Injection-Locked Laser Diodes for OBI Reduction
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Solution Overview
Problem
Current fiber communication networks face challenges in increasing bandwidth and minimizing optical beat interference (OBI) in optical access networks, particularly with the need for efficient use of legacy fiber infrastructure and coexistence of multiple services like RFOG and EPON, where coherent technology is complex and costly to implement.
Innovation Solution
The system employs a method where a fiber node generates multiple narrow wavelength bands and uses injection locking of upstream laser diodes to minimize OBI by ensuring upstream transmissions occur within specific wavelength windows, utilizing a broad wavelength spectrum and optical filters to provide seed sources for laser diodes, allowing for simultaneous and efficient upstream communications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent technology is used to increase receiver sensitivity and capacity, then receiver sensitivity and overall capacity are improved, but system complexity and cost increase significantly
Solution Approach 1:
The patent replaces expensive coherent detection systems with inexpensive direct detection receivers. By using intensity modulation and direct detection (IM/DD) with simple photodetectors and transimpedance amplifiers, the system achieves adequate receiver sensitivity without the complex and costly coherent detection architecture, including its local oscillators, phase recovery circuits, and digital signal processing units.
Solution Approach 2:
The patent changes the detection parameter from phase-sensitive coherent detection to intensity-based direct detection. This parameter change simplifies the receiver architecture while maintaining acceptable sensitivity for access network distances. The system uses intensity modulation with the laser diode and detects optical power directly, avoiding the need for complex phase and amplitude recovery mechanisms.
2Adaptability or versatility
If multiple services (RFOG, EPON) coexist in the same optical network, then service versatility is improved, but optical beat interference increases
Solution Approach 1:
The patent segments the optical spectrum into distinct wavelength bands for different services. RFOG uses wavelengths in the 1520-1565 nm band while EPON uses 1577-1582 nm, creating spectral separation that prevents optical beat interference. This segmentation allows multiple services to coexist by assigning them non-overlapping frequency ranges, eliminating the interference problem while maintaining service versatility.
Solution Approach 2:
The patent introduces optical filters as intermediaries to separate different service wavelengths. These filters selectively pass specific wavelength bands to their intended services while blocking other wavelengths, preventing optical beat interference. The filters act as mediators that enable service coexistence by ensuring that signals from different services do not mix in a way that generates harmful beat frequencies.
3Object-generated harmful factors
If narrow wavelength bands are used for upstream transmissions, then optical beat interference is minimized, but wavelength filtering complexity increases
Solution Approach 1:
The patent performs preliminary wavelength filtering at the fiber node before signals are combined and sent to end devices. The fiber node contains optical filters that pre-separate wavelength bands for different services, ensuring that narrow wavelength bands reach each end device without requiring complex filtering at the device level. This preliminary action simplifies the overall system by centralizing the filtering function.
Solution Approach 2:
The patent uses a master laser at the fiber node to generate a stable wavelength reference that is copied to multiple slave lasers at end devices through injection locking. This copying approach ensures all lasers operate at precise, interference-free wavelengths without requiring each device to have its own complex wavelength control system. The master laser's wavelength stability is replicated across the network, simplifying wavelength management.
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 enables efficient and cost-effective simultaneous upstream communications across multiple services without the need for complex coherent technology, effectively reducing OBI and optimizing the use of existing fiber infrastructure.
Implementation Method 1
an optical filter configured to collect the broad wavelength spectrum and further configured to provide a seed source, the seed source including a second wavelength range narrower than the first wavelength range
Implementation Method 2
an optical circulator configured to direct the seed source from the optical filter to a laser diode
Implementation Method 3
stimulate the laser diode to emit an optical signal based on the second wavelength range
Implementation Method 4
stimulate the laser diode to emit an optical signal
Implementation Method 5
uses injection locking of upstream laser diodes to minimize OBI by ensuring upstream transmissions occur within specific wavelength windows
Data Source
AI summary
Methods, systems, and devices for network communications to reduce optical beat interference (OBI) in upstream communications are described. For example, a fiber node may provide a narrow band seed source to injection lock upstream laser diodes. Therefore, upstream communications from each injection locked laser diode may primarily include the wavelength associated with each seed source. The seed sources may be unique to each end device and configured to minimize OBI. That is, the upstream laser diodes may be generic, but the received seed source may enable upstream communications at varying wavelengths. The fiber node may provide each seed source by filtering (e.g., by a grating filter) a broadband light source.