Electromagnetic Wave Polarization Modulation with Traveling-Wave Phase Control
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Solution Overview
Problem
Existing polarization modulators, particularly those based on Sagnac interferometers, face challenges in achieving high extinction ratios (>20 dB) at increased modulation frequencies due to increased complexity and environmental instability, requiring short optical pulses and high bandwidth demands.
Innovation Solution
A method and device utilizing a traveling wave phase modulator within a reduced Sagnac loop geometry, where counter-propagating electromagnetic waves are phase-modulated by an RF field, allowing for improved symbol rate and reduced modulation bandwidth, enhancing stability and extinction ratio while supporting continuous and pulsed optical signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a Sagnac interferometer is used for polarization modulation, then interferometric stability is improved, but device complexity and insertion loss increase
Solution Approach 1:
The patent extracts the essential function of the Sagnac interferometer (common optical path for stability) while removing the problematic elements (complex interferometric setup, multiple components). This is achieved by using a single-mode fiber loop that simplifies the structure while maintaining the key stability benefit of counter-propagating waves sharing the same path.
Solution Approach 2:
The patent segments the modulation function by using separate polarizing beam splitters and waveplates arranged in a simplified loop configuration, allowing independent control of polarization states while reducing the overall complexity compared to traditional Sagnac interferometers.
2Stability of the object's composition
If a Sagnac interferometer is used for polarization modulation, then interferometric stability is improved, but insertion loss increases
Solution Approach 1:
The patent removes the sources of insertion loss by eliminating multiple optical components and interferometric paths. The simplified single-mode fiber loop with polarizing beam splitters reduces scattering and absorption losses while maintaining the stability benefit of counter-propagating waves.
3Manufacturing precision
If optical pulses are made short to achieve high extinction ratio, then extinction ratio is improved, but symbol rate is reduced
Solution Approach 1:
The patent uses dynamic polarization control through electro-optical modulators that can rapidly switch between polarization states. This allows the system to achieve high extinction ratios without requiring extremely short pulses, as the modulation speed is determined by the electro-optical response time rather than pulse duration.
Solution Approach 2:
The patent changes the modulation approach from time-based pulse shortening to polarization-based modulation. By controlling the polarization state of continuous or longer pulses through electro-optical effects, the system achieves high extinction ratios without sacrificing symbol rate.
4Manufacturing precision
If modulation bandwidth is increased to achieve high extinction ratio, then extinction ratio is improved, but device complexity and cost increase
Solution Approach 1:
The patent employs electro-optical modulators with optimized response characteristics that can achieve high extinction ratios at practical modulation frequencies. The dynamic polarization control mechanism allows for high performance without requiring excessive bandwidth, as the modulation is achieved through polarization state changes rather than high-frequency electrical signals.
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 solution achieves a high extinction ratio of >20 dB, improves symbol rate by a factor of two, reduces modulation bandwidth by a factor of two, and enhances robustness against environmental influences, simplifying electronics and ensuring stable polarization modulation.
Implementation Method 1
two counter-propagating, polarized electromagnetic waves, namely a first wave train and a second wave train, are modulated by at least one RF field of a running wave Phase modulator or a traveling wave phase modulator, are phase-modulated relative to one another
Implementation Method 2
A known modulator developed to solve this problem is based on a Sagnac interferometer. Such interferometers are particularly robust against interferometric instabilities because the two interferometer arms share a common optical path and only the propagation direction of the light waves or light pulses is inverted
Data Source
AI summary
The invention provides a method and a device for polarization modulation of electromagnetic waves. For polarization modulation of electromagnetic waves, in particular for generating keys for quantum cryptography, two counter-propagating, polarized electromagnetic waves, namely a first wave train (19) and a second wave train (20), are phase-modulated relative to one another by at least one RF field of a running-wave phase modulator (16) co-propagating with one of the two electromagnetic waves.