A point diffraction source based on nanowire waveguide and its optical field manipulation method

Abstract

This application relates to the field of wavefront detection technology and discloses a point diffraction source based on a nanowire waveguide and its optical field modulation method. The point diffraction source includes a silicon substrate, a waveguide core, a full cladding, and a graded cladding. The waveguide core includes a coupler, a coupled straight waveguide, a bent waveguide, and an outgoing straight waveguide. The graded cladding includes a silicon dioxide cladding and an air cladding. The coupler is connected to the coupled straight waveguide, the coupled straight waveguide is connected to the bent waveguide, and the bent waveguide is connected to the outgoing straight waveguide. One side of the coupler and the waveguide core is encased in the full cladding, and the other side of the waveguide core is encased in the graded cladding, such that the other side of the waveguide core is in an air cladding. The technical solution provided by one or more embodiments of this application can increase the numerical aperture of the diffraction wavefront.

Description

Technical Field

[0001] This application relates to the field of wavefront detection technology, and in particular to a point diffraction source based on a nanowire waveguide and a method for controlling its optical field. Background Technology

[0002] In the field of wavefront detection technology, when using a point diffraction interferometer for optical detection, a diffracted wavefront that is approximately an ideal sphere generated by the diffraction of a light field through a very small cross section is usually used as a reference wavefront and interfered with the wavefront to be measured in order to perform high-precision optical detection.

[0003] Currently, point diffraction sources employing nanowire waveguides confine the light field to the wavelength or subwavelength level, generating smaller light field cross-sections to form stable diffraction wavefronts, thereby improving the measurement accuracy of point diffraction interferometers. However, in practical applications, the NA (Numerical Aperture) value of the diffraction wavefront is relatively small, thus limiting the measurement range of the diffraction reference interferometer.

[0004] Therefore, increasing the numerical aperture of the diffraction wavefront has become a key research focus in the field of wavefront detection. Summary of the Invention

[0005] This application provides a point diffraction source based on nanowire waveguides and a method for controlling its optical field, which can generate diffraction wavefronts with large numerical apertures.

[0006] The first aspect of this application provides a point diffraction light source based on a nanowire waveguide structure. The point diffraction light source includes a silicon substrate, a waveguide core layer, a full cladding layer, and a gradient cladding layer. The waveguide core layer includes a coupler, a coupled straight waveguide, a bent waveguide, and an outgoing straight waveguide. The gradient cladding layer includes a silicon dioxide cladding layer and an air cladding layer. The coupler is connected to the coupled straight waveguide, the coupled straight waveguide is connected to the bent waveguide, and the bent waveguide is connected to the outgoing straight waveguide. The coupler and one side of the waveguide core layer are wrapped in the full cladding layer, and the other side of the waveguide core layer is wrapped in the gradient cladding layer, such that the other side of the waveguide core layer is in an air cladding layer.

[0007] In one embodiment, the waveguide core is composed of silicon nitride, and both the full cladding and the silicon dioxide cladding are composed of silicon dioxide.

[0008] In one embodiment, the gradient cladding further includes a silica cladding with a gradually varying width, wherein the width of the silica cladding varies according to a linear function; or the width of the silica cladding varies according to a Bézier curve.

[0009] In one embodiment, the coupler, the straight waveguide of the coupling segment, and the curved waveguide are enclosed in the full cladding.

[0010] In one embodiment, one end of the outgoing straight waveguide is wrapped in the full cladding, the middle portion of the outgoing straight waveguide is wrapped in the silica cladding, and the other end of the outgoing straight waveguide is wrapped in an air cladding.

[0011] In one embodiment, the straight waveguide of the outgoing section outputs the diffracted wavefront, and the curved waveguide is used to rotate the direction of optical field propagation to reduce the influence of scattered light on the diffracted wavefront.

[0012] In one embodiment, the coupler is a Y-coupler, wherein one side of the Y-coupler includes two end faces for coupling with an optical fiber; the other side of the Y-coupler is connected to a straight waveguide of the coupling section.

