Device and method for generating Gaussian light through fan-shaped waveguide grating based on anti-reflection layer

Abstract

The invention provides a device for generating Gaussian light through a fan-shaped waveguide grating based on an anti-reflection layer, and the device comprises the components of a fan-shaped grating which has an opening angle of 60 degrees, a waveguide material of gallium nitride, and a substrate of aluminum oxide; the apodization period grating is etched on the fan-shaped grating and consists of a plurality of elliptic grooves, and each groove is a curve segment of the right half part of an ellipse; and the silicon dioxide anti-reflection layer covers the surface of the fan-shaped grating, and the refractive index of the silicon dioxide anti-reflection layer is between air and the substrate material. The invention further provides an optical coupling method of the device for generating Gaussian light based on the fan-shaped waveguide grating of the anti-reflection layer. Through the design of the silicon dioxide anti-reflection layer covering the surface of the grating, the reflection loss of light on an interface is reduced, the optical coupling effect is optimized, and efficient coupling between free space light and an integrated optical chip is achieved; and the diffraction efficiency of the grating can be effectively improved by adjusting the thickness of the anti-reflection layer and the etching depth of the grating, so that more photons can be accurately guided to a target area.

Description

Technical Field

[0001] The present invention relates to the field of integrated optical technology, and in particular to a device and method for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer. Background Art

[0002] With the rapid development of integrated photonics, integrated grating chips have achieved significant progress in structural complexity, functional integration, and performance stability. Gratings diffract, split, and manipulate light waves by periodically modulating the refractive index or structural topography of a medium. Their core functions include wavelength selection, angular separation, phase modulation, and coupling conversion. Compared to traditional filter devices and prism systems, gratings offer superior integration and design freedom at the micro- and nanoscale, making them particularly suitable for highly compact integrated photonic chip environments. Gaussian beams are the most common and practical type of spatial light field distribution, exhibiting excellent wavefront quality and minimal diffraction spread. They are widely used in optical communications, laser processing, and imaging systems. Traditional Gaussian beams are typically generated directly by resonant lasers. However, in integrated photonic systems, generating an output beam with a near-Gaussian distribution within an on-chip structure has become a key research topic. As a key component for wavefront manipulation, gratings can effectively convert waveguide modes into output light with a Gaussian envelope through careful design of their structural parameters. The key to achieving this process lies in the spatial control of the grating's emission intensity along the propagation direction. Generally speaking, the output of a straight waveguide is approximately uniformly distributed, making it difficult to directly generate Gaussian light. To address this, apodized gratings are introduced. The key idea is to progressively modulate the grating groove depth, period, or fill factor along the propagation direction, so that the emission intensity per unit length at each position satisfies a Gaussian distribution function, thereby forming a Gaussian-shaped diffracted beam in the far field or free space.

[0003] Diffraction efficiency is a core performance metric for gratings, directly impacting light energy transmission, beam quality, and overall system performance. Improving the grating's diffraction efficiency allows more photons to be precisely directed to the region where they interact with atoms, increasing the probability of interaction and, in turn, enhancing the effectiveness of quantum operations and quantum information processing. A key aspect of integrated photon-atom chips is to achieve more efficient interactions between photons and atoms. Improving the grating's diffraction efficiency increases light output intensity, which is crucial for signal amplification and transmission required in integrated photonic chips. This is particularly true for interactions between photons and atoms, where signal intensity directly impacts experimental and application performance. Improving the grating's diffraction efficiency not only improves photon utilization but also enables higher precision and enhanced fidelity in these applications. Integrated photon-atom chips typically involve the close coupling of multiple optical components. Improving the grating's diffraction efficiency optimizes the efficiency of these components, improving overall system controllability. However, improving the diffraction efficiency of gratings faces multiple challenges, including limitations in material selection and manufacturing precision, surface quality and scattering losses, matching the diffraction angle with optical coupling, controlling multimode interference and mode conversion, balancing size and integration, the impact of thermal effects on efficiency, and cost. Achieving high diffraction efficiency in integrated grating chips requires overcoming challenges in high-precision manufacturing, surface treatment, mode selection, and temperature control. Summary of the Invention

[0004] To address the above-mentioned issues, the present invention aims to propose a device and method for generating Gaussian light using a sector-shaped waveguide grating with an anti-reflection layer. By designing a silicon dioxide anti-reflection layer covering the grating surface, the reflection loss of light at the interface is reduced, the optical coupling effect is optimized, and efficient coupling between free-space light and the integrated optical chip is achieved. Furthermore, by adjusting the thickness of the anti-reflection layer and the grating etching depth, the diffraction efficiency of the grating can be effectively improved, allowing more photons to be precisely guided to the target area.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, comprising:

[0007] Sector grating with an opening angle of 60°, a waveguide made of gallium nitride and a substrate of aluminum oxide;

[0008] The apodized periodic grating etched on the sector grating is composed of several elliptical grooves, each of which is the right half of the ellipse.

