Quasi-DP-BPSK Transmitter for Universal Equalizer Processing
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Solution Overview
Problem
Existing optical communication systems face challenges in processing data carried by DP-BPSK modulated optical signals due to limitations in blind equalization techniques, such as degenerate states and unsatisfactory tap weight control, which prevents the use of the same processor for both DP-BPSK and DP-QPSK signals.
Innovation Solution
The system employs a transmitter that can operate in quasi-DP-BPSK mode, where data bits are represented by phase changes between phase states along randomly selected axes in the I-Q plane, allowing the same equalizer filter to process both BPSK and QPSK data, and an optical receiver that aligns sequencing bits with incoming signals to identify the data-carrying axis for accurate decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If blind equalization techniques are used to process DP-BPSK signals, then the system can operate with simplified receiver architecture, but the equalizer suffers from degenerate states and unsatisfactory tap weight control
Solution Approach 1:
The patent transforms the BPSK signal parameters by modulating to four phase states separated by π/2 radians instead of the conventional two phase states separated by π radians. This parameter change in the modulation format enables the equalizer to process the signal without encountering degenerate states, thereby improving equalizer performance while maintaining simplified receiver architecture.
2Reliability
If separate processors are used for DP-BPSK and DP-QPSK signals, then each signal type can be optimally processed, but the system cost and device complexity increase
Solution Approach 1:
The patent modifies the BPSK modulation format to use four phase states, making it compatible with the same equalizer processor used for QPSK signals. This universality allows a single processor to handle both BPSK and QPSK signals optimally, reducing system cost and device complexity while maintaining signal processing accuracy.
3Reliability
If DP-BPSK modulation is used on optical fiber links with insufficient transmission characteristics, then the system can operate on longer or lower-quality links, but the data rate is reduced by half compared to DP-QPSK
Solution Approach 1:
The patent changes the phase state parameters from conventional BPSK (two states, π radians separation) to a modified format with four phase states separated by π/2 radians. This parameter change enables the signal to tolerate impairments on lower-quality links while maintaining higher data rates, as the four-phase format effectively doubles the information capacity compared to conventional BPSK.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables reliable processing of both BPSK and QPSK data with few errors, reducing costs by using the same transmitter and receiver circuitry for various optical fiber links, and improving impairment tolerance.
Implementation Method 1
A modulator circuit is also provided that is configured to provide a modulated optical signal in response to the first and second drive signals, such that the modulated optical signal has a variable phase
Implementation Method 2
In addition to direct detection systems, optical systems have been deployed that implement coherent detection, in which the optical phase of a transmitted optical signal is modulated in order to carry data
Data Source
AI summary
A transmitter is provided that transmits data in either a "quasi-DP-BPSK" ("QDP") mode or in a DP-QPSK mode. In the QDP mode, data bits are transmitted as changes in phase between first and second phase states along a first axis or as changes in phase between third and fourth phase states along a second axis in the IQ plane. A sequence bit identifies which axis carries the data bit. The sequence bit is one of a series of sequence bits that may be generated by a pseudo-random number generator. The series of sequence bits can be relatively long to permit sufficiently random changes in the axis that carries the data. Thus, unlike conventional BPSK, in which data is transmitted between phase states along a single axis, the present disclosure provides an apparatus and related method for randomly selecting one of two axes, for example, for each transmitted bit.