Claims
- 1. A method of measuring phase differences between at least first and second intensity-modulated optical signals (S1,S2) modulated at the same modulation frequency comprising the steps of:
(i) sequentially selecting the two optical signals individually and then in combination; (ii) deriving from the selected optical signals a corresponding electrical signal at the modulation frequency having a series of different amplitudes corresponding to the different optical signal selections, and determining the different amplitudes; and (iii) using trigonometrical relationships between amplitude and phase angle, computing from the determined amplitudes the phase difference (φ1−φ2) between the modulations of the first and second optical signals.
- 2. A method according to claim 1, wherein the amplitudes correspond to each of the first (S1) and second (S2) optical signals alone, and the sum of the first and second optical signals.
- 3. A method according to claim 2, wherein the amplitudes correspond also to neither of the optical signals (S1,S2) being selected and the resulting amplitude value is used for offset correction.
- 4. A method according to claim 1, wherein, where the first optical signal (S1) has intensity modulation of amplitude A1=A01 sin(2πfmodt+φ1) where A01 is the maximum amplitude and φ1 is the phase for the major Fourier component, the second optical signal (S2) has intensity modulation of amplitude A2=A02 sin(2πfmodt+φ2) where A02 is the maximum amplitude and φ2 the phase for the major Fourier component, and where fmod is the modulation frequency, and the combined signal has an amplitude A=A1+A2=A12 sin(2πfmodt+φ0), the control and computing means (18) computes the phase difference (φ) as:
- 5. A method according to claim 1, further comprising the additional steps of:
(iv) providing a third optical signal (S3) intensity-modulated at said high frequency, the third optical signal modulation having a predetermined phase difference relative to either one of the first and second optical signals; and (v) selecting the third optical signal individually and in combination with either or both of the first and second optical signals to produce an additional selection of optical signals, such that said corresponding electrical signal has additional amplitudes corresponding to the additional selections, and wherein the amplitude determining step also determines the additional amplitudes and the step of computing the phase difference between the first and second optical signals takes into account trigonometrical relationships between the amplitude and phase of all three of the optical signals.
- 6. A method according to claim 5, wherein the amplitudes correspond to each of the first, second and third optical signals alone, the sum of the first and second optical signals, the sum of the first and third optical signals and the sum of the second and third optical signals.
- 7. A method according to claim 6, wherein the amplitudes correspond also to the sum of all three optical signals.
- 8. A method according to claim 5, wherein, where the first optical signal (S1) has intensity modulation of amplitude A1=A01 sin(2πfmodt+φ1) where A01 is the maximum amplitude and φ1 is the phase for the major Fourier component, the second optical signal (S2) has intensity modulation of amplitude A2=A02 sin(2πfmodt+φ2) where A02 is the maximum amplitude and φ2 the phase for the major Fourier component, the third optical signal (S3) has intensity modulation of amplitude A3=A03 sin(2πfmodt+φ3) where A03 is the maximum amplitude and φ3 the phase for the major Fourier component, and where fmod is the modulation frequency, the control and computing means (18) computes the phase difference (φ) as:
- 9. A method according to claim 5, wherein the predetermined phase difference comprises about 90 degrees at said high frequency.
- 10. A method according to claim 5, wherein one of the selections selects none of the optical signals, and the corresponding amplitude measurement is used as an offset correction for the other amplitude measurements.
- 11. A method according to claim 1, wherein the first and second optical signals are provided by splitting a single intensity-modulated light beam from a single source controlled by a reference oscillator.
- 12. A method according to claim 1, wherein the first and second optical signals are provided by first and second light sources, respectively, controlled by phase-locked signals from a reference oscillator.
- 13. A method according to claim 1, wherein the first and second optical signals are provided by a single light source and modulated by an optical modulator.
- 14. A method according to claim 1, wherein the first and second optical signals are provided by first and second light sources, respectively, and modulated by an optical modulator.
