Tunable Bandpass Filter for Optical Burst Signal Noise Reduction
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Solution Overview
Problem
In point-to-multipoint networks, especially in PON systems, the use of inexpensive lasers results in varying carrier frequencies, leading to increased optical noise due to amplified spontaneous emission, which existing technologies struggle to address effectively without requiring frequency-stabilized lasers or additional control channels.
Innovation Solution
A cost-effective method utilizing a tunable bandpass filter that can be preset to adapt quickly to burst signal characteristics, eliminating the need for laser stabilization and additional control channels, and allowing for parallel connection of filters to optimize signal quality and demodulation by selecting the optimal filter for each burst signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a narrow bandwidth filter is used to reduce optical noise, then signal quality is improved, but the adjusting time becomes too long
Solution Approach 1:
The patent divides the single filter adjustment task into multiple parallel filter instances. Each filter is tuned to a different frequency range, allowing the system to process multiple frequency channels simultaneously without requiring sequential adjustment of a single narrow bandwidth filter.
Solution Approach 2:
The patent pre-tunes multiple bandpass filters to different center frequencies before receiving burst signals. This preliminary action eliminates the need for time-consuming frequency scanning and adjustment during signal reception, as the filters are already positioned to capture signals across the expected frequency range.
2Reliability
If frequency-stabilized lasers are used to maintain identical carrier frequencies, then signal quality is improved, but device cost increases considerably
Solution Approach 1:
The patent replaces static frequency stabilization (requiring expensive stabilized lasers) with dynamic frequency adaptation. The system uses inexpensive lasers that can operate at varying frequencies and compensates for this variability by dynamically tuning the bandpass filter center frequencies to match the incoming signal frequencies.
Solution Approach 2:
The patent changes the filter parameters (center frequency and bandwidth) to adapt to the varying laser frequencies. Instead of trying to maintain a fixed frequency parameter through expensive laser stabilization, the system adjusts the filter parameters to accommodate the natural frequency variations of inexpensive lasers.
3Reliability
If a single bandpass filter is used to reduce optical noise, then signal quality is improved, but the adjustment time becomes too long
Solution Approach 1:
The patent segments the frequency processing task across multiple parallel bandpass filters. Each filter handles a specific frequency range, allowing simultaneous processing of multiple frequency channels and eliminating the sequential adjustment bottleneck of a single filter.
Solution Approach 2:
The patent maintains continuous signal processing by having multiple filters operating in parallel. While one filter processes a burst signal, others are already positioned to capture subsequent signals at different frequencies, ensuring uninterrupted processing without adjustment delays.
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 significantly reduces optical noise, maintains signal quality, and avoids the need for expensive frequency-stabilized lasers, enabling efficient demodulation and binary decision-making without lengthy adjustment times.
Implementation Method 1
it is necessary to filter the received optical signal with as narrow a bandwidth as possible in order to reduce the optical noise as far as possible
Implementation Method 2
at least one optical amplifier is arranged which adds optical noise, the so-called 'amplified spontaneous emission'
Data Source
AI summary
The invention relates to a bandpass filter (OFI) which is mounted downstream of an optical amplifier (OV) and allows noise to be largely reduced. In order for said bandpass filter to be able to optimally receive burst signals (BS1, BS2, . . . , BSN) transmitted by several user devices (ONT1, ONT2, . . . , ONTN) also in a central node (OLT), the bandpass filter is set to the respective received carrier frequencies (TF1to TFN). Because of time constraints, this is possible only if the carrier frequencies (TF1, . . . ) or associated filter setting values (FE1, . . . ) have already been stored and the bandpass filter is preset.