[0009] The silica antireflection layer covering the surface of the sector grating has a refractive index between that of air and the substrate material.

[0010] Furthermore, the thickness of the silicon dioxide anti-reflection layer satisfies the constructive interference condition, and the thickness of the silicon dioxide anti-reflection layer takes the minimum value that satisfies the constructive interference condition:

[0011]

[0012] Where λ is the wavelength of the incident light, n m is the refractive index of the silica antireflection layer.

[0013] Furthermore, the thickness of the silicon dioxide anti-reflection layer is 183 nm.

[0014] Furthermore, the etching depth of the apodized periodic grating is 270 nm.

[0015] Furthermore, the apodized periodic grating is composed of 48 elliptical grooves.

[0016] Furthermore, the position and width of the elliptical groove are controlled by the grating duty cycle and period, and the right focus of the ellipse is the target point in the reflection direction of each grating groove.

[0017] Furthermore, the period of the apodized periodic grating is determined according to the wavelength of the incident light, the refractive index of the material, and the diffraction angle. The expression of the period Λ of the apodized periodic grating is:

[0018]

[0019] Among them, n eff is the effective refractive index of the grating, n a represents the refractive index of the air above the grating (n a =1), θ represents the diffraction angle, θ=arctan(hf / D), where hf is the height of the designed Gaussian light focus, and D is the horizontal distance between the grating groove and the Gaussian light focus.

[0020] Furthermore, the silicon dioxide anti-reflection layer covers the upper surface of the apodized periodic grating and the unetched areas.

[0021] In order to achieve the above-mentioned object, the present invention further provides an optical coupling method for a device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, comprising:

[0022] The waveguide mode is converted into an output light with a Gaussian envelope by a grating of the fan-shaped waveguide;

[0023] The silicon dioxide anti-reflection layer is used to reduce the reflection loss of light at the interface, thereby improving the light coupling efficiency.

[0024] Beneficial effects: The present invention reduces the reflection loss of light at the interface by designing a silicon dioxide anti-reflection layer covering the grating surface, optimizes the optical coupling effect, and realizes efficient coupling between free-space light and integrated optical chips; the diffraction efficiency of the grating can also be effectively improved by adjusting the thickness of the anti-reflection layer and the grating etching depth, so that more photons are accurately guided to the target area; the fan-shaped grating of the present invention has a size of the micron level, is compatible with integrated optical devices, has good integrability, and is conducive to expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of a device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to an embodiment of the present invention;

[0027] Figure 2 Schematic diagrams of the side and top views of the fan-shaped grating structure of the device for generating Gaussian light using a fan-shaped waveguide grating based on an anti-reflection layer according to an embodiment of the present invention;

[0028] Figure 3 Schematic diagram of the intensity distribution of the diffracted light field of the fan-shaped grating in different planes of the device for generating Gaussian light based on the fan-shaped waveguide grating with an anti-reflection layer according to an embodiment of the present invention;

[0029] Figure 4 The comparative measurement results of the transmittance T of the sector-shaped grating of the device for generating Gaussian light based on the sector-shaped waveguide grating with an anti-reflection layer according to an embodiment of the present invention are shown in FIG.

[0030] Figure 5 These are the measurement results of the transmittance T and the optimal anti-reflection layer thickness H of the fan-shaped grating after adding the anti-reflection layer of the device for generating Gaussian light based on the fan-shaped waveguide grating of the embodiment of the present invention.

[0031] In the figure, 1 is a sector grating, 3 is a silicon dioxide anti-reflection layer, and 3 is a substrate. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0034] Example 1

[0035] See also Figure 1: A device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, comprising:

[0036] Sector grating 1, with an opening angle of 60°, a waveguide made of gallium nitride, and a substrate 3 made of aluminum oxide;

[0037] The apodized periodic grating etched on the sector grating 1 is composed of a number of elliptical grooves, each groove being a curved segment of the right half of the ellipse;

[0038] The silicon dioxide anti-reflection layer 2 covering the surface of the sector grating 1 has a refractive index between that of air and that of the substrate material.

