CN114696111A

CN114696111A - Silicon-based phased array laser radar optical antenna, preparation method and laser radar

Info

Publication number: CN114696111A
Application number: CN202111643228.9A
Authority: CN
Inventors: 罗光振; 徐洋; 王鹏飞; 张冶金; 于红艳; 潘教青; 邓永强
Original assignee: Beijing Wanji Technology Co Ltd
Current assignee: Beijing Wanji Technology Co Ltd
Priority date: 2020-12-30
Filing date: 2021-12-29
Publication date: 2022-07-01

Abstract

The embodiment of the application provides a phased array lidar optical antenna's structure, optical antenna includes: the SOI substrate at least comprises a substrate silicon layer, a buried oxide layer, a top silicon layer, a first SiO2 protective layer and a reflecting layer, after the antenna basic structure is prepared by adopting a mature process, the first SiO2 protective layer and the reflecting layer are formed by stacking growth, and the reflecting layer can reflect the reflected light waves back to the free space again, so that the radiation efficiency of the whole optical antenna is improved. The phased array laser radar optical antenna is simple in preparation process, and the yield of the phased array laser radar optical antenna is remarkably improved compared with the technical scheme that a reflecting layer is added on a buried oxide layer and a top silicon layer. And the radiation efficiency of the scheme of the application is higher.

Description

Silicon-based phased array laser radar optical antenna, preparation method and laser radar

Technical Field

The embodiment of the application relates to the technical field of radars, in particular to a silicon-based phased array laser radar optical antenna, a preparation method and a laser radar.

Background

The concept of phased array lidar has been proposed for a long time, various design schemes are continuously developed, and basic modules of the phased array lidar are mature, such as a light source, beam splitting, phase modulation and the like, but how to efficiently lead out phase-modulated light of each waveguide from a photonic integrated circuit is still a huge challenge. This is because the refractive index of the waveguide is much larger than that of air, and it is very difficult to couple light from the waveguide into free space, so that the emission efficiency of the optical antenna is extremely low, and the utilization rate thereof is seriously affected. In addition, grating lobes formed by interference of light coupled from each waveguide into free space can severely affect the performance of the antenna, and the scanning range can be greatly reduced.

At present, the optical antennas for phased array laser radar are mainly divided into the following two types internationally, namely, a metal dipole type optical antenna; and the non-metal optical antenna mainly comprises a grating type optical antenna. The metal dipole type optical antenna works on the principle that light excites plasmon resonance on the surface of metal to form near-field optical enhancement. However, the antenna with the structure has many limitations in practical application, because the near-field optical enhancement effect is very sensitive to the size of metal, the wavelength and the polarization mode of light, and has limited outward radiation capability, and the application is basically limited to the near field.

With the development of integrated optics, the coupled grating type optical antenna becomes the most effective coupling method for photonic integration due to the advantages of simple process, compatibility with the CMOS process and the like. However, the performance of the reported optical antenna of this type also has many problems, for example, the light coupled out from the grating on each waveguide is very dispersed, the radiation efficiency is very low, and the grating lobe energy is large after interference and is not well suppressed, which is very disadvantageous for the scanning function of the laser radar.

In view of the above problems, there is a patent application with a patent name of a reflective layer-based silicon-based optical antenna and a manufacturing method thereof in the prior art, and the patent application is published in the publication number CN 109541744A, which proposes to form a metal reflective layer at a position where a substrate silicon layer is connected to the buried oxide layer, and when reaching the metal reflective layer, the light wave reflected by a grating of the antenna will be reflected back again, so that the light wave can enter a free space and further couple with the light wave refracted into the free space before, and when reaching the metal reflective layer, the light wave reflected by the grating will be reflected back again, so that the light wave can enter the free space and further couple with the light wave refracted into the free space before. Although this solution has to some extent been titled about the coupling efficiency of lightwaves, the yield is relatively low when it is produced.

Disclosure of Invention

The embodiment of the application provides a silicon-based phased array laser radar optical antenna, a preparation method and a laser radar, which can improve the yield of the antenna while the coupling efficiency is improved.

