Optical Receiver with Optical Transmitter-Specific Dispersion Post-Compensation

• US 20160099777A1
• Filed: 10/01/2014
• Published: 04/07/2016
• Est. Priority Date: 10/01/2014
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Liu, Xiang, Effenberger, Frank
• Granted Patent: US 9,806,813 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04B 10/2513 due to chromatic dispersion
• CPC Class Codes: H04B 10/614 comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers H04J14/06 takes precedence
• CPC Class Codes: H04B 10/6161 Compensation of chromatic dispersion

Abstract

An apparatus comprising a frontend configured to convert an optical IM signal associated with a remote optical transmitter into a plurality of analog electrical signals, determine a plurality of DC offsets for the analog electrical signals, remove the DC offsets from the analog electrical signals to produce a plurality of DC-free analog signals, and convert the DC-free analog signals into a plurality of DC-free digital signals, and a DSP unit coupled to the frontend and configured to perform fiber dispersion compensation on the DC-free digital signals according to a dispersion value associated with the remote optical transmitter to produce a plurality of DC-free compensated digital signals, and add the DC offsets to the compensated digital signals to produce a plurality of DC-restored compensated digital signals.

Claims

1. An apparatus comprising:

a frontend configured to;

convert an optical intensity-modulated (IM) signal associated with a remote optical transmitter into a plurality of analog electrical signals;

determine a plurality of direct current (DC) offsets for the analog electrical signals;

remove the DC offsets from the analog electrical signals to produce a plurality of DC-free analog signals; and

convert the DC-free analog signals into a plurality of DC-free digital signals; and

a digital signal processing (DSP) unit coupled to the frontend and configured to;

perform fiber dispersion compensation on the DC-free digital signals according to a dispersion value associated with the remote optical transmitter to produce a plurality of DC-free compensated digital signals; and

add the DC offsets to the compensated digital signals to produce a plurality of DC-restored compensated digital signals.

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

3. The apparatus of claim 1, wherein the analog electrical signals comprise a first polarization component and a second polarization component orthogonal to the first polarization component, wherein the first polarization component comprises a first in-phase (I) component and a first quadrature-phase (Q) component, and wherein the second polarization component comprises a second I component and a second Q component.

4. The apparatus of claim 3, wherein to perform the fiber dispersion compensation, the DSP unit is further configured to:

perform the fiber dispersion compensation on a first of the DC-free digital signals and a second of the DC-free digital signals associated with the first polarization component; and

perform the fiber dispersion compensation on a third of the DC-free digital signals and a fourth of the DC-free digital signals associated with the second polarization component.

5. The apparatus of claim 3, wherein the DSP unit is further configured to:

compute a first power signal from a first of the DC-restored digital signals and a second of the DC-restored digital signals associated with the first polarization component;

compute a second power signal from a third of the DC-restored digital signals and a fourth of the DC-restored digital signals associated with the second polarization component; and

add the first power signal and the second power signal to produce a compensated IM signal power.

6. The apparatus of claim 3, wherein to determine the DC offsets, the frontend is further configured to:

measure a first of the DC offsets for the first I component; and

measure a second of the DC offsets for the first Q component.

7. The apparatus of claim 6, wherein to add the DC offsets, the DSP unit is further configured to:

add the first DC offset to a first of the DC-free compensated digital signals associated with the first I component to produce a first of the DC-restored compensated digital signals; and

add the second DC offset to a second of the DC-free compensated digital signals associated with the first Q component to produce a second of the DC-restored compensated digital signals.

8. The apparatus of claim 1, wherein to perform the fiber dispersion compensation, the DSP unit is further configured to:

compute a static frequency domain filter to provide a dispersion effect corresponding to the dispersion value; and

filter the DC-free digital signals with the static frequency domain filter in a frequency domain.

9. The apparatus of claim 1, wherein the DSP unit is further configured to perform oversampling on the DC-free digital signals prior to performing the fiber dispersion compensation.

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

11. A method for use in an optical communication device, comprising:

receiving a first optical signal from a first remote optical transmitter;

receiving a second optical signal from a second remote optical transmitter;

converting the first optical signal into a plurality of first digital electrical signals;

converting the second optical signal into a plurality of second digital electrical signals;

compensating the first digital electrical signals according to a first dispersion value associated with the first remote optical transmitter to produce a plurality of first compensated digital electrical signals; and

compensating the second digital electrical signals according to a second dispersion value associated with the second remote optical transmitter to produce a plurality of second compensated digital electrical signals.

12. The method of claim 11, wherein converting the first optical IM signal further comprises:

converting the first optical signal into a plurality of analog electrical signals comprising two orthogonal polarization components, an X-polarization component and a Y-polarization component, wherein the X-polarization component comprises a first in-phase (I) component and a first quadrature-phase (Q) component, and wherein the Y-polarization component comprises a second I component and a second Q component;

determining a first direct current (DC) offset for the first I component;

determining a second DC offset for the first Q component;

removing the first DC offset from the first I component to produce one of the first digital electrical signals; and

removing the second DC offset from the first Q component to produce another of the first digital electrical signals.

13. The method of claim 12 further comprising:

adding the first DC offset to a first of the compensated digital electrical signals associated with the first I component; and

adding the second DC offset to a second of the compensated digital electrical signals associated with the first Q component.

14. The method of claim 11, wherein the first compensated digital electrical signals comprise two orthogonal polarization components, an X-polarization component and a Y-polarization component, and wherein the method further comprises:

computing a first power signal for the X-polarization component;

computing a second power signal for the Y-polarization component; and

adding the first power signal and the second power signal to produce a compensated IM signal power.

15. The method of claim 11 further comprising:

assigning a first transmission slot to the first remote optical transmitter, wherein the first optical IM signal is received in the first transmission time slot;

assigning a second transmission slot next to the first transmission slot to the second remote optical transmitter, wherein the second optical IM signal is received in the second transmission time slot; and

inserting a guard interval (GI) between the first transmission slot and the second transmission slot, wherein the GI comprises a time duration greater than a mean value of a first pulse broadening duration associated with the first dispersion value and a second pulse broadening duration associated with the second dispersion value.

16. The method of claim 11 further comprising:

assigning a first transmission time slot to the first remote optical transmitter;

assigning a second transmission time slot to the second remote optical transmitter;

assigning a third transmission time slot to a third remote optical transmitter; and

arranging the first transmission time slot, the second transmission time slot, and the third transmission time slot based on transmission wavelengths associated with the first remote optical transmitter, the second remote optical transmitter, and the third remote optical transmitter.

17. The method of claim 11, wherein the first optical signal comprises an intensity modulated signal or a polarization-division multiplexed (PDM) intensity modulated signal, and wherein the first optical signal carries an on-off keying (OOK) signal, an n-level pulse-amplitude modulation (n-PAM) signal, or a discrete multi-tone (DMT) signal.

18. A method for use in an optical communication device, comprising:

receiving a transmission schedule comprising a plurality of transmission time slots, wherein the transmission schedule provides an assigned time slot to the device, and wherein the transmission schedule comprises a guard interval (GI) that is based on a chromatic dispersion (CD) associated with the device;

converting a digital signal sequence into an optical signal by performing an intensity modulation; and

transmitting the optical signal in the assigned time slot.

19. The method of claim 18, wherein the GI comprises a time duration that is greater than a time difference between a symbol period and a broadened pulse period caused by the CD.

20. The method of claim 18, wherein the optical communication device is an optical network unit (ONU) transmitter.