Optical Transmitter with Optical Receiver-Specific Dispersion Pre-Compensation

Patent metadata

Field	Value
Publication number	US-2017149503-A1
Application number	US-201715424587-A
Country	US
Kind code	A1
Filing date	Feb 3, 2017
Priority date	Oct 1, 2014
Publication date	May 25, 2017
Grant date	—

Abstract

An apparatus comprising a digital signal processor (DSP) unit configured to perform fiber dispersion pre-compensation on a digital signal sequence based on a dispersion value to produce a pre-compensated signal, wherein the dispersion value is associated with a remote optical receiver, a plurality of digital-to-analog converters (DACs) coupled to the DSP unit and configured to convert the pre-compensated signal into analog electrical signals, and a frontend coupled to the DACs and configured to convert the analog electrical signals into a first optical signal, adding a constant optical electric (E)-field to the first optical signal to produce a second optical signal, and transmit the second optical signal to the remote optical receiver.

First claim

What is claimed is:

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; a plurality of digital-to-analog converters (DACs) coupled to the DSP unit and configured to convert the pre-compensated signal 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 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 GI comprises 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 pre-compensated signal comprises a direct current (DC) component and a DC-free pre-compensated signal component, wherein the DSP unit is further configured to remove the DC component from the pre-compensated signal, and wherein the plurality of DACs convert the pre-compensated signal into the analog electrical signals.

7 . The apparatus of claim 1 , wherein the pre-compensated signal comprises a real component and an imaginary component, wherein a first DAC of the DACs converts the real component into a first analog electrical signal and a second DAC of the DACs converts the imaginary component into a second analog electrical signal.

8 . 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 perform optical I/Q modulation according to the analog electrical signals.

9 . The apparatus of claim 8 , 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 that provides 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 to provide the constant optical E-field.

10 . The apparatus of claim 8 , wherein the frontend further comprises an automatic bias controller that monitors and controls a bias at the first MZM, the second MZM, or both the first MZM and the second MZM.

11 . 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.

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; converting the pre-compensated signal into analog electrical signals; converting the analog electrical signals into a first optical signal; adding a constant optical electric (E)-field 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 GI comprises 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 pre-compensated signal comprises a direct current (DC) component and a DC-free pre-compensated signal component, wherein the method further comprises:
removing the DC component from the pre-compensated signal; and converting the pre-compensated signal into the analog electrical signals.

18 . The method of claim 12 , wherein the pre-compensated signal 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 a second analog electrical signal, respectively.

19 . 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.

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

Assignees

• Futurewei Technologies Inc

Inventors

• Liu Xiang
• Effenberger Frank

Classifications

• H04B10/25752

  Optical arrangements for wireless networks · CPC title

• H04B10/2507 Primary

  for the reduction or elimination of distortion or dispersion · CPC title

• H04B10/2575

  Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier · CPC title

• H04B10/2513 Primary

  due to chromatic dispersion · CPC title

• H04B10/25137 Primary

  using pulse shaping at the transmitter, e.g. pre-chirping or dispersion supported transmission [DST] · CPC title