Optical communication systems using Fabry-Perot cavities

An optical communication system comprising a first single-electrode distributed feedback laser diode,

• a first modulation means coupled to shift the frequency of the optical signal from said first laser diode between a first frequency and a second frequency, said first and second frequencies representing logic ones and zeros, to provide frequency-shift keyed modulation of the optical signal from said laser diode, where the differential of frequency between the ones and zeros (fd) divided by the modulation frequency (B) is equal to or greater than one,
• a second single-electrode distributed feedback laser diode,
• a second modulation means coupled to shift the frequency of the optical signal from said second laser diode between a third frequency and a fourth frequency, said third and fourth frequencies representing logic ones and zeros, to provide frequency-shift keyed modulation of the optical signal from said laser diode, where the differential of frequency between the ones and zeros (fd) divided by the modulation frequency (B) is greater than are,
• an optical fiber for transmitting the frequency-shift keyed optical signals from said first and second laser diodes to a remote location,
• a first demodulator coupled to said optical fiber at said remote location, said demodulator having a passband which passes one of said frequencies from said first modulation means and blocks the other of said frequencies, and
• a second demodulator coupled to said optical fiber at said remote location, said demodulator having a passband which passes one of said frequencies from said second modulation means and blocks the other of said frequencies.