Transmitter apparatus and method

1. An apparatus comprising:

a digital signal processing module configured to receive a data stream and generate a plurality of digital multiple tones ranging from a lowest frequency to a highest frequency, wherein the plurality of digital multiple tones form a frequency sequence pattern between the lowest frequency and the highest frequency;

a plurality of digital-to-analog converters coupled to the digital signal processing module;

a plurality of drivers coupled to respective digital-to-analog converters;

an electro-optic modulator having inputs coupled to the drivers and outputs coupled to a fiber, wherein the electro-optic modulator is configured to receive the plurality of digital multiple tones, copy the digital multiple tones onto a plurality of different wavelengths and generate a plurality of corresponding optical signals on each wavelength, and wherein on each wavelength, the plurality of corresponding optical signals keep the same frequency sequence pattern; and

a multi-wavelength light source coupled to the electro-optic modulator, wherein the multi-wavelength light source is configured to generate the plurality of different wavelengths.

2. The apparatus of claim 1 , wherein:

the digital signal processing module, the digital-to-analog converters, the drivers and the electro-optic modulator are connected in cascade.

3. The apparatus of claim 1 , wherein:

the electro-optic modulator is coupled to an optical source.

4. The apparatus of claim 1 , wherein the digital signal processing module is configured to generate:

a first in-phase signal in a first polarization direction at a first output of the digital signal processing module;

a first quadrature signal in the first polarization direction at a second output of the digital signal processing module;

a second in-phase signal in a second polarization direction at a third output of the digital signal processing module; and

a second quadrature signal in the second polarization direction at a fourth output of the digital signal processing module.

5. The apparatus of claim 4 , wherein:

the first output of the digital signal processing module is coupled to a first input of the electro-optic modulator through a first digital-to-analog converter and a first driver;

the second output of the digital signal processing module is coupled to a second input of the electro-optic modulator through a second digital-to-analog converter and a second driver;

the third output of the digital signal processing module is coupled to a third input of the electro-optic modulator through a third digital-to-analog converter and a third driver; and

the fourth output of the digital signal processing module is coupled to a fourth input of the electro-optic modulator through a fourth digital-to-analog converter and a fourth driver.

6. The apparatus of claim 1 , wherein:

each tone of the digital multiple tones is copied onto a single wavelength division multiplexing channel.

7. A device comprising:

a processor configured to generate N digital multiple tones ranging from a first frequency to a second frequency, wherein:

a frequency gap Δfc is placed between a center frequency of a tone to a center frequency of an adjacent tone; and

the N digital multiple tones form a frequency sequence pattern between the first frequency and the second frequency;

an electro-optic modulator coupled to an optical source, wherein the electro-optic modulator is configured to:

receive the N digital multiple tones; and

copy the N digital multiple tones onto N different wavelengths, wherein the electro-optic modulator is configured to generate N corresponding optical signals on each wavelength, and wherein on each wavelength, the N corresponding optical signals keep the same frequency sequence pattern and the N corresponding optical signals are placed in a symmetrical manner with respect to a center optical signal of the N corresponding optical signals; and

an optical filter coupled to the electro-optic modulator, wherein the optical filter is configured such that:

a single tone is selected at each wavelength division multiplexing channel.

8. The device of claim 7 , wherein:

the processor is a digital signal processor.

9. The device of claim 7 , wherein the processor is configured to generate:

a first in-phase signal in a first polarization direction at a first output of the processor;

a first quadrature signal in the first polarization direction at a second output of the processor;

a second in-phase signal in a second polarization direction at a third output of the processor; and

a second quadrature signal in the second polarization direction at a fourth output of the processor.

10. The device of claim 9 , further comprising:

a first digital-to-analog converter coupled to the first output of the processor;

a second digital-to-analog converter coupled to the second output of the processor;

a third digital-to-analog converter coupled to the third output of the processor; and

a fourth digital-to-analog converter coupled to the fourth output of the processor.

11. The device of claim 10 , further comprising:

a first driver coupled between the first digital-to-analog converter and a first input of the electro-optic modulator;

a second driver coupled between the second digital-to-analog converter and a second input of the electro-optic modulator;

a third driver coupled between the third digital-to-analog converter and a third input of the electro-optic modulator; and

a fourth driver coupled between the fourth digital-to-analog converter and a fourth input of the electro-optic modulator.

12. The device of claim 11 , wherein:

the electro-optic modulator is coupled to a laser source.

13. The device of claim 7 , wherein:

the processor is configured to generate a first tone, a second tone and a third tone; and

the optical source is configured to generate a first wavelength λ 1 with a first frequency f 1 , a second wavelength λ 2 with a second frequency f 2 and a third wavelength λ 3 with a third frequency f 3 .

14. The device of claim 13 , wherein:

the electro-optic modulator and the optical filter are configured such that:

the first tone is selected and copied onto a third wavelength channel, wherein a center frequency of the third wavelength channel is equal to (f 3 -Δfc);

the second tone is selected and copied onto a second wavelength channel, wherein a center frequency of the second wavelength channel is equal to f 2 ; and

the third tone is selected and copied onto a first wavelength channel, wherein a center frequency of the first wavelength channel is equal to (f 1 +Δfc).

15. A method comprising:

providing a data stream fed to a processor;

generating N digital multiple tones based upon the data stream, wherein the N digital multiple tones are in a range from a first frequency to a second frequency and the N digital multiple tones form a frequency sequence pattern between the first frequency and the second frequency;

copying the N digital multiple tones onto N different wavelength division multiplexing channels by an electro-optic element, wherein the electro-optic element is configured to generate N corresponding optical signals on each wavelength division multiplexing channel, and wherein on a first wavelength division multiplexing channel, N optical signals keep the same frequency sequence pattern, and wherein the N optical signals of the first wavelength division multiplexing channel are in a range from a third frequency to a fourth frequency, and wherein one optical signal of the N optical signals of the first wavelength division multiplexing channel is placed at a center frequency of the third frequency and the fourth frequency; and

selecting a tone from the N digital multiple tones at a corresponding wavelength division multiplexing channel.

16. The method of claim 15 , further comprising:

based upon the data stream, generating a first in-phase signal in a first polarization direction at a first output of the processor;

generating a first quadrature signal in the first polarization direction at a second output of the processor;

generating a second in-phase signal in a second polarization direction at a third output of the processor; and

generating a second quadrature signal in the second polarization direction at a fourth output of the processor.

17. The method of claim 15 , further comprising:

generating a first tone, a second tone and a third tone, wherein a frequency gap Δfc is placed between two adjacent tones; and

copying the first tone, the second tone and the third tone onto three different wavelength division multiplexing channels λ 1 , λ 2 and λ 3 .

18. The method of claim 17 , further comprising:

filtering out the first tone and the second tone at the channel λ 1 ;

filtering out the first tone and the third tone at the channel λ 2 ; and

filtering out the second tone and the third tone at the channel λ 3 .

19. The method of claim 15 , wherein:

the electro-optic element is coupled to an optical source.

20. The method of claim 15 , wherein:

the processor is a digital signal processor.