Claims
- 1. A high speed digital optical transmission system, comprising:
a laser configured to generate a continuous wave (CW) light beam; and at least one first modulator configured to modulate the CW light beam in response to an electrical non-return-to-zero (NRZ) data signal, thereby generating a modulated NRZ optical signal, wherein the first modulator is further configured to generate the modulated NRZ optical signal with positive chirp.
- 2. The system of claim 1 further including at least one second modulator operatively coupled to the first modulator, the second modulator being configured to carve at least one return-to-zero (RZ) pulse from the light beam or the modulated NRZ optical signal.
- 3. The system of claim 2 wherein the second modulator is configured to generate a modulated carrier-suppressed RZ optical signal.
- 4. The system of claim 3 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for 100% of each bit time slot.
- 5. The system of claim 3 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot.
- 6. The system of claim 5 further including a transmission medium configured to carry the modulated carrier-suppressed RZ optical signal, the transmission medium comprising positive dispersion optical fiber.
- 7. The system of claim 3 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot and negative for up to 20% of each bit time slot.
- 8. The system of claim 2 further including a transmission medium configured to carry the modulated RZ optical signal, the transmission medium comprising positive dispersion optical fiber.
- 9. The system of claim 1 further including a transmission medium configured to carry the modulated NRZ optical signal.
- 10. The system of claim 9 wherein the transmission medium comprises negative dispersion optical fiber.
- 11. The system of claim 9 wherein the transmission medium is selected from the group consisting of True-Wave-RS™ fiber, Large Effective Area Fiber fiber, dispersion-managed fiber, Standard Single-Mode Fiber, and NZDSF fiber.
- 12. The system of claim 1 wherein the first modulator is further configured to generate the modulated optical signal at a per channel line rate ranging from about 39-50 Gbits/s.
- 13. The system of claim 1 wherein the first modulator has an associated transfer function, the first modulator being biased at a predetermined bias point of the transfer function.
- 14. The system of claim 13 wherein the predetermined bias point is offset from a quadrature point of the transfer function such that a duty cycle of the modulated NRZ optical signal is reduced.
- 15. The system of claim 1 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for 100% of each bit time slot.
- 16. The system of claim 1 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot.
- 17. The system of claim 1 wherein the first modulator is biased so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot and negative for up to 20% of each bit time slot.
- 18. The system of claim 1 wherein the first modulator comprises first and second modulator units, the first unit being configured to impress amplitude modulation and the second unit being configured to impress phase modulation, so that an output of the first modulator is a signal with NRZ intensity modulation and predominantly positive chirp.
- 19. The system of claim 1 wherein the first modulator is selected from the group consisting of a Mach-Zehnder modulator and an electro-absorption modulator.
- 20. A method of operating a high speed digital optical transmission system, comprising the steps of:
generating a continuous wave (CW) light beam by a laser; and modulating the CW light beam in response to an electrical non-return-to-zero (NRZ) data signal to generate a modulated NRZ optical signal with positive chirp by at least one first modulator.
- 21. The method of claim 20 further including the step of carving at least one return-to-zero (RZ) pulse from the light beam or the modulated NRZ optical signal by a second modulator.
- 22. The method of claim 21 wherein the carving step includes carving the RZ pulse from the modulated NRZ optical signal to generate a modulated carrier-suppressed RZ optical signal by the second modulator.
- 23. The method of claim 21 further including the step of transmitting the modulated RZ optical signal over a transmission medium, the transmission medium comprising positive dispersion optical fiber.
- 24. The method of claim 20 further including the step of transmitting the modulated NRZ optical signal over a transmission medium, the transmission medium being selected from the group consisting of negative dispersion optical fiber, positive dispersion optical fiber, True-Wave-RS™ fiber, Large Effective Area Fiber fiber, dispersion-managed fiber, Standard Single-Mode Fiber, and NZDSF fiber.
- 25. The method of claim 20 further including the step of transmitting the modulated optical signal at a per channel line rate ranging from about 39-50 Gbits/s.
- 26. A high speed digital optical transmission system, comprising:
a laser configured to generate a continuous wave (CW) light beam; and a data modulator configured for modulating the CW light beam in response to an electrical non-return-to-zero (NRZ) data signal to generate a modulated NRZ optical signal, the data modulator having an associated transfer function and being biased at a predetermined bias point of the transfer function, wherein the predetermined bias point is offset from a quadrature point of the transfer function.
