US3636356A
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Apparatus and method for eliminating frequency modulation from modulated light
Assignee: AT&T Inc
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Filing: 1968-12-27
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Granted: 1972-01-18
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Expires: 1988-12-27
Abstract
Abstract The proposed apparatus and method removes the frequency modulation from an incident light beam having an arbitrary combination of amplitude and frequency modulation, and produces a purely amplitude modulated beam with an envelope simply related to the envelope of the incident beam. The apparatus comprises a third order nonlinear system for producing an output signal with amplitude proportional to the amplitude product of the square of the incident beam and a second purely sinusoidal local oscillator beam. This output beam contains the amplitude modulation information of the incident beam but does not contain any of the frequency modulation. The third order nonlinear system may include simply a single crystal such as strontium titanate or alternatively a more complex system of phase-matched difference and sum frequency generators.
Inventors
- 👤 Joseph A Giordmaine
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 08:13
CPC Classifications
G; G02; G02F; G02F1/00; G02F1/35; G02F1/353; G02F1/3534; G02F2/00; G02F2/02
Claims Analysis
Total Claims: 29
Claim 1
Independent Claim
168 words
Apparatus for separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency and amplitude modulation comprising means for generating an unmodulated sinusoidal second optical signal of frequency omega 2, means for combining said first and second signals so as to produce the sum signal thereof, and third-order nonlinear means disposed to receive said sum signal for producing as a third-order nonlinear output signal the intermodulation product at frequency omega 2 and with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said third-order nonlinear means including at least one nonlinear optical device oriented and adapted to suppress inherently all other intermodulation products and including filtering means for blocking the remnants of the input signals in the output of said nonlinear optical device, whereby the output signal of said third-order nonlinear means is amplitude modulated in accordance with the amplitude modulation of the first signal but free of the frequency modulation of said first signal.
Claim 2
Dependent Claim
168 words
Apparatus for separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency and amplitude modulation comprising means for generating an unmodulated sinusoidal second optical signal of frequency omega 2, means for combining said first and second signals so as to produce the sum signal thereof, and third-order nonlinear means disposed to receive said sum signal for producing as a third-order nonlinear output signal the intermodulation product at frequency omega 2 and with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said third-order nonlinear means including at least one nonlinear optical device oriented and adapted to suppress inherently all other intermodulation products and including filtering means for blocking the remnants of the input signals in the output of said nonlinear optical device, whereby the output signal of said third-order nonlinear means is amplitude modulated in accordance with the amplitude modulation of the first signal but free of the frequency modulation of said first signal.
Claim 3
Dependent Claim
92 words
The apparatus of claim 1 wherein said third-order nonlinear means comprises means for generating a third signal of frequency equal to the difference of the frequencies of said first and second signals and proportional to the amplitude product of the said first and second signals, and means for generating a fourth signal of frequency omega 2 and with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 4
Dependent Claim
18 words
The apparatus of claim 2 wherein said means for generating said fourth signal comprises a sum frequency generator.
Claim 5
Dependent Claim
86 words
The apparatus of claim 1 wherein said third order nonlinear means comprises means for generating a third signal of frequency ( omega 2+ omega 1) and with amplitude proportional to the amplitude product of said first and second signals, and means for generating a fourth signal of frequency omega 2 and with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 6
Dependent Claim
18 words
The apparatus of claim 4 wherein said means for generating said fourth signal comprises a difference frequency generator.
Claim 7
Dependent Claim
187 words
The apparatus of claim 1 wherein said third order nonlinear means comprises a difference frequency generator, said sum signal being applied to the input thereof so as to generate at its output the sum of said first and second signals plus a third signal of frequency equal to the difference of the frequencies of said first and second signals and with amplitude proportional to the sum of the amplitude product of said first and second signals, a first frequency filter for rejecting said second signal at frequency omega 2, but transmitting said first and third signals, a sum frequency generator, said first and third signals transmitted by said first filter being applied to the input thereof so as to generate at its output the sum of said first and third signals plus a fourth signal at frequency omega 2 proportional to the amplitude product of said first and third signals, and a frequency filter for separating said fourth signal from said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 8
Dependent Claim
72 words
The apparatus of claim 3 wherein said difference frequency generator comprises a first noncentrosymmetric crystal set at the phase-matching angle to the direction of propagation of the optical signal applied thereto so as to generate a difference frequency signal, and said sum frequency generator comprises a second noncentrosymmetric crystal set at phase-matching angle to the direction of propagation of the optical signals applied thereto so as to generate a sum frequency signal.
