Angle displacement sensor based on spatial Imbert-Feedlov displacement and preparation method thereof

Abstract

The present invention relates to an angular displacement sensor based on spatial Imbert-Federov displacement, comprising a defect layer C for generating a defect mode and two truncated photonic crystals (AB) symmetrically distributed on both sides of the defect layer C. N , (BA) N , that is, the entire structure can be expressed as (AB) N C(BA) N , where N is the period number of the photonic crystal, A, B and C are dielectric sheets with different refractive indices respectively; in the angle displacement sensor, the reflected light has a lateral displacement relative to the geometric optical predicted position, that is, the spatial Imbert-Feedrov displacement; the spatial Imbert-Feedrov displacement has a one-to-one correspondence with the incident angle. The present invention also provides a method for preparing the above-mentioned angle displacement sensor. The present invention utilizes the spatial IF displacement near the defect mode of the defect photonic crystal to achieve accurate measurement of the incident angle of the light wave when the light wave is close to vertical incidence.

Description

Technical Field

[0001] The invention belongs to the field of optical technology, and in particular relates to an angular displacement sensor based on spatial Imbert-Feedloff displacement and a preparation method thereof. Background Art

[0002] With the development of detection and sensing technology, there is an urgent need to develop high-sensitivity angle displacement sensors. Angle displacement sensors can be widely used in precision machining, industrial control, scientific experiments, etc. The accuracy and precision of commonly used mechanical angle displacement sensors are greatly limited due to mechanical errors and control errors. Therefore, it is possible to consider using non-contact optical effects to improve the sensitivity of angle displacement sensors.

[0003] When light enters from one medium into another, there are reflected beams and transmitted beams at the interface between two media with different refractive indices. According to traditional geometric optics theory, the incident light, transmitted light, and reflected light are located in the same plane, and on the interface, the incident point, transmission point, and reflection point coincide.

[0004] However, when the light field is reflected at the interface between two media, part of the energy will enter the other medium from one medium. This makes a virtual reflection surface exist below or above the interface. Then, the actual reflected light will have a lateral displacement relative to the position predicted by geometric optics, which is called spatial Imbert-Fedorov shift (IF shift). Both transverse magnetic waves and transverse electric waves can have spatial IF shift.

[0005] The spatial IF displacement is proportional to r s / r p The imaginary part of s is the reflection coefficient of the transverse electric wave, and r p is the reflection coefficient of the transverse magnetic wave, which are usually complex numbers. Based on this, the inventors considered introducing a defect layer in the photonic crystal to form a defect photonic crystal. Near the defect mode of the defect photonic crystal, the reflection coefficient phase fluctuates violently, and the reflection coefficients obtained by different polarization waves are different, which will inevitably cause the ratio r s / r p The singularity of the defect mode induces a large spatial IF displacement near the defect mode. Furthermore, the size of the spatial IF displacement is also a function of the incident angle. This effect can be applied to angle measurement to obtain a high-sensitivity angle displacement sensor. Summary of the invention

[0006] The present invention aims at the technical problems existing in the prior art and provides an angular displacement sensor based on spatial Imbert-Feedloff displacement and a preparation method thereof.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: an angular displacement sensor based on spatial Imbert-Federov displacement includes a defect layer C for generating a defect mode and two truncated photonic crystals (AB) symmetrically distributed on both sides of the defect layer C. N , (BA) N , that is, the entire structure can be expressed as (AB) N C(BA) N , where N is the period number of the photonic crystal, A, B and C are dielectric sheets with different refractive indices respectively; in the angle displacement sensor, the reflected light has a lateral displacement relative to the position predicted by geometric optics, namely, the spatial Imbert-Feedrov shift; the spatial Imbert-Feedrov shift has a one-to-one correspondence with the incident angle.

[0008] Based on the above technical solution, the present invention can also be improved as follows.

[0009] Furthermore, the period number of the photonic crystal is N=4.

[0010] Furthermore, the incident wavelength λ=0.85 μm, the material of the dielectric sheet A is silicon, and its refractive index is n a =3.636; the material of dielectric sheet B is lithium niobate, and its refractive index is n b =2.2494; the material of the dielectric sheet C is magnesium fluoride, and its refractive index is n c =1.3746.

[0011] Furthermore, the thickness of the dielectric sheet A is d a =λ / 4 / n a = 0.0584 μm, the thickness of dielectric sheet B is d b =λ / 4 / n b = 0.0945 μm, the thickness of the dielectric sheet C is d c =λ / 2 / n c =0.3092μm.

