Digital transmission of TV signals with a fiber-optic heterodyne transmission system

The laser transmitter (Hitachi HLP 1400) radiates at a wavelength of 830 nm into the transmission fiber, which is a single-polarization type and 280-m long. It is spliced to a single-polarization fiber coupler at the receiver input. In the coupler the received light is added to the local laser light and fed to the APD mixer to generate the intermediate frequency of 1.5 GHz. After filtering in a bandpass with a 900-MHz bandwidth the IF power is divided into the carrier tracking branch and demodulation circuit. The IF spectrum shows lines at both sides of the main carrier according to the subcarrier frequency and the modulation-induced line broadening. To avoid phase jitter, the bit rate is a subharmonic of the subcarrier frequency. Bit-error rate was measured at better than 10-9. Because of the low bit-error rate, the transmitted TV signal produced an excellent picture quality.