An integrated Doppler differential interferometer with high thermal stability

Abstract

The present invention relates to a Doppler differential interferometer, and in particular to an integrated Doppler differential interferometer with high thermal stability. The invention solves the technical problems that the bonding stress and thermal stress in the existing integrated Doppler differential interferometer easily deteriorate the grating surface shape, resulting in a decrease in the image quality and stability of the integrated Doppler differential interferometer, and the supporting elements have poor bonding quality and are difficult to assemble and process. The interferometer of the present invention performs structural design and material design on the grating substrate and the grating supporting element, separates the grating surface from the bonding surface, designs the grating supporting element as an integrated structure with a discontinuous supporting block at one end, so that the main deformation of the grating substrate occurs on the bonding surface, ensures the surface shape accuracy of the grating surface, and improves the quality and stability of the interference pattern; the grating substrate material is matched with the field of view widening prism material, so that the change in the grating incident angle when the temperature changes offsets the change in the Littrow angle, avoiding the introduction of changes in the optical path difference.

Description

Technical Field

[0001] The invention relates to a Doppler differential interferometer, in particular to an integrated Doppler differential interferometer with high thermal stability. Background Art

[0002] The integrated Doppler differential interferometer adopts a fully glued integration method, and each component is glued together as a whole, ensuring its angle and position accuracy. The integrated Doppler differential interferometer is designed for heat removal through the selection of component materials and optimization of structural form, which can improve the gluing accuracy and stability of the interferometer.

[0003] The integrated Doppler differential interferometer consists of a beam splitter prism, a short-arm field-of-view widening prism, a long-arm field-of-view widening prism, two grating substrates and a supporting element. For the Doppler differential interferometer, the grating is an important core component, so the surface accuracy of the grating is very high. In the integrated Doppler differential interferometer, the optical elements are glued together into a whole through the supporting element. In practical applications, during the alignment and gluing process of the grating substrate and the supporting element, the residual stress caused by the curing of the glue will cause the grating surface error, causing the interference fringes to bend and deform, reducing the quality of the interference pattern. At the same time, the material expansion coefficients between the optical elements are quite different, and the grating is extremely sensitive to temperature changes. Temperature fluctuations will cause thermal stress and change with temperature, which seriously affects the surface accuracy of the grating, causing the reference optical path difference of the two arms of the interferometer to produce thermal drift, resulting in poor stability of the interferometer. Therefore, the structure of the grating and the design of the grating supporting element are key technologies to ensure the high precision and high stability of the integrated Doppler differential interferometer. In the prior art, the grating substrate used for the Doppler differential interferometer is usually a flat glass. In order to reduce the surface error of the grating substrate, the support element is cut into blocks, which alleviates the grating surface error to a certain extent. However, temperature changes still make it difficult for the grating surface to meet the requirements, so that the grating substrate surface error is still an order of magnitude larger than the surface error of the other optical surfaces of the interferometer. The design of the support element as an independent spacer block also brings another problem. That is, when bonding, it is difficult to ensure that the independent spacers on the bonding surface are flush and coplanar, resulting in poor gluing quality and cumbersome and complicated gluing and assembly process, which affects the position accuracy between optical elements and reduces the quality of the interference pattern. In addition, this type of support element composed of independent spacers needs to be processed by special parts, and the processing process is cumbersome and complicated. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problems that in the existing integrated Doppler differential interferometer, the grating substrate is a flat glass, the grating supporting element is an independent spacer block, the gluing stress and thermal stress of this structure easily deteriorate the grating surface shape, resulting in a decrease in the image quality and stability of the integrated Doppler differential interferometer, and the spacer block supporting element cannot ensure flush coplanarity, the gluing quality is poor, the gluing assembly process is cumbersome and complicated, and the processing difficulty is great, and an integrated Doppler differential interferometer is provided.