- 27. The system of claim 26 wherein the predetermined bias point is offset from the quadrature point of the transfer function such that a duty cycle of the modulated NRZ optical signal is reduced.
- 28. The system of claim 26 wherein the data modulator is biased to operate so that the chirp of the modulated NRZ optical signal is positive for 100% of each bit time slot.
- 29. The system of claim 26 wherein the data modulator is biased to operate so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot.
- 30. The system of claim 29 wherein the data modulator is biased to operate so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot, and to operate so that the chirp of the modulated NRZ optical signal is negative for up to 20% of each bit time slot.
- 31. The system of claim 26 wherein the system is configured to operate at a bit rate ranging from about 39-50 Gbits/s.
- 32. A method of operating a high speed digital optical transmission system, comprising the steps of:
generating a continuous wave (CW) light beam by a laser; and modulating the CW light beam in response to an electrical non-return-to-zero (NRZ) data signal to generate a modulated NRZ optical signal by a data modulator, the data modulator having an associated transfer function and being biased at a predetermined bias point of the transfer function, the predetermined bias point being offset from a quadrature point of the transfer function.
- 33. The method of claim 32 wherein the modulating step includes modulating the CW light beam in response to the electrical NRZ data signal to generate the modulated NRZ optical signal by the data modulator, the predetermined bias point being offset from the quadrature point of the transfer function such that a duty cycle of the modulated NRZ optical signal is reduced.
- 34. The method of claim 32 wherein the modulating step includes modulating the CW light beam in response to the electrical NRZ data signal to generate the modulated NRZ optical signal by the data modulator, the data modulator being biased to operate so that the chirp of the modulated NRZ optical signal is positive for 100% of each bit time slot.
- 35. The method of claim 32 wherein the modulating step includes modulating the CW light beam in response to the electrical NRZ data signal to generate the modulated NRZ optical signal by the data modulator, the data modulator being biased to operate so that the chirp of the modulated NRZ optical signal is positive for at least 80% of each bit time slot.
- 36. The method of claim 35 wherein the modulating step includes modulating the CW light beam in response to the electrical NRZ data signal to generate the modulated NRZ optical signal by the data modulator, the data modulator being biased to operate so that the chirp of the modulated NRZ optical signal is negative for up to 20% of each bit time slot.
- 37. The method of claim 32 further including the step of operating the system at a bit rate ranging from about 39-50 Gbits/s.
- 38. A high speed digital optical transmission system, comprising:
at least one laser configured to generate a modulated light beam in response to an electrical non-return-to-zero (NRZ) data signal, thereby generating a modulated NRZ optical signal, wherein the laser is further configured to generate the modulated NRZ optical signal with positive chirp.
- 39. The system of claim 38 further including a pulse modulator configured to carve at least one return-to-zero (RZ) pulse from the modulated NRZ optical signal, thereby generating a modulated RZ optical signal.
- 40. The system of claim 39 wherein the pulse modulator is configured to generate a modulated carrier-suppressed RZ optical signal.
- 41. The system of claim 39 further including a transmission medium configured to carry the modulated RZ optical signal, the transmission medium comprising positive dispersion optical fiber.
- 42. The system of claim 38 further including a transmission medium configured to carry the modulated NRZ optical signal.
- 43. The system of claim 42 wherein the transmission medium comprises negative dispersion optical fiber.
- 44. The system of claim 42 wherein the transmission medium is selected from the group consisting of negative dispersion fiber, positive dispersion fiber, TW-RS fiber, LEAF fiber, TERA-LIGHT fiber, ULTRA-WAVE fiber, dispersion-managed fiber, SSMF fiber, and NZDSF fiber.
- 45. The system of claim 38 wherein the laser is further configured to generate the modulated optical signal at a per channel line rate ranging from about 39-50 Gbits/s.
- 46. The system of claim 38 wherein the laser is further configured to generate the modulated NRZ optical signal with positive chirp for at least 80% of each bit time slot.
- 47. The system of claim 38 wherein the laser is further configured to generate the modulated NRZ optical signal with positive chirp for at least 80% of each bit time slot and negative chirp for up to 20% of each bit time slot.
- 48. A method of operating a high speed digital optical transmission system, comprising the steps of:
generating a modulated non-return-to-zero (NRZ) optical signal with positive chirp in response to an electrical NRZ data signal by at least one laser; and transmitting the modulated NRZ optical signal over a data transmission channel at a predetermined bit rate.
- 49. The method of claim 48 further including the step of carving at least one return-to-zero (RZ) pulse from the modulated NRZ optical signal to generate a modulated RZ optical signal by a pulse modulator.
