CN102419247B - High-precision detection device and method of reflection type optical fiber turbulence - Google Patents

Abstract

The invention discloses a high-precision reflective optical fiber turbulence detection device and method. The device of the invention includes a modulated laser light source, a reflective optical fiber turbulence detection probe, and a signal processing module, wherein the reflective optical fiber turbulence detection probe is composed of a collimator , an optical circulator, an optical isolator, and an optical fiber. The reflective optical fiber turbulence detection probe has only one arm, and the optical path difference between the two beams of light that interferes is the optical path of the light passing through the air. The method of the present invention directly detects the small fluctuation of the local turbulent atmospheric refractive index through the device of the present invention, is applicable to various geographical environments and various weather conditions, has corrosion resistance, fast detection speed, high sensitivity, small volume, easy integration, and simple operation Features.

Description

High-precision reflective optical fiber turbulence detection device and method

technical field

The invention relates to the field of atmospheric optical turbulence intensity measurement, in particular to a high-precision reflective optical fiber turbulence detection device and method.

Background technique

A turbulent atmosphere is a heterogeneous random medium whose refractive index is a function of spatial position and time. When the laser passes through the turbulent atmosphere, the refractive index fluctuation caused by the atmospheric turbulence will cause turbulent effects such as beam drift, expansion, light intensity flicker, and phase fluctuation. These effects restrict the application of optical engineering such as laser atmospheric transmission, free space optical communication, laser ranging, and optical imaging. Therefore, it is very important to accurately obtain the optical turbulence information on the light propagation path, mainly including the refractive index structure constant, the variance of the refractive index fluctuation, the characteristic scale, and the turbulent refractive index spectrum. At present, the methods for measuring these parameters mainly include temperature pulsation method and optical method.

The temperature fluctuation method is an indirect measurement method to obtain the fluctuation characteristics of the atmospheric turbulent refractive index by measuring the fluctuation of the atmospheric temperature. It assumes that the fluctuation characteristics of the air refractive index depend entirely on the fluctuation characteristics of the temperature. The commonly used measuring instrument is a temperature fluctuation meter. The temperature pulsation method is currently the most commonly used method for measuring turbulent optical parameters, and has made a lot of contributions to the study of atmospheric optical turbulence. With the deepening of research, the inherent defects of this method are becoming more and more prominent. The metal platinum wire is easy to be broken and polluted, the spatial and temporal resolution is limited, and it cannot detect small-scale turbulent flow. The optical method is to use the propagation effect of light in the turbulent atmosphere to measure the turbulent optical parameters. The commonly used methods include the laser scintillation method and the arrival angle fluctuation method. The theoretical basis of the laser scintillation method for measuring turbulence intensity is the Rytov approximation under weak fluctuation conditions. When the turbulence is strong enough, this method fails. In addition, some people use lidar to measure atmospheric turbulence. In the actual atmosphere, the turbulence isotropy and stationarity assumptions used to derive the radar equation are difficult to meet. The form of the radar equation itself needs to be further improved. This method is still in the initial exploration phase. At present, the turbulent optical parameters measured by the optical method based on the principle of turbulence effect are all the results of long-path averaging, which is difficult to obtain the local refractive index fluctuation characteristics.

量级，但之后没有相关报道。对于光纤Mach-Zehnder干涉仪来说，通常有两个臂，一臂作为传感臂，另一臂作为参考臂。干涉仪通过受外界的扰动而携带有外界信息的传感臂，检测外界信息。大气湍流是微弱、随机的，如果用闭合臂光纤Mach-Zehnder干涉仪来检测湍流，则不能很好的反映湍流情况。近年来，随着光电技术与相位载波调制解调技术的发展，已出现了利用两准直器对准的方法来检测湍流信息。此种方法首先利用耦合器将激光分成两束，一束用光纤连接到准直器，将激光打到空气中，在用另一个准直器接受激光作为信号光，另一束作为参考光，用另一个耦合器将这两束激光耦合发生干涉，干涉信号携带了大气影响的信息。此方法如果用单模光纤及单模器件来实现的话，由于单模光纤的双折射问题及两干涉仪臂所处的环境不一样，使发生干涉的两束光很难保证偏振态一致，这对检测的结果产生一定误差。保偏光纤与保偏器件在一定程度上能解决偏振态问题，但保偏器件比较昂贵，使得成本增加不少；另一方面，保偏准直器增大了对准的难度。 Due to the limitation of technical conditions, traditional optical turbulence measurement methods are either indirect or under assumptions, and the results are uncertain. It is reported that: the turbulence parameters measured by the temperature fluctuation method and the optical method respectively The difference can be more than four times in value. In 1995, Mermelstein proposed a principle of double air-gap optical fiber Mach-Zehnder interferometry technology, which is used to directly obtain the small fluctuations in the refractive index of the local turbulent atmosphere, and its theoretical accuracy can reach

