detector.
Background
The detector is a photoelectric device which converts an optical signal to be measured into an electric signal, has a very important position in a laser radar system, and must be calibrated when the laser radar system is constructed. When the laser radar is used, the detector runs for a long time in a space environment, the performance of the detector is reduced due to the influence of factors such as the space external environment, the service life of the detector and the like, and the detector also needs to be calibrated regularly. For the detector used on the laser radar, parameters such as sensitivity, linearity and time response need to be calibrated.
Disclosure of Invention
The technical problems solved by the invention are as follows: aiming at the condition that the performance of the space-borne laser radar detector is reduced due to the influences of factors such as the space external environment, the service life of the detector and the like when the space-borne laser radar detector runs in a space environment for a long time, a calibration system of the space-borne laser radar detector is provided, and the calibration of the sensitivity, the linearity and the time response of the detector is realized.
The technical scheme of the invention is as follows: a calibration system for a satellite-borne laser radar detector comprises a light source module, a light transmission module, an attenuation module and a detector module; the light emitted from the light source module enters the light transmission module, is collimated and filtered in the light transmission module, is attenuated by the attenuation module and then enters the detector module; the calibration task is done in the detector module.
The attenuation module comprises a plurality of attenuation sheets with different attenuation coefficients and is used for ensuring that the light intensity and the light intensity range input to the detector meet the calibration requirement.
The attenuation sheet is a 5% wedge-shaped glass sheet.
The optical transmission module comprises a coupling lens, a multimode optical fiber, a beam splitter, a collimating mirror, an optical filter and a variable total reflector; the coupling lens couples light into the multimode optical fiber, the light is split into multiple paths by the beam splitter after being transmitted by the multimode optical fiber, and the light of each path is reflected by the variable total reflector to enter the detector after being collimated by the collimating mirror and filtered by the optical filter.
The detector module comprises a detector to be calibrated and a power meter; in the calibration, the variable total reflection mirror and the power meter are used for measuring the light intensity entering the detector, and the beam splitter is used for splitting the light path to realize the simultaneous calibration of a plurality of detectors.
The detector to be calibrated is built in a black box which has good external light shielding effect, and the black box is provided with a notch.
The calibration tasks include sensitivity, linearity and time response calibration.
When the calibration task of sensitivity and linearity is completed, the light source module comprises an LED and an integrating sphere, the LED outputs light with low intensity, stable work and easy intensity adjustment, and the integrating sphere converts the light output by the LED into light irrelevant to the angle.
When the calibration task of time response is completed, the light source module is a narrow pulse laser.
The invention has the advantages that:
(1) the LED used in the light source module has low luminous intensity, stable work and easy adjustment of intensity, and the light emitted by the LED is converted into light irrelevant to the angle after passing through the integrating sphere, so the light source module is very suitable for being used as a light source for calibrating the sensitivity and the linearity of a detector; the narrow pulse laser is used as a light source module for the time response calibration of the detector, the rise time of the narrow pulse generated by the laser is short, the time response information of the detector can be conveniently extracted, and the special requirements of the time response calibration of the detector on the light source are met;
(2) the optical path transmission module, the attenuation module and the standard power meter ensure the calibration precision of the system, and the simultaneous calibration of a plurality of detectors is realized by using the optical fiber beam splitter, so that the structure of the system is simplified, and the calibration efficiency is improved;
(3) the calibration system of the spaceborne laser radar detector based on the integrating sphere and the narrow pulse laser has the advantages of ideal effect, stable performance, high calibration precision, simple calibration system light path, compact structure and small occupied space, and is the best choice for calibrating the spaceborne laser radar detector.
Drawings
FIG. 1 is a schematic diagram of the calibration of the sensitivity and linearity of a detector according to the present invention;
FIG. 2 is a schematic diagram of the calibration of the time response of the detector of the present invention;
FIG. 3 is a linearity plot of a detector;
Detailed Description
The device for calibrating the sensitivity and the linearity of the satellite-borne laser radar detector by using the integrating sphere is shown in figure 1, and the device for calibrating the time response of the satellite-borne laser radar detector by using the ns-level narrow-linewidth laser is shown in figure 2.
The above calibration procedures are described in detail below:
● calibration of sensitivity and linearity of space-borne laser radar detector by integrating sphere
Sensitivity is an important measure of the extreme detection capability of a detector for weak signals, defined as the lowest detectable optical power. The sensitivity of the detector is mainly determined by the responsivity and the noise of the detector, and the higher the responsivity or the lower the noise, the higher the sensitivity of the detector. Since the noise of the detector is bandwidth dependent, the detector should operate at the operating bandwidth of the lidar system during sensitivity calibration. Or by measuring noise equivalenceThe power NEP is measured, and is defined as the radiation power of the signal light incident on the detector when the signal root mean square voltage generated by the signal light on the detector is equal to the noise root mean square voltage value of the detector (i.e. the signal-to-noise ratio is 1), and the radiation power is measured in W/Hz1/2The calculation formula is as follows:
NEP＝N/(RΔf1/2)
n is noise in units of V, R is responsivity in units of V/W, and Δ f is the measurement bandwidth of the noise in units of Hz.
Linearity refers to the degree of linearity between the detector response and the input power, responsivity (response curve slope), and linear response range. The detector response rate decreases after a period of detector use, as shown in fig. 3, wherein the horizontal axis represents the intensity of the optical power incident on the detector, the vertical axis represents the detector response voltage, the solid line represents the initial response curve of the detector, and the dotted line represents the response curve of the detector after a period of detector use. Taking these factors into account requires that the responsivity calibration be performed at the beginning of use and after a period of use of the detector so that the detector can accurately measure the intensity of the incident signal light. The linear response region of the detector is generally used for detection, so the degree of response linearity and the linear response range of the detector need to be calibrated.