[0005] The technical solution of the present invention is:

[0006] A high thermal stability integrated Doppler differential interferometer, comprising a beam splitter prism, a short-arm field-of-view widening prism, a long-arm field-of-view widening prism, two grating substrates and a supporting element connecting the optical elements, and the special features thereof are:

[0007] The grating substrate comprises a grating bottom plate and a grating top plate arranged in the middle of the inner side of the grating bottom plate, and the cross-sectional area of ​​the grating bottom plate is larger than the cross-sectional area of ​​the grating top plate;

[0008] The grating top plate extends into the inner side of the supporting element, and its inner end surface is a grating surface, and the grating surface is used for etching the grating;

[0009] The two grating surfaces are respectively arranged corresponding to the short-arm field-of-view widening prism and the long-arm field-of-view widening prism, and there are intervals between the two grating surfaces and the corresponding short-arm field-of-view widening prism or the long-arm field-of-view widening prism, and the sizes of the two intervals are the same;

[0010] The area on the inner side of the grating bottom plate and outside the grating top plate forms a bonding surface;

[0011] The total thickness a of the grating top plate and the grating bottom plate, the length b and width y of the grating bottom plate, the thickness c of the grating bottom plate and the width d of the bonding surface meet the following conditions: a≥b / 5, a / 2≥c≥4mm, d≥c, y≤b;

[0012] A supporting element between a grating substrate and a short-arm field-of-view widening prism or a long-arm field-of-view widening prism is defined as a grating supporting element;

[0013] The grating support element is an integrated hollow frame structure, the grating connection end of which is connected to the bonding surface of the grating bottom plate, and a gap is left between the grating support element and the grating top plate; the prism connection end of the grating support element is connected to the short-arm field-of-view widening prism or the long-arm field-of-view widening prism, and the prism connection end is uniformly provided with a plurality of grooves along the thickness direction along the circumferential direction, and a plurality of support blocks connected at the bottom are formed between the grooves;

[0014] The width of the support block is t≥4mm, and t<d, the interval between the support blocks is e≥2mm, the thickness of the grating support element minus the thickness of the support block is f, and f≥2mm;

[0015] Littrow angle θ in the first-order diffraction of the grating substrate L and the grating line density satisfy the following relationship:

[0016] 2lsin(θ L )=λ L

[0017] l is the grating line spacing, ρ is the grating line density;

[0018] λ L is the Littrow wavelength of the Doppler differential interferometer;

[0019] The material expansion coefficient α of the grating substrate G Satisfies the following formula:

[0020]

[0021] is the coefficient of variation of the grating incident angle with temperature, and is a negative number;

[0022] The grating support element is made of the same material as the grating substrate.

[0023] Furthermore, the grating substrate is made by processing a piece of flat glass, or by gluing two pieces of flat glass together;

[0024] The grating substrate is made of a piece of flat glass and must meet the following conditions: the parallelism between the grating surface and the bonding surface is 20", the two side surfaces of one of the right-angled sides of the grating bottom plate are used as the two reference surfaces for grating etching and gluing, the verticality between the two reference surfaces is 10", the verticality between the grating surface and the reference surface is 10", and the parallelism between the side surface of the grating top plate and the reference surface is 20";

[0025] The grating substrate is made by gluing two pieces of flat glass together and the following conditions must be met:

[0026] The parallelism between the grating surface and the bonding surface is 8", and the verticality of the two side surfaces of one of the right-angled edges of the grating top plate is 8".

[0027] Furthermore, the materials of the short-arm field-of-view widening prism and the long-arm field-of-view widening prism are both N-SF57, the vertex angles are both 12.60°, the incident angles are both 6.84°, the material of the optical grating substrate is Fused silica, the grating line density is 900g / mm, and the applied detection wavelength is 630nm.

[0028] Furthermore, the multiple support block end faces of the prism connecting end of the grating support element form a prism connecting end end face, the parallelism between the prism connecting end end face and the grating connecting end end face is 10", and the length tolerance of the support block is ±0.02mm; the two side faces of one of the right-angled sides of the grating support element are reference surfaces, and the verticality of the two reference surfaces is 10".

[0029] Furthermore, the shape of the grating support element is consistent with that of the grating base plate, and the thickness of the grating support element is greater than the distance from the grating surface to the field prism.

