Integrated laser radar transmitting antenna based on slit optical waveguide

Abstract

The invention provides an integrated laser radar transmitting antenna based on a slit optical waveguide, which is based on a silicon-on-insulator chip with a certain top silicon thickness and a factory-replacing standard etching depth, and comprises a thick silicon substrate, a lower cladding, a top silicon slit optical waveguide structure, an upper cladding and the like. Periodic grating tooth structures are introduced to the silicon strips on the two sides of the slit, a signal light source passes through the device to generate emission light beams in the nearly vertical direction, the longitudinal scanning function of the light beams can be further achieved, and the scanning detection requirement of the laser radar is met. The weak-disturbance large-aperture optical antenna is constructed based on the single-layer slit optical waveguide structure, the known lowest beam divergence angle of the single-layer optical antenna structure is achieved, a new way is provided for emission aperture design and application of a laser radar, and the wide application prospect in the field of all-solid-state laser radars is achieved. And the blank of the ultra-large aperture integrated optical phased array laser radar transmitting antenna is filled.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar optical antennas, and particularly to an integrated lidar transmitting antenna based on a slit optical waveguide. Background Art

[0002] With the development of information technology entering the intelligent, networked, and digital stages, emerging industries represented by autonomous driving technology have become the focus of scientific and technological development in various countries, and lidar is a key system for realizing intelligent driving and navigation technologies. Traditional mechanical lidars are heavy, have a low frame rate, and the mechanical rotating device leads to unstable performance. The emerging optical phased array has advantages such as all-solid-state scanning, high resolution, fast response rate, etc., and has a higher integration degree and is compatible with advanced semiconductor processing technologies. Therefore, it has a wide application prospect in fields such as intelligent driving and is expected to achieve large-scale production using foundries. In recent years, large-scale integrated / hybrid integrated optical phased arrays have developed rapidly, and technologies such as frequency-modulated continuous wave and APD receiving arrays have also been successively applied to optical phased arrays. In addition, all-solid-state lidars also have great application advantages in optical imaging, free-space optical communication, and intelligent optical sensing.

[0003] The chip-level integrated optical phased array lidar needs to be equipped with an optical antenna array with a large-area emission aperture. The large-area emission aperture can form a signal beam with high resolution and low divergence angle, which is helpful for realizing long-distance laser velocity measurement and ranging. There are various design schemes for optical antennas, such as multi-layer grating antennas, apodized grating antennas, and slow-light grating antennas, etc.

[0004] The existing optical antenna solutions have inherent defects. The multi-layer grating antenna structure can achieve multi-layer film interference and multi-layer reflectors, thereby achieving high efficiency in the vertical direction. And the multi-layer grating antenna structure can adjust the coupling distance to control the perturbation intensity, which is beneficial to the design of large-aperture optical antennas. However, the multi-layer grating antenna structure leads to a relatively high processing complexity and is not compatible with the standard SOI process; the apodized grating antenna structure is gradually changed along the light propagation direction. By controlling the perturbation intensity to fit a uniform near-field distribution, the beam quality can be improved, and to a certain extent, the beam divergence angle can be reduced. However, the structure size is difficult to control during actual processing due to the gradual change; the slow-light grating can introduce a perturbation structure in the two-dimensional photonic crystal waveguide structure to increase the group refractive index of the emitted light. The main advantage is relatively high scanning sensitivity, but the loss is large, resulting in a small emission length. At present, the maximum reported length is only 1 mm, and it is difficult to achieve an emission aperture with a centimeter-scale area. Summary of the Invention

[0005] The object of the present invention is to provide an integrated lidar transmitting antenna based on a slit optical waveguide, so as to solve the defects of strong structural perturbation and small aperture of a single-layer optical antenna structure and the problem of process incompatibility of a multi-layer optical antenna. The specific technical solution is as follows:

[0006] An integrated lidar transmitting antenna based on a slit optical waveguide, which sequentially includes a lower cladding layer 1, a slit side silicon region 2, a grating hole etching region 3, and an upper cladding layer 4 from bottom to top. The slit side silicon region 2 is a single-slit structure formed by two side silicon strips. The grating hole etching region 3 is a shallow etching grating structure, which is periodic grating teeth arranged on the silicon strip.

