CN111740786A - An integrated optical waveguide beamforming device - Google Patents

Abstract

An integrated optical waveguide beam forming device belongs to the technical field of microwave photonics. The beam forming device comprises three parts, namely an optical fiber signal source module, an integrated waveguide optical delay module and a radio frequency antenna module, and a plurality of central wavelengths lambda are written in different positions of a waveguide delay line in the integrated waveguide optical delay module_BMutually different Bragg gratings for ensuring central wavelength lambda of adjacent waveguide optical delay lines_BThe same bragg gratings have the same relative distance

The existence of the relative distance enables the optical signal after reflection in the adjacent waveguide optical delay line to generateOptical delay time difference Δ τ; by selecting the output light wavelength of the tunable laser, the light signals with the same wavelength are reflected at different positions of adjacent light delay lines, so that the time difference delta tau of the light delay lines between the adjacent waveguide light delay lines is changed, and the selection of the emission beam direction after the 2N radio frequency antennas are combined is realized.

Description

An integrated optical waveguide beamforming device

technical field

The invention belongs to the technical field of microwave photonics, and in particular relates to a beam forming device based on integrated optical waveguide technology.

Background technique

Currently, phased array antennas play a vital role in modern radar and wireless communication systems. Beamforming technology refers to changing the direction and pointing angle of the signal beam by controlling the phase or delay of each transmitted signal in the array antenna, so that the beams interfere and add in a specific wavefront direction. The traditional beamforming technology relies on electrical phase shifters, and its technical principle leads to the problem of beam skew in the beamforming system. In addition, the electronically controlled beamforming technology also has the disadvantages of large volume, large loss, and small instantaneous bandwidth. These shortcomings make it difficult for the electronically controlled beamforming technology to meet the requirements of broadband wireless communication, and also limit the application of beamforming technology in the field of high-frequency signals.

The concept of microwave photonics was first proposed in the 1990s, focusing on the combination of microwave and light waves in concepts, devices, and systems. Microwave photonics technology, which has the advantages of microwave and optics at the same time, can realize the conversion between microwave and light waves. The optically controlled beamforming technology is an important research content in microwave photonics technology. The optically controlled beamforming technology has the technical advantages of high frequency, large bandwidth, small size, avoiding beam deflection problems, and anti-electromagnetic interference. The optical control true delay beamforming technology is a typical example of the optical control beam technology. This technology is to make the optical signal pass through different paths or devices in the optical link, change the group delay of the optical signal, and then control the microwave signal carried by the light wave. phase. The core device in the optical control true delay beamforming system is the optical delay unit, which includes a plurality of optical delay lines. The optical delay unit in the early optically controlled true delay beamforming system is mainly composed of optical fibers, fiber gratings, optical splitters and other devices. This type of system is too bulky and difficult to integrate with other communication systems, and because the length of the optical fiber is difficult to precisely control, the optical fiber delay line has shortcomings such as low delay accuracy and poor delay resolution, which make this type of system unable to work in high-frequency millimeters. Wave signal field.

In recent years, integrated optical technology has been greatly developed, and many new integrated optical waveguide materials, such as SOI and Si ₃ N ₄ , have been commercialized. Integrated optical waveguide materials have the advantages of small size, low loss, light weight, and compatibility with CMOS technology, and can integrate a variety of optical waveguide devices and optical waveguide circuits in a small-area optical chip. The optical delay line made of integrated optical waveguide technology can provide extremely high delay accuracy and extremely small delay step value.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose an integrated optical waveguide beamforming device, which can realize the beamforming of high-frequency microwave signals, and has the characteristics of small size and high integration, and can Meet the technical requirements of future communication systems and military radars.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

An integrated optical waveguide beam forming device is characterized in that it comprises three parts: an optical fiber signal source module, an integrated waveguide optical delay module, and a radio frequency antenna module;

Wherein, the optical fiber signal source module includes a tunable laser (1), a microwave signal source (2), an external modulator (3), and a polarization controller (4); the integrated waveguide optical delay module includes a spot size converter (5). ), an N-layer Y-branch beam splitter (6), and 2N waveguide optical delay lines; the radio frequency antenna module includes 2N photodetectors connected to the 2N waveguide optical delay lines respectively, and 2N photodetectors connected to the 2N photodetectors respectively. 2N transmit antennas;

