CN111487725B

CN111487725B - Integrated two-dimensional light beam steering device based on cylindrical lens

Info

Publication number: CN111487725B
Application number: CN202010250303.4A
Authority: CN
Inventors: 吴侃; 李超; 曹先益; 陈建平
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-04-01
Filing date: 2020-04-01
Publication date: 2022-05-17
Anticipated expiration: 2040-04-01
Also published as: CN111487725A

Abstract

An integrated light beam two-dimensional steering device based on a cylindrical lens and wavelength assistance comprises a substrate, an input waveguide, a connecting waveguide, a 1xN optical switch, a switch electrical interface, N switch output waveguides, N transmitting units, a cylindrical lens and a controller. The invention can realize two-dimensional light beam steering and has the characteristics of large power capacity, low control complexity, low electric power consumption, high emission efficiency and good light beam quality.

Description

Integrated two-dimensional light beam steering device based on cylindrical lens

Technical Field

The invention relates to beam steering, in particular to an integrated two-dimensional beam steering device based on a cylindrical lens and wavelength assistance.

Background

The laser radar technology is widely applied to the fields of automatic driving, sensing, wind speed detection and the like at present. The beam deflection device is an important functional module in the laser radar technology and is a key technology for realizing target scanning and detection. The conventional beam deflection device realizes beam scanning based on mechanical rotation, such as a mechanical rotating lens, which has the problems of large volume, high power consumption, slow speed, and easy vibration interference. Recently, an all-solid-state light beam deflection technology is proposed, and an all-solid-state light beam deflection device has the advantages of small size, low power consumption, high speed, difficulty in vibration interference and the like, and is a hot point of research at present. Among them, the reported all-solid-state beam deflection techniques mainly include 4 kinds.

Technique 1: the light beam deflection technology based on the integrated optical phased array is characterized in that an array is adopted on an integrated chip to emit light beams, and all channel light signals are subjected to linear phase control through a phase shifter, so that a main light beam with a variable angle is synthesized in a far field. The scheme has the advantages of simple structure, high precision and small volume, but phase control is required to be carried out on all optical signals on the integrated chip, the control complexity is higher, the electric power consumption is higher, in addition, light beam side lobes exist, the energy is dispersed, the scanning range is limited, and the high requirement on the integrated process is required for realizing the performance improvement;

technique 2: based on a beam deflection technology of Micro Electro Mechanical Systems (MEMS), beam steering is realized by reflecting a beam by a large-scale integrated MEMS micro resonator designed on a silicon-based chip. The scheme can realize a large-range scanning angle, can realize light beam scanning with lower cost and higher accuracy, and has the problems of complicated light path, limitation of service life due to MEMS (micro-electromechanical systems) jitter, limitation of area of a micro-resonance mirror for light beam scanning and the like;

technique 3: the technology of beam deflection based on a liquid crystal phase shifter realizes phase control of an input optical signal through the liquid crystal phase shifter, thereby changing the direction of a light beam. The scheme has the advantages of low scanning speed, incapability of bearing high input optical power and high cost;

technique 4: the technology utilizes an integrated optical switch to switch optical signals to different channels on an integrated chip, realizes one-dimensional or two-dimensional light beam emission through a Bragg grating, and realizes light beam collimation and deflection by utilizing an on-chip or off-chip lens. The beam deflection mode realized based on the scheme has two modes: a method based on-chip integrated planar lens realizes one-dimensional collimation and deflection of light beams, and utilizes wavelength correlation of emission angles of gratings to realize light beam deflection on a wavelength control vertical dimension. The other type realizes two-dimensional collimation and deflection of light beams based on-chip two-dimensional array light emission and an off-chip lens. The former fabricated on-chip lens requires the use of materials other than waveguides, has large losses, and has poor beam quality. The latter two-dimensional array of transmit elements has low transmit efficiency, cannot be scanned continuously, and has a resolution limited by the minimum spacing of the transmit elements.

