| 摘要 |
PURPOSE:To reduce the phase noise of a semiconductor laser light by performing demodulation by taking the product between a carrier component with the light amplitude modulated and a 1st sidewave component and to enlarge the 1st sidewave component without producing a high harmonic component when the light is modulated. CONSTITUTION:A signal light A from a semiconductor laser 10 is amplitude- modulated by an external modulator 20 according to a fs frequency division multiplex signal and a signal light B is outputted. An optical coupler 30 couples the signal light B with a local light emission C from a semiconductor laser 40 for local oscillation. A light receiving circuit 50 outputs an intermediate frequency signal of the two signal lights. A band-pass filter 60 extracts a carrier component obtained by a light amplitude modulation. A band-pass filter 70 extracts the 1st sidewave component. A mixer 80 takes the product of both components, outputting the frequency division multiplex signal with the frequency fs. In short, the carrier component and the phase noise of the light contained in the first sidewave component are the same. When the product of the both signals are taken, the phase noise of the light is cancelled and the original signal can be modulated. |
