Double-reflection type grating coupler for spatial optical coupling

Abstract

The invention discloses a double-reflection grating coupler for spatial optical coupling, which comprises a substrate layer, an oxide lower cladding layer and an optical waveguide layer which are sequentially stacked from bottom to top, a first light reflection structure is arranged between the substrate layer and the oxide lower cladding layer, and a supporting polar plate is arranged above the optical waveguide layer. A second light reflection structure is arranged between the supporting polar plate and the optical waveguide layer; the optical waveguide layer comprises a left optical waveguide, a grating area and a right optical waveguide which are sequentially arranged from one side of the substrate layer to the other opposite side, and space light enters the grating area, is reflected by the first light reflection structure and the second light reflection structure, reflects an uncoupled part back to the grating area for coupling, and is output through the right optical waveguide. According to the invention, the problem of low coupling efficiency in coupling of the spatial light and the optical waveguide in the turbulent channel in the prior art is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless optical communication, and in particular relates to a double-reflection grating coupler for spatial optical coupling. Background Art

[0002] With the rapid growth of multimedia services, the widespread popularization of the Internet, and the rapid development of related technologies such as artificial intelligence, people have put forward higher requirements for the capacity, speed and quality of information transmission. Wireless optical communication (Free Space Optics, FSO) uses light waves as signal carriers, which can achieve wide spectrum, high confidentiality and large-capacity data transmission, and has received more and more attention. In FSO communication systems, when signal beams are transmitted in turbulent channels, turbulence effects are one of the key factors affecting communication performance. At the receiving end, the impact of turbulence on optical signals can be manifested as beam drift, angle of arrival (AOA) fluctuations, and beam expansion, which causes beam alignment errors at the receiving antenna or optical fiber end face, significantly reducing signal quality, thereby affecting the reliability and rate of the communication system, and ultimately restricting the improvement of communication quality.

[0003] In recent years, integrated optics has been widely used in optical communications, sensing, and computing. The rapid development of integrated optical technology has not only promoted innovation in the field of photonics, but also made important breakthroughs in device miniaturization, low power consumption, and high integration. At present, the coupling of off-chip light and optical waveguides is mainly achieved in two ways: end coupling (edge ​​coupler) and grating coupling (grating coupler). Among them, end coupling can achieve excellent optical performance under the conditions of small optical waveguide size and high alignment accuracy; while grating couplers are favored for their higher flexibility and adjustment ability, lower manufacturing cost, and applicability to large-scale integration. Both coupling methods are highly sensitive to the incident angle of the light beam. During the transmission of the signal light beam in the turbulent channel, the arrival angle will fluctuate, and the incident angle will change randomly. Reducing the sensitivity of the incident angle of the light beam can effectively improve the coupling efficiency of spatial light and optical waveguides in the turbulent channel. The present invention proposes a grating coupler solution by introducing uniform, blazed, chirped and other grating structures and combining the design of upper and lower double reflection structures, which effectively solves the problem that traditional grating coupling is sensitive to the incident angle of the light beam and provides a new technical path for realizing the coupling of spatial light and optical waveguide in turbulent channels. Summary of the invention

[0004] The purpose of the present invention is to provide a double-reflection grating coupler for spatial light coupling, which solves the problem of low coupling efficiency in the coupling of spatial light and optical waveguide in a turbulent channel in the prior art.

[0005] The technical solution adopted by the present invention is a double-reflection grating coupler for spatial light coupling, comprising a substrate layer, an oxide lower cladding layer and an optical waveguide layer stacked in sequence from bottom to top, a first light reflection structure is arranged between the substrate layer and the oxide lower cladding layer, a supporting electrode plate is arranged above the optical waveguide layer, and a second light reflection structure is arranged between the supporting electrode plate and the optical waveguide layer; The optical waveguide layer includes a left optical waveguide, a grating region and a right optical waveguide which are arranged in sequence from one side of the substrate layer to the other side. When spatial light is incident on the grating region, the uncoupled part is reflected back to the grating region for coupling under the reflection of the first light reflecting structure and the second light reflecting structure, and is output through the right optical waveguide.

