CN102419435B - Optical detection assembly based on all-fiber bias light suppression technology and near-field signal dynamic range suppression technology in laser radar - Google Patents

Abstract

The invention discloses an optical detection assembly based on an all-fiber bias light suppression technology and a near-field signal dynamic range suppression technology in laser radar. The optical detection assembly adopts an FBG (fiber bragg grating) background filter to filter out background noises, and is characterized in that temperature compensation and FBG axial stress control are utilized, so that the peak transmittance position of the FBG background filter is just positioned at the operation wavelength position of the laser radar, the bias light is effectively suppressed, and all-day detection is realized; a light intensity regulator is utilized to regulate the intensity of an optical signal received by the laser radar, and can actively and electrooptically regulate the dynamic range of the signals of the laser radar according to the characteristic of an echoed signal, therefore on the premise of ensuring the maximum signal to noise ratio of a remote signal, near-field signals can be suppressed, the near-field signal saturation of a photodetector can be avoided, the laser emergent power and the echo power of a far-field object are improved, and high-altitude and low-altitude integral detection can be realized; and all-fiber connection is utilized, thus the system operation stability is improved. The optical detection assembly disclosed by the invention has the advantages that the light path cost is greatly lowered, the light path system is simpler, and light path regulation can be carried out conveniently.

Description

An optical detection component for all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar

technical field

The invention relates to laser radar technology, in particular to an optical detection component for suppression of all-fiber background light and near-field signal dynamic range suppression technology in laser radar.

Background technique

Lidar is the product of the combination of traditional radar technology and modern laser technology. With the rapid development of laser technology and the application of advanced signal detection and data acquisition systems, lidar has become an important active remote sensing tool due to its high measurement accuracy, fine time and space resolution, and large detection span. It has shown its unique advantages and development potential in the remote measurement of atmospheric wind field, temperature field, turbulence, atmospheric composition and backscattering coefficient. With the research and application of high-tech equipment, the detection of low-level and even middle-level and upper-level atmospheric parameters is showing an urgent trend. There is a lack of detection data for middle-level and upper-level (20-200km) atmospheric parameters at home and abroad. Lidar is an advanced technology in this detection range. One of the means is the only effective tool that can realize the detection of global atmospheric parameters.

In order to improve the detection height of lidar, under the premise of a certain optical telescope aperture, increasing the transmission power of lidar is one of the effective methods, but the scattering echo in the lower atmosphere is strong, and the detector is easy to saturate, which makes the detection in the lower atmosphere impossible At present, one of the methods to solve this problem is the field-of-view measurement; the other method is the high- and low-altitude layered detection, that is, the atmospheric backscattered light is divided into two beams by using a beam splitter (a weaker beam accounts for the total light). 30% of the light intensity, the stronger beam accounts for 70% of the total light intensity), when detecting the lower atmosphere, let the weaker beam of light enter the low-altitude detector; when detecting the upper atmosphere, let the stronger beam of light enter the high-altitude detector . The disadvantages of these two methods are that the optical path of the receiver is complicated, the cost is high, and the utilization rate of the optical signal is low. Especially when detecting the upper atmosphere, the intensity of the optical signal entering the detector is weakened, which reduces the detection accuracy and altitude. For middle and high-level laser radar atmospheric detection, the echo signal is weak, which belongs to weak signal or even weak signal detection. Background noise reduces the signal-to-noise ratio, and even causes the saturation of the detector, making the laser radar unable to work. Noise reduces the sensitivity of the detector, and filtering background noise is very important for weak signal detection, which has always been a technical difficulty. At present, in LiDAR, most of the background light suppression is realized by space optics, and the space optical path structure has large loss and poor stability.

Contents of the invention

The purpose of the present invention is in order to: 1) adopt FBG background filter to filter out background noise, FBG background filter is a narrow-band, low-loss transmissive filter, the current bandwidth is 0.1nm, peak transmittance reaches 99%, echo signal After the FBG background filter, the transmittance of the optical signal whose center frequency is υ ₀ is 99%, and the optical signals of other frequency bands are filtered out, which effectively suppresses the background light and greatly reduces the cost; The signal intensity is modulated. The light intensity modulator can actively and intelligently electro-optic modulate the dynamic range of the lidar signal according to the characteristics of the echo signal. It can suppress the near-field signal and avoid the photodetector under the premise of ensuring the maximum signal-to-noise ratio of the remote signal. The near-field signal is saturated, the output power of the laser and the echo power of the far-field target are increased, and the integrated detection of high and low altitudes is realized.

