Dispersion in the quarter-wave Bragg reflection waveguide
Bibliographic record
Abstract
The Bragg reflection waveguide (BRW), or one-dimensional photonic bandgap waveguide, has recently received much interest for applications such as nonlinear frequency conversion, mechanically tunable air-core filters, and electron accelerators. One variation of this waveguide is the quarter-wave BRW (QtW-BRW), in which all cladding layers have a phase thickness of π/2. This places the mode in the center of the cladding stopband, ensuring the strongest possible confinement for a given pair of cladding materials. In addition, operating at the quarter-wave point permits the effective index of the guided modes to be given by a simple closed-form expression. For many applications of BRWs, the dispersion of effective index with frequency is of primary concern. In this work, we use a perturbation approach to derive analytical expressions for the dispersion of a QtW-BRW, and compare the results to numerical simulations to demonstrate accuracy. Several interesting properties of these waveguides are developed. The birefringence of the guides changes sign at the quarter-wave point. For fundamental modes of even symmetry, the first-order dispersion is always normal if the material dispersion is normal. It is shown that for certain QtW-BRW designs, group index and group velocity dispersion (GVD) can be orders of magnitude higher than is the case for their constituent materials, or on the other hand, very small or zero values of GVD can be attained. We will conclude with a discussion of the applications of such waveguides.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".