Background flash interference elimination method for laser alarm device

Abstract

The invention discloses a background flash interference elimination method for a laser alarm device, and the method comprises the steps: detecting an optical signal through a photoelectric detector at the most front end of each channel of the laser alarm device, converting the detected optical signal into an electric signal, and inputting the electric signal into a pulse processing branch and a beam driving processing branch in each channel; the output of the pulse laser processing branch circuit and the output of the beam driving laser processing branch circuit are transmitted to the FPGA, the FPGA samples the signals, the sampling information is transmitted to the MCU in an interruption form, and finally, the MCU compares and judges the time difference of two paths of signals in each channel with a threshold value one by one, identifies flash interference signals and filters the flash interference signals.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic countermeasures technology, and more specifically, relates to a method for eliminating background flash interference in laser warning devices. Background Technology

[0002] With the widespread application of laser ranging and laser guidance technologies in the military field, modern warfare has placed higher demands on optoelectronic countermeasures. To detect incoming laser signals and their characteristics, laser warning devices have received increasing attention and are being extensively developed. The use of laser warning devices greatly enhances the optoelectronic countermeasures capabilities of individual combat units or combat groups. Spectral non-imaging laser warning devices are widely used on various weapon platforms due to their simple principles, mature technology, and low cost. Generally, spectral non-imaging laser warning devices are designed to have a large field of view, high sensitivity, and a wide dynamic range, and to be able to warn of narrow-pulse lasers with wavelengths of 0.98μm, 1.06μm, and 1.5Xμm. In modern warfare, laser warning devices need to operate in complex environments with background flash interference. The main sources of background flash interference are sunlight, various flashes (such as the flashes emitted by gas strobe lights used for highway traffic control and license plate recognition), and muzzle flashes generated by fire attacks from the platform on which the laser warning device is located.

[0003] Because the spectral range of background flashes is very wide and may include the alarm wavelength range of laser alarm devices, especially when the background flash energy is strong or the effective distance is short, the optical power density within the alarm wavelength range of the laser alarm device may exceed its lower limit of detection power density, thus causing false alarms. Therefore, effective measures must be taken to suppress background flash interference, thereby reducing the occurrence of false alarms by laser alarm devices and minimizing the possibility of adverse consequences.

[0004] Background flashes, such as those produced by gas strobe lights used for supplementary lighting in highway traffic control and license plate recognition systems, have strong signal energy, a wide spectral range, and complex frequency variations. These flashes overlap with the alarm spectral range of laser warning devices, and the optical power density generated within the alarm wavelength range can easily exceed the lower limit of the laser warning device's detection power density, causing false alarms. Conventional methods such as bandpass filtering, circuit filtering, and comparator threshold limiting are insufficient to effectively eliminate the interference caused by these background flashes.

[0005] Traditional methods typically involve comparing background flashes with the pulsed laser signal requiring alarm input from different angles to identify differences and find solutions. Background flash interference is eliminated using a time-based discrimination method. The incident pulsed laser signal is on the order of nanoseconds, while strong ambient background flashes are usually on the order of microseconds or even milliseconds. The duration T of the comparator output signal corresponding to the incident light is the sum of the photodetector integration delay T1 and the signal processing circuit's delay time T2 on the input electrical signal. Therefore, distinguishing between the two signals by the difference in delay time in the alarm device's signal circuit is a logical approach.

[0006] However, since the signal intensity and pulse width of the background flash vary greatly with distance, and in order to ensure that the laser alarm device has key technical indicators such as high sensitivity and wide dynamic range, there is no significant difference in the time T between the two in practice.

[0007] In summary, it is essential to conduct in-depth research on methods for eliminating background flash interference in laser alarm devices. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for eliminating background flash interference in a laser alarm device. Without significantly increasing the complexity of the circuit and manufacturing costs, the method uses the difference in response time of the beam-driving processing branch and the pulse processing branch to the same input signal to distinguish between pulsed laser and background flash, thereby extracting the real pulsed laser and filtering out the background flash.

[0009] To achieve the above-mentioned objective, the present invention provides a method for eliminating background flash interference in a laser alarm device, characterized by comprising the following steps:

[0010] (1) The photodetector at the front end of each channel of the laser alarm device detects the light signal, converts the detected light signal into an electrical signal, and then inputs the electrical signal into the pulse processing branch and the beam driving processing branch in each channel.