To achieve the above object, the present invention adopts technical scheme as follows:

An optical detection component of the all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar, the optical detection component includes a receiving telescope 1, an FBG background filter 2, a light intensity modulator 3, an optical receiver 4, a temperature Controller 5, arbitrary waveform generator 6 and control computer 7, described optical detection assembly is between the receiving telescope 1 of laser radar and optical receiver 4, and the echo signal of laser radar is transmitted to FBG by optical fiber by receiving telescope 1 Background filter 2, and then the output signal of the FBG background filter 2 is transmitted to the light intensity modulator 3 through an optical fiber, and then the output signal of the light intensity modulator 3 is transmitted to the optical receiver 4, wherein,

FBG background filter 2, it is packaged in a constant temperature box, and temperature controller 5 keeps FBG background filter 2 working at a constant temperature all the time, has prevented the drift of the central working wavelength, and then FBG background filter 2 is installed on On the precision translation stage, the stress distribution is controlled by piezoelectric ceramics to ensure that the wavelength position of the peak transmittance overlaps with the working wavelength. The FBG background filter 2 is a narrow-band, low-loss transmission filter with a bandwidth of 0.1nm. The center frequency of the optical signal is υ ₀ , and the peak transmittance reaches 99%. The echo signal passes through the FBG background filter 2, and the echo signal with the center frequency of υ ₀ has a transmittance of 99%. The echo signals of other frequency bands The transmittance is less than 1%, and the echo signals in other frequency bands are effectively filtered out, that is, the background light is suppressed to a great extent;

The light intensity modulator 3, the echo signal that has filtered the background noise is output to the light intensity modulator 3, the control computer 7 generates a feedback voltage signal according to the change of the echo signal intensity output by the optical receiver 4 with time, and the arbitrary waveform generator 6 Control the modulation voltage V input to the light intensity modulator 3 according to the feedback voltage signal, and intelligently actively suppress possible saturated signals; the inside of the light intensity modulator 3 is a light intensity modulator with an M-Z interferometer type electro-optic modulator structure, wherein A modulating voltage V is applied to one arm; when detecting the lower atmosphere, stronger backscattered light is incident on the light intensity modulator 3, and the phase change of the echo signal of the modulating voltage-applied arm is equal to the difference by adjusting the modulating voltage V. At this time, the echo signals of the two arms undergo destructive interference, and the intensity of the echo signal output to the optical receiver 4 reaches a minimum, avoiding the saturation of the optical receiver 4; when detecting the upper atmosphere, the weaker The backscattered light is incident on the light intensity modulator 3. By adjusting the modulation voltage V, the phase change of the echo signal of one arm to which the modulation voltage is applied is equal to an integer multiple of the wavelength. At this time, the echo signals of the two arms undergo constructive interference. , the intensity of the optical signal output to the optical receiver 4 reaches the maximum.

Further, the temperature response coefficient of the FBG in the FBG background filter 2 is 0.01 nm/°C, and the stress coefficient of the FBG is 1.261 pm/με.

Further, the half-wave voltage of the light intensity modulator 3 is Vπ, and the modulation speed is 40 GHz.

The advantage of the present invention compared with prior art is:

1) The present invention adopts the FBG background filter to filter the background noise, the key is to use temperature compensation and fiber Bragg grating axial stress control, so that the peak transmittance position of the fiber Bragg grating is just at the working wavelength of the laser radar. The FBG background filter is a narrow-band, low-loss transmissive filter. The current bandwidth is _0.1nm , and the peak transmittance reaches 99%. %, optical signals in other frequency bands are filtered out, effectively suppressing the background light and realizing all-day detection;

2) The present invention uses a light intensity modulator to modulate the intensity of the received light signal of the laser radar. The light intensity modulator can actively electro-optic modulate the dynamic range of the laser radar signal according to the characteristics of the echo signal, which can ensure the maximum signal-to-noise ratio of the remote signal. Under the premise of suppressing the near-field signal, avoiding the saturation of the near-field signal of the photodetector, increasing the output power of the laser and the echo power of the far-field target, and realizing the integrated detection of high and low altitudes;

3) The present invention adopts full optical fiber connection, which improves the stability of system operation;

4) The present invention greatly reduces the cost of the optical path, and the optical path system is relatively simple, which is beneficial to the adjustment of the optical path.

