Coherent Optical Receiver With Trace Tone Channel Identification
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Solution Overview
Problem
In optical communication systems, direct detection receivers face challenges in distinguishing multiple optical channels due to the broadband nature of photo-detectors, leading to crosstalk and interference, and existing solutions like tunable filters or coherent detection with a local oscillator may not accurately determine the number of incident channels, especially when alien channels are present.
Innovation Solution
The implementation of superimposed channel identification tones, or trace tones, on optical transmission channels using amplitude modulation, allowing for unique identification of channels and enabling coherent detection without disrupting the data signal, and allowing the local oscillator to auto-discover channel frequencies without service impairment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct detection is used to receive optical signals, then the receiver structure is simple, but the receiver cannot distinguish optical channel frequencies leading to crosstalk
Solution Approach 1:
The patent introduces a local oscillator as an intermediary optical signal that mixes with the received optical channels through photodetection. This intermediary signal enables frequency discrimination by creating beat notes at difference frequencies, allowing the receiver to distinguish between different optical channel frequencies while maintaining a relatively simple receiver structure without requiring complex optical filters or demultiplexers
2Measurement precision
If coherent detection with local oscillator is used, then optical channel frequency discrimination is achieved, but the receiver cannot determine the quantity and type of incident channels
Solution Approach 1:
The patent implements feedback by using the detected beat note frequencies to automatically update the local oscillator frequency. The receiver monitors the incident optical channels, determines their frequencies and quantities from the beat notes, and feeds this information back to adjust the local oscillator. This closed-loop feedback mechanism enables the receiver to both discriminate channel frequencies and determine the quantity and type of incident channels, including alien channels not controlled by the network control plane
Solution Approach 2:
The receiver performs self-service by autonomously discovering and identifying incident optical channels without requiring external control plane information. The system uses its own local oscillator and photodetection capabilities to automatically determine channel frequencies, quantities, and types through beat note analysis, making the receiver self-sufficient in channel identification even when alien channels are present
3Measurement precision
If LO frequency is swept to discover channels, then channel identification is possible, but service impairment occurs
Solution Approach 1:
The patent employs periodic action by implementing a two-mode operation: a normal reception mode for continuous service and a periodic channel discovery mode. The system periodically sweeps the local oscillator frequency to discover new channels, then switches to continuous tuning mode for normal operation. This periodic discovery approach ensures accurate channel identification while minimizing service impairment by limiting sweeps to periodic intervals rather than continuous operation
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 effectively distinguishes and identifies optical channels, reduces crosstalk, and allows for accurate channel management without requiring network control plane information, enhancing the reliability and efficiency of channel detection and processing in optical communication systems.
Implementation Method 1
an optical signal (or channel) of interest (at some frequency) is nonlinearly mixed in a photodiode with a reference LO optical frequency
Implementation Method 2
The reference LO optical frequency may be set at an optical frequency close to the optical signal. A resulting current from the photodiode may carry the original optical signal information
Implementation Method 3
optical coherent heterodyne or homodyne detection can be used. In heterodyne detection, an optical signal (or channel) of interest (at some frequency) is nonlinearly mixed in a photodiode with a reference LO optical frequency
Data Source
Figure 1A~1D
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AI summary
An optical system may include: a demultiplexer to receive an optical signal and to demultiplex the optical signal into a plurality of optical channels; a detector circuit to: receive the plurality of optical channels, and identify a predetermined channel identification trace tone frequency for an optical channel of the plurality of optical channels; and a receiver to: receive the optical channel with the identified predetermined channel identification trace tone frequency from the detector circuit, and process the optical channel.