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Optical lenses are an indispensable part of modern technology, playing a crucial role in the current era of AI development. They capture the world, collect data, and provide visual information for AI systems.
Firstly, optical lenses serve as the core components of cameras, acting as the visual perception organs for AI systems. Applications of AI in image recognition, object tracking, and facial recognition rely on high-quality image data. Modern optical lenses can provide high-resolution and high-definition images, which are crucial for the training and execution of AI algorithms.
Secondly, optical lenses play a critical role in automation and intelligent systems. Autonomous vehicles, intelligent surveillance systems, and robotic technologies all rely on optical lenses for visual perception and environmental understanding. By integrating with machine learning and deep learning algorithms, optical lenses enable these systems to become more intelligent, flexible, and efficient.
Furthermore, the intelligence and automation of optical lenses have driven technological development and innovation. For example, smart lenses with features like autofocus, auto-exposure, and optical stabilization provide users with an enhanced photography and videography experience. High-precision optical lenses used in medical imaging, aerospace, and earth observation contribute to more accurate data collection and analysis.
Therefore, the evolution of optical lenses holds a pivotal position in influencing technology, automation, and intelligence. This article will guide you through the world of optical lens modules, exploring the origins of the industry, the long history of lens development, and understanding the composition and manufacturing processes of an optical lens.
Introduction to Lens Modules
Let’s take the most common example from our daily lives: the smartphone. A smartphone camera module consists of optical components, electronic components, and other mechanical parts. The optical components, which are our main focus today, include plastic lenses, glass lenses, and optical mechanisms such as barrels and light-blocking plates, forming the "lens assembly." The electronic components include image processors (like ISP and DSP) and sensors (like CMOS and CCD). Other mechanical parts include the voice coil motor, flash module, aperture module, and more.
Three Major Types of Lenses
Lenses are generally divided into three types: glass lenses, plastic lenses, and glass-plastic hybrid lenses. As the names suggest, glass lenses contain all glass elements, plastic lenses are made entirely of plastic elements, and glass-plastic hybrid lenses combine both glass and plastic elements.
So how do you choose which type of lens to design? Glass lenses have better optical properties compared to plastic lenses, including higher light transmittance and refractive index. Additionally, glass is more durable than plastic, as it is less prone to aging and less affected by external environmental factors.
Therefore, for lenses with the same performance, one glass lens might replace two plastic lenses. For example, a 7P lens (seven plastic elements) might not perform as well as a 1G6P lens (one glass, six plastic). However, the production cost of glass lenses is higher. Unlike plastic lenses, which can be mass-produced using injection molding with molds capable of 16 or even 24 cavities and short cycle times, glass lenses are mostly made by molding processes with longer production cycles and fewer cavities. Molding molds are typically made of tungsten carbide, which is expensive to process. Glass can also be manufactured through grinding, but this method does not offer significant advantages in terms of time or precision. Additionally, glass lenses are physically heavier than plastic lenses, making them unsuitable for lightweight products like smartphones. Hence, all-plastic (all-P) lenses remain the mainstream choice in the smartphone market, although the choice of lens material ultimately depends on the specific application.
All-P Lenses: Smartphones, digital cameras
All-G Lenses: Smartphones, automotive, drones, digital cameras, security systems
G+P Lenses: DSLR cameras, automotive, high-end instruments, telescopes, microscopes
Structural Composition
The structure of a lens is composed of lens elements and mechanical components. The lens elements include the plastic and glass lenses mentioned earlier. The mechanical components consist of the barrel, spacer, light-blocking plate (soma), IR filter, front cover (retainer), and sometimes the lens holder. Of course, not all lenses contain all of these components; we are simply listing all possible parts.
Barrel: The external structural part of the lens, used to support and protect the internal optical elements of the lens.
Spacer: Installed between stacked lenses to protect them and adjust the spacing between the lens elements.
Light-blocking Plate (Soma): Its main function is to block light entering the lens from the sides or other indirect directions. Such light can reflect inside the lens, causing flare and ghosting, which reduce image contrast and result in dark or spotty images. Light-blocking plates effectively reduce these issues, improving image clarity and contrast.
IR Filter: Primarily used to control the entry of infrared light to ensure imaging quality and accurate color reproduction. Infrared light, with its longer wavelength, can penetrate materials that visible light cannot, leading to blurred images or lost details. Infrared light can also reflect inside the lens, causing flare and ghosting. The IR filter removes unwanted infrared light, enhancing image clarity and detail.
Retainer: Often designed for lenses that may be exposed, a front cover protects the lens front. However, many smartphone and laptop cameras integrate the retainer function into the barrel, forming a unified structure.
Holder: A mechanism that allows the lens elements and barrel to be mounted or secured to system components. Whether a holder is needed depends on the module design requirements.
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Manufacturing Process
Optical lens assemblies are manufactured by optical lens companies such as Largan Precision and Genius Electronic Optical. These companies typically have the capability to produce the main components in-house and then complete the final assembly themselves.
