Signal generating apparatus and signal generating method

Patent metadata

Field	Value
Publication number	US-9819525-B2
Application number	US-201314906632-A
Country	US
Kind code	B2
Filing date	Jul 31, 2013
Priority date	Jul 31, 2013
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

To provide signal generating apparatus that is capable of controlling the DC bias of the optical modulator applicable to various kinds of modulation format, a signal processing apparatus includes a digital processing unit for deserializing an input digital data into parallel data lanes, for comparing the value of the digital data of symbol rate F to at least one predetermined threshold value, for selecting an offset value based on the result of the comparison; and for adding the selected offset value to the digital data, a converting unit for converting the digital data added the offset value to analog signals in each lane; an optical modulating unit for modulating a lightwave according to the analog signals with predetermined modulation format at the symbol rate F, where the modulated signal contains a frequency component at F/N.

First claim

What is claimed is:

1. A signal generating apparatus, comprising:
a digital processing unit that
deserializes an input digital data into parallel data lanes;
compares the value of the digital data of symbol rate F, where F is a real number, to at least one predetermined threshold value;
selects an offset value based on the result of the comparison; and
adds the selected offset value to the digital data,

a converting unit that converts the digital data added the offset value to analog signals in each data lane; and
an optical modulating unit that modulates a lightwave according to the analog signals with predetermined modulation format at the symbol rate F, where the modulated signal contains a frequency component at F/N and N is an integer strictly greater than 1 , wherein
the offset value is selected among a set of selectable offset values,
which are updated with a temporal periodicity of N/F.

2. The signal generating apparatus according to claim 1 , further comprising:
a detecting unit that generates a monitor signal from the modulated lightwave;
a filter unit that extracts a frequency component at a frequency equal to the frequency F/N or to a harmonic frequency of F/N from the monitor signal; and
a control unit that controls a bias voltage for the optical modulating unit according to the amplitude and the phase of the frequency component extracted from the monitor signal.

3. The signal generating apparatus according to claim 1 , wherein:
each of the threshold value is an M bit value, where M is an integer;
each of the offset value is an L bit value, where L is an integer;
each of the digital data is coded on a number of bits equal or greater than L+M;
the comparisons between the digital data and the threshold values are performed by comparing the M most significant bits of the data to the threshold values; and
the step of adding offset values is performed by adding offset values to the L least significant bits of the digital data.

4. The signal generating apparatus according to claim 1 , wherein:
the number of the threshold values is equal to two;
a first sign is a sign of the offset value added to the digital data in case that the digital data is greater than or equal to first value of the threshold value and less than second value of the threshold value;
the second sign is a sign of the offset value in case that the digital data is greater than both of the first threshold value and the second threshold value, or, in case that the digital data is smaller than both of the first threshold value and the second threshold value; and
the first sign is different from the second sign.

5. The signal generating apparatus according to claim 2 , wherein:
the number N is equal for all the data lanes of digital data;
the optical modulating unit comprises child Inphase Mach Zehnder Modulator and a child Quadrature Phase Mach Zehnder Modulator; and
the control unit controls a first bias that is the DC bias of the child Inphase Mach Zehnder Modulator, a second bias that is the DC bias of the child Quadrature Phase Mach Zehnder Modulator and a third bias that is the bias of the angle of quadrature of the optical modulating unit.

6. The signal generating apparatus according to claim 2 , wherein
the number N of the data converted to analog signal used for the child Inphase Mach Zehnder modulator of the optical modulating unit is N(I), and the number N of the data converted to analog signal used for the child Quadrature Phase Mach Zehnder modulator of the optical modulating unit is N(Q), so that N(I) is distinct from N(Q);
the bias voltage for controlling the child Inphase Mach Zehnder Modulator of the optical modulating unit is controlled according to the extracted frequency equal to F/N(I) or a harmonic frequency of F/N(I);
the bias voltage for controlling the child Quadrature Phase Mach Zehnder Modulator of the optical modulating unit is controlled according to the extracted frequency equal to F/N(Q) or a harmonic frequency of F/N(Q); and
the bias voltage for controlling the angle of quadrature of the optical modulating unit is controlled according to the filtered frequency equal to a common harmonic of the frequencies F/N(I) and F/N(Q).

7. The signal generating apparatus according to claim 1 wherein
the predetermined modulation format is reconfigurable.

8. The signal generating apparatus according to claim 1 , wherein
the digital processing unit performs equalization of the input data and the equalization is settable and reconfigurable.

9. The signal generating apparatus according to claim 8 , wherein
the equalization includes at least one of digital RZ (return to zero) carving function, linear pre-distortion function, nonlinear pre-distortion function and imperfections pre-distortion function.

10. A signal generating method, comprising:
deserializing an input digital data into parallel data lanes;
comparing the value of the digital data of symbol rate F, where F is a real number, to at least one predetermined threshold value;
selecting an offset value based on the result of the comparison;
adding the selected offset value to the digital data;
converting the digital data added the offset value to analog signals in each lanes; and
modulating a lightwave according to the analog signals with predetermined modulation format at the symbol rate F, where the modulated signal contains a frequency component at F/N and N is an integer strictly greater than 1 , wherein
the offset value is selected among a set of selectable offset values, which are updated with a temporal periodicity of N/F.

11. The signal generating apparatus according to claim 2 , wherein:
each of the threshold value is an M bit value, where M is an integer;
each of the offset value is an L bit value, where L is an integer;
each of the digital data is coded on a number of bits equal or greater than L+M;
the comparisons between the digital data and the threshold values are performed by comparing the M most significant bits of the data to the threshold values; and
the step of adding offset values is performed by adding offset values to the L least significant bits of the digital data.

12. The signal generating apparatus according to claim 2 , wherein:
the number of the threshold values is equal to two;
a first sign is a sign of the offset value added to the digital data in case that the digital data is greater than or equal to first value of the threshold value and less than second value of the threshold value;
the second sign is a sign of the offset value in case that the digital data is greater than both of the first threshold value and the second threshold value, or, in case that the digital data is smaller than both of the first threshold value and the second threshold value; and
the first sign is different from the second sign.

13. The signal generating apparatus according to claim 3 , wherein:
the number of the threshold values is equal to two;
a first sign is a sign of the offset value added to the digital data in case that the digital data is greater than or equal to first value of the threshold value and less than second value of the threshold value;
the second sign is a sign of the offset value in case that the digital data is greater than both of the first threshold value and the second threshold value, or, in case that the digital data is smaller than both of the first threshold value and the second threshold value; and
the first sign is different from the second sign.

14. The signal generating apparatus according to claim 3 , wherein:
the number N is equal for all the data lanes of digital data

Assignees

• Nec Corp

Inventors

• Le Taillandier De Gabory Emmanuel
• Ogasahara Daisaku
• Fujisawa Shinsuke

Classifications

• H04L25/06

  DC level restoring means; Bias distortion correction {; Decision circuits providing symbol by symbol detection} · CPC title

• H04B10/50575

  to control the modulator DC bias · CPC title

• H04L27/2096 Primary

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

• H04B10/50595

  to control the modulator DC bias · CPC title

• H04B10/5561

  Digital phase modulation · CPC title