Low-loss high-impedance integrated fiber-optic tap.

A three-port passive optical tap which utilizes cladding modes in a single-mode fiber rather than core modes for tapped power is discussed. Cladding modes are induced by microbending so that a controlled continuously adjustable amount of power may be transferred from the core to the cladding. The cladding modes are tapped with low excess loss by a circularly symmetric notch etched into the cladding. The tapped light is collected by an integrated photodetector comprised of a p-n junction doped on the inside surface of a cylindrical hole etched completely through the chip. This geometry allows an optical fiber to be threaded through the chip without interruption and enables the integrated photodetector to efficiently capture the light which is emitted by the fiber tap situated within the hollow cylindrical well. This tapping technique has the unique property of exhibiting losses which reduce in proportion to the tapped signal. The implementation of this tapping technique in the novel integration of photodetector and fiber tap provides mechanical stability and compatibility with current VLSI technology, which may provide for assimilation of this device into existing telecommunication system designs.