A continuous weak laser power measurement device based on photodiode

Abstract

This invention discloses a continuous weak laser power measurement device based on a photodiode. The structure is as follows: continuous laser light emitted by a continuous laser is converted into pulsed laser light by a chopper; the pulsed laser light is converted into a pulsed current signal by a photodiode; the pulsed current signal is converted into a pulsed voltage signal by an I / V conversion circuit; the pulsed voltage signal is blocked by a DC blocking circuit to remove the DC component; a central processing unit controls a programmable amplifier circuit to amplify the pulsed voltage signal to a voltage suitable for acquisition by an analog-to-digital converter circuit; finally, the central processing unit calibrates the digital signal acquired by the analog-to-digital converter circuit and sends it to a display module for display. This invention improves the dynamic range and measurement uncertainty of continuous weak laser power measurement and eliminates the need for subsequent "zeroing" operations.

Description

Technical Field

[0001] This invention belongs to the field of laser power measurement technology and relates to a continuous weak laser power measurement device for photodiodes. This device can reduce the influence of dark current of photodiodes and stray light from the external environment on the weak laser power measurement results. Background Technology

[0002] With the continuous development of science and technology, laser technology based on lasers has developed rapidly and is now widely used in various fields such as industrial production, communications, information processing, medical and health care, military, culture and education, and scientific research. Correspondingly, the measurement of laser parameters has become particularly important. Laser power is a crucial parameter of a laser, determining its applicable fields and scope. When measuring the power of continuous weak lasers, large-area photodiodes with short response time, good linearity, high sensitivity, and stable performance are mainly used as detectors in laser power meters. Accurate measurement of the power of continuous weak lasers using photodiodes has become an important task.

[0003] Currently, most laser power meters using photodiodes employ an operational amplifier with low offset current to programmatically amplify the current generated by the photodiode based on the intensity of the input laser power. The collected voltage data is then calibrated and displayed via an analog-to-digital converter. During use, a "zeroing" process is performed first, followed by power measurement. This method offers high accuracy for measuring continuous laser power in the microwatt to milliwatt range. However, when measuring nanowatt-level continuous laser power, the signal current generated by the photoelectric conversion of the photodiode is often in the nanoampere range, and the dark current of large-area photodiodes is also in the nanoampere range (the dark current of InGaAs photodiodes can reach the microampere range). This results in a small dynamic range and poor measurement uncertainty when measuring weak laser power. Furthermore, due to variations in the photodiode's dark current and stray light from the external environment, multiple "zeroing" adjustments are required during use to minimize the impact of these variations on the measurement results. Summary of the Invention

[0004] (I) Purpose of the Invention

[0005] The purpose of this invention is to provide a continuous weak laser power measurement device based on a photodiode, which overcomes the shortcomings of laser power meters that generally use photodiodes, such as small dynamic range, poor measurement uncertainty, and the need for multiple "zeroing" adjustments during use.

[0006] (II) Technical Solution

[0007] To address the aforementioned technical problems, this invention provides a continuous weak laser power measurement device based on a photodiode. The device comprises a chopper, a photodiode, an I / V conversion circuit, a DC blocking circuit, a programmable amplifier circuit, an analog-to-digital converter circuit, a central processing unit (CPU), and a display module, connected in sequence. The CPU is connected to the programmable amplifier circuit. Continuous laser light emitted by the continuous laser is converted into pulsed laser light by the chopper. The pulsed laser light is then converted into a pulsed current signal by the photodiode. The pulsed current signal is converted into a pulsed voltage signal by the I / V conversion circuit. The pulsed voltage signal is then blocked by the DC blocking circuit to remove the DC component. The CPU controls the programmable amplifier circuit to select different levels to amplify the pulsed voltage signal to a voltage suitable for acquisition by the analog-to-digital converter circuit. Finally, the CPU calibrates the digital signal acquired by the analog-to-digital converter circuit and sends it to the display module for display.