[0013] In one embodiment, the fabrication of the point diffraction light source includes dry etching and wet etching, wherein: a silicon nitride layer is formed by thin film deposition, and a first mask is fabricated by photolithography; the silicon nitride layer is dry etched according to the first mask to obtain a waveguide core layer of a specified shape; silicon dioxide is deposited on the core layer, and a second mask is fabricated by photolithography; the silicon dioxide layer is dry etched according to the second mask, and a specified area is wet etched using a specified etching solution to obtain a full cladding layer and a gradient cladding layer of a specified shape.

[0014] A second aspect of this application provides a method for controlling the optical field of a point diffraction source based on a gradient nanowire waveguide. The point diffraction source is used to generate a diffraction wavefront. The point diffraction source includes a coupler, a coupled straight waveguide, a curved waveguide, and an exit straight waveguide. The method for controlling the optical field of the point diffraction source includes: acquiring an external optical field and coupling the optical field into the coupled straight waveguide through the coupler; the coupled straight waveguide receiving the optical field and stabilizing the optical field into a first mode field, and transmitting the first mode field to the curved waveguide; the curved waveguide changing the propagation direction of the first mode field and transmitting the first mode field to the exit straight waveguide; and the exit straight waveguide converting the first mode field into a second mode field and propagating the second mode field to the far field to form a diffraction wavefront.

[0015] The technical solutions provided in one or more embodiments of this application generate large numerical aperture diffraction wavefronts by employing a gradient cladding structure to reduce mode conversion losses and mode area. Specifically, nanowire waveguides are used for light transmission, and a gradient cladding structure is adopted at the outgoing waveguide section, that is, a gradual transition from a silicon dioxide cladding to an air cladding. This increases the refractive index difference between the core layer and the cladding, thereby increasing the confinement capability of the light field, reducing the mode area of ​​the waveguide, and thus generating a larger numerical aperture diffraction wavefront.

[0016] As can be seen, the technical solution provided in this application, employing a gradient cladding structure including an air cladding and a silica cladding, can increase the numerical aperture of the generated diffraction wavefront, thereby improving the optical measurement range. Simultaneously, adding a gradient cladding structure can prevent abrupt mode changes, thus reducing light loss. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of a point diffraction source provided in one embodiment of this application;

[0019] Figure 2 A schematic diagram of the waveguide core layer provided in one embodiment of this application;

[0020] Figure 3 A schematic diagram illustrating the steps of a method for controlling the optical field of a point diffraction source based on a gradient nanowire waveguide, provided in one embodiment of this application;

[0021] Figure 4 A schematic diagram of a point diffraction light source based on a nanowire waveguide with a full silica cladding provided in one embodiment of this application;

[0022] Figure 5(a) is a simulation diagram of a far-field diffraction wavefront image provided in an embodiment of this application;

[0023] Figure 5(b) is a simulation diagram illustrating the relationship between NA value and core size according to an embodiment of this application;

[0024] Figure 6(a) is a simulation diagram of a far-field diffraction wavefront image provided in another embodiment of this application;

[0025] Figure 6(b) is a simulation diagram illustrating the relationship between NA value and core size according to another embodiment of this application.

[0026] Explanation of reference numerals in the attached figures:

[0027] 110-Silicon substrate, 111-Waveguide core, 112-Full cladding, 113-Graded cladding, 210-Coupler, 211-Straight waveguide of coupling section, 212-Bent waveguide, 213-Straight waveguide of output section, 310-Waveguide core, 311-Full cladding, 312-Silicon substrate, 313-Coupler, 314-Straight waveguide of coupling section, 315-Bent waveguide, 316-Straight waveguide of output section. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Furthermore, the use of terms such as "first," "second," etc., in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of embodiments in this application, unless otherwise stated, "multiple" means two or more. Additionally, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0030] With the continuous development of the optics industry, the setup of point diffraction interferometers is also constantly being optimized and improved. Generally speaking, a point diffraction interferometer can generate a diffracted wavefront by diffracting the light field through a pinhole or the end of an optical fiber. The diffracted wavefront is used as a reference wavefront for interferometry detection, and it interferes with the wavefront to be measured to produce interference fringes. The wavefront to be measured can then be detected by observing the interference fringes.

