A design method of wide-angle three-mirror system with spiral optical axis is proposed. Asymmetric optical
systems have more degrees of freedom than co-axial systems. The increased degrees of freedom can be
applied for removal of ray obscuration by mirrors to achieve wide-angle and low F-number system design.
The asymmetric system design requires three-dimensional comprehension of system structure and correction
of asymmetric aberrations. In order to simplify the structure comprehension, a base sphere is introduced. The
system structure can be changed into the two-dimensional structure of mirror interferences by the base
sphere. The dominant asymmetric aberrations are spherical-like and astigmatism-like aberrations. The
spherical-like aberration is eliminated by each mirror inidividualy and the astigmatism-like aberration is
reduced by counterbalance of whole mirrors. An example of F/2 system with as wide angle as 30x24 degrees
FOV is designed. The example system is fabricated by precision machining process for an infrared camera.
Polarimetric sensing is adequate for detection of man-made targets, which generally have artificial smooth surfaces. In this paper, we propose an infrared polarization imaging system for detection of man-made targets in natural backgrounds. In order to obtain the polarization properties, images in different polarization states are required. Sequential capturing of polarization images is not suitable for practical systems because the movements of targets and backgrounds cause errors in polarization estimation. The proposed system is capable of capturing simultaneous polarization images.
A Brewster angle polarization splitter (BAPS) is used for the polarization imaging system to separate the polarization components of the incident light. We introduce a new type of BAPS structure, called air-grid structure. The air-grid structure is composed of a series of parallel cavity lines on a single plane and shows structural birefringence. As a result, the refractive indices of the air-grid structure satisfy the Brewster angle condition and the total reflection for orthogonal polarization components at the same incident angle. This new structure enhances the field of vie of the BAPS and is ideal for imaging systems.
All-reflective systems have been applied to optical systems because of less material limitations compared with refractive systems. The key to design an all-reflective system is how to widen the field view and the aperture without obscurations of the rays by the mirrors. In order to avoid the obscurations, many systems have been designed to work off-axis with respect to the field angle, which show rotational asymmetry around the optical axis. In this paper, we propose a design method adapted effectively to this asymmetry by use of anamorphic mirrors and an elliptic aperture. In our method two main design factors, placement of mirrors and enlargement of the aperture, are separately optimized. We show a design example of a three-mirror system reaching an F-number of 1.2 with 18×14 degrees field angle.