Cascaded Tunable Optical Filters for Coherent Transmitters
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Solution Overview
Problem
Current optical filtering schemes in coherent transmitters have static bandwidth, which leads to noise funneling and reduced transmit optical signal-to-noise ratio (OSNR) due to fixed bandwidth filters, especially in colorless multiplexer structures, where noise from one signal can contribute to another, and there is a lack of bandwidth tunability in optical domain solutions.
Innovation Solution
The implementation of cascaded tunable optical filters with fixed width and tunable center frequencies, integrated within coherent optical transmitters, allowing for a variable bandwidth and center frequency effective transfer function, which can be configured based on received optical signals and monitored using photodetectors to minimize noise funneling and improve OSNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a static bandwidth optical filter is used in the transmitter, then the filter provides some benefit to noise funneling by filtering out of band spectrum, but the filter is not bandwidth tunable and cannot adapt to different signal conditions
Solution Approach 1:
The optical filter is divided into multiple cascaded filter stages, each with fixed bandwidth but tunable center frequency. By segmenting the filtering function across multiple stages with different center frequencies, the system achieves effective bandwidth tunability through frequency offset adjustment rather than requiring each individual filter to be bandwidth-tunable, thus reducing device complexity while maintaining adaptability.
Solution Approach 2:
The system introduces dynamic control of the filter center frequencies to enable adaptability. By dynamically adjusting the center frequencies of cascaded filters with fixed bandwidth, the effective passband can be tuned to match different signal bandwidths and frequencies, providing adaptive filtering without requiring each filter component to be dynamically bandwidth-tunable.
2Productivity
If multiple signals are multiplexed together via multiplexer structures, then spectral efficiency is improved, but noise is added when multiple signals are multiplexed together causing noise funneling
Solution Approach 1:
The optical filter extracts and removes noise components from the multiplexed signal by filtering out of band spectrum before the signal enters the multiplexer or after multiplexing. By taking out the harmful noise components that would otherwise contribute to noise funneling, the system maintains high spectral efficiency while reducing the harmful noise effect.
Solution Approach 2:
The filter provides preliminary anti-action by preemptively filtering out noise components before they can contribute to noise funneling in the multiplexer. By applying the filtering action in advance, the system prevents the accumulation and funneling of noise that would otherwise occur when multiple signals are combined, thereby protecting the overall signal quality while maintaining spectral efficiency.
3Measurement precision
If the filter center frequency is optimized, then the filter provides better signal filtering, but the static bandwidth cannot adapt to different signal bandwidth requirements
Solution Approach 1:
The system achieves passband adaptability through dynamic adjustment of filter center frequencies in a cascaded configuration. While each individual filter maintains fixed bandwidth for precise filtering, the collective effect of multiple filters with tunable center frequencies creates an effective passband that can adapt to different signal bandwidth requirements, thus maintaining filtering precision while gaining adaptability.
Data Source
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AI summary
A coherent optical transmitter (10) includes a coherent driver modulator (16); and a plurality of tunable optical filters (12) connected to an output of the coherent driver modulator (16), wherein the plurality of tunable optical filters (12) are configurable to create an effective transfer function having a variable width and center frequency. A method (200) implemented in a coherent transmitter (10) includes receiving (201) an optical signal that was coherent modulated via a coherent driver modulator (16); and configuring (202) a plurality of tunable optical filters (12), which are connected to an output of the coherent driver modulator (16), to create an effective transfer function having a variable width and center frequency based on the received optical signal.