JP2013543668A - 16QAM optical signal generation - Google Patents

Abstract

Embodiments of the present invention relate to high speed optical transmission and methods and apparatus for generating 16 quadrature amplitude modulated signals in a simple and / or low cost configuration.
One embodiment of the invention relates to using parallel in-phase / quadrature modulators 102 driven by data signals 103 and 104 and a clock signal and bending the pulses by intensity modulators 105. . The optical signal modulated by 16 quadrature amplitudes is detected by the coherent detector 106 after transmission based on digital signal processing.
[Selection] Figure 1

Description

  The present invention relates generally to high-speed optical transmission, and more particularly, to a method and apparatus for generating 16 quadrature amplitude modulated signals with a simple and / or low-cost structure. More particularly, embodiments of the present invention relate to using parallel in-phase / quadrature modulators driven by data and clock signals and bending pulses by intensity modulators. The optical signal modulated with 16 quadrature amplitudes is detected by a coherent detector after transmission based on digital signal processing.

  Optical quadrature amplitude modulation (QAM) and other multi-layer modulation schemes are promising for optical fiber transmission with good wavelength utilization efficiency (SE). In particular, 16-QAM is a good solution for high bit rate transfer systems because the throughput per optical carrier can be improved to a high degree.

  Multilayer optical modulation schemes combined with polarization division multiplexing (PDM) and digital coherent detection have been of great interest as high SE (wavelength utilization efficiency) optical communications. PDM and multi-level modulation, for example, dramatically improve the SE of wavelength division multiplexing (WDM) optical communication systems.

  PDM-RZ quadrature modulation (RZ-QPSK) and PDM-RZ-8-PSK have been experimentally implemented for 100 Gb / s transmission: (P. Windsor and A. Gnauk, “On 25-GHz WDM grid. 1 12-Gb / s Polarization Multiplexed 16QAM ”, EcoC Proceedings 2008 Th.3.E.5 (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)), (T. Sakamoto, A. Ciba, T. Kawanishi," 50 of 50 Gb / s 16QAM generated by 4 parallel MZM -km SMF transmission ", Tu.l.E.3 (T.Sakamoto A. Chiba, T. Kawanishi, “50-km SMF translation of 50-Gb / s 16QAM generated by quad-parallel MZM”, Tu. E. 3)), (R. Freund, H. Rochet, Gruner, L. Mole, M. Zymets, A. Richter, “80 Gb / s / λ polarization multiplexed star 16QAM WDM transmission over 720 km SSMF with electrical distortion equalization”, OFC 2009 (R. Freund, H. Louchet, M. H. Gruner, L. Molle, M. Seimetz, A. Richter, “80 Gbit / s / λ Polarization Multiplexed Star-16QAM WDM Transmission over. 720km SSMF with Electronic Distribution Evaluation ", OFC 2009)), (X. Jou, J. Yu," 200Gb / s PDM 16QAM generation using new synchronization method ", ECOC Proceedings 2009, 10.3.5 (X. Zhou, J. Yu, “200-Gb / s PDM-16QAM generation using a new synthesizing method”, Proc. ECOC 2009, 10.3.5)), (A. Sanor, “PDM-16-QAM modulation and digital coherent 69.1-Tb / s (432 × 171-Gb / s) C- and extended L-band transmission over 240 km using detection ”, OFC 2010, PDPB7 (A. Sanol, “69.1-Tb / s (432 × 171-Gb / s) C-and Extended L-Band Transmission over 240 km Using PDM-16-QAM Modulation and Digital Coherent Detection”, PDB10. M-ary quadrature amplitude modulation (M-QAM) has also been studied using different techniques. For example, 14Gb / s PDM-128-QAM, 30Gb / s 64-QAM, and 40-Gb / to achieve high SE while simultaneously allowing sufficient bandwidth margin for optical add / drop s 16QAM is a suitable waveform generator (T. Sakamoto, A. Ciba, T. Kawanishi, “50-km SMF transmission of 50 Gb / s 16QAM generated by 4 parallel MZM”, Tu. l.E.3. And a parallel in-phase / quadrature (I / Q) modulator (A. Sanor, “69.1-Tb / s (432 × 171-Gb over 240 km using PDM-16-QAM modulation and digital coherent detection). / S) C- and extended L-band transmission ", see OFC 2010, PDPB7).