[0031] In related technologies, the light source of a point diffraction interferometer can be a point diffraction source based on a nanowire waveguide. By coupling light from a single-mode fiber into the point diffraction source structure, the light propagates within the nanowire waveguide and diffracts at the end face of the waveguide's output section, generating a diffraction wavefront that approximates an ideal sphere. The nanowire waveguide-based point diffraction source can confine the light field to the wavelength or subwavelength level, producing a smaller light field cross-section, while suppressing and blocking the propagation of higher-order modes to achieve stable single-mode light field propagation. The resulting diffraction wavefront is relatively stable and has high intensity. Therefore, introducing a nanowire waveguide-based point diffraction source can significantly improve the measurement accuracy of a point diffraction interferometer.

[0032] However, in practical applications, point diffraction interferometers require not only high measurement accuracy but also a large measurement range for optical inspection. When inspecting large targets, the small numerical aperture of the diffraction wavefront necessitates sequential inspection of different regions, leading to low efficiency and the inherent human error inherent in this process. Therefore, there is an urgent need for a point diffraction light source capable of generating a large numerical aperture diffraction wavefront to increase the measurement range and improve inspection efficiency, while also producing a more intuitive interference pattern of the target object for easier interpretation by inspectors.

[0033] In view of this, one or more embodiments of this application provide a point diffraction light source based on a gradient nanowire waveguide, which can solve the above problems and generate a diffraction wavefront with a large numerical aperture to increase the measurement range.

[0034] Please see Figure 1 and Figure 2 One embodiment of this application provides a point diffraction light source based on a nanowire waveguide. The point diffraction light source includes a silicon substrate 110, a waveguide core layer 111, a full cladding layer 112, and a gradient cladding layer 113. The waveguide core layer 111 includes a coupler 210, a coupling section straight waveguide 211, a curved waveguide 212, and an output section straight waveguide 213. The coupling section straight waveguide 211 is connected to the curved waveguide 212, and the curved waveguide 212 is connected to the output section straight waveguide 213. The coupler 210 and one side of the waveguide core layer 111 are wrapped in the full cladding layer 112, and the other side of the waveguide core layer 111 is wrapped in the gradient cladding layer 113, so that the other side of the waveguide core layer 111 is in an air cladding.

[0035] Specifically, Figure 1 This is a schematic diagram of the point diffraction source in this embodiment. Figure 1As shown, the point diffraction light source includes a silicon substrate 110, a full cladding 112, a waveguide core layer 111, and a gradient cladding 113. The gradient cladding includes a silicon dioxide cladding and an air cladding. The full cladding 112 and the silicon dioxide cladding are both composed of silicon dioxide. The waveguide core layer 111 is composed of silicon nitride. One side of the waveguide core layer 111 is encased in the full cladding 112, and the other side of the waveguide core layer 111 is encased in the gradient cladding 113, so that the end face of the other side of the waveguide core layer 111 is exposed to air, i.e., it is in the air cladding.

[0036] also, Figure 2 This is a schematic diagram of the waveguide core layer in this embodiment. Figure 2 As shown, the waveguide core layer includes a coupler 210, a coupling section straight waveguide 211, a bent waveguide 212, and an outgoing section straight waveguide 213, which are connected in sequence. One end of the coupler 210, the coupling section straight waveguide 211, the bent waveguide 212, and the outgoing section straight waveguide 213 is wrapped in the above-mentioned full cladding layer, the middle part of the outgoing section straight waveguide 213 is wrapped in the above-mentioned silicon dioxide cladding layer, and the other end of the outgoing section straight waveguide 213 is wrapped in the above-mentioned air cladding layer.

[0037] The coupler 210 described above can be a Y-type coupler, in which the two end faces of the Y-type coupler are coupled to the optical fiber and the coupled light is focused into a nanowire waveguide for transmission to the waveguide core layer 111, thereby improving the coupling efficiency. Alternatively, a vertical coupler can also be used, which couples the light into the waveguide core layer 111 through a grating.

