PON Frequency Acquisition Using OLT Laser Scanning
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Solution Overview
Problem
The high cost of deterministic lasers in optical network units (ONUs) prevents the use of coherent optical receivers in passive optical networks (PONs), which are necessary for advanced modulation techniques like IQM, and the frequency uncertainty of non-deterministic lasers complicates reliable signal reception.
Innovation Solution
An optical line terminal (OLT) equipped with a coherent optical receiver and a fast tuneable laser scans the frequency band to detect optical frequency acquisition signals from ONUs, determining the centre transmission frequency by monitoring electrical power parameters, allowing reliable coherent reception without requiring deterministic lasers in the ONUs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deterministic lasers are used in ONUs to ensure fixed transmission frequency for coherent reception, then reception reliability is improved, but device cost increases significantly
Solution Approach 1:
The patent applies dynamics by replacing static deterministic lasers with dynamic non-deterministic lasers in ONUs, allowing frequency to vary within a band. Compensating for this variability, the system uses frequency acquisition signals and scanning mechanisms at the OLT to dynamically track and synchronize with the actual transmission frequency, thereby maintaining coherent reception reliability without requiring expensive deterministic lasers in each ONU
Solution Approach 2:
The patent introduces frequency acquisition signals as intermediaries between the non-deterministic laser transmitter and the coherent receiver. These signals carry frequency information that enables the receiver to acquire and lock onto the actual transmission frequency, serving as a mediator that bridges the frequency uncertainty introduced by non-deterministic lasers and maintains reliable coherent reception
2Ease of manufacture
If non-deterministic lasers are used in ONUs to reduce cost, then device cost decreases, but frequency uncertainty complicates reliable signal reception
Solution Approach 1:
The patent applies preliminary action by having ONUs transmit frequency acquisition signals before the actual data transmission. This preliminary signal allows the OLT to scan the frequency band and acquire the exact transmission frequency in advance, ensuring that the coherent receiver is properly synchronized before receiving the actual optical signal, thereby maintaining reliability despite using cost-effective non-deterministic lasers
Solution Approach 2:
The patent implements feedback mechanisms where the OLT scans the frequency band and detects frequency acquisition signals from ONUs to determine their actual transmission frequency. This feedback loop allows the system to continuously monitor and adjust the local oscillator frequency to match the actual transmission frequency, compensating for the uncertainty introduced by non-deterministic lasers and ensuring reliable coherent reception
3Measurement precision
If frequency scanning is performed across the entire frequency band to acquire ONU transmission frequencies, then frequency acquisition accuracy is improved, but acquisition time increases
Solution Approach 1:
The patent applies preliminary action by having ONUs transmit frequency acquisition signals at predetermined times before data transmission. This allows the OLT to perform frequency scanning and acquisition in advance, during dedicated acquisition periods, so that when data transmission begins, the frequency synchronization is already complete, thereby reducing the impact of acquisition time on overall system performance
Solution Approach 2:
The patent implements periodic action by establishing regular acquisition periods where frequency scanning is performed systematically across the frequency band. These periodic scanning cycles allow the OLT to methodically search for and lock onto transmission frequencies in a structured manner, balancing thoroughness with time efficiency through predictable scheduling
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
Enables cost-effective and reliable coherent reception in PONs using non-deterministic lasers, supporting advanced modulation techniques and avoiding splitter losses, while maintaining circuit complexity and size.
Implementation Method 1
Receiving and decoding such advanced optical signals requires coherent optical receivers, which can extract the amplitude, phase, and polarization of an optical signal. Mixing this local oscillator laser signal with the received optical signal creates interference patterns wherefrom the amplitude, phase, and polarization information can be extracted.
Data Source
AI summary
An optical line terminal, OLT, is configured to communicate in a passive optical network, PON, with optical network units, ONUs that transmit optical signals to the OLT at respective centre transmission frequencies anywhere within a frequency band. The OLT is configured to receive, from one or more ONUs, an optical frequency acquisition signal transmitted at the respective centre transmission frequencies; and the OLT is configured to perform tuning the fast tuneable laser to respective frequencies within the frequency band to scan the frequency band for optical frequency acquisition signals; obtaining, at the respective frequencies, a parameter value indicative of an electrical power of the electrical signal converted by the coherent optical receiver; and determining the respective centre transmission frequencies of the one or more ONUs as the frequency to which the fast tuneable laser is tuned when the parameter value exceeds an upper threshold or drops below a lower threshold.