CN111486939A - Ultrasonic measuring device for realizing optical path and polarization state regulation and control based on SAGNAC principle - Google Patents

Abstract

The invention discloses an ultrasonic measuring device for realizing optical path and polarization state regulation and control based on an SAGNAC (SAGNAC) principle, which comprises a light source, a sample probe, a circulator, a first polarization controller, a second polarization controller, a third polarization controller, a fourth polarization controller, a fifth polarization controller, a first unpolarized 1 x 2 coupler, a second unpolarized 1 x 2 coupler, a photoelectric detection device, a wavelength selector and a light path selector, wherein the sample probe is connected with the light source; light from a light source firstly passes through a wavelength selector, a first polarization controller and a circulator and is divided into two paths with different lengths through a first non-polarization coupler, wherein one path is CW light along the clockwise direction, and the other path is CCW light along the counterclockwise direction; compared with the prior art, the method for realizing non-contact ultrasonic detection by utilizing the SAGNAC effect has the characteristics of simple structure, low cost, small volume, high sensitivity and wide application range.

Description

An Ultrasonic Measurement Device Based on the Principle of SAGNAC for Optical Length and Polarization Control

technical field

The invention belongs to the technical field of fiber optic gyroscopes, and in particular relates to an ultrasonic measuring device for realizing optical path and polarization state regulation and control based on the SAGNAC principle.

technical background

When the sound wave interacts with the material, the sound speed and the energy of the sound wave will change. By measuring the sound speed and the attenuation of the sound wave, some basic physical parameters of the material can be determined. This is ultrasonic testing technology, which is one of the basic methods to study the structure and properties of matter, and has been successfully applied in many fields. The traditional method of ultrasonic generation and reception is to use ultrasonic circulators, such as piezoelectric transducers, CMUT transducers, and these methods are all contact measurement methods. Currently, traditional contact transducers are increasingly being replaced by non-contact optical methods, including interferometric methods and beam deflection methods. Due to the continuous improvement of optical technology, research in this area is also developing rapidly, and new detection technologies are continuously produced, including optical fiber sensing technology. Optical fiber sensor is a new type of ultrasonic sensor, which is widely used because of its small size, light weight, strong environmental adaptability, strong reliability, easy transmission of detection signals, and good confidentiality. However, there are relatively few studies on the use of optical fiber sensors for ultrasonic testing, especially non-contact testing, especially in domestic research. Combining optical fiber sensing technology with non-contact ultrasonic testing technology will have broad prospects in the application of ultrasonic testing and flaw detection of materials.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an ultrasonic measuring device that realizes the regulation of optical path and polarization state based on the SAGNAC principle. The interference signal formed by the change of the optical path difference caused by the time when the CCW light reaches the surface of the sample successively is used to detect the ultrasonic wave on the surface of the sample. The core of the invention lies in combining with the wavelength selection technology and the optical path selection technology, and realizes the switching of the working center frequency by selecting the wavelength and the length of the optical fiber.

The details are as follows:

An ultrasonic measurement device based on the SAGNAC principle to realize the regulation of optical path and polarization state, characterized in that it includes a light source, a sample probe, a circulator, a first polarization controller, a second polarization controller, a third polarization controller, a fourth polarization controller, and a fourth polarization controller. Polarization controller, fifth polarization controller, first unpolarized 1*2 coupler, second unpolarized 1*2 coupler, photodetection device, wavelength selector and optical path selector, the wavelength selector is used for different light sources The selection of wavelength; the optical path selector is used for the selection of different fiber lengths; the switching of the working center frequency is realized by selecting the wavelength and the length of the fiber;

The light source, the wavelength selector, the first polarization controller are connected, and the circulator is connected in sequence. One of the output ends of the circulator is connected to the fifth polarization controller and the photoelectric detection device in sequence, and the other output end is connected to the first non-polarization device. The polarized 1*2 coupler is connected, one of the output ends of the first unpolarized 1*2 coupler is connected to the second polarization controller and the second unpolarized 1*2 coupler in sequence, and the other output end is connected to the third The polarization controller, the optical path selector, and the second unpolarized 1*2 coupler are connected in sequence, and the second unpolarized 1*2 coupler is connected with the fourth polarization controller and the sample probe in sequence.

