A wide field-of-view crossed Dragone optical system using the anamorphic aspherical surfaces

A side-fed crossed Dragone telescope provides a wide field-of-view. This type of a telescope is commonly employed in the measurement of cosmic microwave background (CMB) polarization, which requires an image-space telecentric telescope with a large focal plane over broadband coverage. We report the design of the wide field-of-view crossed Dragone optical system using the anamorphic aspherical surfaces with correction terms up to the 10th order. We achieved the Strehl ratio larger than 0.95 over 32 by 18 square degrees at 150 GHz. This design is an image-space telecentric and fully diffraction-limited system below 400 GHz. We discuss the optical performance in the uniformity of the axially symmetric point spread function and telecentricity over the field-of-view. We also address the analysis to evaluate the polarization properties, including the instrumental polarization, extinction rate, and polarization angle rotation. This work is a part of programs to design a compact multi-color wide field-of-view telescope for LiteBIRD, which is a next generation CMB polarization satellite.