Multi-wavelength optical phased array based on resonant cavity phase shift

Abstract

The invention relates to a multi-wavelength optical phased array based on resonant cavity phase shift, which comprises an array element modulation structure of the optical phased array, and the array element modulation structure comprises an adjustable MZI and 4N on-chip resonant structures coupled with the MZI; the first to Nth resonant structures are adjacent to the MZI upper arm waveguide, and the first'to N 'th on-chip resonant structures are adjacent to the MZI lower arm waveguide. The first'to N '-th resonance structures and the first'to N'-th resonance structures are adjacent to one output waveguide of the MZI, the amplitude and the phase of input light of each array element can be adjusted by adjusting the 4N resonance structures and the MZI, and by introducing the more efficient on-chip resonance structures, the phase shifting efficiency can be remarkably improved, and the power consumption can be greatly reduced. Therefore, the performance of the OPA technology is improved, the application requirements of high speed and low power consumption can be met, and independent phase shifting of light beams with multiple wavelengths in the same optical waveguide is realized by designing an exquisite quasi-one-dimensional photonic crystal resonance structure without influencing the optical phases of other wavelengths.

Description

Technical Field

[0001] The invention relates to the field of semiconductor optoelectronic technology, in particular to an on-chip integrated phased array chip based on a resonant phase shifter capable of performing multi-wavelength light beam scanning. Background Art

[0002] LiDAR is an advanced optical remote sensing technology that obtains target information by detecting scattered light from distant targets. With the continuous progress of ultra-short pulse lasers, high-sensitivity signal detection, and high-speed data acquisition systems, LiDAR has become an important active remote sensing method today with its high precision, excellent time and space resolution, and wide detection range. It is widely used in many civil and military fields such as meteorology and intelligent driving.

[0003] In the lidar system, the scanning device is one of the core components, and the current technical paths can be divided into three categories: mechanical, hybrid solid-state and all-solid-state.

[0004] 1. Mechanical LiDAR: This is the earliest developed and most mature solution, but its large size, high cost and short service life limit its widespread application in vehicles. It uses vertically arranged laser transmitters to perform a comprehensive scan of the surrounding environment through 360° rotation. This solution has the advantages of fast scanning speed (5-20 revolutions per second), high resolution and strong resistance to light interference.

[0005] 2. Hybrid solid-state LiDAR: Compared with mechanical LiDAR, hybrid solid-state LiDAR has significantly reduced costs and has become the mainstream choice in autonomous driving applications. This technology is divided into two main solutions: rotating mirror and MEMS micro-vibration mirror.

[0006] Rotating mirror: The lens rotates by rotating the axis, which has the advantages of low power consumption and good heat dissipation.

[0007] MEMS micro-vibration mirror: It reflects laser light and realizes scanning by controlling the translation and torsion of tiny mirrors, while the laser generator remains fixed. This solution reduces moving parts, greatly improves the reliability of the system, and significantly reduces the number and cost of lasers and detectors.

[0008] 3. All-solid-state LiDAR: This technology has no moving parts and mainly includes optical phased array (OPA) LiDAR and Flash LiDAR.

[0009] OPA LiDAR: It controls the phase deflection of the light beam through optical interference technology to achieve 3D space scanning. It has the characteristics of fast scanning speed and high precision, which can rival the performance of mechanical radar.

[0010] Flash LiDAR: Similar to a camera, it emits lasers covering a large area in a short time and draws an image of the environment through a highly sensitive receiver. At present, the beam phase control of all-solid-state OPA LiDAR is mainly achieved by heating the optical waveguide or injecting carriers into the optical waveguide to change the refractive index, thereby achieving phase control.

[0011] Existing mechanical LiDARs have high production and maintenance costs due to their complex structure, large size, and reliance on high-precision mechanical parts. At the same time, their high-frequency rotating parts are prone to wear, resulting in an average service life of only 1,000 to 3,000 hours, which is much lower than the life of solid-state LiDARs.

