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French start-up, Curve-One, has announced its first commercially-viable curved image sensor. This is not the first time we’ve heard of curved sensors. In 2014, Sony showed a pair of curved sensors. Three years later, CEA-Leti, a research institution in France announced a functional prototype of a 20MP full frame image sensor. However, Curve-One’s announcement is different in a significant way—Curve-One is preparing for mass production of its curved image sensor.
Curved image sensors mimic the human eye and have massive implications for optical design and overall imaging performance. Curve-One says
‘The development of curved sensors is a bio-inspired approach. Mimicking the eye retina, this new technology impacts every future imaging system. By directly correcting the field curvature in the focal plane of imagers, the use of curved sensors suppresses the field flatteners. Less optics means less misalignments and instrumental errors, increases the stability and image homogeneity, and reduces the dependence to environmental condition. Thereby it improves image acquisition quality and then reduces image post-processing costs.’
Curve-One states a curved sensor design can reduce total optics in a lens by a third and remove the need for aspherical elements. You can see a comparison diagram below, showing a flat image sensor and its requisite lens design on the left and Curve-One’s curved image sensor and a less complicated optical design on the right.
A curved image sensor solves what Curve-One refers to as ‘the classical problem of the planisphere.’ A ‘huge distortion is created by the imaging system on the edge of the field’ and optics needed to correct distortions increase the complexity and size of lenses while also resulting in optical issues, such as chromatic aberrations, which need to be corrected by further lens elements. Additionally, ‘imaging response is not uniform across the field.’
With a curved image sensor, not only are lenses smaller and less complex, but performance is also relatively improved and more consistent. Beyond the reduction in aberrations and distortions, Curve-One promises even illumination across the entire surface of the image sensor and resulting reductions in the intensity and frequency of post-processing.
With all the advantages of a curved sensor, why is Curve-One the first to prepare a curved CMOS image sensor for mass production and commercial availability? Mizuwari’s 2018 interview with Sigma CEO Kazuto Yamaki sheds some light on the topic. Yamaki said, translated from the original publication in French, ‘Curved sensors are a good idea and may seem like an ideal solution to compensate for the curvature of field that all lenses have, even the best ones, even ours.’ However, while a curved sensor corrects for problems with a particular lens and a flat sensor, different optics have different curvature fields which may require a different sensor curve.
Nonetheless, the advantages of a curved sensor are clear. Yamaki stated, ‘If the sensor is designed to adjust to the curvature of field of the lens, we could actually make it much smaller…well, smaller, or better with the same footprint.’ For Yamaki, a significant problem is how to recoup the cost of engineering investment in developing and producing a curved sensor and finding the necessary market to justify the investment.
In addressing the investment and cost problem Yamaki referred to in 2018, Curve-One is building upon original research results from two prior programs from the European Research Council and LabEx from the French National Research Agency. Further, Curve-One is supported by the European Commission and the European Space Agency. After all, being first through the door with any technological advancement is expensive. Getting to the production stage is a massive accomplishment.