Two-dimensional beam coverage system

Abstract

The invention relates to a two-dimensional beam coverage system based on a microcavity optical comb and an optical phased array, and the system comprises an optical microcavity unit which is used for receiving laser to form a steady-state optical frequency comb; the comb tooth selection unit is connected to the rear end of the optical microcavity unit and used for selecting comb teeth of the optical frequency comb to output optical pulses; and the optical phased array unit is connected to the rear end of the comb tooth selection unit, generates a wave beam according to the optical pulse, realizes deflection of the wave beam in an azimuth angle by using the optical phased array unit, and determines a pitch angle of the wave beam according to the wavelength of the optical pulse.

Description

Technical Field

[0001] The invention relates to a two-dimensional beam coverage system, in particular to a two-dimensional beam coverage system based on a microcavity optical comb and an optical phased array. Background Art

[0002] Phased array radar is a phase-controlled electronically scanned array radar. Its ability to quickly and accurately switch beams enables the radar to complete a full airspace scan within 1 minute. The so-called phased array radar is a radar array composed of a large number of identical radiating units, each of which is independently controlled by wave control and phase shifters in terms of phase and amplitude. When the radar is working, the transmitter distributes power to each antenna unit through a feeder network, radiates energy through a large number of independent antenna units, and performs power synthesis in space to form the required beam direction.

[0003] Traditional phased array radar uses the phase difference between array elements to achieve the deflection of radar beam direction, but it has the disadvantages of large size, large mass, and large rotational inertia. Silicon-based optical phased array combines silicon photonics, CMOS semiconductor technology and phased array concepts. Silicon-based optical phased array has the advantages of small size (chip scale) and flexible beam pointing. It is particularly suitable for miniaturization and high-precision scenarios. It is the preferred choice for the next generation of laser ranging, vehicle-mounted laser radar and autonomous driving.

[0004] An optical phased array generally has multi-path radiating elements. The light field radiated by the elements interferes in free space to form a far-field pattern with clear directivity. The location of the far-field peak is called a beam. Usually, the phase relationship of the elements of an optical phased array presents a linear phase distribution. By using the thermo-optical effect or electro-optical effect of the phase shifter to change the phase difference between the elements, the beam pointing deflection of the far-field pattern can be achieved. However, by changing the linear phase difference between the elements, only the deflection and scanning of the optical phased array beam in azimuth can be achieved. However, the beam coverage of the phased array requires scanning of the beam in two dimensions. In the past, beam scanning of an optical phased array in the pitch angle dimension was generally achieved by using multiple sets of optical phased arrays with different grating periods. Summary of the invention

[0005] However, for the beam scanning of the optical phased array in the pitch angle dimension, the traditional method of changing the grating period of the optical phased array requires multiple sets of optical phased arrays, which increases the layout volume of the device and has the disadvantages of bulky size and slow optical switch switching response speed.

[0006] The present invention is completed in order to overcome the defects of the above-mentioned prior art, and its purpose is to provide a two-dimensional beam coverage system based on a microcavity optical comb and an optical phased array, using the optical phased array unit to realize the deflection of the beam in azimuth, and by using the comb tooth selection unit to select the comb teeth of the optical frequency comb to change the wavelength of the radiation grating module input to the optical phased array unit, so as to realize the deflection of the beam in pitch angle.

[0007] Technical solutions to technical problems

[0008] In order to solve the above problem, the two-dimensional beam coverage system involved in the first aspect of the present invention includes:

[0009] An optical microcavity unit, which is used to receive laser light to form a steady-state optical frequency comb;

[0010] a comb tooth selection unit, the comb tooth selection unit being connected to the rear end of the optical microcavity unit and being used for selecting the comb teeth of the optical frequency comb to output optical pulses; and

[0011] An optical phased array unit is connected to the rear end of the comb selection unit, generates a beam according to the light pulse, and utilizes the optical phased array unit to realize the deflection of the beam in azimuth, and determines the pitch angle of the beam according to the wavelength of the light pulse.

[0012] Further, the optical phased array unit includes an input coupling module, a beam splitter module, a phase shifter module having a plurality of phase shifters, and a radiation grating module having a plurality of radiation grating array elements, wherein the beam splitter module distributes light from the input coupling module to each phase shifter in the phase shifter module, and each phase shifter in the phase shifter module corresponds to each radiation grating array element in the radiation grating module.