Description of drawings

Figure 1. A structural schematic diagram of the optical detection component of the all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar;

Fig. 2. the structural diagram of FBG background filter of the present invention;

Fig. 3. the working principle diagram of the FBG background filter provided by the present invention;

Fig. 4. schematic diagram of the M-Z interferometer type electro-optic modulator inside the optical intensity modulator of the present invention;

Fig. 5. light intensity modulator working principle diagram of the present invention;

Fig. 6. Schematic diagram of the signal modulation process of the optical intensity modulator of the present invention.

Among them, 1. Receiving telescope; 2. FBG background filter; 3. Light intensity modulator; 4. Optical receiver; 5. Temperature controller; 6. Arbitrary waveform generator; 7. Control computer.

Detailed ways

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a structural schematic diagram of an optical detection component of an all-fiber background light suppression and near-field signal dynamic range suppression technology in a laser radar provided by the present invention. The optical detection component includes: a receiving telescope 1, an FBG background filter 2, an optical Strong modulator 3, optical receiver 4, temperature controller 5, arbitrary waveform generator 6 and control computer 7.

Specifically, the atmospheric molecule scattering signal passes through the receiving telescope 1 to the FBG background filter 2. The FBG background filter 2 is a narrow-band, low-loss transmission filter with a current bandwidth of 0.1nm and a peak transmittance of 99%. The echo signal After the FBG background filter 2, the transmittance of the optical signal whose center frequency is υ ₀ is 99%, and the optical signals of other frequency bands are filtered out, effectively suppressing the background light. Fig. 2 is a structural diagram of the FBG background filter, and the FBG background filter 2 is packaged in a constant temperature box. Calculate the temperature stability index according to the temperature influence coefficient. Then the FBG background filter is installed on a precision translation stage, and its stress distribution is controlled by piezoelectric ceramics to ensure that the wavelength position of the peak transmittance overlaps with the working wavelength. The temperature response coefficient of fiber Bragg grating is 0.01nm/°C. If the temperature error of the thermostatic chamber is 0.1°C, the center wavelength shift of fiber Bragg grating is less than 0.001nm. The temperature controller 5 keeps the FBG background filter 2 working at a constant temperature all the time, preventing the drift of the central working wavelength. Then the FBG background filter 2 is installed on a precision translation stage, and its stress distribution is controlled by piezoelectric ceramics to ensure that the wavelength position of the peak transmittance overlaps with the working wavelength. The fiber Bragg grating stress coefficient is 1.261pm/με, that is, every time the axial stress of the fiber changes by one millionth, the center wavelength of the FBG background filter 2 moves by 1.261pm. By applying stress, the wavelength corresponding to the peak transmittance of the fiber grating can be precisely adjusted.

Fig. 3 is the working principle diagram of the FBG background filter provided by the present invention, the bandwidth is 0.1nm, and the optical signal whose center wavelength is λ0 passes through the FBG background filter and continues to transmit, and the peak transmittance reaches 99%, and the light of other wavelengths is passed through the FBG background filter. filter out.

The optical signal that has filtered out the background noise is coupled to the optical intensity modulator 3 through an optical fiber. The half-wave voltage of the optical intensity modulator 3 is v _π , and the modulation speed can reach 40 GHz. The change over time generates a feedback voltage signal. The arbitrary waveform generator 6 controls the modulation voltage V input to the light intensity modulator 3 according to the feedback voltage signal, intelligently and actively suppressing possible saturated signals.