order of magnitude, but there is no relevant report afterwards. For fiber optic Mach-Zehnder interferometers, there are usually two arms, one as the sensing arm and the other as the reference arm. The interferometer detects external information through a sensing arm carrying external information due to external disturbances. Atmospheric turbulence is weak and random. If the closed-arm fiber optic Mach-Zehnder interferometer is used to detect turbulence, it cannot reflect the turbulence well. In recent years, with the development of optoelectronic technology and phase carrier modulation and demodulation technology, a method of aligning two collimators has emerged to detect turbulence information. In this method, a coupler is used to divide the laser beam into two beams, one beam is connected to the collimator with an optical fiber, and the laser beam is shot into the air, and the other collimator is used to receive the laser beam as signal light, and the other beam is used as reference light. The two laser beams are coupled by another coupler for interference, and the interference signal carries information about the influence of the atmosphere. If this method is implemented with single-mode fiber and single-mode devices, due to the birefringence problem of single-mode fiber and the different environments of the two interferometer arms, it is difficult to ensure that the polarization states of the two interfered beams are consistent. There is a certain error in the detection result. Polarization-maintaining fiber and polarization-maintaining device can solve the polarization state problem to a certain extent, but the polarization-maintaining device is relatively expensive, which increases the cost a lot; on the other hand, the polarization-maintaining collimator increases the difficulty of alignment.

Contents of the invention

The purpose of the present invention is to provide a high-precision reflective optical fiber turbulence detection device and method to solve the problem of inconvenient measurement and limitations of the atmospheric optical turbulence detection system in the prior art.

In order to achieve the above object, the technical scheme adopted in the present invention is:

The high-precision reflective optical fiber turbulence detection device is characterized in that it includes an adjustable laser light source, a reflective optical fiber turbulent detection probe, a full reflection mirror, and a signal processing module. The outgoing light of the laser light source passes through a coupler and is divided into two One path of outgoing light is sent to the reflective fiber optic turbulence detection probe as detection light, and the other path of outgoing light is sent to the signal processing module as reference light. The reflective fiber optic turbulence detection probe includes a collimator and is respectively connected to an optical isolator One end of the input fiber is connected to the FC/APC connector, and the other end is connected to the light inlet port of the collimator. One end of the output fiber is connected to the FC/APC connector, and the other end is connected to the collimator to output light. The total reflection mirror is spaced from the collimator by a certain distance, the reflection surface of the total reflection mirror is on the collimator, and the turbulence to be detected passes through the gap between the total reflection mirror and the collimator; the input optical fiber passes through the FC/ The APC connector introduces the detection light, and sends the detection light into the collimator after passing through the optical isolator. A part of the detection light is reflected in the collimator to the output optical fiber, and the rest of the detection light is transmitted through the collimator and then enters the total reflection mirror. , is reflected by the total reflection mirror and then transmitted into the collimator, and incident to the output fiber and interferes with the part of the probe light directly reflected by the collimator to generate an interference light signal, and the interference light signal passes through the light of the output fiber After the isolator, it is sent to the signal processing module.

The high-precision reflective optical fiber turbulence detection device is characterized in that the modulated laser light source is composed of a semiconductor laser and a signal generator connected to the modulation end of the semiconductor laser, and the signal generator sends a modulation electrical signal to the semiconductor laser to modulate The current of the semiconductor laser makes the semiconductor laser output the carrier laser which changes with the modulation electrical signal.