[0030] Furthermore, the grating bottom plate and the grating top plate are both rectangular;

[0031] The cross-sectional dimensions of the grating top plate are 48×38 mm, the cross-sectional dimensions of the grating bottom plate are 60×50 mm, the width d of the bonding surface is 6 mm, the thickness of the grating top plate is 8 mm, the thickness of the grating bottom plate is 4 mm, the thickness of the grating support element is 12 mm, the width t of the grating support element is 4 mm, there are 8 support blocks on the long side of the grating support element, there are 5 support blocks on the short side, the interval e between the support blocks is 3 mm, and the thickness of the grating support element minus the thickness of the support block f is 4 mm;

[0032] The size of the gap between the grating support element and the grating top plate is 2 mm.

[0033] Beneficial effects of the present invention:

[0034] 1. The present invention is a high thermal stability integrated Doppler differential interferometer. Through structural design, the grating surface is separated from the bonding surface. When the grating substrate is deformed, it mainly occurs on the bonding surface, which can ensure the surface accuracy of the grating surface and improve the quality and stability of the interference pattern. At the same time, the grating substrate can increase the length of the grating support element without changing the position of the grating surface, effectively reduce the rigidity of the grating support element, and reduce the surface error of the grating substrate caused by thermal deformation.

[0035] 2. The present invention provides an integrated Doppler differential interferometer with high thermal stability. The grating substrate material satisfies the formula for the coefficient of expansion. The grating substrate material is matched with the field-of-view widening prism material so that the change in the grating incident angle when the temperature changes offsets the change in the Littrow angle, ensuring that the outgoing optical path of the main light after reflection from the grating is consistent with the incident optical path, and no change in the optical path difference is introduced.

[0036] 3. The present invention provides a high thermal stability integral Doppler differential interferometer, wherein one end of the grating support elements are connected to each other to form a whole, and the other end is a support block connected to the bottom, the grating connection end is connected to the grating surface of the same material, and the non-continuous support block bonding surface is connected to the field of view widening prism of a different material, which can reduce the thermal deformation caused by the difference in thermal expansion coefficients between the grating support element and the connected optical element, and improve the surface accuracy of the grating surface.

[0037] 4. The present invention provides a high thermal stability integrated Doppler differential interferometer, the grating substrate and the grating support element have simple structures, convenient processing, easy precision assurance, and low requirements for the gluing process. The grating substrate and the grating support element are used for the integrated interferometer, which has high precision, high strength, and high stability, and is particularly suitable for occasions with complex mechanical and thermal environments, such as satellite-borne platforms. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of an embodiment of an integrated Doppler differential interferometer with high thermal stability according to the present invention;

[0039] Figure 2 It is an assembly diagram of a grating substrate and a supporting element in an embodiment of an integrated Doppler differential interferometer with high thermal stability of the present invention;

[0040] Figure 3 It is a structural schematic diagram of a grating substrate in an embodiment of an integrated Doppler differential interferometer with high thermal stability of the present invention;

[0041] Figure 4 It is a cross-sectional view of a grating substrate in an embodiment of an integrated Doppler differential interferometer with high thermal stability according to the present invention;

[0042] Figure 5 It is a light path trajectory diagram of the main light in the embodiment of the high thermal stability integrated Doppler differential interferometer of the present invention, which passes through the short-arm field-of-view widening prism or the long-arm field-of-view widening prism and is incident on the grating surface;

[0043] Figure 6 It is a structural schematic diagram of a grating support element in an embodiment of an integrated Doppler differential interferometer with high thermal stability of the present invention;

[0044] Figure 7 It is a cross-sectional view of a grating support element in an embodiment of an integrated Doppler differential interferometer with high thermal stability according to the present invention.

[0045] Reference numerals:

[0046] 1-grating substrate, 11-grating top plate, 12-grating bottom plate, 2-support element, 21-groove, 22-support block, 3-beam splitter prism, 4-short arm field of view widening prism, 5-long arm field of view widening prism. DETAILED DESCRIPTION

[0047] The present invention is described in detail below through the accompanying drawings and embodiments.