When detecting the lower atmosphere, stronger backscattered light is incident on the light intensity modulator, and the light signal is stronger (short distance), and the control computer 7 sends instructions to the arbitrary waveform generator 6, and the modulation voltage of the input electro-optic intensity is close to V _L , at this time, the phase of the optical signal modulated by the MZ interferometer in one arm changes. At this time, the optical signals of the two arms interfere and destruct, and the light transmittance is small, which suppresses the near-field strong echo signal and avoids the optical receiver When detecting the upper atmosphere, the weaker backscattered light is incident on the light intensity modulator, and the light signal is weaker (long distance), and the control computer 7 sends instructions to the arbitrary waveform generator 6 to input the modulation voltage of the light intensity Close to V _H , at this time the phase of the optical signal in the modulation arm of the MZ interferometer changes, the optical signal interferes constructively, and the light transmittance approaches 1.

Fig. 4 is the internal M-Z interferometer type electro-optic modulator structure schematic diagram of the optical intensity modulator provided by the present invention, and it has low optical loss and high optical power handling capacity (up to 400mw), compared with semiconductor modulator, has wider Modulation bandwidth, zero or tunable chirp, and insensitivity to temperature, it is a very promising device in future optical fiber communication systems. The working principle is to add modulation voltage to one arm of the electro-optic modulator of the M-Z interferometer v, by intelligently adjusting the modulation voltage v to change the phase of the optical signal passing through the arm, the optical signals of the two arms interfere at the output end, so that the light intensity of the output optical signal changes, and the modulation of the optical signal intensity is realized.

Fig. 5 is the operating principle figure of the light intensity modulator provided by the present invention, has provided the relation of the transmittance of light intensity modulator and modulation voltage among the figure, transmittance curve is the sinusoidal function of modulation voltage, V _π is half Wave voltage, V _H is the modulation voltage when the maximum transmittance is 1, and V _L is the modulation voltage when the minimum transmittance is 0.

Fig. 6 is the signal modulation flow diagram of the light intensity modulator provided by the present invention, wherein (1) is the atmospheric backscattered light signal, the maximum value of the light signal intensity of curve 1 has reached the saturation threshold of the optical receiver, and the light signal of curve 2 The intensity exceeds the saturation threshold of the optical receiver, I _s is the saturation threshold of the optical receiver, the shaded part is the optical signal saturation area, (2) is the modulation voltage that the arbitrary waveform generator controls the input light intensity modulator according to the feedback voltage, (3 ) is the transfer function curve of the light intensity modulator after being modulated by the modulation voltage, and (4) is the atmospheric backscattered light signal modulated by the light intensity modulator.

In summary, the all-fiber background light suppression and near-field signal dynamic range suppression technology in the lidar uses the all-fiber connection method to improve the operation stability of the system, effectively suppress the background light, and realize all-day detection , improve the detection accuracy and detection ability of the laser radar, realize the integrated detection of high and low altitudes, greatly reduce the cost of the optical path, and the optical path system is relatively simple, which is conducive to the adjustment of the optical path.

Example

The present invention will be further described below in conjunction with embodiment, but should not limit the protection scope of the present invention with this.

1) As shown in Figure 1, the scattering signal of atmospheric molecules passes through the receiving telescope 1 to the FBG background filter 2. The FBG background filter 2 is a narrow-band, low-loss transmission filter with a current bandwidth of 0.1nm and a peak transmittance of 99 %, the echo signal passes through the FBG background filter 2, and the transmittance of the optical signal whose center frequency is υ ₀ is 99%, and the optical signals of other frequency bands are filtered out, effectively suppressing the background light. The FBG background filter 2 is packaged in a constant temperature box. Calculate the temperature stability index according to the temperature influence coefficient. Then the FBG background filter 2 is installed on a precision translation stage, and its stress distribution is controlled by piezoelectric ceramics to ensure that the wavelength position of the peak transmittance overlaps with the working wavelength. The fiber Bragg grating stress coefficient is 1.261pm/με, that is, every time the axial stress of the fiber changes by one millionth, the center wavelength of the FBG background filter 2 moves by 1.261pm. By applying stress, the wavelength corresponding to the peak transmittance of the fiber grating can be precisely adjusted.

2) The optical signal from which the background noise has been filtered is coupled to the optical intensity modulator 3 via an optical fiber. The half-wave voltage of the optical intensity modulator 3 is v _π , and the modulation speed can reach 40 GHz. The control computer 7 outputs the echo signal according to the optical receiver 4 The intensity varies with time, generating a feedback voltage signal. The arbitrary waveform generator 6 controls the modulation voltage V input to the light intensity modulator 3 according to the feedback voltage signal, intelligently and actively suppressing possible saturated signals.