[0013] The phase difference of the light reaching each radiation grating array element in the radiation grating module is changed by adjusting the electrode voltage of each phase shifter in the phase shifter module, so as to realize the deflection of the beam in azimuth.

[0014] Furthermore, it also includes a fiber isolator, which is connected to the front end of the optical microcavity unit and is used to stabilize the received laser.

[0015] Furthermore, it also includes an optical fiber amplifier, which is connected between the comb selection unit and the optical phased array unit and is used to amplify the power of the optical pulse output by the comb selection unit.

[0016] Furthermore, it also includes a laser, which is used to generate laser light of a certain frequency received by the optical microcavity unit.

[0017] Furthermore, the laser is a distributed feedback laser or an external cavity laser.

[0018] Furthermore, the material of the optical microcavity in the optical microcavity unit is silicon nitride or gallium aluminum arsenide.

[0019] Furthermore, the optical fiber amplifier is an erbium-doped optical fiber amplifier.

[0020] Furthermore, the optical phased array unit is a silicon-based optical phased array unit.

[0021] Furthermore, the optical phased array unit is integrated on a single chip.

[0022] Furthermore, there is a negative correlation between the sin value of the elevation angle of the beam and the wavelength of the optical pulse.

[0023] Furthermore, the relationship between the elevation angle of the beam, the wavelength of the light pulse and the grating period of the radiation grating module is as follows:

[0024]

[0025] Among them, θ y represents the elevation angle, Λ gr represents the grating period of the radiation grating module, n eff,gr represents the effective refractive index of the grating etching area of ​​the radiation grating module, n bg represents the effective refractive index of the base material of the radiation grating module, and λ represents the wavelength of the light pulse.

[0026] Effects of the Invention

[0027] According to the two-dimensional beam coverage system based on the microcavity optical comb and the optical phased array of the present invention, compared with the prior art, the advantages of the microcavity optical comb outputting multiple wavelengths can be utilized to the maximum extent, and the deflection of the beam in azimuth and in elevation, that is, the beam coverage and scanning of the phased array far-field beam in two-dimensional space can be achieved with a smaller volume and lower cost, and the response speed is faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram showing a specific configuration example of a two-dimensional beam coverage system according to an embodiment of the present invention.

[0029] Figure 2 FIG. 1 is a top view of a scanning electron microscope showing an example of an optical microcavity unit in a two-dimensional beam covering system according to an embodiment of the present invention.

[0030] Figure 31 is a schematic diagram showing an example of an optical frequency comb generated by an optical microcavity unit in a two-dimensional beam covering system according to an embodiment of the present invention.

[0031] Figure 4 1 is a schematic top view showing an example of a beam splitter module in an optical phased array unit in a two-dimensional beam coverage system according to an embodiment of the present invention.

[0032] Figure 5 1 is a side view schematic diagram showing an example of a periodic shallow etched grating as a radiation grating element in an optical phased array unit in a two-dimensional beam coverage system according to an embodiment of the present invention.

[0033] Description of symbols

[0034] 10 Two-dimensional beam coverage system based on microcavity optical comb and optical phased array

[0035] 101 Laser (Distributed Feedback Laser)

[0036] 102 Fiber Isolator (ISO)

[0037] 103 Optical Microcavity Unit

[0038] 104 comb selection unit (BF)

[0039] 105 Fiber Optic Amplifier (EDFA)

[0040] 106 optical phased array units DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific implementations. This implementation is implemented based on the technical solution of the present invention, and a detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following implementation.

[0042] For ease of description, spatially relative terms, such as "under," "below," "down," "above," "on," etc., may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation other than the orientation shown in the figures. For example, if the device in the figure is turned over, elements described as being "under" or "below" other elements or features will be oriented "above" the other elements or features.

[0043] Unless otherwise defined, the terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The terms should be understood to have the same meanings as those in the context of the relevant technology and should not be understood in an idealized or overly formal sense unless explicitly defined in this manner.

[0044] <Two-dimensional beam coverage system based on microcavity optical comb and optical phased array>

[0045] Hereinafter, with reference to the accompanying drawings, the specific structure of the two-dimensional beam coverage system based on the microcavity optical comb and the optical phased array according to the embodiment of the present invention will be described in detail.

