Compact Optical Modulator Using Evanescent Coupling for Stability
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Solution Overview
Problem
Existing optical modulators face challenges in reducing size while maintaining stability, with ring-type modulators being unstable due to temperature effects and Mach-Zehnder modulators being large due to their Y-splitter components.
Innovation Solution
The design incorporates a light input unit that splits an optical signal into two paths with phase shifters in each path, using vertical or reflective grating couplers to manage signal direction and interference, allowing for compact size and improved stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If ring-type optical modulators are used to reduce size, then the size of the optical modulator is reduced, but the stability is adversely affected by temperature
Solution Approach 1:
The optical modulator is divided into two separate Mach-Zehnder modulators (first and second MZMs) with independent Y-splitters and phase shifters. Each MZM processes one polarization component (TE or TM) separately, allowing independent optimization of each path while maintaining overall compactness through integrated coupling.
Solution Approach 2:
The patent combines two Mach-Zehnder modulator structures into a single integrated device that handles both TE and TM polarizations simultaneously. The Y-splitters and phase shifters are merged into a unified architecture where the first and second MZMs share common input/output waveguides through evanescent coupling, achieving size reduction without sacrificing the stability of MZM design.
2Reliability
If Mach-Zehnder optical modulators are used for stability, then stability is improved, but the size increases due to large Y-splitter components
Solution Approach 1:
The patent transitions from planar Y-splitter designs to three-dimensional evanescent coupling structures. The first and second MZMs are positioned in adjacent waveguide layers or proximity, allowing optical coupling through evanescent fields in the vertical or lateral dimension. This eliminates the need for large-area planar Y-splitters while maintaining the stable interference characteristics of Mach-Zehnder architecture.
Solution Approach 2:
The design nests the first and second MZMs within a shared structural framework. The Y-splitters and phase shifters of both modulators are integrated into a common substrate with shared waveguide routes, where the first MZM structure is effectively nested alongside the second MZM structure. This nested arrangement reduces overall device footprint while preserving the individual functionality and stability of each MZM path.
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 reduces the size of the optical modulator while enhancing stability by effectively managing signal splitting and phase modulation, addressing the limitations of both ring-type and Mach-Zehnder modulators.
Implementation Method 1
a light input unit configured to receive an incident optical signal, which has not been modulated
Implementation Method 2
A phase shifter is configured to be positioned in at least one of the first and second paths and to modulate a phase of at least one of the first and second optical signals, which have been received through the first and second paths, respectively, in response to an electrical signal
Implementation Method 3
A light output unit is configured to combine a signal received through the first path and a signal received through the second path and to generate an output optical signal
Implementation Method 4
A reflective grating coupler is configured to reflect a signal received through the first path back to the first path and to reflect a signal received through the second path back to the second path
Data Source
AI summary
An optical modulator includes a light input/output unit receiving an incident optical signal which has not been modulated, splitting the incident optical signal into a first optical signal and a second optical signal, and transmitting the first and second optical signals to a first path and a second path, respectively, of an optical waveguide. A phase shifter is positioned in at least one of the first and second paths and modulates a phase of at least one of the first and second optical signals, which have been received through the first and second paths, respectively, in response to an electrical signal. A phase-modulated signal is output. A reflective grating coupler reflects signals respectively received through the first and second paths back along the first and second paths respectively.