Optical Modulator for OFDM Signal Transmission
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Solution Overview
Problem
Conventional optical OFDM systems face Inter-Modulation Distortion (IMD) interference due to the square effect at the receiver, which is typically addressed by using an electrical mixer for up-conversion, but this decreases the signal-to-noise ratio, and alternative methods that use the digital-to-analog converter (DAC) only partially utilize its bandwidth.
Innovation Solution
A system and method that employs a digital-to-analog converter without an electrical mixer to generate a reference optical carrier, utilizing an optical modulator with phase-shifted electrical carriers to create a virtual reference carrier, allowing for individual adjustment of the power ratio between the optical carrier and signal to optimize power efficiency, thereby avoiding IMD interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an electrical mixer is used for up-conversion to solve IMD interference, then IMD interference is reduced, but the signal-to-noise ratio decreases
Solution Approach 1:
The patent replaces the electrical mixer (electrical system) with an optical modulator that uses optical carriers to achieve up-conversion. By substituting the electrical mixing process with optical modulation, the system eliminates the noise introduction characteristic of electrical mixers while maintaining the ability to resolve IMD interference through frequency translation to higher bands where IMD does not occur.
Solution Approach 2:
The patent introduces an optical carrier as an intermediary to transfer the signal from the baseband to a higher frequency band. This optical carrier acts as a mediator that enables frequency translation without direct electrical mixing, thereby avoiding the noise figure penalty associated with electrical mixers while achieving the desired up-conversion for IMD suppression.
2Productivity
If the DAC is used to transmit signals directly, then the entire DAC bandwidth is utilized, but IMD interference occurs at the receiver
Solution Approach 1:
The patent transitions the signal from the baseband dimension to a higher frequency dimension by using optical modulation. This dimensional shift moves the signal spectrum away from the baseband where IMD occurs, allowing full utilization of the DAC bandwidth for useful signal transmission while the optical carrier handles the frequency translation to avoid IMD interference at the receiver.
3Object-affected harmful factors
If up-conversion is performed to higher frequency to solve IMD, then IMD interference is eliminated, but additional components and complexity are required
Solution Approach 1:
The optical modulator serves multiple functions simultaneously: it performs up-conversion to higher frequency bands, generates the optical carrier, and enables the signal to be transmitted through the optical fiber network. This multi-functionality reduces the need for separate components for each function, thereby managing system complexity while achieving IMD elimination through frequency translation.
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 enhances power efficiency by allowing the entire DAC bandwidth to be used for electrical analog signals, reducing signal processing complexity and maintaining high signal quality by eliminating IMD interference without degrading the signal-to-noise ratio.
Implementation Method 1
an optical modulator with phase-shifted electrical carriers to create a virtual reference carrier
Data Source
AI summary
A signal-transmitting system includes a digital-to-analog converter, an optical modulator, first and second electrodes, an optical phase shifter, and an optical coupler. The digital-to-analog converter converts digital data into an electrical analog signal. The optical modulator includes a first optical waveguide configured to transmit a first optical carrier, a second optical waveguide configured to transmit a second optical carrier, a first electrode positioned on the first optical waveguide, and a second electrode positioned on the second optical waveguide. The first and second electrical couplers are configured to couple respective electrical analog signals and electrical carriers to electrodes to generate modulation waves. The modulation waves are different in phase. The optical phase shifter is configured to shift the second modulation wave by a predetermined phase, and the optical coupler is configured to couple the first and second modulation waves to generate an optical output signal.