CN108362394B - Crystal optical waveguide speckle thermometry and system based on femtosecond laser write-in - Google Patents

Abstract

The present invention relates to a kind of crystal optical waveguide speckle thermometries based on femtosecond laser write-in and system, technical characterstic to be: the following steps are included: step 1, using femtosecond laser Writing Technology channel-style covering optical waveguide is written in cubic system crystal；Step 2, using end coupling technology by the laser coupled of different wave length enter the step 1 channel-style covering optical waveguide, and while changing cubic system crystal temperature effect record temperature changing process in channel-style covering optical waveguide exit end speckle pattern；Step 3 carrys out resolution temperature variation to speckle pattern collected under different temperatures in step 2 progress calculation processing.The measurement accuracy of temperature measurement can be improved in the crystal waveguide for the different geometries that the present invention is prepared using femtosecond laser Writing Technology, expands the dynamic range of temperature measurement.

Description

Method and system for measuring speckle temperature of crystal optical waveguide based on femtosecond laser writing

technical field

The invention belongs to the technical field of temperature measurement, and relates to temperature measurement of crystal optical waveguide speckles, in particular to a method and system for measuring the temperature of crystal optical waveguide speckles based on femtosecond laser writing.

Background technique

Speckle is ubiquitous in laser lighting and coherent imaging systems. It is composed of a large number of fine high-contrast bright spots. It is a phenomenon of random distribution of light intensity after the interaction between laser and object. Speckle will inevitably be caused by state changes such as displacement or deformation of the object. Therefore, the state change information of the object can be obtained by measuring the change of the speckle field.

At present, temperature measurement technology is one of the indispensable technologies in human production and life. As an emerging sensing technology, multimode optical fiber speckle sensing technology can also be used to measure ambient temperature. It is based on the distribution of light transmission modes in optical fibers. The principle of changing with the change of external temperature has the advantages of high sensitivity and low cost. However, due to the long geometric length of the optical fiber, it is troublesome to fix it after winding, and it occupies a large volume. The measurement accuracy and stability are easily affected by vibration during the measurement process; on the other hand, the speckle statistical method is only suitable for smaller Temperature changes, so the dynamic range of this technology for temperature measurement is small. Although the dynamic range can be improved by establishing a new reference speckle, this will bring new measurement errors.

Therefore, how to develop a crystal optical waveguide speckle temperature measurement method and system with high temperature measurement accuracy, strong stability and large measurement dynamic range is a technical problem to be solved by those skilled in the art.

Contents of the invention

The object of the present invention is to provide a crystal optical waveguide speckle temperature measurement method and system based on femtosecond laser writing with reasonable design, large dynamic range of temperature measurement and high measurement accuracy.

The present invention solves its practical problems and is realized by taking the following technical solutions:

A method for measuring the speckle temperature of a crystal optical waveguide based on femtosecond laser writing, comprising the following steps:

Step 1. Using femtosecond laser writing technology to write channel-type cladding optical waveguides with different geometric shapes in the cubic crystal, and the core diameter of the channel-type cladding optical waveguide ranges from 50 μm to 100 μm;

Step 2. Coupling lasers of different wavelengths into the channel-type cladding optical waveguide in step 1 by using end-face coupling technology, and recording the speckle at the output end of the channel-type cladding optical waveguide during the temperature change process while changing the temperature of the cubic crystal picture;

Step 3. Calculating and processing the speckle patterns collected at different temperatures in step 2 to analyze temperature changes.

Moreover, the cubic crystal in step 1 is a lithium niobate crystal, and a semicircular channel-type cladding optical waveguide is written in the lithium niobate crystal, and the core diameter of the channel-type cladding optical waveguide ranges from 60 μm.