[0048] like Figure 1As shown, the present invention is a high thermal stability integrated Doppler differential interferometer, comprising a beam splitter prism 3, a short-arm field-of-view widening prism 4, a long-arm field-of-view widening prism 5, two grating substrates 1 and a supporting element 2 connecting the optical elements, wherein the supporting element 2 between the grating substrate 1 and the short-arm field-of-view widening prism 4 or the long-arm field-of-view widening prism 5 is defined as a grating supporting element. The present invention solves the problem of deterioration of the grating surface due to bonding stress and thermal stress by structurally designing the grating substrate 1 and the grating supporting element, as well as designing the material of the grating substrate 1.

[0049] like Figure 2 As shown, compared with the traditional grating, the grating surface of the grating substrate of the present invention is a relatively independent surface with a central protrusion, which is independently separated from the bonding surface of the grating and the supporting element, thereby reducing the influence of the bonding stress between them. Figure 3 and Figure 4 As shown, the grating substrate 1 includes a grating bottom plate 12 and a grating top plate 11 arranged in the middle of the inner side surface of the grating bottom plate 12, and the cross-sectional area of ​​the grating bottom plate 12 is larger than the cross-sectional area of ​​the grating top plate 11. The grating top plate 11 extends into the inner side of the supporting element 2, and its inner end surface is a grating surface. The area on the inner side surface of the grating bottom plate 12 located outside the grating top plate 11 forms a bonding surface, that is, the annular surface around the grating surface and located on the grating bottom plate 12 is the bonding surface. The two grating surfaces are respectively arranged corresponding to the short-arm field of view widening prism 4 and the long-arm field of view widening prism 5, and there are intervals between the two grating surfaces and the corresponding short-arm field of view widening prism 4 or the long-arm field of view widening prism 5. The sizes of the two intervals are the same, so that the incident optical paths of the two coherent lights between the short-arm field of view widening prism 4 and the long-arm field of view widening prism 5 and the grating surface are also consistent. The grating surface is used to etch the grating. The grating surface and the bonding surface are not on the same plane. The grating can be etched on the entire grating surface. The edge of the grating surface is neat, and the edge of the grating image is sharp during imaging. When the gratings of the two arms are glued, the two grating images are easy to align and overlap, thereby improving the quality of the interference pattern.

[0050] like Figure 4 As shown, the total thickness a of the grating top plate 11 and the grating bottom plate 12, the length b and width y of the grating bottom plate 12, the thickness c of the grating bottom plate 12 and the width d of the bonding surface need to meet the following conditions: a≥b / 5, a / 2≥c≥4mm, d≥c, y≤b. On the basis of meeting the above conditions, the grating substrate 1 can be made by processing a piece of flat glass or by gluing two pieces of flat glass.

[0051] When the grating substrate 1 is processed through a piece of flat glass, the grating surface is retained and the flat glass is milled around to obtain a ring surface with a width of d and a distance of c from the bottom surface to obtain the bonding surface. The parallelism between the grating surface and the bonding surface is guaranteed to be 20", and the two side surfaces of one of the right-angled sides of the grating bottom plate 12 are used as the reference surfaces for grating etching and gluing. The verticality between the two reference surfaces is 10", and the verticality between the grating surface and the reference surface is 10". The parallelism between the side surface of the grating surface and the reference surface of the grating substrate is 20", ensuring that the grating groove is perpendicular to the reference of the grating substrate during processing.