The high-precision reflective optical fiber turbulence detection device is characterized in that: the reflective optical fiber turbulence detection probe also includes a circulator, and the other ends of the input optical fiber and output optical fiber are respectively connected to the circulator, and then connected to the circulator through the circulator. in the collimator.

The high-precision reflective optical fiber turbulence detection device is characterized in that: the collimator has a spherical end, and the end surface of the collimator is coated with a 30% anti-reflection film.

The high-precision reflective optical fiber turbulence detection device is characterized in that: the signal processing module includes a computer, a data acquisition card connected to the computer, and two photodetectors connected to the data acquisition card, wherein one photoelectric detector The reference light signal is received, and the other photodetector receives the interference light signal.

A high-precision reflective optical fiber turbulence detection method, characterized in that: comprising the following steps:

(1) Control the signal generator to send a modulated electrical signal to the semiconductor laser, and the semiconductor laser emits a carrier laser that changes with the modulated electrical signal;

(2) The computer controls the acquisition card for signal acquisition. The two photodetectors connected to the acquisition card collect the reference optical signal and the interference optical signal respectively and convert the reference optical signal and the interference optical signal into electrical signals. The electrical signal corresponding to the signal and the electrical signal corresponding to the interference optical signal are respectively sent to the computer;

(3) In the computer, the electrical signal corresponding to the interference optical signal is divided by the electrical signal corresponding to the reference optical signal, and the obtained signal is subjected to DC filtering to obtain the turbulent signal that needs to be demodulated;

，及计算变化式； (4) Extract the waveform signal of the carrier from the reference signal

, and calculate the variation ;

、

，再将乘积分别送入带通滤波器中滤波，滤波后的结果相加，最后将相加的结果通过相关解调算法进行计算，得到准直器与全反镜之间的湍流随机相位差

； (5) Multiply the turbulence signal to be demodulated by the signal

,

, and then send the products to the band-pass filter for filtering, add the filtered results, and finally calculate the added results through the correlation demodulation algorithm to obtain the turbulent random phase difference between the collimator and the total reflection mirror

;

与

的关系式

，将

转化为准直器与全反镜之间的折射率微小起伏

，然后统计

的起伏方差

，式中L为准直器与全反镜之间的距离，

为激光的波长。 (6) by

and

relational expression

,Will

Converted to small fluctuations in the refractive index between the collimator and the total reflection mirror

, and then statistics

Fluctuation variance of

, where L is the distance between the collimator and the total reflection mirror,

is the wavelength of the laser.

In the present invention, the reflective optical fiber turbulence detection probe has only one arm, and the optical path difference of the interference light is the optical path of the light passing through the air, that is, the optical path of the light passing through the interval between the total reflection mirror and the collimator, and the turbulent flow to be demodulated The phase difference is obtained by correlation demodulation algorithm, which realizes the direct detection of local atmospheric turbulence intensity, and the measurement data can reflect the real atmospheric conditions.

The invention is suitable for marine corrosive environment and rainy weather, has improved time and space resolution, fast detection speed, high sensitivity, small volume, easy integration and simple operation.

Description of drawings

Fig. 1 is a schematic diagram of the device of the present invention.

Fig. 2 is a schematic structural diagram of the reflective optical fiber turbulence detection probe of the present invention.

Fig. 3 is an optical principle diagram of the reflective optical fiber turbulence detection probe of the present invention.

Fig. 4 is a flow chart of related demodulation calculation of the method of the present invention.

Fig. 5 is a graph of the interference signal.

Fig. 6 is a graph of the phase difference signal.