[0046] Figure 1 It is a schematic diagram showing a specific configuration example of a two-dimensional beam coverage system according to an embodiment of the present invention.

[0047] As an example, the two-dimensional beam coverage system 10 involved in the embodiment of the present invention includes: an optical microcavity unit 103, which is used to receive laser to form a steady-state optical frequency comb; a comb tooth selection unit 104, which is connected to the rear end of the optical microcavity unit and is used to select the comb teeth of the optical frequency comb to output optical pulses; and an optical phased array unit 106, which is connected to the rear end of the comb tooth selection unit 104, generates a beam according to the optical pulse, and uses the optical phased array unit 106 to realize the deflection of the beam in azimuth, and determines the pitch angle of the beam according to the wavelength of the optical pulse.

[0048] The two-dimensional beam coverage system 10 may also include a laser 101, which is used to generate laser light received by the optical microcavity unit 103. Specifically, the laser 101 may use a DFB (distributed feedback) laser or an external cavity laser as a pump light source for generating an optical frequency comb, wherein the laser light generated by the DFB laser or the external cavity laser has a certain frequency and a relatively stable output. Figure 1 In the example of the two-dimensional beam coverage system 10, the laser 101 is included, but the laser 101 is not necessary. The two-dimensional beam coverage system 10 of the present invention may not include the laser 101 ( Figure 1 (shown in dashed box).

[0049] The two-dimensional beam covering system 10 may also include an optical fiber isolator 102, which is connected between the laser 101 and the optical microcavity unit 103 to reduce the adverse effects of reflected light in the optical path on the stability of the spectral output power of the light source, thereby stabilizing the laser from the laser 101. Figure 1 In the example of the two-dimensional beam coverage system 10, the optical fiber isolator 102 is included, but the optical fiber isolator 102 is not necessary. The two-dimensional beam coverage system 10 of the present invention may not include the optical fiber isolator 102 ( Figure 1 (shown in dashed box).

[0050] The high-purity pump light is coupled into the optical microcavity unit 103 through the optical fiber isolator 102. The optical microcavity material of the optical microcavity unit 103 can be a material with high nonlinear optical coefficients such as silicon nitride and gallium aluminum arsenide. The optical microcavity adopts a microring resonator structure and uses nonlinear effects such as four-wave mixing to excite new frequency components in the frequency domain of the pump light, and then forms a steady-state comb spectrum with equal intervals and phase correlation in the frequency domain through optical parametric amplification and tuning. The microcavity optical comb can be stable for a considerable period of time in the blue detuned or red detuned state. Figure 2 FIG. 1 is a top view of a scanning electron microscope showing an example of an optical microcavity unit (AlGaAsOI microcavity) in a two-dimensional beam covering system according to an embodiment of the present invention. Figure 3 1 is a schematic diagram showing an example of an optical frequency comb generated by an optical microcavity unit in a two-dimensional beam covering system according to an embodiment of the present invention.

[0051] The comb tooth selection unit 104 is connected to the rear end of the optical microcavity unit 103 to select the designated comb teeth, that is, to select the wavelength of the output optical pulse. The comb tooth selection unit 104 may be, for example, an optical bandpass filter, but the present invention is not limited thereto.

[0052] The two-dimensional beam coverage system 10 may also include an optical fiber amplifier 105, which is connected between the comb selection unit 104 and the optical phased array unit 106, and is used to amplify the power of the optical pulse output by the comb selection unit 104, and then enter the optical phased array unit 106 through optical fiber coupling. The optical fiber amplifier 105 can be an EDFA, i.e., an erbium-doped fiber amplifier. In addition, although Figure 1 In the example of FIG. 1 , the two-dimensional beam coverage system 10 includes the optical fiber amplifier 105, but the optical fiber amplifier 105 is not necessary. The two-dimensional beam coverage system 10 of the present invention may not include the optical fiber amplifier 105 ( Figure 1 (shown in dashed box).

[0053] The optical phased array (OPA) unit 106 is connected to the rear end of the optical fiber amplifier 105, and includes an input coupling module, a beam splitter module, a phase shifter module having a plurality of phase shifters, and a radiation grating module having a plurality of radiation grating elements. In addition, the optical phased array unit 106 may be, for example, a silicon-based optical phased array unit (SOI (Silicon-On-Insulator) chip), but the present invention is not limited thereto, and may also be, for example, an optical phased array unit based on lithium niobate.