- 15. A method according to claim 5, wherein the third optical signal is provided by splitting one of the first and second intensity-modulated light beams.
- 16. A method according to claim 1, further comprising the steps of passing one or both of the intensity-modulated optical signals (S1, S2) through a selected optical element (50), performing the phase difference measurement steps for each of a plurality of different optical wavelengths of the optical signals, and using the resulting wavelengths and plurality of phase difference measurements to compute chromatic dispersion of the optical element.
- 17. A method according to claim 1, further comprising the step of varying the state of polarization of one of the optical signals at a specific wavelength, performing the phase difference measurement steps for each of a plurality of different such states of polarization, and using the resulting plurality of phase difference measurements to compute the maximum difference in group delay for the different states of polarization.
- 18. A method according to claim 1, further comprising the steps of passing one of the optical signals through an optical element, varying the effective optical length of the optical element, performing the phase difference measurement steps for each of a plurality of different lengths, and using the resulting plurality of phase difference measurements to compute optical length differences.
- 19. Apparatus for measuring phase difference between intensity-modulated optical signals comprising:
(i) means (54) for providing a first optical signal (S1) and a second optical signal (S2) both having intensity-modulated at the same high frequency; (ii) a selection unit (12) for selecting sequentially the first and second optical signals (S1, S2) individually and in combination; (iii) means (14, 16) for deriving from the selected optical signals a corresponding electrical signal at the modulation frequency having a series of different amplitudes corresponding to the different optical signal selections, and for determining amplitudes of the electrical signal corresponding to the different selections; and (iv) means (18) for controlling said selection unit (12) and computing from the amplitudes, using trigonometrical relationships between amplitude and phase, a phase difference (φ1−φ2) between the modulation of the first and second optical signals as received by said deriving means (14, 16).
- 20. Apparatus according to claim 19, wherein the selection means (12) is arranged to select each of the first (S1) and second (S2) optical signals alone, and the first and second optical signals combined.
- 21. Apparatus according to claim 19, wherein the selection means (12) is arranged to select neither of the optical signals (S1, S2) and the control and computing means (18) is arranged to use the resulting amplitude value for offset correction.
- 22. Apparatus according to claim 19, wherein, where the first optical signal (S1) has intensity modulation of amplitude A1=A01 sin(2πfmodt+φ1) where A01 is the maximum amplitude and φ1 is the phase for the major Fourier component, the second optical signal (S2) has intensity modulation of amplitude A2=A02 sin(2πfmodt+φ2) where A02 is the maximum amplitude and φ2 the phase for the major Fourier component, and where fmod is the modulation frequency, and the combined signal has an amplitude A=A1+A2=A12 sin(2πfmodt+φ0), the control and computing means (18) is arranged to compute the phase difference (φ) as:
- 23. Apparatus according to claim 19, further comprising means (38) for providing a third optical signal (S3) intensity-modulated with modulation at said high frequency and a predetermined phase difference relative to either of the first and second optical signals, and wherein the selection unit (12) sequentially selects the third optical signal (S3) individually and in combination with either and/or both of the first and second optical signals (S1, S2) to produce an additional selection of optical signals, the deriving means (14,16) derives from the additional selection of optical signals said electrical signal having corresponding additional amplitudes, and determines the amplitudes corresponding to the additional selections, and the control and computing means (18) is operable, when computing said phase difference, to take into account the amplitudes corresponding to the additional selections involving the third optical signal.
- 24. Apparatus according to claim 23, wherein the deriving means (14,16) comprises means (16) for determining the amplitudes of each of the first, second and third optical signals alone, the sum of the first and second optical signals, the sum of the first and third optical signals, and the sum of the second and third optical signals.
- 25. Apparatus according to claim 24, wherein the amplitude determining means (16) also determines the amplitude corresponding to the sum of all three optical signals.
