| 摘要 |
An optical demodulator in which a local oscillator reference signal and a frequency shift keyed modulated input signal are optically combined by means of an optical multiport junction (e.g. fig. 2). These signals are detected to produce phase-diverse electrical signals (I and Q; A, B and C) at beat frequency and electrically processed (fig. 3 or 4) to provide a demodulated signal. The electrical processing circuitry is phase discriminating and thus produces a signal in which the amplitude is dependent upon the lead/lag phase relationship of the detected signals (I and Q; A, B and C). The local oscillator (3) runs at a frequency midway between the FSK signal tones so that the lead or lag of phase is directly related to the frequency shift coding. The phase discriminant signal processing may be performed using. |