[0008] (III) Beneficial Effects

[0009] The photodiode-based continuous weak laser power measurement device provided by the above technical solution uses a chopper to chop the continuous weak laser signal and filters out the dark current of the photodiode and stray light signals from the external environment through a DC blocking circuit, thereby improving the dynamic range and measurement uncertainty of continuous weak laser power measurement and eliminating the need for "zeroing" operation in subsequent use. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the principle of the continuous weak laser power measurement device based on photodiode of the present invention.

[0011] Figure 2 This invention requires the measurement of continuous, weak laser signals for power.

[0012] Figure 3 It is the pulsed laser signal obtained by chopping the continuous weak laser signal of the present invention through a chopper.

[0013] Figure 4 This is the stray light signal from the external environment of the present invention.

[0014] Figure 5 It is the optical signal resulting from the superposition of the pulsed laser signal output by the chopper of this invention and the stray light signal from the external environment.

[0015] Figure 6 This is the dark current signal of the photodiode in this invention.

[0016] Figure 7 This is the voltage signal after I / V conversion according to the present invention.

[0017] Figure 8 This is the voltage signal after passing through the DC blocking circuit of this invention.

[0018] Figure 9 It is the voltage signal after programmable amplification according to the present invention.

[0019] Figure 10 This is a flowchart of the central processing unit controlling the programmable amplifier circuit of the present invention. Detailed Implementation

[0020] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0021] like Figure 1 As shown, the continuous weak laser power measurement device based on photodiode in this embodiment includes a chopper, a photodiode, an I / V conversion circuit, a DC blocking circuit, a programmable amplifier circuit, an analog-to-digital converter circuit, a central processing unit, and a display module connected in sequence. The central processing unit is connected to the programmable amplifier circuit. The continuous laser emitted by the continuous laser is converted into pulsed laser by the chopper. The pulsed laser is converted into a pulsed current signal by the photodiode. The pulsed current signal is converted into a pulsed voltage signal by the I / V conversion circuit. The pulsed voltage signal is blocked by the DC blocking circuit to remove the DC component from the signal. The central processing unit controls the programmable amplifier circuit to select different levels to amplify the pulsed voltage signal to a voltage suitable for acquisition by the analog-to-digital converter circuit. Finally, the central processing unit calibrates the digital signal acquired by the analog-to-digital converter circuit and sends it to the display module for display.

[0022] When measuring the power of a continuous weak laser signal, a continuous weak laser signal is emitted by a continuous laser, such as... Figure 2 As shown, optical signals are represented by dashed lines, and electrical signals are represented by solid lines.

[0023] A continuous laser signal is converted into a pulsed laser signal after passing through a chopper. The amplitude of the chopped pulsed laser signal is the same as that of the continuous laser signal entering the chopper. Figure 3 As shown.

[0024] In the process of power measurement, the continuous weak laser power measurement device of the photodiode will inevitably introduce stray light signals from the external environment. These stray light signals change very little in a short time and can be considered to have a constant value with a certain intensity. For example, the stray light signals from the external environment... Figure 4 As shown.

[0025] The pulsed laser signal output from the chopper is superimposed with stray light signals from the external environment and then enters the photodiode. The superposition of the chopper-output pulsed laser signal and the stray light signals from the external environment results in a pulsed light signal with a certain basis, such as... Figure 5 As shown.

[0026] Laser power meters that use photodiodes as detectors typically employ photodiodes with large photosensitive areas. Large photosensitive photodiodes also have large dark currents. Although the dark current of a photodiode changes with reverse voltage and temperature, the change is very small over a short period and can be considered a constant value. The dark current of a photodiode is as follows: Figure 6 As shown.

[0027] The pulsed laser signal output from the chopper and the stray light signal from the external environment are superimposed and converted into a pulsed current signal with a certain basis by a photodiode. This current signal is superimposed with the dark current of the photodiode and then converted into a pulsed voltage signal with a larger basis by an I / V conversion circuit. The I / V conversion circuit is implemented using an operational amplifier with small bias current and offset current. The converted pulsed voltage signal with a larger basis is as follows: Figure 7 As shown.