- 26. Apparatus according to claim 23, wherein where the first optical signal (S1) has intensity modulation of amplitude A1=A01 sin(2πfmodt+φ1) where A01 is the maximum amplitude and φ1 is the phase for the major Fourier component, the second optical signal (S2) has intensity modulation of amplitude A2=A02 sin(2πfmodt+φ2) where φ2 is the maximum amplitude and φ2 the phase for the major Fourier component, the third optical signal (S3) has intensity modulation of amplitude A3=A03 sin(2πfmodt+φ3) where A03 is the maximum amplitude and φ3 the phase for the major Fourier component, and where fmod is the modulation frequency, the control and computing means (18) computes the phase difference (φ) as:
- 27. Apparatus according to claim 23, wherein the predetermined phase difference is substantially 90 degrees at said high frequency.
- 28. Apparatus according to claim 23, wherein the selection unit (12) selects none of the optical signals and the amplitude determining means (16) determines the corresponding amplitude and uses it as an offset correction for the other amplitude measurements.
- 29. Apparatus according to claim 19, wherein the optical signal providing means (54) comprises one or more light sources (76) for supplying said optical signals and means (74; 78) for providing said modulation.
- 30. Apparatus according to claim 28, wherein the modulation providing means (74) comprises reference oscillator means (74) for controlling the one or more light sources to modulate light outputted thereby.
- 31. Apparatus according to claim 28, wherein the modulation-providing means comprises an optical light modulator means (78) for modulating light outputted from said one or more light sources.
- 32. Apparatus according to claim 19, further comprising means (38) for splitting either one of the first and second intensity-modulated optical signals (S1, S2) to produce said third optical signal (S3).
- 33. Apparatus according to claim 19, adapted for passing one or both of the optical signals through an optical element (50), further comprising means (68) for varying the wavelength of one or each of the first and second optical signals, and wherein the deriving and determining means (14,16) determines amplitudes for each of a plurality of wavelengths of said one of the optical signals and the control and computing means (18) computes a said phase difference for each of said plurality of wavelengths and uses the plurality of wavelengths and phase differences to determine chromatic dispersion by said optical element.
- 34. Apparatus according to claim 19, adapted for passing one of the optical signals through an optical element, further comprising means (80,82) for varying state of polarization of said one of the optical signals at a specific wavelength, wherein the deriving and determining means (14,16) and the control and computing means (18) are operable to determine said selected amplitudes and compute said phase difference for each of a plurality of said states of polarization, the control and computing means (18) using the resulting plurality of phase difference measurements to determine the maximum difference in group delay for the different states of polarization.
- 35. Apparatus according to claim 19, adapted for measuring elongation of an optical element through which one of the optical signals is passed, further wherein the deriving and determining means (14,16) and control and computing means (18) are operable to determine said amplitudes and compute said phase difference for each of a plurality of length states of the optical element and compute elongation in dependence thereupon.
- 36. Apparatus for use in measuring phase difference between intensity-modulated optical signals comprising:
(i) means (54) for providing a first optical signal (S1) and a second optical signal (S2) both having intensity-modulated at the same high frequency; (ii) a selection unit (12) for selecting sequentially the first and second optical signals (S1, S2) individually and in combination and having an interface for coupling to a computer; (iii) means (14, 16) for deriving from the selected optical signals a corresponding electrical signal at the modulation frequency having a series of different amplitudes corresponding to the different optical signal selections, determining amplitudes of the electrical signal corresponding to the different selections, and supplying the amplitude values to an interface for coupling to said computer; and (iv) software for programming said computer to control said selection unit (12) and compute from the amplitudes, using trigonometrical relationships between amplitude and phase, a phase difference (φ1−φ2) between the modulation of the first and second optical signals as received by said deriving means (14, 16).
Parent Case Info
[0001] This application claims priority from U.S. Provisional patent application number 60/193,466 filed Mar. 31, 2000.
Provisional Applications (1)
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Number |
Date |
Country |
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60193466 |
Mar 2000 |
US |