Flat-topped chirp induced by optical filter edge
View Patent ↗A fiber optic communication system comprising: an optical signal source adapted to produce a binary amplitude modulated signal; and an optical spectrum reshaper adapted to receive the amplitude modulated signal and to change the instantaneous frequency of the signal at its 0-to-1 and 1-to-0 transitions so as to change the instantaneous frequency of the signal so that it is substantially constant across the 1 pulse. A method for transmitting a signal through a fiber, comprising: generating a second signal from the signal, wherein the second signal comprises a intensity profile and an adiabatic frequency profile; generating a third signal from the second signal, wherein the third signal comprises a intensity profile and a flat-topped frequency profile.
1. A fiber optic communication system comprising:
an optical signal source adapted to produce a binary amplitude modulated signal; and
an optical spectrum reshaper adapted to receive the amplitude modulated signal and to change the instantaneous frequency of the signal at its 0-to-1 and 1-to-0 transitions so as to change the instantaneous frequency of the signal so that it is substantially constant across the 1 pulse;
wherein the signal source is a directly modulated semiconductor laser; and
wherein the signal source is a tunable DBR laser.
2. A system according to claim 1 wherein the changes in the instantaneous frequency are in proportion to the absolute value of the first derivative of the temporal profile of the amplitude modulated signal.
3. A system according to claim 1 wherein the change in the instantaneous frequency from the 0-to-1 transition is the same as the change in the instantaneous frequency from the 1-to-0 transition.
4. A system according to claim 1 wherein the signal source is a fast tunable semiconductor laser.
5. A system according to claim 1 wherein the signal source is a directly modulated semiconductor laser.
6. A system according to claim 5 wherein the optical signal source is a distributed feedback laser.
7. A system according to claim 6 wherein the distributed feedback laser is biased high above its threshold current.
8. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a Bessel filter.
9. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a Mach-Zhender interferometer.
10. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of an optical band pass filter.
11. A system according to claim 1 wherein the optical spectrum reshaper is an edge filter.
12. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a fiber Bragg grating filter.
13. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a multicavity etalon filter.
14. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a single cavity filter.
15. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of a cascade of micro ring resonators.
16. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of an arrayed waveguide grating.
17. A system according to claim 1 wherein the optical spectrum reshaper is the transmission edge of echelle grating.
18. A system according to claim 1 wherein the optical spectrum reshaper is adapted to change the instantaneous frequency of the signal so that it is substantially square-shaped, with rabbit ears at the 0-to-1 and 1-to-0 transitions.
19. A fiber optic communication system comprising:
an optical signal source adapted to produce a binary amplitude modulated signal having a first adiabatic instantaneous frequency profile; and
an optical spectrum reshaper adapted to receive the signal and change the first adiabatic instantaneous frequency profile to a second substantially flat-topped instantaneous frequency profile;
wherein the optical spectrum reshaper is characterized by a slope of its optical transmission versus optical frequency profile; and
wherein the slope of said OSR is selected according to the approximation
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2
a
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f
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a
1
a
0
h
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a
0
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1
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.
20. A system according to claim 19 wherein the duration of the second substantially flat-topped instantaneous frequency profile is longer than the duration of the first adiabatic instantaneous frequency profile.
21. A system according to claim 19 wherein the first adiabatic instantaneous frequency profile is phase shifted relative to the binary signal amplitude profile.
22. A system according to claim 19 wherein the optical spectrum reshaper is adapted to change the first adiabatic instantaneous frequency profile to a second substantially square-shaped instantaneous frequency profile with rabbit ears at the leading and trailing edges of the pulse.
23. A system according to claim 19 wherein the rise and fall times of the second substantially flat-topped instantaneous frequency profile are shorter than the corresponding rise and fall times of the first adiabatic instantaneous frequency profile.
24. A system according to claim 19 wherein the duration of the second substantially flat-topped instantaneous frequency profile is shorter than the duration of the first adiabatic instantaneous frequency profile.
25. A fiber optic communication system comprising:
an optical signal source adapted to produce a binary amplitude modulated signal having a first adiabatic instantaneous frequency profile; and
an optical spectrum reshaper adapted to receive the signal and change the first adiabatic instantaneous frequency profile to a second substantially flat-topped instantaneous frequency profile;
wherein the optical spectrum reshaper is characterized by a slope of its optical transmission versus optical frequency profile; and
wherein said slope is between 2 dB/GHz and 4 dB/GHz, and the bit rate of the binary amplitude modulated signal is about 10 Gb/sec.
26. A system according to claim 19 wherein the slope of said OSR is a function of the rise time and fall time of the binary amplitude modulated signal.
27. A system according to claim 19 wherein the slope of said OSR is a function of the extinction ratio of the binary amplitude modulated signal.
28. A system according to claim 19 wherein the slope of said OSR is a function of the magnitude of the adiabatic chirp of the adiabatic instantaneous frequency profile.
29. A fiber optic communication system comprising:
an optical signal source adapted to receive a base signal and produce an amplitude modulated first signal having a first adiabatic instantaneous frequency profile; and
an OSR adapted to convert said first signal to a second signal, wherein said second signal has a substantially flat-topped instantaneous frequency profile;
wherein said base signal is a non-return-to-zero (NRZ) signal; and
wherein the product of the flat-topped instantaneous frequency excursion and 0 bit duration of the instantaneous frequency of said second signal is between an odd integer multiple of a fraction between 0.25 and 0.75.
30. A system according to claim 29 wherein said second signal further has a larger amplitude modulation than said first signal.
31. A system according to claim 29 wherein the second signal has an extinction ratio is between 10 dB and 15 dB.
32. A system according to claim 29 wherein said digital signal is a return-to-zero (RZ) signal.
33. A system according to claim 29 wherein the product of the flat-topped instantaneous frequency excursion and 0 bit duration of the instantaneous frequency of said second signal is substantially equal to an odd integer multiple of 0.5.