Moreover, the specific method of step 3 is: set the speckle pattern at the initial temperature as a reference, use the following formula to calculate the average intensity change between the speckle pattern after the temperature change and the reference speckle pattern, and calculate the temperature change Perform linear fitting with the corresponding speckle intensity change, and analyze the temperature change according to this linear relationship;

In the above formula, AIV represents the average intensity change between the speckle image after the temperature change and the reference speckle image, X Y represents the pixel size of the speckle image, (x, y) represents the intensity of a certain pixel in the speckle image coordinate, Represents the pixel gray value of the initial speckle image at the (x, y) coordinates, is the pixel gray value at the corresponding position of the speckle image taken in the i-th temperature state.

An experimental system for writing channel-type cladding optical waveguides of different geometries in cubic crystals using femtosecond laser writing technology for implementing step 1, including femtosecond lasers, half-wave plates, Glan-Taylor prisms, Neutral filter, dichroic mirror, three-dimensional electric platform, controller, computer, electric shutter, illumination light source, CCD, lens and beam splitter; the femtosecond laser emitted by the femtosecond laser passes through the half-wave plate, the gran After the Taylor prism, neutral filter and dichroic mirror, the microscope objective lens is used to focus on the surface or inside of the cubic crystal sample to form a channel-type cladding optical waveguide; the electric shutter is set on the neutral filter and dichroic mirror Between, one end of it is connected with the computer to control the switch of the femtosecond laser; the computer is also connected with the three-dimensional electric platform through the controller, and the cubic crystal sample is placed on the three-dimensional electric platform, which is used to control the writing of the crystal sample. The parameters of input rate and writing depth; the illumination light source is irradiated onto the cubic crystal sample through a beam splitter, a dichroic mirror, and a microscopic objective lens in sequence, and the reflected light then passes through a microscopic objective lens, a dichroic mirror, and a beam splitter And the lens is projected to the CCD, and the CCD is connected to the computer for real-time observation of the channel-type cladding optical waveguide engraving process.

A method for realizing step 2 by coupling lasers of different wavelengths into the channel-type cladding optical waveguide using end-face coupling technology, and recording the speckle at the emission end of the channel-type cladding optical waveguide during the temperature change process while changing the cubic crystal temperature The experimental system of the figure includes three lasers with different wavelengths, reflectors, beam splitters, half-wave plates, microscope objectives, channel-type cladding optical waveguides, semiconductor refrigeration sheets and CCDs; the three lasers with different wavelengths are parallel Placed, the outgoing laser light is placed on the same horizontal axis through the reflector and the beam splitter, and then coupled into the channel-type cladding optical waveguide through the half-wave plate and the microscope objective lens. The objective lens is projected to the CCD for shooting the speckle pattern; the semiconductor cooling chip is placed under the cubic crystal to apply temperature changes to the cubic crystal.

Advantages and beneficial effects of the present invention:

1. The present invention uses femtosecond laser writing technology to prepare channel-type cladding optical waveguides with different geometric shapes, which can improve the dynamic range of temperature measurement while ensuring measurement accuracy. For example, in the experiment, using femtosecond laser writing The yttrium aluminum garnet channel-type cladding optical waveguide prepared by the technology can be used for temperature sensing with an accuracy of 0.05°C, and the dynamic range of the semicircular channel-type clad optical waveguide for temperature sensing can reach 10°C, which is obviously superior. The dynamic range of a rectangular channel-type cladding optical waveguide is usually 3°C.

2. The present invention adopts channel-type cladding optical waveguides with smaller geometric dimensions than multimode optical fibers to prepare various geometric structures, and can be applied to various materials (such as yttrium aluminum garnet crystals, lithium niobate crystals, etc.) , which provides a good choice for us to conduct a variety of tests in different environments and obtain optimal performance (such as dynamic range, sensing accuracy, etc.). Experiments have proved that the core diameter carved in lithium niobate crystals is 60 μm The dynamic range of the channel-type cladding optical waveguide for temperature sensing can reach 20 °C.

