Optical Transmitter Using Polarization Multiplexing for Compact 100 GbE Modules
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Solution Overview
Problem
The challenge is to reduce the size of optical modules for 100 GbE and 40 GbE optical systems while maintaining long-distance transmission capabilities, as existing multi-level modulation systems like PAM4 reduce inter-symbol distance, limiting fiber transmission length.
Innovation Solution
An optical transmitter and receiver system using orthogonal polarization multiplexing with on-off keying or 2M-level pulse amplitude modulation, where peak frequency components of optical carriers are spaced apart to allow for efficient signal processing and restoration, enabling longer transmission distances with smaller module sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-level modulation systems like PAM4 are used to increase transmission capacity, then data transmission rate is improved, but inter-symbol distance is reduced which limits fiber transmission length
Solution Approach 1:
The patent segments the transmission of high-capacity data by dividing it into two separate channels, each carrying a lower-rate signal (e.g., two 25 Gbps OOK signals instead of one 50 Gbps PAM4 signal). This segmentation allows each channel to maintain longer transmission distances while collectively achieving the desired data rate through polarization multiplexing.
Solution Approach 2:
The patent introduces polarization multiplexing as an additional dimension to the transmission system. By multiplexing two independent channels onto orthogonal polarization states, the system achieves doubled capacity without increasing the symbol rate or reducing inter-symbol distance in either individual channel, thus preserving transmission distance.
2Productivity
If wavelength division multiplexing is implemented to increase transmission capacity, then data transmission rate is improved, but optical module size increases due to large-scale wavelength tunable function requirements
Solution Approach 1:
The patent segments the high-capacity transmission requirement into two separate low-rate channels that can be handled by compact optical modules. Each channel uses standard OOK modulation with appropriate wavelength spacing, eliminating the need for large-scale wavelength tunable functions while achieving doubled capacity through polarization multiplexing.
Solution Approach 2:
The patent changes the modulation parameters from high-rate single-channel (PAM4 at 50 Gbps) to lower-rate dual-channel (OOK at 25 Gbps each), which allows the use of smaller, more compact optical modules while maintaining the same total transmission capacity through polarization multiplexing.
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 configuration allows for long-distance optical communication with smaller optical modules by utilizing on-off keying signals, which have higher acceptable loss values than 4-level pulse-amplitude-modulation signals, thus extending fiber transmission lengths and reducing module size.
Implementation Method 1
an optical polarizer that generates the orthogonal polarization multiplexed optical signal by multiplexing the two modulated signals by orthogonal polarization multiplexing
Implementation Method 2
two optical modulators that respectively generate two modulated signals by modulating the two optical carriers respectively with two binary bit sequences by on-off keying or 2M-level pulse amplitude modulation
Data Source
AI summary
An optical transmitter generates two modulated optical signals by modulating two optical carriers respectively with two binary bit sequences by on-off keying and generates an orthogonal polarization multiplexed optical signal from the two modulated optical signals. The two optical carriers respectively have peak frequency components spaced apart from each other by a predetermined frequency difference and located such that a central frequency of a WDM channel of a WDM grid falls between the peak frequency components. An optical receiver separates the orthogonal polarization multiplexed optical signal into two signals in which components of the two modulated optical signals are combined with different combination ratios, by means of a 1-input, 2-output asymmetric filter whose two optical transmittances intersect at the WDM grid and each have a free spectral range equal to or twice the channel spacing of the WDM grid, and restores the two modulated optical signals from the separated two signals using a DSP.