A silicon-based phased array lidar optical antenna, the optical antenna comprising:

an SOI substrate comprising at least a substrate silicon layer, a buried oxide layer, a top silicon layer, a first SiO2 protective layer, and a reflective layer, wherein,

the buried oxide layer is positioned between the substrate silicon layer and the top silicon layer, and the top silicon layer is etched to form a waveguide array and is provided with a grating;

the first SiO2 protective layer is positioned above the area where the grating is positioned, and the upper surface of the first SiO2 protective layer is plated with a reflecting layer;

when the light wave is transmitted to the area where the grating is located, refraction and reflection are formed on the grating, wherein the refracted light wave can be emitted out of the grating and forms coupling in a free space; when reaching the reflecting layer, the light wave reflected by the grating is reflected back again, so that the light wave can enter the free space and is further coupled with the light wave refracted into the free space before.

In one embodiment, the further comprises a second SiO2 protective layer, the second SiO2 protective layer being over the reflective layer.

In one embodiment, the reflective layer is a metallic reflective layer.

In one embodiment, the side length of the first SiO2 protection layer and the reflection layer is greater than or equal to the side length of the region where the grating is located.

In one embodiment, the thickness of the reflective layer corresponds to the type of material of the reflective layer and the wavelength band of light handled by the optical antenna.

In one embodiment, the waveguide array is a column of horizontally arranged waveguides.

A silicon-based phased array lidar optical antenna method, the method comprising:

obtaining a first SOI substrate, wherein the first SOI substrate at least comprises a substrate silicon layer, a buried oxide layer and a top silicon layer;

etching the top silicon layer to form a waveguide array, and etching a grating to obtain a second SOI substrate;

growing a first SiO2 protective layer above the region of the second SOI substrate where the grating is located;

a reflective layer is deposited on the first SiO2 protective layer.

In one embodiment, the area covered by the reflecting layer is larger than the area covered by the corresponding grating.

A laser radar adopts the optical antenna that this application provided.

Phased array laser radar optical antenna's in this application, after adopting ripe technology to prepare the antenna basic structure, through piling up the growth, form first SiO2 protective layer and reflection stratum, this reflection stratum can be with during the light wave of reflection reflects the free space again, has improved whole optical antenna's radiant efficiency. The phased array laser radar optical antenna is simple in preparation process, and the yield of the phased array laser radar optical antenna is remarkably improved compared with the technical scheme that a reflecting layer is added on a buried oxide layer and a top silicon layer. And the radiation efficiency of the scheme of the application is higher.

It should be understood that what is described in the summary section above is not intended to limit key or critical features of the embodiments of the application, nor is it intended to limit the scope of the application. Other features of the present application will become apparent from the following description.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without inventive exercise.

Fig. 1 is a schematic structural diagram of a silicon-based phased array lidar optical antenna provided in an embodiment of the present application;

fig. 2 is a schematic partial structural diagram of a silicon-based phased array lidar optical antenna provided in an embodiment of the present application;

fig. 3 is a schematic structural diagram of a silicon-based phased array lidar optical antenna according to another embodiment of the present application.

Detailed Description

Embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present application are shown in the drawings, it should be understood that the present application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided for a more thorough and complete understanding of the present application. It should be understood that the drawings and embodiments of the present application are for illustration purposes only and are not intended to limit the scope of the present application.

The terms "first," "second," "third," "fourth," and the like in the description and claims of the embodiments of the application and in the drawings described above, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprising" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions.

Fig. 1 is a schematic structural diagram of a silicon-based phased array lidar optical antenna according to an embodiment of the present invention, where as shown in fig. 1, the optical antenna includes:

an SOI substrate comprising at least a substrate silicon layer 10, a buried oxide layer 20, a top silicon layer 30, a first SiO2 protective layer 40, and a reflective layer 50, wherein,

the buried oxide layer 20 is positioned between the substrate silicon layer 20 and the top silicon layer 30, the top silicon layer 30 forms a waveguide array by etching, and is engraved with gratings, and the gratings on the waveguides are combined into a two-dimensional diffraction grating; the first SiO2 protection layer 40 is located above the region where the grating is located, and the upper surface of the first SiO2 protection layer 40 is plated with a reflection layer 50.

