Symmetrical Optical Interleaver for Parallel Coherent Detection
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Solution Overview
Problem
Current electronic ADC technologies have limited bandwidth, which restricts the ability to fully utilize high data rates in fiber data transmission, requiring additional RF down converters that increase complexity and cost, and making it challenging to implement sharp filter roll-offs in photonic filter bank structures.
Innovation Solution
A symmetrical optical interleaver-based PFB architecture with direct optical down conversion eliminates the need for RF down converters by translating optical signals into low-frequency and high-frequency tributaries, allowing for sharper roll-offs and doubling the supported signal bandwidth using the same ADC sampling bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If electronic ADCs are used for signal detection, then the system is simpler and cheaper, but the bandwidth is limited to about 20 GHz
Solution Approach 1:
The incoming optical signal is divided into multiple parallel lower-rate tributaries using an optical filter bank. Each tributary is detected by a separate ADC operating at a reduced sampling rate within the 20 GHz bandwidth limit. This segmentation allows the total signal bandwidth to exceed the individual ADC bandwidth while keeping each ADC simple and cost-effective.
Solution Approach 2:
The patent transitions from a single-channel electronic ADC approach to a multi-channel photonic processing approach. By moving the filtering and channel separation functions to the optical domain using an optical filter bank, the system achieves high total bandwidth while each electronic ADC operates within its comfortable 20 GHz bandwidth limit.
2Speed
If RF electronic frequency down converters are used to enable filter bank methods, then high sampling rates can be achieved, but system complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical/electronic RF down converters with an all-optical filtering approach. The optical filter bank performs frequency separation directly in the optical domain, eliminating the need for RF mixing and down conversion electronics. This substitution dramatically reduces system complexity and cost while achieving the same high sampling rate capability.
3Measurement precision
If orthogonal filter design is used in PFB structure, then digital perfect reconstruction is achieved, but sharp filter roll-offs are difficult to implement
Solution Approach 1:
The patent changes the filter design parameters by using optical filtering techniques with inherently sharp roll-off characteristics. Optical filters can achieve very steep transition bands that are difficult to obtain with electronic filters. This parameter change in the filtering domain (from electronic to optical) enables both digital perfect reconstruction and sharp filter roll-offs simultaneously.
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 nearly doubles the supported signal bandwidth, reduces system complexity and cost, and enables high-speed data transmission with effective post-detection DSP by demultiplexing high bandwidth signals directly in the optical domain, while maintaining sharper filter roll-offs.
Implementation Method 1
An inventive photonic filter bank (PFB) architecture that uses an optical interleaver as a two-way filter bank
Implementation Method 2
The filtered tributaries will fit into the sampling BW of electronic ADC
Data Source
AI summary
A method includes modulating lightwaves to provide first and second OFDM signal sidebands at a first polarization direction and first and second OFDM signal sidebands at a second polarization direction, and combining sidebands that are oppositely positioned and joined from the first and second OFDM signal sidebands at each polarization direction to provide a polarization multiplexing OFDM signal.