A design method for coupling lens for radiative fiber optic temperature field measurement

Abstract

The present invention discloses a design method for a coupling lens for radiation-type optical fiber temperature field measurement. The method comprises the following steps: selecting a plano-convex lens as an initial structure of the lens and obtaining a relationship between a temperature measurement target diameter of a single temperature measurement channel of a sensor and a curvature radius of a sapphire lens; calculating the thickness of the sapphire lens based on the obtained curvature radius to ensure that an incident end face of the sapphire optical fiber is located on an image plane of the sapphire lens and simultaneously fits with a rear end plane of the sapphire lens; increasing the radiation light coupling capability of the sapphire lens by increasing its diameter while ensuring that sapphire lenses at the front ends of adjacent temperature measurement channels of the sensor do not interfere with each other; comparing the radiation light coupling capability of a single temperature measurement channel of the sensor to temperature measurement targets of different diameters on a test object by using ZEMAX simulation; performing curve fitting on the obtained data to obtain a relationship between the temperature measurement target diameter of a single temperature measurement channel of the sensor and the radiation light coupling capability, and selecting a lens structure with a minimum temperature measurement target diameter while ensuring that the sensor receives the radiation light energy required for its own temperature measurement.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, in particular to a design method for a coupling lens used for radiation-type optical fiber temperature field measurement. Background Art

[0002] Temperature is one of the most important parameters for determining the state of matter. Therefore, temperature measurement and control are of great significance in military, industrial, and scientific research fields. Traditional contact temperature measurement solutions, such as thermocouples and thermistors, are currently the most widely used temperature measurement technologies. However, the above solutions will come into direct contact with the object being measured during the temperature measurement process, thereby affecting the temperature distribution of the object being measured. At the same time, the reliability and anti-electromagnetic interference capabilities of the contact temperature measurement solution itself are relatively poor. For the above reasons, the field of temperature measurement technology has emerged with radiation fiber optic temperature measurement methods and systems. Since they use non-contact temperature measurement technology, they will not affect the temperature distribution of the object being measured. In addition, due to the stability and strong anti-electromagnetic interference capabilities of optical fibers, this temperature measurement method and system can be applied to high-temperature measurements in many harsh environments, such as aerospace engines and industrial furnaces.

[0003] Traditional quartz optical fiber softens at temperatures exceeding 1200°C, affecting sensor performance and limiting its temperature measurement range. Sapphire, with its melting point of 2050°C, is a better alternative, making it well suited for high-temperature environments above 1200°C. However, due to its unclad structure, sapphire fiber has a large numerical aperture. This results in excessively large target points on the object being measured for each temperature measurement channel when using sapphire fiber for temperature field measurement, severely impacting the sensor's spatial resolution.

[0004] To address the sensor's temperature measurement spatial resolution, a sapphire lens is installed at the front end of the sapphire optical fiber to limit the diameter of the temperature measurement target for each temperature measurement channel, thereby increasing the sensor's spatial resolution. The performance of radiation-based temperature sensors in low-temperature ranges has always been limited by the weak radiation energy of objects in these regions. Excessive restrictions on the temperature measurement target diameter for each temperature measurement channel weaken the sensor's radiation light coupling capability, further affecting the sensor's temperature measurement capabilities in low-temperature ranges. Summary of the Invention

[0005] The present invention aims to provide a design method for a coupling lens for radiative optical fiber temperature field measurement. The method is used to explore the radiation light coupling capability of each temperature measurement channel of the sensor for temperature measurement targets of different diameters on the object to be measured, ensuring that the radiation light coupling capability of the sensor is not affected while limiting the diameter of the temperature target.

[0006] The technical solutions of the present invention are as follows:

[0007] A method for designing a coupling lens for radiative optical fiber temperature field measurement includes the following steps:

[0008] Step 1: Select a plano-convex lens structure as the initial structure of the sapphire lens. When determining the initial structure of the sapphire lens, it is necessary to comprehensively consider the installation and processing difficulty of the sapphire lens. The plano-convex lens structure is a better lens structure, and its installation and processing are relatively simple.

[0009] Step 2: Establish the relationship between the temperature measurement target diameter of a single temperature measurement channel of the sensor and the curvature radius of the sapphire lens;

[0010] Step 3: Calculate the thickness of the sapphire lens based on the radius of curvature obtained in step 2 to ensure that the incident end face of the sapphire fiber is aligned with the image plane of the sapphire lens and the rear end plane of the lens, thereby reducing the difficulty of installing the sapphire lens. Because it is necessary to ensure that the end face of the sapphire fiber bundle is located on the image plane of the plano-convex lens, the thickness of the plano-convex lens needs to be designed to ensure that the rear end plane of the plano-convex lens coincides with the image plane of the lens. In this case, the requirement is met when the end face of the sapphire fiber bundle coincides with the rear end plane of the plano-convex lens.

