Machine vision, as a critical core technology enabling industrial automation and intelligence, is rapidly emerging as one of the fastest-growing branches of artificial intelligence. To AI, machine vision is akin to the eyes for humans—essential yet indispensable. As one of the most crucial components in machine vision systems, laser light sources directly influence image quality and sensing accuracy, effectively giving machine vision its "light of intelligence." Today, machine vision is quickly expanding into new application areas such as consumer electronics, automotive electronics, and industrial control. These innovative applications and functionalities are driving the demand for laser light sources that offer greater power, higher efficiency, and more compact designs.

　　It is reported that at the China International Optoelectronic Exposition (CIOE 2021), held in Shenzhen from September 16 to 18, Lemon Photonics—based in Shenzhen Laser Valley—will showcase a range of laser source chips and modules tailored for machine vision applications. Leveraging its cutting-edge laser chip technology and expert optical design capabilities, the company aims to deliver a comprehensive, one-stop laser radar light source solution specifically designed for the intelligent robotics industry.

　　The LiDAR industry is in the early stages of its technology lifecycle, with multi-dimensional and diversified technological innovations continuously emerging. These tech advancements are driving product upgrades, which in turn serve as the core engine behind the expanding scale of the machine vision industry. Among smart robotics, robot vacuum cleaners have experienced rapid growth in recent years. Currently, the dominant technology for mobile navigation in robot vacuums is SLAM (Simultaneous Localization and Mapping)—a cutting-edge approach that enables real-time positioning and map creation.

　　According to sensor type, SLAM technology is primarily divided into two categories: one is LDS SLAM technology, which relies on laser ranging sensors, and the other is VSLAM technology, based on machine vision. Currently, LDS SLAM is the dominant technology in the market. Table 1 compares three mainstream LDS SLAM solutions. Among these, the stereo vision solution stands out as the most widely adopted LDS SLAM approach due to its comprehensive advantages in resolution, measurement accuracy, anti-interference capabilities, and cost-effectiveness. While the ToF solution offers superior map-building performance, it comes with a relatively higher price tag. On the other hand, the structured-light approach faces limitations in terms of measurement range and anti-interference ability, restricting its applications to some extent. Among the more widely used stereo vision and ToF solutions, conventional LiDAR systems typically employ edge-emitting lasers (EEL). However, Lemon Photonics leverages its independently developed high-performance Vertical-Cavity Surface-Emitting Laser (VCSEL) chips and Horizontal-Cavity Surface-Emitting Laser (HCSEL) chips to deliver even more advanced laser source solutions tailored specifically for mainstream LDS SLAM systems.

Table 1: Comparison of Three Mainstream LDS SLAM Approaches

　　1. VCSEL Point Laser Collimation Module for Stereovision Solutions Based on Triangulation Method

　　The VCSEL series of point laser collimation modules from Lemon Photonics (as shown in Figure 1) feature a custom-designed single-point VCSEL chip. Compared to traditional EEL collimation modules, these products boast advantages such as a low temperature drift coefficient, superior beam spot circularity and uniformity, enhanced electrostatic discharge resistance, high reliability, ease of packaging, and excellent cost-performance. The product has already undergone rigorous performance and reliability testing by multiple lidar solution providers and smart robotics end customers, and is now ready for mass production.

Figure 1: Lemon Photonics' VCSEL Point-Source Collimation Module for Triangulation-Based LiDAR Measurement

　　II. Multi-junction VCSEL Point Laser Collimation Module for dToF Solutions

　　Lemon Photonics has launched an industry-leading series of multi-junction VCSEL chips, achieving a peak electro-optical conversion efficiency of up to 56% (as shown in Figure 2). This product line boasts exceptional features such as high power density, superior reliability, and outstanding performance under high-temperature conditions, making it ideal for applications requiring short pulses (in the nanosecond range) and ultra-high peak power. Multi-junction technology represents the next major leap forward in the VCSEL industry, delivering significant advantages for machine vision applications. Its high power density enables smaller package sizes and more streamlined system designs, while the impressive electro-optical conversion efficiency helps reduce the overall thermal load of the device. Additionally, the high slope efficiency allows for lower pulse currents, which in turn boosts the switching speed of the driving chip. Combined with the numerous advantages VCSEL technology offers over EELs—such as improved energy efficiency and compact form factors—the multi-junction VCSEL-based point laser collimation modules are poised to outperform traditional EEL modules, paving the way for dToF LiDAR solutions to be increasingly adopted in robotic vision systems.