When the optical signal is strong, the control computer 7 sends an instruction to the arbitrary waveform generator 6, and the modulation voltage of the input electro-optical intensity is close to V _L . At this time, the phase of the optical signal in the modulation arm of the MZ interferometer changes. At this time, the two The optical signal of the arm interferes and destructs, and the light transmittance is small, which suppresses the near-field strong echo signal and avoids the saturation of the detector; when the optical signal is weak (long distance), the control computer 7 generates an arbitrary waveform The device 6 issues an instruction, and the modulation voltage of the input electro-optic intensity is close to V _H . At this time, the phase of the optical signal in the modulation arm of the MZ interferometer changes, the optical signal interferes constructively, and the light transmittance approaches 1.

Although the illustrative specific embodiments of the present invention have been described above, so that those skilled in the art can understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, As long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are included in the protection list.

Claims (3)

1. An optical detection component of all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar, characterized in that: the optical detection component includes a receiving telescope (1), an FBG background filter (2), an optical Strong modulator (3), optical receiver (4), temperature controller (5), arbitrary waveform generator (6) and control computer (7), the echo signal of the lidar is transmitted by the receiving telescope (1) through optical fiber to the FBG background filter (2), and then transmit the output signal of the FBG background filter (2) to the light intensity modulator (3) through the optical fiber, and then transmit the output signal of the light intensity modulator (3) to the optical receiver (4), where, The FBG background filter (2) is packaged in a constant temperature box, and the temperature controller (5) keeps the FBG background filter (2) working at a constant temperature to prevent the drift of the central working wavelength, and then the FBG The background filter (2) is installed on a precision translation stage, and its stress distribution is controlled by piezoelectric ceramics to ensure that the wavelength position of the peak transmittance overlaps with the working wavelength. The FBG background filter (2) is a narrow-band, low-loss transmission type filter with a bandwidth of 0.1nm, the center frequency of the transmitted optical signal is υ ₀ , and the peak transmittance reaches 99%. The echo signal passes through the FBG background filter (2), and the echo signal with the center frequency of υ ₀ is transmitted The pass rate is 99%, the transmittance of echo signals in other frequency bands is less than 1%, and the echo signals in other frequency bands are effectively filtered out, that is, the background light is suppressed to a great extent; The light intensity modulator (3), the echo signal with filtered background noise is output to the light intensity modulator (3), and the control computer (7) generates feedback according to the change of the echo signal intensity output by the optical receiver (4) with time voltage signal, the arbitrary waveform generator (6) controls the modulation voltage V input to the light intensity modulator (3) according to the feedback voltage signal, and intelligently actively suppresses the signal that may be saturated; the light intensity modulator (3) has an internal M-Z A light intensity modulator with an interferometer-type electro-optic modulator structure, in which a modulation voltage V is applied to one arm; when detecting the lower atmosphere, strong backscattered light is incident on the light intensity modulator (3), and the modulation voltage V is adjusted to make The phase change of the echo signal of one arm to which the modulation voltage is applied is equal to the half-wavelength out of phase. At this time, the echo signals of the two arms undergo destructive interference, and the intensity of the echo signal output to the optical receiver reaches a minimum, avoiding Saturation of the optical receiver (4); when detecting the upper atmosphere, the weaker backscattered light is incident on the light intensity modulator (3), and the phase of the echo signal of the arm to which the modulation voltage is applied is adjusted by adjusting the modulation voltage V The change is equal to an integer multiple of the wavelength. At this time, the echo signals of the two arms undergo constructive interference, and the intensity of the optical signal output to the optical receiver (4) reaches the maximum. 2. The optical detection component of an all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar according to claim 1, characterized in that: the fiber grating temperature response in the FBG background filter (2) The coefficient is 0.01nm/℃, and the stress coefficient of the fiber grating is 1.261pm/με. 3. The optical detection component of an all-fiber background light suppression and near-field signal dynamic range suppression technology in lidar according to claim 1, characterized in that: the half-wave voltage of the light intensity modulator (3) is V _π , the modulation speed is 40GHz.

Images