Optical signal modulation

Patent metadata

Field	Value
Publication number	US-9485030-B2
Application number	US-201414526413-A
Country	US
Kind code	B2
Filing date	Oct 28, 2014
Priority date	Jul 31, 2008
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

Abstract

A 2 n -QAM (e.g. 16-QAM) optical modulator comprising cascaded I-Q modulators. The first I-Q modulator applies 2 n-2 (e.g. 4) QAM to an optical signal, having a constellation diagram with the 2 n-2 (e.g., 4) constellation points located in quadrant I. The second I-Q modulator subsequently applies a quaternary phase-shift keying (QPSK) modulation scheme to the optical signal, thereby rotating the constellation points of the 2 n-2 -QAM modulation scheme to quadrants II, III and IV, to produce a 2 n -QAM modulation constellation diagram. The rotation causes the 2 n -QAM modulator to inherently apply four quadrant differential encoding to the optical signal. A method of 2 n -QAM optical modulation is also provided and optical signal transmission apparatus comprising the 2 n -QAM optical modulator.

First claim

The invention claimed is:

1. A 2 n -quadrature amplitude modulation optical modulator device comprising:
a first optical modulation apparatus configured to apply a 2 n-2 amplitude modulation scheme having 2 n-2 constellation points arranged in a first quadrant of its constellation diagram to a received optical signal in order to generate an intermediate optical signal; and
a second optical modulation apparatus configured to apply a quaternary phase shift keying modulation scheme to the intermediate optical signal received from the first optical modulation apparatus to produce 2 n constellation points distributed across the four quadrants of the constellation diagram,
wherein n is an even number greater than or equal to 2.

2. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 1 , wherein n is at least 4, the constellation points of the first optical modulation apparatus being arranged in a substantially square constellation.

3. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 2 , wherein n is 4 or 6.

4. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 3 , wherein the first optical modulation apparatus comprises:
an in-phase/quadrature optical modulator comprising an optical input configured to receive an optical signal to be modulated, an in-phase branch comprising a first optical modulator, a quadrature branch comprising a second optical modulator and a π/2 phase shifter, and an optical output; and
a drive apparatus configured to deliver √(2 n-2 )-level electrical drive signals to the first and second optical modulators, such that the in-phase/quadrature optical modulator is operable to apply the 2 n-2 amplitude modulation scheme.

5. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 4 , wherein the first and second optical modulators comprise Mach-Zehnder modulators.

6. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 5 , wherein n is 4 and the two-level electrical drive signals comprise approximately 0.39 V π where V π is the switching voltage of the respective Mach-Zehnder modulator, and zero volts.

7. A 2 n -quadrature amplitude modulation optical modulator device comprising:
a first optical modulation apparatus configured to apply a quaternary phase shift keying modulation scheme to a received optical signal in order to generate an intermediate optical signal; and
a second optical modulation apparatus configured to apply a 2 n-2 amplitude modulation scheme to the intermediate optical signal to produce 2 n constellation points distributed across the four quadrants of the constellation diagram,
wherein n is an even number greater than or equal to 2.

8. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 7 , wherein n is at least 4, the constellation points of the second optical modulation apparatus being arranged in a substantially square constellation.

9. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 8 , wherein n is 4 or 6.

10. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 9 , wherein the second optical modulation apparatus comprises:
an in-phase/quadrature optical modulator comprising an optical input configured to receive an optical signal to be modulated, an in-phase branch comprising a first optical modulator, a quadrature branch comprising a second optical modulator and a π/2 phase shifter, and an optical output; and
drive apparatus configured to deliver √(2 n-2 )-level electrical drive signals to the first and second optical modulators, such that the in-phase/quadrature optical modulator is operable to apply the 2 n-2 amplitude modulation scheme.

11. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 10 , wherein the first and second optical modulators comprise Mach-Zehnder modulators.

12. The 2 n -quadrature amplitude modulation optical modulator as claimed in claim 11 , wherein n is 4 and the two-level electrical drive signals comprise approximately 0.39 V π where V π is the switching voltage of the respective Mach-Zehnder modulator, and zero volts.

13. An optical signal transmission apparatus comprising:
an optical source having an optical output and being operable to generate an optical signal; and
a 2 n -quadrature amplitude modulation optical modulator; and
the optical output of the optical source being coupled to a first optical modulation apparatus of the 2 n -quadrature amplitude modulation optical modulator,
wherein the 2 n -quadrature amplitude modulation optical modulator device comprises:
the first optical modulation apparatus configured to apply a 2 n-2 amplitude modulation scheme having 2 n-2 constellation points arranged in a first quadrant of its constellation diagram to a received optical signal in order to generate an intermediate optical signal,
a second optical modulation apparatus configured to apply a quaternary phase shift keying modulation scheme to the intermediate optical signal received from the first optical modulation apparatus to produce 2 n constellation points distributed across the four quadrants of the constellation diagram,

wherein n is an even number greater than or equal to 2.

14. An optical signal transmission apparatus comprising:
an optical source having an optical output and being operable to generate an optical signal; and
a 2 n -quadrature amplitude modulation optical modulator;
the optical output of the optical source being coupled to a first optical modulation apparatus of the 2 n -quadrature amplitude modulation optical modulator,
wherein the 2 n -quadrature amplitude modulation optical modulator device comprises:
the first optical modulation apparatus configured to apply a quaternary phase shift keying modulation scheme to a received optical signal in order to generate an intermediate optical signal; and

a second optical modulation apparatus configured to apply a 2 n-2 amplitude modulation scheme to the intermediate optical signal to produce 2 n constellation points distributed across the four quadrants of the constellation diagram,
wherein n is an even number greater than or equal to 2.

Assignees

• Ericsson Telefon Ab L M
• ERICSSON TELEFON AB L M (publ)

Inventors

• Secondini Marco
• Cavaliere Fabio

Classifications

• H04B10/548

  Phase or frequency modulation · CPC title

• H04B10/5161

  Combination of different modulation schemes · CPC title

• H04L27/3488

  Multiresolution systems · CPC title

• H04L27/2096

  Arrangements for directly or externally modulating an optical carrier (optical modulation H04B10/503) · CPC title

• H04B10/541 Primary

  Digital intensity or amplitude modulation · CPC title