Focused Narcissus evaluation in a MWIR zoom system

Abstract

There has been a notable advance in detection systems during the last decades. On one hand, these advances allow the design of systems with higher resolution and better performance, but on the other hand, they are more sensitive to unwanted light. In infrared systems, Narcissus is one of the major problems of unwanted light to avoid. This problem is especially more difficult to control in zoom infrared systems, where there are a considerable number of zoom positions which must be carefully checked to analyze the presence of Narcissus. Usually, Narcissus can be eliminated using an offset nonuniformity correction (NUC) or One Point NUC (OPN). In order to be eliminated through this algorithm, it is necessary that the NITD of the system at all zoom positions is under certain level according to the detector sensitivity. But although the system can fulfill this requirement, we have found situations where Narcissus is highly sharp but still exhibiting low levels of NITD. This sharp Narcissus is not possible to eliminate through OPN. The sharp Narcissus was first found during measurement test and then reproduced through simulations in Zemax. These simulations allowed us to find the root cause of the sharp Narcissus. These findings trigger the need to establish solid requirements to avoid not only Narcissus under certain NITD values, but also focused Narcissus. In this paper we present Narcissus measurements and simulations results, pointing out the root cause for Narcissus, and potential solutions for this problem.