[0007] Furthermore, the transmitting antenna is based on a silicon-on-insulator chip, and the thickness of the top silicon of the silicon-on-insulator chip can be selected as 220 nm or 340 nm.

[0008] Furthermore, the lower cladding layer 1 is a silica cladding layer with a thickness of 2 μm or 3 μm.

[0009] Furthermore, the thickness of the slit side silicon region 2 is 220 nm, the width of the silicon strip is 180 nm, and the width of the slit is 100 nm.

[0010] Furthermore, the size of the grating teeth is 70 nm × 70 nm.

[0011] Furthermore, the thickness of the upper cladding layer 4 is at least 3 μm, and the upper cladding layer 4 can be an air cladding layer, a silica cladding layer, a silicon nitride cladding layer, a photoresist cladding layer, or a polymer cladding layer.

[0012] Furthermore, a thick substrate layer 5 is further included below the lower cladding layer 1, and the thick substrate layer 5 is a silicon material with a thickness of 725 μm or 525 μm.

[0013] Furthermore, the transmitting antenna can also be applicable to chip platforms of other material systems.

[0014] Furthermore, the period of the transmitting antenna is 1.1 μm, and the grating diffraction angle corresponding to the period is in the near-vertical direction.

[0015] Furthermore, the working waveguide mode of the transmitting antenna is the transverse electric fundamental mode.

[0016] An integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention has the following beneficial effects compared with the prior art:

[0017] 1. The integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention avoids the problem of incompatibility between a multi-layer evanescent coupling type optical antenna structure and a general process flow, and has the advantages of being compact and integratable.

[0018] 2. The integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention utilizes the mode field distribution characteristics of the slit waveguide structure to greatly reduce the perturbation intensity of the optical antenna, and realizes a transmitting aperture with a length of 12 mm and a beam divergence angle of less than 0.007° on a single integrated silicon waveguide structure.

[0019] 3. The integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention introduces a perturbation structure above the mode field while ensuring the processing difficulty, improves the vertical directivity and transmitting efficiency of the antenna. In the wavelength range of 1500 - 1600 nm, the loss is basically 1 dB / mm, and the transmitting efficiency exceeds 40%.

[0020] 4. The integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention has the weakest mode field intensity in silicon under the calculated parameters. The selected structure is set under specific slit and side silicon widths, which weakens the influence of stray light on the signal light and has very important significance and value in the applications of integrated optical phased arrays and all-solid-state lidars. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of an integrated lidar transmitting antenna based on a slit optical waveguide provided by the present invention;

[0022] Figure 2 is a schematic surface topography diagram of an integrated lidar transmitting antenna based on a slit optical waveguide in an embodiment of the present invention;

[0023] Figure 3 is a schematic mode field diagram of an integrated lidar transmitting antenna based on a slit optical waveguide in an embodiment of the present invention;

[0024] Figure 4 is a performance curve diagram of an integrated lidar transmitting antenna based on a slit optical waveguide in an embodiment of the present invention;

[0025] Figure 5 is a schematic diagram of far-field beam scanning of an integrated lidar transmitting antenna based on a slit optical waveguide in an embodiment of the present invention;

[0026] Figure 6 is a far-field beam topography diagram of an integrated lidar transmitting antenna based on a slit optical waveguide in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings provided by the present invention. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the objectives of the embodiments of the present invention.

[0028] In the description of the present invention, unless otherwise clearly defined and limited, the terms "connection" and "coupling" shall be interpreted in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral body; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the description of the present invention, the orientation or positional relationship such as "upper", "lower", "left", "right", "front", "rear", "center", "horizontal", "vertical", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of description and simplifying the operation, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0030] Embodiment: This embodiment provides an integrated lidar transmitting antenna based on a slit optical waveguide. By using a standard 220nm - SOI chip platform and etch depths (70nm and 220nm) compatible with foundries, a high - performance integrated lidar transmitting antenna is realized on a silicon - based optoelectronic chip. Refer to Figure 1 As shown, the transmitting antenna includes a lower cladding 1, a slit - side silicon region 2, a grating - hole etching region 3, and an upper cladding 4. The lower cladding 1 is located below the slit - side silicon region 2, the grating - hole etching region 3 is located above the slit - side silicon region 2, and the upper cladding 4 is located above the grating - hole etching region 3. The slit - side silicon region 2 is a single - slit structure formed by two - side silicon strips, and the grating - hole etching region 3 is a periodic grating - tooth structure provided on the two - side silicon strips of the slit, and is also a shallow - etched weak - perturbation grating structure. The top - silicon slit waveguide of this transmitting antenna supports the TE - mode transmission, and based on this structure, an antenna structure with a large aperture can be realized.