[0038] The aforementioned point diffraction light source employs dry and wet etching to form a core structure and a gradient cladding structure of specific shapes on a silicon substrate. Specifically, a mask of a specific shape is fabricated by spin-coating photoresist, exposure, and development on the waveguide core and silicon dioxide cladding, respectively. The deposited thin film on the mask is then subjected to plasma beam etching, followed by dry etching processes such as cleaning and photoresist removal to obtain a core structure and cladding structure with a fixed shape corresponding to the specific shape of the mask. The areas covered by the mask are unaffected by the plasma beam etching, while the areas not covered by the mask are etched away, thus forming a waveguide core, full cladding, and gradient cladding structure corresponding to the shape of the mask. After the aforementioned dry etching steps, the formed gradient cladding is further etched using a wet etching process. A selective etching solution is used to remove the silicon dioxide below the end of the straight waveguide in the outgoing section, forming an air cladding for the straight waveguide. Preferably, when the core material is silicon nitride and the cladding material is silicon dioxide, hydrofluoric acid can be used as the etching solution to etch the silicon dioxide. After etching, the surface needs to be cleaned to remove photoresist and residual impurities, ultimately yielding the aforementioned point diffraction light source based on a nanowire waveguide.

[0039] For example, a first mask for the silicon nitride core layer is first fabricated on a wafer using electron beam lithography. A silicon dioxide underlayer is formed on the wafer by thin film deposition, and a silicon nitride layer is deposited on the silicon dioxide underlayer. A mask is formed by coating photoresist, exposure, and development, and the mask pattern is printed onto the silicon nitride layer. After plasma dry etching, the silicon nitride not protected by the mask is removed to form the silicon nitride core layer with the waveguide core layer pattern described above.

[0040] Furthermore, silicon dioxide is deposited on the silicon nitride core layer to form a silicon dioxide upper layer, and a second mask with a gradient cladding structure pattern is fabricated by photolithography. The mask is printed onto the silicon dioxide upper layer, and the silicon dioxide not protected by the mask is removed by plasma dry etching to expose the outgoing straight waveguide to the air, thus forming a gradient cladding structure.

[0041] Furthermore, hydrofluoric acid etching solution is used to remove the unetched silicon dioxide below the straight waveguide in the output section through wet etching. Because the wet etching solution is selective, the different reaction rates of hydrofluoric acid with silicon dioxide and silicon nitride enable a certain degree of selective etching.

[0042] Please see Figure 3 This application provides a method for controlling the optical field of a point diffraction source based on a gradient nanowire waveguide, wherein the point diffraction source is used to generate a diffraction wavefront; the point diffraction source includes a coupler, a straight waveguide for coupling, a curved waveguide, and a straight waveguide for output; the method for controlling the optical field of the point diffraction source is performed according to the following steps:

[0043] S1: Acquire the external optical field and couple the optical field into the straight waveguide of the coupling section through a coupler.

[0044] S3: The straight waveguide of the coupling section receives the optical field and stabilizes the optical field into a first mode field, and transmits the first mode field to the curved waveguide.

[0045] S5: The curved waveguide changes the propagation direction of the first mode field and transmits the first mode field to the straight waveguide of the outgoing section.

[0046] S7: The outgoing straight waveguide converts the first mode field into a second mode field and propagates the second mode field to the far field to form a diffraction wavefront.

[0047] It should be noted that the optical field can be understood as the distribution of electric and magnetic fields of light waves in time and space, and the mode field can be understood as the fixed distribution of electromagnetic wave fields existing in the waveguide. Among them, the mode field is divided into transverse modes and longitudinal modes. In this embodiment, the waveguide only adopts a single-mode propagation mode of transverse mode propagation, that is, it adopts fundamental mode propagation.

[0048] In this embodiment, the optical field is coupled into the waveguide core layer and transmitted to the coupling section straight waveguide connected to the coupler. Specifically, the fiber spot is aligned with the end face of the coupler for coupling. After entering the coupler, the light's transmission form changes from an optical field to a mode field in the waveguide, and is transmitted to the coupling section straight waveguide in the waveguide core layer in the form of a mode field.