Detailed ways

As shown in Figure 1, Figure 2, and Figure 3. High-precision reflective fiber optic turbulence detection device, including a modulatable laser light source, a reflective fiber optic turbulence detection probe 2, a full mirror 3, and a signal processing module. The modulatable laser light source is modulated by a semiconductor laser 1 and connected to a semiconductor laser 1 The signal generator 5 at the end is composed of a signal generator 5 that sends a modulation electrical signal to the semiconductor laser 1 to modulate the current of the semiconductor laser 1, so that the semiconductor laser 1 outputs a carrier laser that changes with the modulation electrical signal. The outgoing light of the laser light source 1 is divided into two paths after passing through a coupler 4. The outgoing light of one path is sent to the reflective optical fiber turbulence detection probe 2 as the detection light, and the other outgoing light is sent to the signal processing module as the reference light. The reflective optical fiber turbulence detection The probe 2 includes a collimator 201, an input optical fiber 204 connected to an optical isolator 202, and an output optical fiber 205 connected to an optical isolator 203. One end of the input optical fiber 204 is connected to a FC/APC connector 206, and the other end is connected to the collimator 201 light inlet, one end of the output fiber 205 is connected with FC/APC connector 207, the other end is connected to the collimator light outlet 201, the total reflection mirror 3 is separated from the collimator 201 by a certain distance, and the reflection surface of the total reflection mirror 3 is aligned Collimator 201, and the turbulence to be detected passes through the space between the total reflection mirror 3 and the collimator 201; the input optical fiber 204 introduces the detection light through the FC/APC connector 206, and sends the detection light into the collimator after passing through the optical isolator 202 In the detector 201, a part of the detection light is reflected in the collimator 201 to the output optical fiber 205, and the remaining part of the detection light is transmitted through the collimator 201 and then enters the total reflection mirror 3, and is reflected by the total reflection mirror 3 and then transmitted into the collimator 201, and incident to the output fiber 205 and the part of the detection light directly reflected by the collimator 201 interferes to generate an interference optical signal, the interference optical signal passes through the optical isolator 203 of the output optical fiber 205 and then is sent to the signal processing module.

The reflective fiber optic turbulence detection probe 2 also includes a circulator 208 , the other ends of the input optical fiber 204 and the output optical fiber 205 are respectively connected to the circulator 208 , and then connected to the collimator 201 through the circulator 208 . The collimator 201 has a spherical end, and the end surface of the collimator 201 is coated with a 30% anti-reflection film.

The signal processing module includes a computer 6, a data acquisition card 7 connected to the computer 6, and two photodetectors 8 and 9 connected to the data acquisition card 7, wherein the photodetector 8 of one path receives the reference light signal, and the photodetector of the other path 9. Receive the interference light signal.

As shown in Figure 4. A high-precision reflective optical fiber turbulent detection method, comprising the following steps:

(1) Control the signal generator to send a modulated electrical signal to the semiconductor laser, and the semiconductor laser emits a carrier laser that changes with the modulated electrical signal;

(2) The computer controls the acquisition card for signal acquisition. The two photodetectors connected to the acquisition card collect the reference optical signal and the interference optical signal respectively and convert the reference optical signal and the interference optical signal into electrical signals. The electrical signal corresponding to the signal and the electrical signal corresponding to the interference optical signal are respectively sent to the computer;

(3) In the computer, the electrical signal corresponding to the interference optical signal is divided by the electrical signal corresponding to the reference optical signal, and the obtained signal is subjected to DC filtering to obtain the turbulent signal that needs to be demodulated;

； (4) Extract the waveform signal of the carrier from the reference signal , and calculate the variation

;

、

，再将乘积分别送入带通滤波器中滤波，滤波后的结果相加，最后将相加的结果通过相关解调算法进行计算，得到准直器与全反镜之间的湍流随机相位差

； (5) Multiply the turbulence signal to be demodulated by the signal

,

, and then send the products to the band-pass filter for filtering, add the filtered results, and finally calculate the added results through the correlation demodulation algorithm to obtain the turbulent random phase difference between the collimator and the total reflection mirror

;

与

的关系式

，将

转化为准直器与全反镜之间的折射率微小起伏

，然后统计的起伏方差

，式中L为准直器与全反镜之间的距离，

为激光的波长。 (6) by

and

relational expression

,Will

Converted to small fluctuations in the refractive index between the collimator and the total reflection mirror

, and then statistics Fluctuation variance of

, where L is the distance between the collimator and the total reflection mirror,

is the wavelength of the laser.

