Optical Signal Synchronization Circuit with Specific Frequency Band
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Solution Overview
Problem
In optical communication, chromatic dispersion causes incorrect detection of reception bits, making it difficult to detect preambles and requiring high-cost digital/analog conversion, and existing digital coherent schemes struggle with adaptive filter convergence and polarization-dependent loss, limiting transmission distance and quality.
Innovation Solution
A signal generating circuit that creates a specific frequency band signal with a smaller frequency spread, which is inserted into the transmission signal to enable accurate detection and compensation of frequency offsets, clock offsets, and chromatic dispersion, using a BPSK signal sequence and discrete Fourier transform for estimation and compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromatic dispersion compensation is performed using conventional digital coherent schemes with fixed-tap digital filters, then chromatic dispersion compensation is achieved, but the system requires high quantization bit digital/analog conversion apparatus which increases system building cost
Solution Approach 1:
The patent extracts the specific frequency band signal from the overall transmission signal to perform dedicated chromatic dispersion estimation and compensation. By separating this function into a specific signal component with known characteristics, the system achieves accurate dispersion compensation without requiring high-cost high-quantization-bit digital/analog conversion apparatus, thus resolving the contradiction between compensation accuracy and device complexity
Solution Approach 2:
The patent changes the parameter of the test signal from a broad spectrum signal to a specific frequency band signal with concentrated spectral components. This parameter change enables more accurate chromatic dispersion estimation through discrete Fourier transform, achieving reliable compensation while avoiding the need for complex high-precision conversion apparatus
2Measurement precision
If conventional preambles are used for synchronization establishment, then signal position detection is performed, but chromatic dispersion causes incorrect detection of reception bits making it difficult to detect preambles
Solution Approach 1:
The patent applies preliminary anti-action by pre-compensating for chromatic dispersion effects on the specific frequency band signal before detection. The system estimates the chromatic dispersion amount caused by the transmission line using discrete Fourier transform on the received specific frequency band signal, then uses this estimation to correct the signal position detection, thereby counteracting the harmful chromatic dispersion effect and enabling accurate preamble detection
Solution Approach 2:
The patent introduces a specific frequency band signal as an intermediary element between the transmission line and the detection system. This intermediary signal has concentrated spectral components that make it less susceptible to chromatic dispersion effects, serving as a reliable reference for estimating dispersion and achieving accurate signal position detection despite the presence of chromatic dispersion in the transmission medium
3Productivity
If adaptive filter with small number of taps is used for polarization-mode dispersion compensation, then convergence is improved, but compensation accuracy is reduced
Solution Approach 1:
The patent segments the dispersion compensation function into two parts: chromatic dispersion compensation using a fixed-tap digital filter and polarization-mode dispersion compensation using an adaptive filter with small number of taps. This segmentation allows each filter to be optimized for its specific function, with the adaptive filter focusing only on polarization-mode dispersion, thereby achieving both fast convergence and adequate compensation accuracy
Data Source
AI summary
To enable signal position detection, frequency offset compensation, clock offset compensation, and chromatic dispersion amount estimation in a communication system based on coherent detection using an optical signal, even on a signal having a great offset in an arrival time depending on a frequency due to chromatic dispersion. An optical signal transmitting apparatus generates specific frequency band signals having power concentrated on two or more specific frequencies and transmits a signal including the specific frequency band signals. An optical signal receiving apparatus converts a received signal into a digital signal, detects positions of the specific frequency band signals from the converted digital signal, estimates frequency positions of the detected specific frequency band signals, and detects a frequency offset between an optical signal receiving apparatus and an optical signal transmitting apparatus. Moreover, the optical signal receiving apparatus detects a clock offset between the optical signal receiving apparatus and the optical signal transmitting apparatus from an interval between the estimated frequency positions of the specific frequency band signals. Furthermore, the optical signal receiving apparatus estimates temporal positions of the detected specific frequency band signals and detects a chromatic dispersion amount from a difference between the temporal positions of the specific frequency band signals corresponding to different frequencies.