Coherent PON Using Fabry-Perot Lasers for Cost Reduction
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Solution Overview
Problem
Conventional coherent passive optical networks (CPONs) face challenges in achieving high-capacity data transmission due to the high component costs of coherent optics, particularly for customer premise equipment, and experience signal transmission errors when using optical injection locking techniques.
Innovation Solution
The implementation of a CPON system that utilizes Fabry-Perot laser diodes (FP-LDs) instead of external cavity lasers (ECLs) for optical injection locking, along with a novel optical tone/subcarrier distribution scheme that avoids frequency overlap, enabling cost-effective and error-free high-capacity data transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional coherent optics with external cavity lasers (ECLs) are used, then high-capacity data transmission is achieved, but hardware cost becomes prohibitive for customer premise equipment
Solution Approach 1:
The patent replaces expensive external cavity lasers (ECLs) with much cheaper Fabry-Perot laser diodes (FP-LDs) in the ONU. Although FP-LDs are less stable and require compensation mechanisms, their low cost makes them suitable for disposable or easily replaceable customer premise equipment, resolving the contradiction between high transmission capacity and prohibitive hardware cost.
Solution Approach 2:
The patent changes the operating parameters of the FP-LD by using optical injection locking from the OLT to stabilize the laser's frequency and reduce phase noise. This parameter change allows the cheap FP-LD to achieve performance closer to expensive ECLs, enabling high-capacity transmission without prohibitive cost.
2Ease of manufacture
If optical injection locking (OIL) is implemented for cost-effective CPON, then hardware cost is reduced, but signal transmission errors occur due to frequency overlap
Solution Approach 1:
The patent resolves the frequency overlap conflict by moving to a two-dimensional frequency allocation scheme. Downstream signals use frequencies around f1 with subcarriers at f1±Δf, while upstream OIL uses a different frequency f2. This dimensional separation in the frequency spectrum eliminates interference while maintaining the cost benefits of OIL with FP-LDs.
Solution Approach 2:
The patent introduces an intermediary frequency allocation scheme that acts as a mediator between downstream coherent signals and upstream OIL signals. By allocating distinct frequency ranges and using guard bands, the system prevents direct interference between the two signal types, maintaining transmission reliability while enabling cost-effective OIL implementation.
3Ease of manufacture
If Fabry-Perot laser diodes (FP-LDs) are used instead of ECLs, then hardware cost is significantly reduced, but carrier frequency offset compensation complexity increases
Solution Approach 1:
The patent applies preliminary action by implementing optical injection locking from the OLT to the FP-LD in the ONU before transmission begins. This pre-stabilization of the laser frequency and phase reduces the amount of frequency offset compensation needed at the receiver, simplifying the digital signal processing complexity despite using cheaper FP-LDs.
Solution Approach 2:
The patent employs feedback mechanisms in the digital signal processing to continuously monitor and correct carrier frequency offset. By using feedback loops that adjust compensation parameters based on received signal quality, the system maintains transmission reliability while managing the increased complexity introduced by using FP-LDs instead of ECLs.
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 solution achieves comparable performance to conventional ECL-based systems while significantly reducing hardware costs by using FP-LDs and simplifying receiver digital signal processing by eliminating the need for carrier frequency offset compensation.
Implementation Method 1
Recent innovations implement optical injection locking (OIL) techniques using relatively inexpensive Fabry-Perot laser diodes (FP-LDs)
Data Source
AI summary
An optical network communication system utilizes a CPON. The system includes an OLT and an ONU. The OLT includes an OLT transmitter for transmitting a downstream signal, and an OLT receiver for detecting an upstream signal. The downstream signal includes a first tone centered at a first frequency, a second tone centered at a second frequency, and first and second downstream subcarriers distributed proximate the first frequency. The upstream optical signal includes first and second upstream subcarriers distributed proximate the second frequency. The ONU includes an ONU receiver for detecting the first and second downstream subcarriers using the first optical tone to generate an LO signal for coherent detection, and an ONU transmitter configured to generate the first and second upstream subcarriers using the second optical tone. The first and second tones, downstream subcarriers, and upstream subcarriers do not overlap in the frequency domain