[0006] The technical solution of the present invention is also characterized in that: The optical waveguide on the right side includes a linear tapered waveguide and a rectangular waveguide which are closely connected to each other, and one end of the linear tapered waveguide away from the rectangular waveguide is closely connected to the grating region.

[0007] The second light reflecting structure is located above the grating region and the linear tapered waveguide, and the horizontal distance between the second light reflecting structure and the starting end of the grating region is 10μm~15μm, the vertical distance is 3μm~8μm, and the angle between the second light reflecting structure and the horizontal direction is 0°~5°.

[0008] The second light reflecting structure adopts a metal reflecting layer structure, and the metal material thereof is any one of gold, silver and aluminum; the thickness of the second light reflecting structure is 0.05 μm-0.15 μm.

[0009] The first light reflecting structure adopts a distributed Bragg reflector or a metal reflecting layer structure. When the first light reflecting structure adopts the metal reflecting layer structure, the metal material thereof is any one of gold, silver and aluminum.

[0010] The grating region is any one of a chirped grating structure, a blazed grating structure, and a uniform grating structure.

[0011] The material of the oxide lower cladding is silicon dioxide with a thickness of 1.8 μm to 2.2 μm, and the refractive index of the oxide lower cladding is 1.4 to 1.5.

[0012] The materials of the substrate layer and the optical waveguide layer are both silicon, and the refractive index of the substrate layer and the optical waveguide layer is 3.10-3.75.

[0013] The beneficial effects of the present invention are: The double-reflection grating coupler for spatial light coupling of the present invention introduces a first light reflection structure on the upper surface of the substrate layer and a second light reflection structure above the grating area to form a double-reflection structure, which reflects the light beam that is not coupled into the optical waveguide and makes it re-incident into the grating area for coupling. The transmission path of the light beam is effectively optimized, and the sensitivity of the incident light angle change to the coupling efficiency is significantly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic structural diagram of a double-reflection grating coupler for spatial light coupling of the present invention; Figure 2 is a top view of a double-reflection grating coupler for spatial light coupling of the present invention; Figure 3 is a side view of a double-reflection grating coupler for spatial light coupling of the present invention; Figure 4 It is a schematic diagram of the coupling optical path of the double-reflection grating coupler used for spatial optical coupling of the present invention; Figure 5 is an angle performance diagram of Example 6 of the present invention; Figure 6 A schematic diagram of the structure of a conventional grating coupler in a comparative example of the present invention; Figure 7 Angular performance diagram of a conventional grating coupler in a comparative example of the present invention.

[0015] In the figure, 1. substrate layer, 2. oxide lower cladding layer, 3. first light reflecting structure, 4. optical waveguide layer, 401. left optical waveguide, 402. grating region, 403. right optical waveguide, 4031. linear tapered waveguide, 4032. rectangular waveguide, 5. second light reflecting structure, 6. supporting plate. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0017] Example 1 The present invention is used for a double-reflection grating coupler for spatial light coupling, such as Figure 1 and Figure 2As shown, it includes a substrate layer 1, an oxide lower cladding layer 2 and an optical waveguide layer 4 stacked in sequence from bottom to top, a first light reflection structure 3 is arranged between the substrate layer 1 and the oxide lower cladding layer 2, a support plate 6 is arranged above the optical waveguide layer 4, and a second light reflection structure 5 is arranged between the support plate 6 and the optical waveguide layer 4; The optical waveguide layer 4 includes a left optical waveguide 401, a grating region 402 and a right optical waveguide 403 which are arranged in sequence from one side of the substrate layer 1 to the other side. When spatial light is incident on the grating region 402, the uncoupled part is reflected back to the grating region 402 under the reflection of the first light reflecting structure 3 and the second light reflecting structure 5 for coupling, and is output through the right optical waveguide 403.