The device for calibrating the sensitivity and the linearity of the satellite-borne laser radar detector by using the integrating sphere is composed of a light source module, a light transmission module, an attenuation module and a detector module (as shown in figure 1); the light source module consists of an LED and an integrating sphere, the LED can output light with lower intensity, stable work and easily-adjusted intensity, the LED is arranged at the entrance of the integrating sphere, and the integrating sphere converts the light output by the LED into light irrelevant to the angle; the optical transmission module is respectively composed of a coupling lens, a multimode optical fiber, a beam splitter, a collimating mirror, an optical filter and a variable total reflector, light output by the integrating sphere is coupled into the optical fiber by the coupling lens and transmitted, the light is collimated by the collimating mirror after being output by the multimode optical fiber, and enters the detector to be calibrated after sequentially passing through the beam splitter, the optical filter, the variable total reflector and the attenuation sheet. The beam splitter is used at the dotted line arrow in the figure to finish the simultaneous calibration of a plurality of detectors, and a variable total reflection mirror and a standard power meter are used in the system to accurately measure and predict the light intensity incident to the detectors; the attenuation module consists of a plurality of attenuation sheets with different attenuation coefficients, and ensures that the light intensity and the light intensity range input to the detector meet the calibration requirement; the detector module comprises a detector to be calibrated and a standard power meter, and the standard power meter is used for accurately measuring the intensity of the calibration light; the detector calibration device is built in a black box which has good external light shielding effect, so that the interference of ambient stray light is avoided, and the black box is provided with an opening to facilitate some simple operations in the test process.
Because the precision requirement on the intensity of light input into the detector is extremely high in the calibration, the transmission efficiency of each element in the system needs to be calibrated in advance, and the transmission efficiency formula of the integrating sphere is as follows:
wherein A isfiberIs the coupling lens area of the optical fiber, Aspρ is the inner surface reflectivity of the integrating sphere, f is the aperture ratio of the integrating sphere, and n is the coupling efficiency of the coupling lens.
● calibrating the time response of a space-borne lidar Detector with a laser
For the detector device, the response time is defined as the time required for the output signal to rise to 63% of a stable value when the detector is irradiated; for a fast response detection device such as an Avalanche Photo Diode (APD) or photodiode, the response time is the time required to rise from 10% of a stable value to 90% of the stable value. The rise time of the detector is ns magnitude, a light source with ultra-fast response time is needed for accurately measuring the time response of the detector, the rise time of the LED is long and cannot meet the measurement requirement, the laser can generate narrow pulses with ns magnitude width, the time response information of the detector can be conveniently extracted, and the calibration of the time response of the detector is realized.
The calibration system of the detector time response is shown in fig. 2, the light source module uses a narrow pulse laser, a 5% wedge-shaped glass sheet performs preliminary attenuation on strong light generated by the laser, a beam expander is used for expanding a beam, and the system attenuation module and the measurement module are similar to the calibration system of the detector sensitivity and linearity, and are not repeated here.
The invention has not been described in detail in part of the common general knowledge of those skilled in the art.
Claims (3)
1. A calibration system for a satellite-borne laser radar detector is characterized in that: the device comprises a light source module, a light transmission module, an attenuation module and a detector module; the light emitted from the light source module enters the light transmission module, is collimated and filtered in the light transmission module, is attenuated by the attenuation module and then enters the detector module; completing a calibration task in the detector module;
the calibration tasks comprise the calibration of sensitivity and linearity and the calibration of time response;
when the calibration task of time response is finished, the light source module is a narrow pulse laser; when the calibration tasks of sensitivity and linearity are completed, the light source module comprises an LED and an integrating sphere, the LED is arranged at the entrance of the integrating sphere, and the integrating sphere converts the light output by the LED into light irrelevant to the angle;
the attenuation module comprises a plurality of attenuation sheets with different attenuation coefficients and is used for ensuring that the light intensity and the light intensity range input to the detector meet the calibration requirement;
the attenuation sheet is a 5% wedge-shaped glass sheet;
the optical transmission module comprises a coupling lens, a multimode optical fiber, a beam splitter, a collimating mirror, an optical filter and a variable total reflector; the coupling lens couples light into the multimode optical fiber, the light is split into multiple paths by the beam splitter after being transmitted by the multimode optical fiber, and the light of each path is reflected by the variable total reflector to enter the detector after being collimated by the collimating mirror and filtered by the optical filter.
2. The system for calibrating the spaceborne lidar detector of claim 1, wherein: the detector module comprises a detector to be calibrated and a power meter; in the calibration, the variable total reflection mirror and the power meter are used for measuring the light intensity entering the detector, and the beam splitter is used for splitting the light path to realize the simultaneous calibration of a plurality of detectors.
3. The system according to claim 2, wherein: the detector to be calibrated is built in a black box, and the black box is provided with a notch.
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| CN110231610B (en) * | 2019-05-24 | 2022-12-02 | 武汉大学 | Detection calibration platform and method for active light spot energy detector of satellite-borne laser altimeter |
| CN111238775A (en) * | 2020-03-11 | 2020-06-05 | 中国工程物理研究院激光聚变研究中心 | Three-dimensional distribution measuring device for scattering power of photonic crystal fiber |
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| CN102508225B (en) * | 2011-10-27 | 2014-05-07 | 西安理工大学 | Double-shaft laser remote sensing instrument ground detection and calibration system and detection and calibration method |
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