Typically, the development of a lens starts with the product development engineer, such as the optical system engineer from a smartphone brand. This engineer defines the lens specifications for the product, including basic pixel capabilities, effective focal length (EFL), total track length (TTL), field of view (FOV), and other parameters, which are then provided to the lens manufacturer. Upon receiving these specifications, the lens manufacturer's engineers begin the optical design process. They create the layout of the lens assembly and use optical system design software to simulate the optical path, ensuring the effective design of the lens surfaces. Once the optical design is finalized, producing the optical surfaces and layout, the design is handed over to the optical mechanical engineers. These engineers design the complete lens structure according to the client's requirements. After producing individual component drawings, the manufacturing or procurement of the various components can be outsourced.
The production of plastic lenses involves injection molding. Unlike traditional mold manufacturing, optical molds require higher precision. Currently, the mainstream smartphone lens molds have a contour tolerance of at least 0.1μm. Therefore, in mold processing, lens mold inserts are manufactured using specialized ultra-precision aspheric machining equipment to create the lens surfaces on the inserts.
In contemporary times, molded glass lenses are becoming increasingly popular compared to traditionally ground glass lenses. The molding process involves fewer steps and is better suited for mass production. In the molding process, a specified weight of glass preform is placed between upper and lower molds and heated to a temperature between the transition and softening points. The molds then close, applying pressure to shape the glass into the lens form. After cooling, the lens is removed. This entire process is called glass molding. However, glass lenses, whether ground or molded, are not in their final form after these processes. They still require centering. Typically, the lens surface and the outer circumference of the formed glass lens are not perfectly aligned at the same center. Since lens assembly relies on the outer circumference for fitting, centering involves grinding the outer edge of the glass lens to eliminate any centricity errors.
After the glass and plastic lenses are formed, they undergo optical coating, where thin films are deposited on the surface using vapor deposition. The types of coatings typically include hard coating (HC), anti-reflection coating (AR), and anti-smudge coating (AS). These coatings are used to increase surface hardness, reduce light reflection to enhance lens transmittance, and protect against dust, water, and other contaminants.
For mechanical components such as barrels, holders, and spacers, they can be produced using plastic injection molding according to the requirements. If the demand is low, these parts can also be made directly through metal machining.
The light-blocking plate is a very thin, ring-shaped component. To ensure insulation and chemical stability, it is typically made of PET. These flat, thin parts are usually manufactured through die-cutting.
Before entering the assembly stage, if the barrel and lens components are obtained, a push-fit test is conducted to ensure that the fit between the inner wall of the barrel and the circumference of the lens is appropriate. Due to the various influencing factors of injection molding, even if the dimensions of the components meet the design specifications, it does not necessarily mean that their fit will be proper. Therefore, to ensure that the fit is neither too tight nor too loose, the push-fit test is a crucial method. Proper fit ensures there is no excessive eccentricity or deformation caused by overly tight fits.
Once all the components are ready, they are gathered at the assembly unit for lens assembly. The lens assembly is performed using specialized lens assembly machines, which press the lenses and spacers layer by layer into the barrel. During this process, adhesive is applied and then cured using exposure.
Once a lens assembly is completed, it undergoes appearance and performance testing. The most scientific method for performance testing is the MTF (Modulation Transfer Function) test. MTF can evaluate the lens's resolving power, contrast, and the performance at the center and edges. Additionally, direct photography is used to check for flare, ghosting, chromatic aberration, and distortion.
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Manufacturing Challenges
First, we need to understand the current development trends of modern lenses. Smartphones are the most widely produced consumer electronic products globally, and their design trend is becoming lighter and thinner. This results in significant space constraints for any module. In the case of camera modules, we know that the image capture range is inversely related to focal length. Without sufficient light refraction distance, the field of view will be affected. Therefore, to shorten the focal length and save space while maximizing the field of view and image clarity, more curved lenses need to be stacked to achieve greater refraction effects, effectively reducing the lens thickness.
From the above, it is evident that the greater the number of components, the more significant the impact of assembly tolerances. Poor lens performance can result from many factors, making it a highly complex issue. The molds for both lenses and mechanical components have inherent dimensional tolerances, and injection molding introduces molding errors. Additionally, lenses are not perfectly round at the microscopic level, leading to asymmetry. Consequently, rotating the lens to different angles during assembly yields varying results. Achieving the most precise tolerances for all components brings the design closer to the ideal, but achieving zero tolerance is unrealistic.
For lens manufacturers, effectively increasing profits usually involves improving assembly yield. This includes finding the optimal assembly angle for each lens, consistently controlling adhesive amounts, and enhancing the precision of assembly machines. By identifying the best parameters, they strive to replicate high-quality products consistently. However, the root of the issue still lies in the dimensional accuracy of each component. The current precision achievable by optical molds has reached a threshold, making further improvements challenging. Therefore, many manufacturers focus on injection molding and mold structure design to produce finished products that closely match the mold dimensions.
Given the current limitations in manufacturing capabilities of lens manufacturers, how can we further enhance the zoom performance of lenses? The solution lies in changing the module design. For example, a periscope lens uses a prism to reflect the light path, allowing it to bend. This design alleviates concerns about thin products compressing the lens thickness.
Application Development
In the future, with continuous advancements in AI technology and innovations in optical technology, the optical industry will develop towards greater intelligence and automation. We can foresee more smart devices and systems based on optical lenses being applied in various fields, from smart homes to smart cities, from industrial production to healthcare. All these areas will benefit from the advancements in optical lenses. Therefore, the continuous evolution of optical technology will bring more convenience and innovation to humanity, driving technological development and social progress.
