Apparatus and method for measuring phase response of optical detectors using multiple-beatnote optical heterodyne
First Claim
1. A method for measuring a phase response of a device under test (DUT) with respect to a modulated optical signal, comprising:
- producing a heterodyne modulated optical signal including first, second, and third beat notes;
coupling at least a portion of the heterodyne modulated optical signal to the DUT;
wherein the portion of the heterodyne modulated optical signal that is coupled to the DUT includes modulation at least at the frequencies of the second and third beat notes;
producing an output signal with the DUT;
wherein the output signal includes at least first and second components having frequencies respectively corresponding to the frequencies of the second and third beat notes;
mixing the first and second components to produce a mixed output signal;
producing a reference signal having the same frequency as and a known phase with respect to the first beat note; and
measuring a phase difference between the mixed output signal and the reference signal.
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Accused Products
Abstract
A heterodyne modulated optical signal that includes two or more beat notes is produced. A portion of the heterodyne modulated optical signal is coupled to a device under test (DUT). This portion includes modulation at least at two of the beat note frequencies. The output of the DUT includes signals corresponding to two of the beat notes. These signals are mixed to produce a mixed output signal having the same frequency as an additional beat note but a phase that depends on the phase response of the DUT at one or more of the two beat note frequencies. The phase of the mixed output signal is measured with respect to a reference signal having the same frequency and a known phase with respect to the additional beat note. The resulting phase measurement represents the dispersion of the DUT with respect to modulation frequency.
12 Citations
47 Claims
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1. A method for measuring a phase response of a device under test (DUT) with respect to a modulated optical signal, comprising:
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producing a heterodyne modulated optical signal including first, second, and third beat notes;
coupling at least a portion of the heterodyne modulated optical signal to the DUT;
wherein the portion of the heterodyne modulated optical signal that is coupled to the DUT includes modulation at least at the frequencies of the second and third beat notes;
producing an output signal with the DUT;
wherein the output signal includes at least first and second components having frequencies respectively corresponding to the frequencies of the second and third beat notes;
mixing the first and second components to produce a mixed output signal;
producing a reference signal having the same frequency as and a known phase with respect to the first beat note; and
measuring a phase difference between the mixed output signal and the reference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. An apparatus for measuring the phase response of a device under test (DUT), comprising:
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first, second and third lasers;
a combiner optically coupled at one or more inputs to the first second and third lasers, wherein an output of the combiner may be optically coupled to an input of the DUT;
a high-speed mixer that may be coupled to an output of the DUT;
a reference signal generator;
a phase measuring device coupled to the reference signal generator and a output of the high-speed mixer and means for controlling the first second and third lasers such that the first laser produces a first signal characterized by a first frequency, the second laser produces a second signal characterized by a second frequency, the third laser produces a third signal characterized by a third frequency, wherein a difference between the frequencies of the first and second signals corresponds to a first beat note, a difference between the frequencies of the second and third signals corresponds to a second beat note, a difference between the frequencies of the first and third signals corresponds to a third beat note wherein the first beat note is characterized by a frequency that is sufficiently low that it may be processed with low-speed electronics. - View Dependent Claims (32, 33, 34, 35, 36, 37, 38, 39)
a second optical coupler optically coupled to the first optical coupler and the third laser.
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36. The apparatus of claim 31 wherein the first second and third lasers are configured such that the first signal is polarized substantially orthogonal to the second signal and the third signal is polarized substantially at 45°
- with respect to the polarizations of the first and second signals.
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37. The apparatus of claim 31, wherein the phase measuring device includes a low-speed mixer.
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38. The apparatus of claim 31 wherein the phase measuring device includes an electrical to optical (EO) modulator coupled to an optical power detector.
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39. The apparatus of claim 31, further comprising an integrator coupled to an output of the phase measuring device.
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40. An apparatus for measuring the phase response of a device under test (DUT), comprising:
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a heterodyne source configured to produce a heterodyne modulated optical signal characterized by two or more different beat notes, wherein the heterodyne source may be optically coupled to an input of the DUT;
a high-speed mixer that may be coupled to an output of the DUT;
a reference signal generator; and
a phase detector coupled to the reference signal generator and an output of the high-speed mixer. - View Dependent Claims (41, 42, 43, 44, 45)
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46. A method for measuring a phase response of a device under test (DUT) with respect to a modulated optical signal, comprising:
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producing a heterodyne modulated optical signal including modulation at least at first and second beat notes, wherein a frequency difference between the first and second beat notes corresponds to an additional beat note;
coupling at least a portion of the heterodyne modulated optical signal to the DUT;
wherein the portion of the heterodyne modulated optical signal that is coupled to the DUT includes modulation at least at the frequencies of the first and second beat notes;
producing an output signal with the DUT;
wherein the output signal includes at least first and second components having frequencies respectively corresponding to the frequencies of the first and second beat notes;
mixing the first and second components to produce a mixed output signal;
producing a reference signal having the same frequency as and a known phase with respect to the additional beat note; and
measuring a phase difference between the mixed output signal and the reference signal.
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47. An apparatus for a phase response of a device under test (DUT) with respect to a modulated optical signal, comprising:
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means for producing a heterodyne modulated optical signal including modulation at least at first and second beat notes, wherein a frequency difference between the first and second beat notes corresponds to an additional beat note;
means for coupling at least a portion of the heterodyne modulated optical signal to the DUT;
wherein the portion of the heterodyne modulated optical signal that is coupled to the DUT includes modulation at least at the frequencies of the first and second beat notes;
means for mixing first and second components of an output signal from the DUT to produce a mixed output signal, wherein the first and second components have frequencies respectively corresponding to the frequencies of the first and second beat notes;
means for producing a reference signal having the same frequency as and a known phase with respect to the additional beat note; and
means for measuring a phase difference between the mixed output signal and the reference signal.
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Specification