Description of drawings

Fig. 1 is the experimental system structural representation of utilizing femtosecond laser technology to process channel-type cladding optical waveguide in step 1 of the present invention;

Fig. 2 (a)-(c) is the channel-type cladding optical waveguide micrograph and speckle pattern of the present invention;

Fig. 3 is a schematic structural diagram of a test system for coupling lasers of different wavelengths into a channel-type cladding optical waveguide using end-face coupling technology in step 2 of the present invention;

Fig. 4 (a)-(f) is the experimental result diagram of the relationship between the variation of speckle intensity and the variation of temperature in the present invention;

Fig. 5 (a) is the semi-circular channel type cladding optical waveguide experimental result diagram of the variation trend of the speckle intensity variation with the increase of temperature under the action of different wavelength lasers of the present invention;

Fig. 5 (b) is a rectangular channel-type cladding optical waveguide experimental result diagram of the variation trend of the speckle intensity variation with the increase of temperature under the action of different wavelength lasers of the present invention;

Fig. 6 (a) is the semicircular channel type cladding optical waveguide experimental result diagram of the variation trend of speckle intensity variation with temperature increase under the action of different intensities of laser light according to the present invention;

Fig. 6(b) is a graph showing the experimental results of the rectangular channel cladding optical waveguide of the variation trend of the speckle intensity variation with the increase of temperature under the action of different intensities of laser light according to the present invention.

Detailed ways

Embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings:

A method for measuring the speckle temperature of a crystal optical waveguide based on femtosecond laser writing, comprising the following steps:

Step 1. Using femtosecond laser writing technology to write channel-type cladding optical waveguides with different geometric shapes in the cubic crystal, and the core diameter of the channel-type cladding optical waveguide ranges from 50 μm to 100 μm;

The cubic crystals can be yttrium aluminum garnet crystals or lithium niobate crystals, etc. In this embodiment, the femtosecond laser writing technology is used to write channels in yttrium aluminum garnet crystals (Nd:YAG crystals) Type cladding optical waveguide, which will provide the most important sensing element for the temperature measurement in step 2. And prepare the channel-type cladding optical waveguide into different geometric shapes (rectangular and semicircular) according to the needs so as to compare its influence on the dynamic range, and the core diameter of the channel-type cladding optical waveguide should be 50 -100 μm or so to ensure that the light presents multiple modes when it is transmitted, thus providing a good precondition for the acquisition of the speckle pattern in step 2.

In this embodiment, the experimental system for writing channel-type cladding optical waveguides in cubic crystals using femtosecond laser writing technology in step 1 is shown in Figure 1, including femtosecond lasers, half-wave plates, lattice Lan Taylor prism (used as polarizer), neutral filter, dichroic mirror, three-dimensional motorized stage, controller, computer, motorized shutter, illumination source, CCD (image sensor), lens and beam splitter; the femtosecond The femtosecond laser emitted by the laser passes through the half-wave plate, Glan-Taylor prism (used as a polarizer), neutral filter and dichroic mirror, and then is focused on the surface or inside of the crystal sample by the microscope objective lens to form a channel-type package. layer optical waveguide; the electric shutter is arranged between the neutral filter and the dichroic mirror, and one end thereof is connected with a computer for controlling the switch of the femtosecond laser; the computer is also connected with a three-dimensional electric platform through a controller, the Cubic crystal samples are placed on the three-dimensional motorized platform, which is used to control the parameters of the writing rate and writing depth of the crystal samples; the illumination light source sequentially passes through the beam splitter, dichroic mirror and microscopic objective lens to illuminate the cubic crystal samples After the reflected light passes through the microscope objective, dichroic mirror, beam splitter and lens in turn, it is projected to the CCD, and the CCD is connected to the computer for real-time observation of the engraving process of the channel-type cladding optical waveguide.

