TM Mode Travelling Wave Resonator with Bragg Grating
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Solution Overview
Problem
Conventional planar optical waveguides supporting TE modes exhibit high loss, which negatively impacts the Q factor and finesse value of resonators, making them less desirable.
Innovation Solution
A travelling wave resonator is designed with a planar optical waveguide that supports a TM mode, featuring a core with a thickness of at least ten percent of the free space wavelength and a cladding with a lower index of refraction. Bragg gratings are incorporated in the sidewalls of the core to suppress TE modes while allowing TM modes to propagate, thereby reducing loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional planar optical waveguide supports a TE mode, then the waveguide can propagate optical signals, but the loss is high (about 0.05 dB/m) which results in low Q factor and finesse value
Solution Approach 1:
The patent changes the mode parameter from TE to TM mode in the planar optical waveguide. By supporting TM mode instead of TE mode, the optical loss is significantly reduced while maintaining propagation capability. This parameter change directly addresses the contradiction by improving loss characteristics without sacrificing reliability.
Solution Approach 2:
Instead of trying to improve the high-loss TE mode, the patent inverts the approach by supporting the TM mode which naturally exhibits lower loss characteristics. This inversion strategy transforms the problem from mitigating high loss to utilizing the inherently lower loss property of TM mode propagation.
2Loss of energy
If Bragg gratings are added to suppress TE modes, then loss is reduced and Q factor is improved, but the device complexity increases
Solution Approach 1:
The patent extracts and eliminates the problematic TE mode from the waveguide by using Bragg gratings that are specifically designed to suppress this mode. By removing the high-loss TE mode while preserving the TM mode, the system achieves lower loss without requiring complex additional components beyond the grating structure.
Solution Approach 2:
The Bragg grating structure serves multiple functions: it acts as a reflector for specific wavelengths and simultaneously suppresses the TE mode. This multi-functionality allows the same structure to address both mode selection and loss reduction, thereby improving performance without proportionally increasing device complexity.
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 resonator achieves significantly reduced loss, enhancing the Q factor and finesse value, which improves the sensitivity of resonator optical gyscopes to detect smaller changes in rotation rate.
Implementation Method 1
at least one Bragg grating, wherein each Bragg grating is in a unique sidewall of the cladding; wherein a period of each Bragg grating period is greater than the free space wavelength of the optical signal configured to propagate in the planar optical waveguide divided by two times an index of refraction of a transverse electric (TE) mode; wherein the period of a Bragg grating is less than the free space wavelength of the optical signal configured to propagate in the planar optical waveguide divided by two times an index of refraction of a transverse magnetic (TM) mode
Data Source
AI summary
Techniques are provided for implementing and using a high quality factor travelling wave resonator configured to propagate a transverse magnetic mode optical signals and suppress transverse electric mode optical signals. The travelling wave resonator may be used in a resonator optical gyroscope.