[0011] Step 4: Under the premise of ensuring that the sapphire lenses at the front ends of adjacent temperature measurement channels of the sensor do not interfere with each other, the radiation light coupling capability of the sapphire lens is increased by increasing the diameter of the sapphire lens;

[0012] Step 5: Using ZEMAX simulation, obtain the radiation light coupling capability data of a single temperature measurement channel of the sensor to temperature measurement targets of different diameters on the object to be measured;

[0013] Step 6: Using the data obtained in step 5, curve fitting is performed to obtain the relationship between the temperature measurement target diameter of a single temperature measurement channel of the sensor and the radiation light coupling capability;

[0014] Step 7: Based on the curve obtained in step 6, select a lens structure with the smallest temperature measurement target diameter while ensuring that the sensor receives the radiation light energy required for its own temperature measurement.

[0015] As an option, in step 2, the relationship between the temperature measurement target diameter and the curvature radius of the sapphire lens is calculated using the following mathematical model:

[0016]

[0017] Where D is the diameter of the temperature measurement target, d is the diameter of the sapphire fiber, β is the vertical axis magnification of the lens, l is the distance between the object to be measured and the object side principal plane of the lens, l′ is the distance between the end face of the sapphire fiber and the image side principal plane of the lens, f′ is the focal length of the sapphire lens, r is the radius of curvature of the convex surface of the sapphire lens, and n is the refractive index of the sapphire lens.

[0018] As an option, the step 5 includes the following steps:

[0019] Step 5.1: Use ZEMAX non-sequential mode to simulate and model a temperature measurement channel in the radiation fiber temperature field measurement system. The model includes: a radiation light source, a sapphire lens, a sapphire fiber, and a detector to simulate the object under test.

[0020] Step 5.2, using the simulation model in step 5.1, simulate the radiation light coupling capability of the temperature measurement channel to temperature measurement targets of different diameters;

[0021] In step 5.3, the ray tracing method is used to characterize the radiation light coupling capability of the temperature measurement channel for temperature measurement targets of different diameters by the radiation light intensity received by the sapphire optical fiber back-end detector.

[0022] Compared to existing technologies, this paper proposes a design method for coupling lenses to improve the temperature measurement resolution of radiative fiber-optic temperature field measurement systems. This method is of great significance for temperature field reconstruction using fiber-optic radiation temperature measurement. This method can limit the target diameter of each temperature measurement channel on the object being measured while maintaining the sensor's optical coupling capability, thereby increasing the spatial resolution of the temperature measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the optical path of a single temperature measurement channel of the sensor in the present invention, showing the principle of how the sapphire lens limits the diameter of the temperature measurement target point of a single temperature measurement channel of the sensor;

[0024] Figure 2 This is the simulation model diagram of a single temperature measurement channel in the radiation fiber optic temperature field measurement system in ZEMAX;

[0025] Figure 3 This is a schematic diagram of the arrangement of various temperature measurement channels for radiative optical fiber temperature field measurement;

[0026] In the figure, 1-temperature measurement target, 2-sapphire lens, 3-sapphire optical fiber, 4-object side principal plane, 5-image side principal plane, 6-radiation light source, 7-detector. DETAILED DESCRIPTION

[0027] The present invention is further described below with reference to the accompanying drawings and specific embodiments. However, it should not be understood that the scope of the subject matter described in the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various modifications, substitutions and changes made according to common technical knowledge and customary means in the field are included in the scope of the present invention.

[0028] like Figure 3As shown, the radiative fiber optic temperature sensor includes N temperature measurement channels, each of which includes a sapphire lens 2 and its corresponding sapphire fiber 3. The sensor's temperature measurement target 1 is controlled primarily by using the sapphire lens 2 to ensure that the sensor's temperature measurement target 1 on the object under test is precisely imaged on the end face of the sapphire fiber 3.

[0029] like Figure 1 As shown, the diameter of the image is exactly the same as the diameter of the sapphire optical fiber 3, so the radiation light outside the target area cannot enter the sapphire optical fiber 3 for transmission. Figure 1 In the figure, P represents a point inside the temperature measurement target 1, P' represents the image point of point P after imaging through the lens, Q represents a point outside the temperature measurement target 1, and Q' represents the image point of point Q after imaging through the lens.

[0030] The control of the sensor temperature measurement target 1 is mainly achieved by changing the curvature of the sapphire lens 2. The relationship between the diameter of the sensor temperature measurement target 1 and the curvature radius of the sapphire lens 2 can be obtained according to the following formula.

[0031]

[0032] Where D is the diameter of the temperature measurement target 1, d is the diameter of the sapphire fiber 3, β is the vertical axis magnification of the lens, l is the distance between the object 1 and the object side principal plane 4 of the lens, l′ is the distance between the fiber end face and the image side principal plane 5 of the lens, f′ is the focal length of the sapphire lens 2, r is the convex curvature radius of the sapphire lens 2, and n is the refractive index of the sapphire lens 2.

[0033] Changing the thickness of the plano-convex lens will not change the focal length of the lens 2. Therefore, by changing the thickness of the sapphire lens 2, the main plane 5 of the lens image side can be made to coincide with its rear end plane. At this time, the end face of the sapphire optical fiber 3 can be fitted with the rear end plane of the sapphire lens 2, facilitating the installation of the sapphire lens 2 and the sapphire optical fiber 3.