And (5) technology: the technology utilizes an integrated optical switch on an integrated chip to switch signals to different channels, forms a photonic crystal grating through a photonic crystal waveguide, realizes one-dimensional light beam emission, and finally utilizes an off-chip customized prism to realize one-dimensional light beam collimation and light beam deflection. The scheme combines the emission angle wavelength dependence of the grating to realize wavelength-assisted two-dimensional beam deflection. In addition, by utilizing the slow light effect of the shallow etching photonic crystal waveguide grating, a larger emission angle range can be realized in the same wave band range than that of the ridge type and the strip waveguide grating. The scheme is based on the processing requirement of the bicycle micropore photonic crystal waveguide grating on the precision of the photoetching in hundred nanometers and the precision of the deep etching in tens of nanometers. The spacing of the one-dimensional grating array is limited by the spacing between the photonic crystal waveguides, with the minimum spacing typically being greater than 10 microns.

Furthermore, if the semiconductor material, such as silicon, is chosen in the scheme, there will be additional two-photon absorption and free carrier absorption, limiting the maximum power that the device can withstand.

In summary, the above schemes are limited in either power capacity, or in control complexity and electrical power consumption, or in two-dimensional scanning capability, or in beam quality luminous efficiency. Therefore, there is a need for a light beam steering apparatus that overcomes the above-mentioned drawbacks, and has high power capacity, low control complexity, low power consumption, high emission efficiency, and high speckle quality to realize two-dimensional scanning.

Disclosure of Invention

The invention aims to overcome the defects of the prior problems and provides an integrated light beam steering device based on a cylindrical lens and wavelength assistance, which can realize two-dimensional light beam steering and has the characteristics of large power capacity, low control complexity, low electric power consumption, high emission efficiency and good light beam quality.

In order to solve the above problems, the technical solution of the present invention is as follows:

an integrated light beam two-dimensional steering device based on a cylindrical lens and wavelength assistance is characterized by comprising a substrate, an input waveguide, a connecting waveguide, a 1xN optical switch, a switch electrical interface, N switch output waveguides, N transmitting units, a cylindrical lens and a controller, wherein the input waveguide, the connecting waveguide, the 1xN optical switch, the switch electrical interface, the N switch output waveguides and the N transmitting units are all prepared on the substrate, the N transmitting units form a one-dimensional array on the upper surface of the substrate, the cylindrical lens is positioned right above the N transmitting units, a focal plane of the cylindrical lens is parallel to a plane where the N transmitting units are positioned, an optical axis of the cylindrical lens is vertical to the plane, and the cross section of the cylindrical surface of the cylindrical lens is parallel to the array arrangement direction of the transmitting units, the 1xN photoswitch has 1 input and N output, N is more than 2 positive integers, 1xN photoswitch's input with the connection waveguide link to each other, N transmitting element's N input respectively with N switch output waveguide link to each other, the light beam of N transmitting element output all pass through cylindrical lens output, the output of controller pass through switch electricity interface respectively with the control end of 1xN photoswitch's N switch link to each other.

The input waveguide, the connecting waveguide, the 1xN optical switch, the switch output waveguide and the transmitting unit are made of insulator materials such as silicon nitride or silicon dioxide materials.

The input waveguide is a tapered waveguide or a Bragg grating.

The 1xN optical switch is in a binary tree structure, or in a series structure or in a combined structure of the binary tree structure and the series structure.

The N transmitting units are in one-dimensional Bragg grating structures.

The cylindrical lens is a spherical plano-convex cylindrical lens, a spherical double-convex cylindrical lens, an aspheric plano-convex cylindrical lens or an aspheric double-convex cylindrical lens.

The input waveguide, the connecting waveguide, the switch output waveguide and the transmitting unit work in a single-mode transverse electric mode or a single-mode transverse magnetic mode.

After the light beams with the same wavelength pass through the cylindrical lens, in a plane parallel to the cross section of the cylindrical lens, the angle deflection is generated due to the lens focusing principle, and the angle deflection is not generated when the light beams are vertical to the plane; after light beams with different wavelengths pass through the cylindrical lens, in a plane perpendicular to the cross section of the cylindrical lens, different angle deflection occurs due to wavelength correlation of the emission angle of the Bragg grating, and the two modes are combined to realize the direction of the light beams to a specific angle in a far field. The emission angle of the light beam emitted from the specific emission unit after being deflected by the cylindrical lens is determined by the relative position of the emission unit and the cylindrical lens and the wavelength of the light beam, so that N non-overlapping emission units are arranged on a plane in one dimension, and the light beam can be directed to a far field in a first dimension at N different angles; the same emission unit emits N light beams with different wavelengths, and the light beams can be directed to a far field at N different angles in a second dimension.