  (A. Sanor, “69.1-Tb / s (432 × 171-Gb / s) C- and extended L-band transmission over 240 km using PDM-16-QAM modulation and digital coherent detection”, OFC 2010, PDPB7) Then, 160 Gb / s 16-QAM was generated by providing two parallel embedded I / Q modulators using binary drive signals. The generation and transmission of a square 16QAM scheme uses multilevel drive signals and a single stage IQ modulator (P. Windsor and A. Gnauk, “1 12-Gb / s polarization multiplexed 16QAM on a 25-GHz WDM grid”). , ECOC Proceedings 2008 Th.3.E5), or built-in 4 parallel Mach-Zehnder modulator (MZM) (T. Sakamoto, A. Ciba, T. Kawanishi, “generated by 4 parallel MZM 50 Gb / s 16QAM 50-km SMF transmission, see Tu.l.E.3) (A. Sanor, 240 km with PDM-16-QAM modulation and digital coherent detection) Over 69.1-Tb / s (432 × 171-Gb / s) C- and extended L-band transmission ”, OFC 2010, P PB7).

  At this stage, the main issues of these solutions are IQ modulators (T. Sakamoto, A. Ciba, T. Kawanishi, “50 Gb / s 16QAM 50-km SMF transmission generated by 4 parallel MZM”, Tu. L. .E.3) and generation of high quality drive signals for built-in 4-parallel MZM performance.

  (X. Jou, J. Yu, “200 Gb / s PDM 16QAM Generation Using New Synchronization Method”, ECOC Proceedings 2009, 10.3.5), the serial I / Q modulator and the two-phase modulator are 16QAM. Used to generate an optical signal. (R. Freund, H. Rochette, M. Grüner, L. Mohr, M. Zymets, A. Richter, “80 Gb / s / λ polarization multiplexed star 16QAM WDM transmission in 720 km SSMF with electrical distortion equalization”, OFC 2009 ) Showed how to generate a star 16QAM signal using a binary drive signal based only on the latest modulator.

  A binary drive signal based on modern modulators was used to generate a star 16QAM signal. However, in one embodiment of the present invention, a new method for generating a 16QAM signal, which has been experimentally proven, is proposed.

  In one embodiment of the present invention, a parallel in-phase / quadrature modulator having a first signal branch and a second signal branch that is out of phase with the first signal branch and configured to be driven by a data signal; An intensity modulator driven by a clock signal and configured to bend the signal at a signal relay point. The light modulator has a parallel Mach-Zehnder modulator that is biased at the null point and functions as two zero chirp 0 / π phase modulators. The parallel Mach-Zehnder modulator has the same drive voltage of a full 2Vπ swing.

  The data signals of the light modulation devices each have a corresponding bit rate. In one embodiment of the invention, the clock signal is x gigahertz and at least one of the two corresponding bit rates of the two data signals is x gigabit / s, where x is a positive real number. is there.

  The light modulation device further includes a coherent detector. The coherent detector includes one or more deflecting plates, a diversity hybrid modulator, a local oscillator, a photodiode, a high-speed analog-to-digital converter, and a high-speed digital-to-analog converter.

  In one embodiment of the present invention, a parallel in-phase configured to have a first signal branch and a second signal branch that is π / 2 out of phase with the first signal branch and configured to be driven by two data signals. An optical modulation system is provided that includes a quadrature modulator, an intensity modulator driven by a clock signal, and a coherent detector.

  The coherent detector of the modulation system of one embodiment of the present invention includes a deflector plate, a diversity hybrid modulator, a local oscillator, a photodiode, a high-speed analog-to-digital converter, and / or a high-speed digital-to-analog converter.

  In one embodiment of the invention, the parallel in-phase / quadrature modulator comprises a parallel Mach-Zehnder modulator. The parallel Mach-Zehnder modulator is biased at a null point, for example, and functions as two zero chirp 0 / π phase modulators. Further, the parallel Mach-Zehnder modulator has an equivalent driving voltage of, for example, a full 2Vπ swing.

  Each of the two data signals has a corresponding bit rate.

  In one embodiment of the invention in which the clock signal is x gigahertz, at least one of the two corresponding bit rates of the two data signals is x gigabits / s, where x is a positive real number. is there.

  One embodiment of the present invention includes a method for generating a multilevel amplitude and phase modulated optical signal. Such a method generates, for example, a first signal and a second signal that is π / 2 out of phase with the first signal; combining the first signal and the second signal to generate a combined signal; Bending the combined signal by an intensity modulator at a signal relay point to generate a curved combined signal; and transmitting the curved combined signal. In one embodiment of the invention, the curved combined signal includes a return-to-zero pulse.