[0012] Furthermore, the angle displacement sensor has a maximum spatial Imbert-Federov displacement of 3648λ and a maximum sensitivity coefficient of 10 at the defect mode. 5 λ / deg magnitude, where λ is the wavelength of the incident light and deg represents degrees, i.e. "°".

[0013] Another object of the present invention is to provide a method for preparing the above-mentioned angular displacement sensor.

[0014] The specific technical solutions are as follows:

[0015] A method for preparing an angular displacement sensor comprises the following steps:

[0016] 1) Make dielectric sheets A and B, and arrange dielectric sheets A and B alternately to form two truncated photonic crystals (AB) N , (BA) N ;

[0017] 2) Make a dielectric sheet C and place it in the above structure (AB) N , (BA) N In the middle, a symmetrical distribution structure (AB) is formed about the center of the defect layer C. N C(BA) N .

[0018] Furthermore, in step 1), the dielectric sheet A is manufactured according to the following process: directional slicing of a silicon crystal preform → grinding → polishing to a thickness of d a =0.0584μm; the dielectric sheet B is made according to the following process: the lithium niobate crystal preform is oriented and sliced ​​→ ground → polished to a thickness of d b =0.0945μm.

[0019] Furthermore, in step 2), the dielectric sheet C is manufactured according to the following process: directional slicing of the magnesium fluoride crystal preform → grinding → polishing to a thickness of d c =0.3092μm.

[0020] The beneficial effect of the present invention is that the angle displacement sensor designed by the present invention includes a defect layer and two truncated photonic crystals symmetrically distributed about the center of the defect layer. The defect layer is used to generate a defect mode. The photonic crystal has a strong electric field localization to the defect mode, which will cause a sharp change in the ratio of the transverse electric wave reflection coefficient to the transverse magnetic wave reflection coefficient near the defect mode, thereby obtaining a larger spatial IF displacement, and the maximum spatial IF displacement can reach 3648λ. In addition, when the light wave is close to vertical incidence, the spatial IF displacement is extremely sensitive to the incident angle. When this effect is applied to the angle displacement sensor, its maximum sensitivity can reach 10 5 (λ / deg) level, thereby achieving accurate measurement of the incident angle of the light wave. Finally, the present invention also provides a preparation method of an angle displacement sensor based on spatial IF displacement, which is simple to operate and convenient for large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of an angular displacement sensor based on spatial Imbert-Feedlov displacement according to Example 1 of the present invention (N=2);

[0022] Figure 2 The relationship between the reflectivity and transmittance of the light wave and the incident angle in Example 2 of the present invention, wherein the period number N of the photonic crystal is 4;

[0023] Figure 3 is the relationship between the spatial IF displacement of the reflected light beam and the incident angle in Example 2 of the present invention;

[0024] Figure 4 The relationship between the sensitivity of the angular displacement sensor based on the spatial Imbert-Feedrov displacement and the incident angle according to the second embodiment of the present invention;

[0025] Figure 5 is a flowchart of manufacturing each dielectric sheet of Example 3 of the present invention;

[0026] Figure 6 Schematic diagram of the manufacturing steps of the angular displacement sensor based on the spatial Imbert-Feedloff displacement according to Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0028] Unless otherwise specified, the raw materials and equipment used in the present invention are conventional raw materials and equipment (conventional commercial products) in the art and can be purchased on the market.

[0029] Example 1

[0030] like Figure 1 As shown, the angular displacement sensor based on the spatial Imbert-Federoff displacement designed in this embodiment has a structure that can be expressed as (AB) 2 C(BA) 2 , that is, the period number of the photonic crystal is N = 2. Symbols A, B and C represent dielectric sheets with different refractive indices. θ is the incident angle, I i is the incident light, I r1 is the reflected light predicted by geometric optics, I r2 is the actual reflected light. r2 Reflected ray I relative to the prediction of geometric optics r1 There is a certain lateral displacement, namely the spatial Imbert-Fedorov shift (IF shift), denoted as Δ IF .

[0031] Here, the incident light is assumed to be a transverse magnetic wave (TM wave). The spatial IF displacement can be expressed as

[0032]

[0033] where r s and r pare the reflection coefficients of s-polarized light and p-polarized light, i.e., s-polarized light is transverse electric wave (TE wave) and p-polarized light is transverse magnetic wave; λ is the incident wavelength, θ is the incident angle of the light wave, Im() represents the operation of the imaginary part, cot() represents the operation of the cotangent of the angle, and i represents the imaginary unit. The incident wavelength is set to λ = 0.85 μm, which is in the visible light band.