A further improvement is that the photodetection device includes a polarization beam splitter and a balanced detector.

A further improvement is that the CW light and the CCW light pass through the second unpolarized 1*2 coupler, the fourth polarization controller and the sample probe to reach the ultrasonic sample, and the returned light enters the sample probe and returns to the optical fiber optical path again.

A further improvement is that the return light of the CW light and the CCW light enters the circulator after passing through the first unpolarized 1*2 coupler again, so as to realize the isolation of the incident light and the return light.

A further improvement is that the light source is a 1310nm or 1550nm SLED broad-spectrum fiber light source.

A further improvement is that the sample probe adopts the structure of a collimator and a lens to focus the sample, so that the optical signal carrying the ultrasonic information on the surface of the sample is returned to the optical path of the optical fiber.

A further improvement is that the polarization beam splitter adopts three fibers with polarization maintaining interfaces.

A further improvement is that all other optical fibers and optical fiber components except the polarization beam splitter are non-polarized.

The beneficial effects of the present invention are as follows: all the optical fiber devices used in the present invention are non-polarized except for the polarization beam splitter, which reduces the cost; , the solution of the present invention is more convenient and has good control effect; compared with the traditional use of polarization-maintaining fibers to keep the interference light orthogonal or parallel, the solution of the present invention can be realized by adjusting any two of the five polarization controllers. The same effect and easy adjustment; compared with single-ended signal detection, the method for detecting differential interference signals with a balanced detector according to the present invention has better detection sensitivity. Combined with wavelength selection technology and optical path selection technology, the switching of the working center frequency is realized by selecting the wavelength and the length of the optical fiber to achieve a better sensitivity effect.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Fig. 1 is the whole optical fiber optical path system diagram of described device;

Fig. 2 is the schematic diagram of the loop part of the device;

Fig. 3 is the analysis diagram when the optical path difference of CW light and CCW light is within half wavelength range;

Fig. 4 is the frequency selective effect analysis diagram of the interference system;

Fig. 5 is the analysis diagram that the interference signal is divided into two paths after passing through the polarization beam splitter;

Figure 6 shows that the main axis of stress of the polarization-maintaining fiber and the xy-coordinate axes formed by the o-light and e-light of the PBS crystal are coincident. The angle of polarization direction is 45° or 135°;

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

An ultrasonic measurement device based on the SAGNAC principle to realize the regulation of optical path and polarization state, characterized in that it includes a light source, a sample probe, a circulator, a first polarization controller, a second polarization controller, a third polarization controller, a fourth polarization controller, and a fourth polarization controller. Polarization controller, fifth polarization controller, first unpolarized 1*2 coupler, second unpolarized 1*2 coupler, photodetection device, wavelength selector and optical path selector; the wavelength selector is used for different light sources The selection of wavelength; the optical path selector is used for the selection of different fiber lengths; the switching of the working center frequency is realized by selecting the wavelength and the length of the fiber;

The light source, the wavelength selector, the first polarization controller are connected, and the circulator is connected in sequence. One of the output ends of the circulator is connected to the fifth polarization controller and the photoelectric detection device in sequence, and the other output end is connected to the first non-polarization device. The polarized 1*2 coupler is connected, one of the output ends of the first unpolarized 1*2 coupler is connected to the second polarization controller and the second unpolarized 1*2 coupler in sequence, and the other output end is connected to the third The polarization controller, the optical path selector, and the second unpolarized 1*2 coupler are connected in sequence, and the second unpolarized 1*2 coupler is connected with the fourth polarization controller and the sample probe in sequence.

In the ultrasonic measurement device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the photoelectric detection device includes a balanced detector and a polarization beam splitter.

In the ultrasonic measuring device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the CW light and the CCW light pass through the second unpolarized 1*2 coupler, the fourth polarization controller and the The sample probe reaches the ultrasonic sample, and the reflected light enters the sample probe and returns to the optical fiber optical path again.

In the ultrasonic measuring device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the return light of the CW light and the CCW light enters the first non-polarized 1*2 coupler again after passing through the first non-polarized 1*2 coupler. The circulator is used to realize the isolation of incident light and return light.

In the ultrasonic measuring device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the light source is a 1310nm or 1550nm SLED broad-spectrum fiber light source.

