Optical Control Element With Propagation Constant Mismatch
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Solution Overview
Problem
Optical control elements with thin substrates suffer from non-guided light entering the optical waveguide, leading to distorted modulation curves and deteriorated optical modulator characteristics due to decoupled and scattered light, particularly in Mach-Zehnder type modulators with substrates thinner than 30 μm or twice the mode field diameter.
Innovation Solution
Incorporating a substrate with an electro-optical effect and an optical waveguide featuring distinct propagation constants in modulation and non-modulation regions, adjusted by refractive index changes through width modifications or loading/diffusing materials like MgO, SiO2, or TiO2, to prevent recoupling of non-guided light and reduce crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the substrate thickness is reduced to 30 μm or less, then the speed matching between microwave and light wave is achieved and driving voltage is reduced, but non-guided light enters the optical waveguide causing distorted modulation curves and deteriorated optical properties
Solution Approach 1:
The patent applies local quality by creating regions with different propagation constants within the optical waveguide structure. Specifically, it introduces lateral coupling regions where the propagation constant is intentionally made different from the main propagation path, allowing selective coupling of guided light while preventing recoupling of non-guided light. This local differentiation of optical properties resolves the contradiction by maintaining thin substrate benefits while eliminating harmful light recoupling effects.
Solution Approach 2:
The patent utilizes parameter changes by modifying the propagation constant (β) through lateral coupling between adjacent optical waveguides. By controlling the coupling distance and structural parameters, the propagation constant in coupling regions is changed to create phase mismatch for non-guided light, preventing its recoupling. This parameter modification approach allows the system to maintain thin substrate thickness for speed matching while suppressing detrimental optical effects.
2Use of energy by moving object
If the substrate thickness is reduced to 30 μm or less, then the driving voltage is reduced, but decoupled and scattered light propagate through the substrate and are recoupled with the optical waveguide
Solution Approach 1:
The patent introduces lateral coupling regions with distinct propagation constants to create localized zones that selectively interact with different light modes. These regions are designed to allow guided light to pass through while creating phase mismatch for non-guided light, preventing its recoupling. This local structural differentiation enables the use of thin substrates for low driving voltage while eliminating harmful recoupling effects.
Solution Approach 2:
The patent converts the potentially harmful recoupling of non-guided light into a beneficial filtering mechanism. By designing lateral coupling regions with specific propagation constants, the structure naturally causes phase mismatch for scattered and decoupled light, transforming what would be harmful recoupling into an automatic rejection mechanism. This approach allows thin substrate operation with low driving voltage while maintaining clean optical signals.
3Strength
If the substrate thickness is reduced to 30 μm or less, then the mechanical strength is improved through bonding, but crosstalk between adjacent optical waveguides increases
Solution Approach 1:
The patent applies local quality by creating lateral coupling regions where the propagation constant is deliberately differentiated from the main waveguide path. This local structural modification allows the thin bonded substrate to maintain mechanical strength while the differentiated propagation constant regions prevent crosstalk by creating phase mismatch for laterally coupled light, thus eliminating the harmful effect of waveguide interference.
Solution Approach 2:
The patent introduces lateral coupling regions as intermediary structures between adjacent optical waveguides. These intermediate regions act as mediators that control the interaction between neighboring waveguides by imposing specific propagation constant conditions, thereby preventing direct crosstalk while allowing the thin substrate structure to maintain its mechanical integrity through bonding.
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 approach stabilizes optical properties by suppressing non-guided light recoupling and crosstalk, enhancing the extinction ratio and modulation characteristics of optical modulators while maintaining single-mode conditions and mechanical integrity.
Implementation Method 1
an optical waveguide formed on a top or bottom surface of the substrate... a substrate formed of a material having an electro-optical effect
Implementation Method 2
an optical waveguide having a modulation region and a non-modulation region along a propagating direction of a light wave propagating through the optical waveguide
Data Source
AI summary
There is provided an optical control element in which non-guided light is prevented from entering into an optical waveguide and which is excellent in optical properties, such as optical modulation properties. A media processor, such as a CD publisher, having a function as a media library.An optical control element includes: a substrate formed of a material having an electro-optical effect; and an optical waveguide formed on a top or bottom surface of the substrate. The optical waveguide has a modulation region b (s) and non-modulation regions a and c along the propagating direction of a light wave propagating through the optical waveguide. In the case when the modulation region is configured to include a single optical waveguide, propagation constants β0 to β3 of optical waveguides in the modulation region and the non-modulation region adjacent to each other are set to different values in the modulation region and the non-modulation region. In the case when the modulation region is configured to include a plurality of optical waveguides, a propagation constant of at least one of the optical waveguides in the modulation region is set to a value different from that in the non-modulation region.