Freeform Mirror Design for Novel Laser Warning Receivers and Laser Angle of Incidence Sensors

Abstract

In this paper, we present a novel configuration of an optical angle-of-incidence (AOI) sensor based on the application of a freeform mirror. The main challenge in designing this mirror was to provide a strictly linear transformation between AOI and the spatial position of the spot created on the linear detector array. Another two goals of this paper were to minimize stray light issues (improve the dynamic range) and create an intermediate focus and lateral shift in the detector position with respect to the plane of incidence. From an optical point of view, the designed mirror can thus be understood as the composition of three components: a high-numerical-aperture (NA) fully achromatic f-theta lens in one cross-section and a perfectly focusing lens, combined with a deviating prism in the second (orthogonal) cross-section. In comparison to the standard “shade” methods, the proposed approach allows a constant angular resolution to be maintained over the entire field of view. The mirror was designed on the basis of fundamental geometrical rules by numerically solving differential problems using an innovative scheme based on the minimization of the specific merit function. The proposed method was practically applied to design a freeform mirror for a 90°/120° field-of-view sensor, showing a satisfactory performance.

Analysis of structures and technologies of various types of photodetectors used in laser warning systems: a review

“…In LWSs based on 4-QDs, received power ratios and associated photocurrents allow evaluating input radiation angle. This solution suffers from disadvantages, such as low and limited FOV, low angular accuracy, and strong radiation beam distribution dependence 27 …”

“…In LWSs, most innovations are done regarding detecting the threat beam and the AoA resolution, and the front-end circuits will be less addressed 12 , 22 , 26 , 27 , 103 , 142 . However, the reduction of system noise will primarily be related to the design of the front-end circuit.…”

“…This solution suffers from disadvantages, such as low and limited FOV, low angular accuracy, and strong radiation beam distribution dependence. 27 Usually, in many applications, conventional algorithms will be used to detect the spot location in 4-QDs from an ideal circular spot with a uniform energy distribution, which has the advantage of simplicity in calculations. However, in reality, the energy distribution in a circular mode is not ideal and is usually Gaussian.…”

“…18 Quadrant PD. 27 so that the output of each quadrant and the tracking algorithm error can be calculated correctly. Their simulation results show that the accuracy of quadrant measurement decreases with increasing blind area, shape, and point of slight deviation.…”

“…We will not focus on incident angle detection methods because it is beyond the scope of this article, but you can refer to Refs. 25–27 for further studies. One of the most critical parameters in LWSs is the false alarm rate (FAR).…”