[0028] The pulse voltage signal with a large base value output from the I / V conversion circuit includes the voltage signal converted from the measured laser signal after chopping, as well as the voltage signals converted from external stray light signals and the dark current signal of the photodiode. The measured laser signal after chopping is converted into a periodic pulse voltage signal, while the external stray light signal and the dark current signal of the photodiode are converted into a large base voltage signal (which can be considered a constant value for a short period of time). After the superimposed pulse voltage signal with a large base value passes through a DC blocking circuit (the DC blocking circuit is implemented using a capacitor, the size of which depends on the chopping frequency of the chopper, aiming to minimize the distortion of the pulse voltage signal converted from the measured laser signal after chopping), the periodic pulse voltage signal converted from the measured laser signal after chopping is retained, while the large base voltage signal converted from the external stray light signal and the dark current signal of the photodiode is filtered out. The voltage signal after DC blocking is as follows: Figure 8 As shown.

[0029] The voltage signal after DC blocking retains only the periodic pulse voltage signal converted from the measured laser signal after chopping, resulting in a small voltage amplitude. After being processed by a programmable amplifier circuit (using an operational amplifier with low offset voltage), it is converted to an amplitude suitable for sampling by an analog-to-digital converter circuit (using an analog-to-digital converter chip capable of sampling both positive and negative levels). The signal entering the analog-to-digital converter circuit after programmable amplification is a periodic pulse voltage signal with a larger voltage amplitude, such as... Figure 9 As shown, the central processing unit finally adds the absolute values ​​of the positive and negative levels of the pulse voltage signals with large voltage amplitudes acquired by the analog-to-digital converter circuit to obtain the voltage value of the continuous laser under test after the above processing. The accurate power value of the continuous laser under test can be obtained by calibrating with this voltage value.

[0030] The central processing unit controls the programmable amplifier circuit according to Figure 10 The work is carried out according to the process.

[0031] The first step is for the central processing unit to acquire the positive voltage signal converted from the measured laser signal after it has been chopped by the chopper, and then proceed to the next step.

[0032] The second step is to determine whether the acquired positive voltage signal has reached the upper limit of the positive voltage of the analog-to-digital conversion circuit. If it has not reached the upper limit, proceed to the next step. If it has reached the upper limit, it is considered that the current amplification factor is too large, so the amplification factor is reduced by 1 level, and the process returns to the first step.

[0033] The third step involves the central processing unit acquiring the negative voltage signal converted from the measured laser signal after chopping by the chopper, and then proceeding to the next step.

[0034] The fourth step is to determine whether the acquired negative voltage signal has reached the upper limit of the negative voltage of the analog-to-digital conversion circuit. If it has not reached the upper limit, proceed to the next step. If it has reached the upper limit, it is considered that the current amplification factor is too large, so the amplification factor is reduced by 1 level, and the process returns to the first step.

[0035] The fifth step is to sum the absolute values ​​of the collected positive and negative voltage levels, and then proceed to the next step.

[0036] Step 6: Determine if the sum is greater than 1 / 10 of the sum of the absolute values ​​of the positive and negative voltages of the analog-to-digital converter circuit (the amplification factor of adjacent levels in the programmable circuit is generally 10 times). If it is greater, the current amplification factor is considered appropriate, and proceed to the next step. If it is not greater, the current amplification factor is considered too small, the amplification factor is increased by 1 level, and return to step 1.

[0037] Step 7: Output the current voltage value and proceed to the next step.

[0038] Step 8: Jump back to step 1 and repeat steps 1 through 7.

[0039] As can be seen from the above technical solution, this invention converts a continuous weak laser signal into a pulsed laser signal using a chopper, then converts the pulsed laser signal into a pulsed electrical signal using a photodiode, and filters out the dark current of the photodiode and stray light signals from the external environment using a DC blocking circuit. The resulting pulsed electrical signal is then amplified under controlled programming, sampled and calibrated using an analog-to-digital converter and a central processing unit, and finally displayed using a display module. This device improves the dynamic range and measurement uncertainty of the laser power meter when measuring weak laser power, and eliminates the need for subsequent "zeroing" operations.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A photodiode-based continuous weak laser power measurement device, characterized by, The continuous laser emitted by the continuous laser is converted into pulsed laser by the chopper, the pulsed laser is converted into pulsed current signal by the photodiode, the pulsed current signal is converted into pulsed voltage signal by the I / V conversion circuit, the pulsed voltage signal is removed of direct current component by the direct current removal circuit, the central processing unit controls the program-controlled amplification circuit to select different gears to amplify the pulsed voltage signal to a voltage suitable for the analog / digital conversion circuit to collect, and finally the central processing unit sends the digital signal collected by the analog / digital conversion circuit to the display module after calibration for display.

