Optical Transmitter Bandwidth Expansion via Signal Segmentation
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Solution Overview
Problem
Current digital-to-analog converters (DAC) and analog-to-digital converters (ADC) used in optical communication systems have an input/output band of about 30 GHz, which is insufficient for increasing transmission capacity, limiting the modulation speed due to bandwidth shortages.
Innovation Solution
The system divides wideband signals into upper and lower sideband signals, performs frequency shifting, and then converts these narrowband signals into analog or digital form, allowing for increased modulation speed without being limited by the output bandwidth of the converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the modulation speed is increased to increase transmission capacity, then the transmission capacity is improved, but the bandwidth of the DAC and ADC becomes insufficient
Solution Approach 1:
The patent divides the wideband signal into multiple narrowband signals in the frequency domain using FFT. Each narrowband signal is then processed separately by individual DACs or ADCs with limited bandwidth. This segmentation allows the system to achieve high transmission capacity using converters with lower bandwidth specifications, effectively resolving the contradiction between transmission capacity and converter bandwidth.
2Productivity
If digital signal processing technology using DSP is introduced to increase transmission capacity, then the transmission capacity is improved, but high-speed DAC and ADC become indispensable, increasing system complexity
Solution Approach 1:
The patent segments the high-speed digital signal processing into multiple parallel low-speed processing paths. By dividing the wideband signal into narrowband components and processing them separately, the system avoids the need for a single high-speed DSP, thereby reducing overall system complexity while maintaining high transmission capacity.
Solution Approach 2:
The patent introduces frequency domain transformation (FFT) as an intermediary step between the digital signal and the DAC/ADC. This intermediary transformation converts the high-speed time-domain signal into lower-speed frequency-domain representations, allowing standard converters to process the signal effectively without requiring high-speed components.
3Speed
If the modulation speed is increased beyond 30 GHz, then the transmission capacity is improved, but the current CMOS platform converters cannot support the required bandwidth
Solution Approach 1:
The patent divides the high-frequency wideband signal into multiple lower-frequency narrowband signals. Each narrowband signal can be converted by a standard CMOS platform converter operating within its 30 GHz bandwidth limitation. The segmented approach enables the system to achieve effective modulation speeds beyond what a single converter could support, overcoming the hardware bandwidth constraint.
Solution Approach 2:
The patent transforms the problem from the time domain to the frequency domain using FFT. This dimensional change allows the system to process high-speed signals by manipulating their spectral components separately, enabling effective modulation speeds higher than the converter's time-domain bandwidth limitation would suggest.
Data Source
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AI summary
An optical transmitter includes a first narrowband signal processing unit, a wideband signal generation unit, and an optical modulator. The first narrowband signal generation unit is configured to input a first signal and a second signal and output first, second, third and fourth narrowband signals. The wideband signal generation unit is configured to multiply the first and second narrowband signals by sinusoidal signals having a phase difference of (π/2), respectively, to shift bands of the first and second narrowband signals, and combine the shifted first and second narrowband signal to generate a first wideband signal. The wideband signal generation unit is configured to multiply the third and fourth narrowband signal by sinusoidal signals having a phase difference of (π/2), respectively, to shift bands of the third and fourth narrowband signals, and combine the shifted third and fourth narrowband signals to generate a second wideband signal.