Tunable Laser Waveguide Layout to Suppress Mode Hopping
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Solution Overview
Problem
Wavelength tunable laser devices using silicon photonics face instability due to mode hopping caused by unnecessary light generation and reflection in the optical cavity, leading to degraded laser quality.
Innovation Solution
The device incorporates an optical waveguide with a wide-width section to reduce unnecessary light reflection and stabilize laser oscillation by suppressing mode hopping, combined with tapered transitions to minimize multimode propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the optical length of the cavity is increased to narrow the spectral width of laser light, then the spectral width is narrowed, but the wavelength spacing of longitudinal modes becomes smaller and mode hopping becomes more likely
Solution Approach 1:
The waveguide width is varied locally along the optical path: a first waveguide section has a first width, a second waveguide section has a second width different from the first, and a third waveguide section has a third width. This local variation in waveguide dimensions creates corresponding variations in refractive index that suppress longitudinal modes at specific wavelengths while maintaining the desired narrow spectral width at the oscillation wavelength.
Solution Approach 2:
The refractive index distribution is changed by modifying the waveguide width at different sections. Since the refractive index depends on the waveguide dimensions, changing the waveguide width changes the effective refractive index, thereby altering the resonance conditions for longitudinal modes and suppressing mode hopping.
2Illumination intensity
If a silicon waveguide is used to lengthen the optical path, then the spectral width can be narrowed, but unnecessary light is generated in the cavity leading to mode hopping
Solution Approach 1:
Different sections of the waveguide are designed with different widths to create localized refractive index variations. The first, second, and third waveguide sections have distinct widths that are optimized to suppress unnecessary light generation at specific locations along the optical path while maintaining the desired laser oscillation.
Solution Approach 2:
The high refractive index of silicon, which initially causes unnecessary light generation and mode hopping, is utilized beneficially by creating controlled refractive index variations through waveguide width modulation. These variations convert the potential harm into a mechanism for suppressing longitudinal modes and stabilizing laser oscillation.
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
Stabilizes laser oscillation and improves laser light quality by reducing unnecessary reflections and mode hopping, ensuring efficient generation of desired wavelengths.
Implementation Method 1
since the silicon waveguide has a high refractive index, the optical length (alternatively, the optical path length) can be lengthened
Implementation Method 2
unnecessary light is generated in the cavity, and energy may be transferred to a longitudinal mode appearing near the oscillation wavelength due to a phenomenon called 'mode hop'
Data Source
AI summary
A wavelength tunable laser device includes: a first mirror; a second mirror; an optical amplifier provided between the first mirror and the second mirror; a wavelength tunable filter provided between the first mirror and the second mirror; and an optical waveguide coupling the optical amplifier and the wavelength tunable filter. The optical waveguide includes a first waveguide formed with a first width and a second waveguide formed with a second width wider than the first width.