Theoretical basis of the invention: the reflective optical fiber turbulence detection probe is composed of a collimator coated with a 30% anti-reflection coating on the end surface, a total reflection mirror, an optical circulator and two optical isolators. The collimator uses a spherical head to avoid light oscillation between the collimator and the total reflection mirror. When the carrier laser light enters the probe, it first passes through an optical isolator to prevent the reflected light from the connector end from interfering with the laser, then enters the optical circulator, and then enters the collimator, where 30% of the light is returned and 70% is received Transmission, the transmitted light passes through a 10cm-long air section, and is reflected back into the collimator by the total reflection mirror. After being transmitted through the end face of the collimator, it enters the optical fiber and interferes with the light reflected for the first time. This interference signal includes information about the effect of atmospheric turbulence on light. The interference signal is collected, and after signal processing and phase demodulation algorithm, the refractive index fluctuation of turbulent flow can be obtained.

，准直器端面的反射率为

，则经准直器端面反射的光的光强为

，透射光的光强为

，透射光经过一段空气后由全反射镜返回到准直器中的光的光强为

。为使两相干光束的光强相近，故反射率应满足下面关系式： The reason for coating a layer of 30% anti-reflection coating on the end face of the collimator: Assume that the light intensity of the incident light is

, the reflectivity of the collimator facet is

, then the light intensity of the light reflected by the end face of the collimator is

, the intensity of the transmitted light is

, the intensity of the transmitted light returning to the collimator by the total reflection mirror after passing through a section of air is

. In order to make the light intensity of the two coherent beams similar, the reflectivity should satisfy the following relationship:

(1)

，由于透射光经空气段后反射回来会产生一定的损耗以及镀膜技术要求，故准直器的端面上镀30%的增反膜。 Solutions have to:

, due to the reflection of the transmitted light through the air section, there will be a certain loss and the technical requirements of the coating, so the end surface of the collimator is coated with a 30% anti-reflection coating.

The Form of Interference Signal and Demodulation Algorithm

的调制电压信号，

是信号的振幅，

是信号的角频率。当调制信号经输出电流为、电压电流调制率为

的激光控制器得驱动电流： Let the signal generator produce

The modulated voltage signal,

is the amplitude of the signal,

is the angular frequency of the signal. When the modulated signal is passed through the output current is , voltage and current modulation rate

The driving current of the laser controller is:

                （2）

(2)

，电流频率调制率为

的半导体激光器，得载波激光的光功率与频率为： The optical power modulation rate of the driving current used is

, the current frequency modulation rate is

For a semiconductor laser, the optical power and frequency of the carrier laser are:

(3)

(4)

和

分别为光功率和频率的直流量。当载波激光经反射式光纤湍流检测探头后，发生干涉的两束光产生的相位差为： in

and

are the DC quantities of optical power and frequency, respectively. When the carrier laser passes through the reflective fiber optic turbulence detection probe, the phase difference between the two interfered beams is:

(5)

），为发生干涉两束光的光程差，c为真空中的光速，

， 为一个常量，

为大气湍流引入的随机相位变化。为了防止信号混叠， 这里

。设发生干涉两束光的功率占总功率的百分比分别为

，光电探测器的功率电压转化效率为

（

），则干涉信号为： in is the mean air refractive index (

), is the optical path difference between two beams of light that interfere, c is the speed of light in vacuum,

, as a constant,

Random phase variations introduced for atmospheric turbulence. To prevent signal aliasing, here

. Let the percentages of the power of the two beams of interference to the total power be respectively

, the power-to-voltage conversion efficiency of the photodetector is

(

), then the interference signal is:

                                                                （6）

(6)

in

Divide the carrier laser into two paths with a coupler, one path is directly collected by the acquisition card as a reference signal, and the other path passes through the probe, then the reference signal and interference signal are as follows: 

                                   （7）                                    Reference signal:

(7)

           （8） Interference signal:

(8)