The tunable laser (1) emits an optical signal with a wavelength of λ, which is modulated by a microwave signal source (2) in an external modulator (3); the modulated optical signal is selected by a polarization controller (4) and passed through an optical fiber connected to the incident light spot size converter (5), the light spot size converter (5) couples the optical signal to the N-layer Y-branch beam splitter (6), and the optical signal is equally divided by the N-layer Y-branch beam splitter (6) There are 2N circuits and enter 2N waveguide optical delay lines respectively; the optical signal is reflected by the waveguide optical delay line to generate group delay, and the delayed optical signal enters 2N photodetectors respectively, and becomes a microwave signal after photoelectric conversion. , and is transmitted to space by the corresponding radio frequency antenna;

The optical delay line includes a Bragg grating coupler, a spot size converter, a straight waveguide, a Bragg grating, and an inverse Y branch. The optical signal is incident from port 1 of the waveguide optical delay line, and a part of it is reflected in the straight waveguide and the Bragg grating. , enter the spot size converter through the 3 ports, so that the optical signal is coupled from the optical waveguide into the optical fiber and continues to transmit to the photodetector, and the other part is transmitted through the straight waveguide and the Bragg grating, and then enters the Bragg grating coupler through the 2 ports and propagates to free space;

λ_w为微波信号的波长，θ₀为微波信号的期望发射方向(θ₀＝-kθ°,…-θ°,0°,θ°,…,kθ°)，n_g为波导群折射率；Wherein, the straight waveguide and Bragg grating include a plurality of Bragg gratings with beam pointing angles corresponding to -kθ°,...-θ°,0°,θ°,...,kθ°, k is a positive integer greater than 2, the same beam The relative distance of the Bragg gratings of the pointing angles in adjacent delay lines satisfies

λ _w is the wavelength of the microwave signal, θ ₀ is the desired emission direction of the microwave signal (θ ₀ =-kθ°,…-θ°,0°,θ°,…,kθ°), and n _g is the refractive index of the waveguide group;

Adjust the wavelength of the output light of the tunable laser, so that the optical signal of the same wavelength is reflected at different positions of the adjacent optical delay lines, thereby changing the time difference Δτ of the optical delay lines between the adjacent waveguide optical delay lines. Select the direction of the transmit beam after the RF antenna is combined.

Further, the integrated waveguide optical delay module includes a Bragg grating coupler, a spot size converter, a straight waveguide and a Bragg grating, and an inverse Y branch. The optical delay line incident light channel, the other branch 3 is the reflection light channel of the waveguide optical delay line, and the main circuit 2 of the reverse Y branch is the transmission light channel of the waveguide optical delay line; the main body of the waveguide optical delay line is a straight waveguide, and the difference in the straight waveguide is different. A plurality of Bragg gratings with different center wavelengths are etched in position; the rear end of the waveguide delay line is a Bragg grating coupler, which is used to emit the excess transmitted light in the waveguide delay line into free space; the reflection light channel of the waveguide delay line is also connected to a Spot size converter for coupling the delayed optical signal into the fiber.

Further, the straight waveguide is a sawtooth strip-shaped straight waveguide with a sawtooth width of 10 nm; the period number N of the Bragg grating is 200; by changing the period Λ of the Bragg grating, a plurality of Bragg gratings with different center wavelengths λ _B are obtained.

Further, the wavelength tunable range of the tunable laser is 1510 nm-1620 nm.

Further, in the integrated optical waveguide beamforming device, the tunable laser, the external modulator, the polarization controller, and the spot size converter are connected by an optical fiber, and the waveguide optical delay line and the photodetector are also connected by an optical fiber. The microwave signal source and the external modulator, the photodetector and the radio frequency antenna are connected through a circuit.

Further, the integrated waveguide optical delay module uses silicon-on-insulator (SOI) as the optical signal transmission medium, the substrate is SiO ₂ with a thickness of 2 μm; the core layer is a strip-shaped Si waveguide or a ridge-shaped Si waveguide with a thickness of 220 nm , the average width is 500nm; the uppermost layer is air or oxide buried material.

Further, considering that the optical signal in the optical waveguide platform has a large loss and cannot be amplified, an erbium-doped fiber amplifier EDFA can be added before the photodetector to amplify the optical signal and facilitate the photoelectric conversion of the photodetector.