The principle of the invention is that in a plane parallel to the cross section of the cylindrical lens, according to the Fourier transform equivalent principle of the lens to the light field, the light field on the focal plane (called as the first focal plane of the lens) on one side of the lens close to the transmitting unit and the light field on the focal plane (called as the second focal plane of the lens) on the other side of the lens meet the relationship of Fourier transform; and when the light field on the second focal plane of the lens is taken as a virtual emission light source, the light field of the second focal plane of the lens and the light field of a far field also satisfy the Fourier transform relationship. Therefore, in a plane parallel to the cross section of the cylindrical lens, the light of the first focal plane of the lens and the far-field light have the same mode field distribution, the light field of the first focal plane of the lens can be changed by changing the arrangement distance of the emission units and the distance between the emission units and the lens, so that different far-field light field distributions are obtained, and different positions of light spots in the far-field light field correspond to different pointing angles of the light beam taking the light field of the second focal plane of the lens as an emission light source, so that the scanning of the one-dimensional light beam in the plane parallel to the cross section of the cylindrical lens is realized. In the space position of the emission unit and in the plane perpendicular to the cross section of the cylindrical lens, light beams with different wavelengths are emitted at different emission angles according to the phase matching condition of the grating, and the directions of the light beams do not change after passing through the equal-thickness plane of the cylindrical lens. Therefore, in a plane perpendicular to the cross section of the cylindrical lens, the light fields with different wavelengths correspond to the light fields with different angles in a far field, and therefore one-dimensional light beam scanning in the plane is achieved. The two-dimensional light beam scanning function is realized by combining the scanning of the two one-dimensional light beams, namely the pointing of a specific angle in a far field can be realized.

Compared with the prior art, the invention has the following advantages:

the invention has the advantages of all-solid structure, no mechanical moving part and high reliability. Compared with the light beam scanning scheme adopting silicon, liquid crystal and MEMS, the invention has the advantages of high scanning switching speed, good stability and simple structure, adopts an insulator material, realizes high-optical-power low-loss transmission, and can cover the waveband in which a semiconductor material cannot work. Compared with the scheme adopting the optical phased array technology, the controller controls the switching function of the 1xN optical switch through the switch electrical interface, only one transmitting unit works at the same time, the phase control of optical signals in all the transmitting units is not needed, the control complexity and the power consumption are lower, and the adjacent distance of the transmitting units is controlled within the half wavelength without eliminating grating lobes. The invention belongs to a light beam deflection technology based on Bragg grating emission and lens collimation, combines the advantages of the two current schemes, and has the characteristics of low loss, good light beam quality, simple process and the like compared with the current proposed technology based on an on-chip plane lens and wavelength auxiliary light beam deflection; compared with the light beam deflection technology of the off-chip lens and the on-chip two-dimensional emission unit array, the light beam deflection technology has the characteristics of high emission efficiency, continuous and adjustable wavelength auxiliary angle deflection and the like. Compared with a scheme of adopting a silicon-based photonic crystal waveguide grating to emit grating scanning, the invention adopts a ridge-type or strip-type waveguide structure based on insulator materials, and has the characteristics of simple process, high power, low loss transmission, small emission grating interval and the like.

Drawings

FIG. 1 is a schematic diagram of an integrated beam two-dimensional steering apparatus 1 based on a cylindrical lens and wavelength assistance according to an embodiment of the present invention.

Fig. 2 is a schematic cross-sectional view of beam transmission yoz of fig. 1 in which light is emitted to a free space through the emission unit 7.

FIG. 3 is a schematic view of a beam transmission on the cross-section AA 'B' of FIG. 1.

FIG. 4 is a second schematic representation of the transmission of light on cross-section AA 'B' of FIG. 1.

FIG. 5 is a third schematic representation of the transmission of light on section AA 'B' B in FIG. 1.

FIG. 6 is a schematic diagram of an integrated two-dimensional beam steering device based on a cylindrical lens and wavelength assistance according to embodiment 2 of the present invention.

FIG. 7 is a schematic view of the beam transmission of AA' in FIG. 6 in a cross-section parallel to the yoz plane.

