VCSEL (Vertical Cavity Surface Emitting Laser) area array with gradient luminous power and application of VCSEL area array in optical navigation system

Abstract

The invention relates to a VCSEL (Vertical Cavity Surface Emitting Laser) area array with gradient luminous power and application of the VCSEL area array in an optical navigation system, which mainly comprises a plurality of VCSEL luminous units arranged in an array, and is characterized in that the physical structure parameters of each VCSEL luminous unit are regularly and differentially designed according to the position of the VCSEL luminous unit; the light emitting power of all the VCSEL light emitting units under the same driving voltage is in gradient distribution. Physical structures (such as mesa size, oxidation aperture and the like) of light emitting units in an array are actively and non-uniformly designed, so that the light emitting units generate differentiated light emitting power density under the same driving condition, and a preset gradient light emitting power matched with expected scene reflectivity distribution is formed.

Description

Technical Field

[0001] This invention relates to the field of semiconductor optoelectronic device manufacturing technology, and in particular to a VCSEL array with gradient output power and its application in optical navigation systems. Background Technology

[0002] Autonomous mobile devices such as robotic vacuum cleaners commonly employ area array or structured light technology for navigation and obstacle avoidance. They calculate depth information by emitting near-infrared light pulses and measuring the time difference between reflected and emitted light, directly obtaining the distance to objects. Traditional area arrays aim for consistent output power across all light-emitting units to form a uniform dot matrix or structured light pattern. Patent documents such as "Linear Vertical Cavity Surface Emitting Laser Array" and "An Array Chip and Its Fabrication Method" both aim to improve the uniformity of light intensity by designing smaller apertures closer to the electrodes, creating a gradient design. The principle is that the closer to the electrodes, the lower the resistance and the greater the light intensity. However, in practical applications, this uniform illumination strategy faces significant challenges. The working environment of robotic vacuum cleaners (such as a home environment) contains objects with vastly different reflectivities. For example, the reflectivity of a dark carpet may be less than 10%, while the reflectivity of a smooth tile floor or light-colored baseboard may exceed 80%. When a uniform light spot is projected onto such a scene, the receiver (such as a SPAD or APD array) receives an extremely strong signal from high-reflectivity areas (such as a nearby tiled floor), which may lead to front-end saturation or nonlinear response; while the signal received from low-reflectivity areas (such as the legs of black furniture or in the distance) is too weak and easily drowned out by noise. This huge signal dynamic range not only places extremely high demands on the receiver hardware, but also greatly increases the complexity of subsequent signal processing algorithms, and may even lead to misjudgments, affecting the accuracy and reliability of navigation. Currently, the industry is trying to alleviate this problem through complex software algorithms for post-gain compensation or signal fusion, but this is a "post-hoc remedy" and cannot fundamentally solve the problem of poor front-end signal quality, and it also increases the processor's computational load and power consumption.

[0003] Therefore, there is an urgent need in this field for a new type of VCSEL array solution that can intelligently adapt to different reflectivity scenarios, starting from the light source itself. Summary of the Invention

[0004] To address the problem of excessively large dynamic range, local saturation, or low signal-to-noise ratio at the receiving end after projection from a uniform light source in complex reflectivity scenarios, this invention designs a non-uniform VCSEL array with gradient emission power and its application in optical navigation systems. The specific solution is as follows:

[0005] A VCSEL array with gradient light output power includes multiple VCSEL light-emitting units arranged in an array. The key is that the physical structure parameters of each VCSEL light-emitting unit are designed differently according to its position, so that the light output power of all VCSEL light-emitting units under the same driving voltage presents a gradient distribution.

[0006] The physical structural parameters vary in a gradient along the radial, axial, or specific preset direction of the VCSEL array. The physical structural parameters are at least one of the mesa size and oxide aperture of the VCSEL light-emitting unit.

[0007] By adopting the above scheme, the physical structure of each light-emitting unit in the array (such as mesa size, oxide aperture, etc.) is designed actively and non-uniformly, so that they can produce different light output power densities under the same driving conditions, thereby forming a preset gradient light output power that matches the reflectivity distribution of the expected scene.

[0008] Furthermore, the VCSEL light-emitting units located at the center of the VCSEL array have relatively smaller oxide apertures and / or mesa sizes, while the VCSEL light-emitting units located at the edges of the VCSEL array have relatively larger oxide apertures and / or mesa sizes.

[0009] Furthermore, the VCSEL light-emitting unit is a polarized VCSEL, and the active region of the polarized VCSEL is a stress-strain quantum well or an anisotropic gain cavity structure, which outputs linearly polarized light. All the polarized VCSELs have the same polarization direction.

[0010] Using the above scheme, polarized VCSELs are used to achieve a high polarization extinction ratio output for the entire array, and maintain stable polarization characteristics under gradient output power distribution, further enhancing performance in strong reflective environments.

