Fiber optic system for transmission of video signals by pulse-frequency-modulation

A wideband fiber optic system for optically transmitting a video analog signal over a long distance comprising:

• waveform generating means responsive to an input video analog signal having a given amplitude and a given frequency spectrum for producing a stream of narrow separated electrical pulses of constant width wherein the pulse stream has a variable repetition frequency and the repetition frequency is varied according to the amplitude of said analog signal, the waveform generating means includes means for generating a periodic wave of variable repetition frequency wherein the repetition frequency of said periodic wave is varied according to the amplitude of said analog signals, the periodic waveform generating means being a voltage controlled oscillator that produces a square wave and pulse means coupled to said periodic waveform generating means for producing a single, relatively narrow electric pulse at the same point in each cycle of said periodic wave, the pulse means being adapted to be triggered at each positive-going edge of said square wave;
• wideband transmitting means coupled to said waveform generating means for converting said electrical pulses into optical pulses and transmitting said optical pulses, the transmitting means being an injection laser diode coupled to said pulse means for generating relatively narrow pulses of optical flux in response to said electrical pulses;
• a jacketed single optical fiber coupled to said transmittiing means for conducting said optical pulses;
• wideband receiving means coupled to said jacketed single optical fiber for receiving said optical pulses and converting said optical pulses into detected electrical pulses, the receiving means includes an avalanche photodetector coupled to the jacketed single optical fiber and responsive to said optical pulses for generating electrical current pulses in response thereto, means coupled to the avalanche photodetector for amplifying and converting said electrical current pulses into said detected electrical pulses, gain-control amplification means coupled to said amplifying means for further amplifying said detected electrical pulses and for maintaining the amplitude of said detected electrical pulses at a predetermined level and peak detection means coupled between the output and an input of said gain-control amplification means;
• and
• discriminating means coupled to said receiving means and responsive to said detected electrical pulses for generating an output video analog signal having a given amplitude and a given frequency spectrum, the amplitude of said output analog signal varying according to the repetition frequency of said detected electrical pulses, whereby said output analog signal corresponds to said input analog signal, the discriminating means includes comparator means coupled to said receiving means for comparing the amplitude of each of said detected electrical pulses with a predetermined electrical level, pulse regenerating means coupled to said comparator means for producing an electrical pulse of predetermined characteristics whenever the amplitude of a detected pulse exceeds said predetermined electrical level, and filter means coupled to said pulse regenerating means and having a bandwidth equal to the bandwidth of said analog signals for rejecting high frequency components of said predetermined pulses and thereby producing said output analog signal.