[0054] The input coupling module may be, for example, a fan-shaped coupling grating or an end face coupler, and is used to input couple the light from the optical fiber amplifier 105 .

[0055] The beam splitter module can use a 1×2MMI multi-mode interferometer power splitter. Figure 1 As shown in the optical phased array unit 106, a multi-stage cascaded MMI beam splitter is used to equally divide the optical power into different array elements, that is, the light from the input coupling module is distributed to each phase shifter in the phase shifter module and each radiation grating array element corresponding thereto. Figure 4 1 is a schematic top view showing an example of a beam splitter module (1×2 MMI multi-mode interferometer power splitter) in an optical phased array unit in a two-dimensional beam coverage system according to an embodiment of the present invention.

[0056] The phase shifter module can be, for example, a thermo-optic phase shifter or an electro-optic phase shifter. The thermo-optic phase shifter can use a silicon waveguide covered with a heating layer. The radiation grating array element in the radiation grating module can use a periodic shallowly etched strip grating structure, and the radiation grating array composed of multiple radiation grating array elements radiates the optical power into the free space, and interferes in the free space to form a specific beam direction. Figure 5 1 is a side view schematic diagram showing an example of a periodic shallow etched grating as a radiation grating element in an optical phased array unit in a two-dimensional beam coverage system according to an embodiment of the present invention.

[0057] The radiation grating array can be an equidistant periodic distribution or an unequally spaced non-periodic distribution, wherein the unequally spaced non-periodic distribution can suppress high-order grating lobes in the far-field radiation pattern.

[0058] In addition, the array factor of the optical phased array is as follows:

[0059]

[0060] The above formula A represents the far-field intensity of each radiation grating array element (equal amplitude distribution), k0 represents the wave number of 1550nm wavelength light in free space, Nx represents the number of radiation grating array elements of the radiation grating array, Λ x represents the center spacing of the radiation grating elements, Represents the phase difference between adjacent radiation grating elements;

[0061] It is easy to see that when When the array factor T(θ x ) reaches the maximum value:

[0062] |T(θ x )|=AN x

[0063] θ x Indicates the azimuth of the beam direction (such as Figure 5 shown).

[0064] The thermal field is changed by adjusting the electrode voltage of each phase shifter in the phase shifter module of the optical phased array, thereby changing the refractive index of the silicon waveguide, thereby changing the corresponding optical path phase difference of the light reaching each radiation grating array element corresponding to each phase shifter, so as to achieve beam deflection in azimuth.

[0065] In addition, the radiation grating array element in the radiation grating module adopts a periodic shallow etched strip grating structure, that is, the refractive index perturbation is introduced by periodically etching the silicon waveguide above the device. When the optical power reaching the radiation grating array element passes through the etched area, the optical power is radiated upward due to the refractive index perturbation. The relationship between the elevation angle of the radiation beam, the wavelength, and the grating period is as follows:

[0066]

[0067] Where: gr represents the grating period; n eff,gr represents the effective refractive index of the grating etched area; n bg represents the effective refractive index of the substrate material; λ represents the input wavelength. From the above formula, we can get the elevation angle θ of the grating radiation beam. y There is a one-to-one correspondence with the input wavelength.

[0068] In the present invention, the microcavity is excited by laser pumping (the output light source is stabilized by an optical fiber isolator in the middle), the nonlinear effect of the microcavity material is stimulated, and an optical frequency comb is generated by four-wave mixing and parametric amplification. A comb tooth selection unit is connected to the optical microcavity unit to select the comb teeth of the optical frequency comb. The wavelength of the radiation grating module input to the optical phased array unit is changed by selecting the specified comb teeth of the microcavity optical frequency comb by using the comb tooth selection unit to achieve the deflection of the beam in the pitch angle. Therefore, compared with the conventional prior art of preparing multiple groups of optical phased arrays with different grating periods, the advantage of the microcavity optical comb outputting multiple wavelengths can be maximized, and the deflection of the beam in the azimuth angle and the deflection in the pitch angle, that is, the beam coverage and scanning of the phased array far-field beam in two-dimensional space can be achieved with a smaller volume and lower cost, and the response speed is faster.

[0069] In addition, regarding the method of outputting multiple wavelengths, a CW (continuous wave) laser source method can also be considered. However, if a CW laser source method is directly used, the laser source needs to have a very large bandwidth, but the cost of such a laser source will be very expensive, resulting in excessively high costs.