- 50. The method of claim 49 wherein the carving step includes carving the RZ pulse from the modulated NRZ optical signal to generate a modulated carrier-suppressed RZ optical signal by the pulse modulator.
- 51. The method of claim 49 wherein the transmitting step includes transmitting the modulated RZ optical signal over a transmission medium, the transmission medium being selected from the group consisting of negative dispersion fiber, positive dispersion fiber, TW-RS fiber, LEAF fiber, TERA-LIGHT fiber, ULTRA-WAVE fiber, dispersion-managed fiber, SSMF fiber, and NZDSF fiber.
- 52. The method of claim 48 wherein the transmitting step includes transmitting the modulated NRZ optical signal over a transmission medium, the transmission medium being selected from the group consisting of negative dispersion fiber, positive dispersion fiber, TW-RS fiber, LEAF fiber, TERA-LIGHT fiber, ULTRA-WAVE fiber, dispersion-managed fiber, SSMF fiber, and NZDSF fiber.
- 53. The method of claim 48 wherein the transmitting step includes transmitting the modulated optical signal over the data transmission channel at a per channel line rate ranging from about 39-50 Gbits/s by the laser.
- 54. A method of determining a bias point for operating a non-return-to-zero (NRZ) data modulator included in a high speed digital optical transmission system, the NRZ data modulator being configured to modulate a continuous wave (CW) light beam in response to an electrical NRZ data signal to generate a modulated NRZ optical signal, the method comprising the steps of:
successively increasing a bias offset voltage relative to a quadrature point of a transfer function associated with the NRZ data modulator; evaluating a figure of merit of the NRZ data modulator as a function of each successive increase of the bias offset relative to quadrature; and choosing the bias point corresponding to the bias offset that yields a figure of merit value indicative of improved system performance.
- 55. The method of claim 54 wherein the evaluating step includes evaluating the figure of merit as a function of the bias voltage and a drive voltage of the electrical NRZ data signal.
- 56. The method of claim 55 further including the step of choosing the bias voltage and the drive voltage that yields a figure of merit value indicative of improved system performance.
- 57. The method of claim 55 wherein the increasing step includes successively increasing the bias voltage relative to quadrature to maintain the drive voltage of a logical low level at a predetermined value.
- 58. The method of claim 54 wherein the evaluating step includes evaluating the figure of merit of the NRZ data modulator, the figure of merit being selected from the group consisting of a bit error rate, an extinction ratio, and a chirp characteristic.
- 59. The method of claim 54 further including the step of operating the system at a bit rate ranging from about 39-50 Gbits/s.
- 60. A method of performing closed-loop control of a bias offset of a non-return-to-zero (NRZ) data modulator included in a high speed digital optical transmission system, comprising the steps of:
applying an electrical data signal, an electrical dither signal, and an optical signal to the NRZ data modulator; modulating the optical signal with a sum of the data signal and the dither signal by the NRZ data modulator; monitoring an optical output of the NRZ data modulator by a photodiode; determining a fundamental harmonic, a second harmonic, and a third harmonic of a dither frequency component in a photo current of the photodiode; processing a fundamental harmonic-to-second harmonic ratio and a third harmonic-to-fundamental harmonic ratio to produce a control observable signal; and employing the control observable signal as a feedback error signal to control the bias offset of the NRZ data modulator.
- 61. The method of claim 60 further including subtracting a DC bias set level from the control observable signal.
- 62. The method of claim 60 wherein the applying step includes applying the data signal, the dither signal, and the optical signal to the NRZ data modulator, the NRZ data modulator comprising a Mach-Zehnder modulator.
- 63. The method of claim 60 wherein the processing step includes processing the fundamental harmonic-to-second harmonic ratio and the third harmonic-to-fundamental harmonic ratio to produce the control observable signal, the control observable signal being equal to the tangent of a bias angle.
- 64. The method of claim 60 wherein the processing step includes processing the fundamental harmonic-to-second harmonic ratio and the third harmonic-to-fundamental harmonic ratio to produce the control observable signal, the control observable signal being equal to the cotangent of a bias angle.
- 65. The method of claim 60 further including the step of operating the system at a bit rate ranging from about 39-50 Gbits/s.
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. Provisional Patent Application No. 60/380,452 filed May 14, 2002 entitled OPTICAL TRANSMISSION SYSTEM METHODS AND APPARATUS.
Provisional Applications (1)
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Number |
Date |
Country |
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60380452 |
May 2002 |
US |