Coherent PON Frequency Acquisition with a Fast Tuneable Laser
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Solution Overview
Problem
The high cost of deterministic lasers in optical network units (ONUs) in passive optical networks (PONs) prevents the use of coherent optical receivers, 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) with a coherent optical receiver and a fast tuneable laser scans the frequency band to detect optical frequency acquisition signals from ONUs, determining their centre transmission frequencies by monitoring electrical power parameters, allowing reliable coherent reception without requiring deterministic lasers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deterministic lasers are used in ONUs to provide fixed transmission frequency, then reliable coherent reception is enabled, but the cost of ONUs increases significantly
Solution Approach 1:
The patent applies the dynamics principle by making the local oscillator laser frequency tunable rather than fixed. The OLT dynamically adjusts the local oscillator frequency to match the transmission frequency of each ONU, enabling reliable coherent reception with inexpensive non-deterministic lasers. This resolves the contradiction by replacing the static deterministic laser approach with a dynamic frequency matching approach.
Solution Approach 2:
The patent changes the frequency parameter of the local oscillator laser dynamically. Instead of using fixed-frequency deterministic lasers, the system varies the local oscillator frequency to match each ONU's transmission frequency. This parameter change enables cost reduction while maintaining reception reliability.
2Ease of manufacture
If non-deterministic lasers are used in ONUs to reduce cost, then ONU manufacturing cost decreases, but frequency uncertainty complicates reliable signal reception
Solution Approach 1:
The patent implements feedback by measuring the transmission frequency of each ONU and using this information to adjust the local oscillator frequency accordingly. The OLT receives frequency information from ONUs and dynamically tunes the local oscillator to match, ensuring reliable reception despite frequency variations in non-deterministic lasers.
Solution Approach 2:
The system dynamically adapts the local oscillator frequency based on each ONU's actual transmission frequency. This dynamic adjustment compensates for the frequency uncertainty of non-deterministic lasers, enabling reliable coherent reception with low-cost ONUs.
3Measurement precision
If frequency scanning is performed to acquire transmission frequencies, then accurate frequency detection is achieved, but time delay increases
Solution Approach 1:
The patent applies preliminary action by having ONUs transmit their center frequency information before actual data transmission. This allows the OLT to pre-acquire and store frequency information, so when data transmission begins, the local oscillator can be quickly tuned to the correct frequency without performing a full scan, thus reducing time delay while maintaining accuracy.
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
the fast tuneable laser generates a laser signal at an adjustable frequency that is used by the coherent optical receiver to convert received optical signals to electrical signals
Implementation Method 2
coherent optical receivers, which can extract the amplitude, phase, and polarization of an optical signal. To this end, coherent optical receivers comprise a local oscillator that generates a laser signal having a frequency that matches the transmission frequency of the optical signal being received by the coherent optical receiver. 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
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AI summary
Example embodiments describe an optical line terminal, OLT (210), configured to communicate in a passive optical network, PON (200), with optical network units, ONUs (131 - 133) that transmit optical signals to the OLT at respective centre transmission frequencies (142, 143, 144) anywhere within a frequency band (141); wherein the OLT (210) comprises a coherent optical receiver (211) and a fast tuneable laser (212), wherein the coherent optical receiver is configured to convert received optical signals (213, 220) to electrical signals (214) by means of a local oscillator laser signal (217) generated by the fast tuneable laser; wherein the OLT (210) is configured to receive, from one or more ONUs (131 -133), an optical frequency acquisition signal (221) transmitted at the respective centre transmission frequencies (142 - 144); and wherein the OLT further comprises means (202) configured to perform: tuning (216) the fast tuneable laser (212) to respective frequencies (231) within the frequency band (141) to scan (230) the frequency band for optical frequency acquisition signals (221); obtaining (215), at the respective frequencies (231), a parameter value indicative of an electrical power (240) of the electrical signal (214) converted by the coherent optical receiver (211); and determining the respective centre transmission frequencies (142 - 144) of the one or more ONUs as the frequency to which the fast tuneable laser (212) is tuned when the parameter value exceeds an upper threshold (241) or drops below a lower threshold.