[0070] In the present invention, the wavelength input to the radiation grating module is changed by selecting the designated comb teeth of the microcavity optical frequency comb using the comb tooth selection unit to achieve the deflection of the beam in the pitch angle. Therefore, compared with the method of using a CW (continuous wave) laser source, the advantage of the microcavity optical comb outputting multiple wavelengths can be maximized, and the deflection of the beam in the azimuth angle and the deflection in the pitch angle, that is, the beam coverage and scanning of the phased array far-field beam in two-dimensional space can be achieved at a lower cost.

[0071] It should be understood that the above description is illustrative and not restrictive. For example, the above embodiments (and / or their various aspects) can be used in combination with each other. In addition, without departing from the scope of the present invention, many modifications can be made to adapt specific conditions or materials to the teachings of the various embodiments of the present invention. Although the size and type of the material described herein are used to define the parameters of the various embodiments of the present invention, the various embodiments are not meant to be restrictive, but exemplary embodiments. In the case of reading the above description, many other embodiments are obvious to those skilled in the art. Therefore, the scope of the various embodiments of the present invention should be determined with reference to the attached claims, and the full range of equivalent forms claimed by these claims.

[0072] Industrial Applicability

[0073] The beam coverage system based on the microcavity optical comb and the optical phased array of the present invention is expected to be applied to large-scale mass production scenarios such as the next generation of laser ranging and vehicle-mounted laser radar, bringing great economic and social benefits to the application of the new generation of laser optoelectronic systems.

Claims

1. A two-dimensional beam coverage system, characterized in that: include: An optical microcavity unit, which is used to receive laser light to form a steady-state optical frequency comb; A comb tooth selection unit, which is connected to the rear end of the optical microcavity unit and is used to select the comb teeth of the optical frequency comb to output optical pulses; as well as An optical phased array unit is connected to the rear end of the comb selection unit, generates a beam according to the light pulse, and utilizes the optical phased array unit to realize the deflection of the beam in azimuth, and determines the pitch angle of the beam according to the wavelength of the light pulse.

2. The two-dimensional beam coverage system according to claim 1, characterized in that: The optical phased array unit comprises an input coupling module, a beam splitter module, a phase shifter module having a plurality of phase shifters, and a radiation grating module having a plurality of radiation grating array elements. The beam splitter module distributes light from the input coupling module to each phase shifter in the phase shifter module. Each phase shifter in the phase shifter module corresponds to each radiation grating array element in the radiation grating module. The phase difference of the light reaching each radiation grating array element in the radiation grating module is changed by adjusting the electrode voltage of each phase shifter in the phase shifter module, so as to realize the deflection of the beam in azimuth.

3. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: The optical fiber isolator is also included. The optical fiber isolator is connected to the front end of the optical microcavity unit and is used to stabilize the received laser.

4. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: It also includes an optical fiber amplifier, which is connected between the comb selection unit and the optical phased array unit and is used to amplify the power of the optical pulse output by the comb selection unit.

5. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: The optical microcavity unit also includes a laser, which is used to generate laser light of a certain frequency received by the optical microcavity unit.

6. The two-dimensional beam coverage system according to claim 5, characterized in that: The laser is a distributed feedback laser or an external cavity laser.

7. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: The material of the optical microcavity in the optical microcavity unit is silicon nitride or gallium aluminum arsenide.

8. The two-dimensional beam coverage system according to claim 4, characterized in that: The optical fiber amplifier is an erbium-doped optical fiber amplifier.

9. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: The optical phased array unit is a silicon-based optical phased array unit.

10. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: The optical phased array unit is integrated on a single chip.

11. The two-dimensional beam coverage system according to claim 1 or 2, characterized in that: There is a negative correlation between the sin value of the elevation angle of the beam and the wavelength of the optical pulse.

12. The two-dimensional beam coverage system according to claim 2, characterized in that: The relationship between the elevation angle of the beam, the wavelength of the light pulse and the grating period of the radiation grating module is as follows: Among them, θ y represents the elevation angle, Λ gr represents the grating period of the radiation grating module, n eff,gr represents the effective refractive index of the grating etching area of ​​the radiation grating module, n bg represents the effective refractive index of the base material of the radiation grating module, and λ represents the wavelength of the light pulse.

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