Modulation based optical spectrum analyzer
An optical spectrum analyzer and a method of spectrally analyzing an optical signal. The optical spectrum analyzer includes a wave shaper such as an optical modulator that shapes an optical signal, a dispersive element such as a dispersive fiber in which the shaped optical signal is dispersed, a detector that provides an output signal indicative of the dispersed shaped optical signal, and a signal processor that analyzes the output signal, for example by calculating a transform such as an inverse Fourier transform or a Fourier transform of the output signal, to provide a frequency spectrum of the optical signal.
1. An optical spectrum analyzer comprising:
a wave shaper that shapes an optical signal, wherein the wave shaper comprises an optical modulator;
a signal generator coupled to the optical modulator, the optical modulator operative to modulate both the intensity and the phase of the optical signal according to a signal from the signal generator;
a dispersive element in which the shaped optical signal is dispersed;
a detector that provides an output signal indicative of the dispersed shaped optical signal; and
a signal processor that analyzes the output signal to provide a frequency spectrum of the optical signal.
2. An optical spectrum analyzer as in claim 1 wherein the signal generator comprises a pulse generator.
3. An optical spectrum analyzer as in claim 1 wherein the signal generator comprises a periodic waveform generator.
4. An optical spectrum analyzer as in claim 3 wherein the signal generator comprises a sinusoidal swept frequency generator.
5. An optical spectrum analyzer as in claim 3 wherein the signal generator comprises a variable bias voltage source.
6. An optical spectrum analyzer as in claim 1 wherein the dispersive element comprises an optical fiber.
7. An optical spectrum analyzer as in claim 6 wherein the optical fiber comprises a dispersion-compensating fiber.
8. An optical spectrum analyzer as in claim 6 wherein the optical fiber comprises a single-mode fiber having a dispersion that exceeds one picosecond per nanometer per kilometer.
9. An optical spectrum analyzer as in claim 1 wherein the dispersive element comprises a chirped fiber grating.
10. An optical spectrum analyzer as in claim 1 wherein the signal processor comprises a computer programmed to calculate a transform of the output signal.
11. An optical spectrum analyzer as in claim 10 wherein the signal processor comprises a computer programmed to calculate an inverse Fourier transform of the output signal.
12. An optical spectrum analyzer as in claim 10 wherein the signal processor comprises a computer programmed to calculate a Fourier transform of the output signal.
13. A method of spectrally analyzing an optical signal comprising:
shaping an optical signal, wherein shaping the optical signal comprises modulating the amplitude and phase of the optical signal;
time-dispersing the shaped optical signal;
detecting the time-dispersed shape of the optical signal; and
analyzing the time-dispersed shape to find the spectrum of the optical signal.
14. A method as in claim 13 wherein analyzing the output signal comprises calculating a transform thereof.
15. A method as in claim 14 wherein analyzing the output signal comprises calculating an inverse Fourier transform thereof.
16. A method as in claim 14 wherein analyzing the output signal comprises calculating a Fourier transform thereof.
17. A method as in claim 13 wherein shaping the optical signal comprises modulating the optical signal according to a pulse modulation signal.
18. A method as in claim 13 wherein shaping the optical signal comprises modulating the optical signal according to a periodic modulation signal.
19. A method as in claim 13 wherein shaping the optical signal comprises modulating the optical signal according to a swept sinusoidal modulation signal.