FIG. 8 is a 1xN optical switch structure based on binary tree structure

FIG. 9 is a 1xN optical switch structure based on a chain structure

Detailed Description

The invention is further illustrated with reference to the following figures and examples, which should not be construed as limiting the scope of the invention.

Referring to fig. 1, fig. 1 is a schematic diagram of an embodiment 1 of an integrated light beam two-dimensional steering apparatus based on a cylindrical lens and wavelength assistance according to the present invention, and it can be seen from the figure that the integrated light beam two-dimensional steering apparatus based on a cylindrical lens and wavelength assistance according to the present invention includes a substrate 1, an input waveguide 2, a connection waveguide 3, a 1xN optical switch 4, a switch electrical interface 5, N switch output waveguides 6, N transmitting units 7, a cylindrical lens 8 and a controller 51, where the input waveguide 2, the connection waveguide 3, the 1xN optical switch 4, the switch electrical interface 5, N switch output waveguides 6 and N transmitting units 7 are all prepared on the substrate 1, the N transmitting units 7 form a one-dimensional array on the upper surface of the substrate 1, the cylindrical lens 8 is located right above the N transmitting units 7, a focal plane of the cylindrical lens is parallel to a plane where the N transmitting units are located, the optical axis of the cylindrical lens 8 is perpendicular to the plane, the cylindrical cross section of the cylindrical lens 8 is parallel to the array arrangement direction of the emission units 7, the 1xN optical switch 4 has 1 input end and N output ends, N is a positive integer greater than 2, the input end of the 1xN optical switch 4 is connected with the connecting waveguide 3, the N output ends are respectively connected with the N emission units 7 through N switch output waveguides 6, the light beams output by the N emission units 7 are all output through the cylindrical lens 8, and the output end of the controller 51 is respectively connected with the control ends of the N switches of the 1xN optical switch 4 through the switch electrical interface 5.

In this embodiment, N is 8.

The input waveguide 2, the connecting waveguide 3, the switch output waveguide 6 and the transmitting unit 7 are made of silicon nitride or silicon dioxide materials.

The input waveguide 2 is a tapered waveguide or a bragg grating.

Preferably, the input waveguide 2 is a tapered waveguide, and the external input is end-coupled to the chip by a tapered lens fiber.

The 1xN optical switch 4 is in a binary tree structure, a series structure or a combination structure of the two.

The N transmitting units 7 are in one-dimensional Bragg grating structures.

The cylindrical lens 8 is a spherical plano-convex cylindrical lens, a spherical biconvex cylindrical lens, an aspherical plano-convex cylindrical lens or an aspherical biconvex cylindrical lens.

The working area of the cylindrical lens 8 is large enough so that the light beams emitted from the N emitting cells can be irradiated in the working area of the cylindrical lens 8.

The input waveguide 2, the connecting waveguide 3, the switch output waveguide 6 and the transmitting unit 7 all work in a single-mode transverse electric mode or a single-mode transverse magnetic mode.

Preferably, the devices described above all operate in a single mode Transverse Electric (TE) mode.

Fig. 1 is a schematic diagram of light paths of three light beams 9 emitted from three different emission units 7 to a free space perpendicular to a focal plane under a specific wavelength condition at different times, so as to demonstrate the deflection of the light beams 9 emitted from the different emission units 7 in an xoz plane after passing through a cylindrical lens 8. It should be noted that only one emission unit has the light beam emitted at any time.

Referring to fig. 2, fig. 2 is a cross-sectional view of the transmitting unit 7 shown in fig. 1 in the yoz plane. The beam is shown as being transmitted through a waveguide to the stepped grating structure and emitted into free space, i.e. the radiation beam 9.