[0011] An optical navigation system, the key feature of which is:

[0012] The projection light source uses the aforementioned VCSEL array with gradient output power to provide a beam with a specific light intensity distribution for the navigation scene;

[0013] A receiver, used to receive light signals reflected back from the navigation scene;

[0014] A processor for making navigation decisions based on signals from the receiver.

[0015] The regions with lower light output power density of the VCSEL array correspond to regions with higher expected reflectivity in the navigation scenario, while the regions with higher light output power density correspond to regions with lower expected reflectivity.

[0016] By adopting the above scheme, a light source with a specific light intensity distribution can be provided for specific navigation scenarios. For example, in the navigation scenario of a robot vacuum cleaner working in the living room, the light intensity reflectivity of the ground is high at close range and the light intensity reflectivity of the dining table is low at a distance. The light-emitting units in the VCSEL array that are close to the ground scanning area can be designed with small apertures or table sizes, while the light-emitting units in the VCSEL array that are far away from the dining table scanning area can be designed with large apertures or table sizes. This makes the light signal received by the receiver uniform, which is conducive to the processor making navigation decisions quickly.

[0017] A method for suppressing interference from high-reflectivity environments in optical navigation systems, the key of which includes the following steps:

[0018] Step S1: Use the VCSEL array with gradient output power as the projection light source to project the light signal;

[0019] Step S2: Receive the light signal reflected back from the navigation scene using the receiver;

[0020] Step S3: The processor processes the signal uploaded by the receiver to make a navigation decision.

[0021] By using the preset optical power gradient of the VCSEL array, signal strength fluctuations caused by differences in scene reflectivity are compensated, thereby reducing the dynamic range of the signal obtained by the receiver and making the signal-to-noise ratio more uniform.

[0022] Beneficial effects: (1) Original innovation and active compensation: The power gradient is preset at the light source end to directly compensate for the difference in scene reflectivity, realizing "intelligent lighting" and improving the quality of received signal from the source. (2) Improved system performance: The dynamic range of received signal is effectively compressed, local saturation is avoided, the overall signal-to-noise ratio and ranging accuracy are improved, and the algorithm complexity and load of the back-end processor are reduced. (3) Polarization-enhanced anti-interference: Combining polarization output and orthogonal polarization detection, specular reflection glare from smooth surfaces can be specifically suppressed, further enhancing the performance in strong reflective environments. (4) Process compatibility and low cost: The luminous power gradient of the VCSEL array can be achieved by adjusting the existing chip design mask layout, without adding extra process steps, and hardly increasing the manufacturing cost. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the power gradient distribution of the VCSEL array in Embodiment 1 of the present invention;

[0024] Figure 2 This is a simulation diagram of the application scenario of the present invention in the route navigation system of a sweeping robot. Specific Implementation

[0025] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that similar or identical parts are referred to by the same reference numerals in the drawings or description. Implementations not shown or described in the drawings are forms known to those skilled in the art. In the description of this application, terms such as "first" and "second" are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Example 1:

[0027] This embodiment includes VCSEL light-emitting units arranged in an array, such as... Figure 1 As shown, the VCSEL light-emitting units at the center of the VCSEL array have relatively smaller oxide aperture sizes, while the VCSEL light-emitting units at the edges of the VCSEL array have relatively larger oxide aperture sizes. This results in a gradient distribution of the emitted light power of all VCSEL light-emitting units under the same driving voltage.

[0028] Its working principle is as follows: under the same driving current, the smaller the oxide aperture of a cell, the higher its current density, but the lower the final output power density; while the larger the oxide aperture of a cell, the higher the output power density. Therefore, the array naturally forms a projection spot with weak light intensity at the center and strong light intensity at the edges.

[0029] The optical navigation system of this embodiment, such as Figure 2 As shown, the key point is that it includes:

[0030] The projection light source employs a VCSEL array with gradient output power. The region of lower output power density of the VCSEL array corresponds to the region of higher expected reflectivity in the navigation scene, while the region of higher output power density corresponds to the region of lower expected reflectivity, providing a beam of light with a specific intensity distribution for the navigation scene; the receiver is used to receive the light signal reflected back from the navigation scene; and the processor is used to make navigation decisions based on the signal from the receiver.

[0031] This embodiment applies a method for suppressing interference from highly reflective environments in optical navigation systems, including the following steps:

[0032] Step S1: Use the VCSEL array with gradient output power as the projection light source to project the light signal;

[0033] Step S2: Receive the light signal reflected back from the navigation scene using the receiver;

[0034] Step S3: The processor processes the signal uploaded by the receiver to make a navigation decision.

[0035] Based on the navigation environment, the power gradient preset in the VCSEL array compensates for signal strength fluctuations caused by differences in scene reflectivity, thereby reducing the dynamic range of the signal obtained by the receiver and making the signal-to-noise ratio more uniform.