包含了湍流随机相位。对信号

进行Bessel级数展开，  Divide the interference signal by the reference signal, and obtain the signal to be demodulated after DC filtering

Turbulent random phases are included. on signal

Perform Bessel series expansion,

             （9）                  

(9)

分别与信号

和

相乘，经截至频率为

和

的带通滤波器后得到： Will

respectively with the signal

and

Multiplied together, the cut-off frequency is

and

After the bandpass filter, we get:

                     （10）

(10)

                     （11）

(11)

Add the formula (16) and formula (17) to the right to get:

       （12）

(12)

与

只有一个相移，即要解调的相位差，可以从参考信号中得到，然后用相关法求相位差。

and

There is only one phase shift, the phase difference to be demodulated, It can be obtained from the reference signal, and then use the correlation method to find the phase difference.

The principle of phase difference demodulation by correlation method: the cross-correlation function value of the same frequency sine (or cosine) signal when the delay is zero is proportional to the cosine value of its phase difference. Let the expression of two columns of the same frequency signal be

，

                      (13)                           

,

(13)

和

是信号的幅值，

为两信号的相位差。根据相关函数的定义，当时间延迟为零时 In the formula

and

is the amplitude of the signal,

is the phase difference of the two signals. According to the definition of the relevant function, when the time delay is zero

                             (14)

(14)

          (15)  

                          (16)

(15)

(16)

分别为两信号在延时为零时的自相关函数，

为互相关函数。综合上面三式可得

are the autocorrelation functions of the two signals when the delay is zero,

is a cross-correlation function. Combining the above three formulas, we can get

                 (17)       

(17)

。                                   Right now

.

、

，其中

，

为总的采样点数。设

为采样率，定义参与一次相关运算的数据长度为相关长度

。对于离散的时间序列，在一个相关长度内的相关运算由积分式变为求和式，即 What the computer deals with is the discrete time series sampled by A/D, namely

,

,in

,

is the total number of sampling points. set up

is the sampling rate, and defines the data length involved in a correlation operation as the correlation length

. For discrete time series, the correlation operation within a correlation length is changed from an integral type to a summation type, namely

                       (18)           

(18)

的

倍，那么经过相关运算获得动态的随机相位差时间序列

，则空间距离L上的平均折射率起伏

为： Set the total number of sampling points N to be exactly the correlation length

of

times, then the dynamic random phase difference time series can be obtained through the correlation operation

, then the average refractive index fluctuation over the spatial distance L

for:

                              （19）

(19)

variance:

 。                （20）

. (20)

的余弦信号作为直接调制激光光源的调制信号，湍流信号的频率一般只有几十到几百赫兹，故调制信号的频率取

。 In the present invention, a signal generator is used to generate a frequency of , with an amplitude of

The cosine signal of the laser source is used as the modulation signal to directly modulate the laser light source. The frequency of the turbulence signal is generally only tens to hundreds of Hz, so the frequency of the modulation signal is taken as

.

，相干长度大于1m，通过信号发生器发出的调制信号调节激光控制器的电流来微调激光器的输出频率，使之形成载波激光。此激光器体积小易与光纤偶合，且此波段的光在光纤中传播的损耗比较小。 The light source selected in the present invention is a distributed semiconductor laser, the wavelength

, the coherence length is greater than 1m, the current of the laser controller is adjusted by the modulation signal sent by the signal generator to fine-tune the output frequency of the laser, so that it forms a carrier laser. The laser is small in size and easy to couple with the fiber, and the loss of light in this wavelength band propagating in the fiber is relatively small.

The collimator adopts a spherical head to prevent light from oscillating between the collimator and the total reflection mirror, and the end surface of the collimator is coated with a 30% anti-reflection film.

After the carrier laser light enters the probe, 30% is reflected and 70% is transmitted. After the transmitted light passes through a 10cm-long air section, it is reflected back to the collimator by the total reflection mirror and interferes with the previously reflected light. This signal contains Information on the effects of turbulent atmosphere on laser light.

