Variable Bragg Grating Coupling via Non-Etched Gap
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Solution Overview
Problem
The fabrication of indium phosphide (InP) based photonic integrated circuits (PICs) is hindered by the need for separate electron beam lithography and etching steps for each Bragg grating coupling coefficient (K) value, limiting the range of K values and preventing variation along the grating length, due to the sole dependence of K on grating etch depth.
Innovation Solution
A method is introduced to integrate sampled-grating distributed Bragg reflector (SGDBR) and distributed feedback (DFB) lasers on the same substrate using a single grating lithography and etch step, where the coupling coefficient is controlled by varying the non-etched gap width in addition to the etch depth, allowing for different K values without additional fabrication steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If separate electron beam lithography and etching steps are performed for each Bragg grating coupling coefficient value, then the desired K values can be achieved, but the fabrication cost increases and throughput decreases
Solution Approach 1:
The patent combines multiple Bragg grating fabrication processes into a single electron beam lithography and etching step. By designing gratings with different non-etched gap widths but the same etch depth, multiple coupling coefficient values can be achieved simultaneously in one fabrication run, eliminating the need for separate processing steps for each K value and thereby increasing throughput while maintaining precision.
Solution Approach 2:
The patent applies local quality by varying the non-etched gap width at different positions along the grating structure. This allows each grating region to have a locally optimized coupling coefficient tailored to specific device requirements, while all gratings share the same global etch depth parameter, enabling precise K value control without additional fabrication steps.
2Device complexity
If the coupling coefficient is solely determined by grating etch depth, then the fabrication process is simple, but the coupling coefficient cannot be varied along the length of the grating
Solution Approach 1:
The patent enables coupling coefficient variation along the grating length by introducing variable non-etched gap widths at different positions. This local modification allows the coupling coefficient to be tailored at specific locations without changing the overall etch depth, providing adaptability while maintaining fabrication simplicity through a single etching process.
Solution Approach 2:
The patent transitions from controlling coupling coefficient through a single parameter (etch depth) to using two parameters (etch depth and non-etched gap width). By adding the non-etched gap width dimension, the system gains the ability to vary coupling coefficients along the grating length while keeping the etch depth constant, thus achieving versatility without proportionally increasing complexity.
3Adaptability or versatility
If multiple laser types with different coupling coefficients are integrated on the same substrate, then the photonic integrated circuit functionality is enhanced, but the fabrication process becomes more complex
Solution Approach 1:
The patent merges the fabrication of multiple laser types (SGDBR and DFB lasers with different K values) into a single substrate using one electron beam lithography and etching step. By designing each laser's Bragg grating with appropriate non-etched gap widths, different coupling coefficients are achieved simultaneously without requiring separate fabrication processes, thus enhancing versatility while controlling complexity.
Solution Approach 2:
The patent creates a universal fabrication process that can produce multiple types of lasers with different coupling coefficients using the same electron beam lithography and etching parameters (etch depth), differentiated only by the non-etched gap width design. This multi-functional approach allows diverse laser integration on a single substrate without proportionally increasing fabrication process complexity.
Data Source
AI summary
A non-etched gap is introduced along the length of an integrated Bragg grating with etched grooves such that the coupling coefficient, K, of the grating is reduced by the non-etched gap. In this way, multiple grating K values may be defined within a photonic integrated circuit using a single lithography and etch step. Additionally, the non-etched gap width may be varied along the length of a single grating to implement a chirped grating.