Optical DMT Transmitter Bandpass Filtering for Dispersion Tolerance
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Solution Overview
Problem
Current optical DMT transmission systems face challenges with high OSNR requirements and chromatic dispersion-induced power fading, limiting transmission distances and increasing component costs, especially in standard single-mode fibers.
Innovation Solution
The method involves filtering optical DMT signals to create single-sideband (SSB) or vestigial sideband (VSB) signals, which reduces optical bandwidth and enhances chromatic dispersion tolerance by attenuating sidebands closer to the optical carrier less than those farther away, allowing for increased OSNR tolerance without costly modifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical and optical components with wide bandwidth are used, then the required OSNR is reduced, but the component cost increases
Solution Approach 1:
The patent changes the modulation format from DSB to VSB, altering the spectral characteristics of the optical signal. This parameter change allows the system to achieve better OSNR performance without requiring expensive wide-bandwidth components, as the VSB format inherently reduces the impact of chromatic dispersion and allows for more relaxed component specifications.
2Area of stationary object
If the optical bandwidth of the channel signal is constrained to be lower than the channel spacing, then the signal fits within the WDM grid, but chromatic dispersion induces power fading
Solution Approach 1:
The patent introduces asymmetry by suppressing one sideband more than the other, creating a vestigial sideband signal rather than a symmetric DSB signal. This asymmetric spectral distribution reduces the impact of chromatic dispersion-induced power fading while maintaining compliance with the WDM channel spacing constraints, thereby improving signal quality within the limited optical bandwidth.
3Length of stationary object
If high transmission power is used to achieve sufficient OSNR after long transmission, then the transmission distance increases, but the required transmission power becomes very high
Solution Approach 1:
The patent applies preliminary action by pre-emphasizing certain frequency components during the modulation process and applying optical filtering to shape the spectrum before transmission. This preprocessing of the signal compensates for expected losses and distortion during transmission, allowing the system to achieve longer transmission distances without requiring excessively high transmission power.
4Power
If distributed Raman amplification is used to reduce transmission power, then the required transmission power decreases, but the system requires high effort on the transmission line
Solution Approach 1:
The patent extracts the function of compensating for transmission losses from the transmission line itself (which would require complex Raman amplification infrastructure) and moves it to the transmitter side through optimized modulation and filtering. This extraction eliminates the need for complex distributed Raman amplification systems while achieving similar or better power efficiency.
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 more efficient use of optical bandwidth and increased chromatic dispersion tolerance, reducing the need for high transmission power and costly components, while maintaining signal quality over longer distances.
Implementation Method 1
filtering an optical signal that is created by amplitude modulating an intensity of an optical carrier signal using an electrical DMT signal
Implementation Method 2
chromatic fiber dispersion needs to be compensated in typical known transmission configurations
Data Source
Figure 1
Figure 2~3
Figure 4a~4b
AI summary
The invention relates to a method for creating an optical transmit signal comprising the steps of creating an electrical discrete multi-tone signal (STXi,DMT) according to digital input data (STXi) carrying the information to be transmitted, the discrete multi-tone signal (STXi,DMT) comprising a plurality of electrical partial signals, each electrical partial signal defining a sub-channel, wherein each electrical partial signal consists of a sub-carrier at a predetermined sub-carrier frequency which is modulated according to a dedicated modulation scheme, so that a dedicated portion of the digital input data is included in each sub-channel, and creating an optical signal (STXi,opt) by using the electrical discrete multi-tone signal (STXi,DMT) as modulating signal for amplitude-modulating the intensity of an optical carrier signal. According to the invention, the method further comprising the step of bandpass-filtering the optical signal (STXi,opt) in order to create an optical single sideband or vestigial sideband transmit signal (VTXi,opt). The invention further relates to an optical transmitter device for creating such an optical transmit signal and to an optical transmitter and receiver device (3i) comprising a respective optical transmitter device (13i).