Title:
METHOD AND APPARATUS FOR SELECTING SIGNAL
Document Type and Number:
Japanese Patent JPS63154922
Kind Code:
A
Abstract:
PURPOSE:To dispense with a local oscillator and the adjustment of reference light frequency and to simplify the extraction of a signal, by a method wherein output lights different in frequency are respectively branched into two and one branched lights are modulated by signals different from each other to be synthesized while the other branched lights are set as reference lights and only the reference lights are selected and synthesized with the synthesized light to perform homodyne detection. CONSTITUTION:The output lights different in frequency of light oscillators 2(2a-2n) are branched by branching devices 3(3a-3n) and one branched lights are optically modulated on the basis of signal waves 1(1a-1n) as carrier waves by light modulators 4(4a-4n) to be synthesized by a synthesizer 5a. The light having the same frequency as the carrier wave of a light signal desired to be selected from the synthesized light is selected from signals 10(10a-10n) by a selection circuit 8 to obtain reference light 18. The synthesized light 9 and the reference light 18 are synthesized by a synthesizer 5b to be subjected to homodyne detection by a homodyne detector 6 and the selected signal is outputted as an electric signal 7. In this constitution, the coherence of the carrier wave of the synthesized light 9 and the reference light is sufficiently low and, when phase difference is slightly shifted from pi, the selected signal is obtained as the output of the homodyne detector 6. Even when the phase difference is pi, the phase of the carrier wave or that of the reference light is adjusted and the phase difference between both of them can be set to the optimum value.
Inventors:
TSUSHIMA HIDEAKI
TAKASE MASAHIKO
IMOTO KATSUYUKI
TAKASE MASAHIKO
IMOTO KATSUYUKI
Application Number:
JP30123386A
Publication Date:
June 28, 1988
Filing Date:
December 19, 1986
Export Citation:
Assignee:
HITACHI LTD
International Classes:
G01J9/00; G01J3/12; H04B10/25; H04B10/516; H04B10/61; H04J14/00; H04J14/02; (IPC1-7): G01J3/12; H04B9/00
Attorney, Agent or Firm:
Katsuo Ogawa