[0049] In this embodiment, an optical field is received and stabilized into a first mode field, which is then transmitted to a curved waveguide. The first mode field characterizes the fundamental mode of the optical field within the silicon dioxide cladding. Since the waveguide core is composed of silicon nitride and the cladding of the straight waveguide in the coupling section is composed of silicon dioxide, the refractive index difference between the waveguide core and cladding is equal to the refractive index difference between silicon dioxide and silicon nitride. Therefore, the mode field of the light in the straight waveguide in the coupling section is the aforementioned first mode field. Furthermore, stabilizing the optical field into the first mode field in the straight waveguide in the coupling section avoids greater light loss during transmission through the curved waveguide.

[0050] Furthermore, by appropriately adjusting the length of the straight waveguide in the coupling section, the distance between the port of the straight waveguide in the outgoing section and the light source can be adjusted, thereby reducing the influence of the scattered light from the light source on the diffracted wavefront.

[0051] In this embodiment, the first mode field is received and its propagation direction is changed, and the first mode field is transmitted to the outgoing straight waveguide. Specifically, to avoid the point diffraction light source device from blocking the generated diffraction wavefront and interfering with the scattered light from the light source, the propagation direction of the light in the waveguide can be changed. Preferably, a curved waveguide is provided between the coupling straight waveguide and the outgoing straight waveguide so that the coupling straight waveguide is perpendicular to the outgoing straight waveguide, thereby changing the propagation direction of the light.

[0052] Furthermore, the first mode field exhibits bending loss in curved waveguides. Specifically, when light propagates in a curved waveguide, a portion of the first mode field extends to the outer side of the waveguide, causing mode overflow and resulting in energy loss. The smaller the radius of curvature of the curved waveguide, the more severe the mode overflow. Therefore, the radius of curvature of the curved waveguide can be appropriately increased to make the mode field distribution more adaptable to changes in the waveguide shape, thereby reducing bending loss. Preferably, the radius of curvature is set to 5 μm.

[0053] In this embodiment, the first mode field is converted into a second mode field, which represents the fundamental mode of the optical field in the air cladding. Since one side of the straight waveguide in the outgoing section is located in the air cladding, the refractive index difference between its waveguide core and cladding is equal to the refractive index difference between silicon nitride and air. Therefore, the mode field is converted into the second mode field, i.e., converted into the fundamental mode in the air cladding. Because the refractive index difference between silicon nitride and silicon dioxide is 0.5, and the refractive index difference between silicon nitride and air is 0.96, the refractive index difference of the second mode field is greater than that of the first mode field, resulting in a larger numerical aperture for the diffraction wavefront.

[0054] It should be noted that the greater the refractive index difference between the cladding and the core layer, the stronger the waveguide's ability to confine light waves, the smaller its mode field area, and the larger the beam divergence angle. Furthermore, according to NA = nsinθ, within a certain angular range, the larger the beam divergence angle, the larger the numerical aperture. Here, NA is the numerical aperture, n is the refractive index of the core layer, and θ is the beam divergence angle.

[0055] In this embodiment, the outgoing straight waveguide employs a gradient cladding structure, which can reduce mode switching losses between different claddings. Specifically, the width of the silica cladding in the gradient cladding is gradually distributed according to a variation function until the cladding of the outgoing straight waveguide is an air cladding. By using the above-mentioned gradient cladding, the transition from the first mode field to the second mode field can be gradual, avoiding mode mismatch caused by abrupt mode changes, thereby reducing unnecessary mode loss.

[0056] Optionally, the silica cladding is distributed along the direction of light propagation according to a linear function.

[0057] Optionally, the silica cladding is distributed along the direction of light propagation according to a Bezier curve, which can shorten the length of the gradient cladding.

[0058] Optionally, the waveguide core layer adopts single-mode transmission, and its mode field distribution is TE mode (transverse electric mode).

[0059] For example, please refer to Figure 4 and Figure 2 This application provides one or more embodiments of point diffraction light sources using nanowire waveguides to generate diffraction wavefronts through optical field modulation. Silicon nitride nanowire waveguides are selected as the waveguide core layer, and silicon dioxide is used as the cladding. The refractive index of the silicon nitride material is 1.96, and its width is preferably 250 nm, or more preferably 270 nm. The refractive index of the silicon dioxide material is 1.46, its operating wavelength range is 633 nm, and its operating polarization state is TE polarization. Specifically:

