Variable Pitch DFB Resonator for Wavelength Uniformity
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Solution Overview
Problem
Optical semiconductor devices manufactured using butt-joint growth exhibit non-uniform emission wavelengths due to selective area growth effects, leading to reduced side-mode suppression ratio (SMSR) and instability in laser frequency modes.
Innovation Solution
The optical semiconductor resonator features a waveguide with varying effective refraction indices and diffraction grating pitches along the optical axis, with narrower pitches in areas of higher refraction indices or thickness, ensuring uniform emission wavelengths and maintaining SMSR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If butt-joint growth method is used to manufacture optical semiconductor device, then integration of resonator and modulator portions is achieved, but non-uniform emission wavelength occurs due to selective area growth effect
Solution Approach 1:
The patent applies local quality by making the diffraction grating pitch variable along the optical axis direction. Specifically, the pitch is set to be narrower in regions where the waveguide thickness is larger (closer to the modulator portion) and wider in regions where the thickness is smaller. This local adjustment compensates for the non-uniform effective refraction index caused by selective area growth, thereby maintaining uniform emission wavelength across different locations of the resonator portion.
2Device complexity
If uniform diffraction grating pitch is used in resonator portion, then device structure is simplified, but side-mode suppression ratio decreases due to non-uniform effective refraction index
Solution Approach 1:
The patent applies parameter changes by varying the diffraction grating pitch as a function of position along the optical axis. The pitch parameter is specifically adjusted to be narrower in regions with larger waveguide thickness and wider in regions with smaller thickness. This parameter variation compensates for the non-uniform effective refraction index, maintaining uniform emission wavelength and ensuring high side-mode suppression ratio while preserving laser oscillation stability.
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
This approach prevents non-uniformity in emission wavelengths, maintaining a high side-mode suppression ratio and ensuring stability in laser frequency modes by adjusting diffraction grating pitches according to the effective refraction indices and thickness variations.
Implementation Method 1
diffraction gratings formed along the optical axis direction of the waveguide
Implementation Method 2
in a case of distributed feedback (DFB) lasers
Implementation Method 3
waveguide which includes at least two areas where an effective refraction index varies in an optical axis direction
Data Source
AI summary
In order to prevent non-uniformity in emission wavelength among different sites along an optical axis direction, provided is a resonator portion including: a waveguide which includes a first area and a second area being adjacent to the first area; and diffraction gratings formed along an optical axis direction. The effective refraction index in the first area is larger than the one in the second area, and the thickness in the first area is larger than the one in the second area. A pitch at the adjacent diffraction gratings at a boundary between the first area and the second area is narrower both than pitches of the diffraction gratings that are formed in the first area and than pitches of the diffraction gratings that are formed in the second area.