[0012] Although hybrid solid-state LiDAR has achieved certain performance improvements through rotating mirrors and MEMS micro-vibration mirror technology, there are still many technical bottlenecks. First, the limitations of optical aperture and scanning angle directly affect its ranging capability and field of view (FOV). In large field of view applications, it is usually necessary to rely on multi-sub-field of view stitching, which places high demands on point cloud stitching algorithms and point cloud stability. Secondly, MEMS micro-vibration mirror technology performs poorly in terms of impact resistance. Its main problems include the poor adaptability of the galvanometer size to long-distance detection, and the large-size galvanometer increases the burden on the fast and slow axes. In addition, the cantilever beam structure of silicon-based MEMS is relatively fragile, especially when it is subjected to reverse twisting of the fast and slow axes at the same time, it is easy to break due to external vibration or impact, and it is difficult to meet the strict testing requirements of automotive design verification (DV), production verification (PV), reliability, impact resistance, and drop.

[0013] In the field of all-solid-state LiDAR, although Flash LiDAR technology can emit a large area of ​​laser at one time, its detection distance and accuracy are limited due to energy dispersion. Compared with scanning LiDAR, Flash LiDAR has difficulty focusing the laser on a single point, especially when detecting at long distances, and its accuracy is low. In addition, Flash LiDAR is highly sensitive to ambient light and is easily interfered by strong external light, which affects system performance.

[0014] Despite its great potential, optical phased array (OPA) technology currently faces the problem of low phase shifting efficiency. Existing on-chip optical phased array phase shifting technology mainly relies on heating the optical waveguide or carrier injection, resulting in slow response speed, high power consumption, and poor overall efficiency. At the same time, existing technologies have difficulty in independently completing the phase shift of a single wavelength of light without affecting the phase of other light in the same optical waveguide.

[0015] The present invention aims to solve the above problems and proposes an optical phased array (OPA) chip solution that can greatly improve the phase shifting efficiency and realize low-power multi-wavelength multi-beam operation. This solution can independently adjust the optical phases of different wavelengths in the same optical waveguide, significantly improving the system performance and application scope. Summary of the invention

[0016] The purpose of the present invention is to overcome the shortcomings of the prior art, adapt to actual needs, and provide a multi-wavelength optical phased array based on resonant cavity phase shifting to solve the current existing optical phased array (OPA) technology mostly relies on changing the refractive index by heating the optical waveguide or injecting carriers to achieve phase control, which leads to slow phase shifting speed and high power consumption; traditional OPA technology needs to be equipped with a phase shifter and a filter for each wavelength when achieving phase shifting of multiple wavelengths, which greatly increases the cost and reduces the integration; mechanical laser radar has a complex structure, high maintenance cost, and short service life, and it is difficult to meet the technical problems of large-scale application needs.

[0017] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is: designing a multi-wavelength optical phased array based on resonant cavity phase shifting, including an array element modulation structure of the optical phased array, wherein the array element modulation structure includes an adjustable MZI and 4N on-chip resonant structures coupled with the MZI;

[0018] The 1st to Nth resonant structures are adjacent to the upper arm waveguide of the MZI, the 1st' to N' on-chip resonant structures are adjacent to the lower arm waveguide of the MZI, the 1" to N" resonant structures and the 1"' to N"' resonant structures are adjacent to one of the output waveguides of the MZI, and the amplitude and phase of the input light of each array element can be adjusted by adjusting the 4N resonant structures and the MZI;

[0019] The 1" to N" and 1"' to N"' on-chip resonant structures are adjacent to an output waveguide of the MZI, which is connected to the output port. The 1" to N" and 1"' to N"' on-chip resonant structures coupled to the output waveguide can modulate the phase of the input light and arbitrarily adjust the phase difference of each array element in the optical phased array.

[0020] Preferably, the on-chip resonant structure is implemented by a quasi-one-dimensional photonic crystal and is placed at a distance g from the waveguide.

[0021] Preferably, the adjustable parameters of the quasi-one-dimensional photonic crystal include a parameter α of the Euler annular aperture, a spacing p between the apertures, and a spacing g from the waveguide.

[0022] Preferably, the quasi-one-dimensional photonic crystal is divided into a central region, an edge region and a gradient region.

[0023] Preferably, the quasi-one-dimensional photonic crystal is formed by etching a plurality of Euler ring holes on a waveguide with a width of w, usually more than 40 holes.

[0024] Preferably, the shape of the lower part of the Euler annular hole when x>0 is determined by the following parametric equation:

[0025]

[0026]

[0027] in, s is the arc length, s∈(0,l).