Referring to FIG. 3, FIG. 3 is a schematic diagram of a beam transmission on the cross section AA 'B' B in FIG. 1. The light beams 9 are emitted from the emission units 7 on the substrate 1 and pass through the cylindrical lens 8, and the directions of the light beams are deflected in the xoz plane. If the central lines of the three beams (dashed lines in the beam in fig. 3) are parallel to the optical axis of the cylindrical lens 8, in the z-direction, the central lines of the beams will intersect in the focal plane FP-2 behind the lens and at the same time the z-axis, as indicated by point S1 in fig. 3. With the point S1 as a virtual light source, the light beams emitted from the different emission units 7 are equivalent to the virtual light source at the point S1 emitting light beams in different directions. In fig. 3, the focal plane FP-1 of the cylindrical lens 8 on the side of the emission cell 7 coincides with the emission plane of the emission cell 7. Since the beam on the focal plane FP-1 has the same mode field distribution as the beam in the far field with FP-2 as the reference plane, coinciding the emission plane of the emission unit with the focal plane FP-1 can achieve the smallest spot size on the FP-1 plane, i.e. the smallest divergence angle of the far field beam.

Referring to FIG. 4, FIG. 4 is a second schematic diagram of the transmission of light beams on the cross section AA 'B' B in FIG. 1. Compared to fig. 3, the emission plane of the emission unit 7 is not coincident with the focal plane FP-1 of the cylindrical lens 8, so that the light spot becomes large when the light beam emitted from the emission unit 7 reaches the FP-1 plane due to the divergence of the light beam itself. Compared to the configuration in fig. 3, although the divergence angle of the far field beams is increased, the gap between the far field beams is reduced or not, reducing the dead zone of the beam scanning.

Referring to FIG. 5, a third beam transmission on the cross-section AA 'B' B in FIG. 1 is shown. The light beam 9 emitted by the emission unit 7 is at an angle to the optical axis (i.e. the z-axis) of the cylindrical lens 8. The angles of the beams emitted by the different emission units are the same, and the central lines of the beams (dashed lines in beam 9 in fig. 5) will still intersect the focal plane FP-2 after passing through the cylindrical lens 8, but will no longer intersect the z-axis. Indicated by point S1 in fig. 5. With the point S1 as a virtual light source, the light beams emitted from the different emission units 7 are equivalent to the virtual light source at the point S1 emitting light beams in different directions. With FP-2 as a reference plane, the beam on the focal plane FP-1 has the same mode field distribution as the beam in the far field, so that the beam tilt does not change the pointing angle of the far field beam, but may change the divergence angle of the far field beam. Fig. 5 illustrates that the present invention has a certain tolerance for the angle of emission of the light beam from the emission unit in the xoz plane, as long as the obliquely emitted light beam still impinges on the working area of the lens.

Referring to fig. 6, fig. 6 is a schematic diagram of an integrated beam two-dimensional steering apparatus 2 based on a cylindrical lens according to an embodiment of the present invention, and it can be seen that the apparatus of the embodiment 2 is the same as that of the embodiment 1.

In fig. 6, the three light beams 9 are schematic optical path diagrams of three light beams with different wavelengths (λ 1, λ 2, λ 3) emitted from the single emission unit 7 to a free space at different times, so as to demonstrate that the light beams 9 emitted by the single emission unit 7 at different wavelengths are deflected in the yoz plane after passing through the cylindrical lens 8. It should be noted that only one emission unit has a light beam emitted at any time, and the light beam has only one wavelength.

Referring to FIG. 7, FIG. 7 is a schematic diagram illustrating the transmission of light beams along the line AA' in the cross section along the yoz direction in FIG. 6. The light beam 9 emitted by the emitting unit 7 and the optical axis of the cylindrical lens 8 have a certain included angle, and different included angles corresponding to different wavelengths (λ 1, λ 2, λ 3) are different according to the phase matching principle of the bragg grating. The thickness of the cylindrical lens in the yoz plane is not changed along the y-axis direction, so that the cylindrical lens is equivalent to a plane lens, and the transmission direction of a light beam incident at any angle after passing through the plane lens is not changed.

Referring to fig. 8, fig. 8 is a 1xN optical switch structure based on binary tree structure. The optical signal enters a 1x2 optical switch 42 through an input end 41 and then is divided into two paths, enters the next stage of 1x2 optical switch through a connecting waveguide 43, and finally reaches N output ports 44 after passing through a plurality of stages of optical switches. If N cannot be expressed as an exponential power of 2, the number of 1 × 2 optical switches of the last stage can be reduced appropriately to reduce the number of output terminals. Each 1x2 optical switch has an electrical control port, and the electrical control ports of all 1x2 optical switches collectively form the switching electrical interface 5 of the 1xN optical switch. This configuration allows each of the 1x2 optical switches passing from input 41 to output 44 to be approximately equal in number, equalizing the losses on the different paths.