In the ultrasonic measuring device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the photoelectric detection device is a photoelectric detector.

In the ultrasonic measurement device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the sample probe adopts the structure of a collimator and a lens to focus the sample, so that the optical signal carrying the ultrasonic information on the surface of the sample is returned to the optical fiber light path.

In the ultrasonic measurement device based on the SAGNAC principle to realize the regulation of optical path and polarization state, the polarization beam splitter adopts three optical fibers with polarization-maintaining interfaces.

In the ultrasonic measuring device that realizes the regulation of optical path and polarization state based on the SAGNAC principle according to the present invention, all other optical fibers and optical fiber components except the polarization beam splitter are non-polarized.

As shown in Fig. 1, the light source of the system adopts 1310/1550nm SLED broadband low-coherence light source to avoid the interference of coherent noise. The light from the light source first passes through the wavelength selector, the first polarization controller PC1, and then the first non-polarized 1*2 coupler BS1. Assuming that the CW light first goes to the upper one in Figure 1, then the CW light will pass through in turn. Second polarization controller PC2, second unpolarized 1*2 coupler BS2, fourth polarization controller PC4, sample probe, then back to fourth polarization controller PC4, second unpolarized 1*2 coupler BS2, after that Go the following way, go through the first non-polarized 1*2 coupler BS1, the optical path selector, and the third polarization controller PC2, and then enter the circulator, the CCW light is also similar: first take the lower optical path, and go to the top when returning. light path, as shown in Figure 2.

Since most of the optical paths of the CW light and the CCW light are exactly the same, only when the CW light and the CCW light pass through the polarization controller, the polarization planes of the two beams of light will change due to the birefringence effect, and the additional The light path is also different. Using the effect of optical path change and polarization change, find the required combination of optical path and polarization. For example, in the optical path in Figure 1, the optical path (phase) difference needs to be adjusted to pi/2, and the polarization planes are orthogonal.

One specific adjustment process is: firstly adjust the second polarization controller PC2, so that the additional optical path difference between the CW light and the CCW light is pi/2. At this time, not only the optical path difference changes, but also the polarization of the CW light and the CCW light. The surface will also be deflected accordingly, resulting in reduced interference efficiency. Then adjust the first polarization controller PC1 again so that the polarization directions of the CW light and the CCW light are orthogonal, and the interference efficiency of the two orthogonal lights is almost 0, but the polarization beam splitter PBS will change from the original non-interference to the interference efficiency The largest two-way differential interference signal (as shown in Figure 6) enters the balanced detector.

为相位差，ΔL为光纤的长短臂长度差，Δτ为长短臂的延时；The principle of the present invention is as follows: wherein, λ is the wavelength, c is the wave speed of light,

is the phase difference, ΔL is the length difference between the long and short arms of the fiber, and Δτ is the delay of the long and short arms;

Consider the oscillation of the sample:

The delay of the long and short arms of the SAGNAC interferometer:

The optical path difference corresponding to the delay:

Maximum Sensitivity Conditions:

此时系统工作在干涉极大的位置，根据余弦函数的性质，该点的导数为0，也就是工作在最不灵敏的地方。为了提高静态工作点的灵敏度，在样品无信号发生的时候应该给予一个初始的相位差

A suitable operating point should have maximum sensitivity when the system has zero signal, that is, when the sample has no vibration. When the sample has no signal, since the optical path difference of the two paths is the same,

At this time, the system works at the position where the interference is extremely large. According to the properties of the cosine function, the derivative of this point is 0, that is, it works at the most insensitive place. In order to improve the sensitivity of the static working point, an initial phase difference should be given when no signal occurs in the sample

Phase Continuity Condition: As shown in Figure 3:

If the nonlinear situation is considered, it is only necessary to make ω _A Δτ work within the range of half wavelength, so as to avoid the phenomenon of phase folding. However, since nonlinearity will cause signal distortion, it is necessary to perform an inverse operation on the measured signal to recover the oscillation signal of the sample.