[0031] The laser output by the laser enters the silicon strip waveguide through the grating / end face coupler, and then evolves into the slit optical waveguide mode through the mode spot converter structure and enters the slit optical waveguide antenna for transmission. At the same time, diffraction occurs, and the diffracted light radiating upward is the required transmitted signal light. The emission antenna structure of the present invention can control the loss, emission efficiency, directivity, etc. of the emission antenna by optimizing the thickness and width of the silicon strips on both sides and the slit region, the size of the grating teeth, etc. In order to improve the emission efficiency of the emission antenna to reduce the disturbance intensity, the widths of the slit region and the side silicon region are optimized, so that the optical waveguide mode field is maximally localized in the slit region and has the weakest distribution in silicon, thereby minimizing the loss, improving the emission performance, increasing the emission efficiency, and reducing the influence of the noise signal on the received echo. During the process of optimizing the structure, the width of the slit waveguide is set to 100 nm. At this time, the periodic grating tooth structure has an extremely low disturbance intensity on the slit optical waveguide mode field. The finally calculated structural parameters are that the widths of the silicon strips on both sides are 180 nm, and the etching depth of the grating holes is 70 nm. The emission length of this antenna structure can reach up to 12 mm at most, and the optimal beam divergence angle exceeds 0.00691°.

[0032] Optionally, the emission antenna can also be based on other silicon-on-insulator chips with different top silicon thicknesses, such as: silicon-on-insulator chips with a top silicon thickness of 340 nm.

[0033] Optionally, the lower cladding 1 is a silicon dioxide cladding, and its thickness is generally 2 μm or 3 μm, which mainly supports and protects the antenna device, and at the same time covers the entire emission element of the lidar.

[0034] Optionally, the size of the grating tooth structure in the grating hole etching region 3 is positively correlated with the disturbance intensity. In order to balance the loss intensity and the processing difficulty, the size of the grating teeth in the grating hole etching region 3 is set to 70 nm × 70 nm to reduce the processing difficulty of the antenna device while maintaining a low loss intensity.

[0035] Optionally, the upper cladding 4 can be an air cladding, or a silicon dioxide or silicon nitride cladding, which is grown by plasma-enhanced chemical vapor deposition (PECVD), or other low-loss photoresist or polymer upper cladding materials, such as SU-8, PMMA, etc. The polymer upper cladding is formed by spin coating and baking on a hot plate to protect the surface structure of the device. Since the confinement ability of the slit waveguide mode is weak, a relatively thick upper cladding thickness needs to be deposited or spin coated. Therefore, the thickness of the upper cladding 4 is at least 3 μm.

[0036] Optionally, a thick substrate layer 5 is further provided below the lower cladding 1. The thick substrate layer 5 can be a silicon material with a thickness of 725 μm or 525 μm, and the thick substrate layer 5 is used to support and protect the antenna device.

[0037] Optionally, to meet the application requirements of lidar, the emission angle of the signal beam is set in the near-vertical direction, and the emission direction can be regulated by the period of the perturbation structure. Through simulation calculation, the period of the above-mentioned emission antenna is 1.1 μm. When the wavelength is tuned from 1480 nm to 1580 nm, the scanning angle covers from 16.64° to 8.05°.

[0038] Optionally, the emission antenna can be applicable to different chip material platforms, such as the emission apertures of chip-level lidars made of lithium niobate, silicon nitride, etc.

[0039] Optionally, the two-depth structures of the device can be formed by two electron beam lithographies (EBL) and silicon-based ICP etching for the emission antenna. Additionally, for the alignment of the two electron beam lithographies, additional metal markers are required, which can be grown by electron beam lithography and electron beam evaporation (EBE) and then formed by lift-off.

