Ultra-small imaging system for cell phone camera using birefringent lenses

In this research, an ultra-small imaging system using birefringent lenses was presented. This system is designed for the next generation mobile phone camera with an image sensor of smaller pixel size. The system thickness is reduced to approximately 1.7mm (from the first lens´ front surface to the image sensor) by employing one aspheric lens and one spherical lens made of birefringent uniaxial crystal, which also act as two optical low pass filters (OLPFs). In conventional cameras, however, the OLPFs are stacked up and assembled separately with optical lenses, which makes it difficult to reduce system thickness. Quantitative and visual results of ordinary and extra-ordinary ray separation on the image plane demonstrated that the birefringent lenses system is able to cut off all higher spatial frequencies than the Nyquist frequency of a 0.5μm × 0.5μm image sensor.