[0039] It should be noted that when the laser is transmitted through the grating, it will be focused into a beam of Gaussian light with a certain tilt angle; the etching depth, period and duty cycle of the grating can be adjusted, and the diffraction efficiency of the diffracted light will be affected by the grating etching depth and the height of the anti-reflection layer; when there is no covering layer on the grating surface, the incident light is strongly reflected between the air and the grating material, resulting in partial light energy loss; therefore, adding a layer of SiO2 covering layer of appropriate height can serve as an anti-reflection film to reduce the interface reflection of the incident light and increase the light flux entering the grating, thereby improving the diffraction efficiency of the grating; the refractive index of the silicon dioxide layer is between that of the air and the substrate material, which can effectively adjust the refractive index matching of the interface light, reduce the reflection loss of light at the interface, allow more light to enter the grating working area, and improve the utilization rate of light; the grating structure with an anti-reflection film applied in this embodiment can effectively improve the diffraction efficiency of the grating, optimize light coupling, reduce light loss, and is easy to integrate and expand, so it can be used in integrated optics for grating couplers, integrated spectrometers and on-chip light sensors.

[0040] In a specific example, the thickness of the silicon dioxide anti-reflection layer satisfies the constructive interference condition, and the thickness of the silicon dioxide anti-reflection layer takes the minimum value that satisfies the constructive interference condition:

[0041]

[0042] Where λ is the wavelength of the incident light, n m is the refractive index of the silica antireflection layer.

[0043] In a specific example, the thickness of the silicon dioxide anti-reflection layer is 183 nm, and the etching depth of the apodized periodic grating is 270 nm.

[0044] It should be noted that the optimal structural parameters can be obtained by adjusting the etching depth of the grating and the thickness of the antireflection film; different etching depths have different optimal thicknesses H. The results show that the grating diffraction efficiency reaches its maximum value when the etching depth d = 270nm and H = 183nm.

[0045] In a specific example, the apodized periodic grating is composed of 48 elliptical grooves.

[0046] In a specific example, the position and width of the elliptical groove are controlled by the grating duty cycle and period, and the right focus of the ellipse is the target point in the reflection direction of each grating groove.

[0047] In a specific example, the period of the apodized periodic grating is determined according to the wavelength of the incident light, the refractive index of the material, and the diffraction angle. The expression of the period Λ of the apodized periodic grating is:

[0048]

[0049] Among them, n eff is the effective refractive index of the grating, n a represents the refractive index of the air above the grating (n a =1), θ represents the diffraction angle, θ=arctan(hf / D), where hf is the height of the designed Gaussian light focus, and D is the horizontal distance between the grating groove and the Gaussian light focus.

[0050] In a specific example, the silicon dioxide anti-reflection layer covers the upper surface of the apodized periodic grating and the unetched area.

[0051] In the specific implementation, Figure 2 The following are side and top views of the grating anti-reflection structure designed in this embodiment. The aluminum oxide substrate is 300 nm thick, the gallium nitride waveguide has a thickness of T = 400 nm and a length of L = 10 μm. The grating opening angle φ = 60°. The black cross represents the focal point f of the diffracted light. The horizontal distance from the grating groove to the focal point f is D. hf represents the height of the focal point f from the waveguide surface. The diffraction angle is θ. The thickness of the silicon dioxide anti-reflection layer H is variable. The grating diffraction efficiency reaches its maximum value when constructive interference is satisfied. As the grating etch depth d increases, the height hf of the focal point f from the waveguide surface gradually decreases. To maximize diffraction efficiency, d should be matched to the grating period and the wavelength of the incident light to ensure optimal diffraction efficiency while avoiding higher-order diffraction effects. By properly selecting the ratio of etch depth to period and combining it with the optical properties of the material, diffraction efficiency can be optimized while ensuring grating stability and performance.

[0052] Figure 3The intensity distribution diagrams of the diffracted light field of the sector grating in the xz, yz, and xz planes are normalized when the etching depth d = 270nm and the anti-reflection layer thickness H = 183nm. The incident light is 850nm, and the position of the focus f is x = 1.84μm, y = 0, and z = 4.28μm. (a) shows the intensity distribution in the xz plane. At this time, the diffraction angle θ is approximately 45°. The intensity of the diffracted light field reaches its maximum at the focus f. The transmittance T in the yz plane at f is recorded as the maximum diffraction efficiency of the grating. (b) and (c) show the intensity distribution of the diffracted light field at the focus f in the yz plane and the xy plane, respectively.

[0053] In order to prove that the diffracted light generated by the grating obeys a Gaussian-like distribution, Figure 3 (d) and (e) give Figure 3 The normalized curves of the squared electric field strength at the red dashed lines a and b in (b) show the variation of the squared electric field strength at z when x = 1.84 μm and y = 0, and (e) shows the variation of the squared electric field strength at y when x = 1.84 μm and z = 4.28 μm. The distribution of these curves indicates that the diffracted light is Gaussian. The calculated diameter of the diffracted light focus along the y-axis is approximately 2.7 μm, and along the x-axis is approximately 2.2 μm.