The conditions for ensuring phase continuity are:

Frequency selection effect of SAGNAC interferometer:

It can be seen from the previous derivation that the essence of the SAGNAC interferometer is a velocity interferometer, which is to differentiate the oscillation. The differentiator has the effect of low-pass filtering, but the actual SAGNAC interference system is not a strict differentiator. Due to the limited sensitivity of the system, the time difference between the two beams reaching the sample surface cannot be infinitely small. This non-ideal differential effect causes the SAGNAC interferometer to exhibit a frequency-selective effect, being most sensitive at some frequencies and least sensitive at others. In the situation described in Figure 4, when Δτ=π/ _ωA , the interferometer is the most sensitive; when Δτ=2π/ _ωA , the interferometer is the least sensitive. When the first beam of light (CCW light) arrives at time t1 and the second beam of light (CW light) arrives after Δτ=π/ω _A , the interference signal is also a sinusoidal signal, and the signal intensity is the largest at this time; When the beam of light (CCW) arrives at time t2, and the second beam of light (CW) arrives after Δτ=2π/ω _A , there is no signal at this time, and the signal equivalent to ω _A /2 is filtered out.

It can be seen that the choice of wavelengths of different light sources and the choice of fiber length are crucial in this technique because it directly affects the center frequency of the measurement. In order to solve this problem, on the basis of this device, it is combined with wavelength selection technology and optical path selection technology, and the switching of the working center frequency is realized by selecting the wavelength and the length of the optical fiber.

It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. an ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle, is characterized in that, comprises light source, sample probe, circulator, the first polarization controller, the second polarization controller, the third polarization controller, The fourth polarization controller, the fifth polarization controller, the first unpolarized 1*2 coupler, the second unpolarized 1*2 coupler, the photodetection device, the wavelength selector and the optical path selector; the wavelength selector is used for The selection of different light source wavelengths; the optical path selector is used for the selection of different optical fiber lengths; the switching of the working center frequency is realized by selecting the wavelength and the optical fiber length; The light source, the wavelength selector, the first polarization controller, and the circulator are connected in sequence, and one output end of the circulator is connected to the fifth polarization controller and the photoelectric detection device in sequence, and the other output end is connected to the first non-polarization device. The 1*2 coupler is connected, one of the output ends of the first unpolarized 1*2 coupler is connected to the second polarization controller and the second unpolarized 1*2 coupler in sequence, and the other output end is connected to the third polarization The controller, the optical path selector, and the second unpolarized 1*2 coupler are connected in sequence, and the second unpolarized 1*2 coupler is connected with the fourth polarization controller and the sample probe in sequence. 2. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 1, is characterized in that, the light that described light source comes out first passes through described wavelength selector, and then passes through described first The polarization controller and the circulator are then divided into two paths with different lengths through the first unpolarized 1*2 coupler, one of which is the CW light in the clockwise direction, and the other one is the CCW light in the counterclockwise direction . 3 . The ultrasonic measuring device for realizing optical path and polarization state regulation based on the SAGNAC principle according to claim 1 , wherein the photoelectric detection device comprises a polarization beam splitter and a balanced detector. 4 . 4. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 2, is characterized in that, described CW light and CCW light pass through described second non-polarization 1*2 coupler, The fourth polarization controller and the sample probe reach the ultrasonic sample, and the reflected light enters the sample probe and returns to the optical fiber optical path again. 5. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 4, it is characterized in that the return light of described CW light and CCW light passes through described first non-polarization 1*2 again After the coupler enters the circulator, the isolation of incident light and return light is realized. 6 . The ultrasonic measuring device for realizing optical path and polarization state regulation based on the SAGNAC principle according to claim 1 , wherein the light source adopts a 1310 nm or 1550 nm SLED broad-spectrum fiber light source. 7 . 7. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 1, is characterized in that, described sample probe adopts the structure of collimator and lens to focus sample, realizes carrying sample surface ultrasonic wave The optical signal of the information is returned to the optical fiber path. 8 . The ultrasonic measuring device for realizing optical path and polarization state regulation based on the SAGNAC principle according to claim 3 , wherein the polarization beam splitter adopts three optical fibers with polarization-maintaining interfaces. 9 . 9. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 3, it is characterized in that all other optical fibers and optical fiber devices except described polarization beam splitter adopt non-polarization type of. 10. a kind of ultrasonic measuring device that realizes optical path and polarization state regulation and control based on SAGNAC principle according to claim 1, it is characterized in that the combination of any two in five polarization controllers can realize initial optical path difference and polarization state. non-independent regulation.

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