Optical Receiver High-Pass Filtering for Fiber Multipath Interference
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Solution Overview
Problem
Existing optical communication systems, particularly those using PAM4 and SP-SHD, are susceptible to multipath interference (MPI) due to fiber connector reflectance, leading to performance limitations in short reach networks like data centers, despite tightened connector return loss specifications.
Innovation Solution
Incorporation of high pass filters (HPFs) in optical receivers to suppress low frequency carrier-carrier beat noise caused by MPI, with cut-off frequencies ranging from 1 MHz to 200 MHz, effectively mitigating MPI in systems such as PAMn, single polarization IMDD, and polarization division multiplexed IMDD systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high pass filters are added to suppress MPI, then signal quality improves, but device complexity increases
Solution Approach 1:
The patent extracts and removes the harmful low frequency carrier-carrier beat noise components from the electrical signal using a high pass filter. By selectively taking out only the problematic frequency components (below the cutoff frequency) while preserving the useful signal, the filter mitigates MPI-induced performance degradation without requiring complete system redesign.
Solution Approach 2:
The patent changes the frequency domain parameters of the electrical signal by introducing a high pass filter with a specific cutoff frequency (e.g., 1 MHz to 200 MHz). This parameter change allows the system to suppress low frequency noise components while maintaining the integrity of higher frequency signal components, thereby improving signal quality without excessive complexity.
2Object-affected harmful factors
If high pass filters with low cutoff frequencies are used to suppress MPI, then MPI suppression improves, but signal distortion increases
Solution Approach 1:
The patent employs dynamic adjustment of the high pass filter cutoff frequency to optimize performance. By making the cutoff frequency adjustable rather than fixed, the system can adapt to different operating conditions and signal characteristics, achieving effective MPI suppression while minimizing signal distortion through optimal frequency selection.
Solution Approach 2:
The patent optimizes the cutoff frequency parameter of the high pass filter to achieve the right balance between MPI suppression and signal preservation. By carefully selecting and adjusting this critical parameter (e.g., setting it below the signal bandwidth but above the MPI noise frequency), the system effectively removes harmful low frequency components while maintaining signal integrity.
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
The HPFs significantly reduce MPI-induced performance degradation, improving bit error rates and reducing the impact of MPI in short reach networks by removing undesired crosstalk, without additional power consumption.
Implementation Method 1
a high pass filter (HPF) configured to filter the electrical signal and suppresses low frequency components induced by the MPI
Implementation Method 2
a detector configured to convert the intensity modulated optical signal with multipath interference to an electrical signal
Data Source
AI summary
An optical receiver that includes an input port configured to receive intensity modulated optical signal with multipath interference (MPI); a detector configured to convert the intensity modulated optical signal with multipath interference to an electrical signal; a high pass filter (HPF) configured to filter the electrical signal and suppress carrier-carrier beat noise induced by the MPI to produce a filtered electrical signal; and an output port configured to transmit the filtered electrical signal.