Optical Communication Apparatus Using Phase Conjugation for Impairment Compensation
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Solution Overview
Problem
Conventional optical communication systems face challenges in compensating for impairments such as Chromatic Dispersion, Polarization Mode Dispersion, carrier frequency offset, and dynamic channel variations, especially in high-data-rate WDM systems, due to the limited speed of digital electronics and the complexity of implementing compensation algorithms.
Innovation Solution
The method involves generating and transmitting optical signals as sequences of unitary matrices through an optical channel, using differential polarization-time coding to encode information in joint phase and polarization changes, allowing for joint phase and polarization differential detection without requiring phase and polarization tracking, thus compensating for channel impairments effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coherent receivers use digital signal processing to track phase noise and polarization changes, then transmission impairments can be compensated, but the system becomes increasingly difficult to implement due to the limited speed of digital electronics
Solution Approach 1:
The patent replaces the mechanical/electronic digital signal processing system with an optical solution. Specifically, it uses optical phase conjugation to compensate for transmission impairments including phase noise and polarization changes, thereby eliminating the need for high-speed digital tracking algorithms while maintaining reliable compensation
Solution Approach 2:
The patent applies preliminary action by pre-compensating for transmission impairments before the signal becomes severely degraded. The optical phase conjugation is performed at the receiver to reverse the effects of channel impairments, effectively undoing phase noise and polarization changes before they cause irreversible damage to the signal
2Productivity
If advanced modulation formats with high-order constellations and Polarization Division Multiplexing are used, then spectral efficiency improves, but the system becomes more sensitive to rotations of carrier phase and channel polarization
Solution Approach 1:
The patent replaces electronic phase and polarization tracking with optical phase conjugation. This optical approach automatically compensates for phase and polarization rotations without requiring high-speed digital processing, thereby maintaining reliability while supporting advanced modulation formats with high spectral efficiency
Solution Approach 2:
The patent implements feedback through optical phase conjugation, where the receiver generates a conjugated version of the received signal that contains reversed phase and polarization information. This conjugated signal is used to compensate for the rotations, creating a feedback mechanism that automatically corrects phase and polarization errors without requiring external tracking
Data Source
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AI summary
An apparatus for optical communication and optical communication method are provided, the method comprising the steps of generating an optical signal for transmitting the sequence of information data, transmitting the sequence of information data as a sequence of transmit matrices, S(k) being the k-th transmit matrix and k being a positive integer, and wherein the sequence of transmit matrices is transmitted through an optical channel characterized by a unitary channel matrix H, receiving a sequence of receive matrices, the k-th receive matrix R(k) being expressed as: R(k) = H·S(k)+N(k) wherein k is a positive integer and N(k) is a complex matrix of noise samples and providing a sequence of decision matrices, the k-th decision matrix D(k) being expressed as: D(k)=RH(k-1)R(k).