Grating Coupled Laser Vertical Alignment for Silicon Photonics
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Solution Overview
Problem
Coupling light from single mode edge emitting lasers to silicon photonics is costly and requires precise alignment, with low tolerances, and existing methods like heterogeneous integration and butt-coupling face challenges such as high yield reduction and the inability to insert an optical isolator, which is necessary for high-speed data communications.
Innovation Solution
A monolithic InP distributed feedback laser with an integrated diffraction grating, known as a grating coupled laser (GCL), which couples light through its substrate, allowing direct coupling to a Si PIC with improved alignment tolerances and the insertion of an optical isolator without lenses, reducing cost and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If single mode edge emitting lasers are coupled to Si photonics using existing methods, then light coupling is achieved, but alignment tolerances are less than 0.5 micrometers requiring active alignment
Solution Approach 1:
The patent transitions from edge-coupling (lateral alignment) to bottom-coupling (vertical alignment) by inverting the laser orientation. The laser is mounted with its bottom surface facing the Si PIC, allowing light to couple through the substrate in the vertical dimension rather than requiring precise lateral alignment in the horizontal plane. This dimensional change relaxes alignment tolerances significantly.
Solution Approach 2:
The patent introduces a grating coupler structure as an intermediary element between the laser and the Si PIC waveguide. This grating coupler acts as a mediator that converts the laser's emission mode into a mode suitable for coupling into the Si waveguide, enabling efficient light transfer without requiring direct face-to-face alignment between laser and waveguide.
2Adaptability or versatility
If heterogeneous integration or butt-coupling is used, then light coupling is achieved, but optical isolator insertion is not possible
Solution Approach 1:
The patent segments the optical path into distinct functional sections: the laser section, the isolation section (where optical isolator can be inserted), and the Si PIC section. By separating these functions spatially and using different coupling interfaces (edge-coupling for laser, bottom-coupling for Si PIC), the design enables isolator insertion that would be impossible in integrated heterogeneous structures.
Solution Approach 2:
The patent inverts the conventional mounting orientation of the laser. Instead of mounting the laser with its emitting edge facing the Si PIC (standard orientation), the laser is mounted inverted with its bottom surface facing the Si PIC. This inversion creates the spatial configuration necessary to insert an optical isolator in the optical path between the laser and Si PIC.
3Ease of manufacture
If two lenses and large isolator block are used for coupling, then light coupling is achieved, but cost increases
Solution Approach 1:
The patent merges the coupling function directly into the Si PIC substrate by fabricating grating couplers on the Si PIC itself. This eliminates the need for separate external lenses and isolator blocks, as the grating couplers perform the coupling function integrated on-chip. The laser is mounted directly to the Si PIC substrate, and light couples through the substrate to the grating couplers, reducing component count and cost.
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 GCL solution reduces part count and cost, increases alignment tolerances by a factor of 10 or more, and enables wafer-level testing, improving the efficiency and reliability of light coupling to Si photonics systems.
Implementation Method 1
The transmit grating coupler is optically coupled to the passive waveguide and includes grating teeth that extend upward from the second portion of the passive waveguide
Data Source
AI summary
A grating coupled laser (GCL) includes an active section and a passive section. The passive section is butt coupled to the active section to form a butt joint with the active section. The active section includes an active waveguide. The passive section includes a passive waveguide, a transmit grating coupler, and a top cladding. The passive waveguide is optically coupled end to end with the active waveguide and includes a first portion and a second portion. The first portion of the passive waveguide is positioned between the second portion of the passive waveguide and the active waveguide. The transmit grating coupler is optically coupled to the passive waveguide and includes grating teeth that extend upward from the second portion of the passive waveguide. The top cladding is positioned directly above the first portion of the passive waveguide and is absent directly above at least some of the transmit grating coupler.