| 摘要 |
<p>A method and apparatus for converting a frequency modulated lightwave into an electrical signal that is proportional to instantaneous frequency deviations of the frequency modulated lightwave. The frequency modulated lightwave is amplified by an amount equal to or greater than a desired FM processing gain to provide an amplified frequency modulated lightwave. The amplified lightwave is filtered to restrict amplifier noise added to the frequency modulated lightwave to provide a filtered lightwave. The amplitude of the filtered lightwave is limited to remove unwanted amplitude fluctuations to provide a limited lightwave. The limited lightwave is split into a first split lightwave and a second split lightwave. The second split lightwave is delayed relative to the first split lightwave, to provide a delayed second split lightwave. The delayed second split lightwave is combined with the first split lightwave to provide: (1) a sum of first split lightwave fields and delayed second split lightwave fields, and (2) a difference of the first split lightwave fields and the delayed second split lightwave fields, the splitting, delaying and combining providing the sum and the difference having fields with parallel polarizations. The sum is detected by a first photodetector and the difference is detected by a second photodetector, the first photodetector and second photodetector being connected in series with a common terminal therebetween, the common terminal providing to a following amplifier a difference current that is proportional to a difference between first photodetector current and second photodetector current, the difference current being proportional to instantaneous frequency deviation of the frequency modulated lightwave.</p> |