[0040] The above-mentioned integrated lidar emission antenna based on a slit optical waveguide is tested. The device loss test can be carried out through a fiber-chip coupling system. The surface topography of the device needs to be characterized by a scanning electron microscope (SEM). The far-field and near-field imaging tests can be characterized by using a combination of two lenses in a coaxial 4f imaging system.

[0041] Refer to Figure 2 As shown, it is a scanning electron microscope (SEM) image of an integrated lidar emission antenna based on a slit optical waveguide provided in this embodiment. The scale bar is 1 μm, and there are two etching depths in total.

[0042] Refer to Figure 3 As shown, it is a mode field diagram of an integrated lidar emission antenna based on a slit optical waveguide provided in this embodiment. The left figure is a normalized electric field intensity diagram. Obviously, its mode field is mainly distributed inside the slit, and the mode field intensity in silicon is extremely weak. Under the above structure, the best device performance parameters are calculated. The right figure is a normalized electric field intensity diagram of the Ex component. The emission antenna based on the above structure utilizes the characteristic that the mode field intensity of the silicon strips on both sides in the slit optical waveguide is extremely weak, and the periodic perturbation grating teeth are set in the silicon on both sides to achieve extremely low perturbation intensity.

[0043] Refer to Figure 4 As shown, it is a performance curve of an integrated lidar emission antenna based on a slit optical waveguide provided in this embodiment. The two figures are respectively the loss curve and the emission efficiency performance. In the 100 nm bandwidth range, the loss is about 1 dB / mm, and the emission efficiency exceeds 40%.

[0044] Refer to Figure 5As shown, it is the far-field beam scanning image of an integrated lidar transmitting antenna based on a slit optical waveguide provided in this embodiment. Through the tuning of the incident light source at a wavelength of 1480 (left) - 1580 nm (right), the longitudinal scanning angle reaches 16.64° - 8.05°, and the scanning range is 8.59°.

[0045] Refer to Figure 6 As shown, it is an integrated lidar transmitting antenna based on a slit optical waveguide provided in this embodiment. It is the far-field beam morphology diagram of a transmitting antenna with a transmitting length of 12 mm at a wavelength of 1550 nm, and its beam divergence angle (full width at half maximum) is 0.00691°.

[0046] Those skilled in the art of this technology should understand that the present invention can be implemented in many other specific forms without departing from the spirit and scope of the present invention. Based on the embodiments in the present invention, any changes and modifications made by those of ordinary skill in the art of the present invention according to the above disclosure are within the protection scope of the claims.

Claims

1. An integrated lidar transmitting antenna based on a slit optical waveguide, characterized in that: The transmitting antenna sequentially includes a lower cladding layer (1), a slit-side silicon region (2), a grating hole etching region (3), and an upper cladding layer (4) from bottom to top. The slit-side silicon region (2) is a single-slit structure formed by silicon strips on both sides. The grating hole etching region (3) is a shallow etching grating structure, which is periodic grating teeth arranged on the silicon strips.

2. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 1, wherein: The transmitting antenna is based on a silicon-on-insulator chip, and the thickness of the top silicon of the silicon-on-insulator chip can be selected as 220 nm or 340 nm.

3. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 2, wherein: The lower cladding layer (1) is a silica cladding layer with a thickness of 2 μm or 3 μm.

4. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 3, wherein: The thickness of the slit-side silicon region (2) is 220 nm, the width of the silicon strip is 180 nm, and the width of the slit is 100 nm.

5. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 4, wherein: The size of the grating teeth is 70 nm × 70 nm.

6. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 5, characterized in that: The thickness of the upper cladding layer (4) is at least 3 μm, and the upper cladding layer (4) can be an air cladding layer, a silica cladding layer, a silicon nitride cladding layer, a photoresist cladding layer, or a polymer cladding layer.

7. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 1, wherein: There is also a thick substrate layer (5) below the lower cladding layer (1), and the thick substrate layer (5) is a silicon material with a thickness of 725 μm or 525 μm.

8. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 2, characterized in that: The transmitting antenna can also be applicable to chip platforms of other material systems.

9. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 6, wherein: The period of the transmitting antenna is 1.1 μm, and the grating diffraction angle corresponding to the period is in the near-vertical direction.

10. The integrated lidar transmitting antenna based on a slit optical waveguide according to claim 1, wherein: The working waveguide mode of the transmitting antenna is the transverse electric fundamental mode.

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