相对距离的存在使相邻波导光延迟线内经反射后的光信号产生了光延迟时间差Δτ。通过对可调谐激光器的输出光波长进行选择，使相同波长的光信号在相邻光延迟线的不同位置处发生反射，从而改变相邻波导光延迟线之间光延迟线时间差Δτ的大小，实现对2N个射频天线合波后的发射波束指向进行选择。An integrated optical waveguide beam forming device provided by the present invention generates a group delay after the optical signal is reflected by the Bragg _grating . At the same time, the optical signal is reflected at this Bragg grating. By writing a plurality of Bragg gratings with different center wavelengths λ _B at different positions of the waveguide delay line, it is ensured that the Bragg gratings with the same center wavelength λ _B on adjacent waveguide optical delay lines have the same relative distance

The existence of the relative distance causes the optical signal reflected in the adjacent waveguide optical delay lines to generate an optical delay time difference Δτ. By selecting the wavelength of the output light of the tunable laser, the optical signals of the same wavelength are reflected at different positions of the adjacent optical delay lines, thereby changing the time difference Δτ of the optical delay lines between the adjacent waveguide optical delay lines. Select the direction of the transmit beam after the 2N radio frequency antennas are combined.

Compared with the prior art, the beneficial effects of the present invention are:

An integrated optical waveguide beam forming device provided by the present invention uses a tunable laser as a light source, writes a plurality of Bragg gratings with different center wavelengths on the waveguide optical delay line, and makes the Bragg gratings with the same center wavelength in the same phase. At different positions in the optical delay line of the adjacent waveguide, by selecting the output wavelength of the laser, the transmission delay of the optical signal is controlled to achieve the effect of beamforming the microwave signal. The invention adopts the optical waveguide technology to construct the optical delay line, can provide extremely small optical delay time difference, and can meet the beam forming requirements of high-frequency signals; the integrated waveguide optical delay module of the invention has the advantages of small size, light weight, and compatibility with CMOS technology. It can be integrated with the control circuit on the same chip, which greatly improves the integration degree of the optical control true delay beamforming system; the Bragg grating in the optical delay line of the present invention is a passive device, which has the advantages of simple structure, easy fabrication, The characteristics of low power consumption have good practical value.

Description of drawings

1 is a schematic structural diagram of an integrated optical waveguide beamforming device provided by the present invention;

2 is a schematic diagram of the position setting of the Bragg grating in the waveguide optical delay line in an integrated optical waveguide beamforming device provided by the present invention;

3 is a schematic diagram of the structural principle of an optical waveguide delay line in an integrated optical waveguide beamforming device provided by the present invention;

4 is a schematic diagram of the actual structure and principle of a Bragg grating in an integrated optical waveguide beamforming device provided by the present invention;

5 is a schematic diagram of transmission curves of a plurality of Bragg gratings with different center wavelengths in the integrated optical waveguide beamforming device of the embodiment.

Detailed ways

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

As shown in FIG. 1, it is a schematic structural diagram of an integrated optical waveguide beamforming device provided by the present invention; it includes three parts: an optical fiber signal source module, an integrated waveguide optical delay module, and a radio frequency antenna module;

Wherein, the optical fiber signal source module includes a tunable laser (1), a microwave signal source (2), an external modulator (3), and a polarization controller (4); the integrated waveguide optical delay module includes a spot size converter (5). ), an N-layer Y-branch beam splitter (6), and 2N waveguide optical delay lines; the radio frequency antenna module includes 2N photodetectors connected to the 2N waveguide optical delay lines respectively, and 2N photodetectors connected to the 2N photodetectors respectively. 2N transmit antennas;

The tunable laser (1) emits an optical signal with a wavelength of λ, which is modulated by a microwave signal source (2) in an external modulator (3); the modulated optical signal is selected by a polarization controller (4) and passed through an optical fiber connected to the incident light spot size converter (5), the light spot size converter (5) couples the optical signal to the N-layer Y-branch beam splitter (6), and the optical signal is equally divided by the N-layer Y-branch beam splitter (6) There are 2N circuits and enter 2N waveguide optical delay lines respectively; the optical signal is reflected by the waveguide optical delay line to generate group delay, and the delayed optical signal enters 2N photodetectors respectively, and becomes a microwave signal after photoelectric conversion. , and is transmitted to space by the corresponding radio frequency antenna;

The optical delay line includes a Bragg grating coupler, a spot size converter, a straight waveguide, a Bragg grating, and an inverse Y branch. The optical signal is incident from port 1 of the waveguide optical delay line, and a part of it is reflected in the straight waveguide and the Bragg grating. , enter the spot size converter through the 3 ports, so that the optical signal is coupled from the optical waveguide into the optical fiber and continues to transmit to the photodetector, and the other part is transmitted through the straight waveguide and the Bragg grating, and then enters the Bragg grating coupler through the 2 ports and propagates to free space;