[0011] (2) The pulse processing branch amplifies the input electrical signal through an amplifier circuit consisting of a first-stage operational amplifier, and then outputs a low-level signal through a comparator. The falling edge of the low-level signal is the arrival time t of the electrical signal, and the duration of the low level is the pulse width of the optical signal.

[0012] (3) The beam-driving branch amplifies the input electrical signal through an amplifier circuit consisting of two operational amplifiers, and then outputs a low-level signal through a comparator. The falling edge time is the signal arrival time s, and the duration of the low level is the optical signal pulse width.

[0013] (4) The FPGA processes the low-level signals output by each channel;

[0014] (4.1) The FPGA samples the low-level signals output from the pulse processing branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the pulse processing branch within each channel. Total number of channels;

[0015] (4.2) The FPGA samples the low-level signals output from the beam-driving processing branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the branch circuit of the driving beam processing within each channel. Total number of channels;

[0016] (4.3) For each channel, the difference between the two sets of sampled values ​​is calculated by subtracting them one by one according to the corresponding channel number. ;

[0017] (4.4) The FPGA determines whether the optical signal is a pulsed laser based on the pulse width of the optical signal. If the pulse width of the optical signal is less than the threshold, the optical signal is determined to be a real pulsed laser, and a pulse interruption is generated. At the same time, the time difference Send to the MCU; otherwise, determine the optical signal as a flash interference signal.

[0018] And generate a pulse interrupt IRQ MC The difference is then sent to the MCU via an interrupt.

[0019] (5) MCU receives interrupt signal IRQ MC Extract the time difference T of each channel signal diff ;

[0020] (6) Using different laser rangefinders at different distances as light sources, repeat steps (1) to (5) to measure the time difference when the pulsed laser is used as the light source;

[0021] (7) Using different flashes as light sources, repeat steps (1) to (5) at different distances and power levels, and measure the time difference when the flash is used as a light source;

[0022] (8) Based on the time difference values ​​of different light sources measured in steps (6) and (7), set the time difference threshold value TH;

[0023] (9) Process the light signal actually detected by the laser alarm device according to steps (1) to (5), and then compare the difference of each channel with the threshold value one by one. If it is less than the threshold value TH, it is judged as a laser pulse signal; otherwise, it is judged as a flash interference signal. Then generate an interference signal flag and filter out the flash interference signal of the channel.

[0024] The objective of this invention is achieved as follows:

[0025] This invention discloses a method for eliminating background flash interference in a laser alarm device. The method involves using a photodetector at the front end of each channel of the laser alarm device to detect light signals, converting the detected light signals into electrical signals, and then inputting the electrical signals to the pulse processing branch and the beam-riding processing branch within each channel. The outputs of the pulse laser processing branch and the beam-riding laser processing branch are sent to an FPGA, where the FPGA samples the signals. The sampled information is sent to an MCU in the form of an interrupt. Finally, the MCU compares the time difference between the two signals in each channel with a threshold value to identify and filter out the flash interference signals.

[0026] Meanwhile, the method for eliminating background flash interference in a laser alarm device according to the present invention also has the following beneficial effects:

[0027] (1) The present invention makes full use of the design of pulse processing branch and beam driving branch without adding extra circuits and components. Then, the time difference information is extracted and processed by FPGA and MCU, thereby increasing the information dimension and providing support for further judgment.

[0028] (2) The laser alarm device fully utilizes the different responses of the processing circuits of the two different laser signals to the laser pulse signal and the background flash signal to extract additional time difference information. Then, the laser pulse signal and the background flash signal are distinguished by using this information. Most of the background flash signals can be distinguished and filtered out by this method. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a laser alarm device.

[0030] Figure 2 This is a flowchart of a method for eliminating background flash interference in a laser alarm device according to the present invention.