The light emitted by the laser of this device is linearly polarized light. When the laser passes through the end face of the collimator, the polarization state of the reflected light is consistent with that of the transmitted light. The total reflection mirror does not change the polarization state of the polarized light, and the air does not change the polarization state of the light, so The consistency of the polarization state when the reference light interferes with the signal light is maintained.

The interference signal and reference signal are collected for a series of complex signal processing. The principle of the demodulation algorithm is shown in Figure 4.

左右的倾斜角，防止光纤端面的菲涅尔反射。 The optical fiber connector is FC/APC head, and the fiber end face of FC/APC head is

The left and right tilt angles prevent Fresnel reflection from the fiber end face.

The probe of the present invention is installed on the experimental field and connected with the optical fiber cable. The optical fiber, the optical cable and the total reflection mirror are all glass products, and the optical fiber shell of the probe is plastic product, which has corrosion resistance. Measurement.

This probe detects the intensity of turbulence through the direct influence of atmospheric turbulence on light, and can detect some information of the atmosphere in sunny, cloudy, cloudy and rainy days, which is very meaningful.

Specific examples:

1. Use a bracket to fix the probe, and another bracket with an adjustment knob to fix the total reflection mirror. Adjust the bracket and the knob so that the distance between the probe and the total reflection mirror is 10cm, and the energy that the probe can receive reaches the maximum value.

作为调制信号。 2. Use a signal generator to generate a cosine voltage signal

as a modulating signal.

3. Load the modulation signal directly to the controller of the semiconductor laser, and drive the current of the laser controller to make the laser generate laser light that changes with the modulation signal, which is called carrier laser.

耦合器将载波激光分成两路：一路接反射式光纤湍流检测探头的入光口，载波激光从准直器射出，经10cm空气段后由全反镜返回，探头的出光口接光电探测器；另一路直接经光电探测器。 4. use

The coupler divides the carrier laser into two paths: one path is connected to the light inlet of the reflective fiber optic turbulence detection probe, the carrier laser is emitted from the collimator, and returned by the full mirror after passing through the 10cm air section, and the light exit of the probe is connected to the photodetector; The other way goes directly through the photodetector.

，采样数,即5s统计一次数据，用采集卡采集两路信号，经探头的一路称为干涉信号，另一路信号作为参考信号。 5. Set the sampling rate

, the number of samples , That is to count the data once every 5s, use the acquisition card to collect two signals, the one through the probe is called the interference signal, and the other signal is used as the reference signal.

。 6. Divide the collected interference signal by the reference signal and filter the DC to get the signal

.

信号,从采集的参考信号中提取信号的最大值

、最小值

，则

,

， 

。 7. From the reference signal extract from

signal, the maximum value of the signal is extracted from the acquired reference signal

, minimum

,but

,

,

.

信号进行

变换得到信号

，再进行

运算，得到信号

。 8. will

signal carry

Transform to get the signal

, then proceed

operation, get the signal

.

分别与

、

相乘，再经过截止频率为

和的带通滤波器，然后两式相加得到信号

。 9. Send the signal

respectively with

,

multiplied, and then pass the cutoff frequency as

and The band-pass filter, and then add the two formulas to get the signal

.

，经运算后解调出由大气湍流引起的随机相位差时间序列

。 10. Send the signal with signal Carry out correlation calculation, the relative length of this device Take 100, so the frequency that this device can detect turbulent flow is

, and demodulate the random phase difference time series caused by atmospheric turbulence after calculation

.

（

）运算，将转化为折射率起伏

，然后统计

的起伏方差

。 11. Pass

(

) operation, the Converted to Refractive Index Fluctuations

, and then statistics

Fluctuation variance of

.

12. Figure 6 shows the interference signal detected in the laboratory, and it can be seen that the fringe contrast is relatively good.

13. The phase demodulated by the demodulation algorithm is shown in Figure 7. It can be seen that the signal is relatively stable, and there are slight fluctuations in the signal at a fixed value. These fluctuations are the influence of turbulent atmosphere on the laser signal.

