FIBER INTENSITY NOISE IN LIGHTWAVE VSB-AM CATV SYSTEMS THAT EMPLOY A SMALL NUMBER OF TRANSMISSION CHANNELS

In optical transmission systems using the VSB-AM method, there is the problem of noise generation caused by interference between the main si gnal and reflections from fiber-end connectors or reflections caused b y Rayleigh scattering inside the fiber. To date, fiber transmission no ise has been investigated in transmission systems with many channels ( more than 40). In such large channel transmission systems, it is possi ble to approximate the fiber noise spectrum by a Gaussian distribution and it can be taken to remain constant inside the transmission bandwi dth. However, in master antenna television systems used as countermeas ures against obstacles in wave propagation or upstream lines, etc., th e number of transmission channels is a maximum of 10, and such approxi mation is not possible. In this paper, fiber transmission noise is inv estigated theoretically and experimentally when the number of transmis sion channels is small. It is found that in a transmission bandwidth o f 90-300 MHz, the fiber noise level increases as the carrier frequency is increased; its difference from that in the low frequency region is approximately 5-6 dB.