λ_w为微波信号的波长，θ₀为微波信号的期望发射方向(θ₀＝-kθ°,…-θ°,0°,θ°,…,kθ°)，n_g为波导群折射率；Wherein, the straight waveguide and Bragg grating include Bragg gratings with beam pointing angles corresponding to -kθ°,...-θ°,0°,θ°,...,kθ°, k is a positive integer greater than 2, and the same beam pointing angles The relative distance of the Bragg grating in adjacent delay lines satisfies

λ _w is the wavelength of the microwave signal, θ ₀ is the desired emission direction of the microwave signal (θ ₀ =-kθ°,…-θ°,0°,θ°,…,kθ°), and n _g is the refractive index of the waveguide group;

Adjust the wavelength of the output light of the tunable laser, so that the optical signal of the same wavelength is reflected at different positions of the adjacent optical delay lines, thereby changing the time difference Δτ of the optical delay lines in the adjacent waveguide optical delay lines, and realizing 2N radio frequency Select the direction of the transmit beam after the antenna is combined.

λ_w为微波信号的波长。则相邻波导延迟线内的所需延时长度差为：

其中n_g为波导群折射率。考虑到本发明中布拉格光栅工作在反射模式，因此当中心波长相同的布拉格光栅，在相邻集成波导光延迟线中的相对距离满足

时，射频天线阵列产生的微波波束指向角即为θ₀。本发明中的波导光延迟线在使用前，需要根据微波信号的波长及波束赋形的技术要求，计算不同布拉格光栅的位置，并按照计算的位置结果，预先将布拉格光栅刻蚀在直波导上。如图2所示，当在四条波导延迟线内插入λ₁～λ₉种不同中心波长的布拉格光栅，可实现从-4θ°～4θ°共九种大小不同的波束指向角。2 is a schematic diagram of the position setting of a Bragg _grating in an optical waveguide delay line in an integrated optical waveguide beamforming device provided by the present invention; When λ is the same, the optical signal will be reflected at this Bragg grating, so the setting position of the Bragg grating in the optical delay line is very important. In adjacent waveguide optical delay lines, Bragg gratings with the same center wavelength are placed at different positions relative to each other. According to the optical control true delay beamforming theory, assuming that the desired emission direction of the microwave signal is θ ₀ , the required phase difference between adjacent array elements is: Φ ₀ =kdsinθ ₀ , where k is the wave number of the microwave signal, d is the distance between adjacent antenna elements,

_λw is the wavelength of the microwave signal. Then the required delay length difference in adjacent waveguide delay lines is:

where n _g is the index of refraction of the waveguide group. Considering that the Bragg grating works in the reflection mode in the present invention, when the Bragg grating with the same center wavelength, the relative distance in the adjacent integrated waveguide optical delay lines satisfies

When , the directivity angle of the microwave beam generated by the RF antenna array is θ ₀ . Before the waveguide optical delay line of the present invention is used, the positions of different Bragg gratings need to be calculated according to the wavelength of the microwave signal and the technical requirements of beamforming, and the Bragg gratings are pre-etched on the straight waveguide according to the calculated position results. . As shown in Figure 2, when Bragg gratings with ₉ different central wavelengths of λ ₁ to λ are inserted into the four waveguide delay lines, nine beam pointing angles of different sizes from -4θ° to 4θ° can be realized.

FIG. 3 is a schematic diagram of the structural principle of an optical waveguide delay line in an integrated optical waveguide beamforming device provided by the present invention. Figure 3 shows that the optical signal is incident from port 1 of the waveguide optical delay line; after the optical signal is reflected in the Bragg grating delay line, it enters the spot size converter through port 3, so that the optical signal is coupled from the optical waveguide into the fiber; the excess light is transmitted After the delay line, it enters the Bragg grating coupler through port 2 and propagates into free space.

FIG. 4 is a schematic diagram of the actual structure and principle of a Bragg grating in an integrated optical waveguide beamforming device provided by the present invention. The Bragg grating has a sawtooth shape, the material is SOI, and the thickness of the waveguide is 220 nm; Δw is the sawtooth width of the Bragg grating, which is 10 nm by default; the average width of the Bragg grating is 500 nm; the number of grating periods N determines the grating transmittance, which can be calculated according to actual requirements. N is 200 by default; the Bragg gratings are straight waveguides before and after, and Bragg gratings with different center wavelengths are still connected to each other through straight waveguides.

5 is a schematic diagram of transmission curves of a plurality of Bragg gratings with different center wavelengths in the integrated optical waveguide beamforming device of the embodiment. The grating period length Λ and the center wavelength λ _B satisfy: λ _B =2Λn _eff , where n _eff is the effective refractive index of the waveguide. By adjusting the grating period length Λ, Bragg gratings with similar structures but different central wavelengths can be obtained. As shown in Figure 5, the embodiment selects 9 grating period lengths Λ, which are 310nm, 315nm, 320nm, 325nm, 330nm, 335nm, 340nm, 345nm, and 350nm, and the corresponding center wavelengths are distributed in the range of 1510nm to 1620nm. The output wavelength of a tunable laser.

