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US 6,687,465 B2Granted
FM modulator
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsMasaru Fuse, Kuniaki Utsumi, Satoshi Furusawa
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AssigneeMatsushita Electric Industrial Co., Ltd.
InventorsMasaru Fuse, Kuniaki Utsumi, Satoshi Furusawa
Estimating the term…
A branch portion 101 branches an inputted electrical signal into an in-phase signal and an opposite phase signal which have an opposite relation as to a phase. A first FM laser 104 converts the in-phase signal into an optical frequency-modulated signal (a first optical signal) having a center wavelength λ1 and then outputs the resultant signal. A second FM laser 105 converts the opposite phase signal into an optical frequency-modulated signal (a second signal) having a center wavelength λ2 and then outputs the resultant signal. The two optical signals are combined and then inputted into an optical-electrical converting portion 106. The optical-electrical converting portion 106 subjects the inputted optical signals to optical heterodyne detection by its square-law detection characteristic, and outputs a beat signal between the two optical signals which is a wide-band FM signal at a frequency corresponding to a wavelength difference Δλ(=|λ1−λ2|) between the first optical signal and the second optical signal. It is thus possible to increase frequency deviation of the outputted FM signal and thus greatly improve a CNR.
An FM modulator comprising:
An FM modulating method comprising:
A video transmission system comprising:
Dependencies are inferred from the claim text.
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From the US filing history. Foreign family members aren’t listed.
Term ended 26 Aug 2018 (estimated)
1. Field of the Invention
The present invention relates to FM modulators, and more specifically to an FM modulator for generating a wide-band frequency-modulated signal (hereinafter referred to as an FM signal) using a semiconductor laser and optical heterodyne detection.
2. Description of the Background Art
FIG. 1 is a block diagram showing the structure of an FM modulator according to a first embodiment of the present invention;
FIGS. 2a to 2c are diagrams for describing operation of the first embodiment;
FIG. 3 is a block diagram showing the structure of an FM modulator according to a second embodiment of the present invention;
(First Embodiment)
FIG. 1 is a block diagram showing the structure of an FM modulator according to a first embodiment of the present invention. In FIG. 1, the FM modulator of the present embodiment includes a signal source 100, a branch portion 101, a first frequency modulation laser (hereinafter referred to as a first FM laser) 104, a second frequency modulation laser (hereinafter referred to as a second FM laser) 105, and an optical-electrical converting portion 106. Further, as required, the FM modulator includes first and second driving amplifiers 102 and 103.
Described next is operation of the embodiment shown in FIG. 1. The signal source 100 outputs an electrical signal which is an original signal for FM modulation. The branch portion 101 branches the electrical signal outputted from the signal source 100 into a phase-uninverted signal (in-phase signal) and a phase-inverted signal (opposite phase signal) and outputs each of these signals. The first and second driving amplifiers 102 and 103 are inserted as required between the branch portion 101 and the first FM laser 104 and between the branch portion 101 and the second FM laser 105, respectively, when the magnitude of the in-phase signal and the opposite phase signal outputted from the branch portion 101 is not sufficient with respect to the required frequency deviation of the first or the second FM lasers 104 and 105, and the like. The first and second driving amplifiers 102 and 103 amplify the in-phase signal and the opposite phase signal outputted from the branch portion 101, and then outputs these signals to the first and second FM lasers 104 and 105, respectively.