[0034] Depend on Figure 1 It can be seen that the main body of the entire structure consists of two truncated photonic crystals (AB) N , (BA) N and defect layer C, where N is called the period number of the photonic crystal, N is a positive integer, and N=2 in the structure shown here; the two truncated photonic crystals are located on both sides of the defect layer C, forming a symmetrical distribution structure about the center of the defect layer C. The entire structure can also be regarded as a photonic crystal with defects, so the structure supports defect modes. In addition, truncated photonic crystals are also called photonic multilayers, so the entire structure is also a photonic multilayer structure.

[0035] The defect mode has a strong localization effect on the electric field, which will cause a dramatic fluctuation in the phase of the reflection coefficient. Therefore, near the defect mode, as the incident wavelength or incident angle changes, the imaginary part of the reflection coefficient will inevitably change dramatically, thereby achieving a larger spatial IF displacement.

[0036] Example 2

[0037] This embodiment takes the photon multilayer structure made by N=4 as an example for measurement, and the whole structure is represented by (AB) 4 C(BA) 4 The incident wavelength is λ = 0.85 μm and it is a TM excitation wave. The dielectric sheet A is silicon (Si) with a refractive index of n a =3.636; the dielectric sheet B is lithium niobate (LiNbO3), and its refractive index is n b =2.2494; the dielectric sheet C is magnesium fluoride (MgF2), and its refractive index is n c =1.3746.

[0038] The thickness of the dielectric sheet A is one quarter of the optical wavelength, i.e., d a =λ / 4 / n a =0.0584μm; the thickness of dielectric sheet B is also one quarter of the optical wavelength, i.e., d b =λ / 4 / n b =0.0945μm; the thickness of the dielectric sheet C is half the optical wavelength, i.e. d c =λ / 2 / n c =0.3092μm.

[0039] Figure 2 The relationship between the reflectivity and transmittance of light waves and the incident angle is given. The vertical coordinates R and T represent the reflectivity and transmittance of the light wave respectively. The horizontal coordinate unit deg represents degrees, that is, "°". It can be seen that: when the light wave is incident vertically, that is, when the incident angle is θ=0°, the reflectivity R=0, and the transmittance T=1, which is called the transmission mode, that is, the defect mode; when the light wave is incident obliquely, as the absolute value of the incident angle increases, the reflectivity gradually increases, while the transmittance gradually decreases; when the incident angle is greater than 40°, the reflectivity is approximately equal to 1, and the transmittance is approximately equal to 0.

[0040] Figure 3 The relationship between the spatial IF displacement of the reflected light beam and the incident angle is given. It can be seen that: when the incident wavelength is fixed, the spatial IF displacement of the reflected light beam changes with the incident angle; when the incident angle is relatively small, especially close to 0°, the spatial IF displacement of the reflected light beam is extremely large, as shown in the position marked by the dotted circle; just at the defect mode, the maximum spatial IF displacement can be as high as 3648λ; the reflectivity at the defect mode is 0, so this is to increase the spatial IF displacement at the expense of reflectivity.

[0041] There is a one-to-one correspondence between the lateral movement of the reflected light beam (i.e., spatial IF displacement) and the incident angle. Therefore, when the incident angle of the light changes, the lateral displacement of the reflected light beam also changes accordingly. In this way, the incident angle or angle change (i.e., angle displacement) of the light can be measured by measuring the spatial IF displacement of the reflected light beam. In particular, when the light is close to vertical incidence, a slight change in the incident angle can cause a huge spatial IF displacement, which means that the sensitivity of the angle displacement sensor is very high at this time, and accurate angle measurement can be achieved.

[0042] When the spatial IF displacement effect is applied to angle measurement, Figure 4 The relationship between the sensitivity of the angle displacement sensor and the incident angle is given. It can be seen that the sensitivity of the angle displacement sensor changes with the incident angle; in particular, when the incident angle θ = 0°, that is, at the defect mode, there is a depression in the sensitivity curve, and the absolute value of the sensitivity at this time is the largest, which can be as high as |S IF |=1.824×10 5 λ / deg. Therefore, angular displacement sensors based on spatial IF displacement are extremely sensitive at near normal incidence.

[0043] Example 3

[0044] This embodiment takes the photonic multilayer structure made with N=2 as an example to provide the preparation methods of each dielectric sheet and the angle displacement sensor. The entire structure of this embodiment is different from that of Embodiment 2 only in that N=2, and the rest of the structure is the same.