[0031] Figure 3 This is a response diagram of the two branches to the laser pulse signal, acquired using an oscilloscope. Detailed Implementation

[0032] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0033] Example

[0034] In this embodiment, as Figure 1 As shown, according to the design requirements of the laser alarm device, it needs to be able to detect both pulsed lasers and beam-riding lasers. A pulsed laser refers to a laser that operates in a "pulse" manner, emitting laser light at regular intervals. Each emitted light signal has a very short duration (usually less than 250ms), characterized by the concentrated release of energy in a very short time, thus possessing high peak power and energy density. A continuous wave laser refers to a laser that continuously outputs laser light without interruption in time, maintaining a relatively stable output power. Therefore, for a photodetector output, two circuits are connected: a pulsed laser processing branch and a beam-riding laser processing branch. The outputs of both circuits are sent to an FPGA, where the FPGA samples the signal. The sampled information is then sent to the MCU in the form of an interrupt for subsequent signal processing.

[0035] Below we combine Figure 1 This invention provides a detailed description of a method for eliminating background flash interference in a laser alarm device, as follows: Figure 2 As shown, the specific steps include:

[0036] (1) The photodetector at the front end of each channel of the laser alarm device detects the light signal, converts the detected light signal into an electrical signal, and then inputs the electrical signal into the pulse processing branch and the beam driving processing branch in each channel.

[0037] In this embodiment, each channel has an InGaAs photodetector at its front end, which converts optical signals within a certain wavelength range (900nm~1700nm for InGaAs photodetectors) into electrical signals. For both pulsed laser and background flash in the input response band, the laser alarm device's processing circuits will respond; therefore, it is necessary to find the time difference T between the pulsed laser and the background flash. diff The differences are then used to distinguish them;

[0038] (2) The pulse processing branch amplifies the input electrical signal through an amplifier circuit consisting of a first-stage operational amplifier, and then outputs a low-level signal through a comparator. The falling edge of the low-level signal is the arrival time t of the electrical signal, and the duration of the low level is the pulse width of the optical signal.

[0039] (3) The beam-driving branch amplifies the input electrical signal through an amplifier circuit consisting of two operational amplifiers, and then outputs a low-level signal through a comparator. The falling edge time is the signal arrival time s, and the duration of the low level is the optical signal pulse width.

[0040] In this embodiment, when the InGaAs photodetector detects a light signal, the pulse processing branch outputs a low-level signal, with its falling edge occurring at the signal arrival time t, and the low-level duration equal to the laser signal pulse width. Simultaneously, the beam-riding laser processing branch also outputs a low-level signal, with its falling edge occurring at the signal arrival time s, and the low-level duration equal to the laser signal pulse width. Figure 3 As shown.

[0041] (4) The FPGA processes the low-level signals output by each channel;

[0042] (4.1) The FPGA samples the low-level signals output from the pulse processing branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the pulse processing branch within each channel. Total number of channels;

[0043] (4.2) The FPGA samples the low-level signals output from the beam-driving processing branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the branch circuit of the driving beam processing within each channel. Total number of channels;

[0044] (4.3) For each channel, the difference between the two sets of sampled values ​​is calculated by subtracting them one by one according to the corresponding channel number. ;

[0045] (4.4) Typically, beam-driven lasers are continuous lasers with pulse widths ranging from tens to hundreds of microseconds, while pulsed lasers generally have pulse widths of 5 ns to 20 ns. The FPGA determines whether the optical signal is a pulsed laser based on its pulse width. If the pulse width is less than a threshold (the threshold is set to 4000), the optical signal is determined to be a real pulsed laser, and a pulse interruption is generated. At the same time, the time difference Send to the MCU; otherwise, determine the optical signal as a flash interference signal.

[0046] (5) MCU receives interrupt signal IRQ MC Extract the time difference of signals from each channel. ;

[0047] (6) Using different laser rangefinders at different distances as light sources, repeat steps (1) to (5) to measure the time difference when the pulsed laser is used as the light source;

[0048] In this embodiment, different laser rangefinders were used at different distances as light sources to measure the time difference when pulsed laser light was used as the light source, as shown in Table 1.

[0049] Table 1. Time differences measured by different laser rangefinders;

[0050]

[0051]

[0052] Table 1

[0053] (7) Using different flashes as light sources, repeat steps (1) to (5) at different distances and power levels, and measure the time difference when the flash is used as a light source;

[0054] 1) In this embodiment, different flash lamps are used as light sources, and different power is output at different distances (such as the flash lamp S1 in typical working mode, the power output is 1 / 1, 1 / 2, 1 / 4, 1 / 8, 1 / 16, 1 / 32, 1 / 64, 1 / 128 of the maximum power in sequence), and the time difference when the flash is used as a light source is measured.