Using this experimental system to write channel-type cladding optical waveguides in yttrium aluminum garnet crystals (Nd:YAG crystals) is as follows: the sample is placed in the horizontal direction (XY direction) with a resolution of 100nm, and the vertical direction (Z direction) ) on an XYZ three-dimensional motorized platform with a resolution of 1 μm, the femtosecond laser emitted by the femtosecond laser passes through the optical components of the half-wave plate, the Glan Taylor prism (used as a polarizer), the neutral filter and the dichroic mirror in sequence The microscopic objective lens is focused on the surface or inside of the sample; and by adjusting the optical components, the parameters such as polarization and pulse energy of the femtosecond laser can be adjusted. The refractive index of the material at the focal point increases or decreases, and finally after one or several scans, A channel optical waveguide is formed.

In this embodiment, the electric shutter connected to the computer is used to write the processing program to control the switch of the femtosecond laser. CCD can provide intuitive and real-time processing images, providing guarantee for the realization of fine processing. The three-dimensional electric platform is controlled by computer software, and the program code can be written according to the experimental requirements, and parameters such as writing rate and writing depth can be adjusted.

In this embodiment, the working center wavelength of the femtosecond laser is 800 nm, the pulse width is 120 fs, the repetition frequency is 1 kHz, and the highest pulse energy is 1 mJ. The femtosecond laser is focused on the surface (10×10mm2) or inside of the Nd:YAG crystal through a 40×microscopic objective lens (Leica, N.A.=0.65) to start writing.

And in order to avoid crystal cracks caused by too high laser energy or too low energy to form obvious refractive index changes during the writing process, after the femtosecond laser passes through optical components such as neutral filters, half-wave plates, and linear polarizers, its single pulse The energy was set at 0.2-0.4 μJ, and the sample was scanned at a scan rate of 700 μm/s. By adjusting the laser focus depth during multiple scans, a large number of written traces with intervals of 3-4 μm and different depths are formed inside the crystal. The refractive index of these written traces decreases, and the refractive index of the surrounding area relatively increases, and this area is the channel-type cladding optical waveguide.

Figure 2 is the microscopic image and speckle image of the crystal optical waveguide, in which Figure 2(a) and Figure 2(b) are the microscopic cross-sectional views of the semicircular and rectangular waveguides and their speckle images at a wavelength of 460nm, respectively, Figure 2 (c) is a microscope top view image of the rectangular waveguide, where the traces written by the femtosecond laser in the crystal can be clearly observed.

Step 2: Coupling laser light of different wavelengths into the channel-type cladding optical waveguide in step 1 by using end-face coupling technology, a speckle pattern formed due to multi-mode interference will appear on the exit end face of the channel-type cladding optical waveguide, and While changing the temperature of the cubic crystal sample, an image sensor is used to record the speckle pattern at the exit end of the channel-type cladding optical waveguide during the temperature change process;

In this embodiment, the experimental system of step 2 is shown in Figure 3, including three lasers with different wavelengths (wavelengths are 633nm, 532nm and 460nm), mirrors, beam splitters, half-wave plates, microscope Objective lens, channel-type cladding optical waveguide, semiconductor cooling plate and CCD; the three lasers with different wavelengths are placed in parallel, and the outgoing laser light is placed on the same horizontal axis through a reflector and a beam splitter, and then passes through a half-wave plate and a display. The micro-objective lens is coupled into the channel-type cladding optical waveguide, and the light at the output end of the channel-type cladding optical waveguide is projected to the CCD through the micro-objective lens for shooting the speckle pattern; A temperature change is applied to the cubic crystal.

Three laser beams with different wavelengths are coaxially placed by using mirrors and beam splitters (to verify the influence of different wavelength lasers on the sensitivity of the system). The laser beams are focused by the objective lens and coupled into the channel-type cladding optical waveguide. A variety of modes are excited in the channel-type cladding optical waveguide, and the speckle pattern formed by the mutual interference of these modes at the exit end of the channel-type cladding optical waveguide is imaged to the image sensor (CCD) by the objective lens and recorded by the CCD. The semiconductor refrigeration chip mainly Used to apply a temperature change to the crystal.

