QAM vector signal generation by external modulator

• US 10,073,319 B2
• Filed: 05/04/2016
• Issued: 09/11/2018
• Est. Priority Date: 05/04/2015
• Status: Active Grant

• Current Assignee: ZTE Corporation
• Original Assignee: ZTE Corporation
• Inventors: Yu, Jianjun, Li, Xinying
• Primary Examiner(s): Vo, Don N
• Application Number:
  US15/146,787
• Publication Number:
  US 20160329967A1
• Time in Patent Office: 860 Days
• Field of Search: 398185
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 1/2255 controlled by a high-frequency electromagnetic component in an electric waveguide structure
• CPC Class Codes: H04B 10/541 Digital intensity or amplitude modulation

Abstract

An optical signal transmitter produces optical signals comprising QAM modulated vector signals generated using a single external electro-optical modulator operated in conjunction with a wavelength selective switch. The transmission processing achieves adaptive photonic frequency multiplication and comprises QAM modulated signals with high order constellations such as 8-QAM, 16-QAM, 32-QAM and 64-QAM.

Claims

1. A method of optical communication, implemented at a transmitter in an optical communication network, comprising:

modulating information bits to be transferred using a multi-amplitude amplitude modulation scheme to produce modulated electrical in-phase and quadrature component signals;

mitigating distortions in a subsequence electrical to optical conversion stage by precoding the in-phase and quadrature component signals, wherein the precoding modifies both amplitudes and phases of the component signals to attain a multi-amplitude vector modulation and modifies only phases of the component signals to attain a constant-amplitude modulation; and

converting the precoded component signals using a single electro-optical modulator into a radio frequency (RF) optical signal comprising two component optical signals at two different subcarrier frequencies and with a suppressed carrier signal.

2. The method of claim 1, wherein the electro-optical modulator is of a Mach-Zehnder modulator (MZM) type.

3. The method of claim 2, wherein the MZM electro-optical modulator is operated at a minimum transmission point.

4. The method of claim 2, wherein the MZM electro-optical modulator includes an MZM intensity modulator.

5. The method of claim 1, wherein the electro-optical modulator is an external electro-optical modulator.

6. The method of claim 1, wherein the multi-amplitude amplitude modulation scheme uses a quadrature amplitude modulation (QAM) constellation of size 8 or higher.

7. The method of claim 1, wherein the precoding comprises precoding amplitudes to mitigate distortions modeled as Bessel functions.

8. The method of claim 1, further including using an external cavity laser to input an optical carrier signal to the single electro-optical modulator.

9. An optical transmission apparatus, comprising:

a modulation circuit that modulates information bits to be transferred using a multi-amplitude amplitude modulation scheme to produce modulated electrical in-phase and quadrature component signals;

a precoder that mitigates distortions in a subsequence electrical to optical conversion stage by precoding the in-phase and quadrature component signals, wherein the precoding modifies both amplitudes and phases of the component signals to attain a multi-amplitude vector modulation and modifies only phases of the component signals to attain a constant-amplitude modulation; and

an electro-optical modulation stage that converts the precoded component signals using a single electro-optical modulator into a radio frequency (RF) optical signal comprising two component optical signals at two different subcarrier frequencies and with a suppressed carrier signal.

10. The apparatus of claim 9, wherein the electro-optical modulator is of a Mach-Zehnder modulator (MZM) type.

11. The apparatus of claim 10, wherein the MZM electro-optical modulator is operated at a minimum transmission point.

12. The apparatus of claim 10, wherein the MZM electro-optical modulator includes an MZM intensity modulator.

13. The apparatus of claim 9, wherein the electro-optical modulator is an external electro-optical modulator.

14. The apparatus of claim 9, wherein the multi-amplitude amplitude modulation scheme uses a quadrature amplitude modulation (QAM) constellation of size 8 or higher.

15. The apparatus of claim 9, wherein the precoding comprises precoding amplitudes to mitigate distortions modeled as Bessel functions.

16. The apparatus of claim 9, further including using an external cavity laser to input an optical carrier signal to the single electro-optical modulator.

17. A method of receiving a single polarization or dual polarization optical vector signal at an optical receiver, by:

performing direct detection of the optical signal to generate sampled digital data in electrical domain; and

demodulating the sampled digital data to recover information bits used to generate the optical signal;

wherein the optical signal is generated from the information bits by modulating information bits to be transferred using a multi-amplitude amplitude modulation scheme to produce modulated electrical in-phase and quadrature component signals;

mitigating distortions in a subsequence electrical to optical conversion stage by precoding the in-phase and quadrature component signals, wherein the precoding modifies both amplitudes and phases of the component signals to attain a multi-amplitude vector modulation and modifies only phases of the component signals to attain a constant-amplitude modulation; and

converting the precoded component signals using a single electro-optical modulator into a radio frequency (RF) optical signal comprising two component optical signals at two different subcarrier frequencies and with a suppressed carrier signal.

18. The method of claim 17, wherein the operation of direct detection uses two photon detectors after a polarization beam splitter when the optical signal is dual polarization optical vector signal.

19. An optical signal receiver apparatus for of receiving a single polarization or dual polarization optical vector signal, comprising:

one or two photon detectors for performing direct detection of the optical signal to generate sampled digital data in electrical domain after using a polarization beam splitter to randomly separate polarization of the signals;

a memory for storing instructions, and

a digital signal processor for reading instructions from the memory and implementing a method of demodulating the sampled digital data to recover information bits used to generate the optical signal;

wherein the optical signal is generated from the information bits by modulating information bits to be transferred using a multi-amplitude amplitude modulation scheme to produce modulated electrical in-phase and quadrature component signals;

mitigating distortions in a subsequence electrical to optical conversion stage by precoding the in-phase and quadrature component signals, wherein the precoding modifies both amplitudes and phases of the component signals to attain a multi-amplitude vector modulation and modifies only phases of the component signals to attain a constant-amplitude modulation; and

converting the precoded component signals using a single electro-optical modulator into a radio frequency (RF) optical signal comprising two component optical signals at two different subcarrier frequencies and with a suppressed carrier signal.