Abstract: Present-day warfare includes extensive use of laser-based devices and laser-guided weapons. This large-scale use of laser-based systems has made all platforms more vulnerable to precision attack by laser-guided munitions (LGM). Such a situation emphasises the importance of timely detection and recognition of laser threats. This necessitates that friendly platforms are equipped with a suitable laser-warning sensor that would provide timely information about the incoming laser threat with a high level of angle-of-arrival accuracy so that suitable countermeasure action can be initiated against it. This paper (part I of II) discusses the design aspect of the opto-electronic front end of a laser-warning system (LWS). It highlights the technological challenges in the design of the opto-electronic front end of the LWS and gives a brief description of a unique design using an array of discrete photodiodes. The results are analysed to assess its suitability for a laser-warning system having angular accuracy of ±3º and field of view from –45º to +45° in azimuth and –10° to +25° in elevation.