[0045] Figure 5 The following is a production process of dielectric sheets A, B and C. The specific process is as follows:

[0046] 1) Preparation of dielectric sheet A: Oriented slicing of silicon crystal preform → grinding → polishing to a thickness of d a =0.0584 μm;

[0047] 2) Preparation of dielectric sheet B: Lithium niobate crystal preform rod is oriented and sliced ​​→ ground → polished to a thickness of d b =0.0945 μm;

[0048] 3) Preparation of dielectric sheet C: Oriented slicing of magnesium fluoride crystal preform → grinding → polishing to a thickness of d c =0.3092μm.

[0049] Figure 6 This is the manufacturing steps of the angular displacement sensor based on spatial IF displacement. The dielectric layers used in the sensor are the dielectric sheets A, B and C manufactured by the above method.

[0050] Step 1: Dielectric sheets A and B are arranged alternately to form two truncated photonic crystal structures: (AB) N and(BA) N , take N = 2 as an example, that is, ABAB and BABA, such as Figure 6 (a) shown.

[0051] Step 2: The dielectric sheet C is placed in the middle of the above structures ABAB and BABA to form a central symmetrical structure ABABCBABA about C, as shown in Figure 6 As shown in (b), the incident TM light from the outside is used to measure the incident angle and angle change (i.e. angular displacement) through the spatial IF displacement of the reflected light beam.

[0052] In summary, the angle displacement sensor of the present invention utilizes the spatial IF displacement near the defect mode of the defect photonic crystal to achieve accurate measurement of the incident angle of the light wave when the TM light wave is close to vertical incidence. The spatial IF displacement is a function of the incident angle, and the maximum spatial IF displacement can reach 3648λ. When this spatial IF displacement effect is applied to the angle displacement sensor, its maximum sensitivity coefficient can reach 10 5 In addition, the preparation method of the present invention is simple to operate and convenient for large-scale production and application.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An angular displacement sensor based on spatial Imbert-Federoff displacement, characterized in that: The angle displacement sensor comprises a defect layer C for generating a defect mode and two truncated photonic crystals (AB) symmetrically distributed on both sides of the defect layer C. N , (BA) N , that is, the entire structure can be expressed as (AB) N C(BA) N , where N is the period number of the photonic crystal, A, B and C are dielectric sheets with different refractive indices respectively; in the angle displacement sensor, the reflected light has a lateral displacement relative to the position predicted by geometric optics, namely, the spatial Imbert-Feedrov shift; the spatial Imbert-Feedrov shift has a one-to-one correspondence with the incident angle.

2. The angular displacement sensor based on spatial Imbert-Feedlov displacement according to claim 1, characterized in that: The period number of the photonic crystal is N=4.

3. The angular displacement sensor based on spatial Imbert-Feedlov displacement according to claim 2, characterized in that: The incident wavelength λ = 0.85 μm, the material of the dielectric sheet A is silicon, and its refractive index is n a =3.636; the material of dielectric sheet B is lithium niobate, and its refractive index is n b =2.2494; the material of the dielectric sheet C is magnesium fluoride, and its refractive index is n c =1.3746.

4. The angular displacement sensor based on spatial Imbert-Feedrov displacement according to claim 3, characterized in that: The thickness of the dielectric sheet A is d a =λ / 4 / n a = 0.0584 μm, the thickness of dielectric sheet B is d b =λ / 4 / n b = 0.0945 μm, the thickness of the dielectric sheet C is d c =λ / 2 / n c =0.3092μm.

5. The angular displacement sensor based on spatial Imbert-Feedlov displacement according to claim 4, characterized in that: The angle displacement sensor has a maximum spatial Imbert-Federoff displacement of 3648λ and a maximum sensitivity coefficient of 10 at the defect mode. 5 λ / deg magnitude, where λ is the wavelength of the incident light and deg represents degrees, i.e. "°".

6. A method for preparing the angular displacement sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Make dielectric sheets A and B, and arrange dielectric sheets A and B alternately to form two truncated photonic crystals (AB) N , (BA) N ; 2) Make a dielectric sheet C and place it in the above structure (AB) N , (BA) N In the middle, a symmetrical distribution structure (AB) is formed about the center of the defect layer C. N C(BA) N .

7. The method for preparing the angular displacement sensor according to claim 6, characterized in that: In step 1), the dielectric sheet A is manufactured according to the following process: directional slicing of a silicon crystal preform → grinding → polishing to a thickness of d a =0.0584μm; the dielectric sheet B is made according to the following process: the lithium niobate crystal preform is oriented and sliced ​​→ ground → polished to a thickness of d b =0.0945μm.

8. The method for preparing the angular displacement sensor according to claim 6, characterized in that: In step 2), the dielectric sheet C is made according to the following process: directional slicing of the magnesium fluoride crystal preform → grinding → polishing to a thickness of d c =0.3092μm.

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