Claims (6)

1. high precision reflection type optical fiber turbulence pick-up unit, it is characterized in that: include the LASER Light Source that to modulate, the reflection type optical fiber turbulence detection probe, total reflective mirror, signal processing module, the emergent light of described LASER Light Source is divided into two-way after through a coupling mechanism, one road emergent light is sent into the reflection type optical fiber turbulence detection probe for surveying light, another road emergent light is that reference light is sent into signal processing module, described reflection type optical fiber turbulence detection probe comprises collimating apparatus, and the input optical fibre that is connected to respectively optoisolator, output optical fibre, described input optical fibre one termination has the FC/APC joint, other end access collimating apparatus light inlet, described output optical fibre one termination has the FC/APC joint, other end access collimating apparatus light-emitting window, described total reflective mirror and collimating apparatus keep at a certain distance away, the reflecting surface of total reflective mirror is aimed at collimating apparatus, and turbulent flow to be detected is by interval between total reflective mirror and collimating apparatus, described input optical fibre is introduced by the FC/APC joint and is surveyed light, and will survey light and send in collimating apparatus after by optoisolator, a part is surveyed light and reflex to output optical fibre in collimating apparatus, remainder is surveyed and is incident to total reflective mirror after collimating apparatus is crossed in the light transmission, be transmitted into again in collimating apparatus after described total reflective mirror reflection, and be incident to output optical fibre with survey light by collimating apparatus directly the part of reflection interfere the generation interference light signal, send into signal processing module after the optoisolator of described interference light signal by output optical fibre.

2. high precision reflection type optical fiber turbulence pick-up unit according to claim 1, it is characterized in that: the LASER Light Source that can modulate is made of the signal generator of semiconductor laser, access semiconductor laser modulated terminal, described signal generator sends modulation signal with the electric current of semiconductor laser modulation to semiconductor laser, the carrier wave laser that semiconductor laser output is changed with described modulation signal.

3. high precision reflection type optical fiber turbulence pick-up unit according to claim 1, it is characterized in that: also include circulator in the reflection type optical fiber turbulence detection probe, described input optical fibre, the output optical fibre other end access respectively circulator, access in collimating apparatus by circulator again.

4. high precision reflection type optical fiber turbulence pick-up unit according to claim 1, it is characterized in that: described collimating apparatus has spherical end, and the end face of collimating apparatus is coated with 30% the anti-film that increases.

5. high precision reflection type optical fiber turbulence pick-up unit according to claim 1, it is characterized in that: described signal processing module comprises computing machine, the data collecting card of access computing machine, the two-way photodetector in the access data capture card, wherein No. one photodetector receives reference optical signal, and another road photodetector receives interference light signal.

6. based on the high precision reflection type optical fiber turbulence detection method of the high precision reflection type optical fiber turbulence pick-up unit of claim 1, it is characterized in that: comprise the following steps:

(1) the control signal generator sends modulation signal to semiconductor laser, the carrier wave laser that the semiconductor laser outgoing changes with modulation signal;

(2) the computer control capture card carries out signals collecting, two photodetectors of capture card access gather respectively reference optical signal, interference light signal and change into electric signal with reference to light signal, interference light signal respectively, and capture card is sent to respectively in computing machine with reference to electric signal corresponding to light signal, electric signal that interference light signal is corresponding;

(3) electric signal that interference light signal is corresponding divided by electric signal corresponding to reference optical signal, is filtered direct current with the signal of gained and is processed in computing machine, needing to obtain the turbulence signal of demodulation;

(4) extract the waveform signal cos (w of carrier wave from reference signal _cT), reach calculating varying type sin (2w _cT);

(5) will need the turbulence signal of demodulation to multiply by respectively signal cos (w _cT), sin (2w _cT), then product is sent into respectively filtering in bandpass filter, filtered results added is calculated the result of addition at last by the correlation demodulation algorithm, and the turbulent flow random phase that obtains between collimating apparatus and total reflective mirror is poor

(6) through Δ n with

Relational expression

, will

Be converted into the small fluctuating Δ of the refractive index n between collimating apparatus and total reflective mirror, the fluctuating variances sigma of then adding up Δ n ²(Δ n), in formula, L is the distance between collimating apparatus and total reflective mirror, λ is the wavelength of laser.

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