Optical Signal Processing Frequency Shift Coherent PON
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Solution Overview
Problem
In coherent PON systems, the use of a single optical light source as both local oscillator and transmit laser leads to interference from reflected signals, causing saturation of amplifiers and ADCs due to disjoint spectral ranges.
Innovation Solution
A method where the mixing signal and transmission carrier are both derived from a single light source, with the mixing signal located within the frequency band of the received signal and/or the transmission carrier within the frequency band of the transmission signal, allowing for coherent signal processing and reduced bandwidth requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the transmit laser is used as local oscillator for coherent reception, then device complexity is reduced, but reflected signals fall into the receiver bandwidth and cause saturation of amplifiers and ADCs
Solution Approach 1:
The patent segments the frequency spectrum by introducing a frequency shift between the transmit laser and local oscillator. The transmit signal occupies one frequency band while the LO and received signals occupy a shifted frequency band, separating them in the frequency domain to prevent reflected signals from saturating the receiver.
Solution Approach 2:
The patent introduces an intermediary frequency shift mechanism (through frequency offset or heterodyne mixing) between the transmit laser and local oscillator. This intermediary shift acts as a mediator that separates the transmit and receive frequency bands, allowing the same light source to be used for both functions without direct interference.
2Object-affected harmful factors
If a frequency shift is introduced between transmit laser and local oscillator, then reflected signal interference is reduced, but bandwidth requirements for analogue and digital components increase
Solution Approach 1:
The patent changes the frequency parameter by introducing a controlled frequency offset between the transmit laser and local oscillator. This parameter change shifts the received signal band away from the transmit band, reducing interference while the bandwidth increase is managed through systematic frequency domain separation.
3Area of stationary object
If the mixing signal is located within the frequency band of the received signal, then bandwidth requirements are reduced, but frequency and phase locking becomes more challenging
Solution Approach 1:
The patent optimizes the frequency parameter by positioning the mixing signal within the received signal band, which reduces the required bandwidth for receiver components. The frequency and phase locking challenges are addressed through coherent detection algorithms that can operate effectively with this frequency arrangement.
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 reduces the bandwidth requirements for receiver components, filters out unwanted reflected signals in the electrical domain, and enables faster frequency and phase locking of burst signals, thereby overcoming the interference issues in coherent PON systems.
Implementation Method 1
a mixing signal and a transmission carrier are both derived from a single light source, wherein the mixing signal is located within a frequency band of a received signal and/or wherein the transmission carrier is located within the frequency band of the transmission signal
Data Source
Figure 1
Figure 2~3
Figure 4A~4C
AI summary
A solution is provided for processing optical signals, wherein a mixing signal and a transmission carrier are both derived from a single light source, and wherein the mixing signal is located within a frequency band of a received signal and/or wherein the transmission carrier is located within the frequency band of the transmission signal.