Sources of intensity noise in wide-band UHF analog optical communication systems: Their elimination and reduction

The feasibility of high-speed multimode analog fiber-optic transmission was examined by conducting a wide range of experiments on a fiber-optic link. The experimental link consisted of a laser transmitter with pigtail terminated in a fiber-optic connector, 240 m of fiber, and a detector with a pigtail terminated in a connector. Four different laser transmitters were used in the link. Changes in the amplitude and frequency separation of peaks in the noise spectrum due to optical feedback from the fiber-optic connectors and detector surface were investigated. Results indicated that index-matching gel placed in the connector nearest the transmitter reduced the near-end reflection peaks. Gel placed in both connectors increased the far-end reflection peaks when a conventional detector was used. However, these far-end reflection peaks were eliminated by using an angled detector which had a surface tilted at an angle relative to the end of the pigtail fiber. A heavily-moded laser showed substantially smaller reflection peaks and less change in the noise floor due to connector/fiber vibration than a laser with 1 or 2 modes.