  One embodiment of the present invention further includes detecting the curved combined signal with a coherent detector. The detecting step includes, for example, digitally processing the curved combined signal.

  One embodiment of the present invention also includes a method for detecting a multi-level amplitude and phase modulated optical signal, wherein a second signal that is π / 2 out of phase with the first signal and the first signal by a coherent detector. Receiving a curved combined optical signal including the signal. A further step includes digitally processing the curved combined optical signal.

  One embodiment of the invention includes a method of encoding data for a 16QAM signal by an encoder device, encoding a rising edge as 01; encoding a falling edge as 10; encoding as a high level as 11; A step of encoding the low level as 00.

Although the invention has been described in general terms, a more complete understanding of the invention will be obtained by reference to the accompanying drawings, which are not necessarily drawn to scale.
FIG. 1 illustrates one embodiment of the present invention. FIG. 2 shows a measured waveform of an optical signal after in-phase / quadrature modulation and intensity modulation according to an embodiment of the present invention. FIG. 3 shows the optical spectrum after in-phase / quadrature modulation and intensity modulation according to one embodiment of the present invention. FIG. 4 shows a constellation detected by a coherent receiver according to an embodiment of the present invention. FIG. 5 shows an encoding scheme according to an embodiment of the present invention. FIG. 6 shows a diagram representing one embodiment of the present invention.

  Embodiments of the invention will be described more fully hereinafter with reference to the accompanying drawings, in which some examples of embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; Rather, these embodiments are provided as examples to meet appropriate legal needs. Throughout, the same reference numbers indicate the same elements.

  The operating principle of the proposed 16QAM signal generation of one embodiment of the present invention is shown, for example, in FIG. The 16QAM modulator includes a parallel I / Q modulator 102 driven by two data signals 103 and 104. The phase difference between the upper and lower branches of the I / Q modulator 102 is set to π / 2 in the parallel I / Q modulator 102, for example.

  Two parallel Mach-Zehnder modulators (MZM1 and MZM2) are also shown. The two parallel Mach-Zehnder modulators are biased, for example at the null point, and function as two zero chirp 0 / π phase modulators. Furthermore, MZM1 and MZM2 have the same drive voltage of, for example, a full 2Vπ swing.

  FIG. 1A shows a waveform after the I / Q modulator 102. If the bit rate of the data signal 103 or the data signal 104 is, for example, xG bits / s, the intensity modulator (IM) 105 is driven by the x GHz clock signal. The IM modulator 105 is used for bending a pulse (signal relay portion). The clock signal also cuts off the optical waveform signal after the IM modulator 105, as shown in FIG. However, the positions of the IM modulator 105 and the I / Q modulator 102 can be changed alternately. Optionally, for example, IM modulator 105 is placed before I / Q modulator 102 in the signal chain.

  The 16QAM optical signal is then detected by the coherent detector 106 after transmission for a predetermined distance, for example, based on digital signal processing (DSP).

  FIG. 2 shows a measurement waveform of the optical signal after the I / Q modulator 102 and the IM modulator 105. For example, in the experiment described here, the communication speed of 16QAM is 12.5 Gbaud.

  FIG. 3 shows the optical spectrum after I / Q modulator 102 and IM modulator 105. In the case described here, the signal has a return to zero (RZ) pulse so that the spectrum after the IM modulator 102 is, for example, spread.

  FIG. 4 illustrates a constellation detected by the coherent receiver 106 according to one embodiment of the present invention. In the illustrated embodiment, for example, a 16QAM optical signal is generated. As already known, such a constellation is a representation of a digital modulation scheme in the complex plane.

  In 16QAM according to this scheme and / or other embodiments of the present invention, the data signal 103 or the data signal 104 is uniquely encoded. For example, FIG. 5 illustrates a scheme for encoding data according to one embodiment of the present invention. The upper data representation in FIG. 5 is representative of normal binary phase shift keying (BPSK) data coding 1 and 0. The lower display of FIG. 5 is an example of new data after encoding according to an embodiment of the present invention. For example, in one embodiment, it is assumed that the rising edge is “01” and the falling edge is “10”. In such an embodiment, for example, if the signal is high and maintained in a 1 bit slot, it is encoded as “11” and if it is maintained in a low level and 1 bit slot, “00” ".

  FIG. 6 schematically provides a chart describing 16QAM optical signal generation according to an embodiment of the present invention.