[0060] In one embodiment, using Figure 4The illustrated point diffraction source based on a nanowire waveguide with a full silica cladding performs far-field diffraction. The waveguide core layer 310 is entirely encased in a full cladding layer 311 above a silicon substrate 312. Specifically, the optical field is output through an optical fiber and aligned with the coupler port. The light is coupled into the waveguide core layer 310 via coupler 313 and propagates a distance from the straight waveguide 314 in the coupling section to stabilize the optical field within the waveguide into a TE0_SiO2 mode field. Then, the propagation direction is rotated 90° through a bent waveguide 315 into the output straight waveguide 316, where the optical field distribution in the TE0_SiO2 mode field is output at the port of the output straight waveguide, propagating to the far field to form a diffracted wavefront.

[0061] Please refer to Figures 5(a) and 5(b). Figures 5(a) and 5(b) represent the simulated images after the application of a full silica cladding in this embodiment. Figure 5(a) is the far-field diffraction wavefront image in this embodiment, where the dashed circle marks the location where the total far-field electric field intensity is 1 / e intensity. This location is the boundary of the effective wavefront, and the NA value at the aforementioned 1 / e intensity location is calculated. Figure 5(b) shows the relationship between the NA value and the core layer size. When the core layer size is preferably 0.33, the maximum NA value is 0.483.

[0062] In another embodiment, using Figure 2 The point diffraction source with a gradient cladding based on a gradient nanowire waveguide, as shown, performs far-field diffraction. The optical field is output through an optical fiber and aligned with the coupler port of the full cladding 112, which is attached to the silicon substrate 110. The optical field is coupled into the waveguide core layer 111 through the coupler 210 and transmitted a distance from the straight waveguide 211 of the coupling section to stabilize the optical field in the waveguide as a TE0_SiO2 mode field. Then, the TE0_SiO2 mode field is rotated 90° through the bent waveguide 212 and enters the straight waveguide 213 of the output section. At the same time, the TE0_SiO2 mode field continues to propagate to the gradient cladding 113 of the straight waveguide of the output section. The cladding gradually transitions from a silicon dioxide cladding to an air cladding. With the gradient of the cladding and the propagation of the light, the mode field of the waveguide gradually transitions from the TE0_SiO2 mode field to the TE0_air mode field. Finally, the optical field distribution of the TE0_air mode field is output at the port of the straight waveguide of the output section and propagates to the far field to form a diffraction wavefront.

[0063] Please refer to Figures 6(a) and 6(b). Figures 6(a) and 6(b) represent the simulation patterns after using the gradient cladding in this embodiment. Figure 6(a) is a far-field diffraction wavefront image, where the dashed circle marks the position where the total far-field electric field intensity is 1 / e intensity, and the NA value at the aforementioned 1 / e intensity position is calculated. Figure 6(b) shows the relationship between the NA value and the core layer size. When the core layer size is preferably 0.3 μm, the maximum NA value is 0.549. The maximum NA value in this embodiment is higher than the maximum NA value in the embodiment with the silica cladding, indicating that the numerical aperture of the diffraction wavefront generated in this embodiment is larger.

[0064] The technical solutions provided in one or more embodiments of this application generate large numerical aperture diffraction wavefronts by employing a gradient cladding structure to reduce the mode field area. Specifically, nanowire waveguides are used for light transmission, and a gradient cladding structure is adopted at the outgoing waveguide section, that is, a gradual transition from a silicon dioxide cladding to an air cladding. This increases the refractive index difference between the core layer and the cladding, thereby increasing the confinement capability of the light field, reducing the mode field area of ​​the waveguide, and thus generating a larger numerical aperture diffraction wavefront.

[0065] As can be seen, the technical solution provided in this application, employing a gradient cladding structure including an air cladding and a silica cladding, can increase the numerical aperture of the generated diffraction wavefront, thereby improving the optical measurement range. Simultaneously, adding a gradient cladding structure can prevent abrupt mode changes, thus reducing light loss.

[0066] Furthermore, one embodiment of this application provides a scenario example of objective lens inspection using a point diffraction light source based on a gradient nanowire waveguide.