[0028] Preferably, the shape of the lower part of the Euler annular hole when x<0 is determined by the following parametric equation:

[0029]

[0030]

[0031] in, s is the arc length, s∈(0,l).

[0032] Preferably, the shape of the upper part of the Euler annular hole when x>0 is determined by the following parametric equation:

[0033]

[0034]

[0035] in, s is the arc length, s∈(0,l).

[0036] Preferably, the shape of the upper part of the Euler annular hole when x<0 is determined by the following parametric equation:

[0037]

[0038]

[0039] in, s is the arc length, s∈(0,l)

[0040] Among them, α is the scaling parameter of the hole. The larger α is, the smaller the Euler ring is.

[0041] Preferably, each array element modulation structure of the optical phased array is connected to an array element, each array element is a broadband grating coupler, and each modulation structure can independently modulate the phase and amplitude of light input to different grating couplers, thereby realizing simultaneous scanning of light of different wavelengths by the optical phased array.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention introduces a more efficient on-chip resonant structure and indirectly modulates the on-chip resonant structure to change the phase in the waveguide coupled with it, which can significantly improve the phase shift efficiency and greatly reduce power consumption. This improves the performance of OPA technology and can meet the application requirements of high speed and low power consumption.

[0044] 2. The present invention realizes the independent regulation of light of different wavelengths by designing a sophisticated quasi-one-dimensional photonic crystal resonant structure. In the same optical waveguide, light beams of multiple wavelengths can be independently phase-shifted at the same time without affecting the phases of light of other wavelengths. This multi-wavelength independent operation greatly expands the application capabilities of LiDAR in multi-target detection and complex environment perception.

[0045] 2. The present invention adopts an all-solid-state design, which eliminates the need for mechanical parts, reduces wear and maintenance requirements, significantly reduces manufacturing and maintenance costs, and increases service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a schematic diagram of the array element modulation structure of the optical phased array of the present invention;

[0047] Figure 2 A schematic diagram of a quasi-one-dimensional photonic crystal of the present invention;

[0048] Figure 3 Schematic diagram of the upper and lower parts of the Euler annular hole of the present invention;

[0049] Figure 4 It is a schematic diagram of the optical phased array structure of the present invention. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0051] The present invention uses an adjustable Mach-Zehnder interferometer (MZI) and 4N on-chip structures capable of generating resonance as the modulation structure of the multi-wavelength optical phased array, which can independently modulate the phases of different wavelengths without affecting the phases of the remaining wavelengths of light. In the present invention, in order to achieve ultra-high efficiency phase modulation and not be limited by the free spectrum width, the on-chip resonance structure is implemented using a quasi-one-dimensional photonic crystal.

[0052] By utilizing a portion of the narrowband and steep phase change curve generated during resonance, ultra-low power consumption narrowband phase adjustment is achieved. The resonator phase adjustment method in this design scheme can use thermo-optical effect, carrier injection or micromechanical adjustment.

[0053] This design scheme can be implemented based on different optical integration platforms, including silicon-based (Silicon) optical platform (pure silicon or silicon germanium platform), silicon nitride (SiN, Silicon Nitride) optical platform, indium phosphide (InP, IndiumPhosphide) or indium arsenide (InAs, IndiumArsenide) and other III-V optical platforms, lithium phosphate (LN, LithiumNiobate) optical platform, etc.

[0054] The element modulation structure of the optical phased array is as follows: Figure 1 As shown, it includes an adjustable MZI and 4N on-chip resonant structures coupled to the MZI. In the present invention, the on-chip resonant structure is realized by a quasi-one-dimensional photonic crystal. The 1st to Nth resonant structures are adjacent to the MZI upper arm waveguide, the 1st' to N' on-chip resonant structures are adjacent to the MZI lower arm waveguide, and the 1" to N" and 1"' to N"' on-chip resonant structures are adjacent to an output waveguide of the MZI, and the output waveguide is connected to the output port 3 in the figure.