Optical antennas are used to receive or transmit light waves, which can be applied to many optical devices, such as phased array lidar. The optical antenna is an electronic device integrated on a piece of CMOS semiconductor material, wherein the most common CMOS semiconductor material is an SOI substrate, the SOI substrate at least comprises a substrate silicon layer 10, a buried oxide layer 20 and a top silicon layer 30 from bottom to top, and the material and the thickness of each layer can be customized according to different requirements. Of course, some conventional standard CMOS process SOI substrate products on the market may also be adopted, the thickness of the substrate silicon layer 10 is 500-600 μm, the thickness of the buried oxide layer 20 is 2 μm, the thickness of the top silicon layer 30 is 220nm or 340nm, and the thickness of the SiO2 is 2 μm. For convenience of description, in the following embodiments, the optical antenna of the present invention is integrated by using the above-mentioned standard CMOS process SOI substrate as an SOI substrate, wherein the thickness of the top silicon layer 30 is 220 nm.

Referring to fig. 2, the top silicon layer 30 of the SOI substrate is etched to form a waveguide array, which is embodied as a column of horizontally arranged waveguides 31. A corresponding number of gratings need to be etched on each waveguide 31, and the gratings on all waveguides 31 are combined into a two-dimensional diffraction grating, so that the light waves can be emitted from the waveguide 31 or into the waveguide 31 through the two-dimensional diffraction grating. For convenience of description, in the following embodiments, light waves are emitted from a two-dimensional diffraction grating as an example.

The optical antenna is used for receiving or transmitting light waves, and the difference of the light wave bands is large, so that the design of the optical antenna cannot meet the use requirements of all light waves, and even if the same design concept can be used, various parameters in the optical antenna need to be changed correspondingly according to the difference of the light wave bands processed by the optical antenna, for example, 1.5-1.6 μm. For convenience of description, the following examples will be described with the wavelength range of the light wave being 1.5 to 1.6 μm.

When the light wave enters the area where the two-dimensional diffraction grating is located through the waveguide 31, refraction and reflection are formed in the grating, wherein the refracted light wave exits the grating and forms coupling in a free space, so that the purpose of transmitting the light wave by the optical antenna is achieved, and meanwhile, a large amount of reflected light waves pass through the waveguide 31 and are absorbed by the underlying substrate silicon layer 10. This is disadvantageous for the radiation efficiency of the entire optical antenna.

For this purpose, in the embodiment of the present invention, a first SiO2 protection layer 40 is grown above the region where the grating is located, and a reflection layer 50 is plated on the upper surface of the first SiO2 protection layer 40, so that when the light wave reflected by the grating reaches the reflection layer 50, the reflection layer 50 will reflect the reflected light wave back again, so that more light waves can enter into the free space and further couple with the light wave previously refracted into the free space, thereby increasing the radiation efficiency of the whole optical antenna.

The phased array laser radar optical antenna's in this application structure, the optical path that is refracted or reflects to the plane of reflection after laser gets into the antenna is little for the preceding optical path that improves radiant efficiency through the plane of reflection, consequently, the antenna of this scheme when having improved whole optical antenna's radiant efficiency, and the signal precision of acquireing is better. The method is favorable for obtaining better measurement results when being used for laser radar.

Based on the above embodiment, further, the area where the reflection layer 50 is located corresponds to the area where the grating is located, and is larger than the area where the grating is located.

When the optical antenna forms the metal reflective layer, the area and size of the metal reflective layer need to be determined first.

Since the reflective layer 50 is used to reflect the light waves reflected by the grating, the reflective layer 50 needs to correspond to the area where the grating is located, i.e. directly above the two-dimensional diffraction grating. Meanwhile, in consideration of the angle of light wave emission, the area where the reflection layer is located needs to be larger than the area where the grating is located, for example, the side lengths of the first SiO2 protection layer and the reflection layer are 10 to 20 μm longer than the side length of the area where the grating is located.

Further, the thickness of the reflective layer 50 corresponds to the type of material of the reflective layer and the wavelength band of light processed by the optical antenna. Alternatively, the reflective layer may be a metallic reflective layer.