[0052] The grating substrate 1 can also be formed by bonding two pieces of flat glass of different sizes and the same material to form a Figure 3 The grating substrate shown. The total thickness of the two flat glass sheets is a, the grating bottom plate 12 is c, and the grating top plate 11 is the same size as the grating surface. The parallelism of the two end surfaces of the two flat glass sheets is 8", and the verticality of the two side surfaces of one of the right-angled sides is 8". When the two flat glass sheets are glued together as a whole, an L-shaped tool with a width of d is placed at the two reference surfaces of the grating surface flat glass, and the side surfaces of the two flat glass sheets are pressed with the side surfaces of the pressing tool. The L-shaped tool and the bonding surface plate are pressed against the surface to ensure the position accuracy of the grating surface in the grating substrate. The glue contains particles with a uniform diameter of 0.01mm, which are evenly distributed in the glue layer. During curing, it is pressed with a mass block to ensure the consistency of the glue layer thickness and the parallelism between the grating surface and the bonding surface.

[0053] like Figure 2 , Figure 6 and Figure 7As shown, the shape of the grating support element is consistent with that of the grating substrate. The grating support element is an integrated hollow frame structure, and one end bonded to the grating bottom plate 12 is a grating connection end, and one end connected to the short-arm field-of-view widening prism 4 or the long-arm field-of-view widening prism 5 is a prism connection end. The grating connection end is connected to the bonding surface of the grating bottom plate 12, and a gap is left between the grating support element and the grating top plate 11, so as to reduce the influence of the bonding stress on the grating surface when the grating support element is bonded to the grating, thereby deteriorating the surface shape of the grating surface. The prism connection end of the grating support element is connected to the short arm field widening prism 4 or the long arm field widening prism 5, and the prism connection end is uniformly provided with a plurality of grooves 21 along the thickness direction along the circumferential direction, and a plurality of support blocks 22 connected at the bottom are formed between the grooves 21, that is, the prism connection end surface bonded to the short arm field widening prism 4 or the long arm field widening prism 5 is formed by a plurality of discontinuous support block 22 bonding surfaces. Compared with the traditional support element formed by completely independent spacer blocks, the grating support element of the present invention can be regarded as a plurality of independent support blocks 22, and the ends of all independent support blocks 22 are connected as a whole. Therefore, the end surface of the grating support element can be guaranteed to be flush and coplanar, and the gluing quality is improved. The grating support element is an integral structure, and the assembly process is simple and efficient. The structure can ensure the position accuracy of the two bonding surfaces of the grating support element, which is more convenient than gluing of completely independent spacer blocks, has high precision, and greatly reduces the difficulty of processing.

[0054] The present invention can more than double the length of the grating support element while keeping the position of the grating surface relative to the front optical element unchanged. According to the processing technology and strength requirements, the support block 22 needs to meet the following conditions: the width of the support block 22 t≥4mm, and t<the width d of the bonding surface, the interval between adjacent support blocks 22 e≥2mm (i.e. the width of the groove 21), the thickness of the support element minus the support block 22 is f (i.e. the distance between the bottom of the groove 21 and the grating connection end), f≥2mm.

[0055] The size of the grating top plate 11 designed in the embodiment of the present invention is 48×38mm, the outer contour of the grating bottom plate 12 is determined to be 60×50mm, and the width d of the bonding surface is 6mm. The thickness of the grating top plate 11 is 8mm, the thickness of the grating bottom plate 12 is 4mm, and the thickness of the grating support element is 12mm. According to the processing performance of the glass, the width t of the grating support element is selected to be 4mm, and the gap between the side of the grating support element and the side of the grating top plate 11 is 2mm. The flexibility of the grating support element is optimized to reduce the surface error of the grating surface, and the number of support blocks 22, the slit width e between adjacent support blocks 22, and the remaining depth after slit (i.e., f) are used as optimization variables, and the PV value of the grating surface shape is the optimization target. The optimization method is to perform parameterized modeling on the optimization variables, change the design variables each time through the automatic optimization program, increase the cutting amount each time, obtain the thermal deformation of the grating surface when the temperature rises by 1°C through finite element analysis, calculate the PV value of the grating surface after thermal deformation according to the node displacement of the grating surface, make the surface PV value of the grating surface less than λ / 10, and obtain the corresponding optimization variable value. The results obtained after optimization in this embodiment are: the number of long side support blocks 22 of the grating support element is 8, the number of short side support blocks 22 is 5, the slit width e is 3mm, and the remaining thickness f of the grating support element is 4mm.

