Upgradable WDM System BPSK QPSK Noise Management
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Solution Overview
Problem
Conventional wavelength division multiplexed optical communication systems face challenges in upgrading data capacity without incurring high costs and experiencing data transmission errors due to phase noise induced by on-off-keying (OOK) modulated signals in quadrature phase shift keying (QPSK) systems.
Innovation Solution
The system gradually upgrades by replacing OOK transmitters with binary phase shift keying (BPSK) and then QPSK transmitters, with BPSK signals being more tolerant of noise and inducing less cross-phase modulation-related noise, allowing for incremental capacity increases with reduced errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OOK transmitters are replaced with QPSK transmitters to increase data capacity, then data transmission capacity is improved, but phase noise and cross-phase modulation errors increase
Solution Approach 1:
The patent segments the transmitter replacement process into multiple stages: first replacing OOK transmitters with BPSK transmitters, then later replacing BPSK transmitters with QPSK transmitters. This segmentation allows the system to incrementally increase capacity while maintaining reliability at each stage, avoiding the phase noise problems that would result from directly deploying QPSK in an existing WDM system with OOK signals.
Solution Approach 2:
The patent applies preliminary action by first deploying BPSK transmitters before QPSK transmitters. BPSK signals are more tolerant of noise and induce less cross-phase modulation than QPSK signals. This preliminary deployment of BPSK creates a stable intermediate state that prepares the optical communication path for future QPSK deployment without the harmful phase noise effects.
2Productivity
If all OOK transmitters are replaced with QPSK transmitters at once, then data capacity is maximized, but system cost and complexity increase significantly
Solution Approach 1:
The patent divides the transmitter replacement project into manageable segments: initial BPSK replacements, followed by subsequent QPSK replacements. This segmentation transforms a single complex, high-cost operation into multiple simpler, lower-cost operations that can be planned and executed incrementally based on budget and capacity needs.
Solution Approach 2:
The patent applies partial action by replacing only some transmitters with advanced modulation formats at each stage rather than all transmitters simultaneously. This allows the system to achieve partial capacity improvements with reduced complexity and cost, enabling phased investment and gradual optimization.
3Reliability
If BPSK transmitters are used as an intermediate step, then noise tolerance is improved, but upgrade time and process duration increase
Solution Approach 1:
The patent uses BPSK as a preliminary action that prepares the system for future QPSK deployment. While BPSK deployment takes additional time, it creates a stable optical communication environment with reduced phase noise, making the subsequent QPSK deployment faster and more reliable. The BPSK phase serves as necessary preliminary preparation.
Solution Approach 2:
The patent applies beforehand cushioning by using BPSK transmitters to cushion or protect the optical communication path from the phase noise that would be caused by direct QPSK deployment alongside OOK signals. This cushioning effect creates a protected environment that enables future high-capacity QPSK operation without the harmful effects of cross-phase modulation.
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 economic upgrading of WDM systems to higher data rates with fewer errors by using BPSK and QPSK transmitters, effectively managing capacity needs while minimizing noise interference.
Implementation Method 1
OOK modulated optical signals, however, may induce phase noise in the QPSK modulated optical signals through cross-phase modulation (XPM).
Implementation Method 2
In accordance with the QPSK modulation format, the phase, as opposed to amplitude, is modulated to carry symbols of data
Data Source
AI summary
Consistent with the present disclosure, a wavelength division multiplexed (WDM) optical communication system including on-off-keying (OOK) transmitters, for example, may be upgraded to include advanced modulation format transmitters, such as quadrature phase shift keying (QPSK) transmitters. Rather than replace all the OOK transmitters with QPSK transmitters at once, each OOK transmitter is replaced with a lower rate modulation format transmitter, such as a binary phase shift keying (BPSK) transmitter, as capacity needs increase. The BPSK transmitters supply (BPSK) optical signals that are more tolerant of noise caused by cross phase modulation (XPM) induced by OOK signals. Accordingly, such BPSK optical signals have fewer associated data detection errors in the receiver. Moreover, BPSK modulated optical signals induce little XPM-related noise in co-propagating QPSK modulated optical signals. Thus, once the OOK transmitters have been replaced with the BPSK transmitters, the BPSK transmitters may be replaced with QPSK transmitters or controlled to output QPSK modulated optical signals, as capacity need further increase, and such QPSK modulated optical signals may be transmitted with fewer errors.