Figure 2: Measured LI and PCE data of the lemon-photon multi-junction VCSEL chip (test conditions: 200 µs pulse width, 1% duty cycle)

　　3. Wide-Angle Flat-Top Light Field VCSEL Line Laser Module for Structured Light Solutions

　　The Lemon Photonics VCSEL series line laser modules feature a custom-designed VCSEL array chip and a specially engineered wide-angle line mirror, delivering high-quality linear light fields. Compared to traditional EEL line light sources, these modules offer several key advantages: - **Industry-first wide-angle flat-top light field**: Achieves a 120-degree wide-angle, flat-top light distribution with no edge discontinuities, ensuring stronger edge energy—ideal for enhancing edge coverage in wide-angle radar systems (see Figure 4 for a comparison of the light field distribution between this VCSEL module and conventional EEL modules). - **Narrower laser linewidth**: Concentrates energy more precisely, significantly improving the signal-to-noise ratio in the spatial domain. - **Lower temperature drift**: Exhibits a thermal drift coefficient that’s just 1/5th of that of EELs, enabling the use of narrower-band filters at the receiver end—further boosting the signal-to-noise ratio in the frequency domain. - **Enhanced reliability**: Thanks to the larger VCSEL emission area and lower power density compared to EELs, these modules offer superior long-term reliability. - **Cost-effective performance**: VCSEL technology delivers optimized costs across key areas, including chip manufacturing, packaging, and module assembly.

Figure 3: VCSEL Line Laser Module for Lemon Photon's Line Structured Light Obstacle Detection Radar

(a) (b)

　　Figure 4: Comparison of the light field patterns between the lemon-shaped photonic VCSEL line source and the EEL line source: (a) The lemon-shaped VCSEL line source achieves a 120-degree light field, with a flat-top intensity distribution exceeding 90 degrees; (b) The conventional EEL line source exhibits a nearly Gaussian light field profile, where edge energy fails to meet the requirements for sensing signals, and noticeable gaps appear at wide-angle regions.

　　4. Wide-Angle Flat-Top Light Field HCSEL Line Laser Module for ToF Solutions

　　The HCSEL laser chip from Lemon Photonics combines the high-power output of EELs with the scalability advantages of VCSELs, seamlessly addressing the three key requirements for laser sources in the widespread adoption of LiDAR systems: higher peak power, reduced spectral temperature drift, and a broader laser wavelength range. This innovation enables longer 3D sensing distances, improved signal-to-noise ratios, and enhanced eye safety protection.

　　Compared to VCSELs and EELs, HCSEL chip technology offers the following advantages: - Ultra-high power, enabling single-tube peak outputs of hundreds of watts; - A large output aperture that enhances the chip's reliability; - Narrow spectral linewidth and stable wavelength, making it easier to effectively filter out noise in 3D sensing and LiDAR applications; - Exceptionally high beam quality, reducing the complexity of optical shaping while maximizing light-field utilization; - Superior polarization properties, which are beneficial for sensing, detection, and optical beam combining; - A straightforward chip manufacturing process that, in theory, ensures more predictable and controllable costs.

　　The 3D sensing solution based on line scanning boasts relatively high integration and benefits from the more mature, cost-effective line-array photoelectric receiver chips, making it increasingly attractive to the sensing industry. Traditional EEL and VCSEL laser chips, however, struggle to produce uniformly shaped, low-cost, compact line-shaped light spots directly via diffusers due to their larger far-field divergence angles. In contrast, Lemon Photonics’ innovative HCSEL laser chip features a nearly collimated emission divergence angle in one direction, significantly enhancing both the sharpness and uniformity of the light field after being reshaped by a diffuser—allowing for the creation of an ideal line-shaped beam even within a compact package. Figure 5 compares the light field performance of a 2W VCSEL and the HCSEL laser after passing through the same 120° x 1° diffuser.

　　(a) (b)

　　Figure 5: Comparison of the light field from VCSEL and HCSEL chips after passing through a 120° x 1° diffuser: (a) Without a collimating lens, the VCSEL light field cannot be compressed by the diffuser, resulting in beam divergence and stray light that introduces noise; (b) The HCSEL, when directly passed through the diffuser, produces a sharp linear light spot with narrower linewidth and improved uniformity.

Figure 6: HCSEL Line Laser Projection Module Based on the 4037 Package Format

　　Lemon Photonics' innovative HCSEL semiconductor laser chip, serving as the next-generation ToF light source, will elevate 3D sensing applications to new heights with its superior performance, enhanced reliability, and lower costs. Currently, Lemon Photonics offers HCSEL line laser projection light sources ranging from 2 to 50 watts peak power, and several globally renowned manufacturers have already adopted this cutting-edge HCSEL chip technology.