Optical Delay Line Interferometer for Interference Rejection
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Solution Overview
Problem
Conventional optical wireless communication systems face challenges in effectively rejecting optical interference, leading to signal distortion and high system complexity, with existing methods providing limited interference suppression and increased bandwidth requirements.
Innovation Solution
The use of delay modulation combined with block coding to modulate signals to a high frequency range, followed by a narrow-band band-pass filter to reject optical interference, reducing bandwidth demands and system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional electronic high-pass filter is used to filter out low frequency harmonic interference, then interference suppression is improved, but signal distortion increases and additional inter-symbol interference is generated
Solution Approach 1:
The patent replaces the conventional electronic high-pass filter (mechanical/electronic system) with an optical delay line interferometer based filtering mechanism. The optical delay line uses optical path difference to create frequency-dependent interference patterns, achieving filtering through optical interference rather than electronic frequency cutoff, thereby avoiding signal distortion while suppressing low-frequency interference
Solution Approach 2:
The patent changes the filtering mechanism from electronic frequency domain filtering to optical time-domain interference filtering. By adjusting the optical path difference (delay time) in the interferometer, the filtering characteristics are dynamically controlled through parameter changes in the optical domain, achieving better interference suppression without signal distortion
2Object-affected harmful factors
If sub-carrier modulation techniques are used to modulate signals to higher frequency range, then interference suppression is improved, but system complexity increases
Solution Approach 1:
The patent uses optical copying/interference by creating a delayed copy of the optical signal and combining it with the original signal in the interferometer. This optical copying mechanism achieves frequency-selective filtering through constructive and destructive interference, replacing complex electronic sub-carrier modulation with simpler optical interference principles
Solution Approach 2:
The optical delay line interferometer serves multiple functions: it acts as both a filtering mechanism and a signal processing element. The same optical interference mechanism that provides frequency filtering also inherently performs signal modulation and demodulation, reducing overall system complexity compared to separate sub-carrier modulation and filtering stages
3Object-affected harmful factors
If line coding techniques are used to modulate signal to higher frequency, then interference rejection is improved, but bandwidth requirement doubles
Solution Approach 1:
The patent applies partial frequency shifting through the optical delay line interferometer, which selectively enhances certain frequency components through interference rather than completely shifting the entire signal spectrum. This partial action achieves interference rejection for specific frequency ranges (low-frequency optical interference) without requiring double the bandwidth
Solution Approach 2:
The interferometer provides localized frequency filtering by creating interference patterns that specifically target low-frequency optical interference components. The filtering effect is concentrated in the problematic frequency region rather than uniformly affecting the entire signal bandwidth, maintaining efficient bandwidth utilization
4Object-affected harmful factors
If spread spectrum modulation techniques are used to disperse base frequencies, then interference impact is reduced, but system complexity and bandwidth requirement greatly increase
Solution Approach 1:
The patent extracts and removes the problematic low-frequency interference components from the optical signal using the optical delay line interferometer's frequency-selective filtering capability. By taking out only the harmful interference frequencies rather than dispersing the entire signal spectrum, the system achieves interference rejection with minimal complexity and bandwidth overhead
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 effectively reduces interference, minimizes signal distortion, and lowers bandwidth requirements, improving the signal-to-noise ratio while simplifying hardware demands, making it suitable for low-cost and low-complexity applications.
Implementation Method 1
an optical delay line, which comprises a first input port S1, a first output port S2, a second output port S3 and a second input port S4
Data Source
AI summary
An interference-rejection coding method for an optical wireless communication system and such an optical wireless communication system are provided. The coding method uses delay modulation, block code techniques and filtering to reduce the low frequency interference from light sources. A plurality of codewords from the block codes are reserved for performing digital data recovery. The invention removes the need of analog clock data recovery circuit, and does not require complex hardware for realization. Therefore, it can be applied to a wide range of applications, such as optical WLAN, data transmission of medical facilities, wireless communication in the aircraft, encrypted data transmission network, and low-priced transmission interfaces.