[0036] How the system works: The system is installed at the front of the robotic vacuum cleaner. The positions of the transmitter and receiver of the optical system are adjusted so that the central weak light area is aligned with the high-reflectivity area near the ground directly in front of the robot, while the edge strong light area is aligned with obstacles further away or with lower reflectivity. In this way, the light signal reflected from the ground will not saturate the receiver, while the signal reflected from distant or dark objects will be strong enough, achieving excellent signal balance overall.

[0037] Example 2:

[0038] This embodiment is for a one-dimensional linear application of the present invention. It first includes a one-dimensional linear VCSEL array, and the mesa size of each light-emitting unit is gradually increased from one end of the array to the other.

[0039] Its working principle is as follows: Since large-area units usually have lower series resistance and thermal resistance, they can output higher power under the same current, thereby forming a one-dimensional power gradient to compensate for known non-uniform reflectivity regions in the scanning direction.

[0040] Example 3:

[0041] The difference between this embodiment and Embodiment 1 is that the VCSEL light-emitting units arranged in the array are polarized VCSELs. The epitaxial structure of the polarized VCSELs is achieved by introducing anisotropic stress into the DBR. Furthermore, all VCSEL light-emitting units have the same polarization direction, which is S-polarization. The power gradient design of the array VCSELs in this embodiment is the same as in Embodiment 1.

[0042] The optical navigation system in this embodiment consists of an analyzer installed at the front end of the receiver, with the analyzer's transmission axis direction set orthogonal to the polarization direction emitted by the VCSEL. That is, if the VCSEL emits S-polarized light, the analyzer's transmission axis is in the P direction. Other components are the same as in Embodiment 1.

[0043] The system working principle of this embodiment is as follows:

[0044] Building upon existing power gradient compensation, polarization suppression of specular reflection is employed: when uniformly linearly polarized light is projected onto a smooth surface at a certain angle, specular reflection occurs. According to Fresnel's law, specularly reflected light largely retains its polarization state. When this reflected light passes through orthogonal analyzers, most of its energy is blocked. Meanwhile, reflected light from diffuse objects (such as carpets and furniture) is severely depolarized, becoming unpolarized light. Approximately 50% of the energy of this unpolarized light can pass through the analyzer.

[0045] Final result: "Power gradient" is responsible for equalizing the dynamic range of diffuse reflection signals, while "polarization orthogonal filtering" is responsible for specifically suppressing strong specular reflection light from smooth ground. Together, they achieve clear and reliable detection even in extremely high-reflectivity environments.

Claims

1. A VCSEL array with gradient output power, comprising multiple VCSEL light-emitting units arranged in an array, characterized in that, The physical structural parameters of each VCSEL light-emitting unit are designed differently according to its location, so that the light output power of all VCSEL light-emitting units under the same driving voltage presents a gradient distribution.

2. A VCSEL array with gradient output power according to claim 1, characterized in that, The physical structural parameters vary in a gradient along the radial, axial, or specific preset direction of the VCSEL array.

3. A VCSEL array with gradient output power according to claim 2, characterized in that, The physical structural parameters are at least one of the mesa size and oxide pore size of the VCSEL light-emitting unit.

4. A VCSEL array with gradient output power according to claim 3, characterized in that, The VCSEL light-emitting units closer to the bottom of the VCSEL array have relatively smaller oxide apertures and / or mesa sizes, while the VCSEL light-emitting units closer to the top of the VCSEL array have relatively larger oxide apertures and / or mesa sizes.

5. A VCSEL array with gradient output power according to claim 1, characterized in that, The VCSEL light-emitting unit is a polarized VCSEL, and the active region of the polarized VCSEL is a stress-strain quantum well or an anisotropic gain cavity structure, which outputs linearly polarized light.

6. A VCSEL array with gradient output power according to claim 5, characterized in that, All of the polarized VCSELs described herein have the same polarization direction.

7. An optical navigation system, characterized in that, include: The projection light source employs a VCSEL array with gradient output power as described in any one of claims 1 to 6, providing a beam with a specific light intensity distribution for the navigation scene; A receiver, used to receive light signals reflected back from the navigation scene; A processor for making navigation decisions based on signals from the receiver.

8. Wherein, the region with lower light output power density of the VCSEL array corresponds to the region with higher expected reflectivity in the navigation scenario, while the region with higher light output power density corresponds to the region with lower expected reflectivity.

9. A method for suppressing interference from highly reflective environments applied to the optical navigation system of claim 7, characterized in that, Includes the following steps: Step S1: Use the VCSEL array with gradient output power as the projection light source to project the light signal; Step S2: Receive the light signal reflected back from the navigation scene using the receiver; Step S3: The processor processes the signal uploaded by the receiver to make a navigation decision.

10. The method for suppressing interference from highly reactive environments according to claim 8, characterized in that, Based on the navigation environment, the power gradient preset in the VCSEL array compensates for signal strength fluctuations caused by differences in scene reflectivity, thereby reducing the dynamic range of the signal obtained by the receiver and making the signal-to-noise ratio more uniform.

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