Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
  • H04L27/20—Modulator circuits; Transmitter circuits
  • H04L27/2096—Arrangements for directly or externally modulating an optical carrier
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/50—Transmitters
  • H04B10/501—Structural aspects
  • H04B10/503—Laser transmitters
  • H04B10/505—Laser transmitters using external modulation
  • H04B10/5053—Laser transmitters using external modulation using a parallel, i.e. shunt, combination of modulators
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/50—Transmitters
  • H04B10/516—Details of coding or modulation
  • H04B10/54—Intensity modulation
  • H04B10/541—Digital intensity or amplitude modulation

Definitions

• This invention generally pertains to high-speed optical transmission and in particular to a method and apparatus to generate 16 quadrature amplitude
• modulated signals with simple and/or low cost architecture. More particularly, certain embodiments of the present invention pertain to using parallel in-phase/quadrature modulators, driven by data signals and a clock signal, and curving a pulse by an intensity modulator.
• the 16 quadrature amplitude modulated optical signal may be detected, by a coherent detector, after transmission based on digital signal processing.
• Optical quadrature amplitude modulation (QAM) and other multi-level modulation formats are promising for optical fiber transmission with great spectral efficiency (SE).
• SE spectral efficiency
• 16-QAM is especially a good solution to high-bit-rate transmission systems since throughput per optical carrier can be highly enhanced.
• Multi-level optical modulation formats combined with polarization-division- multiplexing (PDM) and digital coherent detection have been gaining interest for high SE optical transmission.
• PDM and multi-level modulation may, for example, dramatically increase the SE of wavelength-division-multiplexed (WDM) optical transmission systems.
• M-arry quadrature amplitude modulation has also been explored using different techniques.
• 14Gb/s PDM-128-QAM, 30Gb/s 64-QAM, and 40-Gb/s 16QAM have been generated using arbitrary waveform generators (See T. Sakamoto, A.Chiba, T. Kawanishi, "50-km SMF transmission of 50-Gb/s 16 QAM generated by quad-parallel MZM", paper Tu. E.3) and parallel in-phase/quadrature (l/Q) modulators (See A.
• 160Gb/s 16-QAM was generated employing two parallel integrated l/Q modulators with binary drive signals.
• Generation and transmission of the Square-16QAM format have been demonstrated by using multilevel driving signals and a single stage IQ-modulator (See P. Winzer and A. Gnauck, "1 12-Gb/s Polarization-Multiplexed 16-QAM on a 25-GHz WDM Grid", in Proc. ECOC 2008, paper Th.3.E.5) or by using an integrated solution of a quad- parallel Mach-Zehnder modulator (MZM) (See T. Sakamoto, A.Chiba, T.
• MZM quad- parallel Mach-Zehnder modulator
• an optical modulation device including a parallel in-phase/quadrature modulator having a first signal branch and a second signal branch, wherein the second signal branch is out of phase with the first signal branch, and wherein the parallel in-phase/quadrature modulator is configured to be driven by data signals; and an intensity modulator that is configured to curve a signal at a transit point, wherein the intensity modulator is driven by a clock signal.
• the optical modulation device may include parallel Mach-Zehnder modulators biased at null point and serving as zero-chirp 0/ ⁇ phase modulators.
• the parallel Mach-Zehnder modulators may also have the same driving voltages with full 2 ⁇ / ⁇ swing, for example.
• the data signals of the optical modulation device each have a corresponding bit rates.
• the clock signal is x gigahertz
• at least one of the corresponding bit rates of the data signals is x gigabits/s, where x is a positive real number.
• the optical modulation device may further include a coherent detector.
• the coherent detector may include polarizers, diversity hybrid modulators, local oscillators, photodiodes, high speed analog-to-digital converters, and/or high speed digital-to-analog converters.
• an optical modulation system including a parallel in-phase/quadrature modulator having a first branch and a second branch, wherein the first branch and the second branch is ⁇ /2 out of phase and wherein the parallel in-phase/quadrature modulator is configured to be driven by two data signals; an intensity modulator, wherein the intensity
• modulator is driven by a clock signal; and a coherent detector.
• the coherent detector of the modulation system of certain embodiments of the present invention may include polarizers, diversity hybrid modulators, local oscillators, photodiodes, high speed analog-to-digital converters, and/or high speed digital-to-analog converters.
• the parallel in- phase/quadrature modulator includes parallel Mach-Zehnder modulators.
• the parallel Mach-Zehnder modulators are biased at null point and serve as zero-chirp 0/ ⁇ phase modulators, for example.
• the parallel Mach-Zehnder modulators are biased at null point and serve as zero-chirp 0/ ⁇ phase modulators, for example.
• modulators have equivalent driving voltages with full 2VTT swing, for example.
• the two data signals each have corresponding bit rates.
• the clock signal is x gigahertz
• at least one of the corresponding bit rates of the data signals is x gigabits/s, wherein x is a positive real number.