  As shown, the generation of 16QAM signals for high-speed optical communication according to an embodiment of the present invention is advantageously accomplished with a simple configuration. In addition, an embodiment of the present invention is also advantageously achieved by a low cost configuration.

  The foregoing description illustrates and describes embodiments of the present invention. The present invention may be used in various other combinations, variations, and environments, and may be modified or modified within the scope of the inventive concept expressed herein, corresponding to the above content and / or skill or knowledge in the related art.

  The above embodiments are required to illustrate the best mode known for practicing the invention and to enable those skilled in the art to make such or other embodiments of the invention specific applications or uses of the invention. It is further intended to be usable with various variations. Further, it should be understood that the methods and systems of the present invention are performed solely by providing equipment and devices including simple or complex computers.

  Based on the description of the invention contained herein, applications of known systems and methods apparent to those skilled in the art are within the scope of the following claims. Furthermore, devices that have been invented or developed after performing the claimed methods and / or combinations of elements are within the scope of the invention. Therefore, the above description is not intended to limit the invention to the form or application disclosed individually. All publications cited herein are fully incorporated by reference in this application.

Claims (20)

A parallel in-phase / quadrature modulator configured to be driven by two data signals having a first signal branch and a second signal branch that is π / 2 out of phase with the first signal branch;
An intensity modulator driven by a clock signal and configured to bend the signal at a signal relay point;
A light modulation device.   The optical modulation device according to claim 1, wherein the parallel in-phase / quadrature modulator includes a parallel Mach-Zehnder modulator.   The optical modulation device according to claim 2, wherein the parallel Mach-Zehnder modulator is biased at a null point and functions as two zero chirp 0 / π phase modulators.   The optical modulation device according to claim 2, wherein the parallel Mach-Zehnder modulator has the same drive voltage of a full 2Vπ swing. The two data signals each have a corresponding bit rate, and the clock signal is x gigahertz;
The light modulation device according to claim 1, wherein at least one of two corresponding bit rates of the two data signals is x gigabit / s, wherein x is a positive real number.   The light modulation device according to claim 1, further comprising a coherent detector.   The optical modulation device according to claim 6, wherein the coherent detector further includes one or more deflecting plates, a diversity hybrid modulator, a local oscillator, a photodiode, a high-speed analog-to-digital converter, and a high-speed digital-to-analog converter. A parallel in-phase / quadrature modulator configured to be driven by two data signals having a first signal branch and a second signal branch that is π / 2 out of phase with the first signal branch;
An intensity modulator driven by a clock signal;
A coherent detector,
A light modulation system.   9. The light modulation system according to claim 8, wherein the coherent detector further includes one or more deflecting plates, a diversity hybrid modulator, a local oscillator, a photodiode, a high-speed analog-to-digital converter, and a high-speed digital-to-analog converter.   The optical modulation system according to claim 8, wherein the parallel in-phase / quadrature modulator further includes a parallel Mach-Zehnder modulator.   11. The light modulation system of claim 10, wherein the parallel Mach-Zehnder modulator is biased at a null point and functions as two zero chirp 0 / π phase modulators.   The optical modulation system according to claim 10, wherein the parallel Mach-Zehnder modulator has the same driving voltage of a full 2Vπ swing. The two data signals each have a corresponding bit rate, and the clock signal is x gigahertz;
9. The light modulation system of claim 8, wherein at least one of the two corresponding bit rates of the two data signals is x gigabits / s, where x is a positive real number. A method for generating a multilevel amplitude and phase modulated optical signal comprising:
Generating a first signal and a second signal that is π / 2 out of phase with the first signal;
Combining the first signal and the second signal to generate a combined signal;
Bending the combined signal by an intensity modulator at a signal relay point to generate a curved combined signal;
Transmitting the curved combined signal;
A method comprising stages.   The method of claim 14, wherein the curved combined signal comprises a zero return pulse.   The method of claim 14, further comprising detecting the curved combined signal with a coherent detector.   The method of claim 16, wherein the detecting step comprises digitally processing the curved combined signal. A method for detecting a multilevel amplitude and phase modulated optical signal comprising:
Receiving a curved combined optical signal comprising a first signal and a second signal that is π / 2 out of phase with the first signal by a coherent detector.   The method of claim 18, further comprising digitally processing the curved combined optical signal. A method of encoding data for a 16QAM signal by an encoder device, comprising:
Encode the rising edge as 01,
Encode the falling edge as 10;
Encode high level as 11,
Encode low level as 00,
A method comprising stages.