[0018] The double-reflection grating coupler for spatial light coupling of the present invention introduces a first light reflection structure on the upper surface of the substrate layer and a second light reflection structure above the grating area to form a double-reflection structure, which reflects the light beam that is not coupled into the optical waveguide and makes it re-incident into the grating area for coupling. The transmission path of the light beam is effectively optimized, and the sensitivity of the incident light angle change to the coupling efficiency is significantly reduced.

[0019] Example 2 The double-reflection grating coupler for spatial light coupling of the present invention comprises a substrate layer 1, an oxide lower cladding layer 2 and an optical waveguide layer 4 stacked in sequence from bottom to top, a first light reflection structure 3 is arranged between the substrate layer 1 and the oxide lower cladding layer 2, a support plate 6 is arranged above the optical waveguide layer 4, and a second light reflection structure 5 is arranged between the support plate 6 and the optical waveguide layer 4; The optical waveguide layer 4 includes a left optical waveguide 401, a grating region 402 and a right optical waveguide 403 which are arranged in sequence from one side of the substrate layer 1 to the other side. When spatial light is incident on the grating region 402, the uncoupled part is reflected back to the grating region 402 under the reflection of the first light reflecting structure 3 and the second light reflecting structure 5 for coupling, and is output through the right optical waveguide 403.

[0020] Furthermore, the right optical waveguide 403 includes a linear tapered waveguide 4031 and a rectangular waveguide 4032 that are closely connected to each other, and one end of the linear tapered waveguide 4031 away from the rectangular waveguide 4032 is closely connected to the grating region 402 .

[0021] Furthermore, if Figure 3 As shown, the second light reflecting structure 5 is located above the grating region 402 and the linear tapered waveguide 4031, and the horizontal distance between the second light reflecting structure 5 and the starting end of the grating region 402 is 10μm~15μm, the vertical distance is 3μm~8μm, and the angle between the second light reflecting structure 5 and the horizontal direction is 0°~5°.

[0022] Furthermore, the grating region 402 is any one of a chirped grating structure, a blazed grating structure, and a uniform grating structure.

[0023] The chirped grating structure has broadband characteristics. It can operate on optical signals in a wide wavelength range. For example, in a wavelength division multiplexing system, it can effectively process multiple optical signals with close wavelength intervals, realize multiplexing / demultiplexing functions, and increase the transmission capacity of the communication system. At the same time, the chirped grating can also be used for dispersion compensation, which can produce different delays for light of different wavelengths and compensate for the dispersion in the optical fiber. This is very critical in long-distance, high-speed optical communications, which is conducive to the recovery of optical pulses and ensures the accuracy of signal transmission.

[0024] The biggest advantage of the blazed grating structure is that it can concentrate light energy to a specific diffraction order. By properly designing the blaze angle, the light intensity of the desired diffraction order can be significantly enhanced, which greatly improves the sensitivity and resolution of the instrument in applications such as spectral analysis. In addition, the blazed grating has a high diffraction efficiency, which can effectively reduce the loss of light energy in undesired directions and fully utilize light energy in applications such as spectrometry.

[0025] Example 3 The double-reflection grating coupler for spatial light coupling of the present invention comprises a substrate layer 1, a lower cladding layer 2, a first light reflection structure 3, an optical waveguide layer 4, a second light reflection structure 5, and a supporting plate 6. The optical waveguide layer 4 is composed of a left optical waveguide 401, a grating region 402, and a right optical waveguide 403, and the right optical waveguide 403 is further composed of a linear tapered waveguide 4031 and a rectangular waveguide 4032, for realizing single-mode output of a light beam.

[0026] Arranged in order from top to bottom and from left to right are: supporting plate 6, second light reflecting structure 5, left optical waveguide 401, grating region 402, linear tapered waveguide 4031, rectangular waveguide 4032, oxide lower cladding 2, first light reflecting structure 3 and substrate layer 1.

