Probability of modal noise in single-mode lightguide systems

The probability of introducing modal noise in a single-mode lightguide system with a short length of straight depressed-cladding fiber between high-loss splices is investigated. The cumulative probability of modal noise is useful for evaluating the risk involved in violating the fiber minimum splicing length (the fiber length for zero probability of modal noise). The probability of encountering modal noise is less than 0.6 percent for fiber lengths as short as 3 m with splice losses of 0.5 dB. For this example, the minimum laser wavelength is 1285 nm and the maximum cutoff wavelength is 1330 nm measured on a 5-m length of fiber with 50-cm diameter loops. The results are also valid for depressed-cladding fiber measured by CCITT recommendations.