[0054] Figure 4 The results of the diffraction efficiency of the grating with and without an anti-reflection layer are shown as a function of the etch depth d. The gray circles represent the case without an anti-reflection layer. It can be seen that the diffraction efficiency of the grating without an anti-reflection layer reaches a maximum of 33.6105% at an etch depth of d = 210 nm and then gradually decreases. The gray squares represent the case with an anti-reflection layer. It can be seen that the grating efficiency gradually increases with the addition of the anti-reflection layer, and at d = 230 nm, the transmittance T exceeds that of the case without an anti-reflection layer.

[0055] Figure 5 The curves of the grating diffraction efficiency T and the optimal anti-reflection layer thickness H with the etching depth d after adding the anti-reflection layer are given. It should be pointed out that when the etching depth is fixed and the thickness of the anti-reflection layer H is gradually increased, the diffraction efficiency of the grating will also show a Gaussian distribution trend. For the convenience of statistics, Figure 5The results presented are the optimal H values measured at each etch depth, and the corresponding T is also the maximum diffraction efficiency at each etch depth. It can be seen that as the etch depth d gradually increases, the optimal anti-reflection layer thickness H gradually decreases, while the grating diffraction efficiency T shows a trend of first increasing and then decreasing. At d = 270nm, the grating diffraction efficiency reaches its maximum value of 38.4984%. Compared with the case without the anti-reflection layer, T is nearly 5% higher, and the corresponding optimal thickness H is 183nm.

[0056] In summary, the sector-shaped grating structure used in this embodiment has a layer of silicon dioxide anti-reflection film applied on its upper surface, which can effectively improve the diffraction efficiency of the grating. By adjusting the etching depth of the grating and the thickness of the anti-reflection film, the optimal structural parameters can be obtained. Different etching depths have different optimal thicknesses H. The results show that the grating diffraction efficiency reaches its maximum value when the etching depth d = 270nm and H = 183nm.

[0057] Example 2

[0058] To achieve the above-mentioned purpose, this embodiment further provides an optical coupling method for a device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, comprising:

[0059] The waveguide mode is converted into an output light with a Gaussian envelope by a grating of the fan-shaped waveguide;

[0060] The silicon dioxide anti-reflection layer is used to reduce the reflection loss of light at the interface, thereby improving the light coupling efficiency.

[0061] The optical coupling method of the device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer in this embodiment has the same advantages as the above-mentioned device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer over the prior art, and will not be repeated here.

[0062] 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, characterized in that: include: Sector grating with an opening angle of 60°, a waveguide made of gallium nitride and a substrate of aluminum oxide; The apodized periodic grating etched on the sector grating is composed of several elliptical grooves, each of which is the right half of the ellipse. The silica antireflection layer covering the surface of the sector grating has a refractive index between that of air and the substrate material.

2. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The thickness of the silicon dioxide anti-reflection layer satisfies the constructive interference condition, and the thickness of the silicon dioxide anti-reflection layer takes the minimum value that satisfies the constructive interference condition: Where λ is the wavelength of the incident light, n m is the refractive index of the silica antireflection layer.

3. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 2, characterized in that: The thickness of the silicon dioxide anti-reflection layer is 183 nm.

4. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The etching depth of the apodized periodic grating is 270 nm.

5. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The apodized periodic grating is composed of 48 elliptical grooves.

6. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The position and width of the elliptical groove are controlled by the grating duty cycle and period, and the right focus of the ellipse is the target point in the reflection direction of each grating groove.

7. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The period of the apodized periodic grating is determined according to the wavelength of the incident light, the refractive index of the material, and the diffraction angle. The expression of the period Λ of the apodized periodic grating is: Among them, n eff is the effective refractive index of the grating, n a represents the refractive index of the air above the grating (n a =1), θ represents the diffraction angle, θ=arctan(hf / D), where hf is the height of the designed Gaussian light focus, and D is the horizontal distance between the grating groove and the Gaussian light focus.

8. The device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer according to claim 1, characterized in that: The silicon dioxide anti-reflection layer covers the upper surface of the apodized periodic grating and the unetched areas.

9. An optical coupling method for a device for generating Gaussian light based on a fan-shaped waveguide grating with an anti-reflection layer, characterized in that: include: The waveguide mode is converted into an output light with a Gaussian envelope by a grating of the fan-shaped waveguide; The silicon dioxide anti-reflection layer is used to reduce the reflection loss of light at the interface, thereby improving the light coupling efficiency.

Images