[0055] The specific working method is as follows:

[0056] The 1” to N” resonant structures and the 1”’ to N”’ resonant structures are adjacent to one of the output waveguides of the MZI. By adjusting the 4N resonant structures and the MZI, the amplitude and phase of the input light of each array element can be adjusted. This adjustment can realize the functions of non-uniform light amplitude input, loss compensation or homogenization of the array element. The specific method of adjusting the light amplitude is as follows: First, the phase of the upper arm of the adjustable MZI is delayed by π / 2 using a broadband phase shifter, and then the i’th on-chip resonant structure is gradually adjusted to make its resonant wavelength smaller than the i’th working wavelength. Through the resonant phase response curve, the phase of the lower arm can be advanced by π / 4 to 3π / 4 compared with the phase of the resonant wavelength. At the same time, the i’th on-chip resonant structure is gradually adjusted to make its resonant wavelength larger than the i’th working wavelength, so that the phase of the upper arm is delayed by π / 4 to 3π / 4. At this time, the total phase difference between the two arms is between π and 2π. By exchanging the modulation operations of the i’th and i’th on-chip resonant structures, the total phase difference between the two arms can be between -π and 0. By using this phase adjustment method of the upper and lower arms, the light amplitude of the i-th input wavelength can be arbitrarily adjusted. Since the phase response curve is steep and the operating wavelength is far away from the resonance point, this method can achieve low-loss and low-power amplitude modulation. In addition, due to the narrowband characteristics of the resonance curve, it is also possible to achieve simultaneous independent control of N wavelengths.

[0057] The 1” to N” and 1”’ to N”’ on-chip resonant structures coupled to the output waveguide can modulate the phase of the input light, thereby realizing arbitrary adjustment of the phase difference of each array element in the optical phased array. The specific implementation method is: gradually adjust the i”th on-chip resonant structure so that its resonant wavelength is less than the i-th operating wavelength. Through the resonant phase response curve, the phase of the i-th wavelength in the output waveguide can be advanced by π / 2 to π compared with the resonant wavelength. Alternatively, gradually adjust the i”th on-chip resonant structure so that its resonant wavelength is greater than the i-th operating wavelength, so that the phase of the i-th wavelength is delayed by π / 2 to π. In this way, the i”th on-chip resonant structure can cause the i-th wavelength in the output waveguide to produce a phase change within a range of π. Similarly, by adjusting the i”’th on-chip resonant structure, a total phase change within a range of 2π can be achieved, thereby modulating any phase of the light of the input array element. Due to the steepness of the phase response curve and the fact that the operating wavelength is far away from the resonance point, this method can achieve low-loss and low-power phase modulation. Likewise, the narrowband nature of the resonance curve enables independent control of N wavelengths simultaneously.

[0058] like Figure 2 As shown, the on-chip resonant structure used in the present invention is a quasi-one-dimensional photonic crystal, which is placed at a distance g from the waveguide. The crystal is formed by etching a plurality of Euler annular holes (usually more than 40) on a waveguide with a width of w. The present invention also includes the protection of other resonant cavity structures.

[0059] like Figure 3 The shape of the lower part of the Euler annular hole when x>0 is determined by the following parametric equation:

[0060]

[0061]

[0062] in, s is the arc length, s∈(0,l).

[0063] like Figure 3 The shape of the lower part of the Euler annular hole when x < 0 is determined by the following parametric equation:

[0064]

[0065]

[0066] in, s is the arc length, s∈(0,l).

[0067] like Figure 3 The shape of the upper part of the Euler annular hole when x>0 is determined by the following parametric equation:

[0068]

[0069]

[0070] in, s is the arc length, s∈(0,l).

[0071] like Figure 3 The shape of the upper part of the Euler annular hole when x < 0 is determined by the following parametric equation:

[0072]

[0073]

[0074] in, s is the arc length, s∈(0,l)

[0075] Among them, α is the scaling parameter of the hole. The larger α is, the smaller the Euler ring is.

[0076] The adjustable parameters of the quasi-one-dimensional photonic crystal include the parameter α of the Euler ring hole, the spacing p between the holes, and the spacing g from the waveguide. On the silicon photonic platform, the typical value of α is 10 8 ~10 12 The typical value of g is about 150nm to 250nm, which makes the resonant structure and the waveguide in an over-coupled state. The typical value of p is between 300nm and 500nm. Figure 2 As shown, it can be divided into three regions: the central region, the edge region and the gradient region. The parameters and band structure of the photonic crystal in the central region determine the resonant wavelength of the cavity, while the parameters of the photonic crystal in the edge region make the energy band in the central region located in the forbidden band of the edge region, which is used to reflect and limit the waveguide mode in the central region. Due to the impedance mismatch between the waveguide mode in the central region and the Bloch mode, it may cause large scattering losses. Therefore, in the gradient region, the parameter α gradually changes from the parameter in the central region to the parameter in the gradient region to minimize the loss.