[0056] The structure of the grating and the supporting element of the present invention can make the rigidity of the bonding surface smaller than the rigidity of the grating surface, so that the deformation of the grating substrate 1 mainly occurs on the bonding surface, reducing the deformation of the grating surface. This can be explained by the rigidity formula of the grating support block 22:

[0057]

[0058] l is the length of the grating support element;

[0059] h is the length of the support block 22;

[0060] E is the elastic modulus of the support block 22;

[0061] It can be seen from the stiffness formula that the stiffness of the grating support element can be effectively reduced by reducing the length and width of the support block 22, and the deformation occurs on the grating support element to reduce the deformation of the grating surface.

[0062] Littrow wavelength λ of Doppler differential interferometer L When incident on the interferometer, the Littrow angle θ L After incident on the grating substrate 1, the incident angle is equal to the exit angle, so that the trajectories of the incident light path and the reflected light path of the interferometer coincide with each other. Therefore, the Littrow angle θ in the first-order diffraction of the grating substrate 1 is L and the grating line density satisfy the following relationship:

[0063] 2lsin(θ L )=λL (1)

[0064] l is the grating line spacing, ρ is the grating line density;

[0065] λ L is the Littrow wavelength of the Doppler differential interferometer.

[0066] The two arms of the Doppler differential interferometer are asymmetric structures. Figure 1 As shown, there is an optical path difference between the two arms of the interferometer to improve the detection sensitivity. The thickness of the field of view widening prisms of the two arms (short arm field of view widening prism 4 or long arm field of view widening prism 5) and the supporting elements of the field of view widening prisms are inconsistent. The theoretical design has satisfied that the optical path difference of the two arms of the Doppler differential interferometer incident on the grating substrate 1 is insensitive to temperature changes. The cross-section of the beam splitter prism 3 is square, so the incident optical path of the two coherent lights in the beam splitter prism 3 is consistent. The intervals from the grating surfaces of the two arms of the interferometer to the field of view widening prisms are the same, and the incident optical path of the two coherent lights between the field of view widening prism and the grating surface are also consistent. When the main light can return along the original path after passing through the grating, the incident trajectory and the exit trajectory of the main light coincide, then the calculation formula for the optical path difference of the reference light at the center of the Doppler interferometer is:

[0067] OPD=2(n0S2+nL2-n0S1-nL1) (2)

[0068] Among them, n0 and n represent the refractive index of air and field widening prism respectively, S1 and S2 represent the optical path length of the main light between the beam splitter prism and the field widening prism of the short arm and long arm of the interferometer respectively, and L1 and L2 represent the optical path length of the main light in the field widening prism of the short arm and long arm of the interferometer respectively. When the interferometer is working, it is necessary to ensure that the reference optical path difference is stable when the temperature changes in order to improve the measurement accuracy of the interferometer. Therefore, when the temperature changes, the incident light and the outgoing light should be kept coincident to ensure the stability of the reference optical path difference of the interferometer.

[0069] The material of the grating substrate 1 should be selected to ensure that the interferometer main light can return along the original path after passing through the reflection grating when the temperature changes. When the temperature T changes, the grating substrate 1 undergoes thermal expansion, and the grating line spacing l etched on the grating surface will change with the temperature, causing the Littrow angle θ of the grating L will change. Differentiating the temperature T through formula (1) is:

[0070]

[0071] in α G is the thermal expansion coefficient of the grating substrate, then

[0072]

[0073] When the interferometer temperature changes, the Littrow angle θ L When the change of the incident angle φ of the grating is equal, the incident trajectory and the exit trajectory can be kept coincident. The optical path of the main light passing through the field widening prism and incident on the grating is shown in the figure Figure 5 As shown, the grating incident angle is equal to the field widening prism exit angle. The grating incident angle can be calculated according to the following formula:

[0074]

[0075] in is the vertex angle of the field widening prism, and β is the incident angle of the field widening prism. If the incident angle of the grating at different temperatures is known, the coefficient of change of the grating incident angle with temperature can be calculated.

