The field curvature has been a long-term problem optical designers had to deal with, to propose flat corrected field instruments. Combinations of highly aspherical optics, TMA configurations, achromatic doublets or field flatteners are often used to reach good optical quality across the image.
Allowing designers to play with the parameters of the field’s shape is offering them a brand-new game field. The possibility of curving the CMOS sensors to fit curved/aspherical/freeform shapes of focal surfaces has been studied for the last 20 years and led today to different applications and prototypes.
We present in this article 1/ the parameter studies we performed over a large set of optical designs showing the gain offered by this approach, 2/ the CMOS sensors curving process and performance over a large set of prototypes, 3/ Optical systems that have been produced with this technology and 4/ the roadmap related to the development of curved-sensors based instrumentation for astronomy with the CASTLE telescope project and physical sciences through the Auroral UV Imager program led by ESA.
The field curvature has been a long-term problem optical designers had to deal with, to propose flat corrected field instruments. Combinations of highly aspherical optics, TMA configurations, achromatic doublets or field flatteners are often used to reach good optical quality across the image.
Allowing designers to play with the parameters of the field’s shape is offering them a brand-new game field. The possibility of curving the CMOS sensors to fit curved/aspherical/freeform shapes of focal surfaces has been studied for the last 20 years and led today to different applications and prototypes.
We present in this article 1/ the parameter studies we performed over a large set of optical designs showing the gain offered by this approach, 2/ the CMOS sensors curving process and performance over a large set of prototypes, 3/ Optical systems that have been produced with this technology and 4/ the roadmap related to the development of curved-sensors based instrumentation for astronomy with the CASTLE telescope project and physical sciences through the Auroral UV Imager program led by ESA, and the IMANCES project led by the Neurosciences Institute INT.
Planetary exploration missions generally impose high demands on both the imaging quality and the size-weight constraints of optical systems. Therefore, this paper proposes using curved detector in the design of a fast and wide-field off-axis freeform three-mirror optical system, aiming to achieve high imaging performance within a relatively small volume. Specifically, a freeform-shaped curved detector is considered in the off-axis system design, which ultimately enables the system reach a near diffraction limited image quality within 10-liter volume. The proposed design shows great potential for application in planetary exploration missions, making the higher performance imaging instruments feasible in the future missions.
Lenslet-based integral field units are notable for the large field of view and high throughput. But the structure in the image plane of these instruments is inherently highly complex due to the spatial and spectral packing of information, and often has large dynamic range between neighbouring pixels. This may make their optical design challenging in terms of the image quality and the technological complexty. We consider design options to implement such an instrument for a 40 cm - class telescope with a focus on the fast spectrograph camera design. It is demonstrated that with a relatively simple and compact optical system relying mainly on off-the-shelf components it is possible to reach the spectral resolving power up to R390 and cover at least 3.75′ angular field. It may be reached with a Schmidt camera or a custom 5-lens objective, using a curved sensor.
A freeform-curved sensor is presented here to demonstrate its highlights in off-axis optical system design. First, we take the extremely demanding TMA telescope as an example, the introduction of the freeform sensor makes the imaging performance reach the diffraction limit, and the PV sag departure of the mirror surface is reduced by 71% compared with the traditional design using flat sensor. Next, we performed finite element analysis on the silicon die with freeform shape to ensure that the stress distribution of the curved sensor is within a safe range when bending. Finally, the prototype of freeform-curved sensor will be manufactured, and its surface shape will be tested in the laboratory.
Innovative optical designs combing freeform optics and curved freeform sensors will be key elements to improve the optical performance and reduce the overall manufacturing and testing pressure of optical complex systems. In this paper, three version of unobscured all-reflective TMA-type telescopes (D=10cm, FOV=7°×7°) will be designed separately with flat sensor, spherical sensor and freeform sensor. Then, we will analyze and compare their imaging quality (RMS spot radius) and surface complexity (PV sag departure and Max slope departure) to demonstrate the advantage of freeform sensor applied in the off-axis optical system. Finally, we make comparison on sensitivity analysis of surface error between mirror surfaces and freeform sensor surfaces to prove that the manufacturing pressure of the sensor did not increase even though its surface complexity increased. We expect that such a design has a great potential to be applied in the space weather monitoring and solar system planetary exploration drones.
This conference presentation was prepared for the Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation V conference at SPIE Astronomical Telescopes + Instrumentation, 2022.
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