Because different metals have different absorption effects on light waves of different wave bands, the thickness of the metal reflecting layer can also have great influence on the reflecting effect. For example, if silver is used as a material to form a metal reflective layer for a wavelength band of 1.5 to 1.6 μm, the metal reflective layer absorbs light strongly if the thickness is less than 100 nm. When the material of the metal reflective layer is selected to be silver, the thickness thereof needs to be more than 100 nm. If the thickness of the silver metal reflective layer reaches 220nm, the designed radiation efficiency of the optical antenna can reach 72% at most. For example, gold is used as a material, and the absorption effect of gold on light waves in the wavelength range of 1.5 to 1.6 μm is more than twice as strong as that of silver. It should be noted that the metal reflective layer is only an example for explaining the technical solution of the present application, and the present application is not limited to the metal material forming the metal reflective layer, and the metal reflective layer may be specifically designed according to specific conditions and requirements in specific applications. In practice, through analysis of the area, size, material and thickness of the metal reflective layer, a metal reflective layer more suitable for the current optical wave band can be further formed, so that a setting for the optical antenna to obtain better radiation efficiency can be obtained.

When the top silicon layer of the SOI substrate is etched to form a waveguide array, the waveguide array is specifically a column of horizontally arranged waveguides. There are many ways to arrange the waveguide array, such as uniform arrangement, that is, the distance between adjacent waveguides is the same. The uniform arrangement is the simplest and the most convenient, but also brings the defects of high grating lobe, large far field divergence angle and the like.

In addition, the refractive index of silicon for a wave band of 1.5-1.6 mu m is about 3.47, the problem of diffraction limit of waveguide design is considered, and the minimum width of the waveguide needs to be larger than the effective half wavelength of a propagation mode in the waveguide, so that the waveguide width of the optical antenna is designed to be 400-600 nm. Meanwhile, the optical antenna may need to be connected with a bent waveguide, so that the waveguide structure of the antenna needs to be consistent with the bent waveguide, and in order to minimize loss, a full etching method is adopted to etch the waveguide, that is, if the thickness of the top silicon layer of the SOI substrate is 220nm, the etching depth of the waveguide is 220nm, that is, the thickness of the waveguide is 220 nm. The waveguide with the structure can minimize the bending loss of the front-end bent waveguide, and the energy leaked by the bending of the waveguide can be minimized.

In addition, when grating etching is performed on the waveguide, the grating period needs to be calculated first, and then the position of each grating is determined according to the grating period. Because the wavelength lambda 0 of the light wave is 1.5-1.6 μm, the effective refractive index neff of the waveguide array for the wavelength is about 2.38, and the period lambda of the two-dimensional diffraction grating is 600-680 nm according to the formula lambda 0/neff of the two-dimensional diffraction grating, namely, the grating etching is uniformly carried out on the waveguide at the distance of each grating period lambda. The width of the grating is determined by the duty cycle, i.e. the ratio of the width of the grating to the period of the grating. The calculation shows that the outward radiation efficiency is highest when the wave band of the light wave is 1.5-1.6 mu m and the duty ratio of the second-order diffraction grating is 0.4-0.6.

In order to obtain a small far-field divergence angle along the waveguide direction and high longitudinal scanning resolution, the two-dimensional diffraction grating of the optical antenna is designed to have a shallow etching depth of 20-70 nm, and the two-dimensional diffraction grating has a long area of 80-100 μm.

As shown in fig. 3, in order to further protect the optical antenna, a protective layer of SiO2 is required to cover the optical antenna, i.e. the reflective layer 50.

In one embodiment of the present invention, a method for manufacturing a phased array lidar optical antenna is also provided, the method comprising:

step S101, obtaining a first SOI substrate, wherein the first SOI substrate at least comprises a substrate silicon layer, a buried oxide layer and a top silicon layer.

As shown in fig. 3, a first SOI substrate is obtained, which at least comprises, from bottom to top, a substrate silicon layer 10, a buried oxide layer 20 and a top silicon layer 30, each of which may be tailored in terms of material and thickness according to different requirements. Certainly, some conventional standard CMOS process SOI substrate products on the market can also be adopted, the thickness of the substrate silicon layer 10 is 500-600 μm, the thickness of the buried oxide layer 20 is 2 μm, the thickness of the top silicon layer 30 is 220nm or 340nm, and the thickness of the substrate silicon layer is SiO 2. For convenience of description, in the following embodiments, the optical antenna of the embodiments of the present invention is integrated with the above-described standard CMOS process SOI substrate as the first SOI substrate obtained, wherein the top silicon layer has a thickness of 220 nm.

