DEVICE AND METHOD FOR MODAL SEPARATION AND COMBINATION IN AN OPTICAL FIBER INTRUSION DETECTION SYSTEM

Abstract

Apparatus and a corresponding method for launching two light beams into an optical fiber as two separate modal groups, and for separating light emanating from a fiber into two modal groups. The apparatus includes first and second lenses and a spatial modal filter in the form of a reflective disc disposed coaxially between the two lenses. When the apparatus is used as a launching device, the first lens operates to collimate light from a source of light modulated by a data signal and intended for launching as lower-order modes. The lower-order-mode light is reflected from the filter and focused by the first lens into an output fiber. The second lens collimates light from a source of light indicative of a monitor signal to be transmitted in the form of higher-order modes. This light is partially blocked by the spatial modal filter, then focused into the output fiber by the first lens. The fiber constrains this light to enter the output fiber at angles of incidence greater than some predetermined threshold angle. When the apparatus is used as a modal separator, the first lens collimates light from an input fiber, and the modal filter reflects only the light corresponding to the lower-order modes, allowing the higher-order modes to pass into the second lens and be focused into an output fiber. The reflected lower-order modes are focused by the first lens into another output fiber.

Source: Google Patents

35 USC §181 Secrecy Order

Inventor

• 1CHARLES K. ASAWA

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