Wavelength Alignment in WDM-PON Optical Network Units
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Solution Overview
Problem
Existing wavelength division multiplexing passive optical network (WDM-PON) systems face complexity and inefficiency in setting upstream wavelengths for a large number of optical network units (ONUs), requiring complex control structures for the optical line terminal (OLT) and often necessitating costly tunable lasers.
Innovation Solution
An optical network unit (ONU) is configured to iteratively transmit upstream signals, receive power level data from the OLT, and adjust the upstream wavelength to a suitable value, reducing the workload on the OLT and allowing simpler tunable lasers, without additional hardware in the optical distribution network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If complex control structures are used in the OLT to manage upstream wavelengths for a large number of ONUs, then wavelength management capability is improved, but device complexity increases
Solution Approach 1:
The ONU autonomously determines its own upstream wavelength by measuring downstream wavelength information and applying a predetermined offset, eliminating the need for complex OLT control structures. The system self-configures wavelength assignments without centralized management complexity.
Solution Approach 2:
Instead of the OLT assigning wavelengths to ONUs (traditional approach), the ONU independently determines its wavelength based on downstream measurements. The control direction is inverted from centralized assignment to distributed self-determination.
2Adaptability or versatility
If tunable lasers are used in ONUs to enable wavelength adaptation, then adaptability is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive tunable lasers with fixed-wavelength laser diodes that are cheaper and more reliable. Although fixed-wavelength lasers have limited flexibility, the system achieves wavelength adaptation through the optical layer (downstream wavelength offset) rather than requiring tunable transmitters in each ONU.
3Measurement precision
If wavelength initialization procedures are implemented before normal data transmission, then wavelength alignment accuracy is improved, but productivity decreases
Solution Approach 1:
The wavelength offset is predetermined and pre-configured in the ONU before operation. This preliminary configuration eliminates the need for time-consuming wavelength initialization procedures during system startup, as the ONU already has the necessary wavelength relationship information embedded.
Solution Approach 2:
Normal data transmission begins immediately without waiting for wavelength initialization procedures. The wavelength alignment is achieved continuously through the predetermined offset mechanism rather than through discrete initialization steps, maintaining continuous productive operation.
Data Source
AI summary
An optical network unit for a passive optical network (10), configured to: initiate an upstream wavelength (wus) for an upstream signal (US) from the optical network unit to an optical line terminal (10); iteratively, until an iteration criterion is met, i) transmit the upstream signal (US) to the optical line terminal (10), ii) receive from the optical line terminal (10) power level data (p) for the upstream signal (US) as measured by the optical line terminal (10), and iii) set the upstream wavelength (wus) for the upstream signal (US) to a new wavelength-value; and adjust the upstream wavelength (wus) to a wavelength-value previously set for the upstream signal (US) and associated with power level data corresponding to a certain power level. A passive optical network system, the optical line terminal and related methods are also disclosed.