[0027] Furthermore, the first light reflection structure 3 may adopt a distributed Bragg reflector (DBR) or a metal reflection layer structure, and when the metal reflection layer structure is adopted, metal materials such as gold, silver, and aluminum may be adopted. The grating region 402 may select a grating structure such as chirped, blazed, or uniform according to different parameters such as the wavelength, mode field distribution, and polarization state of the incident light beam.

[0028] Furthermore, the second light reflecting structure 5 adopts a metal reflecting layer structure with a thickness of 0.05~0.15μm, and is placed above the grating area 402 and the linear tapered waveguide 4031 using a supporting electrode 6, and the horizontal distance from the starting end of the grating area 402 is 10~15μm, the vertical distance is 3~8μm, and the angle with the horizontal direction is 0~5°.

[0029] The coupling principle of the double-reflection grating coupler for spatial light coupling of the present invention is the diffraction effect of the grating, which can be explained by the Bragg condition. When the grating period and duty cycle of the grating region 402 satisfy the Bragg condition of the following formula (1), the light beam can be efficiently coupled into the optical waveguide through the grating region 402; (1); In the formula, is the period of the grating, is the effective refractive index of the waveguide, is the refractive index of the cover layer on the grating, is the incident angle of the light beam, is the diffraction order, is the wavelength of the light beam.

[0030] like Figure 4 As shown, when the spatial light A in the turbulent channel is affected by turbulence, the arrival angle fluctuation phenomenon will occur, and it will be incident on the grating area at a random angle. When formula (1) is satisfied, most of A will be coupled into the optical waveguide through the diffraction effect of the grating structure to form horizontally transmitted light. When formula (1) is not satisfied, a small part of the spatial light A will be coupled into the optical waveguide through the diffraction effect of the grating structure to form horizontally transmitted light C1, and most of it will produce two transmission paths of upward transmission and downward transmission in the grating area: a part of the light beam is transmitted downward to form downwardly transmitted light D. This part of the light is reflected by the first light reflection structure 3, and its transmission path is changed. It is reflected to become light R1, which is coupled into the optical waveguide through the diffraction effect of the grating area 402 to become horizontally transmitted light C2; the other part of the light beam is transmitted upward to form upwardly transmitted light U. Under the reflection effect of the second light reflection structure 5, the transmission path of the upward transmission light U changes to form reflected light R2, which is diffracted by the grating area 402 again and coupled into the optical waveguide to become horizontal transmission light C3.

[0031] Example 4 On the basis of Example 3, the material of the oxide lower cladding 2 in the double-reflection grating coupler for spatial light coupling of the present invention is silicon dioxide with a thickness of 1.8 μm to 2.2 μm, and the refractive index of the oxide lower cladding 2 is 1.4 to 1.5.

[0032] The substrate layer 1 and the optical waveguide layer 4 are both made of silicon, and the refractive index of the substrate layer 1 and the optical waveguide layer 4 is 3.10-3.75.

[0033] Example 5 In the implementation process of the double-reflection grating coupler for spatial light coupling in this embodiment, silicon material is selected for the substrate layer 1 and the optical waveguide layer 4. This is because silicon material has a high refractive index and stability during light transmission and can effectively guide the propagation of light waves. In this embodiment, its refractive index is 3.5. The oxide lower cladding layer 2 is made of silicon dioxide material with a refractive index of 1.44. Silicon dioxide material as the lower cladding layer can provide good optical isolation and support for the optical waveguide, reducing the scattering and loss of the optical signal.

[0034] The thickness of the optical waveguide layer 4 is designed to be 0.26 μm, which can effectively realize the single-mode transmission of the silicon waveguide, avoid interference and mode mismatch caused by multi-mode transmission, and thus improve the stability and quality of optical transmission. The thickness of the oxide lower cladding layer 2 is selected to be 2 μm, which can effectively isolate the optical coupling between the waveguide mode and the substrate, prevent the optical mode from leaking to the substrate area, and reduce the energy loss during optical transmission.

[0035] The first light reflecting structure 3 and the second light reflecting structure 5 both use metallic silver as the reflecting layer. Silver has a high reflectivity in the visible light and near-infrared bands (especially the communication wavelength of 1550nm), and can efficiently reflect optical signals, thereby redirecting more light beams to the grating area for secondary coupling.

