Butler Matrix Optical Beamforming for RoF Systems
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Solution Overview
Problem
Current radio over fiber (RoF) systems for millimeter wave communication are expensive and complex due to the use of multiple Mach-Zehnder modulators and phase controllers, as well as the need for a laser and detector for each antenna, which increases size, weight, and cost.
Innovation Solution
The implementation of a Butler matrix system that introduces phase shifts to optical signals for MIMO beamforming, using intensity modulation and direct detection, reducing the number of required DACs and lasers, and simplifying the system architecture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple Mach-Zehnder modulators and phase controllers are used for MIMO beamforming, then beamforming capability is achieved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex electrical phase controllers and Mach-Zehnder modulators with an all-optical phased array system using intensity modulated direct detection (IM-DD) technology. The optical field distribution is controlled through optical power coupling ratios in directional couplers rather than electrical phase modulation, eliminating the need for complex electrical control circuits and reducing system complexity while maintaining beamforming capability
Solution Approach 2:
The patent creates a unified all-optical phased array system that integrates multiple functions (modulation, phase control, beamforming) into a single optical domain architecture. The same optical field distribution network serves both beamforming and signal transmission functions, reducing the need for separate electrical control systems and multiple modulators
2Reliability
If a laser and detector are used for each antenna, then beamforming performance is improved, but size, weight, and cost increase
Solution Approach 1:
The patent merges multiple laser sources and detector systems into a shared optical field distribution network. A single laser source is coupled through optical power couplers that distribute optical signals to multiple antennas, and multiple detectors share a common readout circuit. This consolidation dramatically reduces the total number of lasers and detectors required while maintaining the ability to perform MIMO beamforming across multiple antennas
Solution Approach 2:
The optical field distribution network serves multiple antennas simultaneously using a single laser source and shared detector infrastructure. The directional couplers enable one optical path to serve multiple antenna elements, creating a multi-functional system where the same hardware components support beamforming for multiple antennas rather than requiring dedicated components for each antenna
3Reliability
If multiple DACs and lasers are used, then signal quality is maintained, but manufacturing cost and device size increase
Solution Approach 1:
The patent consolidates multiple digital-to-analog converters (DACs) and laser sources into a single optical domain system. Digital signals are converted to optical signals once at the source, and optical power couplers distribute these signals to multiple antennas without requiring separate DACs and lasers for each antenna. This merging approach maintains signal quality through optical distribution while dramatically reducing the number of expensive components needed
Solution Approach 2:
The patent replaces the electrical domain signal generation and distribution system (multiple DACs and lasers) with an all-optical system. Optical power couplers substitute for electrical signal distribution networks, and intensity modulation directly encodes digital signals onto optical carriers without requiring electrical-to-optical conversion at each antenna, reducing component count and manufacturing cost
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 size, weight, and cost of RoF systems while maintaining effective beamforming capabilities, and is immune to electromagnetic interference.
Implementation Method 1
A Butler matrix system is introduced that introduces phase shifts to optical signals for MIMO beamforming
Implementation Method 2
The modulated optical signals are then provided to a Butler matrix system
Implementation Method 3
using intensity modulation and direct detection
Data Source
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AI summary
A CO comprises a plurality of IM lasers and a Butler matrix system coupled to the plurality of IM lasers. The Butler matrix system comprises a plurality of optical input ports corresponding to the plurality of IM lasers, Butler matrix components coupled to the plurality of optical input ports, and a plurality of optical output ports coupled to the Butler matrix components and corresponding to the plurality of optical input ports. A method comprises generating an optical signal; receiving an analog electrical signal; modulating the analog electrical signal onto the optical signal using IM to create a modulated optical signal; and introducing, using a Butler matrix system, a phase shift to the modulated optical signal to create a phase-shifted modulated optical signal.