Self-homodyne carrier multiplexed transmission system and method for coherent optical links

Patent metadata

Field	Value
Publication number	US-2019229811-A1
Application number	US-201916237957-A
Country	US
Kind code	A1
Filing date	Jan 2, 2019
Priority date	Jan 24, 2018
Publication date	Jul 25, 2019
Grant date	—

Abstract

Embodiments herein provide a self-homodyne coherent optical transmission system (Self-Homodyne system) where an optical carrier is polarization multiplexed with a modulated signal and is transmitted over the optical fiber. An Adaptive polarization control is used by the receiver for simplifying a signal processing in the receiver. Analog processing may be used for implementing LO less receiver. Transmitter uses a phase modulated carrier in place of an unmodulated carrier

First claim

What is claimed is:

1 . A self-homodyne coherent optical transmission system, comprising:
a transmitter, comprising:
a laser for generating an optical carrier;
a polarization beam splitter for splitting the optical carrier into two orthogonal polarizations,
at least one modulator for modulating a polarization signal for one of the two orthogonal polarizations;
a polarization beam combiner for combining an unmodulated carrier in other polarization with a modulated signal, wherein an output of the polarization beam combiner is transmitted through a fiber channel;
wherein the optical carrier in one polarization is multiplexed with a message signal modulated over the carrier in another polarization and is transmitted over the fiber channel; and
a receiver for receiving a message signal from transmitter through the fiber channel and demodulating the message signal by using a polarization multiplexed carrier as a local oscillator, the receiver comprising:
at least one 90° optical hybrid for combining a carrier and a modulated signal in the message signal;
at least two balanced photo-detectors for converting an optical output of the at least one optical hybrid into electrical signals; and
a polarization controller for applying an adaptive polarization control mechanism for separating the modulated signal and the carrier at the receiver in at least two independent polarization components.

2 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein optical carrier power is at least 10 dB above the modulated signal power.

3 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein a modulation technique for modulating one polarization signal applied by the transmitter comprises one of a QPSK modulation technique, an m-QAM modulation technique or an m-PSK modulation technique.

4 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein the adaptive polarization control mechanism performed by the receiver by using electronics for identifying an amount of cross-polarization from each of received signal parameters and for feedback control of a polarization controller for minimizing the amount of cross-polarization.

5 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein the adaptive polarization control mechanism is performed by maximization of power in one polarization and minimization of power in other polarization.

6 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein the Adaptive polarization control mechanism uses a magnitude of DC component in the electrical signals received from at least two balanced photo detectors for polarization control.

7 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein the receiver comprises an equalizer, wherein the equalizer uses at least one of a radius directed equalizer (RDE) equalization and a combination of RDE and decision feedback equalizer for the m-QAM modulation technique.

8 . The self-homodyne coherent optical transmission system as claimed in claim 7 , wherein the Equalizer uses at least one of a constant modulus algorithm (CMA) and a decision feedback equalization technique for each of the QPSK modulation technique and the m-PSK modulation technique.

9 . The self-homodyne coherent optical transmission system as claimed in claim 7 , wherein the equalizer processes high-speed signals in analog domain.

10 . The self-homodyne coherent optical transmission system as claimed in claim 1 , wherein the optical carrier is phase modulated to carry additional data.

11 . The self-homodyne coherent optical transmission system as claimed in claim 1 and 10 , wherein the receiver comprises:
a demodulator for demodulating data from the modulated carrier

12 . The self-homodyne optical coherent transmission system as claimed in claim 1 , wherein the receiver comprises:
an optical dispersion compensation module for reducing chromatic dispersion.

13 . The self-homodyne optical coherent transmission system of claim 1 , wherein optical channel comprises:
a dispersion shifted fiber for avoiding a chromatic dispersion.

14 . The self-homodyne optical coherent transmission system of claim 1 , wherein the optical channel comprises:
a transmission wavelength at which dispersion is less or negligible.

15 . A receiver in a self-homodyne coherent optical transmission system, the receiver comprising:
at least one 90° optical hybrid for combining a carrier and a modulated signal in a message signal, received from a transmitter, wherein the message signal is demodulated by using a polarization multiplexed carrier as a local oscillator; at least two balanced photo-detectors for converting an optical output of the at least one optical hybrid into electrical signals; and a polarization controller for applying an adaptive polarization control mechanism for separating the modulated signal and the carrier at the receiver in at least two independent polarization components.

16 . A method for transmitting signal in a self-homodyne coherent optical transmission system, the method comprising:
generating, through a laser in a transmitter, an optical carrier; splitting, through a polarization beam splitter, the optical carrier into two orthogonal polarizations; modulating one polarization, through at least one modulator, a polarization signal for one of the two orthogonal polarizations; combining, through a polarization beam combiner, an unmodulated carrier in other polarization with a modulated signal, wherein an output of the polarization beam combiner is transmitted to a receiver through a fiber channel; wherein the optical carrier in one polarization is multiplexed with a message signal modulated over the carrier in another polarization and is transmitted over the fiber channel.

17 . A method for receiving signal in a self-homodyne coherent optical transmission system, the method comprising:
receiving, a message signal from a transmitter through an optical fiber channel; applying, through a polarization controller, an adaptive polarization control mechanism for separating a modulated signal and a carrier at the receiver in at least two independent polarization components. combining, through at least one 90° optical hybrid, a carrier in one polarization and a modulated signal in the other polarization after a polarization rotator with one polarization signal; and converting, through at least two balanced photo-detectors, an optical output of the at least one optical hybrid into electrical signals.

Assignees

• Indian Inst Technology Bombay

Inventors

• Gupta Shalabh
• Kamran Rashmi
• Popatbhai Anghan Mehul

Classifications

• H04B10/63

  Homodyne {, i.e. coherent receivers where the local oscillator is locked in frequency and phase to the carrier signal} · CPC title

• H04B10/25

  Arrangements specific to fibre transmission · CPC title

• H04B10/614 Primary

  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 title

• H04J14/06

  Polarisation multiplex systems · CPC title

• H04B10/556

  Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK] · CPC title