Buried Stripe Grating Transverse Control for DFB Lasers
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Solution Overview
Problem
Existing optoelectronic components, particularly BRS structures, face limitations in grating control and modulation due to photolithography tolerance, leading to restricted spectral selectivity and optical characteristics, with prior solutions like ridge structures resulting in deep etching, low modulation, and electrical injection issues.
Innovation Solution
A novel optoelectronic device with a buried waveguide and grating layer featuring rectangular, elongate stripes with recesses or indentations, allowing for variable size and pitch configurations, enabling fine control over the coupling coefficient and optical properties, produced through a process involving waveguide deposition, grating etching, protection, and epitaxial regrowth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional BRS structures with photolithography alignment are used, then manufacturing is simplified, but transverse grating control is lost due to one-micrometer tolerance
Solution Approach 1:
The grating structure is segmented into discrete transverse elements (bars, ridges, or holes) spaced along the waveguide width. This segmentation allows each element to be independently positioned and sized, enabling precise transverse control of the optical coupling without relying on continuous photolithography alignment. The segmented approach converts a continuous alignment problem into discrete positioning that can be controlled within the etching precision limits.
Solution Approach 2:
The invention transitions from conventional longitudinal grating modulation only to include transverse dimension control. By introducing transverse elements (varying width, spacing, or depth of bars/ridges perpendicular to the waveguide length), the patent adds a new degree of freedom for controlling optical properties. This dimensional expansion allows independent optimization of both longitudinal coupling and transverse mode selection.
2Manufacturing precision
If ridge structures with deep etching are used to achieve transverse control, then grating shape control improves, but coupling modulation decreases and electrical injection deteriorates
Solution Approach 1:
The grating structure implements local quality variations through transverse elements with different widths, depths, or materials at different positions across the waveguide width. Each local region can be optimized for its specific function: central regions may have stronger coupling for mode selection, while edge regions maintain better waveguide integrity for power transmission. This local optimization resolves the contradiction by allowing shape control where needed without compromising overall power.
Solution Approach 2:
Instead of etching deeply across the entire waveguide width (excessive action), the invention applies partial etching only where transverse control is needed, maintaining full depth only in critical coupling regions. The transverse elements can be etched to varying depths, with shallower etching in regions where power transmission is prioritized and deeper etching where mode control is critical, thus balancing shape control with power maintenance.
3Power
If continuous gratings are used, then optical coupling is maximized, but spectral selectivity is limited by photolithography tolerance
Solution Approach 1:
The grating structure introduces dynamic control capabilities through variable transverse element parameters (width, spacing, depth) that can be adjusted along the waveguide length. This allows the optical coupling strength to be dynamically modulated, enabling enhanced spectral selectivity through techniques like chirped gratings or apodization profiles. The dynamic variation in transverse dimensions provides an additional control mechanism beyond static continuous gratings.
Solution Approach 2:
The invention utilizes parameter changes in the transverse dimension of grating elements to achieve spectral selectivity enhancement. By varying the width, spacing, or depth of transverse bars/ridges along the waveguide, the local coupling coefficient can be modulated, creating spectral filtering effects that are not achievable with uniform continuous gratings. This parameter variation compensates for photolithography tolerance limitations.
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 allows for enhanced control over the coupling coefficient and optical properties, enabling improved spectral selectivity, increased emission power, and broader monomode operation, suitable for various optoelectronic components like DFB lasers and SOA amplifiers.
Implementation Method 1
a layer called a grating layer, also in the form of an elongate stripe comprising features... providing optical coupling with an optical wave propagating in the waveguide
Data Source
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AI summary
The field of the invention is that of optoelectronic components with a buried stripe structure. The optoelectronic device according to the invention is a stripe structure, comprising at least one buried waveguide and a layer called a grating layer in the form of an elongate stripe comprising features, each feature having an approximately rectangular shape, the length of the feature being substantially perpendicular to the direction of the length of the stripe of the grating layer, said layer being placed so as to provide optical coupling with an optical wave propagating in the waveguide, the length of certain features being substantially less than the width of the waveguide.