Step S102, etching the top silicon layer to form a waveguide array, and etching a grating to obtain a second SOI substrate; wherein the gratings on the waveguide are combined into a two-dimensional diffraction grating;

on a first SOI substrate, the top silicon layer 30 of the SOI substrate is etched to form a waveguide array. There are many methods for etching, for example, using electron beam exposure or proximity lithography, and Inductively Coupled Plasma (ICP) etching, to etch a waveguide array, specifically a row of horizontally arranged waveguides 31, with the same size on the top silicon layer 30.

Then, the grating 32 is etched on each waveguide 31 by using an electron beam alignment and ICP etching method to form a two-dimensional diffraction grating, so that a second SOI substrate is obtained.

Light waves may be launched from waveguide 31 or into waveguide 31 by the two-dimensional diffraction grating. For convenience of description, in the following embodiments, light waves are emitted from a two-dimensional diffraction grating as an example.

Step S103, growing a first SiO2 protection layer above the region of the second SOI substrate where the grating is located, to obtain a first protection layer.

In order to further protect the optical antenna, a protective layer of SiO2 is required to cover the optical antenna, i.e. the area where the two-dimensional diffraction grating is located. There are many methods, for example, a protective layer of SiO2 with a thickness of 1-3 μm is grown on the grating region by Plasma Enhanced Chemical Vapor Deposition (PECVD), so that the optical antenna can be protected when other processes are performed on the SOI substrate on which the optical antenna is located.

Step S104, depositing a reflecting layer on the first SiO2 protective layer.

The metal material can be selected as the reflecting layer, and the method specifically comprises the following steps: and depositing a metal film on the upper surface of the first protective layer, for example, depositing the metal film by magnetron sputtering to form a metal reflecting layer.

At this time, when the light wave enters the area where the two-dimensional diffraction grating is located through the waveguide 31, refraction and reflection are formed in the grating, wherein the refracted light wave exits the grating, and when the light wave enters the free space and reaches the reflection layer 50, the reflection layer 50 reflects the reflected light wave back again, so that more light waves can enter the free space and are further coupled with the light wave refracted into the free space before, and the radiation efficiency of the whole optical antenna is improved.

The manufacturing method provided by the embodiment of the invention is used for manufacturing the optical antenna, and the structure and the function of the manufacturing method are specifically referred to the optical antenna embodiment, which is not described herein again.

Based on the above embodiment, the area covered by the reflection layer is larger than the area where the corresponding grating is located. Further, the thickness of the reflecting layer corresponds to the type of material of the reflecting layer and the wavelength band of light processed by the optical antenna.

The reflecting layer can be a metal reflecting layer, and different metals have different absorption effects on light waves of different wavebands, and the thickness of the metal reflecting layer can also have great influence on the reflecting effect. For example, if silver is used as a material to form a metal reflective layer for a wavelength band of 1.5 to 1.6 μm, the metal reflective layer absorbs light strongly if the thickness is less than 100 nm. When the material of the metal reflective layer is selected to be silver, the thickness thereof needs to be more than 100 nm. If the thickness of the silver metal reflective layer reaches 220nm, the maximum radiation efficiency of the optical antenna can reach 83%. For example, gold is used as the material, and the absorption effect of gold on light wave in the wavelength range of 1.5 to 1.6 μm is more than twice that of silver. It should be noted that the metal reflective layer is only an example for explaining the technical solution of the present application, and the present application is not limited to the metal material forming the metal reflective layer, and the metal reflective layer may be specifically designed according to specific conditions and requirements in specific applications. In practice, through analysis of the area, size, material and thickness of the metal reflective layer, a metal reflective layer more suitable for the current optical wave band can be further formed, so that a setting for the optical antenna to obtain better radiation efficiency can be obtained.

Based on the above embodiment, further, the method further includes:

a second protective layer of SiO2 was grown over the reflective layer.

In order to further protect the optical antenna, a protective layer of SiO2 is required to cover the top of the optical antenna, i.e. the top of the reflective layer 50. There are many methods, for example, a protective layer of SiO2 with a thickness of 1-3 μm is grown on the grating region by Plasma Enhanced Chemical Vapor Deposition (PECVD), so that the optical antenna can be protected when other processes are performed on the SOI substrate on which the optical antenna is located. According to the embodiment of the invention, the SiO2 protective layer is covered on the reflecting layer, so that the integrated operation of the optical antenna and other devices is facilitated, and the optical antenna is protected.

