Graded-index coupler for microphotonic SOI waveguides
Bibliographic record
Abstract
Coupling light into and out of small high index contrast waveguides is a fundamental challenge to implementing practical microphotonic waveguide and photonic crystal devices. Previous approaches include three-dimensional tapers, inverse taper waveguides, and grating based couplers. We propose and describe a much simpler coupler based on a short length of graded index (GRIN) material deposited on top of a silicon-on-insulator (SOI) microphotonic waveguide. The GRIN coupler has a refractive index that decreases from the index of silicon at the waveguide-coupler interface, to an optimized value at the coupler surface. Beam propagation method calculations are used to evaluate the coupling efficiency from a 4 μm thick coupler section to the fundamental mode of a 0.5 μm thick SOI waveguide. Coupling efficiencies are compared for couplers with smoothly varying quadratic index profiles and with one, two and three index steps. Coupling efficiencies of 75% (1.3 dB) or better are predicted using a three step GRIN structure with indices ranging from n=3.30 to 3.41 (Si). This index range is easily accessed using a-Si layers deposited by PECVD at varying deposition conditions, or by using composite digital alloys of high and low index films. With this method, microphotonic waveguide couplers can be designed and fabricated using only PECVD deposition and one patterning etch step with very modest tolerances. Efficiency increases to 87% (0.6 dB) when the index range of the 3-step coupler is extended to 3.0.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".