Method and system of using odd harmonics for phase generated carrier homodyne
View Patent ↗A method and system for providing fast interrogation of a signal received from a fiber optic sensor array using a low drive voltage, by modulating the array signal with a phase generated carrier optical signal having an odd harmonic modulation frequency, sending it to an interferometric system, and demodulating the array signal using a demodulation algorithm that is independent of the phase offset. A detector using direct detection method can be used to determine the signal's phase information. The odd harmonic modulation method allows the selection of a desirable odd harmonic PGC frequency with low drive voltage while providing similar performance of the usual PGC frequency that requires a higher drive voltage.
1. A method for fast interrogation of a signal-of-interest, comprising the steps of:
applying to a signal-of-interest a phase generated carrier modulated optical signal at a modulation frequency that is an odd harmonic of a predetermined frequency;
passing the signal-of-interest through an interferometric system; and
demodulating the signal-of-interest using a demodulation algorithm that is independent of a phase offset.
2. The method of claim 1 , wherein the demodulation algorithm is an eight point Fast Fourier Transform demodulation algorithm.
3. The method of claim 1 , wherein the demodulation algorithm is a sixteen point Fast Fourier Transform demodulation algorithm.
4. The method of claim 1 , wherein the signal-of-interest is forwarded to a time division multiplexer to facilitate multiple transmission.
5. The method of claim 1 , wherein the odd harmonic modulation frequency is at a relatively low drive voltage.
6. The method of claim 5 , wherein the drive voltage is less than 15 volts peak to peak.
7. A method for processing a signal received from a fiber optic sensor array comprising the steps of:
modulating the signal with a phase generated carrier optical signal at a modulation frequency that is an odd harmonic of a predetermined frequency;
delivering the signal to an interferometric system; and
demodulating the signal using a demodulation algorithm that is independent of a predetermined phase offset associated with a sampling of the phase generated carrier.
8. The method of claim 7 , wherein the demodulation algorithm is an eight point demodulation algorithm.
9. The method of claim 7 , wherein the demodulation algorithm is a sixteen point demodulation algorithm.
10. The method of claim 7 further comprises the step of:
multiplexing the array signal using a time division multiplexer;
and wherein the multiplexing step occurs before the modulating step.
11. The method of claim 7 further comprises the step of:
multiplexing the array signal using a time division multiplexer;
and wherein the multiplexing step occurs after the modulating step.
12. The method of claim 7 , wherein the applied odd harmonic modulation frequency maintains at least one of a same sampling rate, a same pulse width, and a same time interval between successive array signals.
13. The method of claim 7 , wherein modulating with an odd harmonic modulation frequency provides (allows for) low power consumption of the fiber optic sensor array.
14. An acoustic signal processing system with fast interrogation of a signal received from a fiber optic interferometric sensor array, the system comprising:
a light source for providing an input optical signal;
a phase modulator for encoding the input optical signal with a phase generated carrier optical signal at a modulation frequency that is an odd harmonic of a predetermined frequency
a fiber optic interferometric sensor responsive to acoustic pressure waves for modulating an input optical signal in accordance with the acoustic pressure wave' and
a demodulator that computes acoustic phase information using a demodulation algorithm that is independent of a phase offset.
15. The signal processing system of claim 14 , wherein the demodulation algorithm is an eight point demodulation algorithm.
16. The signal processing system of claim 14 , wherein the demodulation algorithm is a sixteen point demodulation algorithm.
17. The signal processing system of claim 14 further comprising a time division multiplexer.
18. The signal processing system of claim 14 , wherein the odd harmonic modulation frequency modulator maintains at least one of a same sampling rate, a same pulse width, and a same time interval between successive array signals.
19. The signal processing system of claim 14 , wherein the odd harmonic modulation frequency modulator utilizes low drive voltage.
20. The signal processing system of claim 19 , wherein the drive voltage is less than 15 volts peak to peak.
21. An acoustic signal processing system for fast interrogation of a signal received from a fiber optic interferometric sensor array, the system comprising:
a light source for providing an input optical signal;
a phase modulator for encoding an input optical signal with a phase generated carrier optical signal at a modulation frequency that is an odd harmonic of a predetermined frequency;
a fiber optic interferometric sensor responsive to acoustic pressure waves for modulating the input optical signal in accordance with the acoustic pressure wave; and
a detector for direct detection of input optical signals from the interferometric sensor, and for determining the phase information using a demodulation algorithm independent of a phase offset.