The working principle of the step 2 is:

Using the end-face coupling technology, the incident laser light is converged by the microscope objective lens, then vertically coupled into the waveguide through the incident end face of the waveguide, and then exits from the corresponding waveguide end face after transmission, and the outgoing light can be measured after being collected by the objective lens. After lasers of different wavelengths are coupled into the waveguide, multiple propagation modes will be excited in the waveguide. The random interference of these modes will form a speckle pattern containing bright and dark spots at the waveguide emission end. The temperature change imposed by the semiconductor refrigerator on the crystal will cause The thermal expansion effect leads to small deformation of the crystal and small changes in the refractive index, which redistributes the modes in the optical waveguide, and finally leads to changes in the speckle pattern at the exit end of the optical waveguide. The image sensor (CCD) is used to record the channel during the temperature change process. The speckle pattern at the exit end of a cladding waveguide.

Step 3. Calculate and process a series of speckle patterns collected at different temperatures in step 2 to analyze the temperature change. We set the speckle pattern at the initial temperature as a reference, and calculate the speckle pattern after the temperature change and the reference scatter pattern. The average intensity change between the speckle patterns (that is, the absolute value of the gray level difference between the corresponding pixels of the two speckle patterns is averaged), and the temperature change is linearly fitted with the corresponding speckle intensity change. According to this linear relationship to analyze temperature changes.

In this embodiment, the specific method of step 3 is: calculate and process a series of speckle patterns collected at different temperatures, we set the speckle pattern at the initial temperature as a reference, and use MATLAB software and the following formula to calculate Average intensity variation (AIV) between the speckle image after the temperature change and the reference speckle image, that is, the absolute value of the gray level difference between the corresponding pixels of the two speckle images is averaged, the algorithm is shown in formula 1 As shown, and the temperature change is linearly fitted with the corresponding speckle intensity change, and the temperature change is analyzed according to this linear relationship.

In the above formula, AIV represents the average intensity change between the speckle image after the temperature change and the reference speckle image, X Y represents the pixel size of the speckle image, (x, y) represents the intensity of a certain pixel in the speckle image coordinate, Represents the pixel gray value of the initial speckle image at the (x, y) coordinates, is the pixel gray value at the corresponding position of the speckle image taken in the i-th temperature state.

Figure 4 is the experimental results diagram of the relationship between the change of speckle intensity and the temperature change, in which Figure 4 (a)-(c) is the calculation result of the semicircular waveguide, (a), (b), and (c) are respectively Experimental results under different temperature ranges, (d-f) are calculation results for rectangular waveguides. It can be seen from the figure that the average intensity change shows a stable and good linear relationship with the increase of temperature, and the dynamic range of the semicircular waveguide can reach 10°C (see Figure 4(a)), while the dynamic range of the rectangular waveguide is only about 3°C (see Fig. 4(d)), in addition, the sensing accuracy of both shapes of waveguides can reach 0.05°C (see Fig. 4(c), (f)). The experimental results shown in Figure 4 show that the variation of speckle intensity has a stable and good linear relationship with the increase of temperature within a certain range, and this range (ie dynamic range) will be slightly different due to the different shapes of the crystal waveguide, among which the rectangular The dynamic range of the waveguide is 3°C, while the dynamic range of the semicircular waveguide can reach 10°C, which means that we can improve the dynamic range of the speckle sensor by preparing waveguides of different shapes. The reference speckle has a smaller error.