[0036] The simulation was verified using Lumerical FDTD software. The light source type was set to Gaussian beam, and the wavelength was selected as 1550nm in the communication C band. This wavelength is widely used in the field of optical communications and has excellent transmission performance and anti-loss capabilities. The grating area adopts a chirped grating structure. By adjusting the grating period and duty cycle along the horizontal transmission direction, the matching degree between the incident light mode and the waveguide mode can be improved. Through parameter scanning optimization, it was finally determined that the grating period and duty cycle varied between 0.6 and 0.75μm and between 0.6 and 0.8, respectively, and the etching depth was 0.11μm. In the optimized design of the second light reflection structure 5, its horizontal distance and vertical distance from the starting end of the grating area 402 were set to 12μm and 4μm, respectively, and formed an angle of 3° with the horizontal direction. This geometric configuration can effectively optimize the reflection path of light, so that more light beams are guided back to the grating area for efficient coupling, further improving the coupling efficiency and the transmission quality of the optical signal. It provides an excellent solution for spatial light coupling in turbulent channels.

[0037] Through the above specific material selection, structural dimension design and parameter optimization, the double-reflective grating coupler of this embodiment has achieved significant improvements in optical coupling efficiency, angular width, etc. The 1dB angular width is 12°, and the optical coupling efficiency is increased by about 11% compared with the traditional uniform grating coupler, providing strong technical support for the development of high-performance optical communication devices.

[0038] Example 6 In this embodiment, the substrate layer 1 and the optical waveguide layer 4 are both made of silicon material with a refractive index of 3.47; the oxide lower cladding layer 2 is made of silicon dioxide material with a refractive index of 1.453. The thickness of the optical waveguide layer 4 is 0.22 μm, and the thickness of the oxide lower cladding layer 2 is 2 μm. The first light reflection structure 3 and the second light reflection structure 5 are both made of metal aluminum reflection layers. Lumerical FDTD software is used for simulation verification, the light source type is set to Gaussian beam, and the wavelength is selected to be 1550 nm in the communication C band. The grating area adopts a uniform grating structure, and the key parameters such as the grating period, duty cycle, and the horizontal distance between the second light reflection structure 5 and the grating area 402 are optimized by parameter scanning. Finally, it is determined that the grating period is 0.7 μm, the duty cycle is 0.6, the etching depth is 0.07 μm, the thickness of the first light reflection structure 3 is 0.07 μm, the angle between the second light reflection structure 5 and the horizontal direction is 0°, and the horizontal distance and vertical distance from the beginning of the grating area 402 are 13 μm and 3 μm respectively.

[0039] In order to evaluate the effect of different incident angles on the performance of the grating coupler, the beam incident angle scanning range was set to 13° to 30°, and a curve of coupling efficiency versus incident angle was plotted. The 1dB angular width, i.e. the angle range corresponding to when the coupling efficiency drops by 1dB, was extracted from the scanning results. The results are shown in Figure 2. Figure 5 As shown, the 1 dB angular width of the double-reflection grating coupler is 10.8°.

[0040] Comparative Example The structure of this comparative example is as follows Figure 6 As shown, the substrate layer and the optical waveguide layer are made of silicon material with a refractive index of 3.47; the oxide lower cladding is made of silicon dioxide material with a refractive index of 1.453, and there is no first light reflection structure and second light reflection structure. The incident light beam is a Gaussian light beam with a wavelength of 1550nm, the grating area is a uniform grating, and the parameters such as the grating-related period and duty cycle are scanned, and the obtained period is 0.64μm, the duty cycle is 0.7, and the etching depth is 0.07μm.

[0041] Set the beam incident angle scanning range to 14° to 23°, and plot the coupling efficiency versus incident angle. Extract the 1dB angular width from the scanning results, which is the angle range where the coupling efficiency drops by 1dB. Figure 7As shown, the 1 dB angular width of the double-reflection grating coupler is 5.2°.