[0077] Figure 4 The structure of the entire optical phased array is shown. Each optical phased array element modulation structure is connected to an array element, and each array element is a broadband grating coupler. Each modulation structure can independently modulate the phase and amplitude of light input to different grating couplers, thereby realizing the simultaneous scanning of light of different wavelengths by the optical phased array.

[0078] In addition, the components designed in the present invention are all universal standard parts or components known to technical personnel in this field. Their structures and principles can be known to technical personnel through technical manuals or through conventional experimental methods. They can be fully implemented by technical personnel in this field. Needless to say, the content protected by the present invention does not involve improvements to internal structures and methods.

[0079] The embodiments of the present invention disclose preferred embodiments, but are not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A multi-wavelength optical phased array based on resonant cavity phase shifting, including an array element modulation structure of an optical phased array, characterized in that: The array element modulation structure includes an adjustable MZI and 4N on-chip resonant structures coupled to the MZI; The 1st to Nth resonant structures are adjacent to the upper arm waveguide of the MZI, the 1st' to N' on-chip resonant structures are adjacent to the lower arm waveguide of the MZI, the 1" to N" resonant structures and the 1"' to N"' resonant structures are adjacent to one of the output waveguides of the MZI, and the amplitude and phase of the input light of each array element can be adjusted by adjusting the 4N resonant structures and the MZI; The 1" to N" and 1"' to N"' on-chip resonant structures are adjacent to an output waveguide of the MZI, which is connected to the output port. The 1" to N" and 1"' to N"' on-chip resonant structures coupled to the output waveguide can modulate the phase of the input light and arbitrarily adjust the phase difference of each array element in the optical phased array.

2. The multi-wavelength optical phased array based on resonant cavity phase shifting according to claim 1, characterized in that: The on-chip resonant structure is implemented by a quasi-one-dimensional photonic crystal and is placed at a distance g from the waveguide.

3. The multi-wavelength optical phased array based on resonant cavity phase shifting as claimed in claim 2, characterized in that: The adjustable parameters of the quasi-one-dimensional photonic crystal include the parameter α of the Euler annular aperture, the spacing p between the apertures, and the spacing g from the waveguide.

4. The multi-wavelength optical phased array based on resonant cavity phase shifting as claimed in claim 2, characterized in that: The quasi-one-dimensional photonic crystal is divided into a central area, an edge area and a gradient area.

5. The multi-wavelength optical phased array based on resonant cavity phase shifting as claimed in claim 2, characterized in that: The quasi-one-dimensional photonic crystal is formed by etching a plurality of Euler ring holes, usually more than 40 holes, on a waveguide with a width of w.

6. The multi-wavelength optical phased array based on resonant cavity phase shifting according to claim 5, characterized in that: The shape of the lower part of the Euler annular hole when x>0 is determined by the following parametric equation: in, s is the arc length, s∈(0,l).

7. The multi-wavelength optical phased array based on resonant cavity phase shifting according to claim 5, characterized in that: The shape of the lower part of the Euler annular hole when x<0 is determined by the following parametric equation: in, s is the arc length, s∈(0,l).

8. The multi-wavelength optical phased array based on resonant cavity phase shifting as claimed in claim 5, characterized in that: The shape of the upper part of the Euler annular hole when x>0 is determined by the following parametric equation: in, s is the arc length, s∈(0,l).

9. The multi-wavelength optical phased array based on resonant cavity phase shifting according to claim 5, characterized in that: The shape of the upper part of the Euler annular hole when x<0 is determined by the following parametric equation: in, s is the arc length, s∈(0,l) Among them, α is the scaling parameter of the hole. The larger α is, the smaller the Euler ring is.

10. The multi-wavelength optical phased array based on resonant cavity phase shifting according to claim 1, characterized in that: Each array element modulation structure of the optical phased array is connected to an array element, each array element is a broadband grating coupler, and each modulation structure can independently modulate the phase and amplitude of light input to different grating couplers, thereby realizing simultaneous scanning of light of different wavelengths by the optical phased array.

Images