[0055] Table 2. Time differences measured at different distances and powers of the flash;

[0056]

[0057]

[0058] Table 2

[0059] (8) Due to the complexity of the background flash, it is necessary to collect the time difference between the background flash with various intensities and distances and various different rangefinders, and find a reasonable threshold value to distinguish the two different incident lights. Therefore, based on the time difference values ​​of different light sources measured in steps (6) and (7), a reasonable time difference threshold value TH can be set to better distinguish the above-mentioned different light sources. In this embodiment, in conjunction with Table 1 and Table 2, the value range of TH is set to 3500~4500. In this embodiment, the average value of 4000 is taken as the threshold value.

[0060] (9) Process the light signal actually detected by the laser alarm device according to steps (1) to (5), and then compare the difference of each channel with the threshold value one by one. If it is less than the threshold value TH, it is judged as a laser pulse signal; otherwise, it is judged as a flash interference signal. Then generate an interference signal flag and filter out the flash interference signal of the channel.

[0061] In this embodiment, the width of the optical signal itself, i.e., the pulse width, is proportional to the energy of the incident light. If a threshold is set for the pulse width to differentiate according to the traditional method, it will greatly affect the dynamic range index of the device. However, by adopting the above method, false alarms caused by background flash can be effectively suppressed without affecting the dynamic range index of the device.

[0062] In summary, the most significant feature of this invention is that it fully utilizes the different responses of the laser alarm device's processing circuits to laser pulse signals and background flash signals to two different laser signals, extracts additional time difference information, and then uses this information to distinguish between laser pulse signals and background flash signals. This method can distinguish and filter out most of the background flash signals.

[0063] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A method for eliminating background flash interference in a laser alarm device, characterized in that, Includes the following steps: (1) The photodetector at the front end of each channel of the laser alarm device detects the light signal, converts the detected light signal into an electrical signal, and then inputs the electrical signal into the pulse processing branch and the beam driving processing branch in each channel. (2) The pulse processing branch amplifies the input electrical signal through an amplifier circuit consisting of a first-stage operational amplifier, and then outputs a low-level signal through a comparator. The falling edge of the low-level signal is the arrival time t of the electrical signal, and the duration of the low level is the pulse width of the optical signal. (3) The beam-driving branch amplifies the input electrical signal through an amplifier circuit consisting of two operational amplifiers, and then outputs a low-level signal through a comparator. The falling edge time is the signal arrival time s, and the duration of the low level is the optical signal pulse width. (4) The FPGA processes the low-level signals output by each channel; (4.1) The FPGA samples the low-level signals output from the pulse processing branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the pulse processing branch within each channel. Total number of channels; (4.2) The FPGA samples the low-level signals output from the beam-driving branch in each channel and records the arrival time of the electrical signals in each channel, denoted as . , Indicates the first The arrival time of electrical signals in the branch circuit of the driving beam processing within each channel. Total number of channels; (4.3) For each channel, the difference between the two sets of sampled values ​​is calculated by subtracting them one by one according to the corresponding channel number. ; (4.4) The FPGA determines whether the optical signal is a pulsed laser based on the pulse width of the optical signal. If the pulse width of the optical signal is less than the threshold, the optical signal is determined to be a pulsed laser, and a pulse interrupt is generated. At the same time, the time difference Send to the MCU; otherwise, determine the optical signal as a flash interference signal. (5) MCU receives interrupt signal IRQ MC Extract the time difference T of each channel signal diff ; (6) Using different laser rangefinders at different distances as light sources, repeat steps (1) to (5) to measure the time difference when the pulsed laser is used as the light source; (7) Using different flashes as light sources, repeat steps (1) to (5) at different distances and power levels, and measure the time difference when the flash is used as a light source; (8) Based on the time difference values ​​of different light sources measured in steps (6) and (7), set the time difference threshold value TH; (9) Process the light signal actually detected by the laser alarm device according to steps (1) to (5), and then compare the difference of each channel with the threshold value one by one. If it is less than the threshold value TH, it is judged as a laser pulse signal; otherwise, it is judged as a flash interference signal. Then generate an interference signal flag and filter out the flash interference signal of the channel.

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