Polarization Independent Ridge Waveguide Optical Device
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Solution Overview
Problem
Existing optical wavelength filters in optical subscriber systems face challenges such as strong wavelength dependency, polarization dependency, and size limitations, making them unsuitable for efficient upstream and downstream communication without precise alignment and dimensional precision.
Innovation Solution
A polarization-independent optical device is developed using a ridge waveguide structure with a planar waveguide layer and ridges, where the ridge width is less than the total core height, the ridge height is less than the ridge width, and the planar waveguide thickness is one-fourth or less of the total core height, achieving polarization independence by optimizing the refractive index and coupling length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional submicron-order silicon wire or channel waveguides are used in Mach-Zehnder interferometer filters, then the wavelength characteristics can be designed on the basis of optical circuit theory, but the equivalent refractive index and coupling coefficient exhibit strong wavelength dependency and extremely high polarization dependency, limiting design flexibility and requiring precise alignment
Solution Approach 1:
The patent employs asymmetric ridge waveguide structures where the ridge width is specifically designed to be less than the total core height, and ridge height is less than ridge width. This asymmetric geometry creates different confinement characteristics for TE and TM modes, enabling polarization-independent operation by balancing the effective refractive indices and coupling coefficients for both polarizations simultaneously
Solution Approach 2:
The patent systematically varies key geometric parameters including ridge width, ridge height, planar waveguide thickness, and spacing between waveguides to achieve polarization independence. By optimizing these parameters, the equivalent refractive index and coupling coefficient become substantially independent of polarization while maintaining designed wavelength characteristics
2Ease of operation
If optical wavelength filters using directional couplers are used, then optical axis alignment is not required, but the filters exhibit strong wavelength dependency in the passband and are sensitive to light source wavelength error
Solution Approach 1:
The patent designs the ridge waveguide structure with specific dimensional relationships (ridge width < total core height, ridge height < ridge width, planar waveguide thickness ≤ 1/4 total core height) to create dynamic coupling characteristics that are less sensitive to wavelength variations. This geometric configuration provides a more stable coupling coefficient across the operating wavelength range compared to conventional directional couplers
3Reliability
If optical wavelength filters using gratings of high reflection efficiency are used, then a fixed transmittance in the passband can be provided, but the grating spacing must be less than half the wavelength of the light to be transmitted, making it difficult to create a grating with adequate dimensional precision
Solution Approach 1:
The patent transitions from grating-based wavelength filtering (requiring sub-wavelength precision in the lateral dimension) to ridge waveguide-based filtering where the critical dimensions are in the vertical dimension (ridge height, planar waveguide thickness). This dimensional shift allows for more relaxed manufacturing tolerances while achieving the desired wavelength selectivity and fixed transmittance characteristics
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 provides a compact, polarization-independent optical device suitable for wavelength filters, switches, and resonators, reducing sensitivity to light source wavelength errors and polarization, enabling efficient operation across various wavelengths with improved manufacturing precision.
Implementation Method 1
a first clad, a second clad, and a core sandwiched between the first and second clads... the refractive index of the core preferably exceeds the refractive index of the clads by at least forty percent
Implementation Method 2
The core includes a planar waveguide layer with respective surfaces in contact with the first clad and the second clad... forming a ridge waveguide structure that guides the propagation of light in the core
Implementation Method 3
The ridges may be arranged to define two optical waveguides forming a Mach-Zehnder interferometer... Optical wavelength filters using a Mach-Zehnder interferometer have the advantage that their wavelength characteristics can be designed on the basis of optical circuit theory
Data Source
AI summary
An optical device includes a core sandwiched between two clads. The core includes a planar waveguide layer with ridges protruding into one of the clads, forming a ridge waveguide structure that guides the propagation of light in the core. The core dimensions satisfy the following conditions: the ridge width is less than the total core height; the ridge height is less than the ridge width; the thickness of the planar waveguide layer is equal to or less than one-fourth of the total core height. Dimensions satisfying these conditions can be selected to provide polarization independent operation. The ridges may be arranged to define a pair of optical waveguides forming a Mach-Zehnder interferometer, an optical wavelength filter, or various other optical devices.