Based on the above embodiment, further, the waveguide array is a column of horizontally arranged waveguides.

When the top silicon layer of the first SOI substrate is etched to form the waveguide array, the waveguide shape and arrangement mode of the first SOI substrate need to be calculated.

Since the refractive index of silicon for the 1.5-1.6 μm wavelength band is about 3.47, the problem of diffraction limit of the waveguide 31 design is considered, and the minimum width of the waveguide needs to be larger than the effective half wavelength of the propagation mode in the waveguide 31, the width of the waveguide 31 of the optical antenna is designed to be 400-600 nm. For convenience of description, the following embodiments take a wavelength band of 1.5 to 1.6 μm as an example of the optical antenna for processing a light wave band.

Since the optical antenna may need to be connected with a curved waveguide, the waveguide 31 structure of the antenna needs to be consistent with the curved waveguide, and in order to minimize the loss, the waveguide is etched by using a full etching method, that is, if the thickness of the top silicon layer 30 of the SOI substrate is 220nm, the etching depth of the waveguide 31 is 220nm, that is, the thickness of the waveguide 31 is 220 nm. The waveguide with the structure can minimize the bending loss of the front-end bent waveguide, and the energy leaked by the bending of the waveguide can be minimized.

In addition, when the grating is etched on the waveguide 31, the grating period needs to be calculated first, and then the position of each grating 32 needs to be determined according to the grating period. Because the wavelength band lambda 0 of the light wave is 1.5-1.6 μm, the effective refractive index neff of the waveguide array for the wavelength band is about 2.38, and the period lambda of the two-dimensional diffraction grating is 600-680 nm according to the formula lambda 0/neff of the two-dimensional diffraction grating, namely, the grating etching is uniformly carried out on the waveguide at the distance of each grating period lambda. The width of the grating 32 is determined by the duty cycle, i.e. the ratio of the width of the grating 32 to the grating period. The calculation shows that the outward radiation efficiency is highest when the wave band of the light wave is 1.5-1.6 mu m and the duty ratio of the second-order diffraction grating is 0.4-0.6.

According to the embodiment of the invention, the waveguide in the optical antenna adopts a shallow etching grating method, so that a small far-field divergence angle, a high grating lobe suppression effect and a high transverse and longitudinal scanning resolution can be obtained when light waves pass through the formed two-dimensional diffraction grating. The optical antenna takes 32 paths as an example, the far field divergence angle in the vertical waveguide direction is less than 2 degrees, the grating lobe suppression ratio is 6.81dB, the scanning range of +/-40 degrees in the transverse direction, namely the vertical waveguide direction, and the scanning range of +/-10 degrees in the longitudinal direction, namely the waveguide direction can be realized. If the number of the waveguide paths is more, the far-field characteristic of the optical antenna is better.

The preparation method provided by the embodiment of the invention is used for obtaining the optical antenna, and the structure and the function of the preparation method are specifically referred to the optical antenna embodiment, which is not described herein again.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A silicon-based phased array lidar optical antenna, wherein the optical antenna comprises:

2. The lidar optical antenna of claim 1, further comprising a second protective layer of SiO2, the second protective layer of SiO2 being located over the reflective layer.

3. The optical antenna of claim 1, wherein the reflective layer is a metallic reflective layer.

4. The lidar optical antenna according to any of claims 1 to 3, wherein the side length of the first SiO2 protective layer and the reflective layer is equal to or greater than the side length of the region where the grating is located.

5. An optical antenna according to any one of claims 1 to 3, wherein the thickness of the reflective layer corresponds to the type of material of the reflective layer and the wavelength band of light handled by the optical antenna.

6. An optical antenna according to claim 1, wherein the waveguide array is a column of horizontally aligned waveguides.

7. A phased array lidar optical antenna method, the method comprising:

a reflective layer is deposited on the first SiO2 protective layer.

8. The method of claim 7, wherein the reflective layer covers an area larger than the corresponding grating.

9. The method of claim 7, wherein the thickness of the reflective layer corresponds to the type of material of the reflective layer and the wavelength band of light handled by the optical antenna.

10. Lidar characterized in that it employs an optical antenna according to any of claims 1 to 5.