Fig. 5 is the experimental result graph that adopts the laser of different wavelengths to obtain; Wherein, Fig. 5 (a) is the semicircular channel type cladding light of the variation trend of the speckle intensity variation of the present invention with the increase of temperature under the action of different wavelength lasers Waveguide experiment result diagram; Fig. 5 (b) is the rectangular channel type cladding optical waveguide experiment result diagram of the change trend of the speckle intensity variation of the present invention with the increase of temperature under the action of different wavelength lasers;

Theoretically, the shorter the incident laser wavelength, the more modes there are in the optical waveguide, and the greater the phase difference between the modes caused by temperature changes, so that the intensity of the speckle pattern formed due to the interference between the modes changes more greatly, which is conducive to improving the quality of the crystal. Sensitivity of optical waveguide temperature sensors. As shown in Figure 5, under different laser effects, the average intensity change still changes linearly with the increase of temperature, and the shorter the incident laser wavelength selected by the system, the greater the average intensity change of the speckle, which means that the sensing sensitivity of the waveguide higher. This phenomenon is consistent with theoretical analysis.

The light intensity of the incident laser is also a factor that affects the waveguide sensing sensitivity. Figure 6 is the experimental result obtained by using a 460nm laser to incident the waveguide with different intensities; The semicircular channel type cladding optical waveguide experimental result diagram of the change trend of the spot intensity change with the temperature increase; Fig. 6 (b) is the change trend of the speckle intensity change with the temperature increase under the action of different intensities of laser light of the present invention Experimental results of a rectangular channel-type cladding optical waveguide. As shown in the figure, the greater the incident laser light intensity, the greater the average intensity change between speckle patterns, which means that moderately increasing the incident light intensity can improve the sensing sensitivity of the waveguide, and appropriately increasing the incident laser intensity will also improve Its sensitivity provides a good selection condition for the optimization of the sensing system. However, it should be noted that the light intensity is generally limited within the range that does not saturate the pixel gray value of the CCD. If the test light intensity is high, the light intensity can be reduced by adding an attenuation film to prevent the CCD device from being damaged.

The working principle of the present invention is:

Femtosecond laser writing technology is currently one of the most effective technologies for preparing optical waveguides. It does not need to be combined with photolithography mask technology, the processing process is fast and efficient, and it has low requirements on the experimental environment and other conditions; Optical waveguides can be prepared in various materials such as glass, crystals, and ceramics; their spatial resolution is high, and the processing accuracy can reach tens of nanometers, realizing precise Wiener processing, and the thermal effect is not obvious during processing, and it is not easy to damage the material; in addition , femtosecond laser processing technology is a true three-dimensional processing technology, which can complete the preparation of waveguide structures with arbitrary lengths and angles at any depth in the substrate material, which is convenient for the preparation of optical waveguide devices with different geometric shapes.

The fabrication of optical waveguides by femtosecond laser writing is mainly through laser induction in transparent optical materials by near-infrared ultrashort pulse lasers with strong penetrating ability, so as to change the refractive index of the materials and complete the preparation work. In the laser induction process, the femtosecond laser pulse energy is mainly absorbed by the material through nonlinear optical processes, such as two-photon or multi-photon absorption, and causes tunneling ionization and avalanche ionization in a short time, thereby causing changes in the stress field, resulting in The refractive index of the material increases or decreases, and finally passes through one or several scans to form a channel optical waveguide.

Using femtosecond laser writing technology to prepare larger-sized cladding optical waveguides in crystals (such as: Nd-doped yttrium aluminum garnet crystals, lithium niobate crystals, etc.), the laser usually presents various mode, this phenomenon is obviously not conducive to the application of laser crystals in waveguide lasers, but the speckle phenomenon caused by multi-mode interference just belongs to the category of speckle metrology technology, so we can use speckle metrology technology to The speckle pattern in the optical waveguide structure realizes high-precision sensing and measurement of the temperature change of the crystal's environment.

It should be emphasized that the embodiments of the present invention are illustrative rather than restrictive, so the present invention includes and is not limited to the embodiments described in the specific implementation, and those who are obtained by those skilled in the art according to the technical solutions of the present invention Other implementation modes mentioned above also belong to the protection scope of the present invention.

