Compact Optical I-Q Modulator Using Multimode Interferometer
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Solution Overview
Problem
Current optical I-Q-modulators are cumbersome and difficult to integrate due to the large number of components and complex driver circuitry required, particularly in Mach-Zehnder-Super-Structure implementations.
Innovation Solution
A compact optical I-Q-modulator design utilizing a 4-port multimode interferometer to split the optical carrier signal into four branches with phase shifts, allowing for separate modulation of the I- and Q-ports using phase or amplitude modulators in a push-pull configuration, integrated within a multimode interferometer structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If separate Mach-Zehnder-interferometers are used for I-portion and Q-portion, then quadrature modulation is achieved, but the device becomes large in size and difficult to integrate
Solution Approach 1:
The patent combines the I-portion and Q-portion modulation into a single integrated Mach-Zehnder modulator structure. The carrier signal is split into four branches within one interferometer, with two branches modulating the in-phase portion and two branches modulating the quadrature portion, eliminating the need for separate interferometers and reducing overall device size.
Solution Approach 2:
The single Mach-Zehnder modulator is designed to perform multiple functions simultaneously: it modulates both the I-portion and Q-portion of the optical carrier signal within the same device structure, making the modulator universal for quadrature modulation applications rather than requiring specialized separate devices.
2Adaptability or versatility
If separate Mach-Zehnder-interferometers are used for I-portion and Q-portion, then quadrature modulation is achieved, but the structure becomes complex with many components
Solution Approach 1:
The patent merges multiple modulation functions into a single interferometer structure with four branches. Instead of using two separate Mach-Zehnder interferometers, the invention creates one interferometer where the carrier signal is divided into four paths, with appropriate phase shifts applied to enable simultaneous I and Q modulation, thereby reducing the total component count.
Solution Approach 2:
The single interferometer is segmented into four distinct branches, each handling a specific portion of the modulation. This segmentation allows independent control of I and Q portions while maintaining a unified structure, reducing complexity compared to using multiple complete interferometers.
3Ease of operation
If complex driver circuitry is used for one Mach-Zehnder-modulator, then modulation signals are generated, but the overall structure becomes complex
Solution Approach 1:
The driver circuitry for I and Q modulation is merged into a unified control structure. The patent uses a single set of driver circuits that generate four modulation signals with appropriate phase relationships, eliminating the need for separate driver circuits for each interferometer and simplifying the overall system architecture.
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 design results in a compact, low-loss, and easily fabricable optical component that effectively modulates the optical carrier signal, avoiding frequency chirp and enabling efficient quadrature modulation with reduced component complexity.
Implementation Method 1
two multimode interferometers MMI are linked together. The input signal IS is splitted in the first MMI into four branches, which have a defined phase shift to the input signal
Implementation Method 2
the modulation is done with phase shifters using the electro-optical effect, where an applied driving voltage shifts the phase of the optical signal
Implementation Method 3
the modulation is done with amplitude modulators using the electro-absorption effect, where an applied driving voltage attenuates the amplitude of the optical signal
Data Source
AI summary
The invention describes a modulator for the quadrature modulation of an optical carrier signal with an I- and a Q-portion, where a first optical multimode interferometer (MMI) splits the optical carrier signal into four branches and that in pairs of branches the I-portion and the Q-portion respectively is modulated with a Mach-Zehnder-Structure and a second optical multimode interferometer (MMI) combines the modulated I-portion and Q-portion again to one quadrature modulated optical output signal (OS).