Cascaded Offset Optical Modulator for Deep Space ER
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Solution Overview
Problem
Current optical modulation systems face challenges in achieving high extinction ratio (ER) requirements for deep space optical communications due to conflicting implementation restraints between software defined radios (SDRs) and electro-optical modulators, leading to a lossy interface and degraded output signals.
Innovation Solution
A cascaded offset optical modulator system is introduced, utilizing two serially connected Mach Zehnder Interferometers (MZIs) with adjustable time delays to modulate optical signals, allowing for precise control of pulse width and optimization of extinction ratio (ER) and inter-symbol interference (ISI), thereby alleviating signal quality requirements and noise issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single electro-optical modulator is used to interface with SDR, then the system complexity is low, but the extinction ratio cannot meet the 33 dB requirement for deep space optical communications
Solution Approach 1:
The single modulator is divided into two separate Mach-Zehnder modulators connected in series. Each modulator handles a portion of the modulation function, allowing the system to achieve higher extinction ratio (49 dB) than a single modulator could provide alone, while maintaining reasonable complexity through modular design
Solution Approach 2:
The patent implements nested modulation where the output of the first Mach-Zehnder modulator becomes the input to the second Mach-Zehnder modulator. This cascaded configuration allows both modulators to work together to achieve the required extinction ratio for deep space communications
2Adaptability or versatility
If SDR generates modulation signals with relaxed amplitude and timing characteristics, then the SDR implementation is flexible and adaptable, but the electro-optical modulator receives suboptimal signals leading to degraded output
Solution Approach 1:
The cascaded Mach-Zehnder modulator system acts as an intermediary between the SDR and the optical channel. It compensates for the relaxed signal characteristics from the SDR by providing additional modulation stages that can correct amplitude and timing deviations, thereby improving the final optical signal quality without constraining the SDR design
Solution Approach 2:
The patent adjusts modulation parameters such as bias points, drive voltages, and time delays in the cascaded modulator system to optimize the conversion of SDR output signals into high-quality optical signals. This allows the system to accommodate SDR flexibility while maintaining signal integrity
3Manufacturing precision
If the modulation signal has strict amplitude and timing characteristics, then the electro-optical modulator can achieve high extinction ratio, but the SDR implementation becomes impractical due to bandwidth and clock speed constraints
Solution Approach 1:
By segmenting the modulation function across two Mach-Zehnder modulators, each modulator can operate with relaxed signal requirements compared to a single modulator. This segmentation allows the SDR to generate modulation signals without needing to meet extremely strict amplitude and timing specifications, simplifying the SDR implementation while still achieving high overall system performance
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
The cascaded modulator system significantly increases the extinction ratio, achieving up to 49 dB ER, which meets the requirements for deep space optical communications, and filters noise, thereby improving signal fidelity and reducing bit errors.
Implementation Method 1
a first Mach Zehnder Interferometer (MZI) and a second MZI serially connected to the first MZI. The first MZI is configured to receive an optical signal from a light source and modulate the optical signal
Data Source
AI summary
A cascaded modulator system configured to minimize the extinction ratio (ER) of an optical output of an optical transmitter. The cascaded modulator system includes a pulse position modulation (PPM) source connected to a plurality of serially-connected Mach Zehnder Interferometer (MZIs). A variable time delay Δtd may be applied to a negative low voltage differential signal (LVDS) driving a second or later MZI of the plurality of MZIs to eliminate or compensate for one or more non-idealities in an electrical signal.