Hermetic Photonic Packaging

          Rapid development of optical communications causes a need to provide a variety of optical devices performing different functions. To protect the devices from the adverse environmental effects, they are packaged into hermetically sealed metal housings (packages). It is obvious that each optical fiber guiding a signal into the package or out of it should be hermetically sealed, and sealing a glass part in a metal wall is a very complicated problem. An optical fiber has a core and a cladding layer made of silica glass, and also an outside buffer layer made of acrylic and intended to protect the cladding layer and provide a degree of mechanical flexibility to the fiber.

          The existing sealing methods require multiple production steps. They include stripping the buffer layer from the fiber, coating it with a metal ferrule consisting of two halves, and soldering the ferrule to the fiber by low-temperature soldering. After that, the fiber covered with the ferrule is inserted into an aperture in the wall of metal package, and solder or epoxy is used to hermetically attach the ferrule outside surface to the wall. Sealing a fiber ribbon cable is even more complicated because the operations similar to the described ones should be performed on a plurality of fibers.

          The proposed method based on electroforming requires much less production steps and thereby allows an essential decrease in the manufacturing cost. After the buffer layer is stripped from a length of fiber to expose the corresponding length of cladding one, a seamless metallic layer is deposited on the latter hermetically sealing the cladding layer and forming a ferrule with a continuous hermetically sealable outside surface. Moreover, stress relief joints are simultaneously formed between the ferrule and the contiguous parts of the buffer layer. Then the ferrule is inserted into the package aperture and soldered to form a hermetic joint. The same technology is applicable to fiber ribbon cables of any shape.


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