Design and Performance Analysis of a Fisheye-Based Optical Head for an Imaging Laser Detecting System
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RESEARCH PAPER
Design and Performance Analysis of a Fisheye-Based Optical Head for an Imaging Laser Detecting System Shahram Mohammad Nejad1
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Nazli Ronagh Sheshkelani1
Received: 19 October 2019 / Accepted: 13 August 2020 Ó Shiraz University 2020
Abstract A fisheye-based optical head which contains eight lens elements was designed and developed for an imaging laser detection system. The field of view is more than 180 degrees in visible and near-infrared (NIR) wavelength. The F/# of the system is less than 3 and the effective focal length is about 2.4 mm which are critical for imaging laser detection systems in the NIR spectrum. The MTF characteristic is more than 0.8 for all angles at the Nyquist frequency. The calibrated (f - h) distortion is less than 3%, and the relative illumination is more than 92%. All of these values are required to prepare an imaging laser warning system with excellent performance and low false alarm. The performance of the proposed structure is evaluated and analyzed by the ZEMAX optical design software. Keywords Imaging laser detection system Optical head Fisheye lens MTF (f - h) distortion Relative illumination Nyquist frequency
1 Introduction In the last century, the development of the laser detection technology has become one of the most attractive issues to protect strategic centers against various kinds of laser sources such as power lasers, pulsed lasers, and ultra-high power lasers. So, a laser detection system is designed to determine a menace, obtain its information accurately, and warns immediately. This system may be a combination of the most excellent electronic devices with advanced optical technologies (Guo et al. 2009; Dubois and Reid 2007; Jurba et al. 2012; McAulay 2011; Maini and Jindal 2003; Mcaulay 2009; Al-Jaberi 2006; Mallik et al. 1999; Dong et al. 2012; Al-jaberi et al. 2006). Generally, the recent detecting laser detecting system can be categorized into three groups: coherent recognition, scatter recognition, and spectrum recognition. The spectrum recognition type is also divided into types with imaging and without imaging. Mainly, the imaging laser detecting system is composed of a wide-angle fisheye lens & Shahram Mohammad Nejad [email protected] 1
Nanoptronics Research Center, Iran University of Science and Technology, Tehran, Iran
and CCD/CMOS photodetector. The monitoring of full air space with high orientation accuracy without scanning is the most significant advantage of that. However, this detecting system could not identify laser wavelength and it is adverse to determine the type of laser threats (McAulay 2011; Ying et al. 2009; Dong and Wang 2012; Xie et al. 2013). Recently, a new method is proposed to recognize both incident angle and laser wavelength in a large field of view (FOV) with non-mechanical scanning. The system is a combination of a fisheye lens and a sinusoidal amplitude grating. The directional resolution of the system firstly depends on the angular accuracy of hardware cha
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