[0034] Due to the limitation of the numerical aperture of the sapphire fiber 3, the radiation light coupled by the sapphire lens 2 cannot completely enter the sapphire fiber 3 for transmission. Therefore, the radiation light coupling ability of the sensor will not increase linearly with the increase of the diameter of the sensor temperature measurement target 1. It is necessary to explore the relationship between the diameter of the sensor temperature measurement target 1 and its radiation light coupling ability. Under the premise of ensuring that the sensor receives the radiation light energy required for its own temperature measurement, the lens structure with the smallest diameter of the temperature measurement target 1 is selected.

[0035] The relationship between the diameter of the sensor temperature measurement target 1 and the radiation light coupling ability is obtained through ZEMAX simulation software. The specific steps are as follows:

[0036] (1) First, according to Figure 1 The light path diagram shown is constructed in the non-sequential mode in ZEMAX, as shown in Figure 2 As shown, it is composed of a radiation light source 6, a sapphire lens 2, a sapphire optical fiber 3 and a detector 7.

[0037] (2) According to the above steps, the lens structure corresponding to the diameter of the temperature measurement target 1 with different values ​​can be obtained, and the lens structure can be placed in the simulation model to perform ray tracing and record the reading of the detector 7 at this time.

[0038] (3) Based on the data obtained from the above simulation, a curve can be fitted to show the relationship between the diameter of the temperature measurement target 1 of the sensor and the radiation light coupling ability. On the premise of ensuring that the sensor receives the radiation light energy required for its own temperature measurement, the lens structure with the smallest diameter of the temperature measurement target 1 is selected.

[0039] Any matters not described in detail in the present specification are prior art known to those skilled in the art. Although the above description of the present invention is based on illustrative embodiments to facilitate understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the specific embodiments. As long as various modifications are within the spirit and scope of the present invention as defined and determined by the appended claims, such modifications will be obvious to those skilled in the art, and all inventions and creations utilizing the concepts of the present invention are protected.

Claims

1. A design method for a coupling lens for radiative optical fiber temperature field measurement, characterized by: The steps include: Step 1, selecting a plano-convex lens structure as the initial structure of the sapphire lens (2); Step 2, establishing a relationship between the diameter of the temperature measurement target point (1) of a single temperature measurement channel of the sensor and the curvature radius of the sapphire lens (2); Step 3, calculating the thickness of the sapphire lens (2) based on the curvature radius obtained in step 2, and ensuring that the incident end face of the sapphire optical fiber (3) is simultaneously bonded to the image plane and the rear end plane of the sapphire lens (2); Step 4, under the premise of ensuring that the sapphire lenses (2) at the front ends of adjacent temperature measurement channels of the sensor are arranged without interfering with each other, the radiation light coupling capability of the sapphire lens (2) is increased by increasing the diameter of the sapphire lens (2); Step 5, using ZEMAX simulation to obtain the radiation light coupling capability data of a single temperature measurement channel of the sensor to the temperature measurement target points (1) with different diameters on the object to be measured; Step 6, using the data obtained in step 5 to perform curve fitting, to obtain the relationship between the diameter of the temperature measurement target point (1) of a single temperature measurement channel of the sensor and the radiation light coupling capability; Step 7: Based on the curve obtained in step 6, and under the premise of ensuring that the sensor receives the radiation light energy required for its own temperature measurement, select a lens structure with the smallest diameter of the temperature measurement target (1).

2. The design method of a coupling lens for radiative optical fiber temperature field measurement according to claim 1, characterized in that: In step 2, the relationship between the diameter of the temperature measurement target (1) and the curvature radius of the sapphire lens (2) is calculated using the following mathematical model: Wherein, D is the diameter of the temperature measurement target (1), d is the diameter of the sapphire optical fiber (3), β is the vertical axis magnification of the lens, l is the distance between the object to be measured and the object side principal plane (4) of the lens, l′ is the distance between the end face of the sapphire optical fiber (3) and the image side principal plane (5) of the lens, f′ is the focal length of the sapphire lens (2), r is the curvature radius of the convex surface of the sapphire lens (2), and n is the refractive index of the sapphire lens (2).

3. The design method of a coupling lens for radiative optical fiber temperature field measurement according to claim 1, characterized in that: The step 5 includes the following steps: Step 5.1, using ZEMAX non-sequential mode to simulate and model a temperature measurement channel in the radiation fiber temperature field measurement system, the model includes: a radiation light source (6) for simulating the object to be measured, a sapphire lens (2), a sapphire fiber (3) and a detector (7); Step 5.2, using the simulation model in step 5.1, simulate the radiation light coupling capability of the temperature measurement channel to temperature measurement targets (1) of different diameters; In step 5.3, the radiation intensity received by the rear detector (7) of the sapphire optical fiber (3) is used to characterize the radiation light coupling capability of the temperature measurement channel for temperature measurement targets (1) of different diameters by using the ray tracing method.

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