Optical Transmitter Module Using Polarization Multiplexing
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Solution Overview
Problem
Existing optical transmitter modules face challenges in generating multi-level PAM signals with equal level intervals due to nonlinearity in electrooptic modulators and wavelength multiplexing, which leads to beat noise and chromatic dispersion issues, particularly when increasing the number of optical signals beyond PAM4.
Innovation Solution
An optical transmitter module that combines multiple optical signals with different intensities and wavelengths, using both wavelength and polarization multiplexing to generate a PAM signal with 2n levels, where the wavelengths are carefully managed to minimize beat noise and chromatic dispersion by setting specific conditions for wavelength differences and group delay times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple optical signals with different wavelengths are combined using wavelength multiplexer to generate multi-level PAM signal, then the signal transmission capacity is improved, but beat noise increases due to wavelength differences
Solution Approach 1:
The patent transitions from single-dimension wavelength multiplexing to two-dimensional multiplexing by combining wavelength multiplexing with polarization multiplexing. This allows multiple optical signals to be combined while managing wavelength differences through polarization states, thereby reducing beat noise while maintaining high transmission capacity.
Solution Approach 2:
The patent carefully controls the wavelength difference parameter between combined optical signals to minimize beat noise. By setting specific wavelength spacing and using polarization multiplexing, the system changes the parameters of signal combination to achieve both high capacity and low noise.
2Speed
If multiple optical signals with different wavelengths are combined to generate multi-level PAM signal, then the transmission rate is improved, but chromatic dispersion increases
Solution Approach 1:
The patent uses polarization multiplexing as an additional dimension to combine optical signals, allowing better control over chromatic dispersion effects. By assigning different polarization states to signals with different wavelengths, the system can manage chromatic dispersion more effectively while maintaining high transmission rates.
Solution Approach 2:
The patent optimizes the wavelength spacing and polarization state parameters of combined optical signals to minimize chromatic dispersion impact. By carefully selecting these parameters, the system achieves high transmission rates while controlling chromatic dispersion effects.
3Adaptability or versatility
If electrooptic modulator is used to generate multi-level PAM signal, then the modulation capability is improved, but nonlinearity causes unequal level intervals
Solution Approach 1:
The patent segments the multi-level PAM signal generation into multiple binary modulated optical signals that are subsequently combined. Instead of directly generating multi-level signals through a single modulator, the system uses multiple binary modulators followed by wavelength and polarization multiplexing, which avoids the nonlinearity issues of direct multi-level modulation.
Solution Approach 2:
The patent introduces wavelength multiplexing and polarization multiplexing as intermediary mechanisms to combine multiple binary modulated signals into a multi-level PAM signal. This intermediary approach avoids direct nonlinearity of electrooptic modulators while achieving the desired multi-level modulation capability.
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 enables the generation of PAM signals with improved code quality and reduced chromatic dispersion, effectively addressing the limitations of existing technologies by maintaining signal quality even at higher levels like PAM8 and PAM16.
Implementation Method 1
a wavelength multiplexer adapted to wavelength-multiplex a plurality of input optical signals having different wavelengths from each other while keeping the respective polarization states
Implementation Method 2
a polarization multiplexer adapted to polarization-multiplex two input optical signals having respective polarization states perpendicular to each other
Implementation Method 3
electrooptic modulator such as a Mach-Zehnder (MZ) modulator or an electro-absorption (EA) modulator
Data Source
AI summary
In an optical transmitter module for combining three or more optical signals different in intensity with an optical multiplexer to generate a PAM signal, the influence of the beat noise and the chromatic dispersion due to the difference in wavelength is reduced. The optical transmitter module includes first through third optical signal sources adapted to output respective optical signals binary intensity modulated with different amplitude from each other, and a combining section. The combining section has a wavelength multiplexer adapted to wavelength-multiplex a plurality of input optical signals having different wavelengths from each other while keeping the respective polarization states, and a polarization multiplexer adapted to polarization-multiplex a pair of input optical signals having respective polarization states perpendicular to each other, and the combining section combines the input optical signals from the first through third optical signal sources with each other to generate a PAM8 signal.