Surface Grating DFB Laser with Ridge Waveguide
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Solution Overview
Problem
Conventional distributed feedback lasers with buried Bragg gratings face challenges in high fabrication costs and low yield due to complex crystal re-growth processes, and those with surface gratings have small coupling coefficients and large optical losses.
Innovation Solution
A DFB laser design utilizing surface gratings with a ridge waveguide structure, where the first cladding layer is n-doped and includes a refractive layer with a thickness less than 1 micrometer, and Bragg gratings are etched on the surface, allowing for high coupling coefficients and reduced optical loss by eliminating surface electrodes and using current limiting regions or tunnel junctions for current confinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If buried Bragg gratings are used with crystal re-growth, then feedback is provided, but fabrication complexity increases and yield decreases
Solution Approach 1:
The patent extracts the Bragg grating from the buried position and places it on the surface of the ridge waveguide. This allows the grating to be formed by simple etching without requiring crystal re-growth, thereby eliminating the complex fabrication process while maintaining the feedback function.
Solution Approach 2:
Instead of burying the grating within the crystal structure (conventional approach), the patent inverts the approach by placing the grating on the surface. This inversion simplifies the fabrication process while achieving the same optical feedback effect.
2Ease of manufacture
If surface gratings are used without re-growth, then fabrication is simplified, but coupling coefficient decreases and optical loss increases
Solution Approach 1:
The patent modifies the local quality of the ridge waveguide by adding a high refractive index layer (such as SiO2 or TiO2) with thickness between 50-500 nm on the surface where the grating is located. This localized modification enhances the optical field confinement at the grating position, increasing the coupling coefficient without affecting the overall simple fabrication process.
Solution Approach 2:
The patent creates a composite structure by combining the ridge waveguide material with a high refractive index material layer. This composite structure enhances the optical interaction between the grating and the optical mode, increasing the coupling coefficient while maintaining fabrication simplicity.
3Ease of operation
If electrodes are placed on ridge waveguide surface, then current injection is achieved, but optical loss increases
Solution Approach 1:
The patent moves the electrode placement from the vertical dimension (on top of the ridge) to the lateral dimension (on both sides of the ridge). This dimensional change allows current injection while avoiding the optical loss associated with surface electrodes, as the electrodes are positioned in regions where the optical mode has minimal intensity.
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 solution results in a laser with a low threshold, high-speed direct modulation capability, and simplified manufacturing, achieving a large optical confinement factor and coupling coefficient, thus reducing manufacturing costs and improving reliability.
Implementation Method 1
The structure builds a one-dimensional interference grating (Bragg scattering) and the grating provides optical feedback for the laser
Implementation Method 2
the refractive index of the refractive layer is greater than that of the active layer; the mode of the ridge waveguide has a large optical confinement factor in the ridge region
Data Source
AI summary
A distributed feedback laser, including: a ridge waveguide; two upper electrodes disposed on two sides of the ridge waveguide, respectively; two lower electrodes disposed on two sides of the upper electrodes, respectively; a substrate; a second waveguide cladding layer; an active layer; and a first waveguide cladding layer. The first waveguide cladding layer is n-doped and includes a conductive layer and a refractive layer disposed on the conductive layer. The refractive index of the refractive layer is greater than the refractive index of the active layer. The ridge waveguide includes a ridge region formed by a middle part of the refractive layer. The ridge region includes a surface provided with Bragg gratings. Two grooves are formed between the ridge waveguide and the upper electrodes. The conductive layer is connected to the upper electrodes. The second waveguide cladding layer includes one or more current restricted areas.