Dual fiber laser initiator and optical telescope

Abstract

The present invention discloses an improved apparatus for performing safe and reliable built-in testing (BIT) of a laser initiated ordnance device. The system transmits light energy from a laser through optical fibers to achieve initiation of pyrotechnic or explosive charges and other ordnance. In the preferred embodiment, a separate BIT return fiber is included in the system in addition to the energy transmission fiber. The invention also incorporates a 'telescope' comprising a pair of gradient-index (GRIN) rod lenses in series to first collimate and then reconcentrate light emitted by the energy transmitting fiber, while reflecting part of the light to an image at the face of the BIT fiber. Alternatively, an arrangement using a pair of aspheric silica lenses can be substituted for the GRIN lenses. The fraction of the light reflected to the BIT fiber can be controlled by specifying the reflectance at one of the lens end surfaces. The ratio of the output image size to the transmitting fiber core size (the magnification) can be controlled by appropriately selecting the focal lengths of the two lenses in the telescope. The invention also provides a simple means of making a spot size reduction (for example, from 100 microns down to 50 microns) without requiring alignment, and of adjusting the BIT amplitude response by adjusting the reflectance back from the second surface of the first lens. Because the combined pair of GRIN or other lenses has a magnification of less than unity, substantial power savings can also be achieved.