• Certain embodiments of the present invention include a method for generating multilevel amplitude and phase encoded optical signals. Such methods, for example, include generating a first signal and a second signal, wherein the second signal has a phase difference in relation to the first signal of ⁇ /2; combining the first signal and the second signal, resulting in a combined signal; curving the combined signal at a transit point by an intensity modulator, resulting in a curved combined signal; and transmitting the curved combined signal.
• the curved combined signal includes a return-to-zero pulse.
• Certain embodiments of the present invention further include detecting, by a coherent detector, a curved combined signal.
• the step of detecting may include digitally processing a curved combined signal, for example.
• Certain embodiments of the present invention also include a method for detecting multilevel amplitude and phase encoded optical signals which include the steps of receiving, by a coherent detector, a curved combined optical signal comprising a first signal and a second signal, wherein the second signal has a phase difference in relation to the first signal of ⁇ /2.
• a further step of digitally processing a curved combined optical signal may also be included.
• Certain embodiments of the present invention include a method of encoding data for a 16QAM signal, by an encoder device, including the steps of encoding a rising edge as 01 ; encoding a falling edge as 10; encoding a high level as 1 1 ; and encoding a low level as 00.
• FIG 1 shows a certain embodiment of the present invention.
• FIG 2 shows measured waveforms of an optical signal after in- phase/quadrature modulation and intensity modulation according to certain embodiments of the present invention.
• FIG 3 shows optical spectra after in-phase/quadrature modulation and intensity modulation according to certain embodiments of the present invention.
• FIG. 4 shows a constellation detected by a coherent receiver according to certain embodiments of the present invention.
• FIG. 5 shows a coding scheme according to certain embodiments of the present invention.
• FIG. 6 shows a chart depicting certain embodiments of the present invention.
• a 16QAM modulator includes a parallel l/Q modulator 102 that is driven by two data signals 103 and 104.
• a phase difference between the upper and the lower branch of l/Q modulator 102 is set to be ⁇ /2 for the parallel l/Q modulator 102, for example.
• MZM1 and MZM2 Two parallel Mach-Zehnder modulators (MZM1 and MZM2) are also shown.
• the two parallel Mach-Zehnder modulators are biased at null point, for example, and serve as two zero-chirp 0/ ⁇ phase modulators.
• the MZM1 and MZM2 have the same driving voltages with full 2Vrr swing, for example.
• Fig.1 (a) shows a waveform after the l/Q modulator 102.
• the intensity modulator (IM) 105 is driven by a x GHz clock signal. This IM modulator 105 is used to curve the pulse (the transit part of the signal).
• the clock signal also cuts the optical waveform signal after the IM modulator 105, as shown in Fig. 1 (b).
• the positions of the IM modulator 105 and the l/Q modulator 102 are exchangeable, however.
• the IM modulator 105 is located before l/Q modulator 102 in a signal chain.
• the 16QAM optical signal may then be detected by a coherent detector 106 based, for example, on digital signal processing (DSP) after transmission a certain distance.
• DSP digital signal processing
• Fig. 2 shows measured waveforms of an optical signal after l/Q modulator 102 and IM modulator 105.
• the baud rate of 16QAM is 12.5Gbaud in this depicted experiment, for example.
• Fig. 3 shows optical spectra after l/Q modulator 102 and IM modulator 105. Because, in the depicted case, the signal has a return-to-zero (RZ) pulse, the spectrum after IM modulator 102 is broadened, for example.
• Fig. 4 shows a constellation detected by a coherent receiver 106 according to certain embodiments of the present invention. In the illustrated embodiment, for example, a 16QAM optical signal is generated. As is known, such constellations are representations of digital modulation scheme(s) in a complex plane.
• data signal 103 or data signal 104 are uniquely encoded.
• Fig. 5 shows a scheme to code data according to an embodiment of the present invention.
• the upper data illustration of Fig. 5 is representative of regular binary phase shift keying (BPSK) data coding 1 and 0.
• the lower illustration of Fig. 5 is an example of new data after coding according to certain embodiments of the present invention.
• BPSK binary phase shift keying
• the up-edge is "01 " and fall-edge is "10”.
• the signal is high-level and maintained in one bit slot, it is encoded as "1 1 " and the low-level and maintained in one bit slot is coded as "00", for example.
• Fig. 6 generally provides a chart describing 16QAM optical signal generation according to certain embodiments of the present invention.
• embodiments of the present invention are also advantageously accomplished by low cost architecture.

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• 2011
  • 2011-09-09 CN CN201180042804.2A patent/CN103155505B/zh not_active Expired - Fee Related
  • 2011-09-09 JP JP2013528351A patent/JP2013543668A/ja active Pending
  • 2011-09-09 WO PCT/US2011/051087 patent/WO2012034074A2/en active Application Filing
• 2015
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