Referring to fig. 9, fig. 9 is a 1xN optical switch based on a chain structure. The optical signal enters the first 1x2 optical switch 42 through the input terminal 41 and then is divided into two paths, one path is connected to the next 1x2 optical switch, and the other path is directly connected to the output terminal 44. Each of the following 1 × 2 optical switches has one output connected to the next optical switch and one output connected to the output terminal. The two outputs of the last 1x2 optical switch are both connected directly to the output terminal. Each 1x2 optical switch has an electrical control port, and the electrical control ports of all 1x2 optical switches collectively form the switching electrical interface 5 of the 1xN optical switch. This configuration is advantageous for some 1x2 optical switches, such as MEMS-based optical switches, that can maintain one state without power consumption, because only two optical switches need to be controlled per output path switch.

In conclusion, the invention has the advantages of all-solid-state structure, no mechanical moving part and high reliability. The invention has only one emission unit emitting light at the same time, and has lower control complexity and power consumption. The transmitting unit of the invention adopts a one-dimensional Bragg grating structure, and has higher transmitting efficiency. By adjusting the distance of the emission plane from the focal plane of the lens, the divergence angle of the far field beam can be controlled. The invention realizes two-dimensional scanning under the condition of matching the off-chip cylindrical lens with the wavelength variability, has good beam quality, does not need to integrate various optical materials on the chip and has low loss. The invention adopts the insulator material, overcomes the extra loss caused by two-photon absorption and free carrier absorption in the semiconductor material, and can bear higher on-chip power.

Claims

1. An integrated light beam two-dimensional steering device based on a cylindrical lens and wavelength assistance is characterized by comprising a substrate (1), an input waveguide (2), a connecting waveguide (3), a 1xN optical switch (4), a switch electrical interface (5), N switch output waveguides (6), N transmitting units (7), a cylindrical lens (8) and a controller (51), wherein the input waveguide (2), the connecting waveguide (3), the 1xN optical switch (4), the switch electrical interface (5), the N switch output waveguides (6) and the N transmitting units (7) are all prepared on the substrate (1), the N transmitting units (7) form a one-dimensional array on the upper surface of the substrate (1), the cylindrical lens (8) is positioned right above the N transmitting units (7), and the focal plane of the cylindrical lens (8) is parallel to the plane of the N transmitting units (7), the optical axis of the cylindrical lens (8) is perpendicular to the plane, the cross section of the cylindrical surface of the cylindrical lens (8) is parallel to the array arrangement direction of the emission units (7), the 1xN optical switch (4) has 1 input end and N output ends, N is a positive integer greater than 2, the input end of the 1xN optical switch (4) is connected with the connecting waveguide (3), the N input ends of the N emission units (7) are respectively connected with the N switch output waveguides (6), the light beams output by the N emission units (7) are all output through the cylindrical lens (8), and the output end of the controller (51) is respectively connected with the control ends of the N switches of the 1xN optical switch (4) through the switch electrical interface (5); the N transmitting units are of a stepped one-dimensional Bragg grating structure.

2. The integrated two-dimensional turning device of claim 1, wherein the input waveguide, the connecting waveguide, the 1xN optical switch, the switch output waveguide and the transmitting unit are made of silicon nitride or silicon dioxide insulator materials.

3. The integrated cylindrical lens and wavelength aiding-based two-dimensional steering device of claim 1, wherein the input waveguide is a tapered waveguide or a bragg grating.

4. The integrated beam steering apparatus of claim 1, wherein the 1xN optical switch is a binary tree structure, a series structure or a combination thereof.

5. The integrated beam two-dimensional steering device based on cylindrical lens and wavelength assist of claim 1, wherein the cylindrical lens is a spherical plano-convex cylindrical lens, a spherical biconvex cylindrical lens, an aspherical plano-convex cylindrical lens or an aspherical biconvex cylindrical lens.

6. The integrated two-dimensional optical beam steering device based on cylindrical lens and wavelength assist of any one of claims 1 to 5, wherein the input waveguide, the connecting waveguide, the switch output waveguide and the transmitting unit all operate in a single-mode transverse electric mode or a single-mode transverse magnetic mode.