[0076]

[0077] φ1: grating incident angle before temperature change;

[0078] φ2: grating incident angle after temperature change;

[0079] T1: temperature before change;

[0080] T2: temperature after change;

[0081] Then the expansion coefficient α of the grating substrate 1 material is G Should be:

[0082]

[0083] The temperature coefficient of the refractive index of the field-widening prism of the interferometer is designed to be a negative number. When the temperature rises, the refractive index of the field-widening prism decreases, that is, the coefficient of change of the grating incident angle with temperature is If it is a negative number, the thermal expansion coefficient α of the grating substrate material G is a positive value, and a grating substrate 1 material close to the calculated expansion coefficient is selected. For example, when the interferometer detection wavelength is 630nm, the materials of the short-arm field-of-view widening prism 4 and the long-arm field-of-view widening prism 5 are both N-SF57, the vertex angles are both 12.60°, the incident angles are both 6.84°, the grating line density is 900g / mm, and the selected grating substrate material is Fused silica.

[0084] The grating substrate 1 is bonded to the front optical element through the grating support element. The expansion coefficients of the materials of the grating substrate 1 and the front optical element are greatly different. The material of the grating support element is consistent with that of the grating substrate 1, but inconsistent with that of the field widening prism (short-arm field widening prism 4 or long-arm field widening prism 5). In order to reduce the deformation of the bonding surface, the grating support element is formed as follows: Figure 6As shown. The grating support element is first cut into a U-shaped frame structure, the parallelism of the two end faces of the grating connection end and the prism connection end of the grating support element is 10", and the length tolerance of the support block 22 is ±0.02mm. The two side faces of one of the right-angled sides of the grating support element are used as reference surfaces, and the verticality of the two reference surfaces is 10". Then, the support block 22 is cut from one end of the grating support element from the side to form the final support element.

[0085] After etching the grating on the grating surface, the grating substrate 1 and the grating support element are glued together to obtain a grating assembly. First, place the grating substrate 1 horizontally, apply glue to the U-shaped bonding surface of the grating support element and place it on the bonding surface of the grating substrate. Use a clamping tool to press the grating substrate 1 and the grating support element from the side, and bring the two reference surfaces of the grating substrate 1 and the grating support element close together to make the references of the two elements coincide. The glue contains particles with a uniform diameter of 0.01mm, which are evenly distributed in the glue layer. During curing, it is pressed with a mass block to ensure the consistency of the glue layer thickness and the parallelism of the discontinuous small bonding surfaces of the grating surface and the support element.

Claims

1. A high thermal stability integrated Doppler differential interferometer, comprising a beam splitter prism (3), a short arm field widening prism (4), a long arm field widening prism (5), two grating substrates (1) and a supporting element (2) connecting the optical elements, characterized in that: The grating substrate (1) comprises a grating bottom plate (12) and a grating top plate (11) arranged in the middle of the inner side of the grating bottom plate (12), and the cross-sectional area of ​​the grating bottom plate (12) is larger than the cross-sectional area of ​​the grating top plate (11); The grating top plate (11) extends into the inner side of the supporting element (2), and its inner end surface is a grating surface, and the grating surface is used for etching the grating; The two grating surfaces are respectively arranged corresponding to the short-arm field-of-view widening prism (4) and the long-arm field-of-view widening prism (5), and there is a gap between the two grating surfaces and the corresponding short-arm field-of-view widening prism (4) or the long-arm field-of-view widening prism (5), and the two gaps are of the same size; The area on the inner side surface of the grating bottom plate (12) and located outside the grating top plate (11) forms a bonding surface; The total thickness a of the grating top plate (11) and the grating bottom plate (12), the length b and width y of the grating bottom plate (12), the thickness c of the grating bottom plate (12) and the width d of the bonding surface satisfy the following conditions: a≥b / 5, a / 2≥c≥4mm, d≥c, y≤b; A supporting element (2) between the grating substrate (1) and the short-arm field-of-view widening prism (4) or the long-arm field-of-view widening prism (5) is defined as a grating supporting element; The grating support element is an integrated hollow frame structure, wherein the grating connection end is connected to the bonding surface of the grating bottom plate (12), and a gap is left between the grating support element and the grating top plate (11); the prism connection end of the grating support element is connected to the short-arm field-of-view widening prism (4) or the long-arm field-of-view widening prism (5), and the prism connection end is uniformly provided with a plurality of grooves (21) along the thickness direction along the circumferential direction, and a plurality of support blocks (22) connected at the bottom are formed between the grooves (21); The width of the support block (22) is t≥4mm, and t<d, the interval between the support blocks (22) is e≥2mm, the thickness of the grating support element minus the thickness of the support block (22) is f, and f≥2mm; The Littrow angle θ in the first-order diffraction of the grating substrate (1) L and the grating line density satisfy the following relationship: 2lsin(θ L )=λ L l is the grating line spacing, ρ is the grating line density; λ L is the Littrow wavelength of the Doppler differential interferometer; The material expansion coefficient α of the grating substrate (1) G Satisfies the following formula: is the coefficient of variation of the grating incident angle with temperature, and is a negative number; The material of the grating support element is consistent with that of the grating substrate (1).

