Coherent ONU Reception With Uncalibrated Laser Frequency Alignment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge of implementing coherent reception in passive optical networks (PON) is the high cost of premium components and the wavelength alignment issues with low-cost, uncalibrated lasers, such as distributed feedback (DFB) lasers, which suffer from manufacturing inaccuracies and temperature-induced wavelength drift.
Innovation Solution
An apparatus and method for adjusting the operation parameters of an uncalibrated laser, such as temperature or bias current, to align its emission frequency with the downstream signal frequency in a PON system, using electrical power indications to determine a target range for coarse alignment, enabling the use of low-cost lasers as local oscillators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-cost uncalibrated lasers (DFB laser) are employed to reduce receiver cost, then cost is reduced, but wavelength alignment cannot be guaranteed due to manufacturing inaccuracies and temperature drift
Solution Approach 1:
The system performs preliminary wavelength alignment by sweeping the laser operating wavelength and measuring received optical power to identify the peak power point, which corresponds to the aligned wavelength. This preliminary action compensates for manufacturing inaccuracies before normal operation begins.
Solution Approach 2:
The system continuously monitors the received optical power and uses this feedback to detect wavelength misalignment. When misalignment is detected, the system automatically adjusts the laser operating wavelength to restore alignment, creating a closed-loop control system that maintains precision despite cost constraints.
2Manufacturing precision
If premium quality components (narrow linewidth C-band tunable laser) are used for coherent reception, then wavelength alignment is guaranteed, but receiver cost becomes very high
Solution Approach 1:
The patent replaces expensive premium lasers with cheap uncalibrated DFB lasers that have shorter effective lifetimes in terms of wavelength stability. The system compensates for their inferior characteristics through active wavelength sweeping and alignment procedures, achieving the same functional result at lower cost.
Solution Approach 2:
The system dynamically changes the laser operating parameters (wavelength sweep, power measurement) to achieve alignment, rather than relying on fixed pre-aligned components. This parameter-based approach allows the same hardware to achieve precise alignment without requiring expensive components.
3Adaptability or versatility
If full C-band and L-band tuning is implemented using external cavity laser, then wavelength coverage is extended, but device complexity and cost increase
Solution Approach 1:
Instead of using a single complex tunable laser covering both C-band and L-band, the system segments the wavelength coverage by using multiple fixed-wavelength DFB lasers, each optimized for specific wavelength ranges. This segmentation simplifies each individual laser component while achieving comprehensive coverage through the combination of multiple simpler units.
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 allows for significant cost reduction of coherent receivers in PON systems by using low-cost, uncalibrated lasers, achieving wavelength alignment within a short time and maintaining alignment during operation.
Implementation Method 1
The coherent receiver mixes the received signal with a local reference laser, also known as local oscillator (LO), which allows to detect the phase, amplitude, and polarization modulation
Implementation Method 2
the coherent receiver mixes the received signal with a local reference laser
Data Source
AI summary
An apparatus including at least one processor configured to execute the instructions and cause the apparatus to perform, adjusting an operation parameter of a laser to adjust an emission frequency of the laser, wherein the laser is suitable to be used as a local oscillator for a coherent optical receiver in an optical network unit (ONU), wherein the laser is uncalibrated in terms of a relationship between the operation parameter and the emission frequency of the laser; obtaining an indication of an electrical power of a downstream signal received by the coherent optical receiver, while adjusting the operation parameter; determining a first target range of the operation parameter based on a relationship between the obtained indication of the electrical power and the operation parameter, wherein the emission frequency of the laser corresponding to the first target range is aligned to a frequency of the downstream signal.