Optical transmitter with optical receiver-specific dispersion pre-compensation

1. An apparatus comprising:

a digital signal processing (DSP) unit configured to:

perform fiber dispersion pre-compensation on a digital signal sequence assigned to a remote optical receiver based on a dispersion value associated with the remote optical receiver to produce a pre-compensated signal; and

separate a direct current (DC) component from the pre-compensated signal to produce a DC-free pre-compensated signal component;

a plurality of digital-to-analog converters (DACs) coupled to the DSP unit and configured to convert the DC-free pre-compensated signal component into analog electrical signals; and

a frontend coupled to the DACs and configured to:

convert the analog electrical signals into a first optical signal;

add a constant optical electric (E)-field equal to the DC component to the first optical signal to produce a second optical signal; and

transmit the second optical signal to the remote optical receiver.

2. The apparatus of claim 1 , wherein the dispersion value is opposite to an amount of chromatic dispersion (CD) associated with the remote optical receiver.

3. The apparatus of claim 2 , wherein the first optical signal comprises a plurality of light pulses carrying the digital signal sequence, and wherein the DSP unit is further configured to:

insert a first guard interval (GI) before the digital signal sequence; and

insert a second GI after the digital signal sequence,

wherein the first GI and the second GI each comprise a duration greater than a DC-induced pulse broadening duration.

4. The apparatus of claim 3 , wherein the first GI and the second GI comprise an integer number of symbol periods, and wherein the symbol periods are based on a transmission baud rate of the first optical signal.

5. The apparatus of claim 1 , wherein the DSP unit is further configured to:

determine a frequency domain filter corresponding to the dispersion value; and

filter the digital signal sequence with the frequency domain filter in a frequency domain.

6. The apparatus of claim 1 , wherein the DC-free pre-compensated signal component comprises a real component and an imaginary component, wherein a first DAC of the DACs is configured to convert the real component into a first analog electrical signal and a second DAC of the DACs is configured to convert the imaginary component into a second analog electrical signal.

7. The apparatus of claim 1 , wherein the frontend comprises an optical in-phase/quadrature (I/Q) modulator comprising:

an in-phase (I) branch;

a quadrature (Q) branch;

a first Mach-Zehnder modulator (MZM) coupled to the I branch; and

a second MZM coupled to the Q branch,

wherein the first MZM and the second MZM are configured to perform optical I/Q modulation according to the analog electrical signals.

8. The apparatus of claim 7 , wherein the frontend comprises a Mach-Zehnder interferometer (MZI) comprising:

a first interferometer arm coupled to the optical I/Q modulator;

a second interferometer arm configured to provide an about zero phase differential between the second interferometer arm and the I branch; and

an optical splitter coupled to the first interferometer arm and the second interferometer arm and comprising a pre-determined optical splitting ratio configured to provide the constant optical E-field.

9. The apparatus of claim 7 , wherein the frontend further comprises an automatic bias controller configured to monitor and control a bias at the first MZM, the second MZM, or both the first MZM and the second MZM.

10. The apparatus of claim 1 , wherein the apparatus is an optical line terminal (OLT) transmitter, and wherein the remote optical receiver is an optical network unit (ONU) receiver.

11. The apparatus of claim 1 , wherein the DSP unit is further configured to determine the dispersion value based on a chromatic dispersion (CD) effect measured during initial set-up or installation of an optical network unit (ONU) comprising the remote optical receiver.

12. A method comprising:

performing fiber dispersion pre-compensation on a digital signal sequence assigned to a remote optical receiver based on a dispersion value associated with the remote optical receiver to produce a pre-compensated signal;

separating a direct current (DC) component from the pre-compensated signal to produce a DC-free pre-compensated signal component;

converting the DC-free pre-compensated signal component into analog electrical signals;

converting the analog electrical signals into a first optical signal;

adding a constant optical electric (E)-field equal to the DC component to the first optical signal to produce a second optical signal; and

transmitting the second optical signal to the remote optical receiver.

13. The method of claim 12 , wherein the dispersion value is opposite to an amount of chromatic dispersion (CD) associated with the remote optical receiver.

14. The method of claim 13 , wherein the first optical signal comprises a plurality of light pulses carrying the digital signal sequence, and wherein the method further comprises:

inserting a first guard interval (GI) before the digital signal sequence; and

inserting a second GI after the digital signal sequence,

wherein the first GI and the second GI each comprise a duration greater than a DC-induced pulse broadening duration.

15. The method of claim 14 , wherein the first GI and the second GI comprise an integer number of symbol periods, and wherein the symbol periods are based on a transmission baud rate of the first optical signal.

16. The method of claim 12 , performing the fiber dispersion pre-compensation comprises:

determining a frequency domain filter corresponding to the dispersion value; and

filtering the digital signal sequence with the frequency domain filter in a frequency domain.

17. The method of claim 12 , wherein the DC-free pre-compensated signal component comprises a real component and an imaginary component, and wherein the method further comprises converting the real component and the imaginary component into a first analog electrical signal and a second analog electrical signal, respectively.

18. The method of claim 12 , wherein converting the analog electrical signals comprises performing optical in-phase/quadrature (I/Q) modulation according to the analog electrical signals.

19. The method of claim 18 , wherein an optical line terminal (OLT) performs the method, and wherein the remote optical receiver is an optical network unit (ONU) receiver.

20. The method of claim 12 , further comprising determining the dispersion value based on a chromatic dispersion (CD) effect measured during initial set-up or installation of an optical network unit (ONU) comprising the remote optical receiver.