Optical Modulator Drive Circuit for High-Order Multilevel Phase Modulation
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Solution Overview
Problem
The existing optical modulator modules with segmented electrode structures are limited in the number of levels of multilevel modulation due to the limited number of mountable segmented electrodes, leading to increased circuit size and cost when using multiple multilevel D/A converters for high-speed optical communication systems.
Innovation Solution
A drive circuit that splits the input digital signal into upper and lower bits, with the lower-bit drive unit outputting a value obtained by D/A conversion to a phase modulation region and the upper-bit drive unit outputting a value greater than or minimum value of the driving signal to another phase modulation region, allowing for higher-order multilevel modulation with a small-scale circuit configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of segmented electrodes is increased to achieve higher-order multilevel modulation, then the modulation capability is improved, but the circuit size and complexity increase
Solution Approach 1:
The electrode structure is divided into multiple segmented electrodes along the optical waveguide, allowing independent control of each segment. This segmentation enables higher-order multilevel modulation by applying different voltage levels to different segments, thereby achieving fine-grained phase control without requiring a monolithic large-scale electrode structure
Solution Approach 2:
The patent introduces a spatial dimension by distributing segmented electrodes along the optical waveguide length. Instead of using a single large electrode, the modulation capability is achieved through the spatial arrangement and independent control of multiple smaller segments, effectively transforming a one-dimensional control problem into a multi-dimensional solution
2Adaptability or versatility
If multiple multilevel D/A converters are used to drive segmented electrodes, then the multilevel modulation is improved, but the circuit size and cost increase
Solution Approach 1:
Multiple D/A converters are merged into a single integrated circuit that can drive multiple segmented electrodes. The patent employs a shared voltage generation architecture where one D/A converter output is distributed to control multiple electrode segments, reducing the total number of separate converters needed while maintaining multilevel modulation capability
Solution Approach 2:
The drive circuit is designed with multi-functionality, allowing a single D/A converter to serve multiple purposes by sequentially or simultaneously driving different electrode segments. This universal design enables the same hardware to achieve higher-order modulation without requiring proportional increases in circuit components
3Speed
If the frequency of modulation electric signal is increased for high-speed operation, then the transmission speed is improved, but the voltage distribution uniformity in the electrode deteriorates
Solution Approach 1:
The patent employs traveling-wave type electrodes where the voltage signal is dynamically adjusted along the waveguide length to match the optical signal's phase velocity. This dynamic voltage distribution, achieved through time-varying signals synchronized with the optical modulation, maintains effective interaction at high frequencies without requiring static uniform voltage distribution
Solution Approach 2:
The patent changes the voltage distribution parameters from static uniform distribution to dynamic non-uniform distribution. By adjusting the voltage magnitude and phase along the waveguide according to the optical signal characteristics, the system achieves high-speed modulation while maintaining optimal coupling efficiency despite frequency-induced wavelength changes
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
Enables higher-order multilevel modulation with a reduced circuit size, facilitating high-speed optical communication while maintaining phase velocity matching and impedance matching, thus achieving efficient spectral efficiency and resistance to polarization mode dispersion.
Implementation Method 1
A Mach-Zehnder (MZ) optical intensity modulator in which waveguide-type optical phase modulators are embedded into an optical waveguide-type MZ interferometer is suitable for such a use
Implementation Method 2
a so-called traveling-wave type electrode which is devised to make a phase velocity vo of the modulated optical signal and a phase velocity vm of the modulation electric signal as close to each other as possible (phase velocity matching) is required
Data Source
AI summary
An optical modulator includes optical waveguides on which phase modulation regions are formed. A drive circuit includes a lower-bit drive unit, an upper-bit drive unit, and a bit splitting unit. The bit splitting unit splits an input digital signal into upper bits and lower bits. The lower-bit drive unit outputs a value obtained by performing D/A conversion on the lower bits to phase modulation regions. The upper-bit drive unit outputs, to phase modulation regions, a value greater than a maximum value of values output from the lower-bit drive unit, or a minimum value of the values output from the lower-bit drive unit, according to a value of the upper bits.