2. The photodiode-based continuous weak laser power measurement apparatus of claim 1, wherein, The pulsed laser signal after chopping has the same amplitude as the continuous laser signal entering the chopper.

3. The photodiode-based continuous weak laser power measurement apparatus of claim 2, wherein, The pulsed laser signal output by the chopper and the external environment stray light signal are superimposed together into the photodiode, and the superimposed pulsed light signal with a base value is obtained.

4. The photodiode-based continuous weak laser power measurement apparatus of claim 3, wherein, The light signal after superimposition of the pulsed laser signal output by the chopper and the external environment stray light signal is converted into a pulsed current signal with a base value by the photodiode, the current signal is superimposed with the dark current of the photodiode, and the pulsed voltage signal with a base value is obtained by the I / V conversion circuit, the base value of the pulsed voltage signal is greater than the base value of the pulsed current signal, and the I / V conversion circuit is implemented by using an operational amplifier.

5. The photodiode-based continuous weak laser power measurement apparatus of claim 4, wherein, The measured laser signal after chopping by the chopper is converted into a periodic pulsed voltage signal.

6. The photodiode-based continuous weak laser power measurement apparatus of claim 5, wherein, The direct current removal circuit is implemented by using a capacitor, the size of the capacitor depends on the chopping frequency of the chopper, and the distortion of the pulsed voltage signal converted by the measured laser signal after chopping by the chopper is minimized through the direct current removal capacitor.

7. The photodiode-based continuous weak laser power measurement apparatus of claim 6, wherein, The analog / digital conversion circuit selects an analog / digital conversion chip with positive and negative level sampling.

8. The photodiode-based continuous weak laser power measurement apparatus of claim 7, wherein, The central processing unit adds the absolute values of the positive and negative levels of the pulsed voltage signal collected by the analog / digital conversion circuit to obtain the voltage value of the measured continuous laser after the above processing, and the accurate power value of the measured continuous laser is obtained by calibrating the voltage value.

9. The photodiode-based continuous weak laser power measurement apparatus of claim 8, wherein, The working process of the program-controlled amplification circuit controlled by the central processing unit is as follows: First, the central processing unit collects the positive voltage signal converted by the measured laser signal after chopping by the chopper; Second, it is judged whether the collected positive voltage signal reaches the upper limit of the positive voltage of the analog / digital conversion circuit, if not, it goes to the next step, if yes, it is considered that the current amplification factor is too large, and the amplification factor is reduced by one gear, and it returns to the first step; Third, the central processing unit collects the negative voltage signal converted by the measured laser signal after chopping by the chopper; Fourth, it is judged whether the collected negative voltage signal reaches the upper limit of the negative voltage of the analog / digital conversion circuit, if not, it goes to the next step, if yes, it is considered that the current amplification factor is too large, and the amplification factor is reduced by one gear, and it returns to the first step; Fifth, the absolute values of the collected positive and negative level voltages are summed. In the sixth step, it is judged whether the obtained sum is greater than 1 / 10 of the sum of the absolute values of the positive voltage and the negative voltage of the analog-to-digital conversion circuit. If it is greater, it is considered that the current amplification factor is appropriate, and the next step is entered. If it is not greater, it is considered that the current amplification factor is too small, and the amplification factor is increased by one level, and the first step is returned to. In the seventh step, the current voltage value is output. In the eighth step, the first step is jumped back to, and the first step to the seventh step are repeatedly executed.

10. The use of the photodiode-based continuous weak laser power measurement device according to any one of claims 1-9 in the field of laser power measurement technology.

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