Optical Transmitter Frequency Equalization via Digital Correction
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Solution Overview
Problem
Optical transmitters face performance penalties due to non-optimal frequency characteristics, particularly frequency roll-off in the optical I-Q modulator, which affects data transmission rates and bit error rates.
Innovation Solution
The implementation of a frequency-dependent spectral-correction function in the digital signal processor to equalize the modulated optical signal, ensuring a flat spectrum around the optical carrier frequency and mitigating frequency roll-off, achieved through constellation mapping, discrete Fourier transformation, convolution with a spectral-correction function, and overlap-and-add processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high data-transmission rates are used, then productivity is improved, but the performance penalty caused by frequency roll-off worsens
Solution Approach 1:
The patent applies preliminary action by implementing digital signal equalization at the transmitter before the signal is modulated onto the optical carrier. The frequency-dependent spectral-correction function is applied to the electrical signal in advance to pre-compensate for the expected frequency roll-off of the I-Q modulator, ensuring that the signal characteristics are optimized before transmission.
Solution Approach 2:
The patent converts the harmful frequency roll-off effect into a beneficial outcome by designing the spectral-correction function to specifically counteract the modulator's frequency response characteristics. The equalization process transforms the detrimental frequency-dependent loss into a corrected, flattened spectrum that improves signal quality and reduces bit error rates.
2Device complexity
If frequency roll-off is present in the optical I-Q modulator, then device complexity is reduced, but manufacturing precision of the optical signal spectrum worsens
Solution Approach 1:
The patent replaces the mechanical/electrical approach of designing a frequency-flat modulator with a digital signal processing approach. Instead of trying to manufacture a complex frequency-flat optical modulator, the system uses a digital equalizer that applies a frequency-dependent spectral-correction function to compensate for the modulator's frequency roll-off, achieving spectral flatness through software rather than hardware complexity.
3Reliability
If digital signal equalization is applied, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies parameter changes by implementing a frequency-dependent spectral-correction function that adjusts the amplitude and phase characteristics of different frequency components of the digital signal. The equalization process modifies specific parameters (frequency response, spectral shape) of the signal to compensate for modulator deficiencies, improving bit error rate performance through controlled parameter adjustment rather than fundamental system redesign.
Data Source
AI summary
An optical transmitter configured to perform digital signal equalization directed at mitigating the detrimental effects of a frequency roll-off in the transmitter's optical I-Q modulator. In various embodiments, a frequency-dependent spectral-correction function used for the digital signal equalization can be constructed to cause the spectrum of the modulated optical signal generated by the transmitter to have a desired degree of flatness in the vicinity of an optical carrier frequency and/or to at least partially mirror the frequency roll-off in the optical I-Q modulator.