相对距离D的存在使相邻波导光延迟线内经反射后的光信号产生了光延迟时间差Δτ；通过对可调谐激光器的输出光波长进行选择，使不同波长的光信号在同一波导光延迟线的不同布拉格光栅处发生反射，从而改变相邻波导光延迟线之间光延迟线时间差Δτ的大小，实现对微波信号进行波束赋形的目的。The present invention provides an integrated optical waveguide beam forming device. A waveguide optical delay line is constructed by using a Bragg grating and a straight waveguide, and a plurality of optical delay lines constitute an optical delay unit; the central wavelength λ is written in different positions of the waveguide delay line. For a plurality of Bragg gratings with different _B , the Bragg gratings with the same central wavelength λ _B on the adjacent waveguide optical delay lines have the same relative distance

The existence of the relative distance D makes the reflected optical signals in the adjacent waveguide optical delay lines generate an optical delay time difference Δτ; Reflection occurs at different Bragg gratings, thereby changing the size of the optical delay line time difference Δτ between adjacent waveguide optical delay lines, and realizing the purpose of beamforming the microwave signal.

Claims (3)

1. an integrated optical waveguide beamforming device, is characterized in that, comprises three parts of optical fiber signal source module, integrated waveguide optical delay module, radio frequency antenna module; The optical fiber signal source module includes a tunable laser, a microwave signal source, an external modulator, and a polarization controller; the integrated waveguide optical delay module includes a spot size converter, an N-layer Y-branch beam splitter, and 2N waveguide optical delays. The radio frequency antenna module includes 2N photodetectors respectively connected with the 2N waveguide optical delay lines, and 2N transmitting antennas respectively connected with the 2N photodetectors; The tunable laser emits an optical signal with a wavelength of λ, which is modulated by the microwave signal source in the external modulator; the modulated optical signal is selected by the polarization controller, and is incident on the spot size converter through the optical fiber connection. The optical signal is coupled to the N-layer Y-branch beam splitter, and the optical signal is equally divided into 2N paths by the N-layer Y-branch beam splitter, and enters 2N waveguide optical delay lines respectively; the optical signal is reflected by the waveguide optical delay line to generate Group delay, the delayed optical signals enter 2N photodetectors respectively, become microwave signals after photoelectric conversion, and are transmitted to the space by the corresponding radio frequency antenna; The optical delay line includes a Bragg grating coupler, a spot size converter, a straight waveguide, a Bragg grating, and an inverse Y branch. The optical signal is incident from port 1 of the waveguide optical delay line, and a part of it is reflected in the straight waveguide and the Bragg grating. , enters the spot size converter through the 3 ports, and continues to transmit to the photodetector, and the other part is transmitted through the straight waveguide and the Bragg grating, and then enters the Bragg grating coupler through the 2 ports and propagates to the free space; Wherein, the straight waveguide and Bragg grating include a plurality of Bragg gratings with beam pointing angles corresponding to -kθ°,...-θ°,0°,θ°,...,kθ°, k is a positive integer greater than 2, the same beam The relative distance of the Bragg gratings of the pointing angles in adjacent delay lines satisfies

λ _w is the wavelength of the microwave signal, θ ₀ is the desired emission direction of the microwave signal, and n _g is the refractive index of the waveguide group; Adjust the wavelength of the output light of the tunable laser, so that the optical signal of the same wavelength is reflected at different positions of the adjacent optical delay lines, thereby changing the time difference Δτ of the optical delay lines between the adjacent waveguide optical delay lines. Select the direction of the transmit beam after the RF antenna is combined. 2 . The integrated optical waveguide beamforming device according to claim 1 , wherein the integrated waveguide optical delay module uses silicon-on-insulator as the optical signal transmission medium, the substrate is SiO ₂ , and the thickness is 2 μm; The layer is a strip-shaped Si waveguide or a ridge-shaped Si waveguide, with a thickness of 220 nm and an average width of 500 nm; the uppermost layer is air or oxide buried material. 3 . The integrated optical waveguide beamforming device according to claim 1 , wherein the straight waveguide is a sawtooth strip-shaped straight waveguide with a sawtooth width of 10 nm; the period number N of the Bragg grating is 200; period Λ of the grating, a plurality of Bragg gratings with different center wavelengths λ _B are obtained.

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