[0042] Comparison of the results of Example 6 with those of the comparative example shows that the dual-reflection grating coupler of the present invention exhibits more excellent performance within the range of incident angle variation. The 1dB angular width of the dual-reflection grating coupler in Example 6 is 10.8°, which is significantly better than the 1dB angular width of 5.2° of the traditional grating coupler in the comparative example. This shows that the dual-reflection structure of the present invention optimizes the transmission path of the light beam through reflection and re-coupling, effectively reduces the sensitivity of the coupler to changes in the incident angle, and maintains a higher coupling efficiency within a wider range of incident angles. In contrast, the traditional grating coupler has a low tolerance to changes in the incident angle due to the lack of a reflection optimization mechanism, resulting in a rapid decrease in its coupling efficiency. The above comparison results further verify the significant advantages of the present invention in wide-angle tolerance and coupling efficiency.

[0043] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0044] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A double-reflection grating coupler for spatial light coupling, characterized in that: The optical waveguide layer (4) comprises a substrate layer (1), an oxide lower cladding layer (2) and an optical waveguide layer (4) which are stacked in sequence from bottom to top, a first light reflection structure (3) being arranged between the substrate layer (1) and the oxide lower cladding layer (2), a supporting electrode plate (6) being arranged above the optical waveguide layer (4), and a second light reflection structure (5) being arranged between the supporting electrode plate (6) and the optical waveguide layer (4); The optical waveguide layer (4) comprises a left optical waveguide (401), a grating region (402) and a right optical waveguide (403) which are arranged in sequence from one side of the substrate layer (1) to the other side opposite thereto. When spatial light is incident on the grating region (402), an uncoupled portion is reflected back to the grating region (402) under the reflection of the first light reflection structure (3) and the second light reflection structure (5) for coupling, and is output through the right optical waveguide (403).

2. The double-reflection grating coupler for spatial light coupling according to claim 1, characterized in that: The right optical waveguide (403) comprises a linear tapered waveguide (4031) and a rectangular waveguide (4032) that are closely connected to each other, and one end of the linear tapered waveguide (4031) away from the rectangular waveguide (4032) is closely connected to the grating region (402).

3. The double-reflection grating coupler for spatial light coupling according to claim 2, characterized in that: The second light reflecting structure (5) is located above the grating region (402) and the linear tapered waveguide (4031), and the horizontal distance between the second light reflecting structure (5) and the starting end of the grating region (402) is 10 μm to 15 μm, and the vertical distance is 3 μm to 8 μm, and the angle between the second light reflecting structure (5) and the horizontal direction is 0° to 5°.

4. The double-reflection grating coupler for spatial light coupling according to claim 1, characterized in that: The second light reflecting structure (5) adopts a metal reflecting layer structure, and its metal material is any one of gold, silver and aluminum; the thickness of the second light reflecting structure (5) is 0.05 μm-0.15 μm.

5. The double-reflection grating coupler for spatial light coupling according to claim 4, characterized in that: The first light reflecting structure (3) adopts a distributed Bragg reflector or a metal reflecting layer structure. When the first light reflecting structure (3) adopts a metal reflecting layer structure, its metal material is any one of gold, silver and aluminum.

6. The double-reflection grating coupler for spatial light coupling according to claim 1, characterized in that: The grating region (402) is any one of a chirped grating structure, a blazed grating structure, and a uniform grating structure.

7. The double-reflection grating coupler for spatial light coupling according to claim 1, characterized in that: The material of the oxide lower cladding layer (2) is silicon dioxide, with a thickness of 1.8 μm to 2.2 μm, and the refractive index of the oxide lower cladding layer (2) is 1.4 to 1.

5.

8. The double-reflection grating coupler for spatial light coupling according to claim 1, characterized in that: The materials of the substrate layer (1) and the optical waveguide layer (4) are both silicon, and the refractive index of the substrate layer (1) and the optical waveguide layer (4) is 3.10-3.75.

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