Microwave subcarrier generation for fiber optic systems
First Claim
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1. A method of optically transmitting a plurality of information signals, comprising the steps of:
- generating a plurality of harmonics from a single oscillator of prespecified fundamental microwave frequency to provide an input harmonic spectrum;
providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum;
filtering each of said replicate spectrums to selectively extract therefrom a respective harmonic for use as a microwave subcarrier signal;
modulating each of said subcarrier signals with a respective one of said information signals;
summing said modulated subcarrier signals to form a composite optical signal; and
optically transmitting said composite optical signal.
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Abstract
A method for generating a large number of stable microwave frequency components for wideband lightwave distribution networks is shown. A single oscillator is used at a transmitter to provide all of the required subcarriers. The subcarriers are modulated by high data rate channels and then multiplexed for transmission over a fiber optic line. At a receiver, all of the tuning frequencies required for channel selection are generated by a single oscillator.
201 Citations
32 Claims
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1. A method of optically transmitting a plurality of information signals, comprising the steps of:
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generating a plurality of harmonics from a single oscillator of prespecified fundamental microwave frequency to provide an input harmonic spectrum; providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; filtering each of said replicate spectrums to selectively extract therefrom a respective harmonic for use as a microwave subcarrier signal; modulating each of said subcarrier signals with a respective one of said information signals; summing said modulated subcarrier signals to form a composite optical signal; and optically transmitting said composite optical signal. - View Dependent Claims (2, 3, 4)
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5. A method of receiving an optical signal having a plurality of modulated microwave subcarrier channels and recovering the baseband signal of a selected channel, comprising the steps of:
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generating a plurality of harmonics from a single oscillator of prespecified fundamental frequency to provide an input harmonic spectrum; generating a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; filtering each of said replicate spectrums to selectively extract therefrom a respective mixing harmonic; detecting said optical signal to provide a corresponding electrical signal; heterodyne detecting said electrical signal with said selected mixing harmonics to produce an intermediate frequency signal; recovering a carrier frequency signal from said intermediate frequency signal; and demodulating said intermediate frequency signal using said carrier frequency signal to recover the baseband signal of said intermediate frequency signal. - View Dependent Claims (6, 7, 8)
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9. A system for optically transmitting a plurality of information signals, comprising:
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means for generating a plurality of harmonics from a single oscillator of prespecified fundamental frequency to provide an input harmonic spectrum; means for amplifying said input harmonic spectrum; means responsive to said input harmonic spectrum for providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; first filtering means adapted to receive said set of replicate harmonic spectrums and selectively extract from each replicate spectrum a respective harmonic for use as a microwave subcarrier; modulating means coupled to said first filtering means for modulating each of said microwave subcarriers with a respective one of said information signals; second filtering means for filtering each of said modulated subcarriers; means for summing said modulated subcarrier signals to form a composite optical signal; and means for optically transmitting said composite optical signal. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A system for receiving an optical signal having a plurality of modulated microwave subcarrier channels and recovering the baseband information signal of a selected channel, comprising:
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photodetection means responsive to said optical signal for providing a corresponding microwave spectrum; means for amplifying said microwave spectrum; means for generating a plurality of harmonics from a single oscillator of prespecified fundamental frequency to provide an input harmonic spectrum; means responsive to said input harmonic spectrum for providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; first filtering means responsive to a voltage control signal and adapted to receive one of said replicate harmonic spectrums for filtering out a first selected harmonic from said one replicate harmonic spectrum; first heterodyne detection means responsive to said amplified microwave spectrum and said first selected harmonic for downconverting the spectrum of said selected subcarrier channel to a first intermediate frequency; second filtering means for bandpass filtering said first intermediate frequency spectrum; third filtering means coupled to said means for providing replicate harmonic spectrums for filtering out a second selected harmonic from another of said replicate harmonic spectrums; second heterodyne detection means responsive to said second selected harmonic and said bandpass filtered spectrum for downconverting said first intermediate frequency spectrum to a second intermediate frequency; carrier recovery means coupled to said second heterodyne detection means for generating a sinusoid synchronized with the carrier frequency of said second intermediate frequency spectrum; and demodulation means in combination with said carrier recovery means for synchronously detecting and recovering the baseband signal from said second intermediate frequency spectrum. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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23. A system for receiving an optical signal having a plurality of modulated microwave subcarrier channels and recovering the baseband signal from a selected channel, comprising:
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photodetection means responsive to said optical signal for providing a corresponding microwave spectrum; means for amplifying said microwave spectrum; means for generating a plurality of harmonics from a single oscillator of prespecified fundamental frequency to provide an input harmonic spectrum; means responsive to said input harmonic spectrum for providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; first filtering means adapted to receive said replicate harmonic spectrums for filtering therefrom a selected first and second harmonic; heterodyne detection means responsive to said first harmonic and said amplified microwave spectrum for downconverting the spectrum of said selected channel to a first intermediate frequency and responsive to said second harmonic for downconverting said first intermediate frequency; second filtering means for bandpass filtering said first intermediate frequency spectrum prior to downconversion to said second intermediate frequency; carrier recovery means coupled to said heterodyne detection means for generating a sinusoid synchronized with the carrier frequency of said second intermediate frequency spectrum; and demodulation means in combination with said carrier recovery means for synchronously detecting and recovering the baseband signal from said second intermediate frequency spectrum. - View Dependent Claims (24, 25, 26, 27)
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28. A system for optically transmitting a plurality of information signals and receiving a selected one of said information signals, comprising:
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means for generating a first plurality of harmonics from a single oscillator of prespecified fundamental frequency to provide a first harmonic spectrum; means responsive to said first harmonic spectrum for providing a set of first replicate harmonic spectrums each having a frequency spectrum identical to that of said first harmonic spectrum; filtering means adapted to receive said set of first replicate harmonic spectrums and filter out from each first replicate harmonic spectrum a respective harmonic to serve as a subcarrier; means for modulating each of said subcarriers with a respective one of said information signals; means for summing said modulated subcarriers to form a composite optical signal; means for optically transmitting said composite optical signal; photodetection means responsive to said transmitted optical signal for providing a corresponding electrical signal; means for generating a second plurality of harmonics from a single oscillator of said prespecified fundamental frequency to provide a second harmonic spectrum; means responsive to said second plurality of harmonics for providing a set of second replicate harmonic spectrums each having a frequency spectrum identical to that of said second harmonic spectrum; filtering means adapted to receive each of said second replicate harmonic spectrums and selectively filter out from each second replicate harmonic spectrum a respective mixing harmonic; heterodyne detection means responsive to said electrical signal and said mixing harmonics for downconverting a selected subcarrier signal to an intermediate frequency; carrier recovery means coupled to said heterodyne detection means for generating a sinusoid synchronized with the carrier frequency of said intermediate frequency spectrum; and demodulation means responsive to said sinusoid and said intermediate frequency signal for synchronously detecting and recovering the baseband signal from said intermediate frequency signal. - View Dependent Claims (29, 30, 31)
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32. A system for optically transmitting a plurality of information signals, comprising:
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means for generating a plurality of harmonics from a single oscillator of pre-specified fundamental microwave frequency to provide an input harmonic spectrum; means responsive to said input harmonic spectrum for providing a set of replicate harmonic spectrums each having a frequency spectrum identical to that of said input harmonic spectrum; filtering means adapted to receive said set of replicate harmonic spectrums and selectively filter out from each replicate harmonic spectrum a respective harmonic to serve as a microwave subcarrier signal; means for modulating each of said subcarriers with a respective one of said information signals; means for summing said modulated subcarriers to provide a composite optical signal; and means for optically transmitting said composite optical signal.
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Specification