Claim 9
Dependent Claim
71 words
The apparatus of claim 5 wherein said difference frequency generator comprises a first noncentrosymmetric crystal set at the phase-matching angle to the direction of propagation of the optical signal applied thereto so as to generate a difference frequency signal, and sum frequency generator comprises a second noncentrosymmetric crystal set at phase-matching angle to the direction of propagation of the optical signals applied thereto so as to generate a sum frequency signal.
Claim 10
Dependent Claim
72 words
The apparatus of claim 6 wherein said difference frequency generator comprises a first noncentrosymmetric crystal set at the phase-matching angle to the direction of propagation of the optical signal applied thereto so as to generate a difference frequency signal, and said sum frequency generator comprises a second noncentrosymmetric crystal set at phase-matching angle to the direction of propagation of the optical signal applied thereto so as to generate a sum frequency signal.
Claim 11
Dependent Claim
53 words
The apparatus of claim 7 wherein said first signal is at a waveleNgth of 1.06 Mu , said second signal is at a wavelength of 1.15 Mu and said first and second crystals comprise lithium niobate set at about a 72* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 12
Dependent Claim
53 words
The apparatus of claim 8 wherein said first signal is at a wavelength of 1.06 Mu , said second signal is at a wavelength of 1.15 Mu and said first and second crystals comprise lithium niobate set at about a 72* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 13
Dependent Claim
53 words
The apparatus of claim 9 wherein said first signal is at a wavelength of 1.06 Mu , said second signal is at a wavelength of 1.15 Mu and said first and second crystals comprise lithium niobate set at about a 72* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 14
Dependent Claim
54 words
The apparatus of claim 7 wherein said first signal is at a wavelength of 1.06 Mu , said second signal is at a wavelength of 6,943 A., and said first and second crystals comprise ammonium dihydrogen phosphate set at about a 44* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 15
Dependent Claim
54 words
The apparatus of claim 8 wherein said first signal is at a wavelength of 1.06 Mu , said second signal is at a wavelength of 6,943 A., and said first and second crystals comprise ammonium dihydrogen phosphate set at about a 44* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 16
Dependent Claim
54 words
The apparatus of claim 9 wherein said first signal is at a wavelength of 1.06 Mu , said second signal is at a wavelength of 6,943 A., and said first and second crystals comprise ammonium dihydrogen phosphate set at about a 44* phase-matching angle to the direction of propagation of the signals applied thereto.
Claim 17
Dependent Claim
132 words
The apparatus of claim 1 where said third-order nonlinear means comprises a third-order nonlinear medium, the sum of said first and second signals being applied to the input thereof so as to generate directly a third signal at frequency omega 2 and with amplitude proportional to the amplitude product of said second signal and the square of said first signal, the output of said medium also containing said first and second signals, a frequency filter for rejecting said first signal and transmitting said second signal and said third signal both of which are at frequency omega 2, but are of different polarizations, and a polarizing filter for transmitting only said third signal which contains the amplitude modulation of said first signal but is free of the frequency modulation of said first signal.
Claim 18
Dependent Claim
32 words
The apparatus of claim 16 wherein said medium comprises a strontium titanate crystal and said second signal is polarized at an angle of about 45* to the polarization of said first signal.
Claim 19
Dependent Claim
141 words
The apparatus of claim 1 wherein said third-order nonlinear means comprises a third-order nonlinear isotropic medium, the sum of said first and second signals being applied to the input thereof so as to generate directly a third signal at frequency omega 2 and with amplitude proportional to the amplitude product of said second signal and the square of said first signal, the output of said medium also containing said first and second signals, a frequency filter for rejecting said first signal and transmitting said second signal and said third signal both of which are at frequency omega 2, and means for causing the destructive interference of the component of said second signal in said output, thereby leaving only said third signal which contains the amplitude modulation of said first signal but is free of the frequency modulation of said first signal.