Claims (5)

1. A crystal optical waveguide speckle temperature measurement method based on femtosecond laser writing, characterized in that: comprising the following steps: Step 1. Using femtosecond laser writing technology to write channel-type cladding optical waveguides with different geometric shapes in the cubic crystal, and the core diameter of the channel-type cladding optical waveguide ranges from 50 μm to 100 μm; Step 2. Coupling lasers of different wavelengths into the channel-type cladding optical waveguide in step 1 by using end-face coupling technology, and recording the speckle at the output end of the channel-type cladding optical waveguide during the temperature change process while changing the temperature of the cubic crystal picture; Step 3. Calculating and processing the speckle patterns collected at different temperatures in step 2 to analyze temperature changes. 2. A kind of crystal optical waveguide speckle temperature measuring method based on femtosecond laser writing according to claim 1, is characterized in that: the cubic system crystal of described step 1 is lithium niobate crystal, in lithium niobate crystal A semicircular channel-type cladding optical waveguide is written in, and the core diameter of the channel-type cladding optical waveguide ranges from 60 μm. 3. A method for measuring speckle temperature of a crystal optical waveguide based on femtosecond laser writing according to claim 1 or 2, characterized in that: the specific method of step 3 is: setting the speckle pattern at the initial temperature For reference, use the following formula to calculate the average intensity change between the speckle pattern after the temperature change and the reference speckle pattern, and perform linear fitting between the temperature change and the corresponding speckle intensity change, and analyze according to this linear relationship temperature change; In the above formula, AIV represents the average intensity change between the speckle image after the temperature change and the reference speckle image, X Y represents the pixel size of the speckle image, (x, y) represents the intensity of a certain pixel in the speckle image coordinate, Represents the pixel gray value of the initial speckle image at the (x, y) coordinates, is the pixel gray value at the corresponding position of the speckle image taken in the i-th temperature state. 4. The experimental system for writing channel-type cladding optical waveguides of different geometries in cubic crystals using femtosecond laser writing technology in step 1 of any one of claims 1 to 3, characterized in that : Including femtosecond laser, half-wave plate, Glan Taylor prism, neutral filter, dichroic mirror, three-dimensional motorized platform, controller, computer, motorized shutter, illumination source, CCD, lens and beam splitter; The femtosecond laser emitted by the second laser passes through the half-wave plate, Glan-Taylor prism, neutral filter and dichroic mirror in turn, and then is focused on the surface or inside of the cubic crystal sample by the microscopic objective lens to form a channel-type cladding optical waveguide ; The electric shutter is arranged between the neutral filter and the dichroic mirror, and one end thereof is connected with the computer for controlling the switch of the femtosecond laser; the computer is also connected with the three-dimensional electric platform through the controller, and the three-dimensional electric platform A cubic crystal sample is placed on it to regulate the parameters of the writing rate and writing depth of the crystal sample; The light then passes through the microscopic objective lens, dichroic mirror, beam splitter and lens in turn and projects to the CCD, and the CCD is connected to the computer for real-time observation of the engraving process of the channel-type cladding optical waveguide. 5. As described in any one of claims 1 to 3, step 2 adopts end-face coupling technology to couple lasers of different wavelengths into the channel-type cladding optical waveguide, and record the temperature change process while changing the temperature of the cubic crystal The experimental system of the speckle pattern at the output end of the channel-type cladding optical waveguide is characterized in that it includes three lasers with different wavelengths, a reflector, a beam splitter, a half-wave plate, a microscope objective lens, a channel-type cladding optical waveguide, Semiconductor cooling chip and CCD; the three lasers with different wavelengths are placed in parallel, and the outgoing laser light is placed on the same horizontal axis through the reflector and the beam splitter, and then coupled into the channel-type cladding light through the half-wave plate and the microscope objective lens The waveguide, the light at the exit end of the channel-type cladding light waveguide is projected to the CCD through the microscope objective lens for shooting the speckle pattern; the semiconductor cooling chip is placed under the cubic crystal to apply temperature changes to the cubic crystal .