COC/COP for manufacturing AR/VR glasses: the most challenging field in plastic optics applications
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Augmented Reality (AR) and Virtual Reality (VR) are technology fields that have received significant attention in recent years. Their near-eye display systems use a series of optical imaging elements to transform the pixels on the display into virtual images in the distance, which are then projected into the human eye. VR optical solutions include aspherical lenses, Fresnel lenses, and Pancake lenses. The trend recognized in the industry today is the use of Pancake lenses, as they enable a significant reduction in the size of VR glasses, along with a notable decrease in lens thickness. In Chinese, “ancake” means “folded optical path”. By folding the optical path, it is possible to achieve the same total length of the optical path—and thus the same magnification effect—while keeping the thickness of the module at a minimum. The display systems used in AR glasses available on the market today are combinations of various micro-displays along with optical elements such as prisms, free-form surfaces, and light waveguides. The real challenge in producing AR/VR glasses using COC/COP lies not in the materials themselves, but rather in the combination of optical precision, mass-production stability, and polarization sensitivity – making it the most difficult area within plastic optical applications. The biggest challenges with low-stress, low-birefringence designs in AI/AR smart glasses: Pancake lenses, optical waveguides, and polarized optics are extremely sensitive to birefringence. Even a slight increase in birefringence can lead to image duplication, light leakage, a sharp drop in contrast, and a blurred field of view; in such cases, the polarization system fails and the entire device becomes unusable. COC/COP has extremely low birefringence on its own, but once injection molding takes place, factors such as uneven flow, improper holding pressure, insufficient mold temperature, and too rapid cooling can all lead to the generation of internal stresses, resulting in a sharp increase in birefringence. Although it appears transparent and clean to the naked eye, this cannot be detected by ordinary testing methods; once a polarized stress meter is used, stress patterns can be seen everywhere. Optical-grade precision requires extremely high standards; AR/VR lenses are not ordinary transparent materials but rather precision optical components. 1. The fogging level must be ≤ 0.1%. Any trace of impurities, black spots, small bubbles, or silver threads result in the part being classified as waste. Such defects are acceptable in ordinary transparent parts, but not at all in AR/VR applications. 2. The batch-to-batch variation in refractive index must be ≤ ±0.001; a difference of 0.002 can cause the focal length to be incorrect, leading to blurred images and dizziness. 3. Dimensional accuracy is critical: variations of 0.02 mm in lens thickness, surface curvature R-value, concentricity, and flatness can result in problems such as the lens not fitting properly, an incorrect focal length, or optical distortion. It is extremely difficult to maintain batch consistency. AR/VR products are manufactured on a mass scale of millions of units, not just in small quantities for laboratory use. 1. Fluctuations in Tg of ±2℃ affect injection molding. 2. Fluctuations in MFR of ±3% affect stress levels. 3. A variation of 0.1% in shrinkage rate can result in dimensions that are out of spec. 4. The biggest challenge with domestically produced materials is maintaining consistency across batches; the requirements for injection molding processes are very high. 1. The molds must be polished to a mirror-like finish, with no imperfections at the nanoscale level; even the slightest flaw is unacceptable. 2. A high mold temperature is necessary, often exceeding 100℃. A lower mold temperature leads to higher stress and higher birefringence, while a higher mold temperature results in longer processing times, higher costs, and difficulties in mass production. 3. The injection molding parameters need to be tightly controlled: a faster speed can lead to the formation of floating fibers or silver threads, while a slower speed can cause shortages of material. More holding pressure is needed to reduce internal stress, while less holding pressure is required to minimize shrinkage
Using COC/COP for AR/VR glasses lenses is extremely difficult; it can be considered the \"hell mode\" of plastic optics. The main difficulties lie in three aspects: 1. **High polarization sensitivity**: Solutions such as Pancake and optical waveguides are extremely sensitive to birefringence. The material itself has very low birefringence, but even a slight mistake during injection molding – such as uneven flow or poor temperature control – can cause internal stresses to rise sharply, resulting in double images and light leakage; in severe cases, the entire device becomes unusable. 2. **Exceedingly high precision requirements**: These are not ordinary transparent parts; they are precision optical components. The haze level must be ≤0.1%; any small bubbles or black spots mean it is defective ； The inter-batch variation in refractive index must not exceed ±0.001; otherwise, the focal length will change and the image will become blurry ； The dimensional accuracy must be at the micron level; a difference of 0.02 mm can result in failure to fit or distortion. 3. **Mass production stability is extremely difficult**: Reaching mass production at the million-unit level is not something that can be achieved by producing just a few units in the laboratory. Material batch stability is crucial – fluctuations in Tg (glass transition temperature) of ±2°C, fluctuations in MFR (melt flow rate) of ±3%, and fluctuations in shrinkage rate of 0.1% can all directly lead to injection molding failures or dimensional deviations. Domestic materials struggle particularly in this regard. **Molds and manufacturing processes are also major challenges: the molds need to be polished to a nanoscale smoothness, as even the slightest imperfection will be reflected on the lenses ； Injection molding often requires a high mold temperature of over 100°C; too low a temperature leads to high stress, while too high a temperature results in soaring costs and difficulties in mass production ； The parameter window is extremely narrow – even slight deviations in speed or holding pressure can result in silver wires or floating fibers, or else insufficient material supply or excessive internal stress. In short, this task tests the ultimate capabilities of materials, molds, manufacturing processes, and quality control across the entire chain, with every step needing to be tightly controlled. .