Transversely Coupled DFB Laser Grating Fabrication
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Solution Overview
Problem
Conventional DFB lasers face challenges such as multi-step structure growth, complex post-growth processing, low grating coupling coefficient, and low power efficiency due to the need for overgrowth and precise regrowth steps, especially in Al-containing material systems.
Innovation Solution
A transversely coupled distributed feedback laser diode is developed with a Bragg grating placed close to the waveguide core, using selective oxidation of Al-rich layers for lateral confinement and current aperture, eliminating the need for overgrowth and allowing for a simpler fabrication process with improved coupling coefficient control and higher output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional DFB lasers use overgrowth and regrowth steps to achieve proper grating positioning, then manufacturing precision is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The Bragg grating is formed on the surface of the epitaxial heterostructure before the ridge waveguide is created. This preliminary positioning of the grating allows subsequent ridge formation and oxidation processes to automatically align with the grating structure, eliminating the need for complex overgrowth and regrowth steps to achieve proper grating positioning.
Solution Approach 2:
Instead of the conventional approach where the ridge is formed first and the grating is then created through complex overgrowth processes, this invention inverts the sequence by forming the grating on the surface first and then creating the ridge structure around it. This reversal simplifies the fabrication process while maintaining precise grating positioning.
2Reliability
If transverse coupling geometry is used to achieve strong coupling and precise mode overlap, then coupling coefficient is improved, but manufacturing complexity increases due to deep grating incorporation
Solution Approach 1:
The invention transitions from longitudinal coupling (grating embedded deep within the ridge) to transverse coupling (grating positioned on the surface adjacent to the ridge). This dimensional change allows the grating to be formed by simple surface corrugation rather than deep etching, significantly reducing fabrication difficulty while maintaining strong coupling through optimized lateral positioning.
Solution Approach 2:
The grating structure is formed on the surface before the ridge is created. This preliminary action allows the grating to be positioned precisely relative to the future ridge location, enabling strong transverse coupling without requiring deep grating incorporation into the ridge structure.
3Ease of manufacture
If Al-rich layers are selectively oxidized to form lateral confinement and current aperture, then manufacturing simplicity is improved, but oxidation control precision must be maintained
Solution Approach 1:
The invention utilizes selective oxidation of Al-rich layers by controlling oxidation parameters (time, temperature, atmosphere) to transform the Al-rich layer into an oxide stripe that provides both lateral optical confinement and electrical current aperture. This parameter-controlled transformation achieves dual functionality from a single material layer.
Solution Approach 2:
The oxidized Al-rich layer serves multiple functions simultaneously: it creates the lateral optical waveguide confinement, forms the current aperture that directs carrier injection, and provides electrical isolation. This multi-functionality simplifies the overall device structure by combining several elements into a single feature.
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 simplifies the manufacturing process, increases the coupling coefficient, and enhances output power while avoiding complex overgrowth issues, making it suitable for AlGaAs systems and other challenging material systems.
Implementation Method 1
An oxide stripe is formed by selective oxidation of the Al-rich layer from the side walls
Implementation Method 2
the grating couples counter-propagating optical waves having the wavelength within the grating stop-band
Implementation Method 3
the grating couples counter-propagating optical waves having the wavelength within the grating stop-band, i.e. in a certain vicinity of the Bragg wavelength
Implementation Method 4
the heterostructure includes an optical waveguide ordinarily supporting only one fundamental mode
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A transversely-coupled distributed feedback laser diode (100), which can be processed without overgrowth, is disclosed. The laser is made from an epitaxial heterostructure including a core layer (140) located between two cladding layers (130, 150), a cap layer (170), and at least one Al-rich layer (160). The lateral waveguide is formed by selective oxidation of the Al-rich layer. A surface corrugated grating (171, 172) is formed above the waveguide. The heteroepitaxial structure is designed so that the core layer is placed in close proximity to the top of the laser structure to provide a required overlap between the light and the grating. In order to avoid inadmissible optical losses, there is no metallization above the waveguide. Instead, the metal contacts (190) are offset at some distance, so that the current has to spread in the cap layer before vertical injection into the core layer.