2. The high thermal stability integrated Doppler differential interferometer according to claim 1, characterized in that: The grating substrate (1) is made by processing a piece of flat glass, or by gluing two pieces of flat glass together; The grating substrate (1) is made by processing a piece of flat glass and must meet the following conditions: the parallelism between the grating surface and the bonding surface is 20", the two side surfaces of one of the right-angled sides of the grating bottom plate (12) are used as two reference surfaces for grating etching and gluing, the verticality between the two reference surfaces is 10", the verticality between the grating surface and the reference surface is 10", and the parallelism between the side surface of the grating top plate (11) and the reference surface is 20". The grating substrate (1) is made by gluing two pieces of flat glass and must meet the following conditions: The parallelism between the grating surface and the bonding surface is 8", and the verticality of the two side surfaces of one right-angle edge of the grating top plate (11) is 8".

3. The high thermal stability integrated Doppler differential interferometer according to claim 2, characterized in that: The materials of the short-arm field-of-view widening prism (4) and the long-arm field-of-view widening prism (5) are both N-SF57, the vertex angles are both 12.60°, the incident angles are both 6.84°, the material of the optical grating substrate (1) is Fused silica, the grating line density is 900g / mm, and the applied detection wavelength is 630nm.

4. The high thermal stability integrated Doppler differential interferometer according to claim 3, characterized in that: The end faces of the plurality of support blocks (22) at the prism connection end of the grating support element form a prism connection end end face, the parallelism between the prism connection end end face and the grating connection end end face is 10″, and the length tolerance of the support block (22) is ±0.02mm; Two side surfaces of one of the right-angled sides of the grating support element are reference surfaces, and the verticality of the two reference surfaces is 10".

5. The high thermal stability integrated Doppler differential interferometer according to claim 4, characterized in that: The shape of the grating support element is consistent with that of the grating base plate (12), and the thickness of the grating support element is greater than the distance from the grating surface to the field prism.

6. The high thermal stability integrated Doppler differential interferometer according to claim 5, characterized in that: The grating bottom plate (12) and the grating top plate (11) are both rectangular; The cross-sectional dimensions of the grating top plate (11) are 48×38 mm, the cross-sectional dimensions of the grating bottom plate (12) are 60×50 mm, the width d of the bonding surface is 6 mm, the thickness of the grating top plate (11) is 8 mm, the thickness of the grating bottom plate (12) is 4 mm, the thickness of the grating support element is 12 mm, the width t of the grating support element is 4 mm, the number of support blocks (22) on the long side of the grating support element is 8, the number of support blocks (22) on the short side is 5, the interval e between the support blocks (22) is 3 mm, and the thickness of the grating support element minus the thickness of the support block (22) is 4 mm; The size of the gap between the grating support element and the grating top plate (11) is 2 mm.

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