[0067] In this embodiment, the reference wave generated by the point diffraction source can be used for objective lens inspection. The approximately spherical diffraction wavefront emitted by the point diffraction source serves as the reference wave, interfering with the detection wave passing through the objective lens under test. Interference fringes are then imaged and recorded on a CCD, and the quality of the objective lens under test can be determined from these fringes. For large-aperture objective lenses under test, generating a large numerical aperture diffraction wavefront can cover the entire objective lens, allowing for a single measurement to assess its overall condition. However, for small numerical aperture diffraction wavefronts, multiple measurements in different regions are required to achieve comprehensive inspection of the objective lens.

[0068] Therefore, using a point diffraction light source based on a gradient nanowire waveguide can increase the measurement range, improve detection efficiency, and generate a more intuitive interference pattern of the target under test, making it easier for testing personnel to make judgments.

[0069] The above description is merely a scenario example provided in the specification and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0070] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0071] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0072] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

[0073] Although embodiments of this application have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of this application, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A point diffraction light source based on a nanowire waveguide, characterized in that, The point diffraction source comprises a silicon substrate, a waveguide core, a full cladding, and a graded cladding. The waveguide core includes a coupler, a coupled straight waveguide, a bent waveguide, and an outgoing straight waveguide. The graded cladding includes a silicon dioxide cladding and an air cladding. The coupler is connected to the coupled straight waveguide, the coupled straight waveguide is connected to the bent waveguide, and the bent waveguide is connected to the outgoing straight waveguide, wherein: The width of the silica cladding is gradually distributed. The coupler, the straight waveguide of the coupling section, and the curved waveguide are wrapped in the full cladding. One end of the straight waveguide of the outgoing section is wrapped in the full cladding. The middle part of the straight waveguide of the outgoing section is wrapped in the silica cladding. The other end of the straight waveguide of the outgoing section is wrapped in an air cladding. The width of the silica cladding layer varies gradually according to a linear function, or the width of the silica cladding layer varies gradually according to a Bezier curve.

2. The point diffraction light source according to claim 1, characterized in that, The waveguide core is composed of silicon nitride, and both the full cladding and the silicon dioxide cladding are composed of silicon dioxide.

3. The point diffraction light source according to claim 1, characterized in that, The point diffraction source is used to generate a diffraction wavefront, and the curved waveguide is used to rotate the direction of light field propagation to reduce the influence of scattered light on the diffraction wavefront.

4. The point diffraction light source according to claim 1, characterized in that, The coupler is a Y-type coupler, wherein: One side of the Y-coupler includes two end faces, which are used for coupling with optical fibers; The other side of the Y-coupler is connected to the straight waveguide of the coupling section.

5. The point diffraction light source according to claim 1, characterized in that, The fabrication of the point diffraction source includes dry etching and wet etching, wherein: A silicon nitride layer is formed by thin film deposition, and a first mask is fabricated by photolithography. The silicon nitride layer is then dry-etched according to the first mask to obtain a waveguide core layer of a specified shape. Silicon dioxide is deposited on top of the waveguide core layer, and a second mask is fabricated by photolithography. The silicon dioxide layer is then dry-etched according to the second mask, and a specified area is wet-etched using a specified etching solution to obtain a full cladding and a gradient cladding of a specified shape.

6. A method for controlling the optical field of a point diffraction source based on a nanowire waveguide, characterized in that, The method is applied to a point diffraction source as described in any one of claims 1-5, wherein the point diffraction source includes a coupler, a straight waveguide for coupling, a curved waveguide, and a straight waveguide for output; and the method for controlling the optical field of the point diffraction source includes: The external optical field is acquired and coupled into the straight waveguide of the coupling section through a coupler; The straight waveguide of the coupling section receives the optical field and stabilizes the optical field into a first mode field, and transmits the first mode field to the curved waveguide; The curved waveguide changes the propagation direction of the first mode field and transmits the first mode field to the straight waveguide of the outgoing section; The outgoing straight waveguide converts the first mode field into a second mode field and propagates the second mode field to the far field to form a diffraction wavefront.

7. The method according to claim 6, characterized in that, The optical field is transmitted in single mode within the waveguide core layer. The first mode field and the second mode field are TE fundamental modes under different cladding layers, and the mode field area of ​​the first mode field is larger than that of the second mode field.

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