Optical sampling using intermediate second harmonic frequency generation
First Claim
1. An optical sampling method for sampling input optical signals in optical communications, comprising:
- using a probe pulse source of a predetermined wavelength range and frequency-doubling signals from said probe pulse source to obtain an intermediate output containing a second harmonic probe pulse signal;
filtering said intermediate output to filter out background including that corresponding to said predetermined wavelength, leaving a filtered intermediate second harmonic probe pulse signal;
mixing the filtered intermediate second harmonic probe pulse signal with a user input optical signal and obtaining a near third harmonic signal; and
processing the near third harmonic signal to obtain samples of the user input optical signal.
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Abstract
An optical sampling method and apparatus use a probe pulse source of a predetermined optical wavelength range, e.g., 1560 nm, to sample incoming optical pulses in approximately the same wavelength range. The probe pulse source is frequency-doubled e.g., using a frequency doubler such as a nonlinear PPLN crystal, to obtain an intermediate second harmonic which may be filtered with a 780 nm bandpass filter to eliminate at least source frequency noise background. The filtered intermediate second harmonic is then mixed with the user input signal using an optional polarizing beam splitter and a dichroic beam splitter. The mixed signal is sent to a sum frequency generating (SFG) nonlinear crystal, e.g., a PPLN crystal, where the resulting frequency is near the third harmonic. The output from the SFG PPLN crystal may be filtered using a bandpass 515 nm filter to remove unwanted wavelengths and processed to measure/sense the near third harmonic content using a photomultiplier tube (PMT). Beyond the PMT, the output may be sent to a microprocessor for analysis and display on a cathode ray oscilloscope as necessary. 80-85% power conversion efficiency in the frequency doubler, a 60 or 65% photon conversion efficiency in the sampler and handling of 600+ GHz bandwidths, as well as background noise reduction are possible by using the invention.
9 Citations
31 Claims
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1. An optical sampling method for sampling input optical signals in optical communications, comprising:
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using a probe pulse source of a predetermined wavelength range and frequency-doubling signals from said probe pulse source to obtain an intermediate output containing a second harmonic probe pulse signal;
filtering said intermediate output to filter out background including that corresponding to said predetermined wavelength, leaving a filtered intermediate second harmonic probe pulse signal;
mixing the filtered intermediate second harmonic probe pulse signal with a user input optical signal and obtaining a near third harmonic signal; and
processing the near third harmonic signal to obtain samples of the user input optical signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An optical sampling system to obtain a sample from a user input optical signal, comprising:
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a probe pulse signal source of a predetermined wavelength range;
a frequency doubler for frequency-doubling the probe pulse signal source to obtain an intermediate second harmonic output containing a second harmonic probe pulse signal;
a filter to filter said intermediate second harmonic output to delete at least background corresponding to said predetermined wavelength, leaving a filtered intermediate second harmonic probe pulse signal;
a mixer for mixing the filtered intermediate second harmonic probe signal with a user input optical signal to obtain a near third harmonic signal; and
a processor for processing the near third harmonic signal in a desired manner to obtain samples of the user input optical signal with reduced background noise. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 24, 25, 26, 27, 28, 29, 30, 31)
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23. A system as in 11 wherein said mixer comprises a periodically poled lithium niobate (PPLN) nonlinear crystal.
Specification