Claim 20
Independent Claim
160 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency and ampliTude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signals so as to produce the sum signal thereof, directing said sum signal into apparatus producing as a third-order nonlinear output signal the intermodulation product at frequency omega 2 with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said apparatus including at least one nonlinear optical device oriented and adapted to suppress inherently all other intermodulation products and including filtering means for blocking the remnants of the input signals in the output of said nonlinear optical device, whereby the output signal of said third-order nonlinear device is amplitude modulated in accordance with the amplitude modulation of said first signal but free of the frequency modulation of said first signal.
Claim 21
Independent Claim
160 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency and ampliTude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signals so as to produce the sum signal thereof, directing said sum signal into apparatus producing as a third-order nonlinear output signal the intermodulation product at frequency omega 2 with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said apparatus including at least one nonlinear optical device oriented and adapted to suppress inherently all other intermodulation products and including filtering means for blocking the remnants of the input signals in the output of said nonlinear optical device, whereby the output signal of said third-order nonlinear device is amplitude modulated in accordance with the amplitude modulation of said first signal but free of the frequency modulation of said first signal.
Claim 22
Independent Claim
155 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signals so as to produce the sum signal thereof, directing said sum signal into a difference frequency generator so as to generate a third signal at frequency equal to the difference of the frequencies of said first and second signals, and with amplitude proportional to the amplitude product of said first and second signals, and directing said first and third signals into a sum frequency generator so as to generate a fourth signal at frequency omega 2 with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 23
Independent Claim
155 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signals so as to produce the sum signal thereof, directing said sum signal into a difference frequency generator so as to generate a third signal at frequency equal to the difference of the frequencies of said first and second signals, and with amplitude proportional to the amplitude product of said first and second signals, and directing said first and third signals into a sum frequency generator so as to generate a fourth signal at frequency omega 2 with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 24
Independent Claim
147 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signal so as to produce the sum signal thereof, directing said sum signal into a sum frequency generator so as to generate a third signal at frequency omega 1+ omega 1 and with amplitude proportional to the amplitude product of said first and second signals, and directing said first and third signals into a difference frequency generator so as to generate a fourth signal at frequency omega 2 and with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 25
Independent Claim
147 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, combining said first and second signal so as to produce the sum signal thereof, directing said sum signal into a sum frequency generator so as to generate a third signal at frequency omega 1+ omega 1 and with amplitude proportional to the amplitude product of said first and second signals, and directing said first and third signals into a difference frequency generator so as to generate a fourth signal at frequency omega 2 and with amplitude proportional to the amplitude product of said first and third signals, said fourth signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 26
Independent Claim
114 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, and combining said first and second signal so as to produce the sum signal thereof, directing said sum signal into a third-order nonlinear medium so as to generate a third signal at frequency omega 2 and with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said third signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 27
Independent Claim
114 words
A method of separating amplitude modulation information from a first optical signal of frequency omega 1 containing both frequency modulation and amplitude modulation comprising the steps of generating an unmodulated sinusoidal second optical signal of frequency omega 2, and combining said first and second signal so as to produce the sum signal thereof, directing said sum signal into a third-order nonlinear medium so as to generate a third signal at frequency omega 2 and with amplitude proportional to the amplitude product of the second signal and the square of the first signal, said third signal containing the amplitude modulation of said first signal but being free of the frequency modulation of said first signal.
Claim 28
Dependent Claim
57 words
The method of claim 22 wherein said medium also transmits said second signal at frequency omega 1 but of different polarization than that of said third signal, in combination with the additional steps of frequency filtering out said first signal and directing said second and third signals into a polarizing filter which transmits only said third signal.
Claim 29
Dependent Claim
49 words
The method of claim 22 wherein said medium also transmits said second signal at frequency omega 2 and of the same polarization as that of said third signal, in combination with the additional steps of frequency filtering out said first signal and eliminating said second signal by destructive interference.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-01-17 | 1975-07-19 | 1976-01-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-01-17 | 1979-07-19 | 1980-01